Abstract:
An improved inspection system for verifying that resistance welding electrodes have been properly dressed; that associated pairs of the electrodes are aligned with each other within predetermined tolerances; and that the pressure applied by a weld gun to the electrodes and material being welded is within predetermined standards. The system incorporates low pressure air apparatus that evaluates the back pressure resulting from the fit of collet geometry relative to the form of the electrode tip, and apparatus to verify the alignment of opposing electrodes with respect to each other and incorporating fiber-optic sensors that evaluate the alignment of collets with respect to each other. The system also provides apparatus for verifying that the proper pressure is applied to the workpieces by the electrodes during the welding operation.

Description:
BRIEF SUMMARY OF THE INVENTION 
     This invention relates to systems for inspecting resistance welding electrodes and, more particularly, to an improved inspection system for verifying that resistance welding electrodes have been properly dressed by an electrode tip dresser; that associated electrodes when installed in a weld gun are aligned with each other within predetermined tolerances; and that the weld pressure provided by the weld gun is within predetermined tolerances. 
     As is well known in the art, during resistance welding processes the tips of the electrodes tend to mushroom (flatten) due to the pressures applied by the associated weld gun and the heat generated by the electrical current that passes through the electrode tips. Also, for example, in the case of welding galvanized steel, a build-up of the brass alloy will form on the surface of the electrode tips. Both of such conditions are causes of poor welds being produced. Consequently, the electrode tips must be dressed periodically to insure that the tip configuration is maintained within predetermined tolerances. As is also well known in the art, in automated welding systems the use of automatic electrode tip dressers has been developed. Although the automated tip dressers are reliable there are cases in which the electrode tips are not properly dressed or are not dressed at all, because of broken or dull dresser cutter blades or other factors. 
     It is also well known in the art of resistance welding that correct alignment of the electrode tips is essential for good tip life and quality of weld. Loss of alignment may indicate that some part of the weld gun or head is not tightly secured or the electrode shank may have become bent in operation. Electrode pressure applied by the weld tips to the workpiece is also very important in producing successful welds. If the weld pressure is not maintained within predetermined parameters and the pressure is greater than required to produce a good weld, a shortened tip life may result. On the other hand, if the pressure is less than required the weld electrodes may not bring the two sheets of workpiece material together so that a proper weld may be made. Electrode tips that are not properly dressed or that are not properly aligned or if the weld pressure is not correct can result in welds of poor quality, and in some cases no welds whatsoever are produced. Consequently, the resulting substandard parts can have various types of negative consequences, such as requiring the reworking of parts, added costs, necessity of parts sorting, possible liability issues, poor customer relations and other adverse consequences. 
     An object of the present invention is to overcome the aforementioned problems which can be created when the tips of resistance welding electrodes are not properly dressed or are not properly aligned or when an improper weld pressure is applied to the associated workpieces, and to provide an improved inspection system for verifying that resistance welding electrode tips have been properly dressed, properly aligned, and that proper weld pressure has been applied to the workpieces thereby reducing the risks involved in the spot welding of metal components, and also reducing the problems that can be caused by welding with electrodes having tips that are not properly dressed, or are not properly aligned, or without proper weld pressure being applied to the workpieces. 
     Another object of the present invention is to provide an improved inspection system incorporating novel low pressure air sensing means for evaluating welding electrode tip faces, physical shape and condition, and the relationship of such tips to predetermined criteria. 
     Another object of the present invention is to provide an improved inspection system incorporating low pressure air sensing means capable of simultaneously sensing two opposing electrode tips to evaluate the suitability thereof for continuing welding operations satisfying predetermined standards. 
     Another object of the present invention is to provide an improved inspection system embodying low pressure air sensing means incorporating interchangeable collets permitting the inspection of welding electrodes of various sizes and shapes merely by interchanging the collets. 
     Another object of the present invention is to provide an improved inspection system that permits two welding electrodes of different sizes and shapes to be inspected at the same time. 
     A further object of the present invention is to provide an improved inspection system for verifying that the tips of welding electrodes have been properly dressed, and which system is capable of being mounted in close proximity to an electrode tip dresser machine and/or a welding gun. 
     Another object of the present invention is to provide an improved inspection system for verifying that the tips of welding electrodes are in correct alignment with each other within predetermined criteria. 
     A further object of the present invention is to provide an improved inspection system for verifying that the pressure applied to the workpieces by the electrodes is correct in accordance with predetermined requirements. 
     Another object of the present invention is to provide an improved inspection system that will verify weld tip geometry, weld tip alignment and weld tip pressure all simultaneously. 
     A further object of the present invention is provide an improved inspection system that will provide an output signal to a machine controller respecting whether the electrode tips meet predetermined requirements concerning tip alignment, tip geometry and weld pressure. 
     Yet another object of the present invention is provide an improved inspection system that is relatively easy to manufacture and assemble at economical cost while providing long life and reliable operation. 
     The above as well as other objects and advantages of the present invention will become apparent from the following description, the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a control unit that may be used in the inspection system embodying the present invention; 
     FIG. 2 is a schematic elevational view of a portion of the inspection system embodying the present invention, showing the same in relationship with respect to a welding gun having opposed welding electrodes; 
     FIG. 3 is an enlarged perspective view of components of the inspection system illustrated in FIG. 2; 
     FIG. 4 is a longitudinal, sectional view of portions of the structures illustrated in FIGS. 2 and 3; 
     FIG. 5 is a cross-sectional view of a portion of the structure illustrated in FIG.  4  and illustrating a properly dressed welding electrode tip inserted therein; 
     FIG. 6 is a cross-sectional view similar to FIG.  5  and illustrating an improperly dressed electrode tip inserted therein; 
     FIG. 7 is a cross-sectional view of another embodiment of the invention and illustrating a light path when the weld electrodes are properly aligned; 
     FIG. 8 is a cross-sectional view similar to FIG.  7  and illustrating a light path when the weld electrodes are improperly aligned; 
     FIG. 9 is a top view of the structure illustrated in FIG. 7; 
     FIG. 10 is a sectional view of another embodiment of the invention incorporating a support column to control the depth of penetration of an electrode if the face thereof is too small; 
     FIG. 11 is a sectional view of another embodiment of the invention having a pair of collets incorporating a secondary air passageway in each collet to verify the diameter of the electrode tip; and 
     FIG. 12 is an exploded sectional view of a portion of the structure illustrated in FIG.  11 . 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings, the present invention is illustrated as embodied in an inspection system, generally designated  10 , which is particularly adapted for use in verifying that resistance welding electrodes have been properly dressed by an electrode tip dresser; that the electrode tip geometry is suitable for welding operations; that opposed electrodes are aligned with each other within predetermined tolerances; and that the weld gun applies the appropriate pressure to obtain a satisfactory spot weld, i.e. the weld pressure exerted by the weld gun meets predetermined criteria. It will be understood however that the present invention is also applicable to other uses. 
     Referring to FIG. 1 of the drawings, a control unit, generally designated  15 , is illustrated therein that may be used in the inspection system  10 . The control unit  15  may be of the type illustrated and described in U.S. Pat. No. 5,814,720, issued to the inventor of the present application on Sept. 29, 1998 for an Air Pressure Sensor Control System, and the entire disclosure of U.S. Pat. No. 5,814,720 is hereby incorporated herein by reference. The control unit  15  includes a bulkhead fitting  12  which is adapted to be connected to a suitable source of air pressure (not shown), the air pressure preferably being supplied at 60-120 PSIG with suitable air filtering whereby dirt particles and other foreign matter are removed from the incoming air. The air flows from the bulkhead fitting  12  through a hose  14  to a conventional air pressure regulator  16  incorporating a conventional air pressure gauge  18 . The air pressure regulator functions to reduce the operating pressure required to operate the system to approximately 0.5 to 8 PSIG depending upon the particular application. The low pressure air is then delivered into a common port manifold  20  through the agency of a hose  22 , the common port manifold being equipped with suitable needle valves, such as  24 , from which the volume of air is then delivered via hoses, such as  26 ,  28 ,  30  and  32  to the inlet end portions of associated switch air passageways internally defined by an electro-pneumatic interface module  38 , four such switch air passageways being internally defined by the electro-pneumatic interface module illustrated in FIG. 1 of the drawings. 
     The internal switch air passageways communicate with conventional pneumatic/electric switches  42  which are adapted to open and close as a function of variations in the air pressure in the switch air passageways. Each pneumatic/electric switch  42  (four such switches being illustrated in FIG. 1 of the drawings) is electrically connected to a terminal block  44  through the agency of wires, such as  46 , the terminal block  44 , in turn, being connected to a conventional programmable logic controller  48  by wires such as  50 , a relay  52  being provided to relay appropriate signals to a welding machine or other equipment being controlled by the air pressure sensor control unit  15 . The air entering the inlet of each switch air passageway flows through such passageway and exits the switch air passageway through hoses such as  54  and  56  to a terminal fitting, such as  58 , connected to a sensor  116  as will be described hereinafter in greater detail. 
     A conventional weld gun  118  is schematically illustrated in FIG. 2 of the drawings, the gun having an upper electrode  120  and a lower electrode  122  which cooperate with each other to resistance weld workpieces disposed between the electrodes  120  and  122  which must be properly dressed through the agency of an automatic electrode tip dresser or other suitable dresser means. The inspection system  10  embodying the present invention may be mounted in close proximity to the weld gun  118  as illustrated in FIG. 2 of the drawings, or the inspection system may be mounted on a dresser machine framework or on a separate pedestal as desired. 
     In addition to the control unit  15 , previously described, the inspection system  10  includes a sensor  116  which is connected by air hoses, such as  56 , to the control unit  15 . The sensor  116  includes a high precision combined light generating and reflected light sensing unit  114  which may be of the type commercially identified as “STM Sensor Incorporated,” Model V6A Optic Amplifier, available from Industrial Control, Inc., Zeeland, Mich. 49464. The unit  114  has a light generating and reflected light cable head  128  effective to detect misalignment of the electrodes as will be described hereinafter in greater detail. A force load cell  182  is also provided which may be identified as “Cooper Instruments and Systems,” Model LZBS 1010 2K, also available from Industrial Control, Inc., Zeeland, Mich. 49464. 
     The sensor  116  includes a top plate  124  and a bottom plate  126 , and the sensor  116  is connected to a manifold  112  by air passageways in the top plate  124  and bottom plate  126 , respectively. Inlet ports such as  142  and  143  on the side of the manifold  112  are connected by air hoses, such as  56 , to the control unit  15 . Means is also provided for back pressure developed at the sensor  116  to be communicated to the control unit  15 . The air entering the passageways  173 A and  173 B and  175 A and  175 B defined by the sensor  116  flows through such passageways and exits to atmosphere if there is no obstruction of orifices defined by the sensor  116 , as will be described hereinafter in greater detail. If there is an obstruction of an orifice, the air will be blocked from exiting the sensor  116  whereupon the associated pneumatic/electric switch  42  will be actuated due to the increase in back pressure thereby providing a circuit to the programmable logic controller  48 , the programmable logic controller, in turn, controlling a welding machine or other equipment through the agency of the relay  52 . It should also be understood that the air volume for each air passageway in the sensor  116  may be adjusted through the agency of the needle valves  24  which control the flow of air through the common port manifold  20 . It should also be pointed out that, if desired, the main components of the control unit  15  may be housed in a conventional NEMA enclosure  60  with the hoses  56  projecting from the enclosure  60 . 
     As shown in the drawings, the sensor  116  includes a pair of interchangeable collets  164  and  166  which are mounted on one end portion of the elongated mounting plates  124  and  126  and retained therein through the agency of retainer rings  136  and  137 , respectively, secured to the mounting plates  124  and  126 , as by screws  138  as illustrated. The mounting plates  124  and  126  are preferably made of aluminum or of any other suitable material having sufficient strength to withstand the forces exerted thereon. As shown in FIGS. 2 and 3 of the drawings, the other end portions of the mounting plates support the amplifier  114  and the manifold  112 . 
     The collets  164  and  166  define concave cavities  168  and  170  of a configuration that is complementary to the face of the tip of the particular electrode being inspected. It will be understood that there are numerous sizes and shapes of welding electrodes that can be used in resistance welding processes, and the collets  164  and  166  are preferably made of hardened steel to resist wear and also withstand the forces applied thereto. As shown in FIG. 4, the collets preferably have a taper  154  at the mouth side thereof to assist in aligning the electrodes with the shaped cavity in the collets. As shown in the drawings, the collets  164  and  166  define a pair of passageways  172  and  174 . One end of the passageway  172  communicates with the cavity  168  while the other end of the passageway  172  communicates with a passageway  173 B connected to the control unit  15  by the passageway  173 A and a hose  56 . One end of the passageway  174  communicates with the cavity  170  while the other end of the passageway  174  communicates with a passageway  175 B which in turn is connected to the control unit  15  by the passageway  175 A and a hose  56 . When the electrode is properly dressed it will restrict the flow of air through the passageways  178  and  180  thereby causing an increase in back pressure in the sensor back to the control unit  15 . The vents  178  and  180  provided in each of the collets allow air to escape to the atmosphere if an electrode tip is not properly dressed and therefore will not create an increase in back pressure within the control system. 
     As is well known in the art, standard welding electrodes are supplied in different diameters and different tip geometries, and special shapes are often produced to meet specific requirements. The inspection system embodying the present invention requires that only the collets need to be changed to match the selected electrodes required for any particular welding application. It will be understood that both of the collets may be of the same configuration or may be of different configurations or they may be matched to any combination of electrodes as required by the particular welding operation. 
     As is well known in the art, the electrodes  120  and  122  must be aligned with each other to obtain a satisfactory weld. As shown in FIGS. 4,  7  and  8 , light emitted from  128  will pass through the passageways  194  and  196  if the electrodes are aligned within predetermined values. When the electrodes are disposed in the cavities  168  and  170  and are misaligned, the collets are allowed to shift laterally within the mounting plates causing a misalignment between the passageways  194  and  196 . The light generated by the cable head  128  will be reflected by the surface of the collet  166  and through the associated passageway  194  back to the cable head  128  and thereafter will be transmitted back to the amplifier  114 . The unit  114  will provide an output to the machine controller (not shown) so that in a conventional manner the machine controller can sound an alarm and/or shut down the welding operation and/or otherwise alert the user thereof that the electrode alignment did not pass inspection. 
     As previously mentioned, the collets  164  and  166  are enabled to shift laterally in relationship to each other. Alignment springs, such as  186 , each in the form of a flexible plug are provided which allow the collets  164  and  166  to reposition themselves when a dislocation force is applied and will return the collets  164  and  166  back to center line with each other when the dislocation force is removed. “O” rings  188  and  190  are provided to maintain the collets on center line within the sensor  116 . When a dislocation force is applied the “O” rings  188  and  190  will collapse and the “O” ring portion on the opposite side of the collet will expand. When the dislocation force is removed the two collets  164  and  166  will return to their neutral position on center line of the sensor  116 . The fiber optic cable head  128  emits a light beam which beam passes through the passage ways  194  and  196 . If the collets  164  and  166  are aligned within predetermined tolerances no output signal will be made. If the collets  164  and  166  are misaligned beyond the acceptable tolerances the light beam emitted from the passageway  194  will impinge on the adjacent surface of the collet  166 . The light is reflected by such surface back through the passageway  194  to the cable head  128  and transmitted back to the unit  114  through the cable  130  and an output signal will be sent to the machine controller. 
     As is well known in the art, the force of the electrodes bearing on the sheet metal must be maintained with respect to predetermined values. If the force is less than required, the electrodes may not bring the two sheets together so that a weld may be made. If the pressure is too high, the tip of the electrode will mushroom at a faster rate and may also cause excessive indentations in the surface of metal being welded. The embodiment of the invention illustrated in FIG. 4 includes a force sensor  182  positioned between the collets  164  and  166 , during inspection of the electrodes, the electrodes  120  and  122  are disposed in the cavities  168  and  170  defined by the collets  164  and  166 . Pressure is then applied by the weld gun as if it were in the weld position. The value of the force applied by the collets  164  and  166  to the force sensor  182  is transmitted by the cable  146  to a conventional amplifier and digital display (not shown) in the machine controller for evaluation by the machine operator. 
     FIG. 5 illustrates the manner in which a properly dressed electrode blocks the passageway  172  and the entrance to the passageway  178  thereby preventing the escape of air to atmosphere through the passageway  178  and providing a circuit to the programmable logic controller  48  in the manner previously described. FIG. 6 illustrates the condition in which an improperly dressed electrode fails to block the passageway  172  and the entrance to the passageway  178  thereby permitting air to escape to atmosphere through the passageway  178  with the result that there will not be an increase in the air back pressure which can be communicated to the unit  15  in the manner previously described. 
     FIG. 10 illustrates an embodiment of the invention wherein support pins  169  and  171  are provided to control the depth of penetration of an electrode into the cavities  168  and  170  if the face of the electrode is too small. This prevents the passageways  172  and  174  from being restricted, and air will flow through the passageways  178  and  180  to atmosphere in the manner previously described. 
     In the embodiment of the invention illustrated in FIGS. 11 and 12, collets  164 C and  166 C are provided, the collet  164 C defining concentric air passageways  172 C and  172 D communicating with the cavity  168 C while the collet  166 C defines concentric air passageways  174 C and  174 D communicating with the cavity  170 C. The collet  164 C also defines an air passageway  178 C one end of which communicates with the cavity  168 C while the other end of the passageway  178 C communicates with atmosphere. The collet  166 C also defines an air passageway  180 C one end of which communicates with the cavity  170 C while the other end of the passageway  180 C communicates with atmosphere. 
     In this embodiment of the invention, as shown in FIGS. 11 and 12, the collet  164 C defines an air passageway  173 C one end of which communicates with the air passageway  172 C while the other end of the passageway is connected to the control unit  15  through the passageway  173 D. The collet  164 C also defines an air passageway  173 E one end of which communicates with the passageway  172 D while the other end of the passageway  173 E is connected to the control unit  15  through the passageway  173 F. The collet  166 C defines an air passageway  175 C one end of which communicates with the passageway  174 C while the other end of the passageway  175 C is connected to the control unit  15  through the passageway  175 D. The collet  166 C also defines an air passageway  175 E one end of which communicates with the passageway  174 D while the other end of the passageway  175 E is connected to the control unit  15  through the passageway  175 F. 
     In this embodiment of the invention if the tip of an electrode inserted in the cavity  168 C blocks the passageway  172 D, such blockage indicates that the tip is too large, and such blockage is communicated to the control unit  15  through the passageways  173 E and  173 F in the manner previously described, the control unit  15  in turn being programmed so as to indicate that the tip of the electrode has blocked the passageway  172 D. On the other hand, if the tip of an electrode inserted in the cavity  168 C blocks the passageway  172 C, such blockage indicates that the electrode is properly dressed as described herein above. It will be understood that similar results will be obtained if the tip of an electrode is inserted in the cavity  170 C, the manner of operation of the collet  166 C and the associated structure described hereinabove will correspond with the manner of operation of the collet  164 C and the associated structure described hereinabove. 
     While preferred embodiments of the invention have been illustrated and described, it will be understood that various changes and modifications may be made without departing from the spirit of the invention.