Abstract:
A system and method for controlling a piston-cylinder assembly of a welding apparatus, the piston-cylinder assembly including a plurality of pressure chambers, wherein the piston-cylinder assembly is operatively coupled to at least one welding electrode of the welding apparatus so as to effect movement of the electrode in a pre-stroke and weld motion, comprises: connecting to a first port of the piston-cylinder assembly a first fluid pressure, the first port in communication with a first pressure chamber so as to effect the pre-stroke motion of the electrode; and connecting to a second port of the piston-cylinder assembly a second fluid pressure, the second port in communication with a second pressure chamber so as to effect the weld stroke motion of the electrode, wherein the second fluid pressure is different from the first fluid pressure.

Description:
RELATED APPLICATION DATA 
     This application claims priority of U.S. Provisional Application No. 60/682,197 filed on May 18, 2005, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to spot welding and, more particularly, to a control system for operating a piston-cylinder assembly of a spot welding gun. 
     BACKGROUND OF THE INVENTION 
     Pneumatic piston-cylinder assemblies are generally known and have utility in a number of different applications. For example, welding systems, such as spot welding guns, employ pneumatic piston-cylinder assemblies to move and hold electrodes at a desired location during a welding operation. As is well known by those having ordinary skill in the art, spot welding is a form of welding wherein a work piece (e.g., two or more pieces of metal) are joined by passing a current between electrodes positioned on opposite sides of the metal pieces. The actual weld is made by the combination of: a) heat generated as the current passes through the metal; b) the pressure applied to the pieces at the weld location; and c) the time the heat and pressure are applied at the weld location. 
     Conventional control systems for spot welding guns, for example, utilize a single pressure source providing a common pressure for effecting motion of the piston-cylinder assembly. Such systems are referred to herein as single pressure systems. The pneumatic pressure from the pressure source, via control valves, is provided to different pressure chambers of the piston-cylinder assembly to effect one of several motions, e.g., a pre-stroke motion or a weld stroke motion. 
     As used herein, pre-stroke (or retract stroke) refers to the motion of the electrodes from an initial starting position to an intermediate position (or from intermediate position to starting position), wherein the tips of the welding apparatus may be near but not contacting the work piece. A weld stroke refers to the motion of the tips from the intermediate position to contact with the work piece, and a return motion refers to the motion from contact with the work piece to the intermediate position. 
     Typically, a first control valve controls pneumatic pressure to a first pressure chamber of the piston-cylinder assembly so as to effect the pre-stroke motion, while a second control valve controls pneumatic pressure to a second pressure chamber of the piston-cylinder assembly so as to effect the weld motion. Alternatively, individual piston-cylinder assemblies (e.g., separate and distinct assemblies) may be employed (e.g., one for the pre-stroke motion and one for the weld motion), wherein each valve controls pneumatic pressure to a respective piston-cylinder assembly. In both scenarios, however, the systems are single pressure systems. 
     In manufacturing environments, it is desirable to increase the speed at which processes occur so as to increase productivity. For example, during the assembly of an automobile or a component of an automobile, there may be a number of spot welds applied to the automobile/component. If the cycle time for each spot weld can be reduced, then more automobiles/components can be processed, thereby increasing productivity. Thus, it is desirable to move the electrode tips of the spot welding gun as fast as possible so as to minimize cycle times and increase productivity. However, bringing the electrode tips in contact with the work piece at a relatively high rate of speed can cause the tips to bounce off the work piece, which can shorten the life of the tips and/or reduce the quality of the weld. 
     To minimize the bounce of the electrode tips as they contact the work piece, it is preferable that the tips approach the work piece at a relatively slow speed. However, this tends to slow the overall cycle time of the welding process, which is undesirable. Further, to enhance the strength and/or quality of the weld, it is desirable to apply a significant force to the work piece at the weld location. The force can be created, for example, by applying relatively high pneumatic pressure to the piston-cylinder assembly. However, this high pressure can take considerable time to build up and/or remove from the piston-cylinder assembly, thereby slowing the cycle time of the welding operation, which also is undesirable. 
     As is evident, a dilemma exists between increasing productivity and enhancing quality of the spot weld. If one chooses to increase the quality of the weld and/or reduce electrode bounce, productivity suffers. Similarly, if one chooses to increase speed to enhance productivity, electrode bounce is increased and weld quality is reduced. 
     SUMMARY OF THE INVENTION 
     The present invention provides control system and method that enables cycle times for a spot welding gun to be reduced relative to conventional approaches, thereby increasing productivity. Further, the tips may be brought into contact with the work piece with low impact, thereby enhancing life of the tips. The invention implements a dual pressure control scheme, which enables the use of high pressure during both pre-stroke motions (i.e., extend and retract) and during the weld stroke return motion of the piston-cylinder assembly (thus providing high speed motion), and lower pressure during welding motions of the piston-cylinder assembly (e.g., to control a force applied to the work piece). Additionally, the invention can include a quick exhaust valve to optimize performance of spot welding gun. The quick exhaust valve enables pneumatic pressure on a front side of the pistons to be metered or dumped during pre-stroke, which allows the piston to move into the pre-stroke position quicker relative to conventional systems, which can further reduce cycle times. 
     According to one aspect of the invention, there is provided a method of controlling a piston-cylinder assembly for a welding apparatus, said piston-cylinder assembly including a plurality of pressure chambers, wherein said piston-cylinder assembly is operatively coupled to at least one welding electrode of said welding apparatus so as to effect movement of said electrode in a pre-stroke and weld motion, comprising: connecting to a first port of the piston-cylinder assembly a first fluid pressure, said first port in communication with a first chamber so as to effect the pre-stroke motion of the electrode; and connecting to a second port of the piston-cylinder assembly a second fluid pressure, said second port in communication with a second chamber so as to effect the weld stroke motion of the electrode, wherein the second fluid pressure is different from the first fluid pressure. 
     According to another aspect of the invention, there is provided a system for operating a piston-cylinder assembly for a welding apparatus, said piston-cylinder assembly including a plurality of pressure chambers, wherein said piston-cylinder is operatively coupled to at least one welding electrode of said welding apparatus so as to effect movement of said electrode in a pre-stroke and a weld motion, comprising: a first fluid pressure source for providing a first fluid pressure; a second fluid pressure source for providing a second fluid pressure, wherein the second fluid pressure is less than the first fluid pressure; a third fluid pressure source for providing a third fluid pressure, wherein the third fluid pressure is less than the second fluid pressure; a first valve coupled to a first pressure chamber and operative to selectively provide the first fluid pressure or third fluid pressure to the first pressure chamber; a second valve coupled to a second pressure chamber and operative to selectively provide the second fluid pressure or third fluid pressure to the second pressure chamber. 
     According to another aspect of the invention, there is provided a welding apparatus, comprising: a plurality of welding electrodes; a piston-cylinder assembly including a plurality of pressure chambers, wherein said piston-cylinder assembly is operatively coupled to at least one of the welding electrodes so as to effect movement of said electrode in a pre-stroke and weld motion; a first valve coupled to a first pressure chamber and operative to selectively provide a first fluid pressure or a third fluid pressure to the first pressure chamber; and a second valve coupled to a second pressure chamber and operative to selectively provide a second fluid pressure or the third fluid pressure to the second pressure chamber. 
     According to another aspect to the invention, there is provided a method of controlling a piston-cylinder assembly for a welding apparatus, said welding apparatus including a pre-stroke motion and a weld motion, comprising: connecting a first fluid pressure source to the piston-cylinder assembly to effect the pre-stroke motion; and connecting a second fluid pressure to the piston-cylinder assembly to effect the weld stroke motion, wherein the second pressure less than the first pressure. 
     According to another aspect of the invention, there is provided a method of controlling a piston-cylinder assembly for a welding apparatus, said piston-cylinder assembly including a first pressure chamber, a second pressure chamber, and a third pressure chamber, wherein said piston-cylinder assembly is operatively coupled to at least one welding electrode of said welding apparatus so as to effect movement of said electrode in a pre-stroke and weld motion, comprising: dumping an exhaust pressure from the third pressure chamber during the pre-stroke motion; and dumping an exhaust pressure from the third pressure chamber when a clamping force applied by the electrodes on a work piece is satisfies a predetermined threshold. 
     According to another aspect of the invention, a quick exhaust assembly for use with a piston-cylinder assembly to which at least one welding electrode is connected for movement toward and away from a part to be welded, said quick exhaust assembly including a first port for connection to a retract chamber of the piston-cylinder assembly; a second port for connection to an extend chamber of the piston-cylinder assembly; a third port for dumping fluid from the first port; a fourth port for metering fluid from the first port chamber; a first valve operable in a first position to connect the first port to the third port, and in a second position to connect the first port to the fourth port; a second valve operable in a first position to direct the first valve to the first position so as to couple the first port to the third port, and operable in a second position to direct the first valve to the second position so as to couple the first port to the fourth port; and a timer circuit connected to the second port and the second valve, wherein the timer circuit is operable to direct the second valve to the second position a predetermined time after pressure is detected at the second port. 
     To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The forgoing and other embodiments of the invention are hereinafter discussed with reference to the drawings. 
         FIG. 1  is a side view of a conventional spot welding gun that can be used in conjunction with the invention. 
         FIG. 2  is side schematic view of a piston-cylinder assembly that can be used in conjunction with the invention. 
         FIGS. 3A-3J  are exemplary schematic diagrams illustrating a control system for operating a spot-welding gun in accordance with the invention. 
         FIGS. 4A and 4B  are front and back views of an exemplary block incorporating the circuit of  FIG. 3A-3J  in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The invention will now be described in more detail with respect to several embodiments. Because the invention was conceived and developed for use in pneumatic spot welding systems, it will be herein described chiefly in this context. However, the principles of the invention in their broader aspects can be adapted to other types of welding systems, such as hydraulically driven systems, for example. 
     As used herein, the term “dump” refers to the exhaust of a fluid without intentional restriction of the fluid flow. For example, fluid that passes through a muffling device that causes some flow restriction prior to the fluid being released into ambient air may be considered as unrestricted flow, since the restriction from the muffling device is to suppress sound, and not to intentionally restrict fluid flow. The term “metering” or “metered” refers to a controlled or regulated flow of a fluid. 
     Referring initially to  FIG. 1 , there is shown a side view of an exemplary C-arm spot welding gun  10  that may be used in conjunction with the present invention. As will be appreciated, there are a number of different welding gun configurations that may be used, and the example of  FIG. 1  is not intended to be limiting in any way. For example, the spot welding gun may be a pinch, scissor, x-gun, or any other type of welding gun used in spot welding applications. The exemplary spot welding gun  10  includes a fixed electrode  12   a  coupled to a support arm  14 , and a moveable electrode  12   b  coupled to an actuator  16 , such as a piston-cylinder assembly, for example. The actuator  16  may include two, three, four or more pressure chambers, and one or more pistons. Located at the end of each electrode  12   a  and  12   b  are welding tips  18 , which make contact with a work piece during a welding operation. 
     For example, a work piece, such as two pieces of metal (not shown) may be placed between the electrode tips  18 . A pre-stroke (retract) valve is energized, which provides full line pressure to effect motion of the piston-cylinder assembly  16  from a start position to an intermediate position (pre-stroke position). Further, a quick exhaust valve removes pressure from a front side of the piston-cylinder assembly  16  during pre-stroke motion. The combination of full line pressure on the back side of the piston and little or no pressure on the front side of the piston enables the piston-cylinder assembly to quickly extend the electrodes into the pre-stroke position. A weld stroke valve then is energized using a selected weld schedule pressure, which may be different from the full line pressure (typically less than full line pressure), and the piston cylinder assembly moves the electrodes from the intermediate position to the weld position. The closure speed of the weld tips  18  is controlled by an adjustable flow control, thus enabling a low impact between the tips  18  and the work piece as they contact each other. Immediately following weld tip contact with the work piece, two actions take place. A pressure sensing proportional/quick dump valve allows the front end of the piston-cylinder assembly  16  to dump (by-passing the flow control), thereby providing weld schedule pressure instantly. Additionally, the proportional/quick dump valve also actuates a feedback sensor to signal that the weld cycle may be initiated. Once the weld cycle is complete, the weld stroke valve is de-energized, allowing the weld tips to open under full line pressure. Then, the retract (pre-stroke) valve is de-energized, allowing the piston-cylinder assembly  16  to open completely under full line pressure. 
       FIG. 2  illustrates an exemplary “three-port” piston-cylinder assembly  16  that may be used in conjunction with the invention. While the invention will be described herein with respect to a three-port piston cylinder assembly, it will be appreciated that features of the invention also may be applied to other types of piston-cylinder assemblies (e.g., two-port or four port piston-cylinder assemblies). The piston-cylinder assembly  16  includes a first piston  20  and a second piston  22 . A first pressure chamber  24  is defined between a back wall  26  of the actuator  16  and the first piston  20 . A second pressure chamber  28  is defined between the first piston  20  and the second piston  22 , and a third pressure chamber  30  is defined between the second piston  22  and a front wall  32  of the actuator  16 . A piston rod  22   a  couples the piston-cylinder assembly  16  to a device, such as the electrode  12   b  of the welding gun  10 . First port  34 , second port  36  and third port  38  are in communication with the first pressure chamber  24 , second pressure chamber  28  and third pressure chamber  30 , respectively. 
     By using dual pressure, a lower “regulated” pressure can be used for the weld stroke, which can provide improved control of the weld force applied to the work piece. Additionally, the regulated pressure can be used during tip dressing, which can reduce the likelihood of stalling a tip dresser motor. Further, the high pressure can be used for the pre-stroke (retract) and weld stroke return motion to effect high speed operation, thereby reducing cycle times. The high pressure also minimizes the likelihood of sticking (i.e., the tips sticking to the work piece) once the weld cycle is complete. 
     With further reference to  FIGS. 3A-3J , there is shown a circuit  40  for operating the piston cylinder assembly  16 , wherein  FIG. 3A  illustrates an exemplary starting position of the piston-cylinder assembly  16 . The circuit  40  includes a first control valve  42  (pre-stroke/retract valve), second control valve  44  (weld valve), a first pneumatic valve  45  (teletimer), a second pneumatic valve  46  (quick exhaust valve), and a first proportional valve  48  (pressure sensing valve). The pre-stroke valve  42  and weld stroke valve  44 , for example, may be electrically operated, while the teletimer  45 , quick exhaust valve  46 , and pressure sensing valve  48  may be pneumatically operated. 
     A fluid pressure supply  50 , such as an air pressure supply or the like, provides a pressure P 1  (e.g., line pressure) and is coupled to first and second ports  42   a  and  42   b  of the pre-stroke valve  42 , and to a first port  52   a  of a pressure reducing valve  52 . A third port  42   c  of the pre-stroke valve  42  is coupled to the first port  34  of the actuator  16  and to a first port  45   a  of teletimer  45 . A second port  45   b  of the teletimer  45  is coupled to a pilot port  46   sa  of the quick exhaust valve  46 . Additionally, first and second ports  47   a  and  47   b  of flow restrictor  47  are coupled to first and second ports  49   a  and  49   b  of check valve  49  (the flow restrictor  47  and check valve  49  represent a pneumatic timer  51 , as discussed below). The first ports  47   a  and  49   a  of the flow restrictor  47  and check valve  49  are coupled to a pilot port  45   sa  of the teletimer  45 , while the second ports  47   b  and  49   b  of the variable flow restrictor  47  and check valve  49  are coupled to the first port  34  of the actuator  16 . 
     A first port  44   a  of the weld valve  44  is coupled to the pressure supply  50 , and a second port  44   b  is coupled to the output  52   b  of the pressure reducing valve  52 , which provides a pressure P 2  (e.g., weld pressure), wherein P 2  is less than P 1 . A third port  44   c  of the weld valve  44  is coupled to a first port  56   a  of check valve  56  and to a first port  58   a  of flow restrictor  58 , and a fourth port  44   d  of the weld valve  44  is coupled to the second port  36  of the actuator  16 . The check valve  56  effectively bypasses the flow restrictor  58  when fluid flow is traveling away from the weld valve  44 , and implements the flow restrictor  58  when fluid flow is toward the weld valve  44 . 
     The quick exhaust valve  46  has a first port  46   a  coupled to the third port  38  of the actuator  16 , a second port  46   b  coupled to a second port  58   b  of flow restrictor  58 , and a third port  46   c  coupled to a first port  60   a  of an optional variable flow restrictor  60  (the third port  46   c  may dump directly to ambient or pass through a sound reducing device prior to being dumped). A second port  60   b  of the second variable flow restrictor  60  is coupled to a third pressure source P 3  (e.g., ambient pressure). As noted above, the pilot port  46   sa  of the quick exhaust valve  46  is coupled to the second port  45   b  of the teletimer  45 . The quick exhaust valve  46 , for example, based on pressure signals provided to the pilot port  46   sa , will shuttle between one of two positions so as to change the coupling of the third port  38  of the actuator  16  (i.e., the first port  46   a  of the quick exhaust valve  46  is selectively coupled to the second port  46   b  or the third port  46   c  of the quick exhaust valve). 
     The pressure sensing valve  48  has a first port  48   a  coupled to the third port  44   c  of the weld valve  44 , and a second port  48   b  coupled to the second port  58   b  of the flow restrictor  58 . A first pilot port  48   sa  is coupled to the second port  36  of the actuator  16 , and a second pilot port  48   sb  is coupled to the first port  48   a  of the pressure sensing valve  48 . 
     The operation of the circuit  40  will now be described in more detail.  FIG. 3A  illustrates an initial position of the piston-cylinder assembly, wherein the first pressure chamber and second pressure chamber are at pressure P 3  and the third pressure chamber is at pressure P 1 .  FIGS. 3B-3E  illustrate the pre-stroke motion of the piston-cylinder assembly  16 , wherein the pre-stroke valve  42  is energized so as to provide pressure P 1  of the pressure supply  50  to the third port  42   c  and, therefore, to the first port  34  of the actuator  16 , thus pressurizing the first pressure chamber  24 . The pressure P 1  also is provided to the pneumatic timer  51 , which acts as an “on-delay” timer, i.e., the timer provides an output at a predetermined time after receiving an input. Thus, when P 1  is provided to the timer  51 , an output signal is not immediately provided to the pilot port  45   sa  of the teletimer  45 , and the teletimer  45  remains in its initial state providing pressure P 1  to the pilot port  46   sa  of the quick exhaust valve  46 . The pressure P 1  at the pilot port  46   sa  of the exhaust valve  46  causes the exhaust valve  46  to shuttle so as to couple the third port  38  of the actuator  16  (and thus the third pressure chamber  30 ) to the flow restrictor  60 , which meters or dumps (depending on whether the flow restrictor  60  is present) pressure P 1  from the third chamber  30 . Preferably, the flow restrictor  60  is set (e.g., adjusted) to have little or no flow resistance, thus creating little or no back pressure on the front side of the second piston  22  as the first and second piston move during the pre-stroke motion. 
     The weld valve  44 , which initially is de-energized, provides pressure P 1  at the third port  44   c  and exhausts the fourth port  44   d . Thus, pressure P 1  is provided to the first port  56   a  of the check valve  56 , the first port  58   a  of the variable flow restrictor  58 , and to the first port  48   a  of the pressure sensing valve  48  (the check valve effectively allows fluid to bypass the variable flow restrictor  58 ). Pressure P 1  then is supplied from the second port  56   b  of the check valve  56  to the second port  48   b  and second pilot port  48   sb  of the pressure sensing valve  48 . Further, the second pressure chamber  28  and the first pilot port  48   sa , by virtue of being coupled to the fourth port  44   d , also are dumped. 
     As a result, the first and second piston  20  and  22  move to the pre-stroke position at a relatively fast rate of speed, since there is little or no back pressure on the front side of the second piston  22  (i.e., no pressure in the third pressure chamber  30 ). When reaching the pre-stroke position, the first pressure chamber  24  may be at pressure P 1 , while the second and third pressure chambers  28  and  30  may be at pressure P 3 . 
     With further reference to  FIG. 3F , as the first and second pistons  20  and  22  reach the pre-stroke position, the timer  51  times out and provides pressure P 1  to the pilot port  45   sa  of the teletimer  45 , which causes the teletimer  45  to shuttle so as to dump the second port  45   b . As the second port  45   b  is dumped, the pressure signal at the pilot port  46   sa  of the quick exhaust valve  46  is removed, and the quick exhaust valve  46  shuttles to the home/default position, coupling the first and second ports  46   a  and  46   b  of the quick exhaust valve  46  and thereby providing pressure P 1  to the third pressure chamber  30 . As a result, a pressure in the third pressure chamber  30  and a pressure in the first pressure chamber  24  are substantially the same (they are both about P 1 ). The third pressure chamber  30  is pressurized to provide metering air for the weld stroke motion, as described below. 
     Next, the weld valve  44  is energized so as to exhaust the third port  44   c  and to couple the fourth port  44   d  to the second pressure supply P 2 , as shown in  FIG. 3G . The second pressure P 2  then is provided to the second port  36  of the actuator  16  and, thus, to the second pressure chamber  28 . Further, since the third port  44   c  is exhausting, pressure in the third pressure chamber  30  is metered through the flow restrictor  58  and also is exhausted through the third port  44   c . As a result, the second piston  22  moves to the weld position at a speed slower than the speed of the pre-stroke motion. As will be appreciated, the speed of the weld stroke can be adjusted by altering the pressure P 2  and/or the flow rate of the flow restrictor  58 . 
     In addition, the first pilot port  48   sa  of the pressure sensing valve  48 , by virtue of being coupled to the second port  36  of the actuator  16 , is at the same pressure as the second pressure chamber  28  (e.g., P 2 ). The second pilot port  48   sb  of the pressure sensing valve  48  is at the same pressure as the third pressure chamber  30  (pressure in the third pressure chamber is decaying from P 1  in  FIG. 3G ). When the pressure in the second pressure chamber  28  reaches a predetermined level (e.g., 80 percent of a target weld pressure), the pressure sensing valve  48  shuttles so as to couple the second port  46   b  of the quick exhaust valve  46  (and thus the third pressure chamber  30 ) to the third port  44   c  of the second valve, thus dumping pressure from the third pressure chamber  30  as shown in  FIG. 3H . In other words, since contact has been made between the tips  18  and the work piece, the pressure in the third pressure chamber  30  is dumped to enable the clamping force applied between the tips  18  and the work piece to build as fast as possible. Further, as the pressure sensing valve  48  shuttles, a signal can be provided to a control module (not shown) to initiate the weld command (i.e., begin the flow of current through the electrodes, tip and work piece). This signal provides confirmation that sufficient pressure is present for initiating a weld, without relying on timers set in control modules or the like. 
     A predetermined time after the weld command has been issued, the weld valve  44  is de-energized so as to couple the third port  44   c  to the pressure supply P 1 , and the fourth port  44   d  is exhausted as shown in  FIG. 3I . Further, the first pilot port  48   sa  and the second pressure chamber  28 , which are coupled to the fourth port  44   d , also are exhausted (dumped), while the second pilot port  48   sb  is provided with pressure P 1  via check valve  56 . This causes the pressure sensing valve  48  to shuttle so as to decouple the second port  46   b  of the quick exhaust valve (and thus the third pressure chamber  30 ) from the fourth port  44   d  of the weld valve  44  (i.e., the third pressure chamber is no longer dumped). As a result, the third pressure chamber  30  is pressurized while the second pressure chamber  28  is dumped, causing the second piston  22  to return to the pre-stroke (also referred to as retract) position as fast as possible. 
     Once the second piston  22  is retracted, the pre-stroke valve  42  is de-energized so as to exhaust the third port  42   c  (and thus dump the first pressure chamber  24 ), as shown in  FIG. 3J . With pressure P 1  in the third pressure chamber  30  and the first and second pressure chambers  24  and  28  being dumped, the first and second piston  20  and  22  rapidly return to the starting position. The process then may be repeated for each additional weld operation. 
     Referring now to  FIGS. 4A and 4B , there is shown front and back views of an exemplary valve block  80  that includes the weld circuit  40 . Mounted on the block are a pre-stroke valve  42 , weld stroke valve  44  and quick exhaust valve  46 . The block may be designed to conform to accepted standard configurations within the art (e.g., ISO). In other words, ports on the block  80  may conform to accepted standards (e.g., size, location, etc.) such that any valve that conforms to the same standard may be used with the block  80 , regardless of the manufacturer of the block and/or valve. Additionally, one or more components (e.g., valves, regulators, etc.) may be integrated into the block  80 . 
     The block  80  may be used to convert an existing application into an application that includes the features of the circuit  40 . For example, a user may have a two-station manifold integrated into an existing system. The user may wish to improve the performance of the system, without significant redesign and/or down time. One approach that may be implemented is to simply remove the existing weld valves and existing weld block from the manifold, place the weld block  80  on the manifold, and then attach the valves to the block  80 . Then, the weld valves can be placed on the block  80 , thereby incorporating the benefits of the circuit  40  into the existing system (.e.g., the block may be sandwiched between the manifold and the valves, wherein the block includes the ports and circuitry described herein). Further, the block  80  can be configured so as to convert a three-port piston-cylinder assembly into a four-port piston-cylinder assembly, and vice versa. For example, the quick exhaust valve  46  can be mounted to a back side of the block (e.g., via fasteners). If the quick exhaust valve  46  is removed from the block  80 , the block converts from a three-port weld block to a four port weld block. Further detail with respect to the block  80  is provided in document WCS-SIF-01-Pneumatic Spotwelding Control Systems Training and Maintenance Manual, issued May 2006, which is incorporated by reference in its entirety. 
     The invention described herein can reduce the cycle time of a welding operation. More specifically, the dual pressure system with the quick exhaust valve  46  enable the pre-stroke/retract and return motions to occur at a relatively high speed and, thus, minimize cycle times. Test have shown that cycle times can be reduced by 100 milliseconds or more depending on the piston-cylinder stroke and/or bore size. Further, the tips are brought together under low impact, and immediately after contact between the electrodes and the work piece, the press force builds up instantly. A signal then is generated to start the weld cycle, which enables a user to reduce the squeeze time down as low as one cycle, thereby providing a significant time savings per weld. 
     Low impact of the electrodes is advantageous for a number of reasons. For example, the slow contact speed of the electrodes with the work piece results in less wear and tear on the electrode tips (e.g., up to 3 times longer life). Additionally, the slow contact speed does not cause bouncing of the electrodes on the work piece, which allows the welding process to start immediately and, thus, reduce cycle times. Further, the slow contact speed creates less noise compared to conventional systems. These advantages are realized with the above discussed cycle time reductions. 
     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.