Patent Grant
7665930
The present invention is related to hydraulically powered doors in general, and in particular to systems for operating hydraulically powered mine doors in cold temperatures.
Mine doors operate under conditions not usually encountered by ordinary doors. A mine door leaf can be subjected to large forces due at least in part to air flow in the mine and consequent air pressure differentials on opposite sides of the door leaf. Mine door leaves can be as large as twenty feet wide and twenty feet high or even larger. Because of their large size, even small pressure differentials result in large forces acting on the door leaves. Mine door leaves have to be sufficiently robust in construction to withstand these large forces. This means that the door leaves tend to be fairly heavy. For example, a door leaf constructed for operation with a pressure differential of twenty inches water gauge may weigh up to two thousand pounds.
The weight of the door leaves in combination with the forces generated by air pressure differentials in the mine makes it difficult to control movement of the door leaves during opening and closing of the door. Likewise, it can be difficult to start the opening movement and complete closing movement of the door leaves. Thus, it is desirable for the opening and closing of the mine doors to be powered by one or more fluid-driven actuators. Hydraulic actuators offer some advantages over pneumatic actuators because the hydraulic fluid is substantially incompressible, making hydraulically-controlled mine doors less susceptible to door leaf runaway.
Mine doors are sometimes installed in relatively cold environments. For example, mines using forced air ventilation systems require doors to be positioned at openings from the surface into the mine to make sure that the air forced into the mine flows through the mine to the intended exhaust outlets rather than back out of the mine through an opening near the forced air inlet. Doors at the openings into the mine may be subjected to cold temperatures (e.g., as low as −50 degrees Fahrenheit) from time to time. Cold temperatures present a problem for operation of hydraulically powered mine doors because the hydraulic fluids used to operate the doors have substantially increased viscosities at these cold temperatures, making the hydraulic fluids too stiff to operate as desired. The lower limit of an acceptable temperature range for a hydraulic fluid varies depending on the characteristics of the particular fluid used in a hydraulic system. Fire-resistant hydraulic fluids, which are required for some mining environments, are particularly susceptible to this problem. However, non-fire resistant hydraulic fluids are also susceptible to cold temperatures.
One partial solution to the problem is to use a tank heater to heat the hydraulic fluid in the reservoir. Unfortunately, this solution does not adequately address all aspects of the problem because the fluid in the hydraulic fluid lines can also be cooled by exposure of the fluid lines to the cold. Further, some hydraulic mine door installations have long hydraulic fluid lines. For example, a single pump may be used to operate the hydraulic actuators for two (or more) different doors in an airlock, as described in more detail in U.S. Pat. No. 6,425,820, the contents of which are hereby incorporated by reference. Moreover, the doors in a mine airlock are often several hundred feet (or more) apart from one another to allow long trains and/or caravans of vehicles to pass through the air lock. Thus, long hydraulic fluid lines are needed to connect the pump to the various doors.
Because of the long fluid lines, a significant amount of hydraulic fluid is contained in the fluid lines (where it receives substantially no heating from the tank heater) rather than in the heated reservoir. Further, the difficulty of moving cold stiff hydraulic fluid through the fluid lines is exacerbated because the long lengths of the fluid lines are associated with a substantial resistance to flow that is independent of the increased viscosity of the hydraulic fluid therein.
Thus, there is a need for hydraulic door installations in general and hydraulic systems for operating doors that facilitate operation thereof in cold environments.
One aspect of the invention is a mine door installation. The installation includes one or more door frames installed in a mine passageway and one or more door leaves mounted on the door frames for movement between open and closed positions of the respective door leaf. Movement of the one or more door leafs between its open and closed positions is powered by a hydraulic system. The hydraulic system includes a hydraulic actuator connected to one of the door leaves for driving movement thereof between open and closed positions of the door leaf. A reservoir of the hydraulic system has a volume for containing a hydraulic fluid used to operate the hydraulic actuator. A fluid circuit provides fluid communication between the at least one hydraulic actuator and the reservoir. The hydraulic system also includes a pump operable to pump hydraulic fluid from the reservoir into the fluid circuit. Further, the hydraulic system includes a fluid circuit flushing system operable to flush hydraulic fluid from the fluid circuit into the reservoir without moving any of the door leaves of the door installation.
Another aspect of the invention is a hydraulic system for operating a hydraulically powered door installation having one or more door frames and or more door leaves mounted on said one or more door frames for movement between open and closed positions of the respective door leaf. The hydraulic system includes a hydraulic actuator for moving one of the door leaves between its open and closed positions. A reservoir has a volume for containing a hydraulic fluid used to operate the hydraulic actuator. An electrical resistance heater is in thermal communication with the volume of the reservoir for heating the hydraulic fluid in the reservoir. A fluid circuit provides fluid communication between the hydraulic actuator and the reservoir. The hydraulic system also includes a pump for pumping hydraulic fluid from the reservoir into the fluid circuit. A fluid circuit flushing system is operable to flush hydraulic fluid from the fluid circuit into the reservoir without moving any door leaves of the door installation.
Still another aspect of the invention is a hydraulic system for operating a hydraulically powered door installation having one or more door frames and or more door leaves mounted on said one or more door frames for movement between open and closed positions of the respective door leaf. The hydraulic system includes a hydraulic actuator for moving one of the door leaves between its open and closed positions. A reservoir has a volume for containing a hydraulic fluid used to operate the hydraulic actuator. A heater is in thermal communication with the volume of the reservoir for heating the hydraulic fluid in the reservoir. The hydraulic system also includes a fluid circuit providing fluid communication between the at least one hydraulic actuator and the reservoir and a pump for pumping hydraulic fluid from the reservoir into the fluid circuit. A fluid circuit flushing system is operable to flush a volume of hydraulic fluid from the fluid circuit without moving any of the one or more door leaves of the door installation. The volume of hydraulic fluid that is flushed from the fluid circuit is at least about 50 percent of a total volume of hydraulic fluid contained in the fluid circuit.
Still another aspect of the invention is a hydraulic system for operating a hydraulically powered door installation having one or more door frames and or more door leaves mounted the one or more door frames for movement between open and closed positions of the respective door leaf. The hydraulic system includes a hydraulic actuator for moving one of the door leaves between its open and closed positions. A reservoir has a volume for containing a hydraulic fluid used to operate the hydraulic actuator. A fluid circuit provides fluid communication between the at least one hydraulic actuator and the reservoir. The hydraulic system also includes a pump for pumping hydraulic fluid from the reservoir into the fluid circuit. A fluid circuit flushing system of the hydraulic system includes a bypass valve moveable between a working position in which fluid can be pumped into the fluid circuit to operate the hydraulic actuator and a bypass position in which fluid can be pumped into the fluid circuit to flush hydraulic fluid from the fluid circuit without operating the actuator. The fluid circuit is arranged so the shortest path through the fluid circuit between the bypass valve and the reservoir is at least about 15 meters.
Another aspect of the invention is a hydraulic system for operating a hydraulically powered door installation having two or more door frames and two or more door leaves with a first door leaf mounted on a first door frame for movement between its open and closed positions and a second door leaf mounted on a second one of the door frames for movement between its open and closed positions. The hydraulic system includes a first hydraulic actuator for moving the first door leaf between its open and closed positions and a second hydraulic actuator for moving the second door leaf between its open and closed positions. A reservoir has a volume for containing a hydraulic fluid used to operate the first and second hydraulic actuators. A fluid circuit provides fluid communication between the first and second hydraulic actuators and the reservoir. The hydraulic system also includes a pump for pumping hydraulic fluid from the reservoir into the fluid circuit. A fluid circuit flushing system is operable to flush hydraulic fluid from the fluid circuit into the reservoir without moving any of the door leaves. The fluid circuit includes first and second fluid sub-circuits. The first fluid sub-circuit is associated with operation of the first hydraulic actuator and not involved with operation of the second hydraulic actuator. The second fluid sub-circuit is associated with operation of the second hydraulic actuator and not involved with operation of the first hydraulic actuator. The fluid circuit flushing system includes first and second bypass valves in the fluid circuit. The first bypass valve is moveable from a working position in which fluid can be pumped into the fluid circuit to operate the first hydraulic actuator and a bypass position in which fluid can be pumped into the fluid circuit to flush hydraulic fluid from a portion of the first fluid sub-circuit without moving the first door leaf. The second bypass valve is moveable from a working position in which fluid can be pumped into the fluid circuit to operate the second hydraulic actuator and a bypass position in which fluid can be pumped into the fluid circuit to flush hydraulic fluid from a portion of the second fluid sub-circuit without moving the second door leaf.
Another aspect of the invention is a method of operating a hydraulically powered door installation in a cold environment. The door installation has one or more door frames and one or more door leaves mounted thereon for movement between open and closed positions of the door leaves. The hydraulic system includes one or more hydraulic actuators, each of which is connected to one of the one or more door leaves for driving movement of the door leaf between its open and closed positions. A reservoir contains a hydraulic fluid used to operate the one or more hydraulic actuators and a fluid circuit provides fluid communication between the reservoir and the hydraulic actuators. The method includes the step of flushing hydraulic fluid that has cooled in the fluid circuit from the fluid circuit into the reservoir by pumping relatively warmer hydraulic fluid from the reservoir into the fluid circuit without operating any of the hydraulic actuators.
Various refinements exist of the features noted in relation to the above-mentioned aspects of the present invention. Further features may also be incorporated in the above-mentioned aspects of the present invention as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the illustrated embodiments of the present invention may be incorporated into any of the above-described aspects of the present invention, alone or in any combination.
Corresponding reference characters indicate corresponding parts throughout the drawings.
Referring now to the drawings,
As shown in
A hydraulic actuator 121 is connected to the door leaf 105 for driving movement of the door leaf between its open and closed positions. As best illustrated in
The hydraulic actuator 121 is suitably a conventional double acting hydraulic cylinder. As is generally known to those skilled in the art, a double acting hydraulic cylinder generally comprises a piston 123 slideably received in a chamber 125 so that the piston separates the chamber into two sections, the volumes of which change as the piston slides axially in the chamber. A rod 127 is secured at one end to the piston 123 and arranged so that the opposite end of the rod extends to the exterior of the chamber 125 through an opening 129 at a rod end 131 of the cylinder. The end 133 of the hydraulic actuator opposite the rod end is referred to herein as the blind end.
Movement of the piston 123 axially in the cylinder 121 is driven by pumping hydraulic fluid into the chamber 125 through a rod end port 135, which is connected to the rod end section 137 of the chamber, or a blind end port 139, which is connected to the blind end section 141 of the chamber. When fluid is pumped into the blind end section 141 of the chamber 125 through the blind end port 139, the piston 123 moves axially in the chamber toward the rod end 131, causing the rod 127 to extend farther from the rod end of the actuator 121 while fluid leaves the rod end section 137 of the chamber through the rod end port 135. Conversely, when fluid is pumped into the rod end section 137 of the chamber 125 through the rod end port 135, the piston moves toward the blind end 133, thereby retracting the rod 127 while fluid leaves the blind end section 141 of the chamber through the blind end port 139. Other hydraulic actuators (including hydraulic actuators that are operable to drive movement of the door leaf 105 in only one direction) can be used instead of the double acting hydraulic cylinder illustrated in the drawings without departing from the scope of the invention.
The hydraulic actuator 121 is a component of one embodiment of a hydraulic system 151 of the present invention, which is illustrated schematically in
The hydraulic system 151 also includes a pump 161 and a fluid circuit 163 that provides fluid communication between the reservoir 153 and the hydraulic actuator 121. The reservoir 153 is suitably a relatively long way away from the hydraulic actuator 121. For example, in one embodiment of the invention, the flow path through the fluid circuit 163 from the reservoir to the hydraulic actuator 121 is suitably at least about 15 meters, more suitably at least about 30 meters, more suitably at least about 50 meters, more suitably at least about 100 meters, still more suitably at least about 500 meters, still more suitably at least about 1000 meters, and still more suitably a distance in the range of about 15 meters to about 7000 meters (7 kilometers). In view of the foregoing, it will be appreciated that at last some of the fluid lines in the fluid circuit are suitably relatively long fluid lines.
One embodiment of suitable fluid circuit 163 is illustrated in
The fluid circuit 163 also includes two fluid lines 171, 173 connecting the directional valve 169 to the hydraulic actuator 121. One of the fluid lines 171 is connected to the rod end port 135 and the other fluid line 173 is connected to the blind end port 139. The fluid lines 171, 173 connecting the directional valve 169 to the actuator 121 are suitably substantially longer than the fluid lines 165, 167 connecting the directional valve to the reservoir 153, as indicated by the breaks therein in
The temperature of the hydraulic fluid 157 in the reservoir 153 is preferably maintained above a lower limit of a desired operating range for the hydraulic fluid. In one embodiment of the invention, a heater is in thermal communication with the volume 155 of the reservoir 153 to heat the hydraulic fluid 157 in the reservoir. For instance, in
Further, a heater is not necessarily required to maintain temperature of the hydraulic fluid 157 in the reservoir in the desired operating range. As shown in
The hydraulic system 151 also includes a fluid circuit flushing system 181 operable to flush hydraulic fluid 157 from the fluid circuit 163 into the reservoir 153 without operating the hydraulic actuator 121 and without moving the door leaf 105. One embodiment of the fluid circuit flushing system 181 is suitably operable to flush at least about 50 percent of the volume of hydraulic fluid 157 in the fluid circuit 163 out of the fluid circuit, more suitably at least about 80 percent of the volume of hydraulic fluid in the fluid circuit, and still more suitably at least about 90 percent of the volume of hydraulic fluid in the fluid circuit. The volume of hydraulic fluid 157 in the fluid circuit 163 can be determined by subtracting the volume of hydraulic fluid in the reservoir 153 and in the chamber 125 of the hydraulic actuator 121, and any other actuators, from the total volume of hydraulic fluid in the hydraulic system 151).
Referring to
The bypass valve 183 is suitably remote from the reservoir 153 and close to the hydraulic actuator 121. For instance, the bypass valve 183 is suitably on the opposite side of the directional valve 169 in the fluid circuit 163 as the reservoir 153. In one embodiment of the invention, the bypass valve is suitably no more than about 15 meters from the hydraulic actuator 121, and more suitably no more than about 10 meters from the hydraulic actuator. The hydraulic system 151 may be arranged so the bypass valve 183 is relatively farther from the reservoir 153 and relatively closer to the hydraulic actuator 121 to facilitate flushing a greater percentage of the volume of hydraulic fluid 157 in the fluid circuit 163 from the fluid circuit into the reservoir. In one embodiment of the invention, for example, the bypass valve 183 is suitably at least about 15 meters away from the reservoir, more suitably at least about 30 meters away from the reservoir, more suitably at least about 50 meters away from the reservoir, more suitably at least about 100 meters from the reservoir, still more suitably at least about 500 meters from the reservoir, and still more suitably at least about 1000 meters from the reservoir. In another embodiment of the invention the fluid circuit 163 of the hydraulic system 151 is arranged so the shortest path through the fluid circuit between the bypass valve 183 and the reservoir 153 is at least about 15 meters, more suitably at least about 30 meters, more suitably at least about 50 meters, more suitably at least about 100 meters, still more suitably at least about 500 meters, and still more suitably at least about 1000 meters from the reservoir. Although the bypass valve 183 and directional valve 169 are two different valves in the illustrated embodiment, the skilled person will recognize that the directional valve and bypass valve may be integrated into a single valve (e.g., suitably by modifying the valve spool 179 of the directional valve to include a bypass position and moving it in the fluid circuit to the position of the bypass valve 183) without departing from the scope of the invention.
Still referring to
The control system 191 is operable to implement a fluid circuit flushing routine, meaning that it has at least one of instructions and circuitry for implementing the fluid circuit flushing routine. The fluid circuit flushing routing includes moving the bypass valve 183 to its bypass position and operating the pump 161 to pump hydraulic fluid 157 from into the fluid circuit 163 while the bypass valve is in its bypass position. The control system 191 also has a timer (not shown) for keeping track of elapsed time during implementation of the steps of the fluid circuit flushing routine. For example, the timer may be operable to measure an amount of time that the pump 161 has been idle and/or an amount of time that the pump has been operating. Information about the activity (or lack thereof) of the pump 161 can be used by the processor in the implementation of the fluid circuit flushing routine to determine whether to initiate or continue flushing of hydraulic fluid 157 from the fluid circuit 163.
The hydraulic system 151 illustrated in
In one embodiment of the invention the fluid circuit flushing routine includes flushing hydraulic fluid 157 from the fluid circuit 163 only if the ambient temperature measured by the ambient temperature sensor 193 (or a temperature of the hydraulic fluid 157 in the fluid circuit) is below a specified temperature. Further, the control system 191 suitably uses information about the temperature of the hydraulic fluid 157 in the reservoir 153 and/or information from the timer about how long the system has been flushing fluid from the circuit 163 to determine whether or not continued flushing of the fluid circuit is called for by the fluid circuit flushing routine. The fluid circuit flushing routine will be discussed in more detail in the description of the operation of the hydraulic system below.
With respect to opening and closing of the door leaf 105, the door installation 101 operates in much the same way as a conventional hydraulically powered door installation. When installed in a mine passageway, the door leaf 105 of the installation is normally in its closed position to inhibit air flow through the mine passageway. Briefly, when the door is to be opened, a user sends a signal to the control system 191 to open the door (e.g., by pushing a palm button (not shown), tripping an automatic switch (not shown), or by another suitable input device). Upon receiving the open door signal, the control system 191 moves the spool 179 of the directional valve 169 to a position in which it directs hydraulic fluid 157 pumped into the fluid circuit 163 by the pump 161 into the blind end section 141 of the chamber 125 in the hydraulic actuator 121. The control system 191 also activates the pump 161 to pump hydraulic fluid 157 into the fluid circuit to extend the rod 127 and thereby move the door leaf 105 to its open position. Similarly, when the control system 191 receives a close door signal input by the user, it positions the directional valve 169 to pump hydraulic fluid 157 into the rod end section 137 of the chamber 125 of the hydraulic actuator 121 and activates the pump 161 to retract the rod 127 of the hydraulic actuator 121 and thereby move the door leaf 105 to its closed position.
One embodiment of a method of the invention includes heating the hydraulic fluid 157 in the reservoir 153. For example, the hydraulic fluid may be heated by the heater 159. Heating of the hydraulic fluid 157 can also be accomplished by arranging the hydraulic system 151 so that the reservoir 153 is located in a relatively warmer environment than other parts of the hydraulic system (e.g., the hydraulic actuator 121 and/or exterior door leaf 105), in which case hydraulic fluid 157 that has cooled in the fluid circuit is automatically heated when it is returned to the reservoir 153 because of the relatively warmer environment surrounding the reservoir. The method also includes pumping the heated hydraulic fluid 157 from the reservoir 153 into the fluid circuit 163 to flush hydraulic fluid that has cooled in the fluid circuit 163 back into the reservoir without operating the hydraulic actuator 121 and without moving any of the one or more door leaves (for instance without moving the single door leaf 105 in the embodiment illustrated in
The method is suitably implemented by the control system 191 as a part of a fluid circuit flushing routine. In one embodiment, the initial step of the fluid circuit flushing routine is to check the ambient temperature measured by the ambient temperature sensor 193 (or a temperature of the hydraulic fluid in the fluid circuit 163) to determine if flushing is needed. The method includes flushing hydraulic fluid 157 from the fluid circuit 163 only when the ambient temperature (or temperature of the hydraulic fluid 157 in the fluid circuit 163) is below a specified temperature. This avoids wasting energy by flushing hydraulic fluid 157 from the fluid circuit 163 when the hydraulic fluid remains sufficiently warm in the fluid circuit 163 (e.g., during warm weather).
If the control system 191 determines that flushing is called for, the control system 191 at least periodically causes relatively warmer hydraulic fluid 157 from the reservoir 153 to be pumped into the fluid circuit 163 to flush the relatively cooler hydraulic fluid that is initially in the fluid circuit back into the reservoir 153 where it can be heated. This replaces the relatively cooler hydraulic fluid 157 that is initially in the fluid circuit 163 with the relatively warmer hydraulic fluid from the reservoir 153. In the embodiment shown in
Flow of hydraulic fluid 157 through the fluid circuit 163 bypasses the hydraulic actuator 121 through the bypass valve 183 and bypass line 187. Accordingly, the flushing of hydraulic fluid 157 from the fluid circuit 163 does not involve operation of the hydraulic actuator 121 or movement of the door leaf 105. Further, because the bypass valve 183 is arranged to be remote from the reservoir (e.g., more than 50 meters away from the reservoir), the fluid circuit flushing routine flushes a substantial percentage of the hydraulic fluid 157 in the fluid circuit 163 back to the reservoir. For example, in one embodiment of the invention suitably at least about 50 percent of the total volume of hydraulic fluid 157 in the fluid circuit 163 is flushed from the circuit, and more suitably at least about 80 percent of total volume of hydraulic fluid in the circuit is flushed, and still more suitably at least about 90 percent of the total volume of hydraulic fluid in the circuit is flushed.
The fluid circuit flushing routine suitably comprises deactivating the pump 161 after the relatively cooler hydraulic fluid 157 has been purged from the part of the fluid circuit that is flushed by the flushing system 181 and returned to the reservoir 153. For example, one embodiment of the fluid circuit flushing routine includes operating the pump 161 to flush hydraulic fluid 157 from the fluid circuit 163 for a specified period of time (e.g., as tracked by the timer of the control system 191) and then turning the pump off. The specified time may be approximately the length of time needed to completely purge the relatively cooler hydraulic fluid 157 from the part of the fluid circuit being flushed by the flushing system 181. In another embodiment, the fluid circuit flushing routine includes operating the pump 161 to flush hydraulic fluid 157 from the fluid circuit 163 until the temperature sensor 195 detects a rise in the temperature of the hydraulic fluid 157 in the reservoir 153, which is a sign that the relatively warmer hydraulic fluid being pumped into the fluid circuit 163 has made its way all the way through the fluid circuit back to the reservoir, and then deactivating the pump.
After the relatively warmer hydraulic fluid 157 that was pumped into the fluid circuit 163 during the flushing has cooled (e.g., as indicated by the amount of time that has elapsed since the pump 161 was last activated and/or by temperature measurement of the hydraulic fluid in the fluid circuit), the control system 191 suitably reactivates the pump 161 to flush the cooled hydraulic fluid from the circuit again in the same manner.
A portion of another embodiment of a hydraulic system of the present invention is substantially the same as the hydraulic system 151 described above except that the portion of the fluid circuit 163 inside the box labeled 201 in
Referring to
The fluid circuit 551 is flushed by a fluid circuit flushing system 581, which includes the bypass valves 283a, 283b gin the fluid sub-circuits 303a, 303b. The control system 191 is operable to flush hydraulic fluid from each of the fluid sub-circuits 303a, 303b without moving any of the hydraulic actuators 121 and without moving any of the door leaves. For example, in one embodiment of the invention, the control system 191 is operable to implement a fluid circuit flushing routine in which the fluid sub-circuits 303a, 303b are flushed sequentially.
In one embodiment of the fluid circuit flushing routine, both of the bypass valves 283a, 283b are initially in their working positions when the control system 191 determines that flushing is called for (e.g., using information such as the signal from the ambient temperature sensor 193, the amount of time elapsed since the pump was operated as measured by the timer, and/or measurement of a temperature of the hydraulic fluid in the fluid circuit 563). To initiate flushing, the control system 191 first moves the directional valve 169a to a position that allows hydraulic fluid 157 to flow from the reservoir to the bypass valve 283a, moves the bypass valve 283a to its bypass position (as shown in
Then the control system 191 moves the bypass valve 283a back to its working position, moves the bypass valve 283b of the second fluid sub-circuit 303b to its bypass position (as shown in
The hydraulic system 651 includes a flushing system 681 that includes the three bypass valves 283a, 283b, 283c in the fluid sub-circuits 303a, 303b, 303c. In one embodiment of the invention, the control system 191 flushes relatively cooler hydraulic fluid 157 from the first fluid sub-circuit 303a (e.g., by operating the pump 161 after moving the valves 283a-283c, 169a-169c if necessary to arrange them as shown in
In view of the foregoing, the skilled person will recognize that the present invention provides flexibility to flush any number of fluid sub-circuits by extrapolation of the foregoing systems and methods.
When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As various changes could be made in the above constructions and methods without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.
| Number | Name | Date | Kind |
|---|---|---|---|
| 2764147 | Brunner | Sep 1956 | A |
| 3530958 | Brannon et al. | Sep 1970 | A |
| 4082331 | Kennedy et al. | Apr 1978 | A |
| 4118894 | Kennedy et al. | Oct 1978 | A |
| 4162718 | Lamprey | Jul 1979 | A |
| 4373294 | Kennedy et al. | Feb 1983 | A |
| 4478535 | Kennedy et al. | Oct 1984 | A |
| 4523406 | Kennedy et al. | Jun 1985 | A |
| 4785915 | Shah et al. | Nov 1988 | A |
| 4911577 | Kennedy et al. | Mar 1990 | A |
| 5118259 | Bishoff | Jun 1992 | A |
| 5168667 | Kennedy et al. | Dec 1992 | A |
| 5240349 | Kennedy et al. | Aug 1993 | A |
| 5971068 | Ochiai et al. | Oct 1999 | A |
| 6032986 | Kennedy et al. | Mar 2000 | A |
| 6164871 | Kennedy et al. | Dec 2000 | A |
| 6425820 | Kennedy et al. | Jul 2002 | B1 |
| 6594954 | Kennedy et al. | Jul 2003 | B1 |
| 6938372 | Kennedy et al. | Sep 2005 | B2 |
| 6955594 | Kennedy et al. | Oct 2005 | B2 |
| 20030079423 | Kennedy et al. | May 2003 | A1 |
| 20050099020 | Kennedy et al. | May 2005 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20080253841 A1 | Oct 2008 | US |
