Abstract:
A double valve is reset when a source of pressurized fluid is connected to a reset port. When the source of pressurized fluid is removed from the reset port, a first reset piston is retracted so that a second pilot chamber receives pressurized fluid while a first pilot chamber continues to be vented. A second reset piston is retracted after a predetermined delay time following retraction of the first reset piston, the predetermined delay time being sufficient to allow the second pilot chamber to become substantially pressurized. If a second pilot valve is actuated when the second reset piston is retracted, then the pressurized fluid in the second pilot chamber drives the second movable valve unit out of a deactuated position during a time that pressurized fluid in the first pilot chamber is insufficient to drive the first movable valve unit out of a deactuated position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   Not Applicable. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
   Not Applicable. 
   BACKGROUND OF THE INVENTION 
   The present invention relates in general to control valves, and, more specifically, to resetting a double valve for controlling a single flow of pressurized fluid in response to simultaneous activation of a pair of control switches. 
   Machine tools of various types operate through a valving system, which interacts with a pneumatically-controlled clutch and/or brake assembly. For safety reasons, the control valves that are used to operate these machine tools require the operator to activate two separate control switches substantially simultaneously to ensure that an operator&#39;s hands are away from the moving components of the machine tool when an operating cycle is initiated. Typically, an electronic circuit responsive to the two control switches generates a pilot control signal applied to the pilot valves for switching the main fluid circuit of the valve to control delivery of compressed air (or other fluid) to the machine tool to perform its operating cycle. 
   Double valves operating in parallel in one valve body have been developed to ensure that a repeat or overrun of a machine tool operating cycle cannot be caused by malfunction of a single valve unit (e.g., a valve becoming stuck in an actuated position). Thus, if one valve unit fails to deactuate at the proper time, the double valve assumes a configuration that diverts the source of compressed air from the machine tool. A double valve is shown, for example, in commonly assigned U.S. Pat. No. 6,478,049 to Bento et al, which is incorporated herein by reference for all purposes. 
   In addition to providing protection against the repeat or overrun of the machine tool, it is desirable to monitor the double valve for a faulted valve unit and to prevent a new operating cycle of the machine tool from being initiated. Thus, prior art systems have caused the double valve to assume a lock-out configuration when a single valve unit is in a faulted condition so that the double valve cannot again be actuated until it has been intentionally reset to clear the faulted condition. 
   More specifically, a double valve assembly includes two electromagnetically-controlled pilot valves. Typically, the pilot valves are normally closed. The double valve assembly includes two movable valve units, each with a respective exhaust poppet between the outlet port and the exhaust port of the double valve and a respective inlet poppet between the outlet port and the inlet port of the double valve. When the pilot valves are normally closed, then the exhaust poppets are normally open and the inlet poppets are normally closed. Each of the pilot valves is moved to an actuated position in response to an electrical control signal from a respective operator-controlled switch, which typically causes the exhaust poppets to close and the inlet poppets to open. Any time that 1) a valve unit fails to deactuate properly, 2) a valve unit fails to actuate properly, or 3) the pilot valves are actuated or deactuated non-simultaneously, then at least one valve unit becomes locked in a faulted position where its exhaust poppet cannot be closed (thereby preventing the outlet from becoming pressurized). 
   In a typical reset operation, one or more faulted movable valve units are returned to their deactuated positions by the application of pressure from a source via a 2- or 3-way control valve to a reset port. The pressure causes a reset piston to extend in a manner that drives or pushes a faulted valve unit out of the faulted position so that the control valve can be actuated to start an operating cycle of the machine tool. If a faulted valve unit is present, then it is desirable for a machine operator to service the control valve to repair the valve unit. However, operators may sometimes attempt to maintain the reset function continuously in order to continue machine tool operations without repairing a faulted valve unit by “tying down” the reset control valve. It is desirable to provide an anti-tiedown function in the design of the double valve so that the tying down of the reset valve cannot prevent the control valve from locking out in response to a faulted valve unit. 
   Prior anti-tiedown mechanisms have required added components that were relatively complicated and that added significant cost to the valves. Furthermore, in some valve configurations, it has been possible to tie down the main pilot switches and operate a machine tool using the reset control as a single control point (thereby defeating the mechanism for requiring simultaneous activation of the two manual switches). Prior anti-tiedown mechanisms have not prevented this type of operation of the control valve. 
   SUMMARY OF THE INVENTION 
   The present invention provides a double valve having a reset mechanism with a low part count that can be easily integrated into the valve and prevents using the reset function to actuate the valve while tying down the main pilot switches. 
   In one aspect of the invention, a method is provided for resetting a double valve. A source of pressurized fluid is connected to a reset port. First and second reset pistons are actuated in response to the pressurized fluid to reset first and second movable valve units of the double valve, respectively. First and second pilot chambers are vented when the first and second reset pistons are actuated, the first and second pilot chambers corresponding to first and second pilot valves for actuating the first and second movable valve units, respectively. The venting prevents the first and second movable valve units from moving out of a deactuated position, respectively. The source of pressurized fluid is removed from the reset port. The first reset piston is retracted so that the second pilot chamber receives pressurized fluid while the first pilot chamber continues to be vented. The second reset piston is retracted after a predetermined delay time following retraction of the first reset piston, the predetermined delay time being sufficient to allow the second pilot chamber to become substantially pressurized. If the second pilot valve is actuated when the second reset piston is retracted, then the pressurized fluid in the second pilot chamber drives the second movable valve unit out of a deactuated position during a time that pressurized fluid in the first pilot chamber is insufficient to drive the first movable valve unit out of a deactuated position. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a double valve according to a first embodiment of the present invention in its normal deactuated position. 
       FIG. 2  is a cross-sectional view of double valve of  FIG. 1  with a valve unit in a faulted position. 
       FIG. 3  is a cross-sectional view of double valve of  FIG. 1  with the reset pistons extended in response to pressure at the reset port. 
       FIG. 4  is a cross-sectional view of double valve of  FIG. 1  just after pressure has been removed from the reset port during a reset operation. 
       FIG. 5  is a cross-sectional view of double valve according to a second embodiment of the present invention in its normal deactuated position. 
       FIG. 6  is a flowchart showing a preferred method of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring now to  FIG. 1 , a control valve system in the form of a double valve  10  includes a housing  11  having an inlet port  12  leading to an inlet chamber  13 , an outlet port  14  leading to an outlet chamber  15 , and an exhaust port  16  leading to an exhaust chamber  17 . Housing  11  may include separate blocks  11   a - 11   d  which may be clamped or bolted together. 
   Chambers  13 ,  15 , and  17  are joined by various passages to create elongated bores for receiving a first movable valve unit  18  and a second movable valve unit  20 . First movable valve unit  18  includes an exhaust piston/poppet  21  slidably received at one end of a stem  22  via a piston  23 . First movable valve unit  18  also includes an inlet poppet  24  and a flow restrictor  25 . A disk-shaped shoulder  26  extends from a spacer  34  that is fixed to stem  22 . Shoulder  26  is slidably received in a passage  27  forming flow restrictor  25  so that pressurized fluid from inlet chamber  13  flows at a reduced rate into a first crossover chamber  28  when shoulder  26  is present in passage  27 . 
   The lower end of stem  22  receives pistons  30  and  31  which are retained by a retainer nut  33  threaded to one end of stem  22 . Pistons  30  and  31  are slidably received in a bushing  32  which is rigidly retained within housing  11 . 
   A spring stop  36  is slidably received on spacer  34  and is urged in an upward direction by a return spring  35 . Beneath movable valve unit  18 , a return chamber  37  is formed which receives part of a reset piston  38  and a piston return spring  40 . 
   First movable valve unit  18  is shown in  FIG. 1  in its deactuated position wherein outlet port  14  is open to exhaust port  16  and closed to inlet port  12 . Thus, exhaust piston/poppet  21  is in its upward, deactuated position wherein an exhaust seal  42  is spaced away from an exhaust seat  41 . At the same time, an inlet seal  44  of inlet poppet  24  is disposed against an inlet seat  43 . 
   Second movable valve unit  20  includes an exhaust piston/poppet  46  slidably received at one end of a stem  47  via a piston  48 . Second movable valve unit  20  also includes an inlet poppet  50  and a flow restrictor  51 . A disk-shaped shoulder  52  extends from a spacer  60  that is fixed to stem  47 . Shoulder  52  is slidably received in a passage  53  forming flow restrictor  51  so that pressurized fluid from inlet chamber  13  flows at a reduced rate into a second crossover chamber  54  when shoulder  52  is present in passage  53 . 
   The lower end of stem  47  receives pistons  55  and  56  which are retained by a retainer nut  58  threaded to one end of stem  47 . Pistons  55  and  56  are slidably received in a bushing  57  which is rigidly retained within housing  11 . 
   A spring stop  62  is slidably received on spacer  60  and is urged in an upward direction by a return spring  61 . Beneath movable valve unit  20 , a return chamber  63  is formed which receives part of a reset piston  64  and a piston return spring  65 . 
   Second movable valve unit  20  is shown in  FIG. 1  in its deactuated position wherein outlet port  14  is open to exhaust port  16  and closed to inlet port  12 . Thus, exhaust piston/poppet  46  is in its upward, deactuated position wherein an exhaust seal  67  is spaced away from an exhaust seat  66 . At the same time, an inlet seal  70  of inlet poppet  50  is disposed against an inlet seat  68 . 
   A fluid passage  72  provides fluid communication between first crossover chamber  28  and return chamber  63  of second movable valve unit  20 . A fluid passage  73  provides fluid communication from first crossover chamber  28  to timing chambers  74  and  75  for providing pressurized fluid to an input of a first pilot valve  76 . A passage  77  is coupled between the output of first pilot valve  76  and the upper surface of exhaust piston/poppet  21 . 
   A fluid passage  78  provides fluid communication between second crossover chamber  54  and return chamber  37  of first movable valve unit  18 . A fluid passage  80  provides fluid communication from second crossover chamber  54  to timing chambers  81  and  82  for providing pressurized fluid to an input of a second pilot valve  83 . A passage  84  is coupled between the output of second pilot valve  83  and the upper surface of exhaust piston/poppet  46 . 
   When units  18  and  20  are in their deactuated positions and no pressure is being applied in any portions of the double valve, then valve units  18  and  20  are held in their upper, deactuated positions by friction (e.g., between pistons  30  and  31  and bushing  32 ). Preferably, the amount of friction provided is sufficient to maintain the movable valve units in their current positions against the force of gravity regardless of what orientation the valve body is placed. 
   When inlet pressure is first applied to inlet port  12 , the movable valve units remain at their deactuated positions as follows. The pressure in inlet chamber  13  immediately reflects the increased pressure at inlet port  12 . The surfaces of first movable valve unit  18  that are open to inlet chamber  13  include a first side  87  of shoulder  26  and an upper surface  89  of piston  30 . These surfaces are provided with equal areas such that inlet pressure against the surfaces creates an upward force against surface  87  which is substantially exactly counterbalanced by a downward force against surface  89 . Similarly, a surface  88  of shoulder  52  has an area substantially equal to a surface  90  of piston  55 . Thus, a net force of substantially zero acts upon each of the movable valve units in response to the build up of pressure in inlet chamber  13 . 
   Due to the imperfect seals of flow restrictors  25  and  51 , pressure begins to build up in crossover chambers  28  and  54 . As pressure builds up in the crossover chambers, the resulting pressure acts upon inlet poppets  24  and  50  to force them against their respective seats  43  and  68 , respectively. The increasing pressure is also communicated to return chambers  37  and  63 , which also creates an upward force to seat the inlet poppets. Pressure from the crossover chambers is also communicated to the timing chambers of pilot valves  76  and  83 . After a short delay, pressure in the crossover chambers, return chambers, and timing chambers equalize with the pressure in inlet chamber  13 . Unlike in the double valve shown in prior U.S. Pat. No. 6,478,049, pressurized fluid is always supplied to crossover chambers  28  and  54  and is allowed to build up to equal the inlet pressure whenever the double valve is not in a faulted state (i.e., there is no fluid path between the inlet and the exhaust). 
   Valve  10  is shown in  FIG. 2  having one movable valve unit in a faulted condition. The faulted state results when first movable valve unit  18  has failed to return to its deactuated position after turning off of pilot valve  76 , for example. First movable valve unit  18  is shown at its intermediate position wherein both exhaust piston/poppet  21  and inlet poppet  24  are in an unseated condition. If movable valve unit  18  is in an actuated (i.e., fully downward) position when it first becomes faulted, return spring  35  will attempt to move first movable valve unit  18  to the intermediate position. Spring stop  36  prevents inlet poppet  24  from being moved to its closed position. With inlet poppet  24  open, second crossover chamber  54  is coupled to exhaust  16  via one or both of the exhaust valves. With second crossover chamber  54  exhausted, return chamber  37  is exhausted so that no return force can be generated on first movable valve unit  18 . Timing chambers  81  and  82  are also exhausted so that double valve  10  is in a locked out condition wherein second movable valve unit  20  cannot be actuated by second pilot valve  83 . Since inlet poppet  50  is closed, pressure builds in first crossover chamber  28  even though the other movable valve unit  18  is faulted. Crossover chamber  28  provides pressure to return chamber  63  and to timing chambers  74  and  75 . Thus, when pilot valves  76  and  83  are actuated, faulted valve unit  18  receives full pressure at the top of exhaust piston/poppet  21  and can move into its fully actuated position. However, since exhaust piston/poppet  46  is open while inlet poppet is open, significant pressure cannot build in crossover chamber  54 . Consequently, pilot valve  83  is not able to provide sufficient pressure to move second movable valve unit  20  from its deactuated position. Thus, double valve  10  remains in a locked out position at least until both movable valve units are reset by reset pistons  38  and  64 . 
   In the event that inlet pressure is turned off while a movable valve unit is in its fully actuated position, then the valve unit is urged into the intermediate position by the corresponding return spring. The return spring cannot move the corresponding movable valve unit beyond the intermediate position due to the corresponding spring stop. The movable valve unit is prevented from moving all the way to its deactuated position by friction and/or gravity depending upon the orientation of the double valve. If inlet pressure is restored, pressure from the flow restrictor corresponding to the non-faulted movable valve unit is supplied into a crossover chamber which is open to exhaust through the faulted inlet poppet and at least the exhaust piston/poppet of the non-faulted unit. Since full pressure builds up in the other crossover chamber (i.e., the crossover chamber fed by the flow restrictor of the faulted valve unit), a downward pressure against the flow restrictor from within the crossover chamber latches the faulted movable valve unit in the intermediate position against the return spring. 
   The resetting of valve  10  will now be described. The reset mechanism is shown in its normal, deactuated state in  FIG. 1. A  reset port  85  communicates with a reset passage  86  for providing reset pressure to reset pistons  38  and  64  which can be driven upward to put first and second movable valve units  18  and  20  in their normal deactuated positions. First reset piston  38  has a lower piston member  111  slidably retained in a first reset chamber  110 . An annular seal  112  on lower piston member  111  engages the wall of first reset chamber  110 . Reset piston  38  also includes a push rod  113  and a first reset poppet  114 . The upper end of first reset chamber  110  communicates with a vent  116  via a passage  115 . 
   Second reset piston  64  has a lower piston member  121  slidably retained in a second reset chamber  120 . An annular seal  122  on lower piston member  121  engages the wall of second reset chamber  120 . Reset piston  64  also includes a push rod  123  and a second reset poppet  124 . The upper end of second reset chamber  120  communicates with vent  116  via a passage  125 . 
   Reset passage  86  communicates directly with the lower end of first reset chamber  110 . Reset passage  86  is coupled to a passage  127  via a flow restrictor  126 , such as an orifice. Passage  127  communicates with the lower end of second reset chamber  120  and with an optional reset timing chamber  128 . 
     FIG. 3  shows control valve  10  with both reset pistons fully actuated by application of pressurized fluid to reset port  85 . The pressurized fluid flows from reset port  85  through passage  86  to first reset chamber  110 , driving lower piston member  111  upward. Push rod  113  engages the lower end of stem  22  and drives first movable valve unit  18  upward to is deactuated position. Simultaneously, first reset poppet  114  moves off seat (i.e., reset valve seal  130  moves off of a reset valve seat  131 ). Thus, return chamber  37  communicates with vent  116  via passage  115 . Since vent  116  is exhausted to atmosphere, second pilot timing chambers  81  and  82  are also exhausted. This prevents second valve unit  20  from being actuated during a reset operation. 
   Pressurized fluid from passage  86  also flows through restrictor  126  to pressurize second reset chamber  120  at a slower rate than first reset chamber  10 . Reset timing chamber  128  may be used to provide an increased difference in the time it takes to actuate (or deactuate) second reset piston  64 . Nevertheless, after a sufficient amount of fluid has passed through restrictor  126 , second reset piston  64  moves to its fully actuated position as shown in  FIG. 3  in order to reset second movable valve unit  20 . The unseating of second reset poppet  124  (i.e., reset valve seal  132  moving off seat  133 ) results in first pilot timing chambers  74  and  75  to be exhausted via passages  73  and  72 , return chamber  63 , and passage  125 , thereby preventing first valve unit  18  from being actuated during a reset operation. 
   After sufficient time has passed to allow both valve units to be reset, the pressure is removed from reset port  85 . Provided that reset port  85  is adequately exhausted, pressure drops in first reset chamber  110  very quickly so that it moves back from its extended position to its retracted position by action of piston return spring  40  as shown in FIG.  4 . The closing of first reset poppet  114  isolates return chamber  37  from vent  116 . If inlet pressure is present, pressure building in crossover chamber  54  eventually pressurizes return chamber  37  and second pilot timing chambers  81  and  82 . Pressure in crossover chamber  54  also forces inlet poppet  24  upward. 
   After first reset piston  38  deactuates, second reset piston  64  remains in an actuated position due to the retention of pressure by flow restrictor  126 . Thus, while pressure is built up in second pilot timing chambers  81  and  82 , first pilot timing chambers  74  and  75  continue to be exhausted through second reset poppet  124 . The time delay for fully deactuating second reset piston  64  depends on the sizes of flow restrictor  126 , second reset chamber  120 , and reset timing chamber  128 . The delay is made long enough to allow second pilot timing chambers  81  and  82  to be substantially pressurized before closing of second reset poppet  124  (and before significant pressure can be built up in first pilot timing chambers  74  and  75 ). Therefore, when second reset piston  64  fully deactuates and if pilot valve  83  is turned on, then second movable valve unit  20  is moved out of its deactuated position and into its actuated position, thereby exhausting crossover chamber  28 , timing chambers  74  and  75 , and return chamber  63 . Consequently, the valve is locked out, thereby preventing the reset function from being used to operate the valve with the pilot valves actuated. 
     FIG. 5  shows an alternative embodiment of a double valve  10 ′, which functions in essentially the same manner as the embodiment shown in  FIGS. 1-4 . Corresponding parts in  FIG. 5  are designated using the same reference numbers with an added prime. Housing  11 ′ includes a first movable valve unit  18 ′ and a second movable valve unit  20 ′. Since the units are identical, only movable valve unit  18 ′ will be described in detail. 
   A valve stem  22 ′ has an exhaust piston/poppet  21 ′ fixedly mounted at one end by a retaining nut  91 . A spacer  92  has disc portions  93  and  94  at each axial end. Exhaust piston/poppet  21 ′ includes a cavity  95 , which is bowl shaped and receives disc portion  93  and an o-ring  96 . O-ring  96  forms a face seal with exhaust seat  41 ′ in the manner described in co-pending application Ser. No. 10/631,191, filed Jul. 31, 2003, incorporated herein by reference. Likewise, inlet poppet  24 ′ has a cavity  97  for receiving disc shaped portion  94  and an o-ring  98 . 
   Also mounted to stem  22 ′ are a spacer  100  and a piston  101 . A boss  103  at the bottom end of stem  22 ′ clamps the poppets, spacers, and piston in a fixed relationship on stem  22 ′. Piston  101  is shaped to provide a flow restrictor  25 ′ between inlet chamber  13 ′ and crossover chamber  28 ′. Piston  101  has a constant diameter throughout inlet chamber  13 ′ so that it has no surfaces for exerting force in an axial direction on movable valve unit  18 ′. However, a top surface  102  is exposed to crossover chamber  28 ′ for generating a downward latching force when in the faulted state as described earlier. 
   A first reset chamber  110 ′ receives first reset piston  38 ′ having a push rod extension  113 ′. Chamber  110 ′ receives reset pressure at reset port  85 ′ via a flow restrictor  126 ′. A first reset poppet  134  includes an o-ring  135 . When poppet  134  is on-seat as shown in  FIG. 5 , first return chamber  37 ′ is isolated from vent  116 ′. When piston  38 ′ is actuated, poppet  134  is opened and an exhaust path is created for return chamber  37 ′ and the opposite pilot timing chambers (not shown). 
   First reset piston  38 ′ has a bottom surface area  136  exposed to reset chamber  110 ′ which is less than the opposing surface area on the top of piston  38 ′ exposed to return chamber  37 ′. Therefore, the valve in  FIG. 5  cannot be reset unless the reset pressure exceeds the pressure that is present in the return chambers. 
   A preferred method of operation of the present invention is shown in FIG.  6 . In step  140 , the reset port is pressurized (e.g., a three-way valve is actuated to couple the reset port to a source of compressed air). In step  141 , the first reset piston is actuated substantially immediately since it is directly coupled to the reset port and no significant volume must first be pressurized. The second reset piston becomes actuated in step  142  after sufficient pressurized fluid has flowed through the flow restrictor and any supplemental reset timing chamber is pressurized. 
   In step  143 , when the respective reset pistons are actuated, they open respective vent valves to vent the opposite pilot timing chambers. After the deactuated positions of the movable valve units are achieved, pressure is removed from the reset port in step  144 . In step  145 , the first reset piston retracts while the second reset piston is held in its extended, actuated position by the slower depressurization of the second reset chamber. In step  146 , the second pilot timing chamber(s) repressurize since the first vent valve has closed (assuming inlet pressure is present). When sufficient pressure has decayed to the reset port through the flow restrictor, the second reset piston retracts in step  147 . 
   Successful reset of the valve units in the present invention depends on the pilot valves being off. If pilot valves are on in step  148 , then the second valve unit actuates (i.e., moves out of the deactuated position) while the first valve unit cannot, which results in a faulted state of the valve. If the pilot valves are off in step  148 , then the first pilot timing chamber(s) repressurizes in step  150  and the valve is in its normal, ready-to-run state.