In an ink jet head that reduces failure or abnormality in ink ejection, electric charge/discharge is applied between opposed electrodes and diaphragms to eject ink droplets from ink nozzles. Each of the opposed electrodes includes a main electrode and a sub-electrode formed on the nozzle side and in common with sub-electrodes for the other diaphragms. Auxiliary electric charge is applied between the sub-electrode and the diaphragms so that the menisci or ink in the ink nozzles vibrate without ejecting unnecessary ink droplets and to shorten the time for tail portions of ejected ink columns to leave the ink nozzles. Ink in ink channels is diffused so that the ink viscosity does not increase due to evaporation of ink solvent. Also, the menisci in the nozzles are drawn into the ink chambers so that unnecessary ink droplets are not ejected immediately after printing ink droplets are ejected.

1. Field of the Invention
The present invention relates to an ink jet head which ejects ink droplets so as to make the ink droplets adhere onto recording paper only when recording is demanded; an ink jet printer thereof; and a method for driving the ink jet head. In particular, the present invention relates to the prevention of a failure or abnormality in ink ejection.
2. Description of the Related Art
Generally, an ink jet head has pressure build-up chambers for applying pressure to ink so as to eject ink droplets. Then, one end of each pressure build-up chamber communicates with an ink tank through an ink supply channel while the other end of the pressure build-up chamber is provided with an ink nozzle for ejecting an ink droplet. In addition, a bottom portion of the pressure build-up chamber is formed to be deformable and used as a diaphragm. This diaphragm is elastically displaced by electromechanically converting means so as to generate pressure for ejecting an ink droplet from the ink nozzle.
A printer using such an ink jet head has excellent features such as low noise, low power consumption, and so on, and it has come into wide use as an output unit for an information processor. On the other hand, in the ink jet head, menisci in the ink nozzles are pushed out in unstable forms by remaining vibration generated in the pressure build-up chambers. As a result, unnecessary ink droplets constructing no printing may be ejected immediately after necessary ink droplets are ejected. The ejection speed of the unnecessary ink droplets constructing no printing is so low that they adhere to nozzle surfaces and cause a phenomenon such as ink nozzle clogging or dot missing. Thus, the reliability on printing is lowered.
Further, when the printer is left for a long time in the state where the ink jet head is not driven, water, or the like, which is a solvent of ink, evaporates through the ink nozzles. As a result, the viscosity of ink in the ink nozzles increases so that the ink nozzles are clogged. Moreover, with the increase of the ink viscosity, the refil speed of the ink nozzles with ink becomes so low that the refill quantity cannot follow the ink ejection quantity. As a result, bubbles are mixed into ink so that the ink jet head is in a non-ejection state where no ink droplet is ejected. Thus, the reliability on printing is lowered in the same manner as mentioned above.
In the background art, for the former where a failure in ejection is caused by ink adhesion to nozzle surfaces, the nozzle surfaces are rubbed with a wiper (wiped) before the beginning of printing or during a rest period of printing, so that the nozzle surfaces are prevented from wetting due to the adhesion of unnecessary ink droplets to the nozzle surfaces. Further, the publication JP-A-4-369542 discloses a technique in which a second voltage different from a first voltage for ejecting ink droplets is applied to electrostrictive members so as to separate ejected ink droplets and reduce the ejection of unnecessary ink droplets.
On the other hand, for the latter where a failure in ejection is caused by ink nozzle clogging and bubbles in ink, the operation of ejecting several shots of ink droplets, that is, so-called pre-ejection is performed before the beginning of printing or during a rest period of printing. Further, the publication of JP-A-9-30007 proposes a method in which a pulse with electric power at the level at which no-ink droplet is ejected from ink nozzles is applied to electrostrictive members so as to micro-vibrate menisci in order to prevent the ink nozzles from being filmed with ink.
However, the above-mentioned background-art techniques have problems as follows.
1. In the wiping operation, there was a problem that printing time was elongated because the ink jet head had to be moved to shelter at a place other than a print area at any time when wiping was performed. In addition, there was a problem that water-repellant coatings on the nozzle surfaces were deteriorated by the repeated wiping of the nozzle surfaces.
2. In the case where a voltage was applied to the electrostrictive members in order to separate ink droplets, characteristic differences between the electrostrictive members might make it impossible to separate the ink droplet well and might eject even unnecessary ink droplets. Thus, there was a problem that it was difficult to attain stable ejection and separation of ink droplets.
3. In the pre-ejection operation, there was a problem that ink irrelevant to printing was markedly consumed so that the life of the ink tank was shortened. In addition, there was a problem that printing time was elongated because the ink jet head had to be moved to shelter at a place other than a print area at any time when pre-ejection was performed.
4. In regard to the driving method to apply such a low pulse voltage as to eject no ink droplets, if this method was applied to an ink jet head using electrostatic driving actuators, it was difficult to set a driving condition on which menisci were vibrated without ejecting any ink. Accordingly, there was a problem that ink droplets were ejected, or enough vibrations of the menisci to avoid a failure in ink ejection were not obtained. In addition, it was necessary to give driving signals to driving elements for all the ink nozzles respectively. Accordingly, there was a problem that driving control was complicated, etc.
It is an object of the present invention to provide an ink jet head that eliminates or reduces printing trouble caused by a failure or abnormality in ink ejection; an ink jet printer using such an ink jet head; and a method for driving such an ink jet head.
(1) An ink jet head according to the present invention comprises a plurality of ink nozzles for ejecting ink, a plurality of ink chambers respectively communicating with a corresponding one of the ink nozzles, ink supply channels respectively supplying ink to a corresponding one of the ink chambers, elastically displaceable diaphragms respectively formed in a wall of a corresponding one of the ink chambers, and opposed electrodes oppositely arranged to the diaphragms through a gaps, to eject ink droplets from the ink nozzles by performing electric charge/discharge between the opposed electrodes and the diaphragms; wherein each of the opposed electrodes comprises a main electrode that can perform electric charge/discharge between it and a corresponding one of the diaphragms independently of the other main electrodes, and a sub-electrode that is electrically connected with the sub-electrodes for the other diaphragms.
In the present invention, the electrodes are driven in a desired combination (driving voltages are applied between the opposed electrodes and the corresponding diaphragm so as to perform electric charge/discharge therebetween), so that the quantity of ink ejected from an ink nozzle (density) can be adjusted in multiple stages. In addition, since each sub-electrode is electrically connected with the other sub-electrodes formed for the other diaphragms, a process for vibrating ink in the ink nozzles can be performed in common for the respective ink chambers. Thus, the control of such a process becomes easy.
(2) In the ink jet head according to the present invention as stated in paragraph (1), each main electrode is electrically charged and discharged selectively in accordance with a printing pattern, and a sub-electrode formed on the ink nozzle side is electrically connected with sub-electrodes formed for the other diaphragms. In the present invention, main electrodes are driven selectively in accordance with a printing pattern so that a process of printing is performed. In addition, sub-electrodes are driven appropriately so that ink in the ink nozzles can be vibrated or the effect of separating ejected ink droplets from the ink nozzles can be enhanced. That is, auxiliary electric charge is performed between a sub-electrode and diaphragm so that parts of the diaphragm are bent toward the sub-electrode. Thus, menisci or ink of the ink nozzles can be vibrated without ejecting unnecessary ink droplets. As a result, the menisci can be prevented from being filmed with ink, without ejecting ink droplets. In addition, ink in ink channels is diffused so that the viscosity of the ink can be prevented from increasing due to the evaporation of the solvent of the ink. Further, if sub-electrodes are driven before ink droplets are ejected, troubles in printing caused by a failure or abnormality in ink ejection can be prevented without consuming ink playing no part in printing, even after no ink droplets has been ejected for a certain time because of no operation of the ink nozzles.
(3) In the ink jet head according to the present invention as stated in paragraph (2), a first gap between the main electrodes and the diaphragms is made different from a second gap between the sub-electrodes and the diaphragms. According to the present invention, for example, auxiliary electric charge is performed between a sub-electrode and diaphragm so that a part of the diaphragm is bent toward the sub-electrode. As a result, the timing when a tail portion of a discharged ink column is separated from ink in the ink nozzle can be hastened so that the effect of separating an ink droplet from the ink nozzle can be further enhanced.
(4) In the ink jet head according to the present invention as stated in paragraph (3), the first gap is set to be larger than the second gap. In the present invention, for example, when a driving voltage equivalent to the driving voltage for a main operation (ink ejection) is applied for an auxiliary operation, a Coulomb force produced in the auxiliary operation is larger than Coulomb force produced in the main operation so that the bending speed of the diaphragm in the auxiliary operation becomes higher than that in the main operation. As a result, the operation that a meniscus in the ink nozzle is drawn into the ink chamber is hastened so that the tail portion of the ejected ink column can be separated more surely in the auxiliary operation. Thus, it is possible to form ink droplets stably.
(5) In the ink jet head according to the present invention as stated in paragraph (2), the main electrodes are provided correspondingly to the diaphragms, and each sub-electrode includes a first sub-electrode provided in common for the plurality of diaphragms so as to face the diaphragms on the ink nozzle side, and one or a plurality of second sub-electrodes provided in common for a plurality of the diaphragms so as to be disposed between the main electrodes and the first sub-electrode.
In the present invention, the sub-electrodes are divided in series so that the electrostatic capacity thereof is reduced. Thus, the time constant of the sub-electrodes are prevented from increasing, so that the difference between the time constant of a circuit associated with a main electrode and the time constant of a circuit associated with a sub-electrode is reduced. As a result, proper control timing can be obtained easily for controlling both the electrodes. In addition, the operation delay among auxiliary actuators formed by the sub-electrode is also reduced so that the proper operations of the main and sub-electrodes can be obtained.
For example, in the case where the main electrode and the sub-electrode are driven simultaneously so that control is made for increasing the quantity of ink to be ejected in comparison with the case where only the main electrode is driven (that is, control is made for adjusting the printing density in multiple stages), or in the case where the sub-electrode is driven at a predetermined time after the main electrode was driven so that control is made for cutting the tail portion (rear end) of the ejected ink column to avoid production of a surplus ink droplet, proper timings of the control can be obtained, since the difference between the time constants of the respective circuits associated with the main electrode and the sub-electrode is small. As a result, precise printing control can be performed. Incidentally, the concept of the time constants of the respective circuits in the present invention will be described in detail later in Embodiment 4. In addition, according to the present invention, the sub-electrode is constituted by a plurality of electrodes so that the ink ejection quantity (density) can be adjusted in more multiple stages. In addition, the sub-electrode is formed in common for a plurality of diaphragms so that increase of the number of wires connecting the electrodes, which is involved by increase of the number of ink nozzles, can be avoided. Thus, increase in size of the ink jet head can be avoided.
(6) In the ink jet head according to the present invention as stated in paragraph (2), each of the main electrodes and sub-electrodes includes an opposed portion formed of ITO and oppositely disposed to the diaphragm, and a lead portion electrically connected with the opposed portion, wherein at least the lead portion of the sub-electrode is formed of metal. In the present invention, at least the lead portion of the sub-electrode is composed of metal so that the time constant of the circuit associated with the sub-electrode is reduced. As a result, the difference between the time constant of the circuit associated with the sub-electrode and the time constant of the circuit associated with the main electrode is reduced.
(7) In the ink jet head according to the present invention as stated in paragraph (6), the metal is composed of gold formed on chromium or titanium. The metal is attached to the substrate stably, so that it withstands long-term use without fear of peeling off.
(8) In the ink jet head according to the present invention as stated in paragraph (2), the diaphragms are formed as a common electrode, and a time constant of a circuit constituted by each electrode of the opposed electrodes and the common electrode is much smaller than a natural vibration period of corresponding one of the ink channels. Accordingly, the difference between the time constants of the respective circuits is also reduced, so that proper control timing can be obtained easily. In addition, an operation delay caused between auxiliary actuators formed by the sub-electrodes is also reduced so that proper operations of the main electrodes and sub-electrodes can be assured.
(9) In the ink jet head according to the present invention as stated in paragraph (2), the main electrodes are provided correspondingly to the diaphragms while a sub-electrode is provided in common for a predetermined number of the diaphragms so as to face the diaphragms on the ink nozzle side, wherein a plurality of umits each having a predetermined number of main electrodes and a sub-electrode are disposed. Since the sub-electrode is divided in parallel so that the respective capacities of the divisional electrodes are reduced, the time constant of the circuit associated with the sub-electrode is prevented from increasing. As a result, the difference between the time constant of the circuit associated with the main electrode and the time constant of the circuit associated with the sub-electrode is reduced. In addition, a sub-electrode is formed in common for a plurality of diaphragms so that, even if the number of ink nozzles increases, the number of wires connected to the sub-electrodes can be prevented from increasing in accordance therewith. Thus, the above-mentioned operations can be attained without increasing the number of wires in the ink jet head or without increasing the number of wires connecting a control circuit with the ink jet head.
(10) In the ink jet head according to the present invention as stated in paragraph (9), every adjacent two of the units are disposed to be symmetrical with respect to a boundary line between the units. Since every two units are arranged in parallel and symmetrically in such a manner, no sub-electrode lies between the main electrode groups of the two units. Therefore, when the ink jet head is manufactured, pattern groups of the main electrodes with one and the same pitch may be produced. Thus, the ink jet head is manufactured easily.
(11) According to the present invention, there is provided an ink jet printer comprising an ink jet head which includes a plurality of ink nozzles for ejecting ink, a plurality of ink chambers communicating with the ink nozzles respectively, ink supply channels for supplying ink to the ink chambers respectively, elastically displaceable diaphragms formed in circumferential walls constituting the ink chambers respectively, and opposed electrodes oppositely arranged to the diaphragms through a gap respectively, to eject ink droplets from the ink nozzles by performing electric charge/discharge between the opposed electrodes and the diaphragms; wherein each of the opposed electrodes are constituted by a plurality of electrodes each of which can perform electric charge/discharge to corresponding one of the diaphragms independently of the other electrodes, and at least one of the plurality of electrodes is electrically connected with the electrodes formed for the other diaphragms. In the present invention, the plurality of electrodes in an opposed electrode are driven in a desired combination, so that the quantity of ink ejected from an ink nozzle (density) can be adjusted in multiple stages. In addition, since at least one of the plurality of electrodes is electrically connected with the other electrodes formed for the other diaphragms, for example, a process for vibrating ink in the ink nozzles can be performed in common for the respective ink chambers. Thus, the control of such a process becomes easy.
(12) In the ink jet printer according to the present invention as stated in paragraph (11), an opposed electrode includes a main electrode to be electrically charged and discharged selectively in accordance with a printing pattern, and a sub-electrode formed on the ink nozzle side and electrically connected with sub-electrodes formed for the other diaphragms. In the present invention, main electrodes are driven selectively in accordance with a printing pattern so that a process of printing is performed. In addition, sub-electrodes are driven appropriately so that ink in the ink nozzles can be vibrated or the effect of separating ejected ink droplets from the ink nozzles can be enhanced.
(13) The ink jet printer according to the present invention as stated in paragraph (12) comprises a main electrode driving circuit for electrically charging/discharging the main electrodes and the diaphragms so that ink droplets are discharged from the ink nozzles; and a sub-electrode driving circuit for electrically charging/discharging the sub-electrodes and the diaphragms in a predetermined period or at a desired time so that ink in the ink nozzles is vibrated. In the present invention, the main electrodes are driven by the main electrode driving circuit so as to eject ink droplets, and the sub-electrodes are driven by the sub-electrode driving circuit so as to vibrate ink in the ink nozzles.
(14) The ink jet printer according to the present invention as stated in paragraph (12) comprises: a main electrode driving circuit for electrically charging/discharging the main electrodes and the diaphragms so that ink droplets are ejected from the ink nozzles; and a sub-electrode driving circuit for electrically charging/discharging the sub-electrodes and the diaphragms at a desired time after electrically discharging the main electrodes, so that ink ejected from the ink nozzles are separated from ink remaining in the ink chambers. In the present invention, the main electrodes are driven by the main electrode driving circuit so as to eject ink droplets, and the sub-electrodes are driven by the sub-electrode driving circuit so as to separate ink ejected from the ink nozzles, from ink remaining in the ink chambers.
(15) According to the present invention, there is provided a method for driving an ink jet head which includes a plurality of ink nozzles for ejecting ink, a plurality of ink chambers communicating with the ink nozzles respectively, ink supply channels for supplying ink to the respective ink chambers, elastically displaceable diaphragms formed in circumferential walls constituting the ink chambers respectively, and opposed electrodes oppositely arranged to the diaphragms through a gap respectively, to eject droplets from the ink nozzles by performing electric charge/discharge between the opposed electrodes and the diaphragms; wherein each of the opposed electrodes is constituted by a plurality of electrodes each of which can perform electric charge/discharge to corresponding one of the diaphragms independently of the other electrodes, and at least one of the plurality of electrodes is electrically connected with the other electrodes formed for the other diaphragms, and wherein the method includes the step of performing electric charge/discharge between the respective electrodes of the opposed electrodes and the diaphragms appropriately so as to eject ink droplets from the ink chambers. In the present invention, a plurality of electrodes of an opposed electrode are driven in a desired combination, so that the quantity of ink ejected from an ink nozzle (density) can be adjusted in multiple stages. In addition, as an auxiliary operation, for example, ink in the ink nozzles can be vibrated, or the effect of separating ink droplets from the ink nozzles can be enhanced.
(16) In the ink jet head driving method according to the present invention as stated in paragraph (15), each of the opposed electrodes includes a main electrode to be electrically charged and discharged selectively in accordance with a printing pattern, and an sub-electrode formed on the ink nozzle side and electrically connected with other sub-electrodes formed for the other diaphragms. This method includes the step of performing electric charge/discharge between the main electrodes and the diaphragms so that ink droplets are ejected from the ink nozzles, and the step of performing electric charge/discharge between the sub-electrode and the diaphragms so that ink in the ink nozzles is vibrated.
In the present invention, the auxiliary electric charge is performed between the auxiliary electrodes and the diaphragms so that parts of the diaphragms are bent toward the sub-electrodes. Thus, menisci or ink of the ink nozzles can be vibrated without ejecting unnecessary ink droplets. As a result, the menisci can be prevented from being filmed with ink, without ejecting ink droplets. In addition, ink in the ink channels is diffused so that the increase in viscosity of the ink caused by the evaporation of the solvent of the ink can be avoided. In addition, if the sub-electrodes are driven prior to the ejection of ink droplets, a trouble in printing caused by a failure or abnormality in ink ejection can be prevented without consuming ink playing no part in printing, even after no ink droplets has been ejected for a certain time because of no operation of the ink nozzles.
(17) In the ink jet head driving method according to the present invention as stated in paragraph (15), each of the opposed electrodes includes a main electrode to be electrically charged and discharged selectively in accordance with a printing pattern and a sub-electrode formed on the ink nozzle side and electrically connected with other sub-electrodes formed for the other diaphragms. The method includes the step of performing electric charge/discharge between the main electrodes and the diaphragms so as to eject ink droplets from the ink nozzles, and the step of performing electric charge/discharge between the sub-electrodes and the diaphragms so that the ink droplets ejected from the ink nozzles are separated from ink remaining in the ink chambers.
In the present invention, auxiliary electric charge is performed between the sub-electrodes and the diaphragms so that parts of the diaphragms are bent toward the sub-electrodes. As a result, the time for tail portions of ejected ink columns to leave the ink nozzles is shortened so that the effect of separating ink droplets from the ink nozzles can be enhanced. In addition, the menisci in the ink nozzles are drawn into the ink chambers on ejecting ink droplets, so that unnecessary ink droplets can be prevented from being ejected immediately after ejecting ink droplets contributing to printing. Thus, if the sub-electrodes are driven at a predetermined interval after the time when the main electrodes have been driven to eject ink droplets, unnecessary ink droplets can be prevented from being ejected after ejecting the necessary ink droplets. Thus, troubles of printing caused by a failure or abnormality in ink ejection can be prevented, even if ink droplets have been continuously ejected from the nozzles for a long time without wiping the nozzle surfaces.
(18) In the ink jet head driving method according to the present invention as stated in paragraph (15), in the step of performing electric charge/discharge between the main electrodes and the diaphragms to eject ink droplets from the ink nozzles, ink droplets ejected previously are separated from ink remaining in the ink chambers when succeeding ink droplets are ejected immediately thereafter. For example, in the case where one dot is formed of a plurality of ink droplets, the operation described in the paragraph (17) can be obtained by ejecting a following ink droplet.
(19) In the ink jet head driving method according to the present invention as stated in paragraph (15), the main electrodes are provided correspondingly to the diaphragms, and the sub-electrodes include a first sub-electrode provided in common for a plurality of the diaphragms so as to face the diaphragms on the ink nozzle side, and one or a plurality of second sub-electrodes provided in common for a plurality of the diaphragms so as to be disposed between the main electrodes and the first sub-electrode, and wherein the main electrodes and the sub-electrodes are driven in a desired combination so that ink droplets are ejected from the ink nozzles. In the present invention, the main electrodes and the sub-electrodes are driven in a desired combination so that the ink discharge quantity (density) can be adjusted in multiple stages.
(20) In the ink jet head according to the present invention as stated in paragraph (6), the metal is formed of chromium, titanium, aluminum, or platinum.
(21) In the ink jet head according to the present invention as stated in paragraph (2), each of the main and sub-electrodes includes an opposed portion formed of ITO and oppositely disposed to said diaphragm, and a lead portion electrically connected with said opposed portion, and at least the lead portion of the sub-electrode comprises a metal thin film and an ITO thin film formed on the metal thin film.
(22) In the ink jet head according to the present invention as stated in paragraph (21), the metal thin film is formed of chromium, titanium, silver, or an alloy composed of silver, palladium and copper.

Ink jet head, ink jet printer, and its driving method


A method is provided for removing iron oxide scale from sheet metal and producing a sheet metal surface with rust inhibitive properties. The sheet metal is advanced through the descaling cell and a slurry mixture is propelled against at least one of the top surface and bottom surface of the sheet metal across the sheet metal width as the material is advanced through the descaling cell. The rate of slurry impact against the at least one of the top surface and bottom surface of the sheet metal is controlled in a manner to remove substantially all of the scale from a surface of the sheet metal, and in a manner to create a passivation layer on the descaled surface of the sheet metal. The passivation layer comprises at least one of silicon, aluminum, manganese and chromium and inhibits oxidation of the descaled surface of the processed sheet metal.

The disclosure pertains to a process for removing undesirable surface material from flat materials either in sheet or continuous form, and from narrow tubular material. In particular, the disclosure pertains to an apparatus and method for removing scale from the surfaces of processed sheet metal or metal tubing by propelling a scale removing medium, specifically, a liquid/particle slurry, against the surfaces of the material passed through the apparatus, and controlling the slurry blasting process in a manners to produce a resultant material that exhibits rust inhibitive properties.
As will be described in further detail below, the methods and apparatuses disclosed herein provide advantages over the apparatuses and methods used in the prior art. Sheet steel (a.k.a. flat roll) is by far the most common type of steel and is far more prevalent than bar or structural steel. Before sheet metal is used by manufacturers it is typically prepared by a hot rolling process. During the hot rolling process, carbon steel is heated to a temperature in excess of 1,500° F. (815° C.). The heated steel is passed through successive pairs of opposing rollers that reduce the thickness of the steel sheet. Once the hot rolling process is completed, the processed sheet metal or hot rolled steel is reduced in temperature, typically by quenching it in water, oil, or a polymer liquid, all of which are well known in the art. The processed sheet metal is then coiled for convenient storage and transportation to the ultimate user of the processed sheet metal, i.e. the manufacturers of aircraft, automobiles, home appliances, etc.
During the cooling stages of processing the hot rolled sheet metal, reactions of the sheet metal with oxygen in the air and with the moisture involved in the cooling process can result in the formation of an iron oxide layer, commonly referred to as "scale," on the surfaces of the sheet metal. The rate at which the sheet metal is cooled, and the total temperature drop from the hot rolling process effect the amount and composition of the scale that forms on the surface during the cooling process.
In most cases, before the sheet metal can be used by the manufacturer, the surface of the sheet metal must be conditioned to provide an appropriate surface for the product being manufactured, so that the sheet metal surface can be painted or otherwise coated, for example, galvanized. The most common method of removing scale from the surface of hot rolled or processed sheet metal is a process known as "pickling and oiling." In this process, the sheet metal, already cooled to ambient temperature following the hot rolling process, is uncoiled and pulled through a bath of hydrochloric acid to chemically remove the scale formed on the sheet metal surfaces. Following removal of the scale by the acid bath, the sheet metal is then washed, dried, and immediately "oiled" to protect the surfaces of the sheet metal from oxidation or rust. The oil provides a film layer barrier to air that shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture.
Virtually all flat rolled steel is pickled and oiled. Because flat rolled steel is so commonly used—it is typically used in automobiles, appliances, construction, and nearly all of our agricultural implements—pickling and oiling, either as an end result pickled product or pickled to produce other common materials such as cold roll, prepaint, galvanize, electro galvanize, etc, is also very common. To illustrate the scope of the practice, one of the largest steel producers in the world operates a very large steel mill that has 16 pickle lines each running about 90,000 monthly tons. Some estimate that there are approximately 100 pickle lines in the U.S. alone with several thousand more located abroad.
The "pickling" portion of the process is effective in removing substantially all of the oxide layer or scale from processed sheet metal. However, the "pickling" portion of the process has a number of disadvantages. For example, the acid used in the acid bath is corrosive; it is damaging to equipment, it is hazardous to people, and is an environmentally hazardous chemical which has special storage and disposal restrictions. In addition, the acid bath stage of the process requires a substantial area in the sheet metal processing facility. Pickling lines are typically about 300-500 feet long, so they take up an enormous amount of floor space in a steel mill. Their operation is also very expensive, operating at a cost of approximately $12/ton-$15/ton. A "pickling and oiling" line with a tension leveler costs approximately $18,000,000.00. Also, it is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture. Oftentimes, free ions from the acid solution (i.e., Cl−) remain on the surface of the metal after the pickling portion of the process, thereby accelerating oxidation unless oiled immediately.
Oiling is also effective in reducing oxidation of the metal as it shields the bare metal surfaces of the sheet metal from exposure to atmospheric air and moisture. However, oiling also has disadvantages. Applying and subsequently removing oil takes time and adds substantial cost both in terms of material cost of the oil product itself, and in terms of the labor to remove oil before subsequent processing of the steel. Like the pickling acid, oil is an environmentally hazardous material with special storage and disposal restrictions. Oil removal products are usually flammable and likewise require special controls for downstream users of the steel product. Also, again, it is critical that the sheet metal be oiled immediately after the pickling process, because the bare metal surfaces will begin to oxidize almost immediately when exposed to the atmospheric air and moisture.
The methods and apparatuses disclosed herein eliminate pickling lines and the need to put oil on the product after pickling. The methods and apparatuses disclosed herein produce a rust inhibitive product, whereas conventional shot blasting and other blasting techniques do not produce a resultant product with rust inhibitive properties, and thus do not replace the need for pickling and oiling. A processing line incorporating the methods and apparatuses disclosed herein avoids the many disadvantages of a pickling and oiling line. For instance, a processing line incorporating the methods and apparatuses disclosed herein is about 100 feet long, thereby saving significant space in a facility. The methods and apparatuses disclosed herein allow for recycling of many of the materials used in the process, without the use of harmful chemicals and acids. Operating costs associated with a processing line using the methods and apparatuses disclosed herein are $7/ton-$10/ton, which is significantly lower than the operating costs of approximately $12/ton-$15/ton associated with a "pickling and oiling" line. The capital cost of a typical line utilizing the methods and apparatuses disclosed herein is about $6,000,000.00, whereas the capital costs for a typical pickling line are about $18,000,000.00.

This patent is subject to a terminal disclaimer.

Method of producing rust inhibitive sheet metal through scale removal with a slurry blasting descaling cell having improved grit flow


The time interval/amplitude level difference between sequential peaks in waveforms of first reproducing signals from a recording medium is detected and stored in a storage. The time interval/amplitude level difference between peaks in a waveform of a second reproducing signal from the recording medium is detected and compared with the time interval/amplitude level difference stored in the storage to thereby perform peak detection in the waveforms thereof. An original bit train of the first reproducing signal corresponding to a maximum-likelihood waveform selected among the waveforms of the first reproducing signals is given as a standardized signal. Data are provided to represent the time interval/amplitude level difference between the sequential peaks in the waveforms of the reproducing signals in a range of electromagnetic signal interference on the recording medium.

The present invention relates to the peak detection and peak sense detection or phase discrimination of a reproducing signal in a system for reproducing a magnetic record on a medium such as a magnetic tape, a magnetic disk, or the like. In particular, it relates to a peak detection system for reducing intersymbol interference (ISI) in code signals to thereby improve the S/N of a reproducing signal.
Maximum-likelihood peak position detection techniques applied to peak detection to equivalently reduce noise have been discussed in: H. Burkhardt, "An Event-driven Maximum-likelihood Peak Position Detector for Run-length-limited Codes in Magnetic Recording", IEEE Transactions on Magnetics, Vol. MAG-17, No. 6, pp. 3337-3339 (1981), and in U.S. Pat. No. 4,644,564.
Digital magnetic recording and signal processing techniques have been discussed in F. Dolivo, "Signal Processing for High-Density Digital Magnetic Recording", IEEE, pp. 1-91-96 (1989).
When magnetic recording is applied to a medium 31 in FIG. 1A, recording bits 30 composed of "1" and "0" (see FIG. 1B) are recorded as the presence and absence of magnetic flux change on the medium 31. Any one of MFM or run-length-limited codes such as (1, 7) code and (2, 7) code systems may be used. This magnetic flux change is read out as a peak 33a of a reproducing signal 33 (see FIG. 1C) from a magnetic head 32. To decide the phase of the peak 33a, the reproducing signal 33b equalized by an equalization circuit 34 (see FIG. 1D) is differentiated by a differentiation circuit 35. The zero-cross points of the differentiated signal waveform 33c (see FIG. 1E) are converted into a peak pulse train 37 by a pulse forming circuit 36 to thereby detect the phase of the signal peak 33a. A peak detection circuit 38 compares the phase of the detected peak pulse 37 (see FIG. 1F) with a detection window signal 37a (see FIG. 1G) having pulses respectively representing the width of a recording bit and judges by the presence and absence of pulses in the windows whether a bit of the reproducing coded signal 39 (see FIG. 1H) is to be "1" or to be "0". Recently, the pulse width of the window signal 37a generated by an oscillator (OSC) 29 on the basis of the signal 37 has been shortened to 18-19 ns.
In the following, detection error which occurs in the aforementioned peak detection systems is described with reference to FIGS. 2A through 2D as a part of the present invention.
As shown in FIG. 2A, the amplitude of a signal is reduced by the presence of adjacent magnetic flux change 40, that is, intersymbol interference (ISI) and nonlinear distortion occurs. As a result, the phase of a waveform peak 42 shifts by a pattern peak shift value 47 from an ideal isolated reproducing signal waveform When noise is superimposed on this signal, the peak 42 shifts further so that it may be out of a window width 43. In this case, a peak pulse 37 (see FIG. 1F) corresponding to the phase of the peak 42 also shifts toward an adjacent window width 44, so that detection error 46 in two bits of the target window width 43 and the adjacent window width 44 may be brought by bit inversion 45.

Peak detection method and apparatus therefor


A protection circuit for protecting a device from destructive electrical conditions, such as ESD, over-voltage, and over-current, while keeping the output impedance of the device's I/O lines to a minimum, and self-regulating power dissipation. The device may comprise a first protection circuit and a second protection circuit coupled to each of one or more I/O lines for providing a primary and a secondary level of protection, respectively, for the I/O lines. The first protection circuit of the device may combine the use of Schottky diodes for voltage clamping, with a current limiting device for self-regulating the power dissipation. The current limiting device may be operable to function as a small, low impedance resistor in a normal operating range and as a controlled power dissipater outside the normal operating range. The device may be a data acquisition device comprised in a data acquisition system.

1. Field of the Invention
This invention relates generally to measurement and data acquisition systems and, more particularly, to a circuit for protecting general-purpose digital input/output lines against destructive electrical conditions.
2. Description of the Related Art
Scientists and engineers often use measurement systems to perform a variety of functions, including measurement of a physical phenomena or unit under test (UUT), test and analysis of physical phenomena, process monitoring and control, control of mechanical or electrical machinery, data logging, laboratory research, and analytical chemistry, to name a few examples.
A typical measurement system comprises a computer system with a measurement device or measurement hardware. The measurement device may be a computer-based instrument, a data acquisition device or board, a programmable logic device (PLD), an actuator, or other type of device for acquiring or generating data. The measurement device may be a card or board plugged into one of the I/O slots of the computer system, or a card or board plugged into a chassis, or an external device. For example, in a common measurement system configuration, the measurement hardware is coupled to the computer system through a PCI bus, PXI (PCI extensions for Instrumentation) bus, a GPIB (General-Purpose Interface Bus), a VXI (VME extensions for Instrumentation) bus, a serial port, parallel port, or Ethernet port of the computer system. Optionally, the measurement system includes signal conditioning devices which receive field signals and condition the signals to be acquired.
A measurement system may typically include transducers, sensors, or other detecting means for providing "field" electrical signals representing a process, physical phenomena, equipment being monitored or measured, etc. The field signals are provided to the measurement hardware. In addition, a measurement system may also typically include actuators for generating output signals for stimulating a UUT.
Measurement systems, which may also be generally referred to as data acquisition systems, may include the process of converting a physical phenomenon (such as temperature or pressure) into an electrical signal and measuring the signal in order to extract information. PC-based measurement and data acquisition (DAQ) systems and plug-in boards are used in a wide range of applications in the laboratory, in the field, and on the manufacturing plant floor, among others.
In a measurement or data acquisition process, analog signals may be received by a digitizer, which may reside in a DAQ device or instrumentation device. The analog signals may be received from a sensor, converted to digital data (possibly after being conditioned) by an Analog-to-Digital Converter (ADC), and transmitted to a computer system for storage and/or analysis. When a measurement system generates an output analog signal, the computer system may generate digital signals that are provided to one or more digital to analog converters (DACs) in the DAQ device. The DACs may convert the digital signal to an output analog signal that is used, e.g., to stimulate a UUT.
Multifunction DAQ devices typically include digital I/O capabilities in addition to the analog capabilities described above. Digital I/O applications may include monitoring and control applications, video testing, chip verification, and pattern recognition, among others. DAQ devices may include one or more general-purpose, bidirectional digital I/O lines to transmit and receive digital signals to implement one or more digital I/O applications.
General-purpose, bidirectional digital I/O lines are typically susceptible to destructive electrical conditions, such as over-voltage, over-current, and electrostatic discharge (ESD). A common solution to protect against over-voltage and/or ESD in electronic devices is to include one or more voltage clamping devices external to the device and on the lines to be protected to prevent damage from these electrical conditions. When the voltage rises above the voltage limit for the device, the voltage clamping devices may protect the device from over-voltage conditions by clamping or fixing the voltage at approximately the voltage limit. The voltage clamping device preferably sinks any excess current to block the current from damaging the device. In some implementations, two clamping diodes external to the device may be used for clamping the signal to the positive voltage rail and ground of the device. The diodes may keep the voltage at the protected node in check, as long as they can withstand the high currents that occur when the diodes starts clamping. Therefore, in some implementations, a clamping circuit such as this one may convert the problem of over-voltage into a problem of over-current.
Diodes typically have a limit on the peak current and the sustained current they can withstand. The sustained or continuous current limit is the maximum current the diodes are guaranteed to withstand for an undefined period of time without damage. Above this limit, the diode may only withstand the current for a limited period of time, i.e., the larger the current, the shorter the period of time. In the case of the circuit including two diodes, they may only offer protection against very short duration over-voltage conditions before the diodes themselves suffer damage. The current through the diodes may only be limited by the small impedance of the diodes themselves and the impedance of the voltage source associated with the voltage rails of the device. The I-V curve of a diode is an exponential function, and it typically does not take too much over-voltage to exceed the maximum continuous current of the diode.
It is an industry standard to protect all input and general-purpose, bidirectional I/O terminals in a semiconductor device with internal clamping diodes similar to the external clamping diodes described above. When the internal diodes are voltage clamping, there may be the added risk of activating a latchup condition which is a potentially self destructing mode the semiconductor can get into where the circuitry draws excess current, and may only get out of it by removing power to the semiconductor. The internal clamping diodes are typically designed to clamp over-voltage or ESD events which are very short on duration.
In other implementations, a resistor in series with the line to be protected may be added to the protection circuit described above to control the current once the diodes enter a clamping mode. The resistor may limit the current through the diodes when they are voltage clamping, which typically extends the over-voltage protection range, because it takes a greater over-voltage to reach the maximum continuous current of the diodes. However, at the same time the resistor may increase the line impedance in normal operation, which may reduce the normal current possible for a given output voltage. In sum, the higher the resistance of the resistor, the higher the over-voltage protection range, but typically the lower the performance of the device.
Furthermore, in the protection circuit described above, which includes the resistor in series with the I/O line, and the internal and external clamping diodes, there may also be a tradeoff between the power dissipation of the components and the level of protection. The equation for the power dissipation on the resistor is proportional to the square of the over-voltage and is inversely proportional to the resistor value. Power dissipation typically becomes an important issue since it is desirable to offer the greatest over-voltage protection while having the resistance of the added resistor to be as small as possible.

Protection circuit for general-purpose digital I/O lines


Methods and apparatus for portable and universal receipt of closed captioning services by a user are provided in accordance with the invention. The invention permits a user to receive closed captioning services wherever he or she may be viewing video content with an audio component in accordance with a video/audio content display system (e.g., television set, computer monitor, movie theater), regardless of whether the content display system provides closed captioning capabilities. Also, the invention permits a user to receive closed captioning services independent of the video/audio content display system that they are using to view the video content. In one illustrative aspect of the present invention, a portable and universal closed caption receiving device (closed caption receiver) is provided for: (i) receiving a signal, which includes closed captions, from a closed caption provider while the user watches a program on a video/audio content display system; (ii) extracting the closed captions; and (iii) providing the closed captions to a head mounted display for presentation to the user so that the user may view the program and, at the same time, view the closed captions in synchronization with the video content of the program.

Closed captioning (CC) integrated circuits or chips exist in many television sets. This chip allows for receipt and decoding of a text-based signal transmitted in association with the transmission of a television signal representing a movie or other television program. The text is intended to be a verbatim representation of the audio content of the program, e.g., what a person in the program is currently saying. One reason such text is used is so that individuals with a hearing impairment have a visual means of receiving the audio content of the televised program.
However, there are many situations when there is no closed captioning service provided on a television. For instance, there may be public and/or private areas where the chip may not be activated, for example, in a fitness club that has television sets for their customers, or a host's house that has not activated a chip although guests may be present that require it. A guest may also not feel comfortable asking a host to activate the closed captioning chip. For these reasons, a televised program that may otherwise have closed captioning service associated therewith, may still not be presented with closed captions.
There are also many other devices for presenting video/audio content that have no means to display closed captions. Computer monitors, for instance, may play a movie or a segment from a news brief (e.g., either from a downloaded feed or from a compact disc or digital video disc), but will often not have the ability to display closed captions. A movie theater display system is another example of one that typically has no ability to display closed captions.
It is to be appreciated that closed captioning services are necessary not only for the hearing impaired population but for foreigners and people who speak a different native tongue. People who speak another language may require closed captions because it will allow a movie, show, or news brief to be translated into their native tongue.
U.S. Pat. No. 5,537,151 issued Jul. 16, 1996 to Orr et al. and entitled "Closed Caption Support with Timewarp," the disclosure of which is incorporated by reference herein, discloses a method of providing closed captioned data to a television viewer which includes: detecting closed captioned data signals transmitted in conjunction with a television signal; decoding the data signals to caption display signals; and displaying the caption display signals on an auxiliary screen separate from a screen displaying the television signals. As stated therein, the Orr et al. method is an attempt to avoid the problem associated with closed caption text obstructing a portion of the video displayed on a television screen. However, while Orr et al. discloses use of an auxiliary screen, the computer which drives the auxiliary screen is tasked with extracting the closed caption portion from the television signal, processing the video signal portion, and sending the processed video signal to the television display. The auxiliary screen is placed near the television display. However, one problem with this arrangement is that the closed caption extractor does not operate independently from, or autonomously with respect to, the television. Another problem is that the auxiliary display is not portable.
Accordingly, there is a need for methods and apparatus which are capable of portably and universally receiving closed captioning services regardless of whether a display device presenting a particular program is capable of, or activated to, display closed captions.

Universal closed caption portable receiver

International Business Machines Corporation


A driving section 4 supplies a reading pulse of ‘H’ to electrodes V1 and V5 simultaneously with completion of exposure to read out electric charges to empty packets below electrodes V1, V2, V5, and V6. Then, the driving section 4 supplies a driving pulse of ‘M’ to electrodes V3 and V7 and a multiplication pulse to the electrodes V2 and V6. At this time, a level of the multiplication pulse supplied to the electrodes V2 and V6 is set so that a potential difference between the electrodes V1 and V3 and the electrode V2 and a potential difference between the electrodes V5 and V7 and the electrode V6 become values required to cause avalanche multiplication. Electric charges accumulated below the electrodes V1 to V3 move into packets formed below the electrodes V2 and V6. The avalanche multiplication occurs at the time of movement. Thus, the electric charges are multiplied.

1. Technical Field
The invention relates to a method of driving a CCD type solid-state imaging device having a plurality of photoelectric conversion elements, which are arranged on a semiconductor substrate in a row direction and a column direction perpendicular to the row direction, and a charge transfer device that reads out electric charges generated in the plurality of photoelectric conversion elements and that transfers the read electric charges in the column direction, which is a charge transfer direction.
2. Description of the Related Art
Japanese Patent Nos. 2609363 and 3483261 disclose a technique for improving the sensitivity of a CCD type solid-state imaging device by multiplying electric charges at the time of charge transfer through avalanche multiplication in a charge transfer channel.
FIG. 11 is partially sectional views schematically illustrating a charge transfer device disclosed in Japanese Patent No. 2609363.
As shown in FIG. 11, a charge transfer device is configured to include a charge transfer channel 200 formed in a silicon substrate, an insulating layer 201 formed on the charge transfer channel 200, and a plurality of electrodes 202 to 205 formed on the insulating layer 201. As shown in FIG. 11(a), a driving pulse on which a reading pulse is superimposed is supplied to the electrode 203 so that a potential well (hereinafter, referred to as "packet") P1 is formed in the charge transfer channel 200 and below the electrode 203 and that electric charges generated in a photoelectric conversion element (not shown) are read out to the packet P1. Then, as shown in FIG. 11(b), a pulse having a predetermined level is supplied to the electrode 204 to form a packet P2 in the charge transfer channel 200 and below the electrode 204. At this time, levels of the pulses supplied to the electrodes 203 and 204 is set so that a potential difference between the packet P1 and the packet P2 becomes a value required to cause the avalanche multiplication.
A difference between depths of the packets P1 and P2 occurs due to a level difference between the pulses supplied to the electrodes 203 and 204. The depth of the packet P2 is larger than that of the packet P1. Accordingly, electric charges existing in the packet P1 move to the packet P2. In this case, since the electric charges move through a high electric field region d generated between the electrodes 203 and 204, the avalanche effect occurs in the high electric field region so that the electric charges are multiplied. After multiplying the electric charges, a level of a pulse supplied to the electrode 204 is changed to a level that causes the packet P2 to be a barrier against the packet P1. Thus, the packet P2 returns to its original state as shown in FIG. 11(c). Then, the electric charges existing in the packet P1 are transferred in the charge transfer direction by supplying transfer pulses to the plurality of electrodes 202 to 205.
In the method of driving a charge transfer device described above, the following problem arises because there is a potential difference between barrier potentials at both ends of the packet P2 for causing the avalanche multiplication as shown in FIG. 11. In the case when the packet P2 is formed as shown in FIG. 11(b), even unnecessary charges (referred to as "unnecessary charges A"), such as noises generated on a surface of the charge transfer channel 200 below the electrode 205, move to the packet P2 together with the electric charges existing in the packet P1. In addition, the unnecessary charges A are also multiplied in the high electric field region between the electrodes 204 and 205. On the other hand, unnecessary charges (referred to as "unnecessary charges B") exist even in the packet P1. Accordingly, the unnecessary charges B are also multiplied in the same manner as described above. Moreover, a region d2 between the electrodes 204 and 205 is larger in electric field than a region d1 between the electrodes 203 and 204. Therefore, the unnecessary charges A are larger in number than the unnecessary charges B. Also, the large electric field causes breakdown of free electrons in the region d2. Accordingly, a multiplication factor of the unnecessary charges A is larger than that of the unnecessary charges B. As a result, S/N is deteriorated.

Method of driving CCD type solid-state imaging device and solid-state imaging apparatus


A cable routing has a body (10) and a plurality of cable passages (22) through the body. Each passage has an entry socket (24) adapted to receive a cable end (20), an exit (26) in line with the entry socket and a lateral opening (28). Each passage also has a cross-sectional reduction between the entry socket (24) and the exit (26) to limit longitudinal movement of a cable (20) along the passage.

This invention relates to a cable routing device, particularly intended for routing optical fibre cables within optical fibre installations, and to a tube retaining clip for use with such routing devices.
Optical fibres are becoming evermore widely used. Where a large number of fibres need to be connected to individual terminal fittings, there is a need for a fibre management system which will ensure that the fibres are correctly handled, not unduly stressed and not damaged, and which also enables the individual fibres to be properly organised so that they can be positioned and routed correctly and can be identified.
Optical fibres are conventionally guided within a protective sheath or outer cable which provides physical protection for the fibre. However where the fibre has to be terminated and/or connected to other fibres, the fibre has to emerge from the outer cable, and at this point care is needed to ensure that the fibre is not mis-handled.


Methods and apparatus for detecting photoacoustic signals in fluid media are described. The present invention differs from conventional photoacoustic spectroscopy in that rather than accumulating the absorbed energy in the fluid of a sample cell, the absorbed energy is accumulated in an acoustic detector or sensitive element. In a preferred embodiment, the acoustic detector comprises piezoelectric crystal quartz. The quartz is preferably in the shape of a tuning fork.

Photoacoustic spectroscopy (PAS) is an analytical method that involves stimulating a sample by light and subsequently detecting sound waves emanating from the sample. Typically, only a narrow range of wavelengths of light are introduced into a sample. Such narrow range of wavelengths of light can be formed by, for example, a laser. Utilization of only a narrow range of wavelengths can enable pre-selected molecular transitions to be selectively stimulated and studied.
A photoacoustic signal can occur as follows. First, light stimulates a molecule within a sample. Such stimulation can include, for example, absorption of the light by the molecule to change an energy state of the molecule. Second, an excited state structure of the stimulated molecule rearranges. During such rearrangement, heat, light, volume changes and other forms of energy can dissipate into an environment surrounding the molecule. Such forms of energy cause expansion or contraction of materials within the environment. As the materials expand or contract, sound waves are generated.
In order to produce a series of sound waves or photoacoustic signals, the light is pulsed or modulated, at a specific resonant acoustic or modulation frequency f. Accordingly, an acoustic detector mounted in acoustic communication with the environment can detect changes occurring as a result of the light stimulation of the absorbing molecule concentration or signal.
Because the amount of absorbed energy is proportional to the concentration of the absorbing molecules, the acoustic signal can be used for concentration measurements.
In typical PAS, a resonant acoustic cavity or sample cell with a quality factor Q is used to isolate and amplify sound wave signals, thereby increasing sensitivity of detection. The light intensity or wavelength is modulated at f. The absorbed energy is accumulated in the acoustic mode of the sample cell during Q oscillation periods. Hence, the acoustic signal is proportional to the effective integration or energy accumulation time t, where t=Q/f. Most often the Q factor is in the range 40–200 and f=1,000–4,000 Hz. For example, if Q=70 and f=1250 Hz, then t=0.056 s
An exemplary prior art apparatus 10 for PAS is shown in FIG. 1. Apparatus 10 comprises a light source 12 configured to emit a beam of radiation into a sample holder 14. Light source 12 can comprise, for example, a laser. Filters (not shown) can be provided between light source 12 and sample holder 14 for attenuating the light prior to its impacting sample holder 14.
Sample holder 14 comprises a sample cell 18 containing a sample 16. Sample cell 18 can comprise a number of materials known to persons of ordinary skill in the art, and preferably comprises a material substantially transparent to the wavelength(s) of light emanating from light source 12. Preferred materials of sample cell 18 will accordingly vary depending on the wavelengths of light utilized in the spectroscopic apparatus.
Sample 16 comprises a material that substantially fills sample cell 18. Such material can be, for example, a fluid such as a liquid or a gas. Sample 16 can, for example, comprise a liquid solution wherein the molecular vibrations that are to be studied are associated with molecules dissolved in the liquid.
Apparatus 10 further comprises an acoustic detector 20 mounted to sample cell 18 and in acoustic communication with sample 16. Acoustic detector 20 can comprise a transducer, such as, for example, a microphone and can be mounted such that a fluid is provided between a surface of detector 20 and sample cell 18. Detector 20 is typically removably mounted to sample cell 18 by, for example, a clamp. Acoustic detector 20 is in electrical communication with an output device 22. Device 22 can be configured to display information obtained from detector 20, and can be further configured to process such information. Output device 22 can comprise, for example, an oscilloscope or a computer.
In operation, a beam of light is generated by source 12 and passed through sample cell 18 to stimulate molecular excitation within sample 16. Non-radioactive decay or molecular rearrangements cause expansions and/or contractions of a material within sample 16 to generate acoustic waves passing from sample 16 through sample cell 18 and to acoustic detector 20. Acoustic detector 20 then detects the acoustic waves and passes signals corresponding to, for example, amplitudes and frequencies of the acoustic waves to output device 22. Output device 22 can be configured to convert information obtained from detector 20 to, for example, a graphical display.
In this way the absorbed laser power is accumulated in the acoustic mode of sample cell 18 for Q acoustic oscillation periods before the sound waves decay. As can be appreciated, the dimensions of sample cell 18 are dependent upon f, where the size of the resonant sample cell cannot be less than half an acoustic wavelength, that is ˜15 cm at f=1,000 Hz. Also, because PAS detectors are sensitive to environmental noise, additional buffer volumes are often added onto the sample cells to suppress background noise.
Achieving longer t's in a fluid-filled sample cell 18 is problematic because of sample cell dimension constraints in addition to intrinsic losses related to gas viscosity and other relaxation processes.
In order to achieve longer energy accumulation times (t's), and therefore better signals, a need exists for methods and apparatus that can detect changes occurring as a result of the light stimulation of an absorbing molecule without the use of a sample cell.


Interface circuits for connecting gallium arsenide circuits with silicon circuits with the interface circuits using a mix of gallium arsenide and silicon devices. Preferred embodiments (200) connect gallium arsenide buffered FET logic circuits (202) with silicon CMOS circuits with a two branch interface circuit under CMOS supply voltages with a BFL logic branch (208-210) merged with a CMOS inverter branch (204-206).

1. Field of the Invention
The present invention relates to electronic semiconductor devices, and, more particularly, to interfaces of silicon-based and III-V-based circuits.
2. Description of the Related Art
Many researchers have investigated growth of semiconductor-device quality gallium arsenide (GaAs) on silicon wafers and fabrication of active devices in the GaAs. Such devices would combine the higher mobility of carriers in GaAs with the greater mechanical strength and thermal conductivity of a silicon substrate. For example, R. Fischer et al, GaAs/AlGaAs Heterojunction Bipolar Transistors on Si Substrates, 1985 IEDM Tech.Dig. 332, report GaAs/AlGaAs heterojunction bipolar transistors grown on silicon substrates and having current gains of .beta.=13 for a 0.2 .mu.m thick base. Similarly, G. Turner et al, Picosecond Photodetector Fabricated in GaAs Layers Grown on Silicon and Silicon On Sapphire Substrates, 1985 IEDM Tech.Dig. 468, report response times of 60 picoseconds for photoconductive detectors fabricated in GaAs on silicon. H. Shichijo et al, GaAs E/D MESFET 1-kbit Static RAM Fabricated on Silicon Substrate, 8 IEEE Elec.Dev.Lett. 121 (1987) reports a static RAM in GaAs on silicon, and H. Tran et al, GaAs/AlGaAs Heterojunction Emitter-Down Bipolar Transistors Fabricated on GaAs-on-Si Substrate, 8 IEEE Elec.Dec.Lett. 50 (1987) reports a vertical heterojunction bipolar transistor in GaAs on silicon. These articles also note that majority carrier devices such as MESFETs fabricated in GaAs on silicon have performance approaching that of homoepitaxial devices; and this has encouraged efforts to integrate GaAs-based optoelectronic and high-frequency devices with high density silicon devices on the same wafer to utilize high-data-rate optical or electrical interconnections, thereby reducing the number of wire interconnections or enhancing system performance through selective use of high speed GaAs devices on silicon VLSI. In order to achieve this goal, however, it will be necessary to develop materials growth and device processing techniques that will permit the coexistance of circuit elements with vastly different fabrication requirements. One of the most promising of these approaches is the patterned growth of GaAs onto a silicon substrate through openings in a protective mask of either silicon nitride (Si.sub.3 N.sub.4) or silicon dioxide (SiO.sub.2). In this scheme, the fabrication of the silicon based devices (which typically require high temperature processing) would be completed prior to the deposition of a protective oxide or nitride overlayer. Single crystal GaAs could then be grown into lithographically defined holes in the overlayer, and GaAs device fabrication would follow.
Previous work has established that epitaxial GaAs can be successfully deposited onto silicon substrates through a patterning mask; see B. Y. Tsaur et al, 41 Appl Phys. Lett. 347 (1982), P. Sheldon et al, 45 Appl. Phys. Lett. 274 (1984), Daniele et al, U.S. Pat. No. 4,587,717, and Betsch et al, U.S. Pat. No. 4,551,394. In addition, the integration of Si and GaAs device structures via this technology has been demonstrated; see H. K. Choi et al, 7 IEEE Elec.Dev.Lett. 241 and 500 (1986); and H. Shichijo et al, Co-Integration of GaAs MESFET and Si CMOS Circuits, 9 IEEE Elec.Dev.Lett. 444 (1988).
The simplest avenue for the patterned growth of GaAs on Si would involve the epitaxial growth of the GaAs onto the original planar silicon surface. However, the final level of the GaAs surface where device fabrication occurs may be several microns above the the level of prefabricated silicon devices. This situation would naturally complicate the interconnect of the two device structures by conventional metallization schemes. Indeed, for integrated circuits with both digital silicon and digital GaAs devices on an underlying silicon substrate, the coplanarity between the surface of the GaAs regions and the surface of the silicon substrate is essential. One method to achieve this coplanarity is by forming recesses in the silicon substrate where the GaAs regions are to be located and then growing a GaAs layer until the surface of the GaAs in the recesses is coplanar with the surface of the silicon substrate outside of the recesses. Typically the recesses will be about two to three microns deep. FIG. 1a illustrates in cross sectional elevation view of a MESFET in a GaAs-filled recess in a silicon substrate connected to a p-channel MOSFET in a n well in the silicon substrate. FIG. 1a is heuristic and does not indicate the interface problem between GaAs circuits and silicon circuits which typically operate at different voltage levels and swings.
Hybrid circuits with GaAs and silicon circuits on seperate substrates which are wired together typically have level translation subcircuits built-in at the input and output of the GaAs circuits to provide compatibility with the silicon circuits. See for example, M. Ino et al, A 1.2 ns GaAs 4 kb Read-Only-Memory Fabricated by 0.5 .mu.m-Gate BP-SAINT, 1987 IEEE GaAs IC Sump. 189; M. Kane, A 1.5 GHz Programmable Divide-by-N GaAs Counter, 23 IEEE J.S.S.C. 480 (1988); G. Schon et al, Fully ECL-Compatible GaAs Standard-Cell Library, 23 IEEE J.S.S.C. 677 (1988); and B. Chappell et al, Fast CMOS ECL Receivers with 100-mV Worst-Case Sensitivity, 23 IEEE J.S.S.C. 61 (1988) which has interfaces for silicon CMOS to silicon ECL. However, these level translation subcircuits must provide high-drive and have large power dissipation.

Interface circuit operable to perform level shifting between a first type of device and a second type of device


Methods and apparatus for arthroscopic tenodesis using sockets in bone created by retrograde cutting. A cannulated pin is drilled through bone and into a joint space in the normal, antegrade direction, guided by a drill guide. A strand provided through the cannulated pin is used to draw a retrodrill cutter into the joint space. The retrodrill cutter is threaded onto the cannulated pin, which is turned for retrograde cutting of a socket into the bone. The method is used to form a pair of sockets in the joint, which accept the respective ends of a replacement graft. The graft is brought into position in the joint space using loops formed in the strands, in a manner similar to introduction of the retrodrill cutter. The reconstruction is completed by securing suture attached to the graft ends with a button implant installed at the bone surface.

Methods of anterior cruciate ligament (ACL) reconstruction (tenodesis) using interference screw fixation are described, for example, in U.S. Pat. Nos. 5,211,647 and 5,320,626. In general, these methods of tenodesis involve drilling a tunnel through the tibia, drilling a closed tunnel (socket) into the femur, inserting a substitute ACL graft into the tunnels, and securing the grafts to the walls of the tibial and femoral tunnels using interference screws or the like. Accurate positioning of the tibial and femoral tunnels is accomplished using a drill guide, examples of which are disclosed in U.S. Pat. Nos. 5,269,786 and 5,350,383, incorporated herein by reference.
One drawback of the described tenodesis methods is that forming the tibial tunnel involves removal of significant amounts of bone material. U.S. Pat. No. 5,603,716 to Morgan et al. discloses a technique for ACL reconstruction that avoids the above-noted problem by forming sockets in both the femur and the tibia using a coring bone harvester. The harvester is impacted into bone to a desired depth so that bone material collects as a bone core within the harvester tube. The bone core is extracted from the bone socket using a simultaneous twisting and pulling motion. Such harvesting of bone cores in the joint is technically difficult.
Accordingly, the need exists for a method of ACL reconstruction that provides tibial socket formation without the need for extracting a bone core to form a bone socket.

ACL reconstruction technique using retrodrill


A floating dock comprises a plurality of floats, and a plurality of connectors for joining the floats together, each float having a top surface, a bottom surface, two opposed side surfaces and two opposed end surfaces. Each of the side and end surfaces have at least one tapered connecting slot formed therein, extending from the bottom surface of the float to the top surface of the float. The connectors have a shape complementary to the connecting slots, whereby a single connector will span between aligned connecting slots on an adjacent pair of floats.

There exists a need, and a substantial market for a durable, simple to assemble, maintain and repair floating dock system. Floating dock systems are key practical alternatives to permanent docks in geographical areas that encounter ice in the wintertime, especially if the ice breaks up and moves in the spring. Moving ice can destroy a dock that is immovably secured to a lake or river bottom.
There have been many forms of floating dock proposed. In a simple form, a floating dock can be built using drums or pontoons fastened together with a dock laid on top. Of course, this sort of custom built dock will only be as good as the person building it is capable of making it. Often, this type of dock is awkward and dangerous to use.
An example of a prefabricated dock that has been marketed is shown in CA2308617 (Gruhn et al). This dock consists of a number of hollow-bottom floats with textured upper surfaces. The floats can be fastened together using custom fabricated fastening elements that fit into custom shaped profiled slots on the sides of the floats. The slots are profiled to provide a fit with the fasteners. While this dock assembly system has some attractive features, there are drawbacks associated with it, particularly the profiled connectors that are used to connect floats together.
These connectors are effective in securing together adjacent floats, but tend to permit more flex than is desirable between adjacent floats. Moreover, the pre-textured upper surface of the floats will dictate that they should all be assembled in a parallel arrangement, which may limit available assembly options.


A safe, economical and predictable process for producing ammonia from a urea solution, preferably where only a small amount of ammonia is required, (i.e. for SCR denitrification for small boilers, flue gas conditioning to enhance precipitator efficiency and/or alleviate plume problems, SNCR and the like), using an ultrasonic processor to cause “cold boiling” of portions of such solution and produce gaseous ammonia.

Ammonia is an extremely important chemical which has innumerable uses in a wide range of areas, for example: process, industry and utility uses. The instant invention is concerned with a method and means to safely produce relatively small amounts (i.e. up to 150 pounds per hour, and perhaps up to 300 pounds per hour) of ammonia from urea, for such uses.
Areas of use for such relatively small quantities of ammonia are quite varied and, for purposes of this discussion, such areas include, but are not limited to: providing ammonia equipment and processes, of the type illustrated in U.S. Pat. No. 2,356,717, to help increase the efficiency of an electrostatic precipitator to remove flyash from the flue gas stream of a fossil fuel burning boiler; to alleviate "blue plume" problems when burning a high sulfur content oil in a boiler such as illustrated in U.S. Pat. No. 5,024,171; and to remove the NOx contaminants contained in a flue gas stream of energy producing boilers or combined cycle systems, in conjunction with selective catalytic reduction (SCR), and/or selective non-catalytic reduction (SNCR), systems (see U.S. Pat. Nos. 4,124,536 and 3,900,554, respectively).
Ammonia for uses such as described above, is often delivered in the form of anhydrous ammonia, or aqueous ammonia. Anhydrous ammonia is used in massive quantities world-wide for many industrial and agricultural purposes. Anhydrous ammonia is gas at ambient temperatures and pressures, and is normally shipped and stored as a liquid, either in pressure vessels at ambient temperature, and high pressure (i.e. over 16 bars ), or in refrigerated vessels at ambient or nearly ambient pressure, and at about −33° C. It is transported in bulk in ships, barges, and railroad tank cars, and in tank trucks on public roads and highways and, in instances of relatively small usage per hour, such as envisioned with the present invention, perhaps in high pressure cylinders. It is frequently used and stored at industrial sites in populated areas. It is now coming into wider use for the removal of NOx from flue gas at power generating stations, industrial heaters, or in combined cycle systems, in urban areas.
Anhydrous ammonia is an extremely hazardous, toxic, and volatile material. In the event of an accidental discharge, it can cause immediate death or injury to humans and animals and rapid death to trees and plants. Both anhydrous liquid ammonia, and concentrated aqueous liquid ammonia, display a deadly characteristic which substantially increases the risk of widespread injury and death in case of a spill. Specifically, upon sudden release to the atmosphere, as might occur in a sudden and accidental discharge, the ammonia can form a cloud produced of an aerosol fog of liquid ammonia droplets. Unlike gaseous ammonia, which, though toxic, is lighter than air and quickly dissipates to harmless concentrations, the cloud can persist for a surprisingly long time, as long as several hours, before it finally disappears. The cloud is typically heavier than air and tends to drift along the surface of the earth, i.e., the ground or the surface of a body of water. The cloud moves with the wind and can sweep over a total area, i.e., a "footprint," much larger than the area covered by the cloud at any one moment. Contact with the cloud may be instantly incapacitating, and a single breath can be fatal.
In addition to the inherent danger of storing, transporting and handling large quantities of ammonia, the expense insofar as safety aspects, insurance costs, specialized training, and the difficult to quantify emotional exposure of living and/or working next to a such potential catastrophe, it is apparent that if another, less hazardous commodity could be transported or stored instead of ammonia, and then be readily converted to ammonia, the hazards associated with ammonia shipment and handling would be considerably reduced. To some extent, attempts have been made in the supply of ammonia for NOx control in power plant and industrial environments by substituting concentrated aqueous liquid ammonia for anhydrous ammonia. Such a solution has achieved only limited success, due to any number of factors, for example: the high energy cost of transporting and vaporizing the water carrier, relatively costly storage facilities; and, even though aqueous ammonia is safer to handle than anhydrous ammonia, it is still difficult and costly to handle in a safe manner.
Urea is an ideal candidate as an ammonia substitute. Urea is a non-toxic chemical compound and, for purposes of this discussion, presents essentially no danger to the environment, animals, plant life and human beings. It is solid under ambient temperatures and pressures. Consequently, urea can be safely and inexpensively shipped in bulk and stored for long periods of time until it is converted into ammonia. It will not leak, explode, be a source of toxic fumes, require pressurization, increase insurance premiums, require extensive safety programs, or be a concern to the plant, community and individuals who may be aware of the transportation and/or storage dangers of ammonia. Further, urea can be used to produce gaseous ammonia:                on-site        on-demand        with rapid response time        with maximum turn down availability        with utmost safety        with significant economies        with automatic operation        with low maintenance
The use of urea with the advantages discussed hereinabove were recognized by Applicant heretofore, as illustrated, described and claimed in his U.S. Pat. No. 6,093,380. In addition to the system described in the '380 Patent, another commercially available system which also produces ammonia form a urea feed stock is shown in U.S. Pat. No. 6,077,491 The prior art systems mentioned in this paragraph have been used primarily for fulfilling relatively larger ammonia requirements and, as such, are not necessarily the most appropriate design for small ammonia production requirements. For example—cost, unnecessarily high pressure and temperature requirements, speciality metals, physical and chemical scale down problems, load following requirements, expensive or ineffective controls for such small ammonia production requirements, and the like.

Method and apparatus for the production of gaseous ammonia from a urea solution


A motion mechanism is described. In one embodiment, the motion mechanism includes a base portion, a flexure portion, and a transducer. The flexure portion includes a payload support portion configured to support a payload, a first plurality of elongated portions extending substantially in a first direction and contacting the payload support portion, wherein the flexure portion contacts the base portion. The transducer is arranged to provide a force to the payload support portion in a second direction when actuated, the second direction substantially orthogonal to the first direction. Other embodiments of the motion mechanism are also described.

Machine tool systems that allow for the machining of a surfaces are known. In particular, machine tool systems which translate diamond cutting tools relative to a surface to cut and machine the surface are known. In these systems motion is provided to the cutting tool, or the surface to be machined or both.


A fault handling process in a computer system subject to CPU design errors and functioning under an operating system (OS) having an integral fault handling module includes the steps of: setting an intercept flag when a central processor fault occurs if the fault is to be directed to a preprocessor; establishing a safestore frame which includes information identifying the type of fault and whether the intercept flag is set; and transferring control to the OS fault handling module; then in the OS fault handling module, determining whether the intercept flag is set; if the intercept flag is not set, handling the fault in the OS fault module; if the intercept flag is set, transferring control from the OS fault module to an Intercept Process written in machine language; and handling the fault in the Intercept Process. This renders the resolution of faults due to correctable CPU design errors independent of the OS employed at a given installation and customizable to a given system without the need to revise the OS fault modules for each OS. As each such design error is worked out (e.g., by installing a substitute integrated circuit in which the error has been corrected), the Intercept Process (and CPU firmware) can be modified to remove monitoring and handling for faults due to the corrected error.

As personal computers and workstations have become more and more powerful, makers of mainframe computers have undertaken to provide features which cannot readily be matched by these smaller machines in order to stay viable in the marketplace. One such feature may be broadly referred to as fault tolerance which means the ability to withstand and promptly recover from hardware faults and other faults without the loss of crucial information. The central processing units (CPUs) of mainframe computers typically have error and fault detection circuitry, and sometimes error recovery circuitry, built in at numerous information transfer points in the logic to detect and characterize any fault which might occur.
The CPU(s) of a given mainframe computer comprises many registers logically interconnected to achieve the ability to execute the repertoire of instructions characteristic of the CPU(s). In this environment, the achievement of genuinely fault tolerant operation, in which recovery from a detected fault can be instituted at a point in a program immediately preceding the faulting instruction/operation, requires that one or more recent copies of all the software visible registers (and supporting information also subject to change) must be maintained and constantly updated. This procedure is typically carried out by reiteratively sending copies of the registers and supporting information (safestore information) to a special, dedicated memory or memory section.
When a fault occurs and analysis determines that recovery is possible, the safestore information is used to reestablish the software visible registers in the CPU with the contents held recently before the fault occurred so that restart can be instituted or tried from the corresponding place in program execution.
The logical design of modern CPUs, particularly mainframes, is enormously complex. Inevitably, logic design errors are present as the design process proceeds. If the specific hardware in which a design error is discovered is still in development, it can simply be corrected, sometimes with appropriate changes in firmware. However, if the faulting condition occurs so rarely and is so elusive that it is only discovered after systems have been installed for commercial and/or other field operation, the correction of the hardware/firmware (for example, by replacing an integrated circuit having the design error with one in which the error has been corrected) can be time consuming. Similarly, if a rarely occurring hardware fault is discovered during development, there may be good reason, such as meeting delivery schedules, to forego any immediate attempt to effect a definitive hardware/firmware correction. In both instances, a conventional, and generally effective, prior art approach has been to set up the CPU firmware to detect and refer faults to a fault processing module written into the operating system.
There are, however, drawbacks to this approach. When design errors are discovered, the resolution process for the resulting fault must be incorporated into the fault handling module operating system itself. This can be not only a formidable task, but the revisions to the operating system in all the systems in existence can be disruptive of normal operation. Further, some mainframe CPUs are configured to run under a plurality of operating systems. This requires changes to the fault processing modules of each operating system which can be accommodated by the CPUs. Still further, certain system design errors are often worked out, even after commercialization, as very large scale integrated circuits are modified and the chips changed out in individual installations. As a result, a feature in the operating system(s) introduced to handle a problem which no longer exists may adversely affect performance and certainly increases the amount of code in the operating system. It is to the solution of these related problems that the present invention is directed.

Fault intercept and resolution process independent of operating system


A method for constructing a latch mapping between a first level description and a second level description of a digital system, wherein the first level description and the second level descriptions identify components in the digital system using a predefined naming convention, is provided. The method includes identifying first latch components in the first level description and, for each identified first latch component, storing a first string comprising a selected property of the first latch component in a first storage. The method further includes identifying second latch components in the second level description and, for each second latch component, storing a second string comprising a selected property of the second latch component in a second storage. The method further includes generating a latch mapping by matching the first strings in the first storage with the second strings in the second storage.

1. Field of the Invention
The invention relates generally to design of digital systems, e.g., a computer or a component of a computer. More specifically, the invention relates to a method and apparatus for constructing a latch mapping.
2. Background Art
Modern computer and electrical engineers use hardware description languages such as Verilog HDL and VHDL to describe a digital system from a functional specification of the digital system. The engineers may describe the digital system at different levels of abstraction. One of the higher-level descriptions of the digital system is the register transfer level (RTL). In the RTL, variables and data operators are used to describe registers and transfer of vectors of information between registers. For example, in the RTL, a very simple digital circuit performing an AND operation may be described as xe2x80x9cOUT=aandb,xe2x80x9d where xe2x80x9candxe2x80x9d represents the AND operation between the variables a and b and OUT represents the output of the digital circuit. The next lower-level description of the digital system is the gate level. At the gate level, the digital system may be described as a set of interconnected logic gates, e.g., AND and OR, and memory components, e.g., flip-flops and latches. FIG. 1 shows a gate level description 2 of the RTL description: xe2x80x9cOUT=aandb.xe2x80x9d The lowest-level description of the digital system is the transistor level. At the transistor level, the digital system may be described as a set of interconnected wires, resistors, and transistors on an integrated circuit (IC) chip. The transistor-level schematic is used to create the physical model of the IC chip. FIG. 2 shows the digital circuit of FIG. 1 at the transistor level. The digital circuit includes two transistors 4, 6 which are coupled to perform an AND operation on input signals a and b.
In practice, a digital system would consist of hundreds of thousands to millions of transistors. Thus, formal verification is important in designing functionally correct digital systems. Formal verification is checking to see whether the system performs its intended function. One form of formal verification called equivalence checking involves proving equivalence between two designs, which may be at the same level or different levels of abstraction. Equivalence checking is often used to prove equivalence between the RTL model and the transistor-level schematic of the digital system. Equivalence checking in sequential circuits, i.e., digital circuits containing latches and flip-flops, typically consists of two steps. The first step involves constructing a latch mapping, also known as a register mapping. The latch mapping identifies corresponding latches in the two designs to be compared. Once the corresponding latches are identified, it is then possible to decompose the designs into corresponding combinational blocks. The second step is to verify whether the corresponding combinational blocks are equivalent. If the combinational blocks are equivalent, then the two designs are functionally equivalent.
There are various techniques for checking equivalence of combinational blocks. See, for example, Jerry R. Burch and Vigyan Singhal, xe2x80x9cRobust Latch Mapping for Combinational Equivalence Checking,xe2x80x9d Proceedings of the 1998 IEEE/ACM international conference on Computer-aided design, 1998, pages 563-569, Pranav Ashar et al., xe2x80x9cUsing Complete-1-Distinguishability for FSM Equivalence Checking,xe2x80x9d Proceedings of the 1996 IEEE/ACM International Conference on Computer-aided design, 1996, pages 346-353, and Andreas Kuehlmann and Florian Krohm, xe2x80x9cEquivalence Checking Using Cuts and Heaps,xe2x80x9d Proceedings of the 34th annual conference on Design automation conference, 1997, pages 263-268.
Various methods are known for constructing latch mapping between two designs. In general, these methods can be divided into three categories: structure mapping, function mapping, and name-matching mapping. Structure mapping involves matching structurally similar latches. For example, the latches 8, 10 shown in FIGS. 3A and 3B are structurally similar because they have their ports xe2x80x9cdxe2x80x9d connected to the same data block xe2x80x9cb1k.d[0],xe2x80x9d their ports xe2x80x9cqxe2x80x9d connected to the same net xe2x80x9c1063,xe2x80x9d and their ports xe2x80x9cclkxe2x80x9d connected to the same net xe2x80x9c2176.xe2x80x9d Thus, the latches 8, 10 will be correlated in the latch mapping. Function mapping involves analyzing and using the functional properties of the latches to correlate the designs. In function mapping, for example, two latches may be correlated because they have one set of ports connected to a net whose function is xe2x80x9caandbandcxe2x80x9d and another set of ports connected to a net whose function is xe2x80x9cclk.xe2x80x9d Name-matching mapping depends on the latches in the two design models having similar labels. For example, the labels xe2x80x9cX1xe2x80x9d and xe2x80x9cSX1xe2x80x9d of the latches 12, 14 shown in FIGS. 4A and 4B are similar because they both contain xe2x80x9cX1.xe2x80x9d Thus, the latches 12, 14 will be correlated in the latch mapping. Typically, there will be mapping rules that indicate which portions of the labels are relevant to latch mapping.
In the practical implementation of formal equivalence, label correspondence can become a weak link. This is because the circuit designer often uses different labels than the logic designer. Also, tools that perform design transformation, such as synthesis or clock tree insertion, often do not preserve labels, especially when the design is being flattened as part of the transformation. Thus, there is a possibility that some latches will be unmapped because they cannot be correlated to other latches. Thus, if two combinational blocks are found to not be equivalent, it may be because of an incorrect label matching rather than a bug in the circuit. This, of course, complicates the debugging process. However, in an environment with a naming convention, it is worthwhile to have a tool that can perform name matching mapping because the function/structure mapping techniques use complex algorithms that can sometimes fail. Also, function/structure mapping techniques are more suited to an environment where equivalence checking is being performed between two designs at the same level (e.g., gate-gate).
In one aspect, the invention is a method for constructing a latch mapping between a first level description and a second level description of a digital system, wherein the first level description and the second level descriptions identify components in the digital system using a predefined naming convention. The method comprises identifying first latch components in the first level description and, for each identified latch component, storing a first string comprising a selected property of the first latch component in a first storage. The method further includes identifying second latch components in the second level description and, for each identified second latch component, storing a second string comprising a selected property of the second latch component in a second storage. The method further includes generating a latch mapping by matching the first strings in the first storage with the second strings in the second storage.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.