Patent Abstract:
An actuator assembly for a welding gun is provided that has at least three positions in the example. The actuator assembly includes separate working and retract actuators. The working actuator includes a working rod movable between first and second positions. The retract actuator includes a retract rod independently movable relative to the working rod between third and fourth positions. The retract actuator is external to and non-concentrically arranged relative to the working actuator in the example shown. Actuation of the working and retract actuators is coordinated to provide at least three positions while enabling the actuators to be changed or modified independently from one another. A latching device is configured to selectively interlock the working and retract actuators to one another automatically in response to movement the working rod from the first position to the second position.

Full Description:
BACKGROUND 
     The application relates to an actuator assembly suitable for use with a resistance welding gun. More specifically the application relates to a resistance welding gun actuator assembly that incorporates an external retract mechanism and an adaptable welding cylinder. 
     Retracting welding guns are well known in the industry and are commonly applied when the welding gun must reach over the workpiece or tooling to weld on a far side. An intermediate or retracted electrode position eliminates the time that might be wasted to fully open the electrodes at each spot to be welded on the workpiece. Retracting welding guns are also used when the space inside of the workpiece or tool is constrained and does not permit full opening of the electrodes. 
     It is common to provide a single retract position in such welding guns. To properly position the resistance welding electrodes relative to the workpiece, the stroke of the retract cylinder may have to be adapted from time to time to accommodate such things as the specific access condition or length of the welding gun arms. In the prior art designs of singular construction where the retract and welding cylinders are integrated, such adaptations can result in a large number of actuators within a particular manufacturing plant. These actuators are also large and expensive because of the high degree of customization. 
     What is needed is an actuator assembly that is compact, easily adaptable between various applications and less expensive. 
     SUMMARY 
     An actuator assembly for a welding gun is provided that has at least three positions in the example. The actuator assembly includes separate working and retract actuators. The working actuator includes a working rod movable between first and second positions. The retract actuator includes a retract rod independently movable relative to the working rod between third and fourth positions. The retract actuator is external to and non-concentrically arranged relative to the working actuator in the example shown. Actuation of the working and retract actuators is coordinated to provide at least three positions while enabling the actuators to be changed or modified independently from one another. 
     A latching device is configured to selectively interlock the working and retract actuators to one another automatically in response to movement the working rod from the first position to the second position. As a result, a separate actuation device is not required to lock the working and retract actuators relative to one another. 
     These and other features of the application can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a welding gun with an example actuator assembly. 
         FIG. 2  is a cross-sectional view of the actuator assembly in  FIG. 1  taken along line  2 - 2 . 
         FIG. 3  is a cross-sectional view of the actuator assembly in  FIG. 2  taken along line  3 - 3 . 
         FIG. 4  is an enlarged cross-sectional view of the actuator assembly shown in  FIG. 2  in a return position. 
         FIG. 5  is cross-sectional view of the actuator assembly shown in  FIG. 4  in a retract position. 
         FIG. 6  is cross-sectional view of the actuator assembly shown in  FIG. 4  in an advance position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A welding gun  10  is shown in  FIG. 1 , which is manipulated using an example actuator assembly  12 . It should be understood that, although the actuator assembly  12  is shown configured for use with a welding gun, the actuator assembly  12  also could be used with riveting tools, clinching and metalworking tools, and other applications. 
     The actuator assembly  12  is secured to a support  14  that includes a rotary bail  16 , which rotationally orients the welding gun  10  relative to a workpiece (not shown) to a desired position. Opposing arms  18  rotate relative to one another about a pivot  20  to close electrodes  22  about the workpiece in a desired manner, as is known. In the example, one of the arms  18  is fixed and the other of the arms  18  is movable relative to the fixed arm. A transformer  24  supplies current to the electrodes  22  to spot-weld the workpiece. 
     In one example configuration, the actuator assembly  12  includes a working actuator  28  and a retract actuator  30  that cooperate with one another to move the electrodes  22  between three or more positions (corresponding to L 1 -L 3  shown in  FIGS. 4-6 ). While a push-type arrangement is shown, it should be understood that the actuator assembly  12  could be configured to a pull-type configuration and still fall within the scope of this application. According, the terms “return,” “retract” and “advance” are meant as relative positions and should be construed broadly. Furthermore, although the example working and retract actuators  28 ,  30  are illustrated as pneumatic cylinders, pneumatic, hydraulic, air-over-oil, electric servo actuators or any combination thereof may also be used. 
     Referring to  FIG. 2 , first and second fluid sources  32 ,  34  selectively provide pressurized fluid to the working and retract actuators  28 ,  30  in response to commands from a controller  36 . Of course, more or fewer fluid sources can be used in conjunction with control valves and vents may be employed to obtain desired movement of the working and retract actuators  28 ,  30 , which is within the scope of one of ordinary skill in the art. The working and retract actuators  28 ,  30  are manipulated independently from one another and can be optimized separately based upon the particular application without requiring an entirely new integrated actuator, as required by the prior art. 
     The working and retract actuators  28 ,  30  respectively include working and retract rods  38 ,  40  that cooperate to manipulate the electrodes  22  through various positions. The working and retract rods  38 ,  40  are non-concentric and parallel in the example shown. An end of the working rod  38  is connected to the movable arm  18 . In the example, a retract actuator  30  is arranged on each of opposing sides of the working cylinder  28 . The number and size of the retract actuators  30  is selected based upon the particular application. The retract rods  40  are secured to the mounting plate  26  by blocks  42 . The working rod  38  extends through an aperture in the mounting plate  26  between the blocks  42 . Brackets  44  secure the retract actuators  30  to the working actuator  28 . 
     The working actuator  28  includes a front block  46  that supports the working rod  38  for axial movement. In the example, the working actuator  28  includes an adaptable cylinder  47  having multiple sections  48 , the number and size of which are selected based upon the desired force for the particular application. Each section  48  includes a cavity  50  having a piston  52  that is connected to the working rod  38 . The working rod  38  is moved axially in fore and aft directions in response to selective pressurization of the chambers on either side of the pistons  52 , as is known. 
     The retract actuator  30  includes a retract cylinder  54  that includes a piston  58  arranged in a cavity  56 . The piston  58  is connected to the retract rod  40 , which is moved axially in the fore and aft directions relative to the retract cylinder  54  in response to selective pressurization of the chambers on either side of the piston  58 , as is known. 
     Referring to  FIGS. 2 and 3 , a latching device  59  is used to affix the front block  46  of the working actuator  28  relative to the mounting plate  26  once the retract actuators  30  have been moved from a return position ( FIGS. 2 and 4 ) to a retract position ( FIG. 5 ). The latching device  59  is shown unlatched in the retract position ( FIG. 5 ) and latched in an advance position ( FIG. 6 ). The retract actuators  30  are mechanically linked to the position of the working rod  38  through the latching device  59 , which latches automatically, to obtain a desired response time and to eliminate separate control elements of some prior art arrangements. 
     The latching device  59  includes opposing plungers  62  received in bores  64  in the front block  46 . The plungers  62  have inner ends that are in engagement with the outer surface of the working rod  38 . The plungers  62  are arrange normal to the working rod  38  and are received in detents  60  in the outer surface when the working rod  38  is positioned as shown in the return and retract positions ( FIGS. 4 and 5 , respectively). 
     The plungers  62  include latches  66  supported at ends opposite the detents  60 . The latches  66  are configured to engage recesses  68  in the blocks  42  when the plungers  62  are forced radially outward relative to the working rod  38  as the working rod moves axially to unseat the plungers  62  from the detents  60 , as shown in the advance position ( FIG. 6 ). Guide pins  74  are secured to each latch  66  and extend through holes  72  in a plate  70  that is secured to the front block  46 . Springs  76  cooperate with the guide pins  74  to bias the latches  66  toward the detents  60 . 
     Referring to  FIGS. 4-6 , the example actuator assembly  12  works by using two retract actuators  30  mounted independently of the main working actuator  28  to provide retract motion ( FIG. 5 ) for the assembly, which provides an intermediate position for improved cycle times.  FIG. 4  show the latches  66  in their retracted position with the ends of the plungers  62  resting in detents  60  in the working rod  38 . When the retract actuators  30  are advanced as in  FIG. 5 , the latching device  59  is aligned so that the working rod  38  can be advanced and the latches  66  engaged. When the working rod  38  is advanced the detents  60  actuate the two plungers  62  that in turn cause the two latches  66  to lock the assembly into retract position. The working rod  38  then proceeds to advance the electrodes towards the workpiece as shown in  FIG. 6 . 
     Example operation of the welding gun  10  with the example actuator assembly  12  is as follows: 
     Return Position 
     Compressed air or other suitable fluid is applied to the return port of the retract cylinders  54  causing the retract rods  40  to extend to a point where the piston  58  is pressing against the end of the cylinder  54 . In this position ( FIG. 4 ) the distance between the moveable mounting plate  26  and the latching device  59  are at the maximum separation. At the same time the working actuator  28  has air from another fluid power valve acting against its piston  52 , causing the working rod  38  to be fully returned (distance L 1 ). The combination of both of these cylinder positions results in the maximum amount of welding electrode opening. 
     Retract (Intermediate) Position 
     The return port is vented to atmosphere while compressed air is applied to the retract port of the retract cylinders  54 . This causes the retract rods  40  to retreat inside the retract cylinders  54  and to pull the mounting plate  26  relatively towards the latching device  59  ( FIG. 5 ) moving the working rod  38  to a distance L 2  relative to the mounting plate  26 . This causes the welding electrodes  22  to move towards each other. During this motion the return air is maintained on the welding cylinder return port(s). 
     Advanced (Welding) Position 
     When the retract position has been achieved, compressed air is applied to the working actuator  28  to advance the working rod  38  to an axial distance L 3 . This causes the latches  66  to advance to prevent the working actuator  28  from working against the retract actuators  30 . As the working rod  38  continues to advance, the welding electrodes  22  are brought into contact with the workpiece with sufficient force to conduct the resistance welding process. 
     Return Position Subsequent to Advanced Position 
     At the completion of the welding process, if the fully returned position of the electrodes  22  is desired, the retract and weld stroke ports are vented to atmosphere and air is applied to the return ports. Once the working rod  38  has started to return causing the latching device  59  to disengage, the retract cylinder return port can be pressurized, thereby fully returning the unit. If opening the welding gun only to the retracted position is desired, the air is retained on the retract advance port and the air is applied to the welding cylinder return port. This will retract the electrodes  22  sufficiently to allow moving to the next weld position. 
     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.

Technology Classification (CPC): 8