A valve for controlling a fluid, in particular for controlling a gas. The valve includes a valve housing having a housing sleeve and an electromagnetic actuator for an armature which is guided in an axially displaceable manner and which cooperates with a valve seat situated on a seating plate so that a fluid flow through outflow orifices in the seating plate is controllable. The armature is guided along an armature sleeve which is situated in the housing sleeve.

A valve is known from practice and is usable, for example, as a gas control valve in a fuel cell or also in a gas-powered engine.
The known valve includes a valve housing which accommodates an in particular electromagnetic actuator for an armature and is provided with a housing sleeve in which the armature is guided in an axially displaceable manner. The armature is used as a valve-closing element and cooperates with a valve seat situated on a seating plate so that a fluid flow through outflow orifices in the seating plate is controllable.
The problem in the case of the known gas valve is that the dry and gaseous medium to be controlled results in high wear demands which necessitate high-precision guiding of the armature. This cannot be reliably ensured by the previously used guiding of the armature in the housing sleeve since the housing sleeve may have the problem of concentricity variations and diameter tolerances resulting from the deep-drawing processes used in the manufacture. The eccentricities and the diameter variations increase the tilting tendency of the armature and may in turn shorten the valve's service life.


One embodiment of the invention provides a smart card having multiple applications installed thereon. One of the multiple applications is designated as a default application which is activated whenever the card is reset. The default application is required to implement a first operation to provide a canonically ordered listing of the multiple applications on the card. The default application may further implement a second operation to allow one of the multiple applications to be selected for activation via an index into the listing.

Most people now have a collection of small plastic cards, representing various credit cards, store cards, identity cards, membership cards, and so on. Information about the card and its owner, such as account details and so on, is normally printed or embossed on the card, and may also be stored in some form of magnetic strip. Note that such cards are simply passive storage devices, and the information that they contain is fixed at card creation time.
In recent years, smart cards have also proliferated. These are similar in scale to traditional credit cards, but incorporate within their plastic cases a microelectronic memory and also (optionally) an embedded processor. It will be appreciated that the computational resources available within a smart card are extremely limited compared to those of a desktop workstation, or even a laptop or handheld device. One especially popular form of smart card is known as a Java Card. This is based on the Java platform developed by Sun Microsystems ("Java" and "Java Card" are trademarks of Sun Microsystems Inc). In such devices, a Java virtual machine (VM) is provided within the smart card to allow the execution of Java applets or applications. Particular advantages of being able to use the Java environment for smart card applications are the inherent security features of the Java environment, plus the ready availability of software development packages for the Java programming language. It is estimated that by the end of 2002 over 200 million Java cards had been shipped. More information about the Java Card smart card platform is available from the page: /products/javacard/ at the web site: http://java.sun.com and from the site: http://wwwjavacardforum.org/, and also from the book: "Java Card Technology for Smart Cards" by Zhiqun Chen, Addison-Wesley, 2000, ISBN 0-201-70329-7.
An Application Programming Interface (API) is defined for the Java Card platform. Applications written in the Java programming language invoke this API to access the Java Card run-time environment (JRE) and any native services. The Java Card API allows application portability, in that the same application can run on any smart card that supports the API. The Java Card API is compatible with international standards, in particular the ISO/IEC 7816 family of standards.
In the desktop environment, there is a clear distinction between a Java applet and a Java application, in particular the absence of a ma in class from the former. Although there is a similar distinction in the smart card environment, applets for use on a Java card platform are not the same as applets that run on a web browser. Programs that run on smart cards may be referred to as either an application or as an applet (the former term will be used generally herein).
The Java Card platform supports multiple applications on a single card. These applications may be separated by firewalls, in order to ensure that they do not interfere with one another. This is particularly of concern if the various applications are operated by different organisations, whose business relationships with the card holder may be independent of one another.
FIG. 1 is a schematic diagram representing the life cycle of a smart card, which in this particular implementation is a Java Card. The life cycle commences with the manufacture of the card, and the initial loading of the base operating system and the Java Card environment (210). Also at this stage, one or more applications may be preloaded (215). Generally, the base operating system and Java Card environment, and also potentially any preloaded applications, may be stored in ROM on the smart card as part of the manufacturing process.
The card is now ready for issue to a card holder (220), which typically involves an appropriate personalisation process, as well as initialisation of the Java environment, and starting the Java virtual machine on the card. The card holder is thereafter able to use the card (230). Note that if the card was originally issued without any preloaded applications, then the card holder may have to load an application prior to making substantive use of the card. In practice however, this situation is rather uncommon, since usually there is at least one preloaded application in order to motivate issuance of the card in the first place.
During the operational lifetime of the card, further application programs may potentially be installed onto the card (235), for example if the card holder signs up to new accounts or services. Conversely, applications may be removed from the card, perhaps because an account is closed.
The last operation shown in FIG. 1 is where the card is terminated (240). This may occur, for example, because the card has a built-in expiry date or is surrendered by the user (perhaps if the user is moving to a new card issuer, or the card is physically damaged).
FIG. 2 is a high-level schematic diagram illustrating the main architectural components in a typical smart card application. Thus smart card 102 belongs to card holder 101. Note that smart card 102 may be used as a standalone device, or may be incorporated into some larger system such as a mobile phone. Smart card 102 interacts with a terminal 110 by exchanging an application protocol data unit (ADPU) 108. The format for the ADPU is defined by the International Standard ISO/IEC 7816-3 and typically comprises a command header portion and a payload portion.
Terminal 110 may be a handheld device, an adjunct to a desktop workstation, a dedicated card reader (analogous to an ATM) or any other suitable system. Communications between the smart card 102 and the terminal 110 may be by wired connection or by wireless link (e.g. radio or some other electromagnetic signal), depending on the particular devices concerned. Terminal 110 may be under the direct control of an operator 111 (such as for a handheld terminal), or alternatively terminal 110 may be automated (such as for an ATM). In this latter situation, the card holder 101 may operate the terminal 110 himself/herself.
Terminal 110 interacts with a back office 130 over any suitable form of network 120, such as the Internet, a local area network (LAN), a wide area network (WAN), and so on. Back office 130 may comprise multiple systems (not explicitly shown in FIG. 1), such as a web server or portal attached to network 120, perhaps with an application server and/or a database system behind. Note that the terminal 110 may be off-line until activated by a smart card 102, a card holder 101 or a terminal operator 111 to access a back office 130 over network 120.
It will also be appreciated that in some situations, terminal 110 may interact with card 102 without reference to any other system (such as back office 130). For example, terminal 110 might be some form of machine, such as a car or a photocopier, and card 102 might be used to control access to the machine.
In operation, the card holder 101 typically places the card 102 into or adjacent the terminal 110, thereby allowing the two to interact, e.g. to perform a debit operation from the card to purchase some goods. This interaction will generally be referred to herein as a session, and normally involves the exchange of multiple messages between the smart card 102 and the terminal 110.
Associated with each applet on smart card 102 is an Application Identifier (AID). The AID is a byte string up to 16 bytes long, whose format is defined by International Standard ISO/IEC 7816-4:2004. According to this standard, the first 5 bytes or octets of the AID represent the registered application provider identifier (RID) and have a value allocated by ISO or one of its member bodies. The RID indicates the merchant or other entity involved with operating the application, hereinafter referred to as the RID operator. The RID operator is generally responsible for the back office system 130, and is depicted as application/RID operator 131 in FIG. 2. The last 11 bytes of the AID constitute the proprietary application identifier extension (PIX). The PIX is determined by the RID operator 131, and can be used to store a reference number or other information associated with the application.
International standard ISO/IEC 7816-4 defines a procedure, namely the Select command, to allow a terminal to specify and launch a desired application on a smart card; selecting an application determines the start of a session. The processing associated with the Select command is illustrated at a high level in the flowchart of FIG. 2A. The processing starts when the smart card 102 is first inserted into the terminal 110. The terminal detects the insertion of the smart card (162), and in response to such detection activates the smart card (164, 172). This activation generally includes providing power to the smart card and launching a default application on the card. The default application is so-called because it is automatically started when the card is reset, such as on power up. In some implementations, the default application is identified as the applet that was most recently running on the card (prior to the reset). In other implementations, the default application may be a fixed applet.
The terminal now determines an application on the card to launch (165), and sends a corresponding Select command using an ADPU 108 to the smart card (166). The ADPU specifies the AID of the selected application for use in this session. The request from the terminal is received by the smart card (174). The request is handled by an applet selector program that is running on the smart card 102 as part of a card executive layer. The applet selector is responsible for locating the application that matches the AID requested from the terminal, i.e. the application that has the same AID as that specified in the request (176). If a matching application is found, then this application on the smart card is duly launched (177). The smart card now returns to the terminal 110 an indication of whether or not the requested application has been successfully launched (179 and 180). (N.B. This last action is optional within the context of ISO/IEC 7816-4, although it is commonly implemented).
FIG. 2B describes a variation on the processing of FIG. 2A (also in accordance with ISO/IEC 7816-4). The operations in FIG. 2B are the same as described above in relation to FIG. 2A until operation 166, in which the terminal 110 supplies the card with an abbreviated or truncated AID (known as a partial AID). For example, the partial AID may comprise the first ten bytes of an AID. In these circumstances, there may be multiple matches against the partial AID. For example, if two applications have AIDs that have their first ten bytes in common and then differ only in the final six bytes of the AID, they will both match the same partial AID of length 10 bytes (or less). One reason for using a partial AID might be if the terminal 110 wants to identify all applications on the card having a particular RID.
Consequently, at operation 176A (corresponding to operation 176 in FIG. 2A), the smart card identifies one of the potentially multiple matching applications on the card. This application identified at operation 176A represents the first matching application. The (first) matching application (if any) on the smart card is now launched (177), and a response is provided to the terminal (179A, 180) indicating whether or not the partial AID request (176) was successful. If this request was successful, then the response 179A also includes the AID of the application that was launched at operation 177. If this AID corresponds to the application desired by the terminal (183), then session processing continues (185). However, if the launched application as indicated by the received AID is not the desired application, then processing at the terminal loops back to operation 166, whereby another request containing the partial AID is sent by the terminal to the smart card 102.
The smart card now identifies at operation 176A the next application that matches the partial AID, launches this next matched application (177), and returns the full AID for this next matched application (179A). In addition, the previously launched application (i.e. the first application) may be terminated (not shown in FIG. 2B). The terminal again tests at operation 183 to determine whether or not the matching application corresponds to the desired application, and if not, then we proceed once again around the above loop.
The procedure of FIG. 2B therefore terminates either when the desired application on smart card 102 has been launched, thereby allowing the session to continue (185), or there are no more applications on smart card 102 that match the partial AID. In other words, the AIDs for all the matching applications (if any) have already been returned one-by-one at operation 179A, and then rejected at operation 183. In this latter case, the smart card fails to find any further matching applications (i.e. the test of operation 176A is negative), and returns a failure indication to the terminal at operation 179A. The terminal then detects that no (further) application has been launched on the card (182), and so aborts the session (184).
Note that to support the above processing, the card 102 needs to ensure that it selects a different matching AID each time it loops through operation 176A (otherwise it may return a matching AID that has already been rejected by the terminal). One mechanism to ensure this is for the smart card to maintain a list of those matching AIDs that have already been returned to the terminal at any previous loops through operation 179A. Alternatively, the smart card may recognise some ordering of the AIDs (for example, based on the binary value of an AID). In this latter case, the smart card notes the matching AID sent last time at operation 179A, and for the next loop through operation 176A selects the next matching AID in the imposed ordering.
It has been suggested that a smart card may include a facility to provide a complete list in a canonical order of all the applications installed on the smart card. (This suggestion is described in a submission by the Netherlands to the standards committee JTC1/SC17 of the ISO/IEC). Each application on a smart card is represented in the list by its AID. The list could then to be used in all presentations by the card of its applications, for example as a directory file. It is also contemplated that the canonically ordered AID list could be used in a variation on the Select command as depicted in FIGS. 2A and 2B. In particular, an index to the list could be encoded over one octet, for instance using values 1 to 253, with the applications specified in the order in which they were originally loaded onto the smart card. This would then allow a desired application to be specified for selection by index value (rather than by AID).
According to this proposal, which is especially relevant to a Java Card implementation, three particular applications are distinguished:                (1) a card management application—this performs functions related to the loading, initialization and removal of other applications.        (2) a card holder personal data application—this typically contains data and functions related to the card holder, such as a user profile, a PIN, biometrics, and name and address. These functions and data may be accessible in the card by other applications as appropriate.        (3) the default application—discussed above. (Note that a card that supports multiple modes of communication with terminal 110 may have a different default application associated with each particular mode of communication).The card management application and the card holder data application are generally preloaded onto a smart card (see operation 215 in FIG. 1).
In the proposal, the three special applications listed above are assigned predetermined index values. In particular, the index value 0 is reserved for the current default application; the index value −2 (254) is reserved for the card holder data application; and the index value −1 (255) is reserved for the card management application. Note that the card holder data application and the card management application will therefore generally appear twice in the list, once at the position in the list that reflects when they were loaded, and once at their reserved location (i.e. −2 and −1 respectively). This submission has not yet been formally adopted by the ISO/IEC.
Most early smart cards were viewed primarily as memory devices. The main purpose of a session involving the card was therefore to read data to or write data from a selected location on the card. The development of Java cards has introduced an application-oriented environment, in which the behaviour of a card is controlled by an application on the card. This has led to the role of a default application as mentioned above to take initial control of a card, pending user selection of a particular desired application. A further submission by the Netherlands to the standards committee JTC1/SC17 of the ISO/IEC has suggested that a default application should firstly be able to provide a list of applications on the smart card and secondly to support selecting an application on the card to run.
Although the Java Card environment supports multiple applications from different RID operators, in practice, a large majority of issued cards originate from and are run by a single RID operator. In other words, applications from one RID operator are typically found on one card, and applications from another RID operator are found on a different card. Moreover, many cards are provided with only a single application. Consequently, relatively little attention has been paid to the handling of smart cards having multiple applications, potentially from a range of different vendors (i.e. from different RID operators).


An apparatus comprises a data storage medium including a piezoelectric material and a ferromagnetic material, an electric field source for applying an electric field to a portion of the data storage medium, and a write pole for applying a magnetic field to the portion of the data storage medium. A method performed by the apparatus is also provided.

Attempts to increase the capacity of magnetic data storage devices must balance writability, grain size and magnetic anisotropy in the magnetic data storage media. Write heads can only generate a limited magnetic field, and this limit is set by the maximum volume magnetization that can be achieved in a material, the maximum current density that can be put through a conductor, and the head-to-media separation. If the anisotropy in the media is lowered to the point where it can be written by the write head and the grains are made small enough to maintain an acceptable signal-to-noise ratio, the media may not be thermally stable for large areal densities. This is referred to as the superparamagnetic limit.
Ferroelectric (FE) data storage media has the advantage that it is written using an electric field, and very large electric field values can be generated with a thin-film device. Thus, FE media with a very large anisotropy can be written by a thin-film device, and a thermally stable FE media with very small domains (and narrow domain walls) can be written. One of the problems with using FE recording is that the readback is difficult. Free electric charge tends to shield the polarization pattern in the FE media, which then requires one to use a write before read method for readback. Since free magnetic charges don't exist, this is not a problem for magnetic media and readback is relatively easy.
Recently, composite materials, combining magnetoelastic and ferroelectric materials, have been developed that have both ferromagnetic (FM) and FE properties above room temperature. Two example composites are BiFeO3—CoFe2O4 and BaTiO3—CoFe2O4. In these examples the BiFeO3 and BaTiO3 are the FE materials and the CoFe2O4 is the FM material.
Others have demonstrated the use of an electric field to switch the magnetization in a BiFeO3—CoFe2O4 composite. The composite consisted of CoFe2O4 nanopillars in a BiFeO3 matrix. The material was deposited using pulsed laser deposition at 700° C. on SrRuO3 and resulted in a fully epitaxial film, including across the BiFeO3—CoFe2O4 grain boundary. The magnetization was saturated by applying a large, uniform magnetic field, and then 50 to 60% of the magnetization was switched by applying an electric field using a piezoelectric force microscope (PFM). The films referred to above were not used for data storage.
There remains a need for a magnetic data storage method and apparatus that can provide adequate thermal stability and adequate signal-to-noise ratio (SNR).

Electric field assisted writing using a multiferroic recording media


A protector for an electrical receptacle. A flat housing has a stepped cylindrical bore communicating from the front of the housing to the rear. A cover including a disc bearing slots fits closely yet rotatably into the larger of the two steps. The slots are configured to correspond to, but to be slightly smaller than, openings formed in a receptacle, so that conductive prongs of a plug may be inserted through the cover into the receptacle. The cover is rotated such that its slots align with those of the receptacle when it is desired to connect a plug to power. The cover may be rotated to misalign the respective slots for safety. When the protector is attached to the front of a receptacle, the smaller step of the bore serves as a stop entrapping the cover in the bore, the receptacle blocking escape of the cover at the other end of the bore. The larger step of the bore is long enough to enable the cover to move axially therein. The cover is pulled by frictional engagement with the prongs when the plug is removed from the receptacle, thereby establishing a gap between the cover and the receptacle. Preferably, the protector has two covers, for protecting a duplex receptacle.

1. Field of the Invention
The present invention relates to electrical receptacles of the type for connecting a removable plug to electrical power. More particularly, the invention provides a safety cover for such a receptacle. The safety cover has individual socket covers which are both axially movable and rotatable. When rotated, they deny direct access to energized conductors. When a plug is not inserted into the protected receptacle, the individual socket covers are spaced away from the receptacle and hence from the energized conductors.
2. Description of the Prior Art
Electrical receptacles for enabling ready connection to electrical power provide an enormous convenience for utilizing electrical appliances, lighting apparatus, and the like. Yet the very power made so available is dangerous to the point of being potentially lethal. Despite these conductors being recessed within the receptacle, they are nonetheless directly accessible. A principal source of trouble is small children, whose curiosity may impel them to experiment by inserting their fingers or other objects into a receptacle. Many household objects are conductive, and it therefore becomes desirable to cover the receptacle when not in use.
The prior art has suggested covers for improving safety of electrical receptacles. U.S. Pat. No. 4,302,624, issued to Frederic M. Newman on Nov. 24, 1981, describes a cover having pivotally mounted access doors which pivot into and out of overlying relationship with each receptacle. By contrast, the present invention has rotatable members which have slots corresponding to those of the receptacle. Rotation about a central axis selectively exposes and covers the slots of the receptacle in the present invention. No member in the present invention pivots out of contact with the receptacle. Also, the rotatable members in the present invention move axially when a plug is inserted and withdrawn. No such feature is seen in the invention of Newman.
Hoods projecting axially from the receptacle are shown in U.S. Pat. No. 4,293,733, issued to George T. Royer on Oct. 6, 1981, and U.S. Pat. No. 4,981,439, issued to Gregory H. Piedmont on Jan. 1, 1991. Piedmont provides an interlocking, removable cover which closes an associated hood. Piedmont's cover is not entrapped within the hood or other structure of the receptacle. Also, Piedmont's cover lacks slots for exposing corresponding slots formed in the receptacle. Even further, Piedmont's cover is not axially movable and rotatable in the manner of the present invention. Royer's hooded protector lacks any cover closing access to the protected receptacle, unlike the present invention.
Protective covers which close over a plug being inserted into the protected receptacle or over its cord are depicted in U.S. Pat. No. 3,363,216, issued to Patrick J. Benedetto on Jan. 9, 1968, U.S. Pat. No. 4,895,999, issued to Bill R. Calderon on Jan. 23, 1990, and U.S. Pat. No. 5,589,665, issued to Randal Scamacca on Dec. 31, 1996. These inventions lack covers rotatably mounted to the receptacle, which covers can both rotate and move axially with respect to the receptacle. By contrast, covers which are both rotatable and axially movable relative to the receptacle and which are permanently mounted to the receptacle are found in the present invention.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.


A dental material comprising a porous ceramics formed into an artificial tooth, an inlay, an onlay, a crown, a crown bridge or into a block shape suitable for CAD/CAM, sintered, having communicating holes, and impregnated with a resin. A porous ceramics formed from a network-forming oxide is applicable, and an intermediate oxide and a network-modifying oxide may also be adopted. The porous ceramics should preferably have a porosity within a range of from 0.5 to 70%. The resin should preferably a polymer of a monomer and/or oligomer containing at least an ethylenic double bond. Prior to impregnation of the porous ceramics with the resin, the porous ceramics should preferably be subjected to a coupling treatment.

1. Field of the invention
The present invention relates to a dental material. More particularly, the present invention relates to a composite dental material which is useful as an artificial tooth, an inlay, an onlay, a crown, a crown bridge and the like.
2. Description of the prior art
A dental material is generally required to satisfy various requirements such as sound mechanical strength and machinability, a low cost, an excellent aesthetic merit, absence of biological detrimentality and a good biological affinity. Various dental materials including resins, composite materials formed by dispersing an inorganic substance in a resin, ceramic materials, amalgams, and alloys of precious and base metals have been developed are now practically applied.
Various resins for dental purposes comprising methacrylate copolymers mainly consisting of methylmethacrylate have been developed and are in use as dental resins. These resins, being excellent in aesthetic merit, color fastness and impact resistance, are low in mechanical strength such as wear resistance and bending strength. The occlusion force during mastication of food, varying between different persons, is believed to be 78 kg on the average, and this occlusion force causes a huge stress on the tip of teeth. For these reasons, a resin as used as a dental material is defective in that is suffers from a considerable wear resulting from mastication over a long period of time, and deformation is easily caused by occlusion.
With a view to overcoming the defects of resins as described above, a composite resin made by mixing and dispersing an inorganic substance in a methacrylate-based copolymer resin has been developed. This material is advantageous in that it has a satisfactory aesthetic merit necessary for the foreteeth, and has an improved mechanical strength over a material made from a resin alone even in the molar segment required to have a mechanical strength sufficient to withstand occlusion. In order to improve physical properties of the composite resin such as mechanical strength and bending strength, and thus to achieve physical properties closer to those of natural teeth, it is necessary to uniformly disperse an inorganic substance throughout the resin, and to improve the filling ratio. The filling ratio can be improved with a resin having a large particle size. When such a resin is attached in the oral cavity as an artificial tooth, an inlay, an onlay, a crown or a crown bridge, however, the composite resin exhibits a rough surface, resulting in unavailability of a smooth and glossy surface, thus leaving a feeling of incompatibility in terms of touch with the palate. Furthermore, when the inorganic substance peels off the resin surface as a result of use for a long time and deposits accumulate at this portion, it is colored and this further reduces aesthetic merit. In the case of a composite resin having a small particle size, in contrast, as compared with those of a large particle size, the total surface area of the inorganic substance for the same volume increases, and along with the increase in viscosity upon dispersion of the inorganic substance in the resin, improvement of the filling ratio is limited to a certain level. At the same time, difficulties are encountered in handling and operability in manufacturing artificial teeth or forming or cutting clinically into an inlay, an onlay, a crown or a crown bridge. When using it in the form of ultra-fine powder, furthermore, weak electric charge of the particle surfaces and Van der Waars force cause easy cohesion of fine particles, making it difficult to obtain a uniform dispersion in the resin. Because coherent particles contain voids, there are difficulties in this case also in manufacturing artificial teeth or forming or cutting clinically into an inlay, an onlay, a crown or a crown bridge. Cohesion leads to a rough surface, leaving a feeling of incompatibility in touch with the palate. Trials are being made to solve the foregoing problems by combining different particle sizes, i.e., coarse and fine particles, charged in the resin so as to achieve presence of fine particles in the gaps between coarse particles. In terms of obtaining a uniform dispersion and a high filling ratio, a satisfactory result has not as yet been achieved. Under these circumstances, a composite resin having satisfactory mechanical strength, color fastness and coloring resistance for a long time has not as yet been obtained.
A porcelain material, which is a ceramic dental material used for long, is high in wear resistance and bending strength, excellent in aesthetic merit, color fastness and coloring resistance, free from biological detrimentality or irritation in the oral cavity, and is a stable dental material exhibiting no change in material quality even in a long-term use. As compared with a resin or a composite resin, however, it is defective in that it is high in cost, poor in elasticity, low in impact resistance because of brittleness, and tends to suffer cracking and fracture. In manufacturing a porcelain material, there occurs a considerable shrinkage caused by firing, thus making it difficult to accurately sinter into a prescribed shape. It is the usual practice to use a porcelain material after polishing and form-correction. Thermal stress during correction polishing causes microcracks which grow larger through repetition of daily occlusion pressure during mastication of food and impact caused by chewing hard food, thus resulting in fatigue breakage, or under an excessive occlusion load, in breakage. When a porcelain material is used as a ceramic tooth in a denture, mechanical holding means such as a pin or a retaining hole is provided in the ceramic tooth to achieve an integral connection of the porcelain material and the resin, because of a very low adhesion between the ceramic tooth and the resin serving as a plate or a support. Such holding means tends however to be subjected to stress concentration, and a defective attachment causes cracks in the surrounding resin or breakage of the ceramic tooth after attachment in the oral cavity. The ceramic tooth may also tend to come off the denture base of resin. For these reasons, manufacture of a satisfactory denture using a ceramic tooth requires skill and a high cost.
An amalgam and metallic materials including precious and base metals satisfying various requirements for physical properties are often kept at a distance for their poor aesthetic merit since they have metallic gloss, and some are eluted and exhibit toxicity, thus giving the risk of exerting an adverse effect on human health.
When any of these dental materials is used for dental therapy in the form of an artificial tooth, an inlay, an onlay, a crown or a crown bridge, it is necessary to use various machines and tools and conduct processing at an accuracy of at least 50 to 100 g m. Skill of a high degree is required until a person becomes capable of manually accomplish processing at such a high accuracy, and it is not easy to maintain accuracy at this level. In addition, it is difficult to conduct such process at a high efficiency, and this forms a cause of a high cost. For the purpose of solving the difficulty of keeping skilled operators, accomplishing processing rapidly at a high accuracy, and reducing the cost, it is now tried to integrally carry out all operations ranging from input of dental processing data, processing, design and to cutting and finish-processing of the dental material by the use of a CAD/CAM system, and there is an increasing demand for developing a dental material more suitable for the CAD/CAM system.


Stability of an unmanned aerial vehicle is sought by using a flight controller of an unmanned aerial vehicle control system for controlling flying by an unmanned aerial vehicle based on an instruction from a first operator. A determiner is used to determine whether a second operator visually recognizes the unmanned aerial vehicle based on a predetermined determination method. A switcher is used to switch, based on a result of the determination obtained by the determiner, from a first state, in which the unmanned aerial vehicle flies in accordance with an instruction from the first operator, to a second state, in which the unmanned aerial vehicle flies in accordance with an instruction from the second operator.

Hitherto, there has been known a technology of flying an unmanned aerial vehicle. For example, in Non-Patent Literature 1, there is described a technology of causing an unmanned aerial vehicle to return to a home point (e.g., location of operator) when the unmanned aerial vehicle is in a lost state, which is a state in which the unmanned aerial vehicle does not receive a control signal from a wireless operation device.
Further, for example, in Patent Literature 1, there is described a technology of determining whether or not an unmanned aerial vehicle is flying within a range capable of being visually recognized by an operator based on a distance between the unmanned aerial vehicle and the operator. In the technology of Patent Literature 1, when it is determined that the unmanned aerial vehicle is not flying within the range capable of being visually recognized by the operator, the unmanned aerial vehicle hovers at the current place.
Further, for example, in Patent Literature 2, there is described a technology of determining whether or not an unmanned aerial vehicle is flying within a range capable of being visually recognized by an operator based on an image picked up by a camera of the unmanned aerial vehicle, for example. In the technology of Patent Literature 2, when it is determined that the unmanned aerial vehicle is not flying within the range capable of being visually recognized by the operator, the unmanned aerial vehicle switches to autonomous flight or hovers at the current place.

Unmanned aerial vehicle control system, unmanned aerial vehicle control method, and program


Mobile battery powered workstation carts for order fulfillment are disclosed herein. In one embodiment, a battery powered workstation cart may comprise a wheeled cart having a frame, a rechargeable lithium battery, a computer, a barcode reader/scanner, a RFID reader/scanner, a printer, an artificial intelligence hub, Wi-Fi, Bluetooth Low Energy (BLE), and/or GPS. The frame may also comprise two side bracket arms and/or shelves, which may be modular to receive various different sized baskets, bins, or totes therein to expedite retail order fulfillment.

With online ordering becoming more popular, more stores are offering in-store pickup and/or local delivery from store. Consumers place their orders online and the store employees then need to fulfill the orders in the store. The store employees currently fill online orders by going through the store or warehouse and gathering the ordered items with a shopping cart or flatbed type of cart before returning to the preparation area. They will also sometimes print labels and then label the items picked. When returning to the preparation area, they must then box or bag the gathered items for the customer. The employees must then print invoices, paperwork, and/or delivery or shipping labels to be added to the order and then complete the order on their computer system before the order is considered to be fulfilled. Currently, the employees often pull the items for the order and put them into a cart, then take the cart to a storage area and load the items onto a rack. When the customer then arrives to pick up the order (or its time to deliver the order), the employees must return to the storage area to reload the items, bring them to the front and then bag the items. This current process introduces redundancies that are an inefficient use of employee time.
Store employees must work in a timely and efficient manner to scan, stock, and organize their inventory, shelves, and stores. They carry portable barcode readers and/or label printers. Scanning out of stock items, returning to the backroom, pulling the items, putting the items out on display, and then scanning those items is very time consuming, while potentially disruptive to the customer experience.
Having a mobile battery powered workstation cart with the computer, printer, labels, bags, bins, baskets, totes, etc. in the form of a shopping cart or flatbed type of cart would be very desirable to increase order fulfillment efficiency. Having the bags, bins, totes, or baskets located on the powered workstation cart will aid in end-to-end order fulfillment (the bags will be used to gather the ordered items and/or then can be given to the customer) and will help eliminate the redundant packing and unpacking process by store employees. Currently, powered workstation carts used by stores are very bulky, difficult to maneuver, and don't contain a modular area for bags, totes, or baskets. An example of a current workstation cart is shown in FIG. 5 for purposes of comparison.
Since the order fulfillment tasks are often completed during store hours and in front of customers, having the workstation in a standard shopping cart shape or a flatbed cart shape would be more familiar and customer friendly. Because customers are familiar with the shape and presence of shopping carts, they will be more comfortable seeing a shopping cart being used for order fulfillment. Additionally, store employees would be comfortable maneuvering the workstation in a shopping cart form, thus reducing liability from accidents. Having a workstation powered by a lithium battery will provide power to the computer, printer, barcode readers/scanners, and other electronic accessories that will aid in the completion of the order fulfillment tasks on the workstation cart.

Battery powered workstation cart for order fulfillment


A power electronic arrangement includes a semiconductor switch structure configured to assume a forward conducting state. A steady-state current carrying capability of the semiconductor switch structure in the forward conducting state is characterized by a nominal current. The semiconductor switch structure is configured to conduct, in the forward conducting state, at least a part of a forward current in a forward current mode of the power electronic arrangement. A diode structure electrically connected in antiparallel to the semiconductor switch structure is configured to conduct at least a part of a reverse current in a reverse mode of the power electronic arrangement. A thyristor structure electrically connected in antiparallel to the semiconductor switch structure has a forward breakover voltage lower than a diode on-state voltage of the diode structure at a critical diode current value, the critical diode current value amounting to at most five times the nominal current.

Many functions of modern devices in automotive, consumer and industrial applications, such as converting electrical energy and driving an electric motor or an electric machine, rely on power electronic arrangements comprising semiconductor devices. For example, power electronic arrangements comprising insulated gate bipolar transistors (IGBTs), thyristors, metal oxide semiconductor field effect transistors (MOSFETs) and diodes, to name a few, have been used for various applications including, but not limited to switches in power drives, power supplies and power converters.
Frequently, such a power electronic arrangement comprises a semiconductor switch, e. g., an IGBT, and a diode connected in antiparallel thereto, wherein the diode may function, for example, as free-wheeling diode. Such a power electronic arrangement may be operated in a forward mode, wherein the semiconductor switch conducts at least a part of a forward current, and in a reverse mode, wherein the diode conducts at least a part of a reverse current.
In certain operating conditions, such as, e. g., a pulse blocking mode of the switch after failure detection, a load current has to flow through the diode, requiring a relatively high surge current capability of the diode. For example, a sufficient surge current capability may be ensured by providing a relatively large active area of the diode. However, this is generally at the expense of higher switching losses.
In certain applications, e. g., High voltage direct current (HVDC) applications, extra devices, such as thyristors, are sometimes provided for surge current events. While this solution may allow for a full optimization of the diodes without surge current constraints, it is generally expensive due to the need for, e. g., a dedicated control board for igniting the thyristor.
It is thus generally desirable to enable a high surge current capability of a power electronic arrangement while at the same time allowing for an optimization of electrical properties with regard to normal operation modes of the power electronic arrangement.


A floor covering repair technique and tool includes placement of a spacer between a patch and a damaged floor covering piece before cutting through both layers. This way, the replacement patch is elevated slightly above the damaged piece and this slight elevation allows for a slight increase in the perimeter/total area of the patch, which offsets the slight retraction/contraction of the edges of the patch and/or the edges of the original flooring after the cut. This results in a more exact fit between the patch and the surrounding, original undamaged when the patch is installed.

1. Field of the Invention
This invention relates generally to flooring and more specifically to repairs for damaged vinyl floors.
2. Related Art
Vinyl as a flooring material has become very popular. Many millions of square feet of vinyl flooring are installed every year. Often, after or during installation, the vinyl flooring is damaged by dents, holes, scrapes or scratches. Then, the vinyl flooring needs to be repaired.
Typically, the repair of this damage to vinyl flooring is done by:                Providing an oversized replacement patch that matches the pattern in the damaged area (for example, by cutting from a roll or large sample of the vinyl);        Aligning the patch and taping it in place;        Cutting through both layers with a utility knife along a cutting line determined to surround and not cut through the damaged area;        Removing the patch and peeling up the damaged flooring with a scraper, taking care not to damage the cut edges, and using a heat gun or iron to soften the adhesive, if necessary;
Applying new flooring adhesive to the newly-cut patch and pressing it in place into the opening created by cutting the damaged flooring from the undamaged vinyl; and
Wiping off any excess adhesive with a damp cloth and covering the patch with a weight for 24 hours.
Preferably, the cut is made along the flooring pattern lines, if any, to make the repair less visible. If it is discovered that the section to be removed isn't attached to the subfloor by adhesive, an attempt to slip some new adhesive underneath the exposed edges of the original vinyl to keep it in place is recommended.
However, whenever this prior art repair technique is practiced, the seam (between the original vinyl and the replaced, repair piece) is noticeable. The seam may be barely noticeable, but it is there nonetheless, and irritating to discriminating homeowners and floor repairmen. The reason for the seam is because typically the cut replacement piece turns out to be slightly smaller than the original damaged piece. Typically, the industry craftsmen have filled this seam with seam sealer or filler. However, it has been a desire in the industry to eliminate this seam space as much as possible.
This imperfect fit may be because the top piece of vinyl is stretched slightly when it is cut with the knife while overlaying the relative soft damaged piece. The damaged piece, on the other hand, is constrained by the supporting floor and is totally and/or substantially bound by an underlying adhesive, so it does not stretch, or stretches less, when cut. After the cut is performed, the replacement piece tends to be slightly smaller than the original damaged piece, leaving a slight seam between the original, undamaged vinyl and the inserted replacement piece.
Alternatively, the imperfect fit may be because, when the semi-elastic replacement patch is cut out from the oversized patch sheet, the replacement patch may tend to contract slightly, that is, the edges of the replacement patch pull inward slightly, which results in a slightly smaller replacement patch than originally intended. Also, when the semi-elastic vinyl material on the floor is cut, the edges around the cut-out damaged piece may tend to contract slightly especially if not totally secured to the floor by adhesive, that is, the edges of vinyl surrounding and defining the opening pulling-back slightly. This would tend to increase the size of the opening in the floor vinyl into which the replacement patch will be placed. Therefore, either the edges of the replacement patch, the edges of the remaining original vinyl, or both, may have retracted in opposite directions, resulting in a small gap between the edges that must be filled and/or hidden.
Thus, whether the imperfect fit occurs due to stretching and subsequent retraction, and/or contraction of edges after they are cut from adjacent vinyl material, the imperfect fit may be attributed to retraction or contraction of the vinyl.
The present invention addresses the need for a closer fit between the inserted replacement vinyl patch piece and the surrounding, original undamaged vinyl, preferably by adapting the method and apparatus for cutting the vinyl patch.


A foam-core fabric-covered headrest snaps in place over the top tube of the frame of any of a wide variety of lawn or beach furniture. The core is a resilient foam cylinder into which is cut or molded a radially directed longitudinal slit leading to a cylindrical axial channel. A cylindrically looped one-piece fabric shell covers the side surface of the foam core--slit, channel and all. Preferably, a tether is provided with which to secure the device to the chair frame. The tether prevents accidental dislodging of the device while the chair is being transported. It also tends to discourage theft and other forms of inadvertent loss.

It is uncomfortable to sit in tube frame lawn chairs for long periods, because typically there is no headrest provided. If one leans one's head back against the horizontal top tube of the frame of the chair this soon becomes painful. The frame normally is hard metal and is so relatively thin that a hard edge (albeit a rounded one) contacts the skull or neck at an uncomfortably focused pressure point or line. While the laced web of the chair does cover the top tube, typically it is very thin, and is comfortably resilient only in those areas where it is suspended off of the frame.
Prior developments in this field may be generally illustrated by reference to the following information disclosure statement:
______________________________________ U.S. PATENT DOCUMENTS U.S. Pat. No. Patentee Issue Date ______________________________________ 4,109,887 W. Wakeland Aug. 29, 1978 4,554,039 M. James Nov. 19, 1985 4,773,707 P. Vadala Sep. 27, 1988 3,046,057 F. Smetko Jul. 24, 1962 5,048,892 M. Ledbetter Sep. 17, 1991 5,281,000 R. Ackley Jan. 25, 1994 2,983,310 W. Warlick et al. May 9, 1961 4,165,125 H. Owen Aug. 21, 1979 ______________________________________
U.S. Pat. No. 5,048,892 teaches attachable cushions--for lawn chairs. Foam tube members are shown therein, as well as inflatable ones. FIG. 2 shows foam members snapped on the frame tubes of the lawn chair. One is shown as a foot rest and the patent also speaks of S using them for the head. Wide, open gaps for entry of frame members allow easy installation of the devices, but may fail to provide them with secure attachment.
U.S. Pat. Nos. 4,109,887 and 4,554,039 teach C-shaped cushions for bed rails. Patents 3,046,057, 4,165,125, and 4,773,707 teach headrest attachments for chairs that fit over the top of a chair and are made of foam. The rest of the patents are representative of what was found in a search of the art.
Of course, pillows become soiled over time, which is why pillowcases have been developed for conventional lozenge-shaped pillows. Because of the particular shape of a snap-on tube pillow, the conventional pillowcase is unsuitable. While a number of patents disclose foam tubes covered by fabric, none disclose a method of using a tube of fabric which does not need to be glued in place on the pillow, and, hence, remains interchangeable. It is especially important to be able to change the covers of such pillows, which will be used for sunbathing and other outdoor activities--wherein body oils and environmental dirt will quickly accumulate.
Another reason for interchangeable covers on pillows, which currently is missing from the snap-on pillow art, is that interchangeability allows for the application of individual taste and sensibility in the selection of a cover, not to mention the ability to alter the appearance of the cover to match the occasion. For example, it would be convenient if a user could have two or more covers for a single pillow--one having the logo of the user's favorite baseball team, one with a football logo, and so on. As is common practice in the T-shirt industry, covers could bear travel, political, humorous and other types of messages, as well as advertising material.
Furthermore, the art does not teach a tether for keeping a snap-on headrest in place--for example, while the chair is being transported. Such a tether would also render the device more resistant to petty theft or loss.


A clock network of a field programmable gate array has a first clock bus extending across the chip in a first dimension. A clock pad can be coupled to the first clock bus if the clock network is to be driven from the clock pad. An output of a selected logic cell can be coupled to the first clock bus if the clock network is to be driven from a logic cell. To increase speed of the clock network, the first clock bus is segmented (in one embodiment, collinearly extending segments can be selectively coupled together via selectively programmable antifuses) so that only a short piece of the first clock bus is used to couple either the pad or the logic cell to the clock network in high speed applications.

A field programmable gate array (FPGA) is a versatile integrated circuit chip, the internal circuitry of which may be configured before packaging by a manufacturer or after packaging by an individual user to realize a user-specific circuit. To configure an FPGA, the user typically configures an on-chip interconnect structure of the FPGA so that selected circuit components in logic modules of the FPGA are electrically connected together in such a way that the resulting circuit is the user-specific circuit desired by the user. In an FPGA employing, for example, amorphous silicon antifuses, selected amorphous silicon antifuses electrically disposed between selected routing conductors in the interconnect structure are "programmed" to connect the selected routing conductors together electrically. Which antifuses are programmed and which antifuses are left unprogrammed determines how the circuit components of the numerous logic modules are interconnected and therefore determines the resulting circuit. FPGAs can employ other types of antifuse structures including, for example, antifuses employing nitrides and oxides. For further details on FPGAs and antifuses, see U.S. Pat. Nos. 5,557,136, 5,544,070, and 5,220,213 all of which are incorporated herein by reference in their entirety.
It is desired to provide a clock network wherein a clock signal can be provided to the clock inputs of flip-flops in numerous logic cells with a minimum delay from a dedicated clock pad to the flip-flop clock inputs. It is also desired to make the clock network versatile so that the clock network can be driven by the output of a logic cell rather than from the dedicated clock pad.

Clock network for field programmable gate array


An array antenna includes radiating antenna elements arranged to form an antenna aperture, the radiating antenna elements including a first group and a second group of radiating antenna elements; a corporate feed network configured to feed the radiating antenna elements, wherein the corporate feed network includes a 4-port device including a sum port, a difference port, a first signal port and a second signal port, with the first signal port coupled via the corporate feed network to the first group of radiating elements and the second signal port coupled via the corporate feed network to the second group; a first phase shift element proximal to the antenna aperture to introduce a first predetermined phase shift to the first group of radiating antenna elements; and a second phase shift element proximal to the second signal port to introduce a second predetermined phase shift to the second group of radiating antenna elements.

Array antennas, such as passive flat plate array antennas, that can provide larger gain and wider bandwidths are in continuous demand for various satellite and point to point communications applications. In a majority of these antennas, the radiating antenna elements are fed by series of corporate feed structures within a corporate feed network that begins with one or two inputs, joined/combined via a (reactive) 3-port T structure. Additional 3-port T structures making up the larger corporate feed network are the main contributors to the amplitude and phase distributions of the radiating elements. These T structures are designed and constructed to provide "widest band" and appropriate power division at each level before ending in the radiating antenna element. To obtain larger gain and bandwidth, it is imperative that each component of the corporate feed network (e.g., each 3-port T structure) and the radiating antenna elements be designed with the lowest possible reflection and the widest bandwidth performance.
However, obtaining a very low reflection (<−40 dB) by each component becomes exceedingly difficult due to the geometry and the manufacturing tolerances associated with today's array antennas. This in turn makes it difficult to achieve very low input reflection coefficient for the entire array. Powerful 3D simulation software has been used to optimize the design and the construction of the feed components. But, the inherent performance limitation of each component set by its boundary conditions, geometrical configuration, and the realistic achievable dimensional tolerances limit the optimized enhancements.
The addition of tuning circuitry to the antenna array input has also been tried to minimize the entire reflection. Unfortunately, the tuning circuitry typically cannot provide the required "wideband" performance if the amplitude of the reflection is large (>−8 dB) and/or highly oscillatory. Furthermore, the tuning circuitry does not provide any benefit with respect to the reflections which occur closer to the radiating antenna elements, hence affecting the radiation pattern.
In view of the aforementioned shortcomings, there is a strong need in the art for an array antenna in which the total input reflection coefficient of the array antenna may be lowered to an acceptable level over wider bandwidth, without reliance on tuning circuitry at the input and without significant degradation of the input reflection or the radiation pattern.


An image forming apparatus has an image supporting member for supporting a toner image, a transfer rotating member forming a nip with the image supporting member and electrostatically transferring the toner image formed on the image supporting member to a recording material, a fixing device for fixing the toner image to the recording material holding the toner image, and a guide member for guiding the recording material so that the angle between the direction of separation of the recording material from the transfer rotating member and the tangent to the image supporting member at the center of the nip is at least 2.degree. in a direction toward the image supporting member. The fixing device has a fixing rotating member, which contacts the toner image on the recording material and to which a bias of the same polarity as that of the toner is applied, and a pressure rotating member in pressure contact with the fixing rotating member so as to hold the recording material between the fixing rotating member and the pressure rotating member.

1. Field of the Invention
The present invention relates to an electrostatic transfer type image forming apparatus, and particularly to an image forming apparatus such as an electrophotographic printer, a copying machine or the like which uses as a transfer device a transfer roller.
2. Description of the Related Art
Although transfer devices used in electrophotographic printers, copying machines and the like have generally employed a corona transfer process, a roller transfer process has recently been used because it generates little ozone and it has good properties for conveying a recording material, and thus can simplify the carriage means of an image forming apparatus. With regard to fixing devices, these generally comprise a heating roller for use as the fixing device.
However, when an OHP film or dry cardboard (weight 100 g/m.sup.2 or more) is used, a toner image on the recording material is electrostatically offset on a fixing roller on the toner side.
Particularly, in a fixing device where for ease of maintenance there is no cleaning member on the heating roller, a fixing ghost occurs due to the re-transfer of the offset toner to the image surface of the recording material at the period of the fixing roller.
Such an offset phenomenon is prevented by applying to the fixing roller a voltage with the same polarity as that of the toner or by grounding the fixing roller through a low-capacity element such as a diode or the like to produce a self bias.
However, when a bias is applied to the fixing roller in an image forming apparatus which uses a transfer roller for electrostatic transfer, there are the following problems.
When an OHP film or a dry cardboard is used as a recording material, the potential of the recording material after transfer depends upon the type and density of the pattern printed, and thus a potential with a polarity reverse to that of transfer charge is sometimes generated. However, when a voltage with a polarity reverse to that of transfer charge is applied to the fixing roller by an electric power source or a diode in order to prevent offset it is necessary to apply a voltage higher than the potential of the recording material after transfer. As a result, a very high voltage (for example, when a negatively charged toner is used, -2 kV or more) is applied to the fixing roller, and leakage to the temperature detection element of a thermistor, to the pressure roller or the like, each of which contact the fixing roller, easily occurs. This causes errors to be produced in the image forming apparatus, and the need for means for preventing the leakage brings about the complication of the apparatus and an increase in the cost thereof.

Electrostatic transfer type image forming apparatus with recording material guide for changing direction of recording material separation from image transfer position


The disclosure concerns to rooms or buildings constructed by raising walls using prefabricated blocks made of Portland cement mortar reinforced with steel fibers. The prefabricated blocks are stable without requiring a mortar mixture, or any additional internal or external structural support for the construction of the walls.

The construction industry is continuously searching for ways to obtain firmness, stability, and high resistance for the use of prefabricated pieces destined to raise walls, rooms, and buildings.
In many cases, the use of larger amounts of elements for the raising of walls has been avoided so the task becomes as simple as possible for the workers without qualification or even by the future occupants of the house.
Unfortunately, the proposed solutions for prefabricated pieces of the prior art that do not require the use of a mortar mixture did not offer satisfactory levels of firmness, stability, or high resistance. At the same time, the proposed solutions in the matter of fit in prefabricated pieces had demonstrated that the use of elements to help in the construction as metal supports or beams had not been totally avoided.
Additionally, the proposed solutions until this moment have not allowed obtaining a suitable finish for the walls including openings for doors and windows or for forming the 90 degree angle when connecting two walls to form a room.
The present invention proposes an alternative to solve these problems.
The present invention includes a prefabricated block and complementary blocks that allows the user to build pillars, walls, rooms, and buildings without the need of an external or internal structural support, adhesive, mortar mixture, support beams, or plaster. The prefabricated blocks and complementary blocks interconnect between themselves and are made of Portland cement mortar reinforced with steel fibers. The Portland cement mortar reinforced with the steel fibers provides the block with enough strength so that the wall, room, or building can be raised without the need of external or internal structural support, adhesive, mortar mixture, or support beams.
The pillars, walls, rooms, and buildings constructed by the blocks and complementary blocks of the present invention are self-locking because their connecting mechanism is absent external or internal structural support, adhesive, mortar mixture, or support beams. In addition, the pillars, walls, rooms, and buildings constructed by the blocks and complementary blocks of the present invention are free-standing because they do not require the use of additional external or internal structural support elements.
The complementary blocks may be derived from the design of the block and they are a lintel beam which can also be used as a career beam or crown beam; a head-block; and a semi-block.
The block and complementary blocks interact in a way that is described next, providing a technical alternative for the solution of the described technical problems. By the interaction of these elements, pillars, walls, rooms, and buildings having firmness, stability, and high resistance and free-standing capacity are constructed, obtaining a suitable finish in spaces destined to openings, doors and windows, as well as a suitable encounter between the right angle walls that offer a solid mechanical entailment between the convergent walls.

Self-locking block and complementary pieces for the raising of pillars and free-standing walls


Disclosed is a method and apparatus for displaying (simulating) grayscale images on a monochrome LCD screen particularly with an objective of providing a comfortable displaying effect that presents no blinking of dots to the user's eyes. In the method, the grayscale image is divided into a sequence of pages of image data each having an array of dots equal to the resolution of the grayscale image such that each pixel on the grayscale image corresponds to a sequence of dots respectively on the corresponding location on the N-1 pages of image data. Black and white colors are assigned to the dots in accordance with a color assignment algorithm that allows the black and white colors to be evenly distributed. When the pages are displayed in succession at a fast rate on the monochrome screen to simulate grayscale image, the black dots or white dots appear evenly on each page so that blinking of dots would not present to the user's eyes.

1. Field of the Invention
The present invention relates to method and apparatus for displaying grayscale images, and more particularly, to a method and apparatus for displaying grayscale images on a monochrome LCD screen.
2. Description of Prior Art
LCD (liquid crystal display) is nowadays in the information age widely used on small-scale data processing units which can be handheld or portable as PDAs (Personal Digital Assistant), notebook computers, subnotebook computers, electronic dictionaries, and the like. A monochrome LCD screen is composed of an array of tiny LCD cells, each capable of displaying only two colors: white and black. Presently, small-scale data processing units are primarily used for word processing purposes so that the LCD only needs to display text or icons. A monochrome screen is thus adequate to support most of the applications on a small-scale data processing unit.
However, with the coming of the multimedia applications, there are demands for the small-scale data processing units to display images. Responding to such demands, there are offered grayscale and color displays. These displays can show grayscale or color images in high resolution but, however, are often expensive to implement. Moreover, these displays often require customized drivers so that cost is high.
On PDAs and electronic dictionaries, a cost-effective method for displaying (simulating) grayscale images on a monochrome screen is to divide a grayscale image into multiple pages of "black and white" images and then display these pages in a predetermined sequence cyclically at a very high rate on the screen. One example of such a method is depicted in FIG. 1. In the example shown, the monochrome LCD screen is used to simulate a 4-level grayscale display. The four gray levels are as listed below:
______________________________________ Gray Level Color ______________________________________ 0 Black 1 Dark Gray 2 Light Gray 3 White ______________________________________
Using the method, an original grayscale image is divided into three pages. If a pixel on the original image has a gray level of 0 (black), the corresponding dots on the three pages are all black; if gray level 1 (dark gray), the corresponding dots on thee first page and the second page are black and that on the third page is white; if gray level 2 (light gray), the corresponding dot on the first page is black and that on the second page and third page are white; and if gray level 3 (white), the corresponding dots on all the three pages are white.
To simulate the grayscale color of a pixel, the three pages are displayed cyclically at a very fast rate in a predetermined sequence from Page 1 through Page 3. In hardware implementation, an LCD cell displays white when a voltage V.sub.rm0 is applied thereto, and displays black when a voltage V.sub.rm3 is applied thereto. Accordingly, to make an LCD cell simulate a gray level 0 color (black), the voltage sequence (V.sub.rm3, V.sub.rm3, V.sub.rm3) is applied cyclically to the LCD cell; to simulate a gray level 1 color (light gray), the voltage sequence (V.sub.rm3, V.sub.rm0, V.sub.rm0) is applied; to simulate a gray level 2 color (dark gray), the voltage sequence (V.sub.rm3, V.sub.rm3, V.sub.rm0) is applied; and to simulate a gray level 3 color (white), the voltage sequence (V.sub.rm0, V.sub.rm0, V.sub.rm0) is applied.
The aforementioned method, however, has a drawback in that blinking of the simulated grayscale image is obvious to the user's eyes. The persistence of vision in the human eye cause the user to perceive the change of dots from black to white or from white to black when the frequency of such a change is low. It can be seen from FIG. 1 that in the aforementioned method the spatial frequency of the layout of the dots is low, allowing the user's eyes to perceive the changes of dots between black and white.
Besides, the period of the voltage sequence applied is too long, so that the frequency of change is low. Assume that the period required to display one page is T, since a total of (N-1) pages are required to simulate an N-level grayscale image, the time needed to display a complete cycle of all the (N-1) pages (call refresh time) is (N-1) * T The rate of tonal change in the simulated grayscale image is thus: EQU F.sub.t1 =1/(N-1)*T!
where f=1/T.
The refresh frequency must be high enough to eliminate the blinking effect of the simulated grayscale image to the user's eyes.

Method and apparatus for non-blinking displaying of grayscale image on monochrome LCD screen


A scanning optical apparatus is provided with a light source, a scanning device and a detector. A light beam generated from the light source is deflected by the scanning device to be scanned on a surface to be scanned. The light beam scanning on the surface to be scanned is detected by the detector. The detector is constructed such that three or more photosensors are closely arranged adjacent one another in the scanning direction. At least one of the photosensors is a division sensor which is arranged symmetrically with respect to the scanning direction.

1. Field of the Invention
The invention relates to a light beam scanning apparatus to scan a scanning object by a light beam in order to record or read an image or the like and, more particularly, to a light beam detecting mechanism in which when a predetermined position serving as a positioning reference point is scanned by a light beam, such a scan is detected and a predetermined signal is generated.
2. Related Background Art
FIG. 1 is a schematic diagram showing the construction of a conventional example of a laser printer in which a light beam scanning apparatus is assembled.
The light scan in the laser printer which is used to record an image or the like is executed in the following manner.
A laser beam which is emitted from a semiconductor laser 701 passes through a collimating lens 702, a cylindrical lens 703, and the like and enters a rotational polygon mirror 704 which is rotated at a predetermined speed. The laser beam is reflected by each surface of the polygon mirror 704, thereby deflecting and scanning within a predetermined angle. After that, the reflected light passes through the optical system such as f.theta. lens group 705, light path folding mirror 708, and the like which are provided to form the beam and to scan at a uniform speed. The light subsequently optically scans a photo sensitive material 709 as a recording medium.
The light scan, printing operation, and the like as mentioned above are executed by a control unit (not shown).
The control unit drives the semiconductor laser 701 by an on/off signal based on an image signal which is supplied from the outside. The laser beam is modulated in accordance with the image signal. The drum-shaped photo sensitive material 709 is rotated in the direction perpendicular to the main scanning direction every main scan. The optical recording operation of an image, characters, or the like is finished by the actuation of the semiconductor laser 701 and the rotation of the photo sensitive material 709.
In order to prevent adverse influence on the image to be formed, the positional precision of the laser scan relative to the image signal needs to be held to an extreme high precision to avoid a variation in the position precision of each main scan. For this purpose, in such a kind of laser printer or the like, there is provided a light beam detecting mechanism having a light beam receiving section 707 for receiving the light folded by a submirror 706 as shown in the diagram and for detecting that the laser beam which had been deflected and scanned by the rotational polygon mirror 704 has reached a predetermined position. The light beam detecting mechanism generates a sync signal to decide the recording starting position on the photo sensitive material 709 on the basis of a detection signal of the light beam receiving section 707. The control unit allows the image signal to be generated in accordance with the timing of the sync signal, thereby always keeping the same writing position.
The laser beam of a predetermined intensity is not always irradiated to the light beam receiving section 707 due to a surface accuracy or a surface inclination of each surface of the rotary polygon mirror, dust, or dirt of the rotary polygon mirror or the optical system, or the like. Therefore, if the apparatus is constructed so as to generate the sync signal when the level of output of the light receiving section exceeds a predetermined threshold value, a variation of the light amount occurs every main scan. If the level of output which is received by the light beam detecting mechanism fluctuates, the generation timing of the sync signal is deviated.
To prevent the above inconveniences, there has been proposed a method whereby two light receiving sections (the first light receiving section and the second light receiving section) are closely arranged on the main scan line, a ratio of output signals of the first and second light receiving sections is obtained by a calculating circuit, and the sync signal is generated when the output signal ratio is equal to a predetermined value.
On the other hand, as for the semiconductor laser, since the output characteristics are easily influenced by a temperature change and a fluctuation of the light amount is large, a method whereby the semiconductor laser device is devised so as to keep a predetermined temperature by a Peltier device or the like and the output fluctuation is suppressed has been proposed.
In the above conventional light beam detecting mechanisms, in case of the light beam detecting mechanism having only one light receiving section, there is a problem such that the generation timing of the sync signal is deviated due to the output fluctuation of the light beam.
In case of the light beam detecting mechanism having two light receiving sections, since the sync signal is obtained by setting off the output fluctuation of the light beams which are irradiated to the light receiving sections, the above problem does not occur. However, there is a problem such that an out-of focus state of the light beam, out-of main scanning position, or the like due to the precision of the whole apparatus by a temperature change, an aging change, or the like cannot be detected.
In case of suppressing the output fluctuation of the semiconductor laser device so as to keep a predetermined temperature by a Peltier device or the like, the generation timing of the sync signal is not deviated. However, since the output characteristics of the semiconductor laser device are also changed by a change with the passage of time, there is a case where a wavelength fluctuation occurs and the laser beam of a wavelength which is different from the initial set wavelength is generated. When the wavelength fluctuates, an out-of focus state generally occurs in the laser scan optical system or the like in which the chromatic aberration is not sufficiently corrected. Any one of the above light beam detecting mechanisms cannot cope with such an out-of focus state.
In many cases, the user is aware of such various inconveniences as mentioned above until after completion of recording, so that both time and costs are wasted.

Scanning optical apparatus having at least one division sensor