AU4981796A

AU4981796A - Positioning and electromagnetic clamping device for welder

Info

Publication number: AU4981796A
Application number: AU49817/96A
Authority: AU
Inventors: Emanuel Liebzon; Abraham Liran; Keith O. Stuart
Original assignee: Aura Systems Inc
Current assignee: Aura Systems Inc
Priority date: 1995-02-21
Filing date: 1996-02-15
Publication date: 1996-09-11
Also published as: EP0812248A1; KR19980702351A; JPH11500068A; CA2213271A1; EP0812248A4; WO1996026038A1; MX9706392A

Description

POSITIONING AND ELECTROMAGNETIC CLAMPING

DEVICE FOR WELDER

FIELD OF THE INVENTION

The present invention relates generally to a combination 10 device for positioning and clamping electrodes into a predetermined location on a workpiece for a weldhead, and more particularly to a device using a ball screw motor and an electromagnetic clamping device for positioning and clamping electrodes into a predetermined position on a workpiece for a i s weldhead.

BACKGROUND OF THE INVENTION

Robotized welding stations are widely used, for example 0 in automotive production lines. The welding stations typically use a commercially available welding gun mounted to an arm of a robot.

As shown in Figure 1 , the typical welding gun 10 has an 5 upper hand 12 and a lower hand 14 that are moveable around a pivot 16. Upper and lower electrode holder arms 18,20 are mounted in the upper and lower hands, respectively. An upper and a lower electrode 22, 24 are mounted on the upper and lower electrode holder arms, respectively, in a manner that 0 allows them to clamp a workpiece 26. The upper hand 12 is pivoted or moved into position to hold the workpiece, and then the upper and lower electrode holder arms apply a clamping force to allow the welding to occur. The pivoting and application of the clamping force is typically completed by a pneumatic cylinder 28. More specifically, a ram 30 of a pneumatic cylinder is connected to the upper hand 12 to pivot the upper hand with respect to the ? pivot in order to move the electrodes to and from the workpiece. A pneumatic locking device, not shown in Figure 1 , is then used to engage the ram and lock the electrodes in position. The locking device optimally prevents any movement of the electrodes during the welding process. Expansion of the t o weld nugget on the workpiece during the welding process may cause movement of the electrodes and result in a defective weld. It is therefore very important that the electrodes do not move during the welding process. It is desirable, therefore, to provide a clamping force on the workpiece when the welding i s occurs. When pneumatic devices are used to provide the clamping force, slow pressure build-up may occur as a result of the length of the air lines, the distance of the pressure reservoir and restrictions in the air lines.

0 By way of example, in one type of prior art pneumatic locking device a brake rod having a plurality of friction wedges extends into an axial bore in an interior end of the ram. The brake rod has a frustro-conical shaped end portion extending axially from the friction wedges. A piston is operable to move 5 the end portion inwardly between the friction wedges to displace the wedges outwardly against an inner surface of the bore of the ram. The piston is displaced to engage the brake by the introduction of pressurized air from a first port, and the locking device is released by the introduction of pressurized air from a second port.

A problem with pneumatic locking devices, however, is that the pneumatic device requires special piping and compressors to operate. Moreover, it is difficult to obtain the 5 necessary amount of consistent clamping force on the workpiece using pneumatics. Therefore, a need exists for an electrode positioning and clamping device that accurately and quickly positions the electrodes and applies a large amount of force on the workpiece during the welding process.

The present invention ove rcomes the problems encountered with pneumatic positioning and locking devices by utilizing a positioning actuator to move the electrodes into the predete rm ined position on the workpiece and an electromagnetic device to clamp the electrodes onto the workpiece.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to overcome one or more disadvantages and limitations of the prior art.

A significant object of the present invention is to provide a device that accurately and quickly positions the electrodes into a predetermined position on a workpiece and applies a substantial amount of force onto the workpiece to prevent movement of the workpiece during the welding process.

According to a broad aspect of the present invention, an improvement in an electrical resistance welding apparatus that includes a welder having a frame and a hand for moving electrodes into and out of clamping engagement with a workpiece includes an electrode positioning actuator for moving the welder hand in order to move the electrodes in and out of engagement with the workpiece and an electromagnetic clamping device for clamping the electrodes onto the workpiece du ring the formation of the weld . The electromagnetic clamping device includes an electromagnet mounted to.the positioning actuator and a ring of magnetic material mounted to the welder frame wherein the electromagnet and the ring are in a normally spaced 5 relationship when the electromagnet is deenergized and such that the ring is adjacent the electromagnet when the electrodes are in clamping engagement with the workpiece.

A feature of the present invention is that the 10 electromagnetic clamping device provides a high clamping force on the workpiece during the welding process that can be easily changed and controlled.

Another feature of the present invention is positioning i actuator of the device provides accurate positioning of the electrodes on the workpiece.

Another feature of the present invention is that the positioning actuator provides high speed motion to quickly o position the electrodes on the workpiece.

These and other objects, advantages and features of the present invention will become readily apparent to those skilled in the art from a study of the following description of an exemplary preferred embodiment when read in conjunction with the attached drawing and appended claims.

BRIEF DESCRIPTION OF THE DRAWING

0 Figure 1 is a side view of a conventional welder with which the present invention is used;

Figure 2 is a cross sectional view of the positioning and electromagnetic clamping device of the present invention; and 5 Figure 3 is a block diagram showing the control circuit of the positioning and electromagnetic clamping of the present invention .

DESCRIPTION OF AN EXEMPLARY PREFERRED EMBODIMENT

Referring now to Figure 1 , a known welder or welding gun

10 with which the positioning and electromagnetic clamping

10 device 40 is used is shown . The positioning and electromagnetic clamping device 40, shown in Figure 2, is preferably mounted to the upper hand 12 of the welder 10.

Referring now to Figure 2, the positioning actuator and i s electromagnetic device 40 is described in detail. The device 40 is a combination device utilizing both a positioning actuator 42 and a clamping device 44. The positioning actuator 42 preferably comprises a motor 46 and an acme or ball screw 48, and the electromagnetic clamping device 44 preferably 0 comprises an electromagnet 50 and a magnetic ring 52. The motor 46 preferably comprises a DC motor that is coupled to the ball screw 48. The ball screw 48 is coupled to the welder hand that positions the electrodes in a predetermined position on the workpiece. For example, in the welder shown in Figure 1. the ball screw 48 could be coupled to the lower hand 14. The DC motor 46 therefore turns the ball screw 48 which, in turn, extends or retracts the welder hand. The pitch of the ball screw and the RPM of the motor are selected to meet the speed requirements for positioning the electrodes on the work piece. 0 It should be noted that, if desired, other types of actuators may be used for positioning the electrodes in connection with the electromagnetic clamping device. For example, electromagnetic actuators, hydraulic actuators or pneumatic actuators may be used as posi tioning actuators in connection with the 5 electromagnetic clamping device. In another aspect of the present invention the electromagnetic clamping device 44 includes the electromagnet 50 and the magnetic ring 52. The electromagnet 50 is preferably mounted to a housing 54 of the positioning actuator 42. The electromagnet 50 is also preferably directly or indirectly coupled to the welding hand that positions the electrodes. The electromagnet 50 is preferably mounted in a coaxial relationship with the positioning actuator 42.

The magnetic ring 52 is preferably coupled to the frame 56 of the weldhead. The magnetic ring 52 has a substantially planar first surface 58 that extends perpendicular to the axis of movement of the positioning actuator.

The electromagnet 50 further comprises a core 60 and a coil 62. The core 60 has a substantially planar first face 64 extending perpendicular to the axis of movement of the positioning actuator. The coil 62 is disposed in an annular channel 65 in the first face 64 of the core 60. The core first face 64 is in a facing relationship to the magnetic ring first surface 58. The positioning of the electromagnet 50 and the magnetic ring 52 is determined so that the face 64 and surface 58 are adjacent each other with a predetermined gap 66 remaining therebetween when the positioning actuator is in its original retracted position. In the embodiment shown, the predetermined gap 66 is preferably a one to two and one-half millimeter gap.

The magnetic ring 52 and electromagnet 50 are provided to hold the positioning actuator in its fully extended position with the requisite force acting on the electrodes to hold them against the workpiece during the welding process. As will be described in greater detail hereinbelow, the electromagnet 50 is turned on by applying a current to the coil 62 upon the positioning actuator bringing the electrodes to their predetermined position on the electrodes and turned off when the welding process is completed so that the positioning actuator can return the electrodes to their retracted position to 5 initiate the next welding cycle. The magnetic force acting on the magnetic ring 52 when the electromagnet 50 is turned on is determined by the size of the electromagnet 50, the gap 66 between its face 64 and the surface of the magnetic ring 58, the area of the surface 58, the volume of the magnetic ring 58

10 and the level of the current in the coils. As a feature of the present invention, the electromagnet 50 and the magnetic ring 58 are coaxially disposed about the positioning actuator 42 so that the force exerted on the electrodes will be uniformly distributed. Another feature of the present invention is that i s the current in the coil of the electromagnet may be predetermined so that the clamping force of the electrodes against the workpiece may be predetermined and varied depending on the material used.

0 With reference to Fig. 3, a control system 68 of the positioning actuator and electromagnetic clamping device 40 is described. A controller 70 of the control system 68 is coupled to the positioning actuator's DC motor 46 through a driver 72, and to the electromagnetic clamping device 44 through a 5 current amplifier 74. The control system 68 further includes a load cell 76 for providing force feedback to the controller 70. The load cell 76 is mounted either external or internal to the positioning actuator 42. The controller 70 receives the force feedback from the load cell 76 and dynamically adjusts the level of current in the electromagnet coil 62 in order to maintain the proper pressure at the electromagnetic clamping device 44.

The sequence of operation of one embodiment of the 5 positioning actuator and clamping device is now described. First, the positioning actuator 42 is energized and actuates the welder arm of the welder moving the electrodes into their predetermined position on the workpiece. When the electrodes contact the workpiece, the positioning actuator motor applies a 5 force of approximately 300 pounds on the workpiece. The electromagnetic clamping device 44 is then energized, applying force across the gap 66 between the electromagnet core first face 64 and magnetic ring first surface 58. Because of the previously described mounting arrangement of the clamping t o device 44, this force is transferred to the electrodes. In the preferred embodiment, the electromagnetic clamping device 44 is capable of providing 1.500 pounds of force, as is required in some spot welding applications. After the welding process is completed, the clamping device 44 is deenergized and the i s positioning actuator 42 retracts the welder hand and electrodes from the workpiece.

There has been described hereinabove an exemplary preferred embodiment of the positioning and electromagnetic

20 clamping device according to the principles of the present invention. Those skilled in the art may now make numerous uses of, and departures from, the above-described embodiments without departing from the inventive concepts disclosed herein. Accordingly, the present invention is to be

25 defined solely by the scope of the following claims.

Claims

THE CLAIMS

I claim as my invention:

i 1 . An improvement in an electrical resistance welding

2 apparatus that includes a welder having a frame and a hand for moving electrodes into and out of clamping engagement with a 4 workpiece, said improvement comprising: an electromagnetic clamping device for clamping the electrodes onto the workpiece during the formation of the weld, said electromagnetic clamping device further comprising an electromagnet mounted to the welder hand and a ring of magnetic material mounted to the welder frame, wherein said o electromagnet and said ring are in a normally spaced i relationship when the electromagnet is deenergized and such 2 that said ring is adjacent said electromagnet when the 3 electrodes are in clamping engagement with the workpiece.

i 2. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 1 wherein said electromagnet further comprises a core, said core having a

4 first face and a channel defined within said first face, and a

5 coil, said coil disposed within said channel.

i 3. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 1 wherein said core includes a substantially planar first face and said magnetic ring includes a substantially planar first surface, wherein said

5 first face and said first surface are adjacent when the electrodes are in clamping engagement with the workpiece.

i 4. An improvement in an electrical resistance welding apparatus utilizing a welder having a hand for moving electrodes in and out of engagement with a workpiece, said improvement comprising: a positioning actuator coupled to the hand for moving the electrodes in and out of engagement with the 7 workpiece, wherein said actuator comprises a motor and a ball s screw coupled to said motor.

i 5. An improvement in an electrical resistance welding

2 apparatus that includes a welder having a frame and a hand for

3 moving electrodes into and out of clamping engagement with a

4 workpiece, said improvement comprising:

5 an electrode positioning actuator, said actuator

6 moving said welder hand in order to move the electrodes in and

7 out of engagement with the workpiece; and

8 an electromagnetic clamping device for clamping

9 the electrodes onto the workpiece during the formation of the

10 weld, said electromagnetic clamping device further comprising

1 1 an electromagnet mounted to.the positioning actuator and a i2 ring of magnetic material mounted to the welder frame i wherein said electromagnet and said ring are in a normally i4 spaced relationship when the electromagnet is deenergized and i5 such that said ring is adjacent said electromagnet when the i electrodes are in clamping engagement with the workpiece.

1 6. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 5 wherein said electromagnet further comprises a core, said core having a

4 first face and a channel defined within said first face, and a ? coil, said coil disposed within said channel.

i 7. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 5 wherein said core

3 includes a substantially planar first face and said magnetic

4 ring includes a substantially planar first surface, wherein said

5 first face and said first surface are adjacent when the

6 electrodes are in clamping engagement with the workpiece.

i 8. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 5 wherein said positioning

3 actuator comprises a motor and a ball screw coupled to said

4 motor. i 9. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 5 further comprising a

3 controller coupled to said positioning actuator and said

4 clamping device, wherein said controller provides current to

5 said clamping device and power to said positioning actuator.

1 1 0. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 9 further comprising a

3 load cell coupled to said controller, said load cell providing

4 feedback to the controller to allow the controller to adjust the

5 level of current applied to the clamping device.

i 1 1 . An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 10 wherein said load cell is mounted to said positioning actuator.

1 12. An improvement in an electrical resistance welding

2 apparatus in accordance with Claim 5 wherein said

3 electromagnetic clamping device is mounted coaxially with

4 said positioning actuator.

i 13. A control system for a welder having arms for

2 holding a workpiece comprising:

3 an electromagnetic actuator for positioning the arms of

4 the welder on the workpiece, said actuator having a motor;

5 an electromagnetic clamping device for providing a

6 clamping force through the welder arms on the workpiece, said

7 clamping device having a core and a coil; s a controller coupled to said actuator and said clamping

9 device for providing a control signal to the actuator and the

10 clamping device; and

1 1 a load cell coupled to said controller for providing a i 2 measurement of the clamping force on the workpiece to the i controller, wherein the controller adjusts the control signal 14 applied to the clamping device in response to the force i s measurement. i 14. A control system for a welder having arms for

2 holding a workpiece in accordance with Claim 13 further comprising a driver coupled to said motor and said controller

4 wherein the control signal is applied to the motor through the

5 driver.

1 15. A control system for a welder having arms for

2 holding a workpiece in accordance with Claim 13 further

3 comprising a current amplifier coupled to the controller and the clamping device, wherein the control signal is applied to

5 the clamping device through the amplifier.

I 16. A control system for a welder having arms for holding a workpiece in accordance with Claim 13 wherein said load cell is mounted to said actuator.