JP2004154868A - Detection method of electrode wear loss in welding gun - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the detection method of an electrode wear amount in a welding gun which can detect the electrode wear loss without causing deformation of a welded object. <P>SOLUTION: Wear amounts of a movable side electrode 6 and a fixed side electrode 7 are measured beforehand by actually performing welding, hereby an electrode wear ratio α being computed, and a position, where the movable side electrode 6 and the fixed side electrode 7 have contacted when both electrodes are made to contact before both electrodes get worn, is memorized beforehand as a reference position. Then, the total of wear amounts of the movable side electrode 6 and the fixed side electrode 7 is computed from difference between the position where the movable side electrode 6 and the fixed side electrode 7 have contacted and the reference position, and the wear loss of the movable side electrode 6 and that of the fixed side electrode 7 are computed, based on the total of wear losses of both electrodes and the electrode wear ratio α. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a resistance welding technique using servo control, and more particularly to a method for detecting an electrode wear amount of a welding gun when a servo motor is used as an electrode driving source of a spot welding gun used by being attached to an industrial electric robot. .

  With conventional resistance welding guns, the electrodes are operated by a drive source such as an air cylinder or motor, and the welding object (workpiece) is sandwiched between the paired electrodes, pressurized and held, and a large current is applied to perform welding. Had gone. Since the pair of electrodes gradually wears due to the pressurization and welding heat at the time of welding, it is necessary to detect the wear amount of the electrodes during operation of the robot and correct the position of the electrodes.

As a method of correcting the position of the electrode, Patent Document 1 describes a case of arc welding, but an automatic alignment that can easily adjust the origin of the welding torch and the workpiece at the start of welding and the position correction when the welding torch is worn (during wear). A welding device is disclosed. This is done by applying the tip of the welding torch to the origin of the work to be welded (workpiece) and setting the position of the welding torch at this time as the origin of the welding torch. The origin of the welding torch is corrected by applying the tip of the welding torch to the workpiece.
JP-A-3-52771

  However, in the method according to Patent Literature 1, the welding torch is directly applied to the workpiece to calculate the wear amount of the welding torch and correct the position of the welding torch. In this case, there is a problem that the workpiece is deformed.

  The present invention relates to a welding gun having a plurality of electrodes to be paired, such as a C-shaped welding gun and an X-shaped welding gun, capable of detecting the amount of wear of the electrodes without causing deformation of the workpiece. It is an object of the present invention to provide a method for detecting the amount of electrode wear.

  In order to achieve the above-mentioned object, in the present invention, the moving electrode as one electrode is operated by a servomotor, and the workpiece is fixed to the moving electrode and the fixed electrode as the other electrode forming a pair. In the welding gun that holds the pinch and presses, the amount of wear of the moving side electrode and the fixed side electrode is measured by actually performing welding in advance, thereby calculating the electrode wear ratio α, and the moving side electrode and the fixed side electrode are measured. The two electrodes are brought into contact before wear occurs, and the contact position at this time is stored in advance as a reference position, and thereafter, the position where the moving-side electrode and the fixed-side electrode contact and the reference position are determined. The sum of the wear amount of the movable electrode and the fixed electrode is calculated from the difference, and based on the total wear amount of the movable electrode and the fixed electrode and the electrode wear ratio α, the wear amount and the fixed amount of the movable electrode are fixed. Side power An electrode wear amount detection method for a welding gun, wherein the electrode wear amount is calculated.

  By adopting such a configuration, before and after the electrodes are worn, the position of the moving electrode when the moving electrode and the fixed electrode are brought into contact with each other is detected, and the difference between the two positions is calculated. To determine the total wear. Here, if the electrode wear ratio α is set as, for example, the ratio of the fixed-side electrode wear amount to the total electrode wear amount, the fixed-side electrode wear ratio is determined based on the determined total electrode wear amount and the electrode wear ratio α. The amount can be calculated. Further, the wear amount of the movable electrode can be calculated by subtracting the wear amount of the fixed electrode calculated from the total wear amount of the electrodes.

  As described above, according to the present invention, the amount of wear of both electrodes is determined by bringing the moving-side electrode and the fixed-side electrode into contact with each other, so that the workpiece is not deformed as in the related art. It has become possible to detect the amount of electrode wear.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an apparatus to which a method for detecting an electrode wear amount of a welding gun according to a best mode for carrying out the present invention is applied. FIG. 2 is a flowchart showing a process flow of a method for detecting an electrode wear amount of a welding gun according to the best mode for carrying out the present invention. FIG. 3 is an operation explanatory view of the C-shaped welding gun. FIG. 4 is an explanatory diagram showing a correction state of the electrode position. The welding gun shown in the present embodiment is a C-shaped welding gun, but may be a welding gun having two pairs of electrodes such as an X-shaped welding gun.

  As shown in FIG. 1, an industrial robot controlled by a servomotor with a position detector (not shown) has another servomotor 3 with a position detector 4 at the arm tip 1 as a drive source of a moving-side electrode 6. A C-type welding gun 2 in which only the movable electrode 6 is opened and closed is attached. The moving-side electrode 6 is driven via the ball screw 5 by the servomotor 3 controlled by an electrode driving circuit 14 in the control device. The fixed electrode 7 is attached to the fixed side of the C-type welding gun 2 and moves up and down the C-type welding gun 2 attached to the robot arm tip 1 controlled by the robot drive circuit 12 in the control device. This makes it move up and down.

  Next, a circuit configuration in the control device will be described. The program data 9 includes the robot position data and the moving-side electrode position data of each welding point in a state where the electrodes are not worn, and the electrode total wear amount detection position (the robot position data and movement when detecting the electrode wear amount). Side electrode position data) is stored in advance. In addition, the reference position writing / wear amount detection switching circuit 16 includes “reference position writing (writing)”, “wear amount detection (detection)”, and a neutral state (a state that is neither “writing” nor “detection”). Can be set to. Here, the position data read from the program data 9 by the program data reading circuit 10 is made different depending on the setting state of the reference position writing / wear amount detection switching circuit 16. That is, when the reference position writing / wear amount detection switching circuit 16 is in the neutral state, the program data reading circuit 10 reads the robot position data and the moving-side electrode position data of each welding point from the program data 9. On the other hand, when the reference position writing / wear amount detection switching circuit 16 is selected to “write” or “detect”, the electrode total wear amount detection position is read from the program data 9. The robot position data is sent to the robot position command creation circuit 11, and the moving-side electrode position data is sent to the electrode command position creation circuit 13.

  The electrode position detection circuit 8 reads the electrode position from the position detector 4. Only when the reference position writing / wear amount detection switching circuit 16 is set to “writing” or “detection” and the position data detected by the position detector 4 does not change, the electrode position detection circuit 8 The electrode position is sent to the reference position writing / wear amount detection switching circuit 16. Here, when the reference position writing / wear amount detection switching circuit 16 is selected as “writing”, the electrode position at this time is written to the electrode total reference position memory 18 as the electrode total reference position. On the other hand, when the reference position writing / wear amount detection switching circuit 16 is selected as "detection", the electrode total wear amount and the fixed-side electrode wear amount are determined from the electrode position, the electrode total reference position and the electrode wear ratio α at this time. It is calculated and written to the electrode total wear amount memory 20 and the fixed-side electrode wear amount memory 15, respectively. The electrode wear ratio α is a ratio of the wear amount of the fixed-side electrode 7 to the total wear amount of the electrodes, and is a value determined by welding conditions such as the type of the electrode used, the type of the work to be welded, and the time for one welding. It is obtained by actually performing welding several times and measuring the amount of wear of the electrodes.

  The output timing of the position data stored in each of the electrode total reference position memory 18, the electrode total wear amount memory 20, and the fixed-side electrode wear amount memory 15 depends on the setting state of the reference position writing / wear amount detection switching circuit 16. different. That is, the electrode total reference position memory 18 outputs data only when the reference position writing / wear amount detection switching circuit 16 is selected as “detection”. The electrode total wear amount memory 20 and the fixed-side electrode wear amount memory 15 output data only when the reference position writing / wear amount detection switching circuit 16 is in the neutral state.

  The fixed-side electrode wear amount output from the fixed-side electrode wear amount memory 15, which is a correction amount, is added to the robot position data of the welding point output from the robot position command creation circuit 11 and sent to the robot drive circuit 12. Similarly, the electrode total wear amount output from the electrode total wear amount memory 20 as a correction amount is added to the moving-side electrode position data of the welding point output from the electrode position command creation circuit 13 and sent to the electrode drive circuit 14. .

  Next, the flow of processing in this embodiment will be described with reference to the flowchart of FIG. 2 and the operation explanatory diagram of the C-type welding gun of FIG. Note that the description of "step **" (** is an integer) in the following description corresponds to the reference numeral indicating the step number in the flowchart of FIG.

  First, detection of the electrode total reference position is performed. As shown in FIG. 3A, two unused pairs of electrodes, namely, the movable side electrode 6 and the fixed side electrode 7 are attached to the C-shaped welding gun 2, and a reference position writing / wear amount detection switching circuit is provided. 16 is set to "write" (referred to as a reference position write mode). The moving electrode 6 moves toward the fixed electrode 7 (step 31), and the current position data P of the moving electrode 6 is read by the position detector 4 and the electrode position detecting circuit 8 (step 32). The current position data P is compared with the position data P 'read in the previous scan, and if they have the same value, as shown in FIG. 3B, the movable electrode 6 comes into contact with the fixed electrode 7 and stops. It is determined that the operation has been performed (Step 33Y), and the operation of the moving-side electrode 6 is stopped by stopping the rotation of the servomotor 3 (Step 35), and the process proceeds to Step 36. On the other hand, if the current position data P and the position data P 'read in the previous scan are not the same value (step 33N), steps 32 to 33 are repeated (step 34). In step 36, since the reference position writing / wear amount detection switching circuit 16 is in the reference position writing mode (step 36Y), the current position data P is stored in the electrode total reference position memory 18 as the electrode total reference position P1. Remember.

  Second, the amount of electrode wear is detected. FIG. 3C shows a state in which the length of two unused pairs of electrodes changes due to wear. The reference position writing / wear amount detection switching circuit 16 is selected to "detect" (wear amount detection mode). The moving electrode 6 moves toward the fixed electrode 7 (step 31), and the current position data P of the moving electrode 6 is read by the position detector 4 and the electrode position detecting circuit 8 (step 32). The current position data P is compared with the position data P 'read in the previous scan, and if they have the same value, the moving side electrode 6 comes into contact with the fixed side electrode 7 and stops as shown in FIG. Then, the operation of the moving-side electrode 6 is stopped by stopping the rotation of the servo motor 3 (step 35Y), and the process proceeds to step 36. On the other hand, if the current position data P and the position data P 'read in the previous scan are not the same value (step 33N), steps 32 to 33 are repeated (step 34). In step 36, since the reference position writing / wear amount detection switching circuit 16 is in the wear amount detection mode (step 36N), the electrode total wear amount Lt is calculated from the current position data P and the electrode total reference position P1 by " Lt = P-P1 "(step 38), and this is stored in the electrode total wear amount memory 20 (step 39). Further, from the electrode wear ratio α (0 ≦ α ≦ 1), the wear amount Ls of the fixed-side electrode 7 is obtained by “Ls = Lt × α” (step 40), and this is stored in the fixed-side electrode wear amount memory 15. (Step 41).

  The position correction of the movable electrode 6 and the fixed electrode 7 is performed as shown in FIG. FIG. 4A shows an initial state before the electrodes are worn. FIG. 4B shows a state in which the fixed side electrode 7 is worn by Ls and the movable side electrode 6 is worn by Lm. As shown in FIG. 4C, the position of the fixed-side electrode 7 is determined by the amount of wear Ls of the fixed-side electrode 7 read from the fixed-side electrode wear amount memory 15 in the direction from the fixed-side electrode 7 to the moving-side electrode 6. The correction is made by operating the C-type welding gun 2 by the amount. As shown in FIG. 4D, the position of the movable electrode 6 is servo-controlled in the direction from the movable electrode 6 to the fixed electrode 7 by the total electrode wear Lt read from the total electrode wear memory 20. The correction is made by rotating the motor 3. Here, the position correction amount of the moving side electrode 6 is not the wear amount Lm of the moving side electrode 6 but the electrode total wear amount Lt. Since the position of the fixed electrode 7 is corrected by operating the C-type welding gun 2, the position of the movable electrode 6 is also adjusted by the wear amount Ls of the fixed electrode 7 when the position of the fixed electrode 7 is corrected. This is because the amount of correction of the movable electrode 6 is the sum of the wear amount Ls of the fixed electrode 7 and the wear amount Lm of the movable electrode 6, that is, the total electrode wear amount Lt.

  As described above, in the present embodiment, the position of the movable electrode 6 when the movable electrode 6 is brought into contact with the fixed electrode 7 before and after the electrode is worn is detected, and the difference between the two positions is detected. Is calculated to obtain the total wear of the electrode, and further, the wear of the fixed-side electrode 7 is obtained from the total wear of the electrode and the electrode wear ratio α. Further, the wear amount of the movable electrode 6 was determined by subtracting the wear amount of the fixed electrode 7 from the total wear amount of the electrodes. According to this method, the amount of wear of both electrodes can be obtained in a short time only by bringing the movable electrode 6 and the fixed electrode 7 into contact with each other. As described above, according to the present embodiment, the amount of wear of both electrodes is determined by bringing the moving-side electrode 6 and the fixed-side electrode 7 into contact with each other, so that the workpiece is deformed as in the related art. Without this, it becomes possible to detect the amount of wear of the electrode.

  The correction of the electrode position is performed before welding the first point after the amount of wear of the electrode has significantly changed due to electrode replacement or electrode polishing, and is performed for each preset number of welding points during welding operation. For example, highly accurate electrode positioning can be performed.

FIG. 1 is a block diagram showing a configuration of an apparatus to which a method for detecting an electrode wear amount of a welding gun according to a best mode for carrying out the present invention is applied. It is a flowchart which shows the flow of a process of the electrode wear amount detection method of the welding gun which concerns on the best mode for implementing this invention. It is operation | movement explanatory drawing of a C type welding gun. FIG. 5 is an explanatory diagram showing a correction state of an electrode position.

Explanation of reference numerals

1 Arm tip 2 C type welding gun (welding gun)
3 Servo motor 6 Moving side electrode 7 Fixed side electrode

Claims (1)

In a welding gun that operates a moving-side electrode as one electrode by a servomotor, and presses and holds an object to be welded between the moving-side electrode and a fixed-side electrode as the other electrode that forms a pair,
The wear amount of the movable side electrode and the fixed side electrode is measured by actually performing welding in advance, and the electrode wear ratio α is calculated thereby,
Before the moving-side electrode and the fixed-side electrode are worn, these two electrodes are brought into contact with each other, and the position where the two electrodes come into contact at this time is stored in advance as a reference position,
Thereafter, the sum of the wear amount of the movable electrode and the fixed electrode is calculated from the difference between the position where the movable electrode and the fixed electrode abut and the reference position,
A welding gun for calculating the amount of wear of the movable electrode and the amount of wear of the fixed electrode based on the total amount of wear of the movable electrode and the fixed electrode and the electrode wear ratio α. Electrode wear detection method.

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