JP2012179657A - Spot welding method using spot welding gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spot welding method using a spot welding gun performable of spot welding in a condition in which fixed pressurizing force is applied constantly to a welding target workpiece, and enhancing the stability of welding quality.SOLUTION: When an operation parameter of the spot welding gun 16 is instructed in a condition without degradation due to secular change of a sliding mechanical part of the spot welding gun 16 with a pair of electrode tips 14a, 14b, a reference tip interval of the pair of the electrode tips 14a, 14b producing a favorable welding condition at a spot welding place of the welding target workpiece 11 is obtained. Moreover, when a prescribed spot welding place of the welding target workpiece 11 is actually welded, a tip interval of the pair of the electrode tips 14a, 14b is made equal to the reference tip interval by position control, and then, the spot welding place of the welding target workpiece 11 is held between the pair of the electrode tips 14a, 14b, and prescribed pressurizing force is added to the welding target workpiece 11 for welding.

Description

  The present invention relates to a spot welding method using a spot welding gun in which at least one of a pair of electrode tips is moved toward the other by a servo motor and welding is performed while a workpiece to be welded is sandwiched between the pair of electrode tips with a predetermined pressure. It is about.

  In spot welding using a spot welding gun, welding is performed in a state in which a predetermined pressing force is applied to an object to be welded between a pair of opposed movable electrode tips and opposed electrode tips. The facing distance between the pair of electrode chips is set to a predetermined distance by moving the movable electrode chip with respect to the facing electrode chip positioned at a predetermined position. Even in the case of a gun in which both of the pair of electrode chips are movable by a link mechanism or the like, the operation of the servomotor is controlled by either one of the electrode chips. The electrode chip controlled in this manner is referred to as a movable-side chip, and the other is referred to as a counter-side electrode chip.

  The movable electrode tip is controlled by a servo motor so as to move at a predetermined moving speed to a predetermined position in a direction in which the facing distance between the pair of electrode chips closes or opens. As a result, the workpiece is pressurized with a predetermined pressure between the pair of electrode tips, so that stable welding quality is maintained.

  However, it is known that a drive mechanism such as a servo motor and a speed reducer provided in a spot welding gun deteriorates due to aging such as wear of a sliding mechanism portion. That is, mechanical elements such as ball screws and bearings change over time due to failure or wear as they are used for a long time. When the secular change occurs, the pressurizing force in the welding gun is lowered. In such a case, the welding robot is diagnosed by measuring the applied pressure at a predetermined timing, and parameters and calibration are adjusted so that the welding quality does not deteriorate.

  As an example of another method, there is disclosed a method of controlling the pressure of a welding gun by detecting the actual pressure and correcting the protruding amount of the electrode (for example, Patent Document 1). In Patent Document 1, “From a motor current signal fed back so that a motor current command value can be calculated from an arbitrary set pressing force in a pressurizing current command circuit and converted from a welding motor current value to an actual pressing force. An actual pressing force is calculated, and when there is a difference between the arbitrary set pressing force and the calculated actual pressing force, the protruding amount of the one electrode is corrected, and the protruding amount of the one electrode is determined by the welding It was calculated by multiplying the deflection amount coefficient Ct of the gun arm by the difference between the arbitrary set pressure and the calculated actual pressure ”.

Japanese Patent Laid-Open No. 06-312273 (page 2, paragraph number [0006])

  Normally, as the production is repeated, the mechanism of the spot welding gun undergoes a change in the lubrication state and wear of the bush and the guide, and the frictional force for driving the mechanism increases. When the friction of the mechanism portion increases, the motor current value required to generate the pressurizing force when the friction is small increases. Therefore, in the method of controlling the applied pressure based on the motor current value, it is necessary to estimate how much the motor current value changes due to the secular change of the mechanism portion of the spot welding gun. In addition, there is a considerable amount of static friction in the spot welding gun mechanism, and when the constant pressure is stabilized from the overshoot direction and when it converges from the undershoot side, the motor current is equivalent to this static friction. It is known that errors always occur. However, the actual applied pressure changes due to the wear of electrode tips and the gap between workpieces to be welded in addition to the aging of the mechanism, so the motor current value changes according to the aging of the mechanism and static friction. Even if it is possible to accurately estimate only the pressure, it is not easy to maintain the applied pressure at a constant value. This is because when there is a gap between the workpieces to be welded, an extra pressing force for filling the gap is required. If the pressing force consumed to fill the gap is not taken into consideration, there is a concern that the applied pressure becomes small and the actual joining state between the workpieces becomes insufficient.

  It is an object of the present invention to provide a spot welding method using a spot welding gun that can perform spot welding with a constant pressure applied to a workpiece to be welded, and can improve the stability of welding quality. Objective.

  In order to achieve the above object, a spot welding method using a spot welding gun according to claim 1 is a method in which at least one of a pair of electrode tips is moved toward the other by a servo motor, and is covered by the pair of electrode tips. In a spot welding method using a spot welding gun that sandwiches a welding workpiece, holds the workpiece to be welded while applying a predetermined pressing force, and welds the workpiece by flowing an electric current, the pair of electrode tips are included. Obtaining a reference tip position of the pair of electrode tips when a good welding state is obtained at a spot welded spot of the workpiece to be welded when teaching operation parameters of a spot welding gun; and When actually welding, the spot welded portion of the workpiece to be welded is sandwiched between the pair of electrode tips. Characterized in that it comprises, and to position control so that the chip position of the pair of electrode tips become equal to the reference chip position.

  According to a second aspect of the present invention, in the spot welding method using the spot welding gun according to the first aspect, after the tip position is made equal to the reference tip position by the position control, the pressure is controlled by pressure control. It further comprises holding for a predetermined period.

  According to a third aspect of the present invention, in the spot welding method using the spot welding gun according to the second aspect, the pressing force is kept constant by holding the current value of the servo motor at a constant value for a predetermined period. It is characterized by holding for a predetermined period.

  According to a fourth aspect of the present invention, in the spot welding method using the spot welding gun according to the second aspect, the disturbance torque of the servo motor is estimated using a disturbance observer, and the disturbance torque is kept constant for a predetermined period. By holding, the pressurizing force is held at a constant value for a predetermined period.

  According to a fifth aspect of the present invention, in the spot welding method using the spot welding gun according to the fourth aspect, when the reference tip position is acquired, the disturbance torque value or the torque command value for the servo motor is set as a reference torque value. The disturbance torque value is compared with the reference torque value during the automatic welding, and a warning is notified when a difference between the disturbance torque value and the reference torque value exceeds a predetermined threshold value. Is further provided.

  Further, the invention of claim 6 is the spot welding method using the spot welding gun according to any one of claims 1 to 5, wherein when the work to be welded is sandwiched between the pair of electrode tips, The amount of elastic deformation of at least one of the electrode tips is calculated by adding the reference tip position and the plate thickness of the workpiece to be welded, and the position of the spot welding spot position of the spot welding gun based on the amount of elastic deformation Correction is performed.

  Further, the invention of claim 7 is the spot welding method using the spot welding gun according to claim 6, wherein the set plate thickness of each spot welding location is used as the plate thickness of the workpiece to be welded. It is characterized by.

  The invention according to claim 8 is the spot welding method using the spot welding gun according to claim 6, wherein the workpiece to be welded is sandwiched between the plate thickness of the workpiece to be welded by the pair of electrode tips. It is characterized by using the measured plate thickness.

  As described above, according to the present invention, the spot welding location of the workpiece to be welded is sandwiched between the pair of electrode tips, and the tip position when a predetermined pressure is applied to the workpiece to be welded is determined based on the operating parameters of the spot welding gun. By performing position control so as to be equal to the reference tip position acquired at the time of teaching, spot welding can be performed without being affected by electrode tip wear, gaps between workpieces to be welded, and the like. Therefore, spot welding can be performed in a state in which a constant pressure is always applied to the workpiece to be welded, and the stability of the welding quality can be improved.

  According to the second aspect of the present invention, after a predetermined pressure is obtained by position control, this pressure is held for a predetermined period by pressure control, so that spattering can be suppressed and welding can be performed. Therefore, the quality reliability of welding can be improved.

  According to the third aspect of the present invention, the pressure value is controlled by maintaining the current value of the servo motor at a constant value, so that pressure can be increased using existing equipment without newly adding a detection means such as a sensor. Control can be performed.

  According to the fourth aspect of the present invention, it is possible to perform pressure control with high accuracy by estimating the disturbance torque of the servo motor using the disturbance observer and maintaining the disturbance torque at a constant value.

  According to the invention described in claim 5, when a difference between the disturbance torque value and the reference torque value exceeds a predetermined threshold value, a warning is notified to find a trouble of the spot welding gun. It is possible to improve the reliability of the production processing system.

  According to the sixth aspect of the invention, by correcting the position of the spot welding gun based on the amount of elastic deformation of the electrode tip, it is possible to prevent the workpiece to be welded from being deformed due to the elastic deformation of the electrode tip. Can do.

  Further, according to the invention described in claim 7, when there is little individual difference in the plate thickness of the workpiece to be welded, the plate thickness of the workpiece to be welded is set to the set plate thickness of each spot welding location, The amount of elastic deformation can be easily obtained.

  Further, according to the invention described in claim 8, when there are many individual differences in the thickness of the workpiece to be welded, the amount of elastic deformation of the electrode tip can be easily achieved by setting the thickness of the workpiece to be welded to the measured thickness. Obtainable.

It is a front view showing one embodiment of a spot welding system for carrying out spot welding using a spot welding gun concerning the present invention. It is a front view which shows the modification of a spot welding system. It is a block diagram which shows a part of structure of the robot control apparatus shown in FIG.1 and FIG.2. It is a flowchart for demonstrating the method of calculating | requiring a spot welding hit point position. It is a flowchart for demonstrating the method of recording a reference electrode tip position etc. at the time of teaching of a welding robot. It is a flowchart for demonstrating the method to pressurize a to-be-welded workpiece | work by position control at the time of automatic welding by a welding robot. It is explanatory drawing which shows the state which is not pressurizing the to-be-welded workpiece | work between a pair of electrode tips. It is explanatory drawing which shows the state which pressurizes a to-be-welded workpiece | work between a pair of electrode tips, and the gun arm which has an opposing side electrode tip is bent. It is explanatory drawing explaining the state which is measuring the plate | board thickness of a to-be-welded workpiece | work. It is explanatory drawing which shows the state by which the to-be-welded workpiece deform | transforms and welding is performed. It is explanatory drawing which shows the state in which welding is performed after correct | amending the spot welding hit point position.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a spot welding system provided with a spot welding gun according to the present invention. The spot welding system is not particularly limited, and includes an articulated welding robot 1 having a spot welding gun 16 and a robot controller 2 that controls the welding robot 1. The work 11 to be welded is held by a holding jig (not shown) provided on the distal end side of a stem erected on the floor. FIG. 1 shows a state in which the workpiece 11 is sandwiched between spot welding guns 16. FIG. 2 shows a modification of the spot welding system in which the spot welding gun 16 is held by the holding jig 15. In FIG. 2, the work 11 to be welded is held by a hand 34 provided on the tip side of the welding robot 1A. The main difference between the spot welding systems shown in FIGS. 1 and 2 is whether the spot welding gun 16 is provided in the welding robot 1 or the holding jig 15. The method of controlling the robot by the robot controller 2 is the same. In FIG. 2, the same reference numerals are given to the same components as those in FIG. 1, and redundant description will be omitted.

  As shown in FIG. 1, the spot welding robot 1 is a general 6-axis vertical articulated robot, and includes a base 3 fixed to the floor so as to be rotatable about a first axis in the vertical direction, and a base 3. The upper arm 4 continues, the forearm 5 following the upper arm 4, the wrist element 6 rotatably connected to the front end of the forearm 5, and the spot welding gun 16 attached to the end of the wrist element 6. The upper arm 4 is attached to the base 3 so as to be rotatable around a second axis in the horizontal direction. A base end portion of the forearm 5 is connected to an upper end portion of the upper arm 4 so as to be rotatable around a third axis in the horizontal direction. A wrist element 6 is connected to the distal end portion of the forearm 5 so as to be rotatable about a fourth axis parallel to the axis of the forearm 5. A wrist element (not shown) is connected to the tip of the wrist element 6 so as to be rotatable about a fifth axis perpendicular to the axis of the forearm 5, and a spot welding gun 16 is perpendicular to the fifth axis. It is mounted so as to be rotatable around the sixth axis.

  The spot welding gun 16 includes a connecting portion (not shown) that is rotatably connected to the wrist element, an inverted L-shaped gun arm 7 that is integrally formed with the connecting portion, and a clamping servo motor 12. Yes. The gun arm 7 includes a counter electrode tip 14a, and a movable electrode tip 14b that is opposed to the counter electrode tip 14a and that can move to and away from the counter electrode tip 14a. The pair of electrode tips 14a and 14b are rod-shaped, and are arranged coaxially in the thickness direction of the work 11 to be welded sandwiched between the pair of electrode tips 14a and 14b.

  The position and posture of the counter electrode tip 14a are controlled by a servo motor that drives each rotating shaft of the welding robot 1. That is, when the opposing electrode tip 14a is positioned at the teaching position (spot welding spot position) in the thickness direction of the workpiece 11, the opposing electrode tip 14a is driven by a servo motor that drives each axis of the robot 1. It has become so. On the other hand, the movable electrode tip 14b is driven by the clamping servo motor 12 of the spot welding gun 16 to a predetermined position in a direction facing the pair of electrode tips 14a and 14b at a predetermined moving speed. Yes.

  The sandwiching servo motor 12 is provided with a power amplifier and an encoder (not shown). The current value is amplified by the power amplifier and provided to the servo motor 12. Further, it is also possible to obtain an estimated torque from the speed of the servo motor 12 via the disturbance observer 48 (see FIG. 3) by feedback control. The encoder is mounted in order to detect the rotation angle of the servo motor 12 around the axis. By the feedback control, the detected rotation angle is fed back, the movable electrode tip 14b is positioned at a predetermined position, and a predetermined pressing force is applied to the workpiece 11 to be welded between the pair of electrode tips 14a, 14b. Yes. In addition, although the pressure sensor which detects an actual pressurizing force is not mounted | worn with the spot welding gun 1 and 1A of this embodiment and a modification, it is also possible to employ | adopt the structure provided with a pressure sensor.

  The robot controller 2 constitutes a digital servo circuit including a CPU, various memories, input / output interfaces, etc. (not shown), and the position of the servo motor 12 that moves the movable electrode tip 14b of the spot welding gun 1, 1A. Control, speed control, torque (current) control, etc. are performed.

  An operation program and teaching data of the spot welding robots 1 and 1A are stored in a memory as a storage unit. The teaching data includes spot welding spot data, which are the positions and postures of the spot welding robots 1 and 1A and the spot welding gun 16 when spot welding a large number of welding locations of the workpiece 11. The position and orientation of the spot welding robots 1 and 1A are not particularly limited, but in the present embodiment, the pair of electrode tips 14a and 14b of the spot welding gun 16 are arranged in the vertical direction.

  FIG. 3 is a block diagram illustrating a part of the configuration of the robot control device. The servo motor 12 provided in the spot welding gun 15 is position-controlled by position information fed back from the pulse encoder, a position command passed from the operation command unit 22 via the shared RAM 42, and a position control gain 46. Note that 1 / s of s, which means an integral operation of the position feedback circuit, is a Laplace operator.

  The servo motor 12 includes an estimated disturbance torque estimated by the disturbance observer 48, a position command value passed from the operation command unit 22 via the shared RAM 42, a torque command passed from the shared RAM 42, Torque is controlled by the torque control gain 50. The estimated disturbance torque is the disturbance torque of the servo motor 12 estimated from the motor control current and the actual motor speed using the disturbance observer 48. In the case of the spot welding gun 16, the disturbance torque added to the servo motor 12 is an electrode. This corresponds to the pressure generated by pressing the tips 14a and 14b against each other and the frictional force accompanying the operation of the movable electrode tip 14b.

  Further, as shown in FIGS. 1 and 2, the robot control device 2 includes a teaching operation panel 8 capable of browsing information in the robot control device 2 and operating and setting the robot control device 2. A peripheral device 9 that communicates with the robot controller 2 is connected via a communication interface.

  4 to 6 show flowcharts of a spot welding method using the spot welding gun 16. FIG. 4 shows a flowchart for obtaining the spot hitting point position. In FIG. 5 and FIG. 6, after obtaining the spot hitting position, the reference tip position of the pair of electrode tips is obtained at the spot hitting position, and the servo motor that moves the movable electrode tip based on the reference tip position during actual automatic welding. A method is shown in which the position of the workpiece is controlled and the workpiece to be welded is sandwiched between a pair of electrode tips. The position of the electrode tip 14b is made equal to the reference tip position by controlling the position of the servo motor 12 to move the movable electrode tip 14b, so that it is sandwiched between the pair of electrode tips 14a and 14b at each spot welding spot position. The applied pressure of the welding work 11 can be maintained at a constant value. Incidentally, in the step of obtaining the spot welding spot, it is naturally possible to adopt a method in which the operator directly operates the welding robot and positions it at a desired position, as in the prior art, in addition to the step shown in FIG. In this case, what is necessary is just to implement the process of FIG.5 and FIG.6 in the positioned position.

  The teaching of the spot welding spot position shown in FIG. 4 is carried out in a state in which there is no deterioration due to aging of the mechanism portion on which the spot welding gun 16 slides, such as when the welding robot of the spot welding system is started up. The method of positioning the counter electrode tip 14a at the spot welding spot position where the end surface of the counter electrode tip 14a is in contact with the lower surface of the workpiece 11 to be welded includes steps S1 to S5. When the thickness of the workpiece 11 to be welded is not constant, the spot welding spot position at each spot welding point is obtained by this method. After the spot welding spot position is obtained, the welding robot 1 is controlled to move to the spot welding spot position according to the operation program.

  First, in step S1, the facing interval between the facing electrode tip 14b and the movable electrode tip 14a of the spot welding gun 16 is secured so that the spacing is wider than the set plate thickness of the workpiece 11 to be welded. Next, the spot welding robot 1 is moved to the welding location of the workpiece 11 to be welded, and the opposing electrode tip 14a and the movable electrode tip 14b are arranged on both sides in the plate thickness direction of the workpiece 11 held by the holding jig. The spot welding gun 16 (opposite electrode tip 14b) is temporarily positioned so that and are positioned respectively.

  In step S2, the movable electrode tip 14b is moved at a constant speed in a direction approaching the counter electrode tip 14a. That is, the movable electrode tip 14b is moved in the direction in which the open space between the pair of electrode tips 14a and 14b is closed. In step S3, the current value of the servo motor 12 that drives the movable electrode tip 14b is monitored to determine when the current value exceeds a predetermined value. By monitoring the current value, it is possible to recognize when disturbance torque is generated in the servo motor 12. When the disturbance torque is generated, the movable electrode tip 14b is in contact with the upper surface of the workpiece 11 to be welded. Specifically, the time when the current value changes stepwise is when disturbance torque is generated. When no disturbance torque is generated, it is determined that there is no workpiece 11 to be welded.

  In step S4, when the disturbance torque is detected, it is considered that the movable electrode tip 14b is in contact with the work 11 to be welded, the movement of the movable electrode tip 14b is stopped, the tip of the movable electrode tip 14b, A chip opening interval with the counter electrode tip 14a is measured. In step S5, the difference obtained by subtracting the preset plate thickness of the workpiece 11 to be welded from the tip opening interval is regarded as the amount of movement of the counter electrode tip 14a, and spot welding having the counter electrode tip 14a is performed. Move gun 16. As a result, the opposing electrode tip 14a is finally positioned at a position in contact with the lower surface of the work 11 to be welded.

  In step S6, the obtained teaching position is stored in the memory as teaching data, and the process ends. The spot welding robot 1 can position the counter electrode tip 14a at the spot welding spot position obtained based on the teaching data.

  Next, a method for holding the work 11 to be welded between the pair of electrode tips 14a and 14b with a predetermined pressure will be described. FIG. 5 shows the reference tip of the electrode tip 14b in a state where there is no deterioration due to aging of the mechanism portion on which the spot welding gun 16 slides when the spot welding system is started up, for example, as in the case of obtaining the spot welding spot position. FIG. 6 is a flowchart of a method for clamping the workpiece 11 to be welded between the pair of electrode tips 14a and 14b with a predetermined pressure during automatic welding.

  In step S6, after positioning the spot welding gun 16 at the spot welding position, the movable electrode tip 14b is moved to pressurize the work 11 to be welded with a predetermined pressure set in the memory. The pressure control at this time is controlled so that the estimated disturbance torque of the servo motor 12 matches the commanded torque command value.

  In step S7, the position of the electrode tip 14b when the predetermined pressure is reached, the work 11 to be welded is energized, and welding is properly performed is stored in the controller memory as the reference electrode tip position h (FIG. 8). To do. The reference electrode tip position h is, for example, based on the position of the electrode tip 14b when the electrode tips 14a and 14b as shown in FIG. This is the relative position of the electrode tip 14b. The position to be the reference position may be anywhere as long as the electrode tip 14b can be operated. At this time, as an option, the torque value of the servo motor 12 can be stored as a reference torque value in step S8.

  In step S9, it is determined whether or not to calculate the deflection amount δ of the gun arm 7 having the opposed electrode tip 14a of the spot welding gun 16 in a state where the work 11 to be welded is pressurized. 7 shows a state when the gun arm 7 is not bent, and FIG. 8 shows a state when the gun arm 7 is bent. If the deflection amount δ is calculated, the process proceeds to step S10, and if not calculated, the process proceeds to step S14.

  In step S10, it is determined whether the thickness of the workpiece 11 to be welded is a specified thickness or a measured thickness. When the plate thickness of the work 11 to be welded is designated, the process proceeds to step S11, where a value obtained by adding the designated plate thickness t to the reference electrode tip position h is defined as a deflection amount δ, and the deflection amount δ is recorded in step S13. On the other hand, when the plate thickness of the work 11 to be welded is set as the measurement plate thickness, the process proceeds to step S12, and the amount obtained by adding the measurement plate thickness to the reference electrode tip position h is set as the deflection amount δ. To do. As shown in FIG. 9, the plate thickness can be measured by sandwiching the work 11 to be welded between the pair of electrode tips 14a and 14b so that the gun arm 7 is not deformed.

  FIG. 10 shows a state in which spot welding is performed while the gun arm 7 is bent. As shown in the drawing, if welding is performed in a state in which the work piece 11 whose one end is a fixed end is bent, the work piece 11 may be deformed by an amount corresponding to the bending of the gun worm 7. For this reason, as shown in FIG. 11, the opposing electrode tip 14a is moved upward together with the spot welding gun 16 by an amount corresponding to the deflection amount δ, that is, the spot welding spot position obtained in steps S1 to S6 is corrected. This makes it possible to perform welding without deforming the work 11 to be welded.

  In step S14, it is determined whether or not the recording of the reference tip position h and the like has been completed at all spot welding spot positions corresponding to the welded portions of the workpiece 11 to be welded. If the recording has not ended, the process returns to step S6 and the steps S6 to S13 are repeated. When the recording is completed, the process proceeds to step S15 and automatic welding is performed.

  As shown in FIG. 6, steps S <b> 15 to S <b> 23 are steps for performing actual spot welding after teaching of operation parameters regarding the spot welding gun 16 is performed. In this step, the work 11 to be welded is not pressurized by pressure control, and the work 11 to be welded is pressurized by position control. Therefore, it is possible to reproduce an appropriate pressurization state (push-in state) without being affected by friction due to aging of the mechanical part of the spot welding gun 16 or a gap between the workpieces 11 to be welded.

  In step S15, the reference tip position h at the target spot welding spot position is read from the memory. In step S16, the servo motor 12 is controlled by position control so that the position of the electrode tip 14b becomes the reference tip position h. At this time, as an option, in step S17, the estimated disturbance torque value of the servo motor 12 is compared with the reference torque value recorded in step S8, and the difference between the disturbance torque value and the reference torque value exceeds a predetermined threshold value. It is also possible to notify a warning in the event of a failure. The warning is performed by notifying the peripheral device and the teaching operation panel of an alarm signal or message so that the worker can understand. Thereby, deterioration of a gun mechanism part and the remarkable change (excessive position shift and a gap) of the welding state of the to-be-welded workpiece | work 11 are detectable.

  In step S18, it is determined whether or not the workpiece 11 to be welded is maintained in a state where it is pressurized with a predetermined pressure by the pair of electrode tips 14a and 14b. If the pressure state is maintained, the process proceeds to step S19. If the pressure state is not maintained, the process proceeds to step S22. In step S19, a method for holding the pressurized state is determined. If the motor current value is held, the process proceeds to step S20, and if the estimated disturbance torque is held, the process proceeds to step S21.

  In step S22, the applied pressure is kept constant by the selected method. By keeping the applied pressure constant, even when the welded portion of the work 11 to be welded is melted or contracted, the occurrence of spatter can be suppressed and good nugget generation can be performed.

  In step S23, it is determined whether or not welding has been completed at all spot welding spot positions. If welding has not been completed, the process returns to step S15, and steps S15 to S22 are repeated. If welding has been completed, the welding operation consisting of steps S15 to S22 is terminated.

  With the above configuration, by controlling the servo motor 12 by position control and pressurizing the workpiece 11 to be welded, it is possible to reproduce welding performed in a state where there is no deterioration of the mechanism portion of the spot welding gun 16, Uniform and high-quality welding can be performed regardless of the deterioration state of the gun mechanism and the state of the workpiece 11 to be welded.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it can deform | transform and implement variously. For example, in this embodiment, a spot welding gun having one movable electrode tip and one counter electrode tip like the spot welding gun 16 has been described, but a pair of electrode tips having a link mechanism or the like. Even in a spot welding gun in which both of them are movable, the embodiment of the present invention is basically applicable.

DESCRIPTION OF SYMBOLS 1,1A Welding robot 2 Control apparatus 3 Base 4 Forearm 5 Upper arm 6 Wrist element 7 Gun arm 11 Work to be welded 12 Servo motor 14a Movable side electrode tip 14b Opposite side electrode tip 16 Spot welding gun

Claims (5)

By moving at least one of the pair of electrode tips toward the other by a servo motor, sandwiching the workpiece to be welded by the pair of electrode tips, holding the workpiece to be welded while applying a predetermined pressure, and passing an electric current In a spot welding method using a spot welding gun for welding the workpiece to be welded,
When teaching operating parameters of a spot welding gun having the pair of electrode tips, a reference tip position of the pair of electrode tips is acquired when a good welding state is obtained at a spot welded portion of the workpiece to be welded. And
When actually welding the workpiece to be welded, the spot welding location of the workpiece to be welded is sandwiched between the pair of electrode tips, and the position control is performed so that the tip positions of the pair of electrode tips are equal to the reference tip position. To do
Holding the applied pressure for a predetermined period by pressure control after making the chip position equal to the reference chip position by the position control, and
A spot welding method using a spot welding gun that performs pressure control by estimating a disturbance torque of the servo motor using a disturbance observer and holding the disturbance torque at a constant value for a predetermined period.   When the reference tip position is acquired, the disturbance torque value or a torque command value for the servo motor is acquired as a reference torque value, the disturbance torque value is compared with the reference torque value during the automatic welding, and the disturbance torque value The spot welding method using the spot welding gun according to claim 1, further comprising notifying a warning when a difference between the reference torque value and a reference torque value exceeds a predetermined threshold value.   When the workpiece to be welded is sandwiched between the pair of electrode tips, the elastic deformation amount of at least one of the electrode tips is calculated by adding the reference tip position and the plate thickness of the workpiece to be welded, The spot welding method using the spot welding gun according to claim 1 or 2, wherein position correction of the spot welding spot position of the spot welding gun is performed based on an elastic deformation amount.   The spot welding method using the spot welding gun according to claim 3, wherein a set plate thickness of each spot welding spot is used as the plate thickness of the workpiece to be welded.   The spot welding method using a spot welding gun according to claim 3, wherein a measured plate thickness measured when the workpiece is sandwiched between the pair of electrode tips is used for the plate thickness of the workpiece to be welded.

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