Resistance welding cell and high-speed follow-up actuator for same

Abstract

A welding actuator is mounted to a frame and moves between retracted and welding positions that are relative to a workpiece. A follow-up actuator is mounted to the welding actuator and has an extended chamber holds a follow-up rod in an extended position when in a pressurized state. A welding tool is supported by the follow-up actuator to weld a fastener to the workpiece in the welding position in response to a welding current. An air supply system is fluidly connected to the extended chamber and maintains the pressurized state prior to a welding cycle. A controller commands the welding actuator from the retracted position to the welding position to operatively engage the workpiece with the welding tool during the welding cycle. The follow-up actuator maintains a welding force on the workpiece in the pressurized state during the welding cycle.

Description

RESISTANCE WELDING CELL AND HIGH-SPEED FOLLOW-UP ACTUATOR FOR SAMETECHNICAL FIELD

[0001] This disclosure relates to a welding cell and an actuator stack used, for example, to secure resistance welding fasteners to stampings.BACKGROUND

[0002] The production of complex assemblies such as vehicles, appliances, consumer goods, and furniture often requires the fabrication of welded subassemblies, such as sheet metal workpieces with one or more welded fasteners. In the production of an assembly as complex as a vehicle, there can be a considerable quantity and variety of such sheet metal workpieces that are produced in a stamping operation for later welding in batches to produce the required welded subassemblies. The finished subassembly is then removed from the machine in preparation for repeating the welding operation.

[0003] As automotive component production costs continue to be pressured lower, labor productivity is under increased scrutiny. The common direction in the industry is to replace labor with significant automation. To be competitive, it is important to maximize the productivity of both the equipment and operator. Much effort is being directed to address this challenge by building equipment that can repeatedly and reliable produce finish welded workpieces.

[0004] One common welding operation that can be difficult is resistance welding fasteners, as welding such components requires consistently maintaining the desired electrode force during the weld. Joining conventional projection weld fasteners to advanced high strength steels (AHSS) can be particularly difficult. Inconsistent welds can result from premature collapse of softened fastener projections. Controlled Pulse Resistance Welding (CPRW) has recently been used to address this challenge, at the same time enabling higher speed welding. CPRW operates with very short weld times, on the order of 5-10 milliseconds. During the weld time, the projections of the resistance weld fastener soften and collapse as they join the fastener to the sheet metal workpiece. Because the fastener travel distance during the projection collapse is on the order of 1 to 2 mm during a portion (perhaps 3 milliseconds) of the 5millisecond heating interval, it is a challenge for the mechanical system of many resistance welding machines to ensure the electrode force is properly maintained. Ensuring consistent force is essential to provide good and low resistance electrical connections at the electrode interfaces and between the fastener projections and workpiece. Repeatable and consistent force at the weld site(s) is also important to ensure containment of the weld metal during the projection collapse and solidification.

[0005] In traditional resistance welding equipment, the requirement for “follow-up” is often addressed for short electrode travel during the weld by the inherent mechanical deflection of machine components. The machine frame, electrode holders and electrodes may in effect act as compressed springs to maintain fairly consistent force during the projection collapse. The problem encountered with relying solely on mechanical deflection is that it is unpredictable and inconsistent in complex mechanical systems, and sometimes just insufficient.SUMMARY OF THE INVENTION

[0006] In one exemplary embodiment, a resistance welding cell includes a frame, a welding actuator that is mounted to the frame and configured to move between retracted and welding positions that are relative to a workpiece, a follow-up actuator that is mounted to the welding actuator, the follow-up actuator has an extended chamber that is configured to hold a follow-up rod in an extended position when in a pressurized state, a welding tool that is supported by the follow-up actuator, the welding tool is configured to weld a fastener to the workpiece in the welding position in response to a welding current, an air supply system that is fluidly connected to the extended chamber and configured to maintain the pressurized state prior to a welding cycle, and a controller that is configured to command the welding actuator from the retracted position to the welding position to operatively engage the workpiece with the welding tool during the welding cycle. The follow-up actuator maintains a welding force on the workpiece in the pressurized state during the welding cycle.

[0007] In a further embodiment of any of the above, the follow-up actuator is removably secured to the welding actuator, and the resistance welding tool is removably secured to a rod on the follow-up actuator, and the resistance welding tool is a resistance projection welding tool.

[0008] In a further embodiment of any of the above, the air supply system includes an air source that is configured to supply an air at a pressure below 100 psi, a pressure increasing device that is configured to increase the pressure of the air to above 120 psi, a reservoir that is configured to store the increased pressurized air, and at least one valve that is configured to regulate the flow of increased pressurized air to the follow-up actuator extended chamber to provide the pressurized state.

[0009] In a further embodiment of any of the above, at least one valve is configured to relieve pressurized air in the follow-up actuator extended chamber to provide the desired pressurized state.

[0010] In a further embodiment of any of the above, the air supply system includes a pressure sensor that is configured to determine a sensed pressure in the air supply system. The controller is in communication with the pressure sensor and configured to maintain the pressurized state for a subsequent welding cycle without re-pressurizing the extended chamber if the sensed pressure is above a predetermined value.

[0011] In a further embodiment of any of the above, the follow-up actuator includes a piston that is arranged in a cavity. The rod is secured to the piston. The piston separates the cavity into the extended chamber and a vented chamber. The vented chamber is configured to be in direct communication with atmospheric pressure.

[0012] In a further embodiment of any of the above, the follow-up actuator is arranged entirely outside of the welding actuator.

[0013] In another exemplary embodiment, a high-speed follow-up actuator assembly includes a housing that provides first and second cavities, the housing has a first mounting feature, first and second pistons that are respectively arranged in the first and second cavities and separate each of the first and second cavities into an extended chamber and a vented chamber, the extended chambers in fluid communication with a pressurized air source, and the vented chambers are configured to be continuously in fluid communication with atmospheric pressure, a rod extends from the housing to an end, the first and second pistons are mounted to the rod, the rod has a second mounting feature, and one of the first and second mounting features is configured to be secured to a welding actuator, and the other of the first and second mounting features is configured to facilitate securing of a welding tool.

[0014] In a further embodiment of any of the above, the assembly includes an air supply system that includes an air source that is configured to supply an air at a pressure below 100 psi, a pressure increasing device that is configured to increase the pressure of the air to above 120 psi, and a reservoir that is configured to store the increased pressurized air, and at least one valve that is configured to regulate the flow of increased pressurized air to the extended chambers to provide the pressurized state.

[0015] In a further embodiment of any of the above, the air supply system includes a pressure sensor that is configured to determine a sensed pressure in the air supply system during a welding cycle. A controller is in communication with the pressure sensor and configured to monitor the signature of sensed pressure during a welding cycle.

[0016] In a further embodiment of any of the above, the controller is configured to maintain the pressurized state if the sensed pressure is higher or lower than a predetermined value.

[0017] In a further embodiment of any of the above, the controller is configured to actuate the at least one valve to supply the increased pressurized air to the extended chambers to reacquire the pressurized state if the sensed pressure is below the predetermined value.

[0018] In a further embodiment of any of the above, the controller is configured to actuate the at least one valve to relieve pressurized air within the extended chambers to reacquire the pressurized state if the sensed pressure is above the predetermined value.

[0019] In a further embodiment of any of the above, rod includes a bore that extends from a terminal end toward the second mounting feature. The first and second pistons are mounted to the rod. First and second holes are respectively adjacent to the first and second pistons and are in fluid communication with the extended chambers respectively of the first and second cavities.

[0020] In a further embodiment of any of the above, the rod includes first and second features along a length, and includes a position sensor that is supported by the housing adjacent to the length, and includes a controller that is in communication with the position sensor and configured to monitor the first and second features during a welding cycle.

[0021] In a further embodiment of any of the above, the assembly includes at least one non-metallic insulative bushings that is arranged in the housing and slidably supports the rod.

[0022] In a further embodiment of any of the above, the first and second pistons each include an annular recess on a face that is exposed to at least one of the extended and vented chambers.

[0023] In another exemplary embodiment, a method of welding a resistance welding fastener includes pre-charging an extended chamber in a follow-up actuator with air to a pressurized state, the follow-up actuator supports a resistance welding tool, advancing a welding actuator that carries the follow-up actuator, the welding tool, and a fastener to engage a workpiece, applying a welding current to the fastener and workpiece during a welding cycle, and maintaining a welding force on the fastener and workpiece with the follow-up actuator in the pressurized state during the welding cycle.

[0024] In a further embodiment of any of the above, the air within the extending chamber in the pressurized state is in a range of 150 psi to 300 psi.

[0025] In a further embodiment of any of the above, the air is compressed during the maintaining step, and the advancing, applying and maintaining steps are performed in a subsequent welding cycle without re-pressurizing the extended chamber.

[0026] In a further embodiment of any of the above, the follow-up actuator includes a rod that is supported by a piston in communication with the extended chamber. A position sensor is adjacent to a length of the rod. The current applying step is performed based on a sensed position of the rod by the position sensor.

[0027] In a further embodiment of any of the above, the pre-charging step is performed prior to the advancing, applying and maintaining steps.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

[0029] Figure 1 is a schematic of an example resistance welding cell.

[0030] Figure 2 is a perspective view of an example resistance welding station.

[0031] Figure 3 is a schematic of an example resistance welding actuator stack including an example high-speed follow-up actuator.

[0032] Figure 4 is the follow-up actuator according to one aspect of the disclosure.

[0033] Figure 5 is a cross-sectional view through the follow-up actuator shown in Figure 4.

[0034] Figure 6 is a schematic of an air supply system used to supply pressurized air to the follow-up actuator disclosure of Figure 5.

[0035] Figure 7 is a flowchart depicting a method of operating a resistance welding station having the disclosed follow-up actuator.

[0036] The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0037] Referring to Figure 1 , a schematic of an example robotic cell 10 is illustrated. The cell 10 includes a first conveyor 12 that feeds a raw workpiece 14 into the cell 10 for one or more operations, such as bending, clinching, coining, forming, piercing, riveting, stamping, and / or resistance welding. A multi-axis robot 16 picks up the raw workpiece 14 and moves it into position at a first welding station 18 for an operation. A first feeder 20 may supply a component to the welding station, such as a resistance welding fastener (e.g., nut, rivet or stud) or other component that may be secured to the raw workpiece 14. Once the operation is completed, the robot 16 may transfer the workpiece to another welding station 22 that receives components from another feeder 24. The feeders 20, 24 are vibratory tumblers, for example, that properly orient the fasteners for use by its respective welding station. A fewer or greater number of welding stations may be provided in the cell 10 than illustrated depending upon the desired operations. Once the operations have been completed on the workpiece, the robot 16 transfers the finished workpiece 28 to another conveyor 26 for processing outside of the cell 10 (e.g., to another manufacturing location or packaging of the finished part).

[0038] The welding station 18 shown in Fig. 2 is a resistance welding machine configured for welding projection weld fasteners, for example. The welding station 18 includes a frame 30 supporting a resistance welding stack or gun, also shown in Figure 3. The resistance welding stack includes a welding actuator 40 having a rod 44 extending from a cylinder 42. One example welding actuator 40 is disclosed in International Application No. PCT / CA2023 / 050927, entitled “HYDRAULIC CYLINDER AND SYSTEM WITH PRESSURE INTENSIFICATION”, filed on July 31 , 2023, which is incorporated herein by reference in its entirety.

[0039] A typical resistance welding stack includes an upper electrode or welding tool 38 operatively mounted (i.e., directly or indirectly) to the welding actuator 40. Opposite the upper electrode is a lower electrode 32. A pin 34 may be provided on the welding tool 38 (Fig. 2) or the lower electrode 32 (Fig. 3) to locate the fastener F relative to the workpiece 14. Other locating techniques may be used if desired.

[0040] A feeder 36 is used to deliver a fastener F (Fig. 3) to either the upper or lower electrodes 38, 32. The welding machine frame 30 maintains the alignment and orientation of the components and includes provisions for leveling to ensure thedesired function. The feeder 34 shown is for feeding projection weld fasteners. The design of the feeder 34 will be based on the requirements of the fastener F to be welded and may for example be a stud, pin, rivet, or other similar resistance projection welded component. The feeder 34 dispenses one fastener F at a time.

[0041] Returning to Figure 2, the frame 30 supports a resistance welding transformer 48, which is electrically connected to one of the electrodes by a shunt 46, that produces the required welding current across the electrodes for achieving the required weld quality. The resistance welding transformer can be of any type, such as alternating current or inverter. A controller 62 as communicates with a weld actuator control system 61 that includes various valves and sensors to achieve desired operation of the welding actuator 40. The controller 62 is in communication with the transformer 48 to time the welding operation and coordinate motion of the welding electrodes to produce the necessary electrode force for welding.

[0042] When a welding cycle is requested, the welding actuator 40 extends to a position that is aligned with the feeder 36 when it advances to deliver a component to be welded. When the feeder 36 retracts to its home or feeder retracted position, the welding actuator 40 extends fully to close the electrodes and press the fastener F to be welded against the workpiece W positioned by the high-speed welding robot 16. During the welding sequence, welding current delivered by the resistance welding transformer 48 creates the heat for welding. At the completion of the weld, the welding actuator 40 is retracted to return the moveable welding tool 38 to its home or retracted position.

[0043] The controller 62 communicates with various sensors 63, such as pin position sensors, to monitor weld quality. Examples relating to suitable pin position sensing can be found in USPN 6,576,859, entitled “Resistance Welding Fastener Electrode,” issued June 10, 2003 and PCT International Application No. PCT / CA2014 / 050896, entitled “Welder with Indirect Sensing of Weld Fastener Position”, filed September 18, 2014, which are incorporated by reference herein in their entirety.

[0044] The sensor(s) can be used to track the electrode and welding pin movement to monitor situations that might generate an error leading to a defective part or a fault in the welding system 10. For example, if the pin locating the fastener is depressed when the welding gun closes on the workpiece presented by the robot, theworkpiece may not have a clearance hole, or the workpiece may have slipped in the robot gripper too far for the floating action of the welding unit to accommodate (discussed in more detail below). In another example, if the electrode is not closed to the expected height, there may be an improper workpiece, fastener, or perhaps two fasteners. In this scenario, the system may first try to eject the fastener and reload. If the same error occurs, the workpiece is replaced as above. The controller 62 in this case can instruct the robot 16 to deliver the workpiece to a containment area and pick up a new workpiece from the conveyor.

[0045] A high-speed follow-up actuator 50 is installed between the welding tool 38 (e.g., upper electrode assembly) and the welding actuator 40, which can be any pneumatic or servoelectric actuator applied to produce resistance welding electrode force. The high-speed follow-up actuator 50 provides electrode force consistently during the welding sequence, which would otherwise not be possible with prior art welding stacks, especially during the collapse (upsetting) of the resistance weld fastener projections. The disclosed follow-up actuator 50 and its associated air supply system overcomes the weaknesses and deficiencies of high inertia mechanical systems (including the machine frame, actuator, and tooling).

[0046] Referring to Figures 3 and 4, the follow-up actuator 50 has a multipiece housing provided by first and second blocks 64, 66 and a mid-plate 68 clamped about first and second sleeves 70, 72 using fasteners 74. The first and second sleeves 70, 72 are sealed respectively relative to the first block 64 and the mid-plate 68 by seals 86 (Fig. 5).

[0047] The follow-up actuator 50 includes a rod 54 slidable relative to its cylinder 52. In the example, the rod 54 is arranged entirely outside of the welding actuator 40, that is, the rod 54 is not integrated with or otherwise a part of the welding actuator 40. In the example, the follow-up actuator 50 is removably secured to the welding actuator 40 by a first mounting feature 76, which enables the device to be retrofitted more easily to a variety of welding actuators 40 based upon the application. The first mounting feature 76 is provided on the first block 64, which includes a bore 78 that receives the rod 44. Slots 82 are provided in the first block 64, which enables a first block to clamp about the rod 44 when a fastener (not shown) is threaded into a hole 80.

[0048] In the example, the resistance welding tool 38 is removably secured to the follow-up actuator rod 54. A feature 84 (e.g., a notch or flat) on the rod 54 cooperates with a matching hole in the insulative bushing 110 in the second block 66 to prevent rotation of the follow-up rod 54 and thereby the welding tool 38. The welding tool 38 may use a set screw or other element to clamp the end of the rod 54. It should be understood that the follow-up actuator 50 may be oriented in reverse, if desired (e.g., the rod 54 secured to the welding actuator 40, and the housing 52 secured to the welding tool 38). Moreover, the welding tool 38 may be integrated with the followup actuator.

[0049] As shown in Figure 5, the follow-up actuator includes first and second cavities 94, 96 respectively including first and second pistons 90, 92. Each piston 90, 92 separates its respective cavity into extended and vented chambers 112, 114. The vented chambers 114 are in direct communication with atmospheric pressure via vents 88, which are unobstructed openings in the housing providing continuously fluid communication with atmospheric pressure regardless of operational state of the welding station 18. Multiple pistons are used to reduce the size and weight of the follow-up actuator 50 by increasing the compression ratio over a single piston actuator.

[0050] The rod 54 is secured to the pistons 90, 92, which are sealed relative to the rod 54 by inner piston seals 98. An outer seal 100 is arranged at the periphery or each piston 90, 92 to seal the piston relative to its sleeve 70, 72. The rod 54 is supported at either end portion by non-metallic, insulative bushings 110 in the first and second blocks 64, 66. A rod seal 102 is arranged between the rod 54 and the midplate 68 to seal and fluidly separate the first and second cavities 94, 96 from one another. The first and second pistons 90, 92 each include an annular recess 116 on a face exposed to at least one of the extended and vented chambers (e.g., on the extended chamber side, as shown) to increase the volume of compressed air and thereby reduce the compression ratio. The desired compression ratio will minimize the internal pressure variation as the follow-up rod position changes. The annular recess 116 also has the positive effect of further reducing weight of the follow-up actuator 50.

[0051] The first block 64 includes an inlet 56 in fluid communication with a passage 87 that provides air to the extended chambers 112 via a bore 104 and holes 106 in the rod 54. The pistons 90, 92 are secured to the rod 54 by retainer clips 108, which enable assembly as well as ensure alignment and communication of the holeswith the extended chambers 112. The bore 104 extends from a terminal end within the first block 64 toward the second mounting feature 84. This removes significant weight from the follow-up actuator 50 as well as provides what is effectively another piston as the air pressure acts to extend the rod 54, further increasing compression ration of the follow-up actuator 50.

[0052] The rod 54 includes first and second features 118a, 118b along a length (e.g., near the end that extends from the housing). A position sensor 58 supported by the housing (e.g., second block 66) adjacent to the length. The controller 62 is in communication with the position sensor 58 and configured to monitor the first and second features during a welding cycle.

[0053] The air supply system 120 is shown schematically in Figure 6. Typically, the welding station 18 is operated in a facility with shop air, which is below 100 psi (typically 65 psi to 80 psi). Such pressure is insufficient to provide the incompressibility desired, so a pressure increasing device 124 like an air pump or a booster regulator is used to increase the pressure to above 120 psi, e.g., 150 psi to 300 psi. Higher pressures may be generated if desired. This highly pressurized air is stored in a reservoir 126 so that it can be quickly supplied to the extended chambers 112 to provide the desired pressurized state before the welding cycle is initiated.

[0054] A manifold 128 has first (inlet) and second (outlet) valves 130, 134 to regulate the flow of increased pressurized air to the extended chambers to provide the pressurized state. Flow from the inlet valve 130 passes through a control orifice 130. When the outlet valve 134 is open to release pressure, the air must first pass through a control orifice 136, which limits the rate of change of charge pressure within the follow-up actuator 50. Slowing the rate of pressure change makes it easier to establish the pre-charge pressure necessary to provide the specific follow-up rod 54 extension when the initial welding force is applied. The valves 130, 134 are two-position valves, for example, that remain closed once the extended chambers 112 reach the pressurized state. A drain valve 138 can be used to manually open the manifold 128 to prepare the follow-up actuator 50 for service. The manifold 128 supplies the pressurized air for the pressurized state through an air hose 142 connected to the inlet 56.

[0055] The air supply system 120 also includes a pressure sensor 140 configured to determine a sensed pressure in the air supply system 120 (downstreamof reservoir 126, indicative of pressure in extended chambers 112) during the welding cycle. Pressure sensor 140 can be monitored by controller 62 to compare the pressure changes measured during the weld, the pressure signature, to confirm the changes are indicative of the expected values corresponding to a weld of high quality. The controller 62 is configured to maintain the predetermined pressurized state of the extended chamber 112 if the sensed pressure is higher or lower than the requirement for the next weld to be performed. The controller 62 is configured to actuate the inlet valve 130 to supply the increased pressurized air from the reservoir 126 to the extended chambers 112 to reacquire the pressurized state if the sensed pressure is below the predetermined value. If the sensed pressure is higher than the predetermined value, outlet valve 134 can be actuated to relieve pressure and establish the predetermined value.

[0056] In operation, a method 150 of welding a resistance welding fastener is illustrated in Figure 7. The method 150 includes pre-charging an extended chamber 112 (two in the example) in the follow-up actuator 50 with air to a pressurized state (block 152). This charge gas pressure, typically in the 150-300 psi range, is the value necessary to permit a high-speed follow-up actuator 50 rod motion slightly more than the maximum travel required by the projection collapse. This ensures the high-speed follow-up device stroke will be sufficient, even if the welding actuator rod is not able to move at all during the weld. The amount of surplus travel is application specific and could be affected by the consistency of the resistance weld fastener projection shape and height; multiple projections with the proper height could require more follow-up travel distance if the projections are not in aligned to have the origins (i.e. , peak) or bases in the same plane; collapse of metallic burrs or protrusions on the projection fastener; additional deflection of the workpiece (e.g., flattening out sheet metal) when distorted during the weld; displacement of workpiece coatings; any additional deflection of the nonlinear mechanical system; and / or any unexpected retraction of the weld actuator rod, such as caused by a mis-timed motion during regulation of force or position by the servo controller.

[0057] The follow-up actuator 50 supports the resistance welding tool 38. The welding actuator 40 is advanced, carrying the follow-up actuator 50, resistance welding tool 38, and the fastener F to operatively engage the workpiece 14 (block 154). A welding current is applied to the workpiece 14 and fastener F during thewelding cycle (block 156). A welding force is applied on the workpiece 14 with the follow-up actuator in the pressurized state (in addition to the force from the welding actuator 40) during the welding cycle (block 158). When the welding electrodes have closed on the workpieces and the high-speed follow-up actuator rod 54 has moved to its initial position, the illustrated position sensor 58 (e.g., proximity switch) will send a signal to the controller 62 that it is in position (neither fully retracted nor fully extended) for the weld to proceed. During the welding sequence, the rod 54 will extend or retract as necessary to maintain the desired electrode force. When the weld is complete, the rod 54 will reach its full extension when the welding actuator 40 begins to retract the electrode from the workpiece 14.

[0058] The air within the extended chambers 112 is compressed while in the pressurized state during the maintaining step. Ideally the advancing, applying and maintaining steps (blocks 154, 156, 158) are performed in a subsequent welding cycle without re-pressurizing the extended chambers 112, which are entirely sealed. Because there is no gas consumed during the normal welding cycle, it is not intended that the follow-up actuator 50 would need charging every weld cycle. In the absence of a failure, any loss of pressure over time would be negligible. Additional charging would only be required in the event of gradual pressure loss due to seal leakage, or if a different (higher or lower) charge pressure is desired.

[0059] Selection of the pressure within the extended chambers 112 can be set or verified by advancing the welding actuator 40 to develop the desired weld force, and simultaneously establishing the high-speed follow-up actuator 50 stroke. If desired, this setting could be accomplished using an automatic teaching sequence to set the pressure, which achieves the desired high-speed follow-up actuator stroke. Static and dynamic performance are usually different so verification should occur with a normal operating sequence - and ideally, a normal welding sequence.

[0060] If the welding station 18 will occasionally be adapted to perform spot welds, instead of removing the high-speed follow-up actuator 50, it can be pressurized to a high value to prevent follow-up rod 54 motion, or to a low value so follow-up rod 54 will be forced to its fully retracted position due to the application of welding force. While the latter is possible, it could be undesirable for materials that are cooling-rate sensitive. In such cases, it is detrimental to weld quality to keep the welding electrodes engaged with the weldment any longer than necessary. Ideally, most of the pre-weldtravel of the high-speed follow-up stroke will be used to respond to the fastener projection upset distance. This will ensure minimal added dwell of the electrodes on the weldment after the end of the hold function.

[0061] The controller 62 may be a hardware device for executing software, particularly software stored in memory. The controller 62 can be a custom made or commercially available processor, a central processing unit (CPU), an auxiliary processor among several processors associated with the controller, a semiconductorbased microprocessor (in the form of a microchip or chip set) or generally any device for executing software instructions.

[0062] In terms of hardware architecture, such a computing device can include a processor, memory, and one or more input and / or output (I / O) device interface(s) that are communicatively coupled via a local interface. The local interface can include, for example but not limited to, one or more buses and / or other wired or wireless connections. The local interface may have additional elements, which are omitted for simplicity, such as controllers, buffers (caches), drivers, repeaters, and receivers to enable communications. Further, the local interface may include address, control, and / or data connections to enable appropriate communications among the aforementioned components.

[0063] The memory can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM, VRAM, etc.)) and / or nonvolatile memory elements (e.g., ROM, hard drive, tape, CD- ROM, etc.). Moreover, the memory may incorporate electronic, magnetic, optical, and / or other types of storage media. The memory can also have a distributed architecture, where various components are situated remotely from one another, but can be accessed by the processor.

[0064] The software in the memory may include one or more separate programs, each of which includes an ordered listing of executable instructions for implementing logical functions. A system component embodied as software may also be construed as a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When constructed as a source program, the program is translated via a compiler, assembler, interpreter, or the like, which may or may not be included within the memory.

[0065] The disclosed input and output devices that may be coupled to system I / O interface(s) may include input devices, for example but not limited to, a keyboard, mouse, scanner, microphone, camera, mobile device, proximity device, etc. Further, the output devices, for example but not limited to, a printer, display, etc. Finally, the input and output devices may further include devices that communicate both as inputs and outputs, for instance but not limited to, a modulator / demodulator (modem; for accessing another device, system, or network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc.

[0066] When the controller 62 is in operation, the processor can be configured to execute software stored within the memory, to communicate data to and from the memory, and to generally control operations of the computing device pursuant to the software. Software in memory, in whole or in part, is read by the processor, perhaps buffered within the processor, and then executed.

[0067] The disclosed follow-up actuator 50 includes a specially configured pneumatic actuator, a pre-charging system, and control hardware. The follow-up actuator 50 can be designed to provide a nominal displacement stroke of 12 mm, which is quite sufficient for most applications where the resistance weld fastener projections are 2 mm or less in height. Any additional displacement stroke can be provided to accommodate a range of anticipated applications involving more than 2 mm of required follow-up stroke; provide supplemental stroke at the time of tooling impact, to absorb any electrode bounce in case the welding actuator exceeds the welding force due to mechanical system inertia or control algorithm overshoot; provide for an initial stroke so a simple switch or sensor can be used to confirm to the resistance welding control that the high-speed follow-up device is maintaining the desired preloaded air pressure and the welding current can be applied; permit an initial stroke tolerance when actuator force is applied; and / or facilitate follow-up stroke responsiveness tuning by adjusting the amount or percentage of compression stroke used prior to initiating the weld. The design can be changed to make the displacement stroke longer or shorter than 12 mm as necessary.

[0068] The internal volume of the air hose 142 acts as a reservoir of compressed gas connected to the high-speed follow-up actuator 50. In the initial steady state, both the high-speed follow-up actuator 50 and the hose 142 will be pressurized to the same pressure. When weld force is applied to the high-speedfollow-up actuator 50 via the welding actuator 40, the contained gas pressure in the extended chambers 112 will be raised above the initial charging pressure (e.g. 150 psi to 300 psi). If the volume of the interconnection hose / lines is excessively large it would reduce the compression ratio and could have an effect on the high-speed tracking performance. During the projection collapse (upset) stroke, the small orifice in the hydraulic hose fitting will restrict the flow of gas between the hose / lines and the followup actuator, so this pressurized volume will have limited ability to help maintain the pressure in the high-speed follow-up actuator. The system would still function, but the pressure drop within the high-speed follow-up actuator will be somewhat higher than optimal.

[0069] The high pressure gas is retained inside the follow-up actuator 50 and under normal conditions it is not exhausted or depleted during a welding cycle. Since the retained high pressure gas is isolated from its source during the welding cycle there is little possibility of external influences on the performance due to the regulator or valve responses.

[0070] It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

[0071] Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples.

[0072] Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.

Claims

CLAIMSWhat is claimed is:1 . A resistance welding cell comprising: a frame; a welding actuator mounted to the frame and configured to move between retracted and welding positions relative to a workpiece; a follow-up actuator mounted to the welding actuator, the follow-up actuator having an extended chamber configured hold a follow-up rod in an extended position when in a pressurized state; a welding tool supported by the follow-up actuator, the welding tool configured to weld a fastener to the workpiece in the welding position in response to a welding current; an air supply system fluidly connected to the extended chamber and configured to maintain the pressurized state prior to a welding cycle; and a controller configured to command the welding actuator from the retracted position to the welding position to operatively engage the workpiece with the welding tool during the welding cycle, wherein the follow-up actuator maintains a welding force on the workpiece in the pressurized state during the welding cycle.

2. The cell of claim 1 , wherein the follow-up actuator is removably secured to the welding actuator, and the resistance welding tool is removably secured to a rod on the follow-up actuator, and the resistance welding tool is a resistance projection welding tool.

3. The cell of claim 1 , wherein the air supply system includes an air source configured to supply an air at a pressure below 100 psi, a pressure increasing device configured to increase the pressure of the air to above 120 psi, a reservoir configured to store the increased pressurized air, and at least one valve configured to regulate the flow of increased pressurized air to the follow-up actuator extended chamber to provide the pressurized state.

4. The cell of claim 1 , wherein at least one valve is configured to relieve pressurized air in the follow-up actuator extended chamber to provide the desired pressurized state.

5. The cell of claim 3, wherein the air supply system includes a pressure sensor configured to determine a sensed pressure in the air supply system, the controller in communication with the pressure sensor and configured to maintain the pressurized state for a subsequent welding cycle without re-pressurizing the extended chamber if the sensed pressure is above a predetermined value.

6. The cell of claim 1 , wherein the follow-up actuator includes a piston arranged in a cavity, the rod secured to the piston, the piston separating the cavity into the extended chamber and a vented chamber, the vented chamber configured to be in direct communication with atmospheric pressure.

7. The cell of claim 1 , wherein the follow-up actuator is arranged entirely outside of the welding actuator.

8. A high-speed follow-up actuator assembly comprising: a housing providing first and second cavities, the housing having a first mounting feature; first and second pistons respectively arranged in the first and second cavities and separating each of the first and second cavities into an extended chamber and a vented chamber, the extended chambers in fluid communication with a pressurized air source, and the vented chambers are configured to be continuously in fluid communication with atmospheric pressure; a rod extending from the housing to an end, the first and second pistons mounted to the rod, the rod having a second mounting feature; and wherein one of the first and second mounting features is configured to be secured to a welding actuator, and the other of the first and second mounting features is configured to facilitate securing of a welding tool.

9. The assembly of claim 8, comprising an air supply system comprising:an air source configured to supply an air at a pressure below 100 psi; a pressure increasing device configured to increase the pressure of the air to above 120 psi; and a reservoir configured to store the increased pressurized air, and at least one valve configured to regulate the flow of increased pressurized air to the extended chambers to provide the pressurized state.

10. The assembly of claim 9, wherein the air supply system includes a pressure sensor configured to determine a sensed pressure in the air supply system during a welding cycle, comprising a controller in communication with the pressure sensor and configured to monitor the signature of sensed pressure during a welding cycle.

11. The assembly of claim 10, wherein the controller is configured to maintain the pressurized state if the sensed pressure is higher or lower than a predetermined value.

12. The assembly of claim 11 , wherein the controller is configured to actuate the at least one valve to supply the increased pressurized air to the extended chambers to reacquire the pressurized state if the sensed pressure is below the predetermined value.

13. The assembly of claim 11 , wherein the controller is configured to actuate the at least one valve to relieve pressurized air within the extended chambers to reacquire the pressurized state if the sensed pressure is above the predetermined value.

14. The assembly of claim 8, wherein rod includes a bore extending from a terminal end toward the second mounting feature, the first and second pistons mounted to the rod, first and second holes respectively adjacent to the first and second pistons and in fluid communication with the extended chambers respectively of the first and second cavities.

15. The assembly of claim 8, wherein the rod includes first and second features along a length, and comprising a position sensor supported by the housing adjacent to the length, and comprising a controller in communication with the position sensor and configured to monitor the first and second features during a welding cycle.

16. The assembly of claim 8, comprising at least one non-metallic insulative bushings arranged in the housing and slidably supporting the rod.

17. The assembly of claim 8, wherein the first and second pistons each include an annular recess on a face exposed to at least one of the extended and vented chambers.

18. A method of welding a resistance welding fastener, comprising: pre-charging an extended chamber in a follow-up actuator with air to a pressurized state, the follow-up actuator supporting a resistance welding tool; advancing a welding actuator carrying the follow-up actuator, the welding tool, and a fastener to engage a workpiece; applying a welding current to the fastener and workpiece during a welding cycle; and maintaining a welding force on the fastener and workpiece with the follow-up actuator in the pressurized state during the welding cycle.

19. The method of claim 18, wherein the air within the extending chamber in the pressurized state is in a range of 150 psi to 300 psi.

20. The method of claim 19, wherein the air is compressed during the maintaining step, and the advancing, applying and maintaining steps are performed in a subsequent welding cycle without re-pressurizing the extended chamber.

21. The method of claim 18, wherein the follow-up actuator includes a rod supported by a piston in communication with the extended chamber, a position sensoradjacent to a length of the rod, the current applying step is performed based on a sensed position of the rod by the position sensor.

22. The method of claim 18, wherein the pre-charging step is performed prior to the advancing, applying and maintaining steps.

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