JP3640132B2 - In-situ indexing method for welding gun - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for determining the original position of a welding gun supported by a welding robot.
[0002]
[Prior art]
Conventionally, spot welding is performed by attaching a welding gun to the tip of a welding robot via a tool changer, driving the welding gun by the robot, and sequentially moving the welding gun to the welding spot position of the workpiece, for example. No. 276279 is known.
The welding gun is attached to and detached from the welding robot at the tool changer site. When the welding gun is an electric servo welding gun, if the welding gun is removed at the tool changer part, the power supply to the welding gun side is cut off and the welding gun side data (encoder data related to the original position etc.) is lost. A battery is usually installed on the welding gun side for data storage. However, the battery increases the weight of the welding gun, limits the driving speed by the robot, requires maintenance such as voltage check and life management, and is in place due to electrode (welding tip) wear (for example, workpiece There is a problem that it cannot cope with the correction of the deviation of the position corresponding to the center in the thickness direction.
Japanese Laid-Open Patent Publication No. 8-276279 proposes in-situ indexing using a limit switch instead of a battery. There, the replaceable servo welding gun is provided with a limit switch for detecting the origin of the movable welding tip, thereby eliminating the battery for maintaining the state on the servo welding gun side.
[0003]
[Problems to be solved by the invention]
However, the conventional method including the method of Japanese Patent Laid-Open No. 8-276279 has the following problems.
It cannot cope with the correction of the displacement of the welding gun due to electrode wear. If this correction is not performed accurately, the pair of electrodes of the welding gun cannot be accurately moved to the spot position, and the electrode is insufficiently pressurized, or the workpiece is deformed or damaged due to excessive pressure of the electrode. May occur.
In the case of JP-A-8-276279, an extra structure such as a limit switch or a mechanism for transmitting a signal from the limit switch to the controller is required.
The object of the present invention can cope with correction of the displacement of the welding gun in-situ due to electrode wear, and does not require additional parts such as a battery for data retention and a limit switch for in-situ indexing. An object is to provide a method for determining the position of a welding gun.
[0004]
[Means for Solving the Problems]
The present invention for achieving the above object is as follows.
(1) The welding robot is driven to press one electrode of the pair of electrodes of the welding gun against the fixed reference contact portion, and the welding gun bracket is applied to the stopper on the one electrode side to The step of determining the amount of wear of the one electrode from the difference between the tip position of the pressed electrode and the electrode position of the electrode when the electrode is pressed against the reference contact portion in a non-wearing state ,
The welding gun actuator is driven to bring the pair of electrodes into contact with each other, and the driving position of the welding gun actuator at that time and the driving position of the welding gun actuator when the pair of electrodes are brought into contact with each other in a non-wearing state. The sum of the wear amounts of both electrodes of the pair of electrodes is obtained from the difference , and the wear amount of the other electrode of the pair of electrodes is subtracted from the wear amount of the one electrode already obtained from the sum of the wear amounts. The desired process;
Correcting the trajectory plan of the welding gun based on the wear amount of the one electrode, and correcting the original position of the welding gun actuator based on the wear amount of the both electrodes;
In-situ indexing method of welding gun including.
[0005]
In the above method (1), the position of the tip of one electrode can be determined by pressing one of the electrodes against a fixed reference contact portion, and the tip position of the electrode that has not been worn (stored in the robot controller). The wear amount of the one electrode can be understood from the comparison with the above.
The welding gun and / or the welding robot can be displaced by equalization, and since it is not possible to know whether the detected displacement of the robot tip position is due to wear or displacement due to equalization, it is detected in a state where the equalization has been pressed, that is, detected. The electrode tip position was determined from the driving position of the welding robot in a state where the displacement of the robot tip position did not include displacement due to equalization.
One electrode may be a fixed electrode or a movable electrode. In the case of the fixed side electrode, the electrode may be pressed as it is against the reference contact portion. In the case of the movable side electrode, the electrode is set in a predetermined reference position (for example, the most pulled position) and fixed in that state ( After applying the brake), the electrode may be pressed against the reference contact portion.
In addition, wear of the other electrode of the pair of electrodes is required. The welding gun is retracted from the reference contact portion, and the welding gun actuator (actuator that moves the electrode toward the opposing electrode) is driven to contact (contact) the pair of electrode tips. The electrode drive position of the welding gun actuator (pressure shaft actuator) at this time, and the electrode drive position (stored in the robot controller) of the welding gun actuator when the electrodes are in contact with both electrodes being worn From this comparison, the total wear amount of both electrodes can be found. By subtracting the wear amount of one electrode obtained in (1) from this sum, the wear amount of the other electrode can be obtained.
Further, the original position of the welding gun is corrected by the amount of wear of the electrode. The welding gun original position by the welding robot is corrected by the amount of wear of one electrode and the driving trajectory is corrected. Based on the wear amount of both electrodes, the original position of the welding gun actuator (for example, the position of the most pulled state) is determined. to correct. As a result, the welding gun is moved to a normal spot position regardless of electrode wear, and spot welding can be executed with a normal pressure.
Also in the method (1), it is not necessary to hold data by the battery, and the original position is not determined by the limit switch. In-situ indexing is performed using only conventional parts.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an outline of an apparatus immediately before performing a welding gun in-situ indexing method according to an embodiment of the present invention, and FIGS. 2 to 4 show an apparatus in which the welding gun in-situ indexing method of the present invention is being performed. The state is shown for each process, and FIG. 5 is a flowchart showing the process.
[0007]
As shown in FIG. 1, the welding gun 1 is composed of, for example, an electric servo welding gun (however, it is not limited to this and may be a welding gun of a type in which an electrode is driven by a cylinder). The welding gun 1 has a pair of electrodes 4 _l and 4 _u . One electrode (for example, electrode 4 _l ) of the pair of electrodes 4 _l and 4 _u is a fixed electrode fixed to the welding gun body (a portion including the bracket 13), and the other electrode (for example, electrode 4 _u). ) Is a movable electrode that is advanced and retracted with respect to the fixed electrode. The movable electrode 4 _u is driven in the actuator axial direction by the welding gun actuator 5. In the case of an electric servo welding gun, the actuator 5 is a motor and a ball screw mechanism, and in the case of a cylinder drive welding gun, the actuator 5 is an air cylinder. 6 represents a transformer.
[0008]
A welding gun 1 is detachably connected to a welding robot 2 via a tool changer 3. The welding robot 2 is composed of, for example, a six-axis robot (may be a robot other than the six-axis robot), and the drive is controlled by a robot controller 7 (computer). The tool changer 3 includes a welding gun side changer 3 a and a welding robot side changer 3 b that are detachable from each other. The welding gun side changer 3 a is fixed to the welding gun 1, and the welding robot side changer 3 b is fixed to the welding robot 2. Has been. When the welding gun side changer 3a and the welding robot side changer 3b are connected, the welding gun 1 is mechanically connected to the welding robot 2 and can also transmit an electrical signal. The electric signal includes, for example, a position signal of the actuator 5 (a signal of the encoder 8 of the servo motor in the case of a servo welding gun) and an input / output signal of the welding robot controller 7.
[0009]
The welding gun 1 and / or the welding robot 2 has an equalize 9. In the illustrated example, the equalizer 9 is located on the welding gun 1 side from the tool changer 3, but the equalizer 9 may be in the welding robot 2 itself. In the illustrated example, the equalize 9 is simulated by an elastic spring that expands and contracts in the operating direction of the welding gun actuator 5 (the operating direction of the pressure shaft).
The base end of welding robot 2 (the end opposite to welding gun 1 connection side) is a fixed point. Further, a reference contact portion (for example, a reference plate) 10 is provided at a position determined with respect to the base end of the welding robot 2.
[0010]
Next, the in-situ indexing method for the welding gun according to the present invention will be described with reference to FIGS.
In FIG. 5, after performing a certain amount of spot welding with the welding gun 1, the welding is performed in step 101 in order to replace the electrode 4 with another welding gun dressed with the electrode 4 or to replace the welding gun 1 with a new electrode. The robot 2 is driven to move the robot gun mounting portion to the welding gun place, the welding gun 1 is removed at the tool changer 3 site, another dressing welding gun 1 is mounted, and the tool is changed. In step 102, the connection of another welding gun 1 at the tool changer 3 is confirmed. If not confirmed, the process returns to step 101 and the welding gun 1 is mounted again. When the connection of another welding gun 1 at the tool changer 3 is confirmed, the process proceeds to step 103 to determine the original position of the welding gun 1.
[0011]
When the tool changer 3 is attached or detached, the original position of the welding gun actuator 5 before removal is lost.
A welding gun in which a certain amount (for example, 500 spot weldings) has been welded and the original position is out of order may proceed to step 103 without replacing the welding gun 1 in order to correct the original position. Includes such cases.
In step 103, the welding robot 2 is driven to move the welding gun 1 to a reference contact portion (for example, a reference plate) 10, and the welding gun 1 is moved between the pair of electrodes 4 _l and 4 _u. The posture where the plate is located. This state is the state of FIG.
[0012]
Next, in step 104, by driving the welding robot 2 (at this time, the welding gun actuator 5 is not driven), one of the pair of electrodes 4 _l , 4 _u (for example, the fixed side electrode 4 _l). ) Is equalized 9 on the electrode 4 _l side to be pressed (this equalization may be on the welding gun side of the tool changer 3 or may be equalized in the welding robot 2; the same applies hereinafter) Until the reference contact portion 10 is pressed. This state is the state of FIG. In FIG. 2, the fact that the equalize 9 has been pushed is shown by simulating that the stopper 11 is in contact with the bracket 13.
In step 105, it is confirmed whether or not the equalize 9 has been pushed, that is, whether or not the stopper 11 has come into contact with the bracket 13. In actuality, as shown in FIG. 5A, the motor current of each axis of the welding robot 2 suddenly increases as soon as the equalize 9 is pushed, so that the motor current of each axis of the welding robot 2 suddenly increases. This is done by detecting whether or not.
[0013]
In step 104, the other electrode of the pair of electrodes 4 _l, 4 _u (e.g., movable electrode 4 _u), and until Oshikiru the electrode 4 _u side equalizing 9 for pressing, even pressed against the reference abutment portion 10 Good. This state is the state of FIG. In FIG. 3, the fact that the equalize 9 has been pushed out is shown by simulating that the stopper 12 has come into contact with the bracket 13. Even in this case, the confirmation of whether or not the equalize 9 in step 105 has been pushed is performed by detecting whether or not the motor current of each axis of the welding robot 2 has suddenly increased. However, when the movable side electrode 4 _u is pressed against the reference contact portion 10, the welding gun actuator 5 is set at a predetermined position, for example, the position where the movable side electrode 4 _u is pulled most, and the movable side electrode 4 _{u is in} that state. Is fixed so that it does not move with respect to the welding gun body (for example, a brake is applied).
[0014]
If the equalization push-off is confirmed in step 105, the process proceeds to step 106, and the tip position of the pressed electrode (for example, the fixed side electrode 4 _l ) is captured (stored) in the memory of the robot controller 7 of the welding robot 2. The electrode tip position is a position including the amount of wear of the electrode. By comparing this position with the electrode position in the non-wearing state of the electrode stored in advance by the robot controller 7 (taking a difference), the wear amount δ _l of the pressed electrode (for example, the fixed side electrode 4 _l ). (Abrasion amount due to dressing or use) is known. Then, the wear amount δ _l is taken into (stored) in the memory of the robot controller 7.
[0015]
Since the original position of the welding gun 1 determined by the amount of wear δ _l and up to six axes of the welding robot is shifted toward the pressed electrode (for example, the fixed side electrode 4 _l ), the original position of the welding gun 1 is corrected accordingly. Need to be done. That is, if the welding gun original position determined by up to six axes of the welding robot is the center of the workpiece thickness direction, for example, the original position in the non-wearing state (the electrode tip position in the equalized push-off state + the equalizing amount) is the electrode wear amount δ _l. It is necessary to make a correction to shift to the pressed electrode side, and a trajectory correction is required for the welding robot 2. This trajectory correction is performed in step 115 (described later).
[0016]
Next, in step 107, the welding robot 2 is driven to retract the welding gun 1 from the reference contact portion 10 so that the reference contact portion 10 is not positioned between the pair of electrodes 4 _l and 4 _u . .
Next, at step 108, the welding gun actuator 5 is driven to move the movable electrode _4u , and the pair of electrodes _4l and _4u are brought into contact with each other and brought into contact with each other. This state is the state of FIG.
In step 109, it is confirmed whether or not the pair of electrodes 4 _l and 4 _u are in contact with each other. In the confirmation, when the welding gun 1 is an electric servo gun, the motor current of the servo motor as a robot actuator that moves the movable electrode 4 _u when the pair of electrodes 4 _l and 4 _u come into contact with each other and come into contact with each other is shown in FIG. As shown in Fig. 4, it rises abruptly, and is performed by detecting the motor current.
[0017]
When the contact between the pair of electrodes 4 _l and 4 _u is confirmed in step 109, the process proceeds to step 110, where the current electrode contact position of the welding gun actuator 5 and the electrode contact position before wear (stored in the robot controller). The total amount δ _t of the wear amount of the pair of electrodes 4 _l , 4 _u is obtained from the difference from the above and taken into the memory of the robot controller 7 (stored).
Next, at step 111, by subtracting the wear amount [delta] _l of the pair of electrodes 4 _l, 4 _u one electrode previously obtained from the sum [delta] _t of the wear amount of the wear amount of the other electrode of the pair of electrodes [delta] _u Ask for. That is,
δ _t −δ _l = δ _u
[0018]
Next, in step 113, the initial position (before electrode wear) of the welding gun actuator 5 obtained from the robot reference position (known) from step 112 is used as the sum δ _t of the wear amount of the pair of electrodes 4 _l and 4 _u. min, by correcting the feel more alert moving to one electrode 4 _l side, the welding gun actuator 5 original position after the electrode wear of (pressure axis) (origin position) is obtained x _0.
Next, at step 114, x ₀ and δ _u obtained above are taken into the memory of the robot controller 7 (δ _l has already been taken at step 106).
The data δ _l for obtaining the original position of the welding gun 1 is data obtained by pressing the electrode against the reference contact portion 10 using the newly mounted welding gun 1 itself, and the original position of the welding gun before the replacement of the welding gun. And data on the pressure axis origin position is not required. Therefore, a battery for data retention is not necessary. Further, data for determining the original position x ₀ of the welding gun actuator 5 also, which was obtained only by contact with each other a pair of electrodes, the battery and for data retention, such as limit switches for position indexing, add No parts are needed.
[0019]
Next, in step 115, the trajectory of the welding gun 1 newly attached to the welding robot 2 or subjected to spot welding a predetermined number of times is corrected from the x ₀ , δ _l , δ _u and the welding gun actuator 5 ( Correct the original position (origin position) of the pressure axis.
After correcting the original position, the welding robot is driven to move the welding gun 1 to the actual work welding position, and the work program (actual spot welding) is executed.
[0020]
【The invention's effect】
According to the welding gun in-situ indexing method of claim 1, the wear amount of the one electrode required for indexing the welding gun in-situ is obtained by pressing one electrode against a fixed reference contact portion. Can do. This method does not require the battery to hold data about the welding gun actuator and does not require a limit switch for position indexing.
Also, by driving the welding gun actuator and bringing the pair of electrode tips into contact (contact), the total amount of wear of both electrodes of the pair of electrodes necessary for indexing the original position (origin position) of the welding gun actuator Can be requested. This method does not require the battery to hold data about the welding gun actuator and does not require a limit switch for position indexing.
Further, the original position of the welding gun is corrected by the wear amount of one electrode, and the welding gun drive locus of the welding robot is corrected by the wear amount of the one electrode. Further, the original position of the welding gun actuator is corrected based on the wear amount of both electrodes. As a result, the welding gun is moved to a normal spot position, and spot welding can be executed with a normal pressure.
[Brief description of the drawings]
FIG. 1 is a schematic front view of an apparatus for performing a welding gun in-situ indexing method according to an embodiment of the present invention.
2 is a schematic partial front view of a state in which one electrode of the welding gun of FIG. 1 is pressed against a reference contact portion.
3 is a schematic partial front view of a state in which the other electrode of the welding gun of FIG. 1 is pressed against a reference contact portion. FIG.
4 is a schematic partial front view of a state in which both electrodes of the welding gun of FIG. 1 are in contact with each other. FIG.
FIG. 5 is a flowchart showing an execution procedure of a welding gun in-situ indexing method according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Welding gun 2 Welding robot 3 Tool changer 4, 4 _l , 4 _u electrode 5 Welding gun actuator (pressure axis actuator)
6 Transformer 7 Robot controller 8 Encoder 9 Equalize 10 Reference contact part (reference plate)
11, 12 Stopper 13 Bracket

Claims (1)

Drive the welding robot and press one electrode of the pair of electrodes of the welding gun against the fixed reference abutment part, hit the welding gun bracket against the stopper on the one electrode side and push the equalization on the one electrode side Determining the amount of wear of the one electrode from the difference between the tip position of the pressed electrode and the electrode position of the electrode when the electrode is pressed against the reference contact portion in a non-wearing state ;
The welding gun actuator is driven to bring the pair of electrodes into contact with each other, and the driving position of the welding gun actuator at that time and the driving position of the welding gun actuator when the pair of electrodes are brought into contact with each other in a non-wearing state. The sum of the wear amounts of both electrodes of the pair of electrodes is obtained from the difference , and the wear amount of the other electrode of the pair of electrodes is subtracted from the wear amount of the one electrode already obtained from the sum of the wear amounts. The desired process;
Correcting the trajectory plan of the welding gun based on the wear amount of the one electrode, and correcting the original position of the welding gun actuator based on the wear amount of the both electrodes;
In-situ indexing method of welding gun including.

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