There is disclosed an optical pickup device including: a blue semiconductor laser which emits a first laser light having a wavelength of 450 nm or less to record on or reproduce from an extra-high density optical disc; a red semiconductor laser which emits a second laser light having a wavelength longer than that of the first laser light to record on or reproduce from a DVD having a low recording density; an objective lens; and an aberration correction element. The objective lens is designed for the extra-high density optical disc, and has a numerical aperture (NA) of 0.75 or more. The aberration correction element passes the first laser light as such and thereafter allows the light to be incident upon the objective lens, whereas the element limits an aperture with respect to the second laser light and diffracts the second laser light so as to correct an aberration with respect to the DVD and thereafter allows the light to be incident upon the objective lens.

1. Field of the Invention
The present invention relates to an optical pickup device and an optical recording medium driving apparatus comprising at least an objective lens having a numerical aperture (NA) of 0.75 or more, and an aberration correction element for correcting a sphere aberration generated by a difference of a substrate thickness between first and second optical recording mediums at a time when the objective lens is used, to selectively record on or reproduce from the first and second optical recording mediums different in substrate thickness using first and second laser lights having different wavelengths.
2. Description of the Background Art
In general, optical recording mediums such as a disc-shaped optical disc and card-shaped optical card have been frequently used, because the mediums are capable of recording information signals such as video information, sound information, and computer data in tracks spirally or concentrically formed in a transparent substrate, and capable of accessing a desired track at a high rate during reproduction of recorded tracks.
As this type of optical recording medium, the optical discs such as a compact disc (CD) and a digital versatile disc (DVD) have already been on the market. In recent years, an extra-high density optical disc (Blu-ray Disc) has been actively developed which is capable of recording or reproducing information signals at a density higher than that of CD, DVD in order to increase the density of the optical disc.
First, for the above-described CD, a disc substrate has heretofore been irradiated with a laser beam obtained by focusing a laser beam having a wavelength of around 780 nm with an objective lens having a numerical aperture (NA) of about 0.45 to record or reproduce the information signal on or from a signal surface which is positioned distant from the laser incident incidence surface of the disc substrate by approximately 1.2 mm.
Moreover, for the above-described DVD, the disc substrate has heretofore been irradiated with the laser beam obtained by focusing a laser beam having a wavelength of around 650 nm with an objective lens having a numerical aperture (NA) of about 0.6 to record or reproduce the information signal on or from the signal surface which is positioned distant from the incidence surface by approximately 0.6 mm. In this case, a recording capacity of the DVD is increased six to eight times that of the CD, and the capacity of one surface is about 4.7 gigabyte (GB) with a diameter of a disc substrate of 12 cm.
Furthermore, the above-described extra-high density optical disc has been developed in which the disc substrate is irradiated with a laser beam having a wavelength of 450 nm or less, which has been focused with an objective lens having a numerical aperture (NA) of 0.75 or more, so as to be capable of recording or reproducing the information signal on or from a signal surface which is positioned distant from the incidence surface by approximately 0.1 mm. In this case, the recording capacity of the surface of the extra-high density optical disc is around 25 gigabytes (GB) with the diameter of the disc substrate of 12 cm.
Additionally, there has been an optical pickup device comprising an objective lens shared with respect to two types of optical discs already on the market such as the CD and DVD and an optical element which transmits all the laser beams having a wavelength of around 650 nm to record on or reproduce from the DVD while interrupts the laser beam having a wavelength of around 780 nm by an outer circular portion thereof and diffracts it by an inner circular portion thereof to record on or reproduce from the CD (see, for example, Japanese Patent Application Laid-Open No. 2000-105943 (pages 4 to 6, FIGS. 1, 10, 11)).
FIG. 1 is a constitution diagram showing one example of a conventional optical pickup device. FIGS. 2A and 2B are explanatory views of a second optical element shown in FIG. 1, where FIG. 2A is a diagram showing the recording or reproducing of the DVD, and FIG. 2B is a diagram showing the recording or reproducing of the CD.
A conventional optical pickup device 110 shown in FIGS. 1, 2A, and 2B is described in the Japanese Patent Application Laid-Open No. 2000-105943. The device will be briefly described with reference to the document.
As shown in FIG. 1, the conventional optical pickup device 110 comprises: a first semiconductor laser 111 which emits a laser light La having a wavelength of 650 nm for a DVD 101; a second semiconductor laser 112 which emits a laser light Lb having a wavelength of 780 nm for a CD 102; a first optical element 113 which corrects an optical axis deviation between the laser light La having a wavelength of 650 nm and the laser light Lb having a wavelength of 780 nm; a correction plate 114 which corrects a phase difference caused by the first optical element 113; a half mirror 115 which transmits the respective laser lights La, Lb emitted from the first and second semiconductor lasers 111, 112 and which reflects each light reflected by a signal surface 101a of the DVD 101 or a signal surface 102a of the CD 102 so as to change a direction of the light by approximately 90°; a collimator lens 116 which forms the laser light La having a wavelength of 650 nm and the laser light Lb having a wavelength of 780 nm into parallel lights; a second optical element 117 which allows the laser light La having a wavelength of 650 nm, transmitted through the collimator lens 116, to be incident upon an objective lens 118 and which interrupts the laser light Lb having a wavelength of 780 nm, transmitted through the collimator lens 116, by the outer circular portion thereof and diffracts the light by the inner circular portion thereof and allows the light to be incident upon the objective lens 118; the objective lens 118 which focuses the laser light La having a wavelength of 650 nm and the laser light Lb having a wavelength of 780 nm to converge the light on the signal surface 101a of the DVD 101 or the signal surface 102a of the CD 102; a Wollaston prism 119 which separates each reflected light from the DVD 101 or the CD 102 into a laser light containing only an s-polarized component, a laser light containing only a p-polarized component, and a laser light containing the s-polarized component mixed with the p-polarized component; and a photodetector 120 which detects the laser light of only the s-polarized component, the laser light of only the p-polarized component, and the laser light of the s-polarized component mixed with the p-polarized component from the Wollaston prism 119.
Here, in the above-described constituting members, as enlarged and shown in FIGS. 2A and 2B, especially the second optical element 117 comprises an outer circular portion 117a and an inner circular portion 117b. Moreover, the outer circular portion 117a of the second optical element 117 has a function of transmitting the laser light La having a wavelength of 650 nm wholly as it is, and diffracting only the laser light Lb having a wavelength of 780 nm outside an optical axis to prevent the light from being incident upon the objective lens 118. On the other hand, the inner circular portion 117b of the second optical element 117 has a function of transmitting the laser light La having a wavelength of 650 nm wholly as it is, and diffracting only the laser light Lb having a wavelength of 780 nm to allow the light to be incident upon the objective lens 118.
In this case, for a sectional structure of the second optical element 117, the outer circular portion 117a includes a concave/convex pattern structure, the inner circular portion 117b roughly has triangular shapes, and a portion corresponding to a slope of each triangular shape has a stair-like pattern structure.
Moreover, as shown in FIG. 2A, in the recording or playback of the DVD 101 by the objective lens 118, the laser light La having a wavelength of 650 nm passes as such without being influenced by the second optical element 117 and is incident upon the objective lens 118. The light is focused onto the signal surface 101a of the DVD 101 having a disc substrate thickness of 0.6 mm by the objective lens 118.
On the other hand, as shown in FIG. 2B, in the recording or playback of the CD 102 by the objective lens 118, for the laser light Lb having a wavelength of 780 nm, a portion incident upon the outer circular portion 117a of the second optical element 117 is largely diffracted outside the optical axis by a concave/convex diffraction pattern, and is not incident upon the objective lens 118. The laser light Lb incident upon the inner circular portion 117b of the second optical element 117 is diffracted to the outside by the triangular stair-like pattern structure, but is incident upon the objective lens 118 without being largely diffracted as in the outer circular portion 117a. Therefore, only the laser light Lb incident upon only the inner circular portion 117b of the second optical element 117 reaches the objective lens 118, and is focused onto the signal surface 102a of the CD 102 having a disc substrate thickness of 1.2 mm by the objective lens 118.
That is, the laser light Lb having a wavelength of 780 nm is substantially interrupted by the outer circular portion 117a of the second optical element 117, diffracted by the inner circular portion 117b, and is incident upon the objective lens 118. In this case, the objective lens 118 is designed for the DVD having a disc substrate thickness of 0.6 nm. Therefore, when the laser light Lb having a wavelength of 780 nm is only interrupted by the outer circular portion and is incident upon the disc substrate having a thickness of 1.2 mm, aberration is generated, and the lens is designed so as to reduce this aberration. Therefore, a diameter of the inner circular portion 117b of the second optical element 117, and a size of the triangular shape which causes diffraction are determined in such a manner that an effective numerical aperture of the objective lens 118 is 0.45 with respect to the laser light Lb having a wavelength of 780 nm. It has also been described that when the signal recording into a recordable/reproducible CD-recordable (CD-R) is considered, an effective numerical aperture of the objective lens 118 is suitable, and therefore the diameter of the inner circular portion 117b of the second optical element 117 is determined so as to set the effective numerical aperture of the objective lens 118 to 0.45 to 0.50.
Additionally, according to the conventional optical pickup device 110, the DVD 101 and the CD 102 can be selectively recorded or reproduced using the objective lens 118 designed for the DVD and the first and second optical elements 113, 117. However, it is clear that anything is not considered with respect to the extra-high density optical disc being developed in the conventional optical pickup device 110.
On the other hand, when proceeding with the development of the extra-high density optical disc, needless to say, there has also been a demand for a recordable or reproducible optical pickup device and optical disc driving apparatus in which an extra-high density optical disc and DVD are used in common. Furthermore, there is also a possibility of a recordable or reproducible optical pickup device and optical disc driving apparatus in which an extra-high density optical disc and CD are used in common.

This patent is subject to a terminal disclaimer.

Optical pickup device and optical recording medium driving apparatus


A method and apparatus for improving co-existence between Bluetooth and 802.11 networks is described. In one embodiment, the invention is a method. The method includes detecting in software a backup in transmission of data through a first wireless channel. The method further includes shifting priority in software from transmission of data through a second wireless channel to transmission of data through the first wireless channel. The method also includes determining in software if the backup eases and shifting priority back in software from transmission of data through the first wireless channel to transmission of data through the second wireless channel. As will be appreciated, characteristics of an embodiment of the invention need not appear in all embodiments within the spirit and scope of the invention.

1. Field of the Invention
The invention generally relates to improved operation of communications devices in a system and more specifically to software involved in Bluetooth and 802.11 networks.
2. Description of the Related Art
As computing power has become more widespread, networking of computers has become more important. Wireline networks have existed and have been fine-tuned through years of use. However, wireless networks offer enhanced flexibility relative to wireline networks, and thus are becoming more popular. Wireless network technology is new relative to wireline networks, and thus has not received the fine-tuning received by wireline networks. Note that for this discussion, networks refer both to local area networks and to other connectivity technology, such as cabling between systems and peripherals for example.
Wireless technology can take a number of forms. Infrared ports allow for connectivity over short distances, and can be suitable for connections between systems and peripherals. Wireless LANs using the IEEE 802.11 standard (such as is described in the ANSI/IEEE Std 802.11, 1999 edition document) can be used for connecting systems in a manner similar to a wireline local area network. Bluetooth (as specified in "Specification of the Bluetooth System", Version 1.1, bearing a publication date of Feb. 22, 2001 and available from the "www.bluetooth.com" website) networks can also be useful for local area networks or for peripheral connectivity. Unfortunately, both 802.11 and Bluetooth operate in the 2.4 GHz band for wireless (RF) transmissions, and can potentially interfere. Moreover, 802.11 and Bluetooth systems can potentially be used in a single system, further allowing for interference between two antennas in the same physical machine.
This confluence of two wireless technologies in the same (general) frequency spectrum suggests that system designers would do well to choose one of the two technologies (Bluetooth or 802.11) but not both, and that IT professionals would then choose one of the two wireless technologies for a given portion of a company. Such a strategy necessarily restricts implementation options available to IT professionals, and thus is undesirable. Thus, it may be desirable to find a way to allow for co-existence between Bluetooth and 802.11. Moreover, it may be preferable to reduce the amount of hardware required to allow for co-existence of the two technologies.

Method and apparatus for improving co-existence between bluetooth and 802.11 networks


A rack-driven auxiliary power steering apparatus prevents a ball nut and a nut pulley from idling due to a slip thereof and increases durability when the drive belt is operated by driving of a motor, and minimizes vibrations and noise transferred through the rack bar, the ball nut, and the nut pulley when the rack bar is slid while the nut pulley and the ball nut are rotating, thereby providing a comfortable steering feeling to the driver.

1. Field of the Invention
The present invention relates to an electric power steering apparatus of the ball screw type, and more particularly to an electric power steering apparatus of the ball screw type which prevents the load from being concentrated on the ball located at the outermost of the ball nut within the inner peripheral screw groove with the ball nut bended, thereby preventing the durability of the ball nut and the ball from being deteriorated.
2. Description of the Prior Art
A general electric power steering apparatus includes a steering system extending from a steering wheel to two wheels, and an auxiliary power mechanism for supplying auxiliary steering power to the steering system.
The auxiliary power mechanism includes a torque sensor for detecting a steering torque applied to a steering wheel by the driver and outputting an electric signal proportional to the detected steering torque, an electronic control unit (ECU) for generating a control signal based on the electric signal transferred from the torque sensor, a motor for generating auxiliary steering power based on the control signal transferred from the electronic control unit, and a belt type power transmission unit for transmitting auxiliary power generated by the motor to a rack bar via a belt.
An electric power steering apparatus of a ball screw type as the auxiliary power mechanism may include a return tube type, a deflector type, an end cap type and so on.
FIG. 1 is a sectional view schematically illustrating the electric power steering apparatus of the ball screw type according to the related art, and FIG. 2 is a sectional view schematically illustrating a portion of the electric power steering apparatus of the ball screw type according to the related art.
As illustrated in the drawings, the rack-driven auxiliary power steering apparatus according to the related art includes a driving unit 120 for generating a power to be controlled by an electronic control unit (ECU) which determines the degree of the steering of a steering wheel 113 by a torque sensor 111 mounted to a top end of a steering column 110, a rack bar 130 for making a tie rod 133 connected to a wheel moved according to the degree of the steering of the steering wheel 113, and a driven unit 140 for transforming the receiving rotating force of the driving unit 120 to an axially moving force and then transmitting it to the rack bar 130.
Here, the driving unit 120 includes an electric motor 121 controlled by an electronic control unit (ECU), a driving pulley 123 coupled to a shaft of the electric motor 121, and a drive belt 125 wound on a driving pulley 123.
The driven unit 140 also includes the ball nut 141 supporting the rack bar 130 within a rack housing surrounding the rack bar 130, and the driven pulley 143 coupled to an outer peripheral surface of the ball nut 141.
The driving pulley 123 connected to the shaft of the electric motor 121 and the driven pulley 143 connected to the ball nut 141 are disposed parallel to each other, the driving belt 125 is mounted on the driving pulley 123 and the driven pulley 143 to transmit a rotating force of the electric motor 121 to the rack bar 130, and the rack bar 130 is moved leftward and rightward by an operation of the ball nut 141 to generate an auxiliary steering force.
An inner peripheral screw groove 201 having a gothic arc-shaped cross-section is spirally formed on an inner peripheral surface of the ball nut 141, an outer peripheral screw groove 203 having a gothic arc-shaped cross-section is spirally formed on an outer peripheral surface of the rack bar 130, a ball is inserted between the inner peripheral screw groove 201 and the outer peripheral screw groove 203. While contacting the inner peripheral screw groove 201 and the outer peripheral screw groove 203, the ball 210 moves along the inner peripheral screw groove 201 and the outer peripheral screw groove 203, rolls from one side to the opposite side, and circulates through the ball circulation passage 205 formed between the end cap 220 and the ball nut 141 coupled to two sides of the inner peripheral surface of the ball nut 141 respectively.
In the rack-driven auxiliary power steering apparatus according to the related art, as there is generally equally formed a center radius of the ball (R, i.e., distance from the axis of the ball nut to a center of the ball) moving along the inner peripheral screw groove 201, the load is concentrated on the ball located at the outermost of the ball nut with the longitudinal direction within the inner peripheral screw groove with the ball nut bended, thereby causing the durability of the ball nut and the ball to be deteriorated.
Further, there is a step between the inner peripheral screw groove and an inlet of the end cap (i.e., part where the ball escapes the inner peripheral screw groove and enters the end cap) at a location where they meet with each other, thereby causing noise and vibrations to be generated as soon as the ball moving along the inner peripheral screw groove from one side to the opposite side enters the inlet of the end cap.

Electric power steering apparatus of ball screw type


A multiple orientation drive device for use with a beverage brewing apparatus. The beverage brewing apparatus is a type having a brew chamber which includes a top and bottom assembly and an elongated brewing component extending into the brew chamber. The elongated brewing component is associated with the drive device such that it is linearly and rotatably shiftable in the brew chamber. The linear and rotatable shifting are independently achieved by the actions of an independent linear drive assembly and an independent rotary drive assembly. The linear drive assembly is associated with the brewing component for linearly driving the brewing component in the brew chamber and the rotary drive assembly is associated with the brewing component for rotating the component independently of the linear drive assembly. The present invention also includes synchronizing the linear drive assembly and rotary drive assembly to simultaneously linearly shift and rotatably shift the brewing component in the brew chamber. A sensor assembly is associated with the drive device to indicate the position of the brewing component in the brew chamber. The sensor assembly is coupled to a control device which in turn is attached to the linear and rotary drive assemblies. The control device selectively energizes and deenergizes the linear and rotary drive assemblies in response to predetermined conditions defined by the control signal from the sensor assembly.

The present invention relates to drive devices for use with a beverage brewing apparatus. More specifically, the present invention envisions a multiple orientation drive device for use in driving a brewing component in a brew chamber of the beverage brewing apparatus.
A number of brewing devices are available which produce a brewed beverage using a substantially automated process. An example of an automatic beverage brewing apparatus is shown in U.S. Pat. No. 5,134,925 to Bunn et al. issued Aug. 4, 1992, incorporated herein by reference. A beverage brewing device as shown in Bunn et al. has a brew chamber which receives a charge of beverage brewing substance and infuses this substance with water to produce a brewed beverage therefrom. The brewed beverage is drained from the brew chamber and dispensed into an appropriate container. The brew chamber has a top assembly and a bottom assembly through which are formed a throat and a drain, respectively. A brewing component or piston extends into the brew chamber selectively shifting through the throat and the drain during a brewing cycle. The brewing component or piston is operated by a drive device attached thereto.
During a brew cycle, the piston is axially shifted downwardly by the drive device to receive a charge of brewing substance. The piston then shifts axially upwardly to close the throat and drain whereupon a quantity of water is dispensed to infuse the brewing substance and produce a brewed beverage. The brewed beverage is drained out of the brew chamber and dispensed into a collection container. Next, the piston is shifted upwardly to disengage a lower portion of the piston from the drain thereby draining the spent beverage brewing substance and any waste water out of the brew chamber. As shown in Bunn et al., the piston includes a flush water bore which extends therethrough to dispense water from a central area of the brew chamber. The piston is axially rotated and linearly shifted through the throat and drain to flush the inside surface of the brew chamber.
The drive device used in Bunn et al. employs a single drive assembly for both rotating and axially shifting the piston. A sensor is mounted in position relative to one of the rotating gears of the drive assembly to detect the movement of magnets mounted in the selected gear. Linear shifting is achieved by a threaded portion of the piston shaft being driven through a fixed, cooperatively threaded nut body. While the integrated rotary and linear drive device as shown in Bunn et al. is effective at driving the piston, there are applications where it is desirable to rotate the piston without linearly shifting it through the brew chamber and also linearly shifting the piston without rotating it in the chamber. As such, the device as shown in Bunn et al. cannot independently rotate nor linearly shift the piston.

Dual motor drive automatic beverage brewing apparatus


Subterranean formation treating fluid concentrates, treating fluids and methods are provided by the present invention. The treating fluid concentrates are basically comprised of water and a substantially fully hydrated depolymerized polymer. The treating fluids which are formed by adding water to the treating fluid concentrates are basically comprised of water, a substantially fully hydrated depolymerized polymer and a crosslinking agent for crosslinking the hydrated depolymerized polymer.

1. Field of the Invention
The present invention relates to methods and compositions for treating subterranean well formations, and more specifically, to improved subterranean formation treating fluid concentrates, treating fluids and methods of using the treating fluids.
2. Description of the Prior Art
Producing subterranean formations penetrated by well bores are often treated to increase the permeabilities or conductivities thereof. One such production stimulation treatment involves fracturing the formation utilizing a viscous treating fluid. That is, the subterranean formation or producing zone therein is hydraulically fractured whereby one or more cracks or xe2x80x9cfracturesxe2x80x9d are produced therein. Fracturing may be carried out in wells that are completed in subterranean formations for virtually any purpose. The usual candidates for fracturing or other stimulation procedures are production wells completed in oil and/or gas containing formations. However, injection wells used in secondary or tertiary recovery operations for the injection of fluids may also be fractured in order to facilitate the injection of the fluids.
Hydraulic fracturing is accomplished by injecting a viscous fracturing fluid into a subterranean formation or zone at a rate and pressure sufficient to cause the formation or zone to break down with the attendant production of one or more fractures. As the fracture is created a portion of the fluid contained in the viscous fracturing fluid leaks off into the permeable formation and a filter cake comprised of deposited gelling agent is built up upon the walls of the fracture which then helps to prevent or reduce further fluid loss from the fracturing fluid to the formation. The continued pumping of the viscous fracturing fluid extends the fractures and a proppant such as sand or other particulate material may be suspended in the fracturing fluid and introduced into the created fractures. The proppant material functions to prevent the formed fractures from closing upon reduction of the hydraulic pressure which was applied to create the fracture in the formation or zone whereby conductive channels remain through which produced fluids can readily flow to the well bore upon completion of the fracturing treatment.
The fracturing fluid must have a sufficiently high viscosity to retain the proppant material in suspension as the fracturing fluid flows into the created fractures. A viscosifier has heretofore often been utilized to gel a base fluid whereby a fracturing fluid having the high viscosity needed to realize the maximum benefits from the fracturing process is provided. After the high viscosity fracturing fluid has been pumped into the formation and fracturing of the formation has occurred, the fracturing fluid generally has been caused to revert into a low viscosity fluid for removal from the formation by breaking the gel. The breaking of viscosified fracturing fluids has commonly been accomplished by adding a breaker to the fracturing fluid prior to pumping it into the subterranean formation.
The fracturing fluids utilized heretofore have predominantly been water based liquids containing a gelling agent comprised of a polysaccharide such as guar gum. Guar and derivatized guar polymers such as hydroxypropylguar are economical water soluble polymers which can be used to create high viscosity in an aqueous fluid and are readily crosslinked which further increases the viscosity of the fluid. While the use of gelled and crosslinked polysaccharide fracturing fluids has been highly successful, the fracturing fluids have not been thermally stable at temperatures above about 200xc2x0 F. That is, the highly viscous gelled and crosslinked fluids lose viscosity with time at high temperatures. To offset the loss of viscosity, the concentration of the gelling agent has been increased which involves increased cost and causes increased friction pressure in the tubing through which the fluid is injected into a subterranean formation which makes pumping of the fracturing fluids more difficult. Thermal stabilizers such as sodium thiosulfate have been included in the fracturing fluids to scavenge oxygen and thereby increase the stabilities of the fracturing fluids at high temperatures. However, the use of thermal stabilizers also increases the cost of the fracturing fluids.
Another problem which has been experienced in the use of gelled and crosslinked polysaccharide fracturing fluids involves the breaking of such fracturing fluids after fractures have been formed. Breakers such as oxidizers, enzymes and acid release agents that attack the acetal linkages in the polysaccharide polymer backbone have been used successfully.
In order to make the heretofore used gelled and crosslinked polysaccharide fracturing fluids carry sufficient proppant, the concentration of the crosslinking agent utilized has often had to be increased which in turn increases the cost and viscosity of the fracturing fluid. The water based fracturing fluids including gelled and crosslinked polysaccharide gelling agents have had significantly reduced fluid loss as compared to other fracturing fluids which reduces or eliminates the need for costly fluid loss additives. However, because the gelled and crosslinked polysaccharides have had high molecular weights, the filter cake produced from the viscous fracturing fluid on the walls of well bores penetrating producing formations and in fractures formed therein is often very difficult to remove.
Another problem experienced in the use of a water based fracturing fluid including a gelled and crosslinked polysaccharide gelling agent is that it must be mixed in holding tanks for a considerable length of time for hydration of the gelling agent to occur. During the fracturing process carried out in a well, the hydrated fracturing fluid generally is pumped out of the holding tanks, mixed with proppant and other additives on the fly and pumped down the well bore to the formation being fractured. If during the job, the down hole pressure profile and other parameters that are obtained in real time indicate that a change in the fracturing fluid properties is required, that is, a change in the fracturing fluid viscosity to prevent a screen out of the fracture or the like, it is generally impossible to do so since it takes a very long time for a change to be made and for the changed fracturing fluid to reach the formation being fractured. Another problem related to pumping the fracturing fluid from holding tanks and combining the proppant material, crosslinker and other additives used on the fly is that the procedure requires the use of expensive metering and other similar equipment.
Finally, in many environmentally sensitive areas, the water based fracturing fluids containing polysaccharide gelling agents must be recovered from the well and disposed of by environmentally appropriate means which increases the overall cost of the fracturing treatment.
Thus, there are needs for improved subterranean formation treating fluids and methods whereby the fluids are not thermally unstable, do not produce insoluble residues, have high proppant carrying capacities, produce easily removed filter cake, do not have to be hydrated in holding tanks for long periods of time, can have their properties changed during use and can be recovered and reused if desired.
The present invention provides subterranean formation treating fluid concentrates, improved treating fluids which can be utilized for fracturing as well as various other subterranean formation treatments and methods of using the treating fluids which meet the needs described above and overcome the deficiencies of the prior art.
A subterranean formation treating fluid concentrate of this invention is basically comprised of water and a depolymerized substantially fully hydrated polymer. The treating fluid concentrate can also include a variety of additives required to be in treating fluids produced utilizing the concentrate such as pH adjusting compounds for adjusting the pH of the treating fluid formed with the concentrate, buffers, dispersants, surfactants for preventing the formation of emulsions between the treating fluid formed with the concentrate and subterranean formation fluids, bactericides and the like.
The treating fluid concentrate is prepared at a location away from the site of a well to be treated and transported to the well site prior to use. The concentrate is substantially fully hydrated and can be stored for long periods of time prior to its use. When used, the concentrate is continuously mixed with water and any additional additives required and pumped into the subterranean formation to be treated by way of the well bore penetrating it. Because there is very little time delay involved in mixing the treating fluid concentrate with additional water and other additives and pumping the treating fluid formed into a subterranean formation, the properties of the treating fluid can be periodically or continuously changed during the time that the pumping of the treating fluid takes place.
The improved subterranean formation treating fluids of this invention are basically comprised of water, a substantially fully hydrated depolymerized polymer, a pH adjusting compound for adjusting the pH of the treating fluid to an optimum level for crosslinking and a crosslinking agent for crosslinking the substantially fully hydrated depolymerized polymer. While the improved subterranean formation treating fluids of this invention can be utilized for carrying out a variety of subterranean well treatments such as fracturing subterranean formations, forming gravel packs in subterranean formations, forming temporary blocking in the well bore, and as completion fluids and drill-in fluids, they are particularly useful as fracturing fluids for producing one or more fractures in a subterranean formation. When utilized as a fracturing fluid, the treating fluid generally contains a crosslinking agent and a proppant material which are mixed with the treating fluid when it is formed by mixing the treating fluid concentrate described above with additional water. The substantially fully hydrated depolymerized polymer utilized in the concentrate and the treating fluid produced therefrom is preferably a depolymerized polysaccharide polymer, and most preferably depolymerized hydroxypropylguar.
The improved methods of treating a subterranean formation penetrated by a well bore are basically comprised of the following steps. A gelled and crosslinked treating fluid is prepared comprised of water, a substantially fully hydrated depolymerized polymer, a pH adjusting compound for adjusting the pH of the treating fluid to an optimum pH for crosslinking and a crosslinking agent for crosslinking the substantially fully hydrated depolymerized polymer. Thereafter, the gelled and crosslinked treating fluid is introduced into the subterranean formation to be treated.
Another improved method of treating a subterranean formation penetrated by a well bore whereby one or more fractures are formed therein basically comprises the following steps. A gelled and crosslinked fracturing fluid is prepared comprised of water, a substantially fully hydrated depolymerized polymer, a pH adjusting compound for adjusting the pH of the fracturing fluid and a crosslinking agent for crosslinking the substantially fully hydrated depolymerized polymer. Thereafter, the subterranean formation is contacted with the gelled and crosslinked fracturing fluid under conditions effective to create at least one fracture in the subterranean formation. After a fracture is created in the formation, a proppant material may be admixed with a portion of the fracturing fluid and introduced into the created fracture to ultimately prop the created fracture in an open position after the completion of the fracturing treatment.
It is, therefore, a general object of the present invention to provide improved subterranean formation treating fluid concentrates, treating fluids and methods.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
As mentioned above, the present invention provides an improved subterranean formation treating fluid which is prepared on the job site in a very rapid manner from a substantially fully hydrated subterranean formation treating fluid concentrate. The treating fluid concentrate is produced at an off-site manufacturing location and can be stored for long periods of time prior to or after being transported to the job site. The improved subterranean formation treating fluid is prepared at the job site by simply mixing the substantially fully hydrated treating fluid concentrate with additional water and any required additives not already contained in the concentrate. The preparation of the treating fluid involves the steps of metering the treating fluid concentrate into a blender wherein it is mixed with the additional water and additives which also may be metered into the blender or otherwise added to the fluid. The mixture then is substantially simultaneously pumped out of the blender and into the subterranean formation to be treated by way of a well bore penetrating it. From when the metering, mixing and pumping process starts to when the formed treating fluid reaches the subterranean formation to be treated involves a time period of only a few minutes which allows changes in the properties of the treating fluid to be made on the surface as required during the time the treating fluid is being pumped. For example, in a fracturing procedure carried out in a subterranean formation to stimulate production from the subterranean formation, changes can be made to the fracturing fluid during the pumping of the fluid in response to continuously monitored down hole parameters to achieve desired fracturing results, that is, the viscosity of the fracturing fluid, the amount of proppant material carried by the fracturing fluid and other properties of the fracturing fluid can be continuously measured on the surface and changed as required to achieve optimum down hole treatment results in real time.
The subterranean formation treating fluid concentrate of this invention is basically comprised of water and a substantially fully hydrated depolymerized polymer.
The substantially fully hydrated depolymerized polymer may be manufactured by various means. The polymer may be manufactured by forming a hydratable polymer having a relatively high molecular weight as a result of derivatization of a polysaccharide and then subjecting it to extensive depolymerization whereby the polymer backbone is divided into short chain polymer segments. The manufacture of such polymers can be made by derivatization and depolymerization techniques known in the art or as described in Provisional U.S. Application No. 60/297,345, entitled xe2x80x9cGalactomannan Compositions and Methods for Making and Using the Same,xe2x80x9d filed Jun. 11, 2001 (Jesse Magallanes, Sylvain Diguet, William Stivers)(hereinafter referred to as the Magallanes application). According to one embodiment of the invention, the depolymerized polymer of the present invention may be prepared by adding the polymer to be depolymerized to a reactor vessel together with a quantity of hydrogen peroxide and water. In a preferred embodiment, the depolymerized galactomannan polymer is prepared by the methods described in the Magallanes application, the entire disclosure of which is incorporated herein by reference. The reactor vessel may be heated to an elevated temperature such as about 100xc2x0 F. to initiate the reaction if the ambient temperature is insufficient to initiate the reaction. Once initiated, the depolymerization reaction is exothermic and the temperature of the reactor vessel generally should be maintained in the range of from about 100-200xc2x0 F. for a sufficient time for the polymer to degrade to the desired molecular weight. Alternatively, the polymer may be formed from lower molecular weight monomers that are polymerized until the desired molecular weight is achieved. The hydratable polymer utilized for forming the short chain segments can be substantially any polysaccharide and is preferably a guar derivative polymer selected from the group consisting of hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar, hydroxyethyl cellulose, hydroxyethyl cellulose grafted with glycidol or vinyl phosphonic acid, carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and the like. Of these, depolymerized hydroxypropylguar is preferred. The depolymerized polymer should have an average molecular weight in the range of from about 25,000 to about 400,000 and preferably has an average molecular weight in the range of from about 100,000 to about 250,000. The depolymerized polymer preferably should have a polydispersity ratio of from 1 to about 12 as determined by gel permeation chromatography as disclosed in xe2x80x9cPractical High Performance Liquid Chromatographyxe2x80x9d edited by C. F. Simpson (Hyden and Son Ltd., 1976). The polydispersity ratio of polysaccharides or other polymers generally can range from about 2 to as much as 250. The depolymerized polymer of the present invention has been found to exhibit the superior properties identified herein when maintained within the indicated polydispersity ratio. If desired for purposes of transportation, storage or otherwise, the depolymerized polymer may be stored in dry form and, when needed, can be rehydrated to form the treating fluid concentrate. The substantially fully hydrated depolymerized polymer is admixed with the water in an amount in excess of about 6% by weight of the concentrate to form the treating fluid concentrate. Preferably, the polymer is present in an amount of from about 6% to in excess of about 30% by weight and most preferably from about 6% to about 20% by weight of the concentrate. The viscosity of the treating fluid concentrate generally may be in the range of from about 15,000 to in excess of about 35,000 cps as determined with a Brookfield DV II+RV spring viscometer manufactured by Brookfield Engineering Laboratories of Middleboro, Mass. The viscosity is determined by measurements performed at a temperature of about 75xc2x0 F. and a rotational speed of 20 rpm using an LV3 bob. Other similar instruments also can be used to measure the viscosity of the fluid concentrate.
The water utilized to form the treating fluid concentrate can be fresh water, unsaturated salt water or saturated salt water. Generally, the substantially fully hydrated depolymerized polymer utilized in the present invention is mixed with the water in an amount in the range of from about 6% to about 30% by weight of the water.
In some instances it may be desirable to add a dispersing agent to the polymer for dispersing the depolymerized hydratable polymer when it has been stored in a dry form and facilitating its rehydration in water. Any of a variety of dispersing agents known to those individuals of ordinary skill in the art may be utilized. A particularly suitable dispersing agent has been found to be a light hydrocarbon oil such as diesel oil, kerosene, olefins or the like. Another dispersing agent is polyethyleneglycol. Of these, diesel oil is preferred. When an oil dispersing agent is utilized, it is included with the polymer in an amount in the range of from about less than 5% to in excess of about 60% by weight of the polymer.
A variety of other additives can be included in a concentrate of this invention at the time of its manufacture. Such additives generally include pH adjusting compounds for adjusting the pH of the treating fluid to an optimum or desired pH for crosslinking when it is formed with the concentrate. Examples of such compounds which can be utilized include, but are not limited to, formic acid, fumaric acid, acetic acid, acetic anhydride, hydrochloric acid, sodium hydroxide, potassium hydroxide, lithium hydroxide, various carbonates or any other commonly used pH control agent which does not adversely react with the polymer to prevent its use in accordance with the method of the present invention. Of these, sodium hydroxide is preferred. When used, the pH adjusting compound is included in the concentrate in an amount in the range of from about 0.5% to about 10% by weight of the water therein.
A pH buffer also can be included in the concentrate. Examples of buffers which can be used include, but are not limited to, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium or potassium diacetate, sodium or potassium phosphate, sodium or potassium hydrogen phosphate, sodium or potassium dihydrogen phosphate and the like. When used, the buffer is included in the concentrate in an amount in the range of from about 0.5% to about 10% by weight of the water therein.
Another additive which can be included in the concentrate is a surfactant for preventing the formation of emulsions between the treating fluid which is formed with the concentrate and subterranean formation fluids. Examples of surfactants which can be used include, but are not limited to, alkyl sulfonates, alkyl aryl sulfonates including alkyl benzyl sulfonates such as salts of dodecylbenzene sulfonic acid, alkyl trimethylammonium chloride, branched alkyl ethoxylated alcohols, phenol-formaldehyde nonionic resin blends, cocobetaines, dioctyl sodium sulfosuccinate, imidazolines, alpha olefin sulfonates, linear alkyl ethoxylated alcohols, trialkyl benzylammonium chloride and the like. Of these, salts of dodecylbenzene sulfonic acids are preferred. When used, the surfactant is included in the concentrate in an amount in the range of from about 0.01% to about 1% by weight of the water in the treatment fluid. Substantially any other surfactant that is known to be suitable for use in the treatment of subterranean formations and which does not adversely react with the fluid of the present invention may be utilized.
Yet another additive which can be included in the concentrate is a clay stabilizer. Examples of clay stabilizers which can be used include, but are not limited to, potassium chloride, sodium chloride, ammonium chloride and tetramethyl ammonium chloride and the like. Examples of some temporary clay stabilizers that are suitable for use in the present invention are disclosed in for example U.S. Pat. Nos. 5,197,544; 5,097,904; 4,977,962; 4,974,678; 4,828,726, the entire disclosures of which are incorporated herein by reference. Of these, potassium chloride and tetramethyl ammonium chloride are preferred. When used, the clay stabilizer is included in the concentrate in an amount in the range of from about 2% to about 20% by weight of the water therein.
When the concentrate of this invention is mixed with additional water and any other desired additives to form a subterranean treating fluid, no hydration time is required since the concentrate is already substantially fully hydrated. The additional water is mixed with the concentrate in a water to concentrate ratio in the range of from about 4:1 to about 20:1 depending upon the final viscosity desired in the treating fluid. The water utilized can be fresh water, unsaturated salt water including brines or seawater, or saturated salt water.
In order to increase the viscosity of the treating fluid formed with the concentrate, a crosslinking agent is mixed with the water and concentrate. The crosslinked short chain segments of the substantially fully hydrated depolymerized polymer in the concentrate are crosslinked by the crosslinking agent thereby producing a viscous treating fluid having unexpected properties. These unexpected properties include the following: (1) The treating fluid including the extensively depolymerized hydrated and crosslinked polymer segments has unexpected thermal stability at temperatures above about 200xc2x0 F. and preferably from about 200 to about 275xc2x0 F. without the use of gel stabilizers. (2) The conventional high molecular weight hydrated polymers utilized in conventional crosslinked treating fluids produce filter cake on the walls of well bores penetrating producing formations and in fractures formed therein which is very difficult to remove. The crosslinked treating fluids of the present invention produce filter cake containing low molecular weight polymer segments which have been discovered to make the filter cake easily removable. (3) As described above, the treating fluids of the present invention do not have to be prehydrated and the treating fluid is mixed with additional water and additives on the surface in a very short time making real time changes in the properties of the treating fluid as it is being pumped possible. (4) The conventional treating fluids formed with crosslinked hydrated polymers produce residue when broken which often damages the treated producing formation. That is, when the heretofore used crosslinked hydrated polymer treating fluids are caused to revert to thin fluids by chemical breakers therein, considerable residue often forms in the broken fluid. This is contrasted with the treating fluids of the present invention which produce very little residue when reduced in viscosity. The treating fluid concentrate utilized in accordance with this invention is processed during its manufacture to remove residue from the concentrate. As a result, the low residue producing treating fluids of this invention produce fractures having higher conductivities than the heretofore used treating fluids. (5) As will be described further hereinbelow, the treating fluids of this invention can, when certain polymers and crosslinkers are employed, include acid reversible crosslink sites. When certain crosslinkers are utilized, the crosslinks are broken simply by lowering the pH to a level below about 9. In this pH range, the treating fluid is not crosslinked and yet the acetal linkages which form the crosslinking sites are stable and can be recrosslinked. This feature allows the treating fluid to be recovered from a treated subterranean formation and well bore and reused rather than having to be disposed of in environmentally sensitive locations. The recovery and reuse of the treating fluids of this invention makes them much more economical to use than conventional prior art fluids.
The improved subterranean formation treating fluids of this invention are basically comprised of water, a substantially fully hydrated depolymerized polymer and a crosslinking agent for crosslinking the hydrated depolymerized polymer. As mentioned above, the water can be selected from fresh water, unsaturated salt water including brines and seawater and saturated salt water.
As indicated above relating to the treating fluid concentrate, the substantially fully hydrated depolymerized polymer in the treating fluid can be a depolymerized polysaccharide and is preferably a substantially fully hydrated depolymerized guar derivative polymer selected from the group consisting of hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar, hydroxyethylguar and carboxymethylhydroxyethylguar. Of these, substantially fully hydrated depolymerized hydroxypropylguar is most preferred. The substantially fully hydrated depolymerized polymer utilized is generally present in the treating fluid in an amount in the range of from about 0.2% to about 5% by weight of the water therein.
Examples of preferred crosslinking agents which can be utilized in the treating fluid include, but are not limited to, boron compounds such as, for example, boric acid, disodium octaborate tetrahydrate, sodium diborate and pentaborates, ulexite and colemanite, compounds which can supply zirconium IV ions such as, for example, zirconium lactate, zirconium lactate triethanolamine, zirconium carbonate, zirconium acetylacetonate and zirconium diisopropylamine lactate, compounds that can supply titanium IV ions such as, for example, titanium ammonium lactate, titanium triethanolamine, titanium acetylacetonate, aluminum compounds such as aluminum lactate or aluminum citrate or compounds that can supply antimony ions. Of these, a borate compound, is the most preferred. The exact type and amount of crosslinking agent or agents used depends upon the specific depolymerized polymer to be crosslinked, formation temperature conditions and other factors know to those individuals skilled in the art. The crosslinking agent utilized is included in the treating fluid in an amount in the range of from about 50 ppm to about 5000 ppm active crosslinker.
As also mentioned above in connection with the concentrate, a pH adjusting compound for adjusting the pH of the treating fluid to the optimum pH for crosslinking can be included in the treating fluid. The pH adjusting compound can be selected from sodium hydroxide, potassium hydroxide, lithium hydroxide fumaric acid, formic acid, acetic acid, hydrochloric acid, acetic anhydride and the like. Of these, sodium hydroxide is preferred. The pH adjusting compound is included in the treating fluid in an amount in the range of from about 0% to about 0.3% by weight of the water in the treating fluid.
When the preferred crosslinking agent is used, that is, a borate compound, the pH adjusting compound is utilized to elevate the pH of the treating fluid to above about 9. At that pH, the borate compound crosslinking agent crosslinks the short chain hydrated polymer segments. When the pH of the crosslinked treating fluid falls below about 9, the crosslinked sites are no longer crosslinked. Thus, when the crosslinked fracturing fluid of this invention contacts the subterranean formation being treated, the pH is lowered to some degree which begins the breaking process. In order to cause the fracturing fluid to completely revert to a thin fluid in a short period of time, a delayed delinker capable of lowering the pH of the treating fluid can be included in the treating fluid. Examples of delayed delinkers which can be utilized include, but are not limited to, various lactones, esters, encapsulated acids and slowly soluble acid generating compounds, oxidizers which produce acids upon reaction with water, water reactive metals such as aluminum, lithium and magnesium and the like. Of these, the esters are preferred. The delinker is included in the treating fluid in an amount in the range of from about 0% to about 1% by weight of the water therein. Alternatively, any of the conventionally used delayed breakers employed with metal ion crosslinkers can be utilized, for example, oxidizers such as sodium chlorite, sodium bromate, sodium persulfate, ammonium persulfate, encapsulated sodium persulfate, potassium persulfate, or ammonium persulfate and the like as well as magnesium peroxide. Enzyme breakers that may be employed include alpha and beta amylases, amyloglucosidase, invertase, maltase, cellulase and hemicellulase. The specific breaker or delinker utilized, whether or not it is encapsulated, as well as the amount thereof employed will depend upon the breaking time desired, the nature of the polymer and crosslinking agent, formation characteristics and conditions and other factors.
When the subterranean formation treating fluid of this invention is utilized for carrying out a fracture stimulation procedure, proppant material is included in at least a portion of the treating fluid as it is pumped into the subterranean formation to be fractured and into fractures created therein. The proppant material is metered into the treating fluid as the treating fluid is formed and, as mentioned above, the quantity of proppant material per volume of treating fluid can be changed as required in real time. Examples of proppant material which can be utilized include, but are not limited to, resin coated or uncoated sand, sintered bauxite, ceramic materials or glass beads. The proppant material utilized is generally included in the treating fluid in an amount in the range of from about 1 to about 24 pounds of proppant material per gallon of the treating fluid.
As mentioned above in connection with the concentrate, additional components that can be included in the treating fluid of this invention and which can be a part of the treating fluid concentrate used to form the treating fluid include a buffer selected from the group consisting of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium or potassium diacetate, sodium or potassium phosphate, sodium or potassium hydrogen phosphate, sodium or potassium dihydrogen phosphate and the like. Of these, sodium carbonate is preferred. The buffer is generally present in the treating fluid in an amount in the range of from about 0% to about 0.3% by weight of water therein.
The treating fluid as well as the concentrate can also include a surfactant for preventing the formation of emulsions between the treating fluid and subterranean formation fluids contacted by the treating fluid. Examples of such surfactants include, but are not limited to, alkyl sulfonates, alkyl aryl sulfonates including alkyl benzyl sulfonates such as salts of dodecylbenzene sulfonic acid, alkyl trimethylammonium chloride, branched alkyl ethoxylated alcohols, phenol-formaldehyde anionic resin blends, cocobetaines, dioctyl sodium sulfosuccinate, imidazolines, alpha olefin sulfonates, linear alkyl ethoxylated alcohols, trialkyl benzylammonium chloride and the like. Of these, dodecylbenzene sulfonic acid salts are preferred. The surfactant is generally present in the treating fluid in an amount in the range of from about 0% to about 0.1% by weight of the water therein.
The treating fluid and the concentrate can also include a clay stabilizer selected, for example, from the group consisting of potassium chloride, sodium chloride, ammonium chloride and tetramethyl ammonium chloride and the like. Of these, potassium chloride and tetramethyl ammonium chloride are preferred. When used, the clay stabilizer is generally present in the treating fluid in an amount in the range of from about 0.5% to about 10% by weight of the water therein.
Other additives can be included in a subterranean formation treating fluid of this invention which are not normally in the treating fluid concentrate used to form the treating fluid. For example, in applications where a fluid loss control agent must be included in the treating fluid, a fluid loss control agent can be metered into the blender during the mixing of the treating fluid. Examples of fluid loss control agents which can be used include, but are not limited to, silica flour, starches, waxes and resins. The fluid loss control agent is included in the treating fluid in an amount in the range of from about 0% to about 1% by weight of water therein.
The subterranean formation treating fluid can also include compounds for retarding the movement of the proppant introduced in the fluid within the created fracture. For example, materials in the form of fibers, flakes, ribbons, beads, shavings, platelets and the like comprised of glass, ceramics, carbon composite, natural or synthetic polymers or metals and the like can be admixed with the fluid and proppant introduced into the subterranean formation to retard or prevent the movement of the introduced proppant. A more detailed description of the forgoing materials is disclosed in, for example, U.S. Pat. Nos. 5,330,005; 5,439,055; and 5,501,275 the entire disclosures of which are incorporated herein by reference. Alternatively, or in addition to the prior materials, a material comprising a tackifying compound may be admixed with the fluid or the proppant to coat at least a portion of the proppant or other solid materials identified above such that the coated material and particulate adjacent thereto will adhere together to form agglomerates which will bridge in the created fracture to prevent particulate flowback. The tackifying compound also may be introduced into the formation with the treatment fluid prior to or after the introduction of the proppant into the formation. The coated material is effective in inhibiting the flowback of fine particulate in the proppant pack having a size ranging from about that of the proppant to less than about 600 mesh. The coated proppant or other material is effective in consolidating fine particulates in the formation in the form of agglomerates to prevent the movement of the fines during production of the formation fluids from the well bore subsequent to the treatment. A more detailed description of the use of the foregoing tackifying compound and the methods of use thereof is disclosed in U.S. Pat. Nos. 5,775,415; 5,787,986; 5,833,000; 5,839,510; 5,871,049; 5,853,048; and 6,047,772 the entire disclosures of which are incorporated herein by reference thereto.
Additional additives that can be included in the treating fluids of this invention which are well known to those skilled in the art include, but are not limited to, scale inhibitors, demulsifiers, clay stabilizers, bactericides, breaker activators and the like.
An improved method of this invention for treating a subterranean formation penetrated by a well bore is comprised of the following steps: (a) preparing a gelled and crosslinked treating fluid comprised of water, a substantially fully hydrated depolymerized polymer and a crosslinking agent for crosslinking said hydrated depolymerized polymer; and (b) contacting said subterranean formation with said gelled crosslinked treating fluid.
Another improved method of the present invention for treating a subterranean formation penetrated by a well bore whereby one or more fractures are formed therein is comprised of the following steps: (a) preparing a gelled and crosslinked fracturing fluid comprised of water, a substantially fully hydrated depolymerized polymer, a crosslinking agent for crosslinking said hydrated depolymerized polymer and a proppant material; and (b) contacting said subterranean formation with said gelled and crosslinked fracturing fluid under conditions effective to create at least one fracture in said subterranean formation.
The water utilized for preparing the gelled and crosslinked fluids called for in the above methods can be fresh water, unsaturated salt water including brines and seawater and saturated salt water. The substantially fully hydrated depolymerized polymer can be a substantially fully hydrated depolymerized polysaccharide and is preferably a substantially fully hydrated depolymerized guar derivative polymer selected from the group consisting of hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar, hydroxyethyl cellulose, grafted hydroxyethyl cellulose, carboxymethyl cellulose, carboxymethylhydroxyethyl cellulose and the like. Of these, depolymerized hydroxypropylguar is preferred. The substantially fully hydrated depolymerized polymer is included in the treating fluid or fracturing fluid in an amount in the range of from about 0.2% to about 5% by weight of the water therein.
The crosslinking agent utilized in the treating fluid and fracturing fluid is preferably selected from the group consisting of boron compounds such as, for example, boric acid, disodium octaborate tetrahydrate, sodium diborate and pentaborates, compounds which can supply zirconium IV ions such as, for example, zirconium lactate, zirconium lactate triethanolamine, zirconium carbonate, zirconium acetylacetonate and zirconium diisopropylamine lactate, compounds that can supply titanium IV ions such as, for example, titanium ammonium lactate, titanium triethanolamine, titanium acetylacetonate, aluminum compounds such as aluminum lactate or aluminum citrate or compounds that supply antimony ions. Of these, a borate compound is the most preferred. The crosslinking agent utilized is included in the treating fluid in an amount in the range of from about 50 ppm to about 5000 ppm active crosslinker.
The fracturing fluid also includes a proppant material which can be resin coated or uncoated sand, sintered bauxite, ceramic materials, glass beads and the like. The proppant material is included in the fracturing fluid in an amount in the range of from about 1 to about 24 pounds of proppant material per gallon of the treating fluid.
The treating or fracturing fluid can also include a pH adjusting compound for elevating the pH of the fluid. The pH adjusting compound can be selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, formic acid, fumaric acid, acetic acid, acetic anhydride, hydrochloric acid and the like. Of these, sodium hydroxide is preferred. The pH adjusting compound is included in the treating or fracturing fluid in an amount in the range of from about 0% to about 0.3% by weight of the water in the treating fluid.
The treating or fracturing fluid can also include a buffer selected from the group consisting of sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium or potassium diacetate, sodium or potassium phosphate, sodium or potassium hydrogen phosphate, sodium or potassium dihydrogen phosphate and the like. Of these, sodium carbonate is preferred. The buffer is generally present in the treating or fracturing fluid in an amount in the range of from about 0% to about 0.3% by weight of water therein.
Another component which can be included in the treating fluid or fracturing fluid is a surfactant for preventing the formation of emulsions between the treating or fracturing fluid and subterranean formation fluids. Examples of surfactants which can be used include, but are not limited to, alkyl sulfonates, alkyl aryl sulfonates including alkyl benzyl sulfonates such as salts of dodecylbenzene sulfonic acid, alkyl trimethylammonium chloride, branched alkyl ethoxylated alcohols, phenol-formaldehyde nonionic resin blends, cocobetaines, dioctyl sodium sulfosuccinate, imidazolines, alpha olefin sulfonates, linear alkyl ethoxylated alcohols, trialkyl benzylammonium chloride and the like. Of these, salts of dodecylbenzene sulfonic acids are preferred. The surfactant is included in the treating or fracturing fluid in an amount in the range of from about 0% to about 0.1% by weight of water therein.
Yet another component which can be included in the treating fluid or fracturing fluid is a clay stabilizer. Examples of clay stabilizers include, but are not limited to, potassium chloride, sodium chloride, ammonium chloride and tetramethyl ammonium chloride and the like. Of these, potassium chloride and tetramethyl ammonium chloride are preferred. When used, the clay stabilizer is included in the concentrate in an amount in the range of from about 0.5% to about 10% by weight of the water therein.
Still another component that can be included in the treating fluid or fracturing fluid is a fluid loss control agent such as, for example, silica flour, starches, waxes and resins. The fluid loss control agent is included in the treating fluid in an amount in the range of from about 0% to about 1% by weight of water therein.
A final component which is usually included in the treating fluid or fracturing fluid is a breaker or crosslink delinker for causing the fluid to quickly revert to a thin fluid. Examples of suitable breakers or delinkers include, but are not limited to, a delayed breaker or delinker capable of lowering the pH of the treating fluid to cause the polymer crosslink to reverse. Examples of delayed breakers or delinkers which can be utilized include, but are not limited to, various lactones, esters, encapsulated acids and slowly soluble acid generating compounds, oxidizers which produce acids upon reaction with water, water reactive metals such as aluminum, lithium and magnesium and the like. Of these, the esters are preferred. Alternatively, any of the conventionally used breakers employed with metal ion crosslinkers can be utilized such as, for example, sodium chlorite, sodium bromate, sodium persulfate, ammonium persulfate, encapsulated sodium persulfate, potassium persulfate, or ammonium persulfate and the like as well as magnesium peroxide. Enzyme breakers that may be employed include alpha and beta amylases, amyloglucosidase, invertase, maltase, cellulase and hemicellulase is preferred. The breaker or delinker is included in the treating or fracturing fluid in an amount in the range of from about 0% to about 1% by weight of water therein.
The subterranean formation treatment fluids of the present invention also may include substantially any of the conventionally known foaming agents which do not adversely react with the fluid constituents such that a gaseous compound such as nitrogen, air, carbon dioxide or another gasifying compound can be admixed with the fluid to form a foam for introduction into the subterranean formation. The gaseous compound can be admixed with the fluid in an amount of from 5% to in excess of 90% to form a foamed treatment fluid for use in stimulating a subterranean formation. When foamed, the fluid of the present invention provides the same benefits as are found in the use of other foamed treatment fluids. The foamed fluid results in less polymer being introduced into the formation, can provide improved fluid loss control and can provide a gas assist in removing the treatment fluid from the well bore at the conclusion of the treatment.


A dual pipe includes an outer pipe having a valley/ridge portion on an outer circumferential surface thereof, and an inner pipe having a valley/ridge portion formed on an inner circumferential surface thereof and inserted into the outer pipe. In the dual pipe, the inner pipe and the outer pipe are threadedly engaged with each other. A low pressure refrigerant passes through the inner pipe. In order to secure a passage of a high pressure refrigerant in a space between the outer circumferential surface of the inner pipe and the inner circumferential surface of the outer pipe, a part of the helical valley/ridge portion formed on the outer circumferential surface of the inner pipe is composed of a multiple-helix helical valley/ridge portion.

A dual pipe is a device for use in a refrigeration cycle and is a device for improving the efficiency of a refrigeration cycle by ensuring that heat exchange occurs effectively between a refrigerant passing through an inner passage and a refrigerant passing through an outer passage.
U.S. Pat. No. 7,866,378 (Patent Document 1) entitled "DOUBLE-WALL PIPE, METHOD OF MANUFACTURING THE SAME AND REFRIGERANT CYCLE DEVICE PROVIDED WITH THE SAME" and U.S. Pat. No. 9,669,499 (Patent Document 2) entitled "DOUBLE-WALL PIPE, METHOD OF MANUFACTURING THE SAME AND REFRIGERANT CYCLE DEVICE PROVIDED WITH THE SAME" disclose a dual pipe for use in a refrigeration cycle. The dual pipe disclosed in the above patent documents includes an outer pipe and an inner pipe inserted into the outer pipe. The inner pipe forms an inner passage for a refrigerant. The space defined by the outer circumferential surface of the inner pipe and the inner circumferential surface of the outer pipe forms an outer passage for the refrigerant.
A plurality of valley/ridge portions extending helically in the longitudinal direction is formed on the outer circumferential surface of the inner pipe. The helical valley/ridge portions are formed by pressing the outer circumferential surface of the inner pipe so that a part of the outer circumferential surface of the inner pipe is recessed along the longitudinal direction. The recessed portions of the outer circumferential surface are valleys, and the non-recessed portions are ridges. Helical valley/ridge portions are not formed on the inner circumferential surface of the outer pipe. In addition, the inner pipe and the outer pipe are bent. Each of the inner pipe and the outer pipe includes a straight portion and a bent portion. The inner diameter of the straight portion of the outer pipe is larger than the imaginary outer diameter defined by the ridges of the inner pipe, so that the inner circumferential surface of the outer pipe and the ridges of the inner pipe do not contact each other in a certain portion. Furthermore, the inner circumferential surface of the bent portion of the outer pipe is configured to make contact with the valleys of the inner pipe. Therefore, the dual pipe disclosed in the above patents is configured so that a refrigerant flows through the helical valleys of the inner pipe and the space between ridges of the inner pipe and the inner circumferential surface of the outer pipe in the straight portion, and flows through the valleys of the inner pipe in the bent portion.
In addition, U.S. Pat. No. 7,886,420 (Patent Document 3) entitled "METHOD OF MANUFACTURING DOUBLE PIPE" discloses a method of manufacturing a dual pipe for use in a refrigeration cycle of a motor vehicle. Circular grooves are formed on the outer circumferential surfaces of the opposite end portions of an inner pipe, and holes are formed in the opposite end portions of an outer pipe. The method of manufacturing a dual pipe disclosed in the above patent includes a step of fixing one end of an outer pipe to an inner pipe, a step of simultaneously bending the inner pipe and the outer pipe, and a step of fixing the other end of the outer pipe to the inner pipe. In the above steps, the circular grooves of the opposite end portions of the inner pipe and the holes of the opposite end portions of the outer pipe are arranged at positions corresponding to each other.
In addition, U.S. Pat. No. 7,887,099 (Patent Document 4) entitled "COMPOUND TUBE AND METHOD OF PRODUCING THE SAME" discloses a configuration for firmly fixing an outer pipe to an inner pipe in a dual pipe. That is, the above patent discloses a dual pipe in which tapering portions are formed on the inner circumferential surfaces of the opposite end portions of the outer pipe, annular swage portions are formed near the opposite end portions having the tapering portions, and the outer pipe is firmly fixed to the inner pipe by brazing.
In the dual pipes disclosed in Patent Documents 1 to 4, the inner circumferential surface of the outer pipe constituting the straight portion and the ridges of the inner pipe are not fixed to each other. Therefore, when vibration propagates to the dual pipe, there is a possibility that, due to the contact of the inner circumferential surface of the outer pipe and the ridges of the inner pipe, frictional noise may be generated and contact portions may be damaged. In addition, if a plurality of bent portions is formed in the dual pipe, difficulties are involved in manufacturing the dual pipe, and the possibility of generation of noise and damage due to vibration grows higher.
Meanwhile, International Publication WO 2017/038961 (Patent Document 5) entitled "METHOD FOR MANUFACTURING DOUBLE PIPE" discloses a method of manufacturing a dual pipe. The dual pipe manufacturing method disclosed in Patent Document 5 is intended to solve the problems of the dual pipe manufacturing methods disclosed in Patent Documents 1 to 4. The dual pipe manufacturing method disclosed in Patent Document 5 includes inserting an inner pipe having an outer diameter smaller than an inner diameter of an outer pipe into the outer pipe, forming a recess by depressing a part of the outer pipe to which the inner pipe is inserted, and fixing the outer pipe and the inner pipe by bringing the recess of the outer pipe into contact with the outer circumferential surface of the inner pipe. The method disclosed in Patent Document 5 is characterized in that the inserting step is facilitated by increasing the difference between the inner diameter of the outer pipe and the outer diameter of the inner pipe, and the inner pipe and the outer pipe are fixed by forming the recess by applying an external force to the outer circumferential surface of the outer pipe to which the inner pipe is inserted. Furthermore, Patent Document 5 discloses a method of fixing an inner pipe and an outer pipe by forming a bent portion and then forming a recess in the outer pipe.


A replacement roller support assembly allows repairing of a conveyor roller support system begins with removing at lease one system roller support from the system base. Next a replacement roller support assembly includes an assembly base with an opening and assembly roller support above each opening for each system roller support removed. The replacement roller support assembly is positioned with the opening and the assembly roller support aligned with the location of the removed roller supports of the system. The support assembly is secured to the system base and the roller is attached to the assembly roller support.

The present invention relates to conveyor belt roller support systems and more specifically to the replacement roller support assembly.
Conveyor belts, for example, in mines rest on a series of idle rollers. The idle rollers in the conveyor belt roller support system are mounted to roller supports which are integral to a base. The bases are mounted on the ground or on frames or rails above the ground. Depending upon the type of conveyor, there may be two V shaped rollers between three supports or a horizontal roller between two to wing rollers between four supports. The roller supports are usually welded to the base.
In the mining industry, it is usually the interior or center roll of supports which are damaged. One of the general practices is to remove the whole conveyor belt roller support system. As one can imagine, in a mine this takes a lot of time and is very difficult. It requires moving a very large and heavy roller support system.
The present replacement roller support assembly allows repairing of a conveyor roller support system in an efficient manner. It begins with removing at lease one system roller support from the system base. Next a replacement roller support assembly includes an assembly base with an opening and assembly roller support above each opening for each system roller support removed. The replacement roller support assembly is positioned with the opening and the assembly roller support aligned with the location of the removed roller supports of the system. The support assembly is secured to the system base and the roller is attached to the assembly roller support.
The assembly base may be V-shaped or a portion of an arch of a circle in cross-section. The assembly base is secured to the system base by a fastener for example through legs of the assembly base or around the two bases.
The assembly base may include a pair of end members joined by a bridge and the end members each include an opening and assembly rollers support. The bridge may have a V-shaped cross section and the end member are also V shaped with parallel legs each extending from the end of the leg of the V. The parallel legs may include apertures receiving a fastener extending across the V. The apertures may be located on a portion of the leg spaced from a portion of the leg which is aligned with the opening. The assembly base may include one opening and assembly roller support centered on the assembly base.
The assembly roller support may include two end walls joined by two side walls. At least one of the end walls includes a recess and a top edge to receive a portion of the roller. A pair of top walls extends from a respective side wall and between the top edges of the end walls. The side walls may be truncated triangles and one of the end walls is inclined at angle to the other end wall. Both end walls may include a recessed and top edge to receive a portion the respective roller.
These and other aspects of the present invention will become apparent from the following detailed description of the invention, when considered in conjunction with accompanying drawings.


A tunable passive anti-jamming antenna array system and method for minimizing the effects of electromagnetic interference in radio frequency antenna systems. The system and method utilize an external array of passive open circuited antennas strategically arranged between an intended receiving antenna unit and interfering signals to disrupt the interference signals and reduce the electromagnetic energy, interference, and noise reaching the intended receiving antenna unit.

Radio frequency (RF) jamming, i.e., intentional or unintentional RF interference, occurs when RF power is transmitted so as to interfere with the reception and interpretation of an RF receiving system and in some cases permanently damage the electronics within the receiving antenna unit. Jamming signals may interfere with or terminate the operation of receivers specifically satellite receivers such as navigation, communication, and global navigation satellite system (GNSS), such as global positioning system (GPS) receivers. In this sense, electromagnetic interference (EMI) generally, and jamming in particular, is considered countermeasures to the intended utilization of RF antenna-receiver systems.
A number of techniques have been developed to mitigate the deleterious effects of EMI on RF antenna-receiver systems. These techniques typically employ additional internal antenna hardware components some having mathematically based software programs to minimize EMI. As a result of the additional hardware and software required by the conventional anti-jamming systems, the conventional system are costly to develop and operate. Thus, there is a need for a more cost-effective and efficient system for mitigating the effects of EMI on RF antenna-receiver systems.

Passive anti-jamming antenna system and method

Microwave Mitigation and Detection (“MMAD”)


A power supply for an implantable cardioverter-defibrillator for subcutaneous positioning between the third rib and the twelfth rib and for providing cardioversion/defibrillation energy to the heart, the power supply comprising a capacitor subsystem for storing the cardioversion/defibrillation energy for delivery to the patient's heart; and a battery subsystem electrically coupled to the capacitor subsystem for providing electrical energy to the capacitor subsystem.

Defibrillation/cardioversion is a technique employed to counter arrhythmic heart conditions including some tachycardias in the atria and/or ventricles. Typically, electrodes are employed to stimulate the heart with electrical impulses or shocks, of a magnitude substantially greater than pulses used in cardiac pacing.
Defibrillation/cardioversion systems include body implantable electrodes and are referred to as implantable cardioverter/defibrillators (ICDs). Such electrodes can be in the form of patches applied directly to epicardial tissue, or at the distal end regions of intravascular catheters, inserted into a selected cardiac chamber. U.S. Pat. Nos. 4,603,705; 4,693,253; 4,944,300; and 5,105,810, the disclosures of which are all incorporated herein by reference, disclose intravascular or transvenous electrodes, employed either alone or in combination with an epicardial patch electrode. Compliant epicardial defibrillator electrodes are disclosed in U.S. Pat. Nos. 4,567,900 and 5,618,287, the disclosures of which are incorporated herein by reference. A sensing epicardial electrode configuration is disclosed in U.S. Pat. No. 5,476,503, the disclosure of which is incorporated herein by reference.
In addition to epicardial and transvenous electrodes, subcutaneous electrode systems have also been developed. For example, U.S. Pat. Nos. 5,342,407 and 5,603,732, the disclosures of which are incorporated herein by reference, teach the use of a pulse monitor/generator surgically implanted into the abdomen and subcutaneous electrodes implanted in the thorax. This system is far more complicated to use than current ICD systems using transvenous lead systems together with an active can electrode and therefore it has o practical use. It has in fact never been used because of the surgical difficulty of applying such a device (3 incisions), the impractical abdominal location of the generator and the electrically poor sensing and defibrillation aspects of such a system.
Recent efforts to improve the efficiency of ICDs have led manufacturers to produce ICDs which are small enough to be implanted in the pectoral region. In addition, advances in circuit design have enabled the housing of the ICD to form a subcutaneous electrode. Some examples of ICDs in which the housing of the ICD serves as an optional additional electrode are described in U.S. Pat. Nos. 5,133,353; 5,261,400; 5,620,477; and 5,658,321 the disclosures of which are incorporated herein by reference.
ICDs are now an established therapy for the management of life threatening cardiac rhythm disorders, primarily ventricular fibrillation (V-Fib). ICDs are very effective at treating V-Fib, but are therapies that still require significant surgery.
As ICD therapy becomes more prophylactic in nature and used in progressively less ill individuals, especially children at risk of cardiac arrest, the requirement of ICD therapy to use intravenous catheters and transvenous leads is an impediment to very long term management as most individuals will begin to develop complications related to lead system malfunction sometime in the 5-10 year time frame, often earlier. In addition, chronic transvenous lead systems, their reimplantation and removals, can damage major cardiovascular venous systems and the tricuspid valve, as well as result in life threatening perforations of the great vessels and heart. Consequently, use of transvenous lead systems, despite their many advantages, are not without their chronic patient management limitations in those with life expectancies of >5 years. The problem of lead complications is even greater in children where body growth can substantially alter transvenous lead function and lead to additional cardiovascular problems and revisions. Moreover, transvenous ICD systems also increase cost and require specialized interventional rooms and equipment as well as special skill for insertion. These systems are typically implanted by cardiac electrophysiologists who have had a great deal of extra training.
In addition to the background related to ICD therapy, the present invention requires a brief understanding of automatic external defibrillator (AED) therapy. AEDs employ the use of cutaneous patch electrodes to effect defibrillation under the direction of a bystander user who treats the patient suffering from V-Fib. AEDs can be as effective as an ICD if applied to the victim promptly within 2 to 3 minutes.
AED therapy has great appeal as a tool for diminishing the risk of death in public venues such as in air flight. However, an AED must be used by another individual, not the person suffering from the potential fatal rhythm. It is more of a public health tool than a patient-specific tool like an ICD. Because >75% of cardiac arrests occur in the home, and over half occur in the bedroom, patients at risk of cardiac arrest are often alone or asleep and can not be helped in time with an AED. Moreover, its success depends to a reasonable degree on an acceptable level of skill and calm by the bystander user.
What is needed therefore, especially for children and for prophylactic long term use, is a combination of the two forms of therapy which would provide prompt and near-certain defibrillation, like an ICD, but without the long-term adverse sequelae of a transvenous lead system while simultaneously using most of the simpler and lower cost technology of an AED. What is also needed is a cardioverter/defibrillator that is of simple design and can be comfortably implanted in a patient for many years.

Power supply for an implantable subcutaneous cardioverter-defibrillator


A device (10) for receiving bars (11) incoming along two parallel guides (12) in a siderurgical facility, in order to lay the bars onto a cooling bed (38) includes at least one first element (15) having, at its bottom portion, two channels (16) each of which displays a downwards orientated opening, the channels being lined up with the parallel guides (12), in order to constitute a substantial extension thereof. For each channel, shutters (23, 24) are provided in order to act as a closure for each of the openings of the channels, the shutters being supported by respective arms (17, 18) swinging arounds respective pivots (19, 20). Each of the arms (17, 18) is linked, through a respective tie-rod (27, 28), to an idle crank (29, 30) installed on a cam (31, 32) rotatably actuated by a ratiomotor (35) in order to reciprocate the shutters (23, 24) between a closed-channel position and an open-channel position.

In the siderurgical facilities for the production of metal bars, the problem is known of the bars, after being cut to their desired length, having to be deposited on a cooling bed. Usually, such bars income, in alternate fashion, along two parallel guides, coming from a cutting unit in which a continuous strand is cut into such bars. The alternate bar incoming is due to the need for interspacing the rapidly arriving bars so as to be able to perform the braking thereof with no mutual impacts, in order to lay said bars on said cooling bed with substantially zero axial speed.

Bar receiving and discharging device in a siderurgical facility


A touch panel and a manufacturing method of the touch panel are provided. The touch panel includes a touch circuit board, a cover plate and a glue layer. The glue layer is arranged between the touch circuit board and the cover plate to bond the touch circuit board and the cover plate. The glue layer contains an epoxy resin main agent and an epoxy resin hardener.

A touch panel is an input module that allows a finger to press or slide on a smooth panel to control the operation of an electronic device. Since touch panels are very light and thin, touch panels are often used in notebook computers, mobile phones, personal digital assistants (PDAs) or other portable electronic devices.
In the existing bonding technologies for the touch panel, a pressure sensitive adhesive (PSA) or a thermosetting double-sided adhesive is used to bond a cover plate and a touch circuit board of the touch panel.
The touch panels using the pressure sensitive adhesive are divided into a non-substrate type and a composite-substrate type. The non-substrate type touch panel only uses the pressure sensitive adhesive to achieve the bonding function. Consequently, the overall thickness of the touch panel is thinner. However, since the pressure sensitive adhesive lacks hardness, the physical strength of the touch panel to withstand the long-term pressing action of the finger is insufficient. The composite-substrate type touch panel uses the pressure sensitive adhesive to bond a multilayered substrate structure. Consequently, the physical strength of the touch panel is increased. However, due to the multilayered substrate structure, the manufacturing process becomes complicated, and the touch panel becomes thicker. In other words, the composite-substrate type touch panel is unable to meet the slimness requirements of the modern electronic devices.
The use of the thermosetting double-sided adhesive to bond the cover plate and the touch circuit board of the touch panel can produce the good physical strength. However, the manufacturing process is more complicated. In addition, the thermosetting double-sided adhesive needs to be stored at low temperature when it is not in use. In other words, it is difficult for manufacturers to instantly control the raw material supply chain on the production line. Consequently, the efficiency of the production line operation is impaired.
For overcoming the drawbacks of the conventional technologies, there is a need of providing an improved touch panel. The raw material is easily stored, the manufacturing process is simplified. In addition, the touch panel is light and thin, and has high physical strength.

Touch panel and manufacturing method thereof


A lighting fixture is disclosed that has two lights sandwiching a pivotable reflector. An upwardly directed lamp is mounted on the reflector to pivot therewith. The down lamp may also be mounted on the reflector to pivot therewith, albeit it need not be. A lower shade can enclose the down lamp. To replace the lower lamp one can pivot the reflector to provide access to the burnt-out lamp.

This invention relates to mountable lighting fixtures (e.g., on a ceiling, a vertical wall or a horizontal surface), and in particular to such lighting fixtures that are designed to permit easier maintenance access.
A wide variety of wall mounted lighting units are known. Some of these, such as chandeliers, are hung from the ceiling. Others, such as wall mounted sconces, extend outward and then upward from a vertical room wall.
Numerous considerations go into optimizing such lighting fixtures. Such fixtures must, of course, project light in a desired manner, and at a desired intensity. However, they should also preferably present a highly ornamental appearance without excessive glare.
Further, such fixtures must be of solid construction, be relatively inexpensive to manufacture, and where low enough to the ground be tamper resistant. Also, such devices should preferably have low energy usage for the degree of light projected.
Apart from this array of standard considerations, one also needs to consider that most such devices use incandescent or fluorescent lamps to project light. While the durable life of such lamps can be quite long in some cases, most such lamps will periodically need to be replaced when they burn out. When a particular building has numerous such lamps, the time spent in replacing burnt out lamps can be significant.
U.S. Pat. No. 6,318,880 is a lighting fixture having a horizontally disposed two-sided reflector. A pair of fluorescent lights are mounted above and below the reflector so that light is projected both up and down in a controllable manner. Because the unit is a table or floor lamp the lamps can readily be reached for replacement by someone standing next to the lamp.
While this design has some advantages as a floor or table lamp design, it suffers from leaving the fluorescent lamps exposed to vandalism. Further, someone directly underneath the lamp might be exposed to an undesirable glare.
Another type of known lighting fixture is taught in U.S. Pat. No. 3,096,029. That unit is for a street light and is provided with a lower transparent bowl above which is mounted a lamp. When the lamp burns out, or there is other need for access to the interior of the fixture, the lamp and bowl can be swung down as a unit to provide access to the lamp and fixture interior. However, this design is set up to project light downward (and not upward), and is somewhat exposed to the risk of vandalism.
Thus, a need still exists for a light fixture that can project light in opposite directions without undesired glare in the downward direction, of undue risk of vandalism, yet provides easy access for maintenance.