JP4880021B2 - Welding workpiece position detection method - Google Patents

Description

  The present invention provides spot welding for spot welding of a welding workpiece by moving the welding workpiece and a spot welding gun relative to each other using an articulated robot and sandwiching the welding workpiece between a movable electrode and a counter electrode facing each other of the spot welding gun. The present invention relates to a method for detecting a surface position of a welding work piece which a counter electrode contacts in a welding system.

  The spot welding system includes a spot welding gun having a movable electrode driven by a servo motor and a counter electrode arranged to face the movable electrode, and an articulated robot that holds the spot welding gun at the tip. After moving the welding workpiece and the spot welding gun relative to each other using an articulated robot, the movable electrode and the counter electrode of the spot welding gun are closed toward the predetermined spot position on the welding workpiece to close the spot welding gun. A welding work is sandwiched between the movable electrode and the counter electrode, and spot welding is performed at the striking point position by applying a voltage between both electrodes in this state. The counter electrode is a fixed electrode generally installed on the gun arm. In spot welding work using such a spot welding system, the movable electrode side surface position and the counter electrode side surface position of the welding workpiece at the spot position are articulated so that the movable electrode and the counter electrode can be positioned at the spot position on the weld workpiece. It is necessary to teach the robot in advance.

  In teaching work, when the operator visually confirms the position of the welding workpiece and operates the articulated robot to close the movable electrode and the counter electrode of the spot welding gun, the movable electrode After the spot welding gun is moved to a position where the counter electrode contacts, the spot welding gun is moved to a desired position, and then the position of the articulated robot and the position of the movable electrode tip are stored. That is, as for the position of the articulated robot and the position of the movable electrode tip, a position based on the position of the welding work is taught.

  In the teaching work as described above, it is necessary to teach the movable electrode and the counter electrode so that they can properly contact the surface of the welding workpiece. When the contact between the movable electrode and the counter electrode and the welded workpiece is determined by the operator's visual observation, the contact cannot be accurately detected depending on the skill level of the operator or the work environment that is difficult to visually check. In addition, detection of the movable electrode side surface position and the counter electrode side surface position of the welded workpiece becomes inaccurate.

  For this reason, Patent Document 1 discloses that when a movable electrode is moved toward a counter electrode by driving a servo motor and comes into contact with the surface of the welded workpiece, a reaction force due to elastic deformation of the welded workpiece, such as a deflection or a dent, is generated. By utilizing the fact that the servo motor current value (ie, torque value) increases by acting on the movable electrode from when the servo motor current value reaches a predetermined threshold value, the movable electrode and the welding workpiece are The thickness of the welding workpiece at the spot position where the distance between the movable electrode and the counter electrode is measured in advance after detecting the surface position on the movable electrode side of the welding workpiece at the spot position from the position of the movable electrode at this time. The movable electrode is welded while the spot welding gun is moved by an articulated robot so that the counter electrode approaches the welding workpiece until it becomes equal to By moving the movable electrode toward the counter electrode at the same moving speed as the spot welding gun servo motor so as to maintain the state of contact in over click, we propose a method for positioning a counter electrode on the welding workpiece.

  Patent Document 2 determines that the movable electrode has come into contact with the welded workpiece in the same manner as Patent Document 1, and the counter electrode is moved toward the welded workpiece by the articulated robot and contacts the surface of the welded workpiece. When the reaction force against the articulated robot reaches a predetermined threshold, the welding with the counter electrode is performed using the fact that the reaction force from the welded workpiece to the articulated robot is generated by the elastic deformation of the welded workpiece. Proposes a method for determining that a workpiece has come into contact. The reaction force to the articulated robot is obtained from the current value of the servo motor that drives each axis of the articulated robot.

JP-A-6-218554 Japanese Patent No. 3337448

  In the method described in Patent Document 1, in order to position the counter electrode on the surface of the welding workpiece, it is necessary to set the thickness of the welding workpiece at each spot position in advance. However, since it takes time to set the thickness of the welding workpiece, there is a problem that it is difficult to set the thicknesses at hundreds of striking positions in actual welding operations. Furthermore, if the thickness of the welded workpiece at each spot position is set based on the value on the design data of the welded workpiece, the counter electrode contacts the welded workpiece due to the existence of gaps between the welded workpieces and individual differences in the welded workpiece. In other cases, the counter electrode is excessively pressed against the welding workpiece to deform the welding workpiece, and in the worst case, the welding workpiece may be plastically deformed or the spot welding gun may be damaged. Therefore, in order to prevent deformation of the welding workpiece and damage to the spot welding gun, the thickness of the welding workpiece must be measured in advance at all spot positions on the welding workpiece before setting the thickness of the welding workpiece. There is also the problem of not becoming.

  On the other hand, in the method described in Patent Document 2, it is not necessary to measure the thickness of the welded workpiece at each spot position as in the method of Patent Document 1. However, the reaction force from the welding workpiece used to detect that the counter electrode contacts the welding workpiece to the articulated robot is caused by the elastic deformation of the welding workpiece that occurs when the counter electrode contacts the welding workpiece. To do. Therefore, in order for the reaction force to exceed the threshold value, it is necessary to deform the welded workpiece to some extent, and the threshold value depends on the rigidity of the welded workpiece. In addition, the change in the current value of the servo motor for driving each axis of the multi-joint robot due to the reaction force from the weld work to the multi-joint robot will affect the stiffness of the spot welding gun arm and multi-joint robot in addition to the stiffness of the weld work. Also depends. Therefore, the reaction force threshold used to detect that the counter electrode is in contact with the weld work varies depending on the combination of the weld work, spot welding gun and articulated robot used, and the counter electrode contacts the weld work. In order to accurately detect this, it is necessary to determine the reaction force threshold after experimentally obtaining it in advance. For this reason, there is a problem that it is difficult to deal with a wide range.

  Therefore, the object of the present invention is to solve the above-mentioned problems existing in the prior art, and in the spot welding system, the welding work piece which the counter electrode contacts without depending on the rigidity of the welding work piece, the spot welding gun and the articulated robot. The object is to be able to accurately detect the surface position.

  In view of the above object, according to the present invention, a spot welding gun having a movable electrode driven by a servo motor and a counter electrode disposed to face the movable electrode, and the spot welding gun An articulated robot that holds one and moves relative to the other, and moves the movable electrode and the counter electrode closer to and away from each other by the servo motor, so that the movable electrode and the counter electrode of the spot welding gun In a spot welding system for spot welding of the welding workpiece with the welding workpiece sandwiched therebetween, a welding workpiece position detecting method for detecting a surface position of the welding workpiece in contact with the counter electrode, wherein the movable electrode is After positioning so as to contact the surface of the workpiece, the servo motor can move the movable electrode in a direction to approach the counter electrode. The spot welding gun and the welding workpiece are made the same as the velocity Vg so that the electrode is moved at a predetermined velocity Vg and at the same time the counter electrode and the welding workpiece are brought close to each other using the articulated robot. By monitoring at least one of the moving speed and acceleration of the movable electrode relative to the counter electrode while relatively moving at a speed, contact between the counter electrode and the welding workpiece is detected, and the counter electrode at the time of detection is detected. There is provided a welding workpiece position detection method for detecting a surface position of the welding workpiece with which the counter electrode contacts from a position.

  Monitoring the moving speed and acceleration of the movable electrode with respect to the counter electrode is equivalent to monitoring the rotational speed and rotational acceleration of the servo motor for driving the movable electrode, respectively. The monitoring includes monitoring of the rotational speed and rotational acceleration of a servo motor for driving the movable electrode.

  In the welding workpiece position detection method, after the movable electrode is positioned so as to contact the surface of the weld workpiece, the movable electrode is moved at a predetermined speed Vg in a direction to approach the counter electrode by a servo motor, and at the same time, The spot welding gun and the welding workpiece are relatively moved at a speed equal to the speed Vg so that the counter electrode and the welding workpiece are brought close to each other using a robot. Therefore, when the counter electrode comes into contact with the welding workpiece, the welding workpiece is sandwiched between the movable electrode and the counter electrode, the movement of the movable electrode with respect to the counter electrode is hindered, and the moving speed of the movable electrode with respect to the counter electrode is previously set. Decrease from the defined value Vg. Similarly, the acceleration of the movable electrode with respect to the counter electrode changes from 0 to a negative value. Therefore, if the time when the moving speed of the movable electrode with respect to the counter electrode decreases from a predetermined value Vg or the time when the acceleration of the movable electrode with respect to the counter electrode changes from 0 to a negative value is detected, the counter electrode contacts the welding workpiece. Can be detected. Furthermore, since the object to be monitored is the moving speed or acceleration of the movable electrode with respect to the counter electrode, which is arbitrarily determined in advance, the characteristics of the individual servo motors, such as the current or torque of the servo motor that drives the electrodes, It does not change depending on the friction characteristics of the electrode drive mechanism. Therefore, it is possible to detect that the counter electrode is in contact with the welding work without being substantially affected by the rigidity of the welding work, the spot welding gun, and the articulated robot.

  In the welding workpiece position detection method, it is preferable that a torque limit is set in a servo motor for driving the movable electrode with respect to the counter electrode. If a torque limit is set for the servo motor for driving the movable electrode, the torque of the servo motor reaches the torque limit when the counter electrode comes into contact with the welding workpiece. A decrease in the moving speed and acceleration of the movable electrode when the counter electrode comes into contact with the welding workpiece can be generated more quickly and more significantly, and the detection accuracy is improved. Moreover, the elastic deformation of the welding workpiece by the movable electrode and the counter electrode can be suppressed.

  It is preferable that the torque limit of the servo motor is determined based on a value of torque of the servo motor when the spot welding gun and the welding workpiece are moved at the same speed as the speed Vg. When the spot welding gun and the welding work are moved relative to each other at the same speed as the speed Vg in order to bring the counter electrode into contact with the welding work, the movable electrode moves at the speed Vg, and the servo motor The motor operates with a minimum torque for maintaining the speed Vg. If this minimum necessary torque is acquired and set as a torque limit, the movement of the movable electrode is immediately restricted when the counter electrode comes into contact with the workpiece, so the movement speed and acceleration of the movable electrode are further reduced. It can be generated quickly and more significantly, and the detection sensitivity can be increased.

  When a torque limit is set for the servo motor, the movable electrode is positioned at a position offset from the surface of the welding workpiece by a predetermined distance after positioning the movable electrode in contact with the surface of the welding workpiece. From the positioned state, the movable electrode is moved at a predetermined speed Vg in a direction in which the servomotor approaches the counter electrode, and at the same time, the counter electrode and the welded workpiece are mutually connected using the articulated robot. It is preferable that the spot welding gun and the welding workpiece are relatively moved at the same speed as the speed Vg so as to approach each other. The offset may be performed in a direction in which the movable electrode is pressed against the welding workpiece, or may be performed in a direction in which the movable electrode is separated. In the state where the movable electrode of the spot welding gun is in contact with the surface of the welding workpiece, the spot welding gun simply vibrates due to the vibration of an articulated robot, etc. The servomotor torque fluctuates even before the counter electrode comes into contact with the welding workpiece, and the torque of the torque for maintaining the movable electrode at the speed Vg becomes unstable. It becomes difficult to make a decision. On the other hand, if the movable electrode is slightly separated from the surface of the welding workpiece, the reaction force from the welding workpiece can be removed. Conversely, if the movable electrode is slightly pressed against the welding workpiece, the reaction force from the welding workpiece to the movable electrode will not be lost, so that a substantially constant reaction force can be stably received. Therefore, by positioning the movable electrode offset from the surface of the welding workpiece, the torque for maintaining the operation at the speed Vg of the movable electrode can be determined stably.

  In the welding workpiece position detection method, at least one of the moving speed and acceleration of the movable electrode with respect to the counter electrode is monitored, and when the moving speed of the movable electrode with respect to the counter electrode changes from a constant to a decrease, or with respect to the counter electrode When the acceleration of the movable electrode changes from 0 to negative, it is determined that the counter electrode is in contact with the welding workpiece, and the moving speed of the movable electrode with respect to the counter electrode changes from a constant to a decrease or You may make it detect the surface position of the said welding workpiece which the said counter electrode contacts from the position of the said counter electrode when the acceleration of the said movable electrode with respect to a counter electrode turns into negative from 0. In this case, as an example, the movable electrode with respect to the counter electrode from the time when at least one value of the moving speed and acceleration of the movable electrode with respect to the counter electrode or the amount of change per unit time becomes a negative threshold value or less. The time is traced back along the time-series waveform of the moving speed or acceleration, and the amount of change per unit time of the moving speed or acceleration of the movable electrode with respect to the counter electrode changes from a negative value to 0 or a positive value. It can be determined that the moving speed of the movable electrode with respect to the counter electrode has changed from a constant to a decrease or the acceleration of the movable electrode with respect to the counter electrode has changed from 0 to negative.

  In the welding workpiece position detection method, at least one of the moving speed and acceleration of the movable electrode with respect to the counter electrode is monitored, and when the moving speed of the movable electrode with respect to the counter electrode decreases or the movable electrode with respect to the counter electrode is detected. When the acceleration of the electrode changes from 0 to negative, the speed at which the spot welding gun and the welding workpiece are relatively moved using the articulated robot is also decreased by the same amount, or the articulated robot is The acceleration that causes the spot welding gun and the welding workpiece to move relative to each other is also reduced by the same reduction amount, and when the movement of the movable electrode or the articulated robot stops, the counter electrode contacts the welding workpiece. From the position of the counter electrode when the movement of the movable electrode or the articulated robot is stopped. May be detected surface position of the welding workpiece to the counter electrode is in contact.

Further, according to the present invention, a spot welding gun having a movable electrode driven by a servo motor and a counter electrode arranged to face the movable electrode, and holding one of the spot welding gun and the welding workpiece is held. An articulated robot that moves relative to the other, the servomotor moves the movable electrode and the counter electrode closer to and away from each other, and the gap between the movable electrode and the counter electrode of the spot welding gun is In a spot welding system that performs spot welding of the welding workpiece with the welding workpiece sandwiched therebetween, a welding workpiece position detection method for detecting a surface position of the welding workpiece in contact with the movable electrode and the counter electrode, wherein the movable electrode and said welding workpiece, sea urchin by you approach from the state separated from each other, the welding workpiece by using the multi-joint robot While relatively moving the spot welding gun, the monitor current or torque of the servo motor, the current or torque or the current or torque each unit time was increased to more than a predetermined threshold value than the respective predetermined values When the amount of change per time increases to a predetermined threshold value or more, it is determined that the movable electrode has contacted the welding workpiece, and the current or torque increases to a predetermined threshold value or more than the respective predetermined value. Or when the current or torque is increased by a predetermined threshold value or more than the amount of change per unit time, the welding electrode contacts the movable electrode from the position of the articulated robot and the position of the articulated robot. Detecting the surface position of the welding workpiece, and detecting the welding workpiece in contact with the counter electrode by the welding workpiece position detecting method described above. Welding workpiece position detecting method characterized by comprising the steps of detecting the surface position is provided.
Further, according to the present invention, a spot welding gun having a movable electrode driven by a servo motor and a counter electrode arranged to face the movable electrode, and holding one of the spot welding gun and the welding workpiece is held. An articulated robot that moves relative to the other, the servomotor moves the movable electrode and the counter electrode closer to and away from each other, and the gap between the movable electrode and the counter electrode of the spot welding gun is In a spot welding system that performs spot welding of the welding workpiece with the welding workpiece sandwiched therebetween, a welding workpiece position detection method for detecting a surface position of the welding workpiece in contact with the movable electrode and the counter electrode, wherein the movable electrode And the welding workpiece are separated from the state of contact with each other using the articulated robot. The current or torque of the servo motor is monitored while the spot welding gun and the spot welding gun are moved relative to each other, and when the current or torque increases to a predetermined threshold value or more than the respective predetermined value, or the unit of the current or torque When the amount of change per time has changed from a negative value to zero or a positive value, it is determined that the movable electrode has moved away from the welding workpiece, and the current or torque is equal to or greater than a predetermined threshold value than the respective predetermined value. Or when the amount of change per unit time of the current or torque changes from a negative value to zero or a positive value, the position of the movable electrode and the position of the articulated robot A step of detecting a surface position of the welding workpiece in contact; and a surface of the welding workpiece in contact with the counter electrode by the welding workpiece position detection method described above. Welding workpiece position detecting method characterized by comprising the steps of detecting a location is provided.

  The welding work position detection method includes calculating the thickness of the welding work from the detected surface position of the welding work contacted by the movable electrode and the detected surface position of the welding work contacted by the counter electrode. The step of obtaining may further be included. As described above, when the thickness of the welded workpiece is obtained, the thickness of the welded workpiece is abnormal when the difference between the two exceeds a predetermined allowable value as compared with the preset thickness of the welded workpiece. Can be determined. Thereby, the operator can find a mistake in the welding work and an installation error, can determine the validity of the detection point, and can prevent an operation error.

  It is preferable that all the above-mentioned welding work position detection methods are implemented by executing a program command for performing welding.

  According to the present invention, the direction in which the movable electrode is brought into contact with the surface of the welding workpiece or the state in which the movable electrode is positioned at a position offset by a predetermined distance from the surface of the required workpiece is approached to the counter electrode. The spot welding gun and the welding workpiece are relatively moved at the same speed as the velocity Vg so that the movable electrode is moved at a speed Vg and the opposing electrode and the welding workpiece are brought close to each other. The movement of the movable electrode with respect to the counter electrode is hindered, and the moving speed of the movable electrode with respect to the counter electrode decreases from a predetermined speed Vg, and the acceleration of the movable electrode with respect to the counter electrode changes from 0 to negative. By utilizing this fact, the moving speed or acceleration of the movable electrode with respect to the counter electrode is monitored, so that the counter electrode contacts the weld work with almost no influence from the rigidity of the welding work, spot welding gun, and articulated robot. The position of the surface of the welding workpiece that is in contact with the counter electrode can be detected from the position data of the counter electrode when it is determined that the counter electrode has contacted the welding workpiece.

  Further, the thickness of the weld work can be accurately obtained from the surface position of the weld work contacted with the obtained counter electrode and the surface position of the weld work contacted with the movable electrode obtained by another method.

1 is an overall configuration diagram of a spot welding system in which a spot welding gun is held by an articulated robot and moved relative to a fixed welding workpiece. 1 is an overall configuration diagram of a spot welding system in which a welding work is held by an articulated robot and moved relative to a fixed spot welding gun. From the state in which the movable electrode is in contact with the surface of the welding workpiece, the servo electrode is used to approach the movable electrode toward the counter electrode at a speed Vg. It is explanatory drawing which shows making it approach at the speed Vr. It is explanatory drawing which shows the principle which measures the thickness t of a welding workpiece from the surface position of the welding workpiece which the movable electrode is contacting, and the surface position of the welding workpiece which the counter electrode is contacting. It is a graph which shows a time-dependent change of the torque of a servomotor when a servomotor is rotated or when a movable electrode is moved. It is a graph which shows the case where it changes with time when the torque of a servomotor when rotating a servomotor or moving a movable electrode overshoots. It is explanatory drawing which shows that when a servomotor is rotated or when a movable electrode is moved, the motor torque takes various time-varying patterns due to the mechanical resistance of the spot welding gun. Indicates that when the servo motor is rotated at a predetermined rotation speed or when the movable electrode is moved at a predetermined movement speed, the motor torque takes various time-varying patterns depending on the positional relationship between the movable electrode and the welding workpiece. It is explanatory drawing. According to the first embodiment of the present invention, the counter electrode comes into contact with the articulated robot by bringing the counter electrode of the spot welding gun closer to the welding workpiece while keeping the movable electrode in contact with the surface of the welding workpiece. It is a flowchart of the method of detecting the surface position of a welding workpiece. The graph which shows the time-dependent change of the torque of the servomotor when implementing 1st Embodiment of the welding workpiece position detection method of this invention, and the rotational speed and rotational acceleration (or moving speed and acceleration of a movable electrode) of a servomotor. It is. It is explanatory drawing of the method of detecting the fall of the rotational speed of a servomotor or the moving speed of a movable electrode based on the variation | change_quantity of the rotational speed of the servomotor or the moving speed of a movable electrode from a reference value. It is explanatory drawing of the method of detecting the reduction | decrease in the speed of a servomotor or the moving speed of a movable electrode based on the variation | change_quantity per unit time of the rotational speed of a servomotor or the moving speed of a movable electrode. It is explanatory drawing of the method of calculating | requiring a change point analytically from the time-sequential waveform of the rotational speed of a servomotor or the moving speed of a movable electrode. It is explanatory drawing of the method of detecting the reduction | decrease in the rotational acceleration of a servomotor, or the acceleration of a movable electrode based on the variation | change_quantity of the rotational acceleration of a servomotor or the acceleration of a movable electrode with respect to a reference value. It is explanatory drawing of the method of detecting the reduction | decrease in the rotational acceleration of a servomotor, or the acceleration of a movable electrode based on the variation | change_quantity per unit time of the rotational acceleration of a servomotor or the acceleration of a movable electrode. It is explanatory drawing of the method of calculating | requiring a change point analytically from the time series waveform of the rotational acceleration of a servomotor, or the acceleration of a movable electrode. According to the second embodiment of the present invention, the counter electrode comes into contact with the articulated robot by bringing the counter electrode of the spot welding gun closer to the welding workpiece while keeping the movable electrode in contact with the surface of the welding workpiece. It is a flowchart of the method of detecting the surface position of a welding workpiece. The graph which shows the time-dependent change of the torque of the servomotor, the rotational speed of the servomotor (or the moving speed of the movable electrode) and the moving speed of the articulated robot when the second embodiment of the welding workpiece position detecting method of the present invention is implemented. It is. It is a graph which shows the time-dependent change of the torque of a servomotor, the rotational acceleration (or acceleration of a movable electrode) of a servomotor, and the acceleration of an articulated robot when 2nd Embodiment of the welding workpiece position detection method of this invention is implemented. .

Hereinafter, some embodiments of the present invention will be described with reference to the drawings. In the drawings, the same parts are denoted by the same reference numerals.
Initially, with reference to FIG.1 and FIG.2, the whole structure of the spot welding system 10 which can apply the welding workpiece position detection method of this invention is demonstrated.

  The spot welding system 10 to which the welding workpiece position detection method of the present invention can be applied includes an articulated robot 12, a spot welding gun 14, a robot control device 16 that controls the operation of the articulated robot 12, and the spot welding gun 14. A spot welding gun control device 18 for controlling the operation is provided, and the articulated robot 12 can relatively move the welding workpiece W and the spot welding gun 14.

  The articulated robot 12 is, for example, a 4-axis vertical articulated type, and includes a base 20 installed on the floor, a swivel base 22 supported on the base 20 so as to be rotatable about the vertical axis J1, and a horizontal axis J2. A lower arm 24 supported at one end by the swivel base 22 so as to be rotatable around, an upper arm 26 supported at the other end of the lower arm 24 so as to be rotatable around the horizontal axis J3, and perpendicular to the horizontal axis J3 A wrist element 28 rotatably supported relative to the upper arm 26 about an axis J4. However, the articulated robot 12 does not have to be a 4-axis vertical articulated type as described above. If the spot welding gun 14 and the welding workpiece W can be moved relative to each other, a 6-axis vertical articulated robot or the like can be used. Type of articulated robot.

  The spot welding gun 14 includes a pair of electrodes composed of a movable electrode 30 and a counter electrode 32 disposed opposite to the movable electrode 30, and the movable electrode 30 is driven by a servo motor 34 to approach and separate from the counter electrode 32. The movable electrode 30 and the counter electrode 32 are closed, the welding workpiece W is sandwiched therebetween, and spot welding is performed by applying a voltage between the movable electrode 30 and the counter electrode 32 in this state. Do. The counter electrode 32 is generally a fixed electrode disposed on the gun arm, but may be driven by a servo motor in the same manner as the movable electrode 30.

  1 and 2, the robot control device 16 and the spot welding gun control device 18 are provided separately, but the robot control device 16 and the spot welding gun control device 18 may be provided integrally. If the spot welding gun 14 and the welding workpiece W can be moved relative to each other, the welding workpiece W is fixed on the workpiece fixing base (not shown) and spotted as shown in FIG. The welding gun 14 may be supported at the tip of the articulated robot 12 so as to be rotatable about the horizontal axis J5. As shown in FIG. 2, the spot welding gun 14 is mounted on a gun stand 36 installed on the floor surface. And the welding workpiece W may be held at the tip of the articulated robot 12. When the welding workpiece W is held at the tip of the articulated robot 12 as in the latter, the robot hand 38 for gripping the welding workpiece W at the tip of the wrist element 28 is horizontal as shown in FIG. It is rotatably mounted around the axis J5.

  In the welding work position detection method according to the present invention, when the counter electrode 32 is positioned at a predetermined position (hereinafter, referred to as a spot position) on the weld work W in the teaching work of the spot welding system 10 or the plate thickness at the spot position. Is used to detect the position of the counter electrode side surface of the welding workpiece W using the counter electrode 32. Further, based on the detected position of the surface of the counter electrode side of the welding workpiece W, it can also be used to correct the spot teaching position data of the spot welding program or create new spot teaching position data.

  In the welding workpiece position detection method according to the present invention, first, the movable electrode 30 needs to be positioned so as to be in contact with the movable electrode side surface of the welding workpiece W. Therefore, a method for positioning the movable electrode 30 so as to be in contact with the movable electrode side surface of the welding workpiece W will be described.

  The most basic method is that the operator operates the spot welding gun 14 and the articulated robot 12 to visually check the positions of the movable electrode side surface of the welding workpiece W and the movable electrode 30 while visually checking the welding workpiece W. Although there is a method of positioning so that the movable electrode 30 is in contact with the surface of the movable electrode, it is possible to position the movable electrode 30 in contact with the movable electrode side surface of the welding workpiece W by using various other methods. it can. For example, as in the prior art, when the articulated robot 12 is operated to close the movable electrode 30 and the counter electrode 32 of the spot welding gun 14, the movable electrode 30 and the counter electrode 32 are positioned on the welding work W. After moving the spot welding gun 14 to a position in contact with the motor, the servo motor 34 is driven to move the movable electrode 30 toward the counter electrode 32, and the current or torque of the servo motor 34 reaches a predetermined threshold value. Sometimes, it is determined that the movable electrode 30 and the welding workpiece W are in contact with each other, and the drive of the servo motor 34 is stopped, so that the movable electrode 30 can be positioned in contact with the movable electrode side surface of the welding workpiece W. .

  Further, instead of moving the movable electrode 30 with respect to the counter electrode 32 by the servo motor 34, the movable electrode 30 and the welding workpiece W are moved by moving the spot welding gun 14 and the welding workpiece W relative to each other using the articulated robot 12. An operation of bringing the movable electrode 30 and the welding workpiece W into contact with each other from a state in which the movable electrode 30 is separated from the welding workpiece W by approaching or moving away from each other, or a state in which the movable electrode 30 and the welding workpiece W are in contact with each other completely. The current or torque of the servo motor 34 is monitored while performing at least a part of the operation, and when the change tendency of the current or torque of the servo motor 34 changes, the movable electrode 30 comes into contact with the welding workpiece W or the movable electrode 30 is determined to be completely separated from the welding workpiece W, and the movable electrode 30 is placed at a position when it is determined that the contact is made or separated. -Decided may be rice.

  As an example of the latter method, for example, when the articulated robot 12 is operated and the movable electrode 30 and the counter electrode 32 of the spot welding gun 14 are closed, the movable electrode 30 and the counter electrode are located at the spot positions on the welding workpiece W. After the spot welding gun 14 is moved to a position where 32 touches, the movable electrode 30 and the welding workpiece W are separated from each other using the articulated robot 12 while the movable electrode 30 is driven at a speed Vg by the servo motor 34. The spot welding gun 14 and the welding workpiece W are moved relative to each other in the direction in which they approach each other, and at the same time, the current or torque of the servo motor 34 is monitored. When the movable electrode 30 comes into contact with the welding workpiece W, the welding workpiece W is pressed against the movable electrode 30 to cause elastic deformation, and the reaction force acts on the movable electrode 30 from the welding workpiece W. In contrast, the torque and current of the servo motor 34 increase in an attempt to maintain the state of moving at the speed Vg. Using this fact, the current or torque of the servo motor 34 is monitored, and when the current or torque of the servo motor 34 starts to increase as compared with a predetermined reference state, the movable electrode 30 It is determined that the welding work W has been touched, and the position at this time is regarded as the position where the movable electrode 30 is in contact with the welding work W, and the movable electrode 30 is positioned at this position. The fact that the current or torque of the servo motor has turned to a tendency to increase as compared with a predetermined reference state indicates that, for example, the current or torque of the servo motor 34 is higher than the current or torque value of the servo motor 34 in the reference state. The increase of the current or torque of the servo motor 34 per unit time is greater than a predetermined threshold value than the amount of change of the current or torque of the servo motor 34 in the reference state per unit time. It can be detected by detecting the increase.

  Note that “when the trend starts to increase compared to the reference state” means that the actual value of the current or torque of the servo motor 34 or the amount of change per unit time is assumed to be in the reference state. This means that the current or torque value of the motor 34 or the amount of change per unit time has increased. The reference state is the current or torque value or unit time of the servo motor 34 in the preliminary operation section after the start of relative movement between the spot welding gun 14 and the welding workpiece W and before the contact between the movable electrode 30 and the welding workpiece W. It is determined from the amount of change per hit.

  As another method, when the articulated robot 12 is operated to close the movable electrode 30 and the counter electrode 32 of the spot welding gun 14, the movable electrode 30 and the counter electrode 32 are placed at the spot positions on the welding workpiece W. After the spot welding gun 14 is moved to the contact position, the movable electrode 30 and the welding workpiece W are pressed against each other using the articulated robot 12 while the movable electrode 30 is driven at the speed Vg by the servo motor 34. The spot welding gun 14 and the welding workpiece W are moved relative to each other in the direction to be separated from each other, and at the same time, the current or torque of the servo motor 34 is monitored. When the movable electrode 30 and the welding workpiece W are pressed against each other and the movable electrode 30 is moved away from the welding workpiece W using the articulated robot 12, the amount of elastic deformation of the welding workpiece W by the movable electrode 30 decreases. Accordingly, the reaction force acting on the movable electrode 30 from the welding workpiece W is also reduced, and the current and torque of the servo motor 34 are reduced. Further, when the movable electrode 30 is completely separated from the welded workpiece W, the elastic deformation of the welded workpiece W due to the pressing of the movable electrode 30 disappears, and the reaction force that acts on the movable electrode 30 from the welded workpiece W is eliminated, and the servo motor 34. The decrease in torque and current also stops and becomes almost constant. Utilizing this fact, the current or torque of the servo motor 34 is monitored, and when the current or torque of the servo motor 34 starts to increase compared to a predetermined reference state (current of the servo motor 34). Or when the decreasing tendency of the torque is finished), it is determined that the movable electrode 30 is completely separated from the welding workpiece W, and the position at this time is regarded as the position where the movable electrode 30 is in contact with the welding workpiece W. The movable electrode 30 is positioned. The fact that the current or torque of the servo motor 34 has started to increase compared to a predetermined reference state (the current or torque decreasing trend of the servo motor 34 has ended) is, for example, the current of the servo motor 34. Alternatively, by analyzing the time series data of the torque, the current value or torque value of the servo motor 34 when the actual value of the current or torque of the servo motor 34 or the amount of change per unit time is assumed to be in the reference state. In addition, it is detected that the value has increased by a predetermined threshold value or more, and the change amount per unit time of the current or torque of the servo motor 34 changes from a negative value representing a monotonous decrease in the reference state to 0 or a positive value. In addition, the change point of the change tendency of the time series waveform of the current or torque of the servo motor 34 can be detected analytically.

  Note that “when the trend starts to increase compared to the reference state (when the decreasing trend ends)” means that the actual value of the current or torque of the servo motor 34 or the amount of change per unit time is It means that the value of the servo motor 34 or the amount of change per unit time when it is assumed to be increased. The reference state is the current or torque value or unit time of the servo motor 34 in the preliminary operation section after the start of relative movement between the spot welding gun 14 and the welding workpiece W and before the separation between the movable electrode 30 and the welding workpiece W. It is determined from the amount of change per hit.

  Thus, instead of the movement of the movable electrode 30 with respect to the counter electrode 32 by the servomotor 34, the movable electrode 30 and the welding workpiece W are moved relative to each other by moving the spot welding gun 14 and the welding workpiece W using the articulated robot 12. From the state in which the movable electrode 30 is separated from the welding workpiece W, or from the state in which the movable electrode 30 and the welding workpiece W are in contact with each other. If at least a part of the separating operation is performed, the moving speed of the movable electrode 30 by the servo motor 34 can be suppressed, and the fluctuation of the current or torque of the servo motor 34 due to the dynamic friction in the movable electrode driving mechanism can be reduced. As a result, it is possible to more accurately detect a change in the change tendency of the current or torque of the servo motor 34 due to the contact between the movable electrode 30 and the welding workpiece W, and to detect the surface position of the welding workpiece W more accurately. It becomes like this.

  In particular, the speed Vg at which the movable electrode 30 is driven by the servo motor 34 is set to 0, and all the operations for bringing the movable electrode 30 and the welding workpiece W into contact with each other or for completely leaving the contacted state by moving the articulated robot 12. If it carries out, when the position of the surface of the welding workpiece W is detected by the movable electrode 30, the movable electrode 30 is not driven by the servomotor 34. Therefore, the current or torque fluctuation of the servomotor 34 due to the dynamic friction in the movable electrode drive mechanism. Is almost gone. Accordingly, it is possible to accurately detect a change in the change tendency of the current or torque of the servo motor 34 when the movable electrode 30 and the welding workpiece W come into contact with each other or when the movable electrode 30 is completely separated from the welding workpiece W. The surface position of the welding workpiece W can be accurately detected.

  Further, the speed Vg at which the movable electrode 30 is driven by the servo motor 34 may be set to an extremely low speed that can eliminate static friction. When the speed Vg at which the movable electrode 30 is driven by the servo motor 34 is set to 0 and the movable electrode 30 is completely stationary with respect to the counter electrode 32, the movable electrode 30 is caused by static friction in the movable electrode drive mechanism. The reaction force received from the welding workpiece W when it is in contact with the welding workpiece W is lost and is not transmitted to the servomotor 34, and the current or torque of the servomotor 34 hardly fluctuates despite receiving the reaction force. A dead zone occurs. Such a dead zone may adversely affect the detection accuracy of the surface of the welding workpiece W by the movable electrode 30 when the static friction is large. On the other hand, if the movable electrode 30 is driven by the servo motor 34 at an extremely low speed at which static friction can be removed, such a dead zone can be eliminated. Further, even if the movable electrode 30 is moved with respect to the counter electrode 32 at a very low speed Vg at which static friction can be removed, the dynamic friction in the movable electrode drive mechanism is reduced. Fluctuations can be minimized.

  Next, a welding work position detection method for detecting the surface position of the welding work that contacts the counter electrode 32 will be described. First, by operating the articulated robot 12 to close the movable electrode 30 and the counter electrode 32 of the spot welding gun 14, to the position where the movable electrode 30 and the counter electrode 32 come into contact with the spot position on the welding workpiece W. The spot welding gun 14 is moved, and the movable electrode 30 is positioned so as to contact the movable electrode side surface of the welding workpiece W by an arbitrary method. Note that only when a torque limit is set for the servo motor 34 that drives the movable electrode 30, after the movable electrode 30 is positioned so as to be in contact with the movable electrode side surface of the welding workpiece W, it is further determined in advance from this position. The movable electrode 30 may be positioned at a position offset by a given distance. The reason will be described later. Next, as shown in FIG. 3, the movable electrode 30 is moved at a predetermined speed Vg by the servo motor 34 in a direction in which the welding work W is in contact with the movable electrode side surface in a direction of approaching the counter electrode 32. At the same time, the articulated robot 12 is used to move the spot welding gun 14 and the welding work W relative to each other at a speed Vr equal to the speed Vg in a direction in which the counter electrode 32 and the welding work W are approached from a state where they are separated from each other. At least one of the moving speed and acceleration of the movable electrode 30 with respect to the electrode 32 is monitored. When contact between the counter electrode 32 and the welding workpiece W is detected by monitoring at least one of the moving speed and acceleration of the movable electrode 30 with respect to the counter electrode 32, the position of the welding workpiece W is detected from the position of the tip of the counter electrode 32 when detected. The counter electrode side surface position is obtained. The moving speed and acceleration of the movable electrode 30 with respect to the counter electrode 32 may be measured directly or may be obtained from the servo motor 34 that drives the movable electrode 30.

  Note that monitoring the moving speed and acceleration of the movable electrode relative to the counter electrode is equivalent to monitoring the rotational speed and acceleration of the servo motor for driving the movable electrode, respectively. The monitoring includes monitoring the rotational speed and rotational acceleration of a servo motor for driving the movable electrode.

  Here, the position data of the position of the tip of the counter electrode 32 when the counter electrode 32 contacts the welding workpiece W is based on the position data of the tip of the wrist element 28 of the articulated robot 12, for example, as follows. Desired.

  The distance from the floor surface to the horizontal axis J2 of the swivel base 22 supported on the base 20, the distance between the vertical axis J1 and the horizontal axis J2, the distance between the horizontal axis J2 and the horizontal axis J3, the horizontal axis Since the inter-axis distance between J3 and the axis J4 is constant, the position of the tip of the wrist element 28 of the articulated robot 12 can be obtained from the rotation angle of each axis of the articulated robot 12. Further, the position from the tip of the wrist element 28 of the articulated robot 12 to the tip of the counter electrode 32 of the spot welding gun 14 is predetermined and is always constant. Therefore, the counter electrode of the spot welding gun 14 is obtained from the positional data of the tip of the wrist element 28 of the articulated robot 12 and the positional relationship between the tip of the wrist element 28 of the articulated robot 12 and the tip of the counter electrode 32 of the spot welding gun 14. The position data of 32 tips is obtained.

  The welding work position detection method described above is not the current or torque of the servo motor that drives the articulated robot 12 or the current or torque of the servo motor 34 that drives the movable electrode 30, but the moving speed of the movable electrode 30 relative to the counter electrode 32 and It is characterized by monitoring at least one of the accelerations. Until the counter electrode 32 contacts the welding workpiece W, the moving speed of the movable electrode 30 with respect to the counter electrode 32 is constant at Vg. On the other hand, when the counter electrode 32 comes into contact with the welding workpiece W while keeping the movable electrode 30 in contact with the welding workpiece W, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32. The movement of the movable electrode 30 with respect to the counter electrode 32 is hindered, and the moving speed of the movable electrode 30 with respect to the counter electrode 32 decreases from a predetermined value Vg and eventually becomes zero. At this time, the acceleration of the movable electrode with respect to the counter electrode 32 changes from 0 to a negative value and eventually becomes 0 again. Therefore, if the moving speed or acceleration of the movable electrode 30 with respect to the counter electrode 32 is monitored, the counter electrode 32 becomes the weld work W with almost no influence of the rigidity of the weld work W, the articulated robot 12 and the spot welding gun 14. The contact can be detected. Further, since the counter electrode side surface position of the welding workpiece W is detected from the position of the counter electrode 32 when the counter electrode 32 contacts the welding workpiece W, the counter electrode 32 is positioned at the spot position on the surface of the welding workpiece W. Prior to this, there is no need to measure the thickness of the welding workpiece W at the hitting point position.

  In the welding workpiece surface detection method of the present invention, it is preferable to set a torque limit on the servo motor 34 that drives the movable electrode 30 relative to the counter electrode 32. If the torque limit is set in the servo motor 34 in this way, the torque of the servo motor 34 immediately reaches the torque limit when the counter electrode 32 contacts the welding workpiece W. As a result, the operation of the movable electrode 30 by the servo motor 34 is limited, and the rotational speed and rotational acceleration of the servo motor 34, that is, the moving speed and acceleration of the movable electrode 30 become more prominent when the counter electrode 32 contacts the welding workpiece W. The contact can be easily detected.

  The torque limit value of the servo motor 34 is determined during the operation in which the counter electrode 32 is brought into contact with the welding workpiece W from the state of being separated from the welding workpiece W by the relative movement of the spot welding gun 14 and the welding workpiece W, that is, the counter electrode 32 is welded. It is desirable to make a determination based on the torque of the servo motor 34 when the movable electrode 30 is moved at the speed Vg with respect to the counter electrode 32 in a state of being separated from the workpiece W. When the movable electrode 30 is operating at the moving speed Vg, the servo motor 34 outputs a torque necessary for moving the movable electrode 30 at the speed Vg. If the torque required to move at this speed Vg is measured during the above operation and set as the torque limit value of the servo motor 34, the welding work W is sandwiched between the counter electrode 32 and the movable electrode 30. The servo motor 34 cannot push back the counter electrode 32 and the welding workpiece W by the movable electrode 30, and the movable electrode 30 cannot maintain the moving speed Vg. That is, since the moving speed of the movable electrode 30 and the acceleration of the movable electrode 30 can be further reduced significantly, it is possible to detect contact with higher sensitivity. When actually setting the torque necessary for moving the movable electrode 30 at the speed Vg as the value of the torque limit of the servo motor 34, it is desirable to add some margin to prevent erroneous detection. . Needless to say, the detection sensitivity can be adjusted by the added margin.

  The timing for determining the value of the torque limit of the servo motor 34 may be any time when the movable electrode 30 is moving at the speed Vg with respect to the counter electrode 32 in a state where the counter electrode 32 is away from the welding workpiece W. Typically, immediately after the movable electrode 30 starts relative movement with respect to the counter electrode 32, the counter electrode 32 is not yet in contact with the welding workpiece. Therefore, based on the torque output of the servo motor 34 at this time, What is necessary is just to determine a value. For example, as shown in FIG. 5, the value of the torque limit may be set based on the torque output of the servo motor 34 after time Ta when the moving speed of the movable electrode 30 with respect to the counter electrode 32 becomes Vg. However, immediately after the start of movement, the servo motor 34 has just started an acceleration operation, and even if the moving speed of the movable electrode 30 reaches Vg, as shown in FIGS. The torque output of the motor 34 is unstable, and overshoot may occur. Therefore, as shown in FIGS. 6A and 6B, the servo motor is based on the torque at the time Tb when a predetermined time has elapsed from the start of the movement and the torque output of the servo motor 34 is stabilized. Preferably, a torque limit value of 34 is determined. In order to prevent the counter electrode 32 from coming into contact with the welding workpiece before setting the torque limit value, the detection operation is performed after securing a sufficient distance by separating the counter electrode 32 and the welding workpiece W. It is preferable to start.

  Furthermore, when it is determined that the counter electrode 32 and the welding workpiece W are not in contact with each other even if a predetermined time has elapsed when the movable electrode 30 is moving at the speed Vg with respect to the counter electrode 32, The torque limit value may be determined based on the torque output of the servo motor 34 within the predetermined time. If the predetermined time is shortened, the set value of the torque limit can be updated periodically at regular intervals. As shown in FIG. 7A, even when the movable electrode 30 is moving relative to the counter electrode 32 at a constant speed, the mechanical resistance (for example, internal friction of the drive portion) existing in the spot welding gun 14 The torque output of the servo motor 34 does not stabilize at a constant value but rises slowly due to the elastic deformation of the conductive portion connecting the movable electrode and the welding transformer (not shown) (FIG. 7B). ), Or may gradually decrease (FIG. 7C) or fluctuate (FIG. 7D). Thus, when the torque output of the servo motor 34 is not stabilized at a constant value, it is an effective means to periodically update the torque limit set value. For example, as shown in FIGS. 7A to 7D, if the torque limit setting value is updated periodically based on the torque of the servomotor 34 at times Tc, Td, and Te at regular intervals ΔT. Appropriate torque limit can be set.

  Only when the torque limit is set for the servo motor 34 that drives the movable electrode 30, the movable electrode 30 may be positioned at a position slightly offset from the position in contact with the movable electrode side surface of the welding workpiece W by a known distance. I mentioned earlier, but here's why.

  When the operation for detecting the contact between the counter electrode 32 and the welding workpiece W is performed in a state where the movable electrode 30 is actually in contact with the surface of the welding workpiece W on the movable electrode side, it occurs when the articulated robot 12 operates. Since the movable electrode 30 is slightly pressed against the welding workpiece W or separated from the welding workpiece W due to minute vibrations, an unstable state occurs where the reaction force from the welding workpiece W is received or not received. Cheap. Since the torque of the servo motor 34 is controlled so as to keep the moving speed of the movable electrode 30 constant, when a reaction force is received from the welding workpiece W, an extra torque is required to push back the welding workpiece W. Therefore, even if the rotational speed of the servo motor 34 or the moving speed of the movable electrode 30 is constant as shown in FIG. 8A, the movable electrode 30 is slightly pressed against or separated from the welding workpiece W. Under the condition, as shown in FIG. 8B, the torque of the servo motor 34 fluctuates between a value T ′ when the reaction force is received from the welding workpiece W and a value T when the torque is not received. Becomes unstable. On the other hand, in order to improve the contact detection sensitivity, the torque limit of the servo motor 34 is preferably set to a value equal to the minimum torque at which the movable electrode 30 can maintain the movement at the speed Vg. Therefore, it is desirable to remove the influence of unstable reaction force transmitted to the movable electrode 30 as much as possible.

  By performing the operation for detecting the contact between the counter electrode 32 and the welding workpiece W with the movable electrode 30 slightly separated from the workpiece W to be welded, the reaction force from the welding workpiece W can be removed, As shown in FIG. 8C, the torque of the servo motor 34 can maintain the value T in a state where the servo motor 34 is not receiving a reaction force from the welding workpiece W. Conversely, if the operation for detecting the contact between the counter electrode 32 and the welding workpiece W is performed with the movable electrode 30 slightly pressed against the workpiece W to be welded, the reaction force from the welding workpiece W is released. Since the servo motor 34 can stably receive a substantially constant reaction force, the servo motor 34 receives the reaction force from the welding workpiece W as shown in FIG. It becomes possible to maintain the value T ′ of the receiving state. That is, it is equivalent to giving a constant bias to the torque output of the servo motor 34. Thereby, since the torque of the servomotor 34 is stabilized, the torque for maintaining the movement of the movable electrode 30 at the speed Vg can be determined accurately and easily. In the case of offset, the detection position of the welding workpiece W by the counter electrode 32 is shifted by the offset distance. However, since the offset distance is a predetermined known value, the detected surface position of the welding workpiece W is detected. If the offset distance is taken into account, an accurate surface position of the welding workpiece W can be obtained.

  Moreover, you may make it set a torque limit to the servomotor (not shown) which drives each axis | shaft J1-J5 of the articulated robot 12. FIG. Thereby, the elastic deformation of the welding workpiece by the movable electrode 30 and the counter electrode 32 can be suppressed. Of course, the torque limit may be set for both or only one of the servo motor 34 that drives the movable electrode 30 and the servo motor that drives each of the axes J1 to J5 of the articulated robot 12.

  Even when a torque limit is set for a servo motor (not shown) that drives the axes J1 to J5 of the articulated robot 12, the spot welding gun 14 and the welding workpiece W are separated from the welding workpiece W due to relative movement. The counter electrode 32 is moved relative to the welding work W at a speed Vr equal to the speed Vg of the movable electrode 30 during the operation of bringing the counter electrode 32 into contact with the welding work W, that is, with the counter electrode 32 away from the welding work W. It is desirable to determine the torque limit value based on the torque of the servo motor of the articulated robot when the articulated robot 12 is operated. The reason and the method for determining the set value of the torque limit are the same as in the case where the torque limit is set in the servo motor 34 that drives the movable electrode 30, and therefore the description thereof is omitted here.

  Further, in the welding work position detection method of the present invention, the operator may proceed one step at a time by manual operation, but the spot welding system 10 may automatically execute a series of steps. For example, in a spot welding program in which a program command for performing all welding spot positions and spot welding is already taught, when the spot welding program is played back by enabling the mode for automatically executing the above process, the welding workpiece position detection program Is automatically reproduced, the articulated robot 12 is automatically moved in the vicinity of each welding spot position, and a program command for performing spot welding is executed, whereby the above-described process is automatically executed and the welding work W The surface position of the welding workpiece W is detected, the hit point teaching position data is corrected based on the detected position, and the correction amount (deviation amount) can also be recorded in the robot controller 16. The recorded correction amount may be displayed on a teaching operation panel provided in the robot control device 16. In addition, when the recorded correction amount is excessive, a line control panel that can notify the teaching operation panel provided in the robot control device 16 as an alarm or communicate with the robot control device 16 as an abnormality in the position of the welding workpiece W. An alarm may be notified to an external control device such as a computer.

  Furthermore, as shown in FIG. 4 using the counter electrode side surface position of the welding workpiece W detected using the welding workpiece position detection method according to the present invention and the movable electrode side surface position of the welding workpiece W, It is also possible to measure the thickness t of the welding workpiece W at the hit point position. The movable electrode side surface position of the welding workpiece W is, for example, from the position data of the tip of the counter electrode 32 of the spot welding gun 14 and the relative position data of the tip of the movable electrode 30 with respect to the tip of the counter electrode 32 of the spot welding gun 14. The position data of the tip of the counter electrode 32 of the spot welding gun 14 can be obtained in the same manner as the method for obtaining the position data of the counter electrode 32 described above, and the movable electrode 30 is brought into contact with the movable electrode side surface of the welding workpiece W. Thus, the position data of the tip of the counter electrode 32 of the spot welding gun 14 can be obtained from the position data of the tip of the articulated robot 12 when the positioning is performed.

  In addition, the detection of the movable electrode side surface position of the welding workpiece W is performed so that, for example, the movable electrode 30 and the welding workpiece W approach each other from a state where they are separated from each other or are separated from a state where they are in contact with each other. The current or torque of the servo motor 34 is monitored while the welding workpiece W and the spot welding gun 14 are moved relative to each other using the articulated robot 12, and when the change tendency of the current or torque changes, the movable electrode 30 The movable electrode 30 is determined based on the position of the movable electrode 30 and the position of the multi-joint robot 12 when it is determined that the welded workpiece W has been touched or the movable electrode 30 has moved away from the welded workpiece W and the current or torque change tendency has changed. This can be done by detecting the surface position of the welding workpiece W in contact. Further, based on the surface position of the welding workpiece W detected in this way, the movable electrode 30 can be accurately positioned at the detected movable electrode side surface position. Therefore, before starting the step of detecting the surface position of the welding workpiece W with which the counter electrode 32 contacts, the movable electrode 30 is positioned to the movable electrode side surface position of the welding workpiece W detected in advance as described above. If so, the surface position of the welding workpiece W with which the counter electrode 32 contacts can be detected more accurately.

  The obtained thickness t of the welding workpiece W at each welding point can be used when the thickness of the welding workpiece W at the welding point needs to be set in advance when teaching the spot welding program. In an actual factory, it may be necessary to set the exact thickness of the welding workpiece W at several hundred welding points. In such a case, the welding workpiece W at each welding point determined as described above is used. Using a thickness of will help. Further, when the spot welding program already taught is corrected, the preset thickness information of the welding workpiece W can be corrected to the actually measured thickness for each hit point as described above. This eliminates the need for the operator to accurately set the thickness information of the welding workpiece W in advance.

  In addition, when the thickness of the welding workpiece W set in advance is compared with the measured thickness of the welding workpiece W, and the difference between the two is excessive, the workpiece thickness is equal to or more than that, It can also be determined that there is an abnormality in the measurement position. For example, when the measured thickness of the welding workpiece W is too thick compared to the set thickness of the welding workpiece W, foreign matter such as an embedded bolt exists between the movable electrode 30 and the counter electrode 32. Therefore, it can be determined that the detection position as the welding spot is inappropriate. Furthermore, even when the welding workpiece W is not properly installed, the difference between the set thickness of the welding workpiece W and the measured thickness of the welding workpiece W becomes excessive, so that it can be determined that the welding workpiece W is abnormal. . In addition, when the difference between the set thickness of the welded workpiece W and the measured thickness of the welded workpiece W is excessive, no abnormalities in the welded workpiece or the welding spot position are observed. It can also be considered that the wear of the electrode 32 may be increased. When these abnormalities are detected, an alarm notification signal may be output to a teaching operation panel provided in the robot control device 16 or an external control device (such as a line control panel or a computer) that can communicate with the robot control device 16. it can.

  Below, some specific embodiment of the method of detecting the counter electrode side surface position of the welding workpiece | work W according to this invention is described. In the welding workpiece position detection method of the present invention, the same effect can be obtained if the spot welding gun 14 and the welding workpiece W can be moved relative to each other by the multi-joint robot 12. First, as shown in FIG. 1, a case where the spot welding gun 14 is held by the articulated robot 12 and moved relative to the welding workpiece W will be described as an example. However, as shown in FIG. 2, the welding workpiece W may be held by the articulated robot 12 and moved relative to the spot welding gun 14. In this case, in the following description, the articulated robot 12 is used. Instead of moving the spot welding gun 14, the welding work W may be moved.

  With reference to FIG. 9, 1st Embodiment of the welding workpiece position detection method of this invention is described. In the first embodiment, in the spot welding system 10 shown in FIG. 1, the articulated robot 12 is moved while moving the movable electrode 30 at a predetermined speed Vg in a direction in which the servomotor 34 approaches the counter electrode 32. Thus, the spot welding gun 14 is held and moved relative to the welding workpiece W fixed to the workpiece fixing table (not shown) in the direction of approaching each other at the same velocity Vr as the velocity Vg.

  In the present embodiment, first, the articulated robot 12 is operated to perform spot welding to a position where the movable electrode 30 and the counter electrode 32 are in contact with the welding location (spot location) on the welding workpiece W. The gun 14 is moved, and the movable electrode 30 is positioned so as to be in contact with the movable electrode side surface of the welding workpiece W (step S100). At this time, the counter electrode 32 is completely separated from the welding workpiece W. The positioning of the movable electrode 30 with respect to the movable electrode side surface of the welding workpiece W may be performed by any method as described above.

  Next, as shown in FIG. 3, the servo motor 34 moves the movable electrode 30 from the state in contact with the movable electrode side surface of the welding work W at a predetermined speed Vg in a direction in which the movable electrode 30 approaches the counter electrode 32. At the same time, the articulated robot 12 is used to move the spot welding gun 14 and the welding workpiece W relative to each other at a speed Vr equal to the speed Vg in a direction in which the counter electrode 32 and the welding workpiece W are approached from a state where they are separated from each other (step S102). ). That is, the counter electrode 32 is moved closer to the welding workpiece W while the movable electrode 30 is kept in contact with the welding workpiece W without changing the relative position between the movable electrode 30 and the welding workpiece W. At the same time, at least one of the moving speed and acceleration of the movable electrode 30 is monitored (step S104). The moving speed and acceleration of the movable electrode 30 may be measured directly, or may be obtained from the rotational speed and rotational acceleration of the servo motor 34 that drives the movable electrode 30. Further, the moving speed and acceleration of the movable electrode 30 relative to the counter electrode 32 are proportional to the rotational speed and rotational acceleration of the servo motor 34 for driving the movable electrode 30, respectively. The rotational speed or rotational acceleration of the servo motor 34 that drives the movable electrode 30 may be monitored. At the time of monitoring, the position data of the tip of the wrist element 28 of the multi-joint robot 12 and the counter electrode 32 together with information on the moving speed or acceleration of the movable electrode 30 or the rotational speed or rotational acceleration of the servo motor 34 at each sampling time. The relative position data of the movable electrode 30 is sequentially recorded.

  Next, it is determined whether or not to set a torque limit on the servo motor 34 that drives the movable electrode 30 of the spot welding gun 14 and the servo motor (not shown) that drives the axes J1 to J5 of the articulated robot 12. (Step S106). When setting the torque limit, the process proceeds to step S108, where the torque limit is set to the servo motor 34 that drives the movable electrode 30 of the spot welding gun 14, and the servo motor that drives each axis J1-J5 of the articulated robot 12. After at least one of the torque limit setting is performed, the process proceeds to step S110. The torque limit of each servo motor is set to a value that can sufficiently output a torque necessary for performing an operation for detecting contact between the counter electrode 32 and the welding workpiece W thereafter. After step S102, the movable electrode moves at the speed Vg, and the tip of the wrist element 28 of the articulated robot 12, that is, the counter electrode 32 moves at the speed Vr. At this time, each servo motor actually outputs. It is preferable to set the torque limit value of each servo motor based on the torque that is being applied. The set value of the torque limit may be a predetermined value. On the other hand, when the torque limit is not set, the process proceeds directly from step S106 to step S110.

  When the counter electrode 32 comes into contact with the welding workpiece W while the movable electrode 30 is kept in contact with the welding workpiece W, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32, and the counter electrode 32 is sandwiched. The movement of the movable electrode 30 with respect to is prevented. Then, since the servo motor 34 is controlled so as to keep the moving speed Vg constant, the servo motor 34 that tries to output a larger torque reaches the output limit of the servo motor 34 and drives the movable electrode 30. The rotational speed of the decreases. As a result, the set speed Vg cannot be maintained, and the moving speed of the movable electrode 30 with respect to the counter electrode 32 decreases from a predetermined value Vg. Further, the acceleration of the movable electrode 30 with respect to the counter electrode 32 changes from 0 to a negative value. Using this fact, the moving speed of the movable electrode 30 with respect to the counter electrode 32 or the rotational speed of the servo motor 34, or the acceleration of the movable electrode 30 with respect to the counter electrode 32 or the rotational acceleration of the servo motor 34 are sequentially checked (step S110). When the moving speed of the movable electrode 30 with respect to the counter electrode 32 or the rotational speed of the servo motor 34 decreases, or when the acceleration of the movable electrode 30 with respect to the counter electrode 32 or the rotational acceleration of the servo motor 34 changes from 0 to a negative value. In addition, it is determined that the counter electrode 32 is in contact with the welding workpiece W. On the other hand, if it is determined that the counter electrode 32 is not in contact with the welding workpiece W, the process returns to step S104 to continue monitoring at least one of the moving speed and acceleration of the movable electrode. Decide whether to reset the limits. When resetting the torque limit, for example, the value of the torque limit based on the torque output by the servo motor 34 that drives the movable electrode 30 and the servo motor that drives each axis of the articulated robot 12 in step S108. Can be re-determined and reset. The torque limit setting value may be updated at a predetermined time interval.

  When a torque limit is set for the servo motor 34 that drives the movable electrode 30, the torque of the servo motor 34 reaches the torque limit earlier than the output limit after the counter electrode 32 contacts the welding workpiece W. The rotational speed of the motor 34 and the moving speed of the movable electrode 30 decrease more rapidly, and at the same time, the rotational acceleration of the servo motor 34 and the acceleration of the movable electrode 30 also change. In particular, when the torque limit of the servo motor 34 is set to a value approximately equal to or slightly larger than the torque of the servo motor 34 before the counter electrode 32 contacts the welding workpiece W, the counter electrode 32 contacts the welding workpiece W. This can be detected immediately.

  When it is determined that the counter electrode 32 is in contact with the welding workpiece W, the movement of the movable electrode 30 with respect to the counter electrode 32 and the operation of the articulated robot 12 are stopped, and it is determined that the counter electrode 32 is in contact with the welding workpiece W. Based on the position data of the tip of the wrist element 28 of the articulated robot 12 and the relative position data of the tip of the counter electrode 32 of the spot welding gun 14 with respect to the tip of the wrist element 28, the position of the surface on the counter electrode side of the welding workpiece W is determined. It detects and complete | finishes the detection process of the surface position of the welding workpiece W (step S112).

  FIG. 10 is a graph showing changes in torque, rotational speed, and rotational acceleration of the servo motor 34 in time series when detecting the counter electrode side surface of the welding workpiece W with which the counter electrode 32 contacts according to the present embodiment. (A) is a graph of torque, (b) is a graph of rotational speed, and (c) is a graph of rotational acceleration. Note that the graph showing the change in the moving speed of the movable electrode 30 with respect to the counter electrode 32 in time series is also the same as FIG. 10B, and the graph showing the change in the acceleration of the movable electrode 30 with respect to the counter electrode 32 in time series. Is the same as that shown in FIG. Further, in FIG. 10, section A is in a state where no detection operation is performed, section B is in a detection operation, the counter electrode 32 is not yet in contact with the welding workpiece W, and section C is in a detection operation. The state where the electrode 32 is in contact with the welding workpiece W is shown.

  Prior to the start of the detection operation, the movable electrode 30 is stationary with respect to the counter electrode 32 and is not driven by the servo motor 34. Therefore, in the section A, the torque of the servo motor 34 is constant at a certain value, and the rotation speed and the rotation acceleration are zero. On the other hand, since the movable electrode 30 is moved at the speed Vg with respect to the counter electrode 32 when the detection operation starts, in the section B, the servo motor 34 is moved until the moving speed of the movable electrode 30 with respect to the counter electrode 32 reaches the speed Vg. When the torque and the rotation speed increase and reach Vg, both become constant. Therefore, the acceleration of the movable electrode 30 with respect to the counter electrode 32 and the rotational acceleration of the servo motor 34 are positive values until the moving speed of the movable electrode 30 with respect to the counter electrode 32 reaches Vg. It becomes. Further, when the counter electrode 30 comes into contact with the welding workpiece W while the movable electrode 30 is in contact with the welding workpiece W in the section C, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32. As a result, the movable electrode 30 is prevented from moving relative to the counter electrode 32. As a result, the servo motor 34 is controlled to keep the moving speed Vg constant, and the torque of the servo motor 34 increases, but eventually reaches the motor output limit or torque limit and becomes constant. FIG. 10A shows that the torque limit of the servo motor 34 is necessary for moving the movable electrode 30 at the speed Vg with respect to the counter electrode 32 in a state where there is almost no load in the section B. In the section B and the section C, the torque of the servo motor 34 shows a substantially constant value. On the other hand, the moving speed of the movable electrode 30 with respect to the counter electrode 32 decreases from a predetermined value Vg and eventually becomes 0, and the movable electrode 30 stops with respect to the counter electrode 32. Therefore, the servo that drives the movable electrode 30 is used. As shown in FIG. 10B, the rotational speed of the motor 34 also decreases from a predetermined value and eventually becomes zero. Further, since the acceleration of the movable electrode 30 with respect to the counter electrode 32 changes with the moving speed of the movable electrode 30 with respect to the counter electrode 32, as shown in FIG. Then, when it turns to a negative value and the movable electrode 30 stops with respect to the counter electrode 32, it becomes 0 again.

  As described above, by setting a torque limit in the servo motor 34, it is possible to prevent the welded workpiece W from being excessively deformed by the movable electrode 30 pressing the welded workpiece W. Furthermore, when the counter electrode 32 comes into contact with the welding workpiece W, the movable electrode 30 is decelerated earlier, and the detection delay when the counter electrode 32 comes into contact with the welding workpiece W can be reduced. Further, if a torque limit is also set for the servo motors that drive the axes J1 to J5 of the articulated robot 12, the counter electrode 32 of the spot welding gun 14 moved by the articulated robot 12 presses the welding workpiece W. It is possible to prevent excessive deformation.

  Further, when the movable electrode 30 is kept in contact with the welded workpiece W, the counter electrode 32 is brought into contact with the welded workpiece W by using the articulated robot 12 to approach the welded workpiece W. When contacting W, the moving speed of the movable electrode 30 or the rotational speed of the servomotor 34 for driving the movable electrode 30 changes from a constant state and gradually decreases. Therefore, if the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 is monitored, the counter electrode 32 is welded when the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 starts to decrease from a substantially constant state. It can be determined that the workpiece W has been touched. Similarly, when the counter electrode 32 is brought into contact with the welding workpiece W by using the articulated robot 12 while keeping the movable electrode 30 in contact with the welding workpiece W, the counter electrode 32 is welded. When contacting the workpiece W, the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34 for driving the movable electrode 30 changes from 0 and turns to a negative value. Therefore, if the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34 is monitored, the counter electrode 32 is welded when the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34 changes from approximately 0 to a negative value. It can be determined that the contact point has been made.

  Further, the position data of the tip of the wrist element 28 of the articulated robot 12 when it is determined that the counter electrode 32 has contacted the welding workpiece W and the relative position of the tip of the counter electrode 32 of the spot welding gun 14 with respect to the tip of the wrist element 28. From the position data, the position data of the tip of the counter electrode 32 when it is determined that the counter electrode 32 is in contact with the welding workpiece W can be obtained. The position of the surface on the counter electrode side of the welding workpiece W can be detected.

  Here, when the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 starts to decrease from a substantially constant state, a time series curve, that is, a waveform of the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 is analyzed. Then, the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 is specified by obtaining a point (hereinafter referred to as a changing point) where the moving speed is changed from a substantially constant state to a decreasing state. The following three are examples of methods for analyzing the time-series waveform of the rotational speed of the servo motor 34 for obtaining the change point. It goes without saying that the method for analyzing the time-series waveform of the moving speed of the movable electrode 30 for obtaining the changing point of the moving speed of the movable electrode 30 is the same.

  (I) As shown in FIG. 11, a point where the amount of decrease with respect to the reference value of the rotational speed of the servo motor 34 exceeds a predetermined threshold value α (> 0) is regarded as a change point. Since the rotational speed of the servo motor 34 finally becomes 0 regardless of the rigidity of the welding workpiece W, the threshold value α may be an arbitrary value in the range from the rotational speed of the servo motor 34 in the section B to 0. The smaller the threshold α is, the earlier it can be detected that the counter electrode 32 has contacted the welding workpiece W. The threshold value α may be determined using a ratio (for example, 10%) with respect to the rotation speed of the servo motor 34 in the section B.

  (Ii) As shown in FIG. 12, the amount of change Δv per unit time Δt of the rotational speed of the servo motor 34, that is, the slope of the time-series waveform of the rotational speed of the servo motor 34 is a predetermined threshold value β. Points that are equal to or less than (≦ 0) are regarded as change points. When the counter electrode 32 comes into contact with the welding workpiece W, as shown in FIG. 12, the moving speed of the servo motor 34 decreases monotonously, so the threshold value β becomes a negative value. If it is desired to detect immediately after the start of the decrease, the threshold value β may be a negative value close to zero.

  (Iii) When the counter electrode 32 comes into contact with the welding workpiece W, the rotation speed of the servo motor 34 shows a monotonous decrease, so that the slope of the time series waveform of the rotation speed of the servo motor 34 becomes a negative value. Therefore, as shown in FIG. 13, first, the change point of the rotation speed of the servo motor 34 is obtained by the method (i) or (ii), and this is used as a temporary change point. The amount of change per unit time of the rotational speed of the servo motor 34 (that is, the slope of the time series waveform of the rotational speed) is obtained by going back in time along the time series waveform of the rotational speed, and the slope of the time series waveform of the rotational speed. The point at which becomes almost zero is regarded as a true change point, and at the true change point, it is considered that the rotational speed has started to decrease from a substantially constant state. Since the time series waveform of the rotation speed of the servo motor 34 is a set of discrete sampling points, there is not always a point where the slope becomes 0 on the time series waveform. Therefore, in practice, the time point of the time series waveform of the rotational speed goes back from the temporary change point (time Td1) along the time series waveform of the rotational speed, and the slope of the rotational speed time series waveform changes from a negative value to 0 or a positive value ( The time Td3) is specified, and the sampling point (time Td2) immediately before that is set as the true change point. According to such a method, as shown in FIG. 13, even when the rotational speed of the servo motor 34 decreases in a curved line, the rotational speed of the servo motor 34 immediately after the rotational speed starts to decrease from a constant state. The time can be specified accurately, and the position of the counter electrode side surface of the welding workpiece W can be accurately obtained.

  Since the moving speed Vg of the movable electrode 30 with respect to the counter electrode 32 is arbitrarily determined in advance, it is not affected by the rigidity of the welding workpiece W, the spot welding gun 14 and the articulated robot, and is constant from the speed Vg. It becomes easy to set the above-described threshold value for specifying a point where the state has changed to a decrease.

  The same idea can be basically applied to the determination of detection based on the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34. When the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34 changes from a substantially zero state to a negative value, the time series curve, that is, the waveform of the acceleration of the movable electrode 30 or the rotational acceleration of the servo motor 34 is analyzed. It is specified by obtaining a point where the acceleration of 30 or the rotational acceleration of the servo motor 34 has turned negative from a substantially zero state (hereinafter referred to as a change point). The following three are examples of the analysis method of the time series waveform of the rotational acceleration of the servo motor 34 for obtaining the change point. It goes without saying that the method for analyzing the time series waveform of the acceleration of the movable electrode 30 for obtaining the change point of the acceleration of the movable electrode 30 is the same.

  (I) As shown in FIG. 14, the point at which the rotational acceleration of the servomotor 34 has a negative value is regarded as a change point. However, since the actual rotational speed of the servo motor 34 changes minutely, in order to prevent erroneous detection, the point at which the rotational acceleration of the servo motor 34 becomes a negative value is not a change point, but is determined in advance. It is preferable to regard the point below the threshold value γ (<0) as the change point. The threshold value γ may be an arbitrary negative value. If the threshold value γ is set to a negative value close to 0, it is possible to quickly detect that the counter electrode 32 has contacted the welding workpiece W.

  (Ii) The rotational acceleration of the servo motor 34 is not limited to a case where the rotation acceleration is negatively stepped from 0 to a negative value (negative acceleration) as shown in FIG. It may change gradually to acceleration. In such a case, as shown in FIG. 15, when the counter electrode 32 comes into contact with the welding workpiece W, the rotational speed of the servomotor 34 decreases monotonously, and accordingly, the rotational acceleration of the servomotor 34 is first increased. Within a very short period of time, the voltage gradually decreases from 0 to a specific negative value, continues to be constant at a specific negative value, and then gradually increases again to reach 0. Therefore, the change amount Δa per unit time Δt of the rotational acceleration of the servomotor 34, that is, the point where the inclination of the time series waveform of the rotational acceleration of the servomotor 34 is equal to or less than a predetermined threshold δ (≦ 0) is changed. Consider a point. If it is desired to detect immediately after the start of the decrease, the threshold value δ may be a negative value close to zero.

  (Iii) When the counter electrode 32 comes into contact with the welding workpiece W, the rotational acceleration of the servomotor 34 decreases from 0, so that the slope of the time series waveform of the rotational acceleration of the servomotor 34 becomes a negative value. Therefore, as shown in FIG. 16, first, the change point of the rotational acceleration of the servo motor 34 is obtained by the method (i) or (ii), and this is used as a temporary change point. The amount of change per unit time of the rotational acceleration of the servo motor 34 (that is, the slope of the time series waveform of the rotational acceleration) is obtained by going back the time along the time series waveform of the rotational acceleration, and the slope of the time series waveform of the rotational acceleration. Is a point where the value becomes almost zero, and at the true point of change, it is considered that the rotational acceleration has started to decrease from a state of almost zero. Since the time series waveform of the rotational acceleration of the servo motor 34 is a set of discrete sampling points, there is not always a point where the slope becomes 0 on the time series waveform. Therefore, actually, the time point of the time series waveform of the rotational acceleration goes back from the temporary change point (time Td1) along the time series waveform of the rotational acceleration, and the slope of the rotational acceleration time series waveform changes from a negative value to 0 or a positive value ( The time Td3) is specified, and the sampling point (time Td2) immediately before that is set as the true change point. According to such a method, as shown in FIG. 16, even when the rotational speed of the servo motor 34 decreases in a curve, immediately after the rotational acceleration of the servo motor 34 turns negative from a substantially zero state. Can be accurately identified, and the position of the counter electrode side surface of the welding workpiece W can be accurately obtained.

  In this embodiment, in order to minimize the deformation of the welding workpiece W by the movable electrode 30 and the counter electrode 32, if it is determined that the counter electrode 32 has contacted the welding workpiece W, the robot controller 16 and the spot The welding gun control device 18 stops the operation of the articulated robot 12 and the servo motor 34, and the position data of the tip of the wrist element 28 of the articulated robot 12 when it is determined that the counter electrode 32 has contacted the welding workpiece W. From the relative position data of the counter electrode 32 of the spot welding gun 14 with respect to the tip of the wrist element 28, the position of the counter electrode side surface of the welding workpiece W is detected. However, when the analysis method (iii) is adopted, the time series data of the rotational speed and / or rotational acceleration of the servo motor 34 necessary for the analysis is prepared at the time when the temporary change point is specified, and the detection operation is performed thereafter. Therefore, the operation of the articulated robot 12 and the servo motor 34 may be stopped when the temporary change point is specified, not after the counter electrode 32 is determined to have contacted the welding workpiece W. Good.

  Further, even after it is determined that the counter electrode 32 and the welding workpiece W are in contact with each other, the articulated robot 12 and the servo motor 34 coast and the articulated robot 12 and the servo motor 34 are stopped. The wrist element 28 of the articulated robot 12 when it is determined that the position of the tip of the 12 wrist elements 28 and the relative position of the tip of the movable electrode 30 with respect to the tip of the counter electrode 32 and the movable electrode 30 and the welding workpiece W are in contact with each other. And the relative position of the tip of the movable electrode 30 with respect to the tip of the counter electrode 32 may be different. Therefore, when the final purpose is to position the movable electrode 30 and the counter electrode 32 of the spot welding gun 14, the counter electrode 32 and the welding workpiece W are in contact with each other in order to correct the coasting of the articulated robot 12. The articulated robot 12 may be moved to the position when it is determined that the servo motor 34 has been rotated.

  With reference to FIG. 17, a second embodiment of the welding workpiece position detection method of the present invention will be described. Also in the second embodiment, similarly to the first embodiment, in the spot welding system 10 shown in FIG. 1, a predetermined speed is set in a direction in which the movable electrode 30 approaches the counter electrode 32 by the servo motor 34. While moving at Vg, the articulated robot 12 holds the spot welding gun 14 and moves relative to the welding work W fixed on the work fixing base (not shown) in the direction of approaching each other at the same speed Vr as the speed Vg. Let However, the second embodiment automatically controls the articulated robot 12 by controlling the moving speed or acceleration of the spot welding gun 14 by the articulated robot 12 so as to always match the moving speed and acceleration of the movable electrode 30. And detecting that the movement speed of the movable electrode 30 has decreased or that the acceleration of the movable electrode 30 has changed from 0 to a negative value by detecting that the articulated robot 12 has stopped. ing.

  Since steps S200 to S208 of the second embodiment are exactly the same as S100 to S108 of the first embodiment, description thereof is omitted here, and only different steps are described. Also in the second embodiment, as shown in FIG. 3, the movable electrode 30 is moved to the counter electrode 32 by the servo motor 34 from a state where the movable electrode 30 is positioned so as to contact the movable electrode side surface of the welding workpiece W. The spot welding gun 14 and the welding workpiece W are moved in a direction in which the counter electrode 32 and the welding workpiece W are moved away from each other by using the multi-joint robot 12 in the direction of approaching the workpiece. Is relatively moved at a speed Vr equal to the speed Vg, and at least one of the moving speed and acceleration of the movable electrode is monitored. If necessary, the servo motor 34 for driving the movable electrode 30 and the articulated robot 12 A torque limit is set for the servo motor that drives each axis (steps S200 to S208). That is, the counter electrode 32 is brought close to the welding workpiece W while keeping the movable electrode 30 in contact with the welding workpiece W, and at the same time, at least one of the moving speed and acceleration of the movable electrode 30 is monitored. The moving speed and acceleration of the movable electrode 30 may be measured directly, or may be obtained from the rotational speed and rotational acceleration of the servo motor 34 that drives the movable electrode 30. At the time of monitoring, the position data of the tip of the wrist element 28 of the multi-joint robot 12 and the counter electrode 32 together with information on the moving speed or acceleration of the movable electrode 30 or the rotational speed or rotational acceleration of the servo motor 34 at each sampling time. The relative position data of the movable electrode 30 is sequentially recorded.

  On the other hand, in the second embodiment, unlike the first embodiment, the robot control device 16 makes the spot by the articulated robot 12 match the moving speed or acceleration of the movable electrode 30 with respect to the counter electrode 32 by the servo motor 34. The moving speed or acceleration of the welding gun 14, that is, the moving speed or acceleration of the counter electrode 32 is controlled (step S210).

  When the counter electrode 32 comes into contact with the welding workpiece W while the movable electrode 30 is kept in contact with the welding workpiece W, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32, and the counter electrode 32 is sandwiched. The movement of the movable electrode 30 with respect to is prevented. Then, since the servo motor 34 is controlled so as to keep the moving speed Vg constant, the servo motor 34 that tries to output a larger torque reaches the output limit of the servo motor 34 and drives the movable electrode 30. The rotational speed of the decreases. As a result, the set speed Vg cannot be maintained, and the moving speed of the movable electrode 30 with respect to the counter electrode 32 decreases from a predetermined value Vg to zero. At this time, the acceleration of the movable electrode 30 with respect to the counter electrode 32 changes from 0 to a negative value.

  Further, in the present embodiment, the spot welding gun 14 and the moving speed of the counter electrode 32 by the articulated robot 12 are controlled so as to match the moving speed of the movable electrode 30 with respect to the counter electrode 32. The moving speed of the spot welding gun 14 and its counter electrode 32, that is, the moving speed of the tip of the wrist element 28 of the multi-joint robot 12 is reduced to a speed Vr (= Vg) as the moving speed of the movable electrode 30 relative to the counter electrode 32 decreases. Decreases to zero. Similarly, when controlling the acceleration of the spot welding gun 14 and its counter electrode 32 by the articulated robot 12 so as to match the acceleration of the movable electrode 30 with respect to the counter electrode 32, the acceleration of the movable electrode 30 with respect to the counter electrode 32 is similarly controlled. Along with the decrease, the acceleration of the spot welding gun 14 and its counter electrode 32 by the articulated robot 12, that is, the acceleration of the tip of the wrist element 28 of the articulated robot 12 is decreased. That is, finally, the movable electrode 30 and the counter electrode 32 are stopped while sandwiching the welding work W. Accordingly, it is determined whether or not the moving speed of the tip of the wrist element 28 of the multi-joint robot 12 has become zero (step S212), and the multi-joint robot when the movable electrode 30 and the counter electrode 32 have stopped is reached. Based on the position data of the tip of the 12 wrist elements 28 and the relative position data of the tip of the counter electrode 32 of the spot welding gun 14 with respect to the wrist element 28, the position of the counter electrode side surface of the welding workpiece W is detected, and the welding workpiece The process of detecting the surface position of W is terminated (step S214).

  FIG. 18 shows changes in the torque and rotational speed of the servo motor 34 and the movement speed of the tip of the wrist element 28 of the articulated robot when detecting the counter electrode side surface of the welding workpiece W that the counter electrode 32 contacts according to the present embodiment. FIG. 3 shows a time-series graph, where (a) is a torque graph of the servo motor 34, (b) is a graph of the rotational speed of the servo motor 34, and (c) is a tip of the wrist element 28 of the articulated robot 12. It is a graph of the moving speed of. Further, FIG. 19 shows changes in the torque and rotational acceleration of the servomotor 34 and the acceleration at the tip of the wrist element 28 of the articulated robot when detecting the counter electrode side surface of the welding workpiece W that the counter electrode 32 contacts according to the present embodiment. (A) is a graph of torque of the servo motor 34, (b) is a graph of rotational acceleration of the servo motor 34, and (c) is a graph of the wrist element 28 of the articulated robot 12. It is a graph of acceleration at the tip. The graph showing the change in the moving speed of the movable electrode 32 with respect to the counter electrode 32 in time series is also the same as FIG. 18B, and the graph showing the change in the acceleration of the movable electrode 32 with respect to the counter electrode 32 in time series. Is the same as FIG. 19B. In FIGS. 18 and 19, section A is a state where no detection operation is performed, section B is a detection operation and the counter electrode 32 is not yet in contact with the welding workpiece W, and section C is a detection operation. A state in which the counter electrode 32 is in contact with the welding workpiece W is shown.

  Prior to the start of the detection operation, the movable electrode 30 is stationary with respect to the counter electrode 32, is not driven by the servo motor 34, and the articulated robot 12 is not driven. Therefore, in section A, the torque of the servo motor 34 is constant, the rotational speed and rotational acceleration are zero, and the moving speed and acceleration of the tip of the wrist element 28 of the articulated robot 12 are also zero. On the other hand, when the detection operation starts, the movable electrode 30 is moved with respect to the counter electrode 32 at a speed Vg, and the spot welding gun 14 and the counter electrode 32 are moved by the articulated robot 12 with respect to the counter electrode 32. It is moved at the same speed as the speed Vg. Therefore, in the section B, the torque and the rotational speed of the servo motor 43 increase until the moving speed of the movable electrode 30 with respect to the counter electrode 32 reaches the speed Vg. The movement speed of the tip of the wrist element 28 increases to a speed Vg and becomes constant. Therefore, the rotational acceleration of the servomotor 34 increases until the moving speed of the movable electrode 30 with respect to the counter electrode 32 reaches Vg, and becomes 0 when reaching the Vg. Acceleration shows similar behavior. Further, when the counter electrode 30 comes into contact with the welding workpiece W while the movable electrode 30 is in contact with the welding workpiece W in the section C, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32. As a result, the movable electrode 30 is prevented from moving relative to the counter electrode 32. As a result, the servo motor 34 is controlled so that the moving speed Vg is kept constant and the torque of the servo motor 34 increases, but eventually reaches the motor output limit or torque limit and becomes constant. .

  FIG. 18A shows that the torque limit of the servo motor 34 is necessary for moving the movable electrode 30 at the speed Vg with respect to the counter electrode 32 in a state where there is almost no load in the section B. In the section B and the section C, the torque of the servo motor 34 shows a substantially constant value. On the other hand, the moving speed of the movable electrode 30 with respect to the counter electrode 32 decreases from a predetermined value Vg and eventually becomes zero, and the movable electrode 30 stops with respect to the counter electrode 32. As shown in FIG. 18B, the rotational speed of the motor 34 also decreases from a predetermined value and eventually becomes 0, and the servo motor 34 stops. Further, since the moving speed of the tip of the wrist element 28 of the articulated robot 12 matches the moving speed of the movable electrode 30 with respect to the counter electrode 32, it decreases from a predetermined value Vg and eventually becomes 0, and the articulated robot 12 also stops. Similarly, the acceleration of the movable electrode 30 with respect to the counter electrode 32 changes from 0 to a negative value and eventually becomes 0 again. The movable electrode 30 stops with respect to the counter electrode 32, so that the servo motor 34 that drives the movable electrode 30. Also, as shown in FIG. 19B, the rotation speed of the servo motor 34 changes from 0 to a negative value and becomes 0 again, and the servo motor 34 stops. Further, since the moving speed of the tip of the wrist element 28 of the articulated robot 12 coincides with the acceleration of the movable electrode 30 with respect to the counter electrode 32, the moving speed changes from 0 to a negative value and becomes 0 again, and the articulated robot 12 also stops. .

  As described above, by setting a torque limit in the servo motor 34, it is possible to prevent the welded workpiece W from being excessively deformed by the movable electrode 30 pressing the welded workpiece W. Further, when the counter electrode 32 comes into contact with the welding workpiece W, the movable electrode 30 is decelerated more quickly, and the detection delay when the counter electrode 32 comes into contact with the welding workpiece W can be reduced. Furthermore, if a torque limit is also set for the servo motors that drive the axes J1 to J5 of the articulated robot 12, the counter electrode 32 of the spot welding gun 14 moved by the articulated robot 12 presses the welding workpiece W. It is possible to prevent excessive deformation.

  Further, since the moving speed of the spot welding gun 14 and the counter electrode 32 by the articulated robot 12 is controlled so as to coincide with the moving speed of the movable electrode 30 with respect to the counter electrode 32, the counter electrode 32 contacts the welding workpiece W. Thus, the welding workpiece W is sandwiched between the movable electrode 30 and the counter electrode 32. When the movable electrode 30 stops with respect to the counter electrode 32, the operation of the articulated robot 12 also stops. Therefore, when the movement of the movable electrode 30 with respect to the counter electrode 32 or the movement of the articulated robot 12 is stopped, it is determined that the counter electrode 32 has contacted the welding workpiece W. There is no need to detect when the moving speed of the movable electrode 30 with respect to the electrode 32 or the rotational speed of the servo motor 34 starts to decrease from a substantially constant state. As a result, in the first embodiment, each threshold value necessary for specifying the time point when the moving speed of the movable electrode 30 or the rotational speed of the servo motor 34 starts to decrease from a substantially constant state is experimentally determined in advance. It becomes unnecessary, and it is possible to detect the position of the counter electrode side surface of the welding workpiece W that the counter electrode 32 contacts without depending on the rigidity of the welding workpiece W, the articulated robot 12 and the spot welding gun 14. Become. Furthermore, since the movable electrode 30 and the counter electrode 32 are finally stopped in contact with the welding workpiece W, the thickness t of the welding workpiece W is measured from the positions of the tips of the movable electrode 30 and the counter electrode 32 at this time. It is also easy to do. The same applies to the case where the spot welding gun 14 and the acceleration of the counter electrode 32 by the articulated robot 12 are controlled so as to coincide with the acceleration of the movable electrode 30 with respect to the counter electrode 32.

  As mentioned above, although this invention was demonstrated based on embodiment shown in figure, this invention is not limited to embodiment mentioned above. For example, in the above embodiment, the moving speed or acceleration of the movable electrode 30 is monitored, and at the same time, the position data of the tip of the wrist element 28 of the articulated robot 12 and the relative position data of the movable electrode 30 with respect to the counter electrode 32 are recorded. Like that. However, since the articulated robot 12 and the movable electrode 30 operate based on operation commands in time series from the robot control device 16 and the spot welding gun control device 18, the articulated robot 12 and the movable electrode that have been executed are operated. The position data of the tip of the wrist element 28 of the articulated robot 12 at the past time and the relative position data of the movable electrode 30 with respect to the counter electrode 32 may be obtained from 30 operation commands.

DESCRIPTION OF SYMBOLS 10 Spot welding system 12 Articulated robot 14 Spot welding gun 30 Movable electrode 32 Counter electrode 34 Servo motor

Claims (11)

A spot welding gun having a movable electrode driven by a servo motor and a counter electrode disposed to face the movable electrode, and holding one of the spot welding gun and the welding workpiece and moving the spot welding gun relative to the other. An articulated robot, the movable electrode and the counter electrode are moved closer to and away from each other by the servo motor, and the welding workpiece is sandwiched between the movable electrode and the counter electrode of the spot welding gun. In a spot welding system that performs spot welding of the welding workpiece position detection method for detecting the surface position of the welding workpiece that the counter electrode contacts,
After positioning the movable electrode in contact with the surface of the welding workpiece, the movable electrode is moved at a predetermined speed Vg in a direction in which the servomotor approaches the counter electrode, and at the same time, the articulated robot is moved. The moving speed and acceleration of the movable electrode with respect to the counter electrode while the spot welding gun and the weld work are moved relative to each other at the same speed as the speed Vg so that the counter electrode and the weld work are moved closer to each other. By detecting at least one of the counter electrode and the welding workpiece, and detecting the surface position of the welding workpiece in contact with the counter electrode from the position of the counter electrode when detected. A method for detecting a position of a welded workpiece.   The welding work position detection method according to claim 1, wherein a torque limit is set in a servo motor for driving the movable electrode with respect to the counter electrode.   The torque limit of the servo motor is determined based on a torque value of the servo motor when the spot welding gun and the welding workpiece are relatively moved at the same speed as the speed Vg. Welding workpiece position detection method.   After the movable electrode is positioned so as to contact the surface of the welding workpiece, the opposing electrode is further moved by the servo motor from a state where the movable electrode is positioned at a position offset by a predetermined distance from the surface of the welding workpiece. The spot welding gun and the welding are moved so that the movable electrode is moved at a predetermined speed Vg in a direction approaching the electrode, and at the same time, the counter electrode and the welding workpiece are brought close to each other using the articulated robot. The welding work position detection method according to claim 2 or 3, wherein the work is relatively moved at the same speed as the speed Vg.   At least one of the moving speed and acceleration of the movable electrode with respect to the counter electrode is monitored, and when the moving speed of the movable electrode with respect to the counter electrode changes from constant to decreasing or the acceleration of the movable electrode with respect to the counter electrode starts from zero. When it turns negative, it is determined that the counter electrode is in contact with the welding workpiece, and when the moving speed of the movable electrode with respect to the counter electrode changes from constant to decrease, or the acceleration of the movable electrode with respect to the counter electrode The welding work position according to any one of claims 1 to 4, wherein a surface position of the welding work with which the counter electrode comes into contact is detected from a position of the counter electrode when the value changes from 0 to negative. Detection method.   A time series of the moving speed or acceleration of the movable electrode relative to the counter electrode from the time when at least one value of the moving speed and acceleration of the movable electrode with respect to the counter electrode or the amount of change per unit time becomes a negative threshold value or less. The movable electrode with respect to the counter electrode is moved back in time along the waveform, and when the amount of change per unit time of the moving speed or acceleration of the movable electrode with respect to the counter electrode changes from a negative value to 0 or a positive value. The welding work position detection method according to claim 5, wherein it is determined that the movement speed of the first electrode has changed from a constant to a decrease or the acceleration of the movable electrode with respect to the counter electrode has changed from zero to negative.   At least one of the moving speed and acceleration of the movable electrode with respect to the counter electrode is monitored, and when the moving speed of the movable electrode with respect to the counter electrode decreases or the acceleration of the movable electrode with respect to the counter electrode changes from 0 to negative Sometimes, the speed at which the spot welding gun and the welding workpiece are moved relative to each other using the articulated robot is also reduced by the same reduction amount, or the spot welding gun and the welding workpiece are used using the articulated robot. The acceleration of the relative movement is also decreased by the same reduction amount, and when the movement of the movable electrode or the articulated robot is stopped, it is determined that the counter electrode has contacted the welding workpiece, and the movable electrode or The welding workpiece that contacts the counter electrode from the position of the counter electrode when the movement of the articulated robot stops. Detecting the surface position, the welding workpiece position detecting method according to any one of claims 1 to 4. A spot welding gun having a movable electrode driven by a servo motor and a counter electrode disposed to face the movable electrode, and holding one of the spot welding gun and the welding workpiece and moving the spot welding gun relative to the other. An articulated robot, the movable electrode and the counter electrode are moved closer to and away from each other by the servo motor, and the welding workpiece is sandwiched between the movable electrode and the counter electrode of the spot welding gun. In the spot welding system for performing spot welding of the welding workpiece position detection method for detecting the surface position of the welding workpiece that the movable electrode and the counter electrode contact each other,
And the movable electrode and the welding workpiece, sea urchin by you approach from the state separated from each other, wherein while the spot welding gun and the welding workpiece by using the multi-joint robot moved relative, the current or torque of the servo motor When the current or torque increases to a predetermined threshold value or more than a predetermined value, or the current or torque increases to a predetermined threshold value or more than a change amount per unit time, the movable When it is determined that the electrode is in contact with the welding workpiece and the current or torque is increased to a predetermined threshold value or more than the predetermined value, or the current or torque is more than the amount of change per unit time. The welding electrode in contact with the movable electrode from the position of the movable electrode and the position of the articulated robot when increased to a predetermined threshold value or more. Detecting a surface position of the click,
Detecting a surface position of the welded workpiece that the counter electrode contacts with the welded workpiece position detecting method according to any one of claims 1 to 7;
Including a welding workpiece position detecting method. A spot welding gun having a movable electrode driven by a servo motor and a counter electrode disposed to face the movable electrode, and holding one of the spot welding gun and the welding workpiece and moving the spot welding gun relative to the other. An articulated robot, the movable electrode and the counter electrode are moved closer to and away from each other by the servo motor, and the welding workpiece is sandwiched between the movable electrode and the counter electrode of the spot welding gun. In the spot welding system for performing spot welding of the welding workpiece position detection method for detecting the surface position of the welding workpiece that the movable electrode and the counter electrode contact each other,
Wherein the movable electrode and the welding workpiece, so away from a state of being in contact with the each other physician, the while the spot welding gun and the welding workpiece by using the multi-joint robot moved relative, current or torque of the servo motor When the current or torque has increased beyond a predetermined threshold value by a predetermined threshold or when the amount of change in the current or torque per unit time has changed from a negative value to zero or a positive value When the current or torque is determined to have moved away from the welding workpiece and the current or torque has increased to a predetermined threshold value or more than the respective predetermined value , or the amount of change per unit time of the current or torque is negative. values from and a position of the movable electrode when it becomes zero or a positive value and the position of the articulated robot of the welding workpiece to the movable electrode contacts the Detecting the surface position,
Detecting a surface position of the welded workpiece that the counter electrode contacts with the welded workpiece position detecting method according to any one of claims 1 to 7;
Including a welding workpiece position detecting method. From the surface position of the welding workpiece is detected the movable electrode contact, with the surface position of the welding workpiece is detected the counter electrode contacts, further comprising the step of determining the thickness of the welding workpiece, claim The welding workpiece position detection method according to 8 or 9 . The welding work position detection method according to any one of claims 1 to 10 , wherein the welding work position detection method is executed by executing a program command for performing welding.

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