JP2007044748A - Robot control method and robot control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for deposition release which can be realized by using an existing equipment without any new equipment investment or remodeling. <P>SOLUTION: When occurrence of deposition between a workpiece W and an electrode of a welding gun 10 is detected after executing the spot welding, the electrode is pressed by the predetermined force against the workpiece W again, an opening/closing part is electrically conducted with the predetermined current for the current-carrying time, the welding gun 10 is turned by a robot 1 in the predetermined direction around the axis of the pressing direction by the predetermined angle, and a series of operations of trying the release of the electrode are performed to melt and separate the deposition of the workpiece W with the electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a robot that performs spot welding by attaching an electric welding gun to the tip, and more particularly, to a robot control method and a control device that release welding that occurs when a workpiece to be welded such as galvanizing is welded.

A configuration example of spot welding by the robot is shown in FIG. In the figure, a configuration is shown in which the articulated robot 1 pressurizes and welds the workpiece W on the jig 40 using an air-driven spot welding gun 17 attached to the tip thereof.
In FIG. 6, the robot 1 and the welding gun 17 are drawn separately in order to explain the overall configuration, but actually the welding gun 17 is attached to the wrist end of the robot 1.
The tip of the welding gun 17 is configured to be openable and closable. An electrode tip 16a is attached to the tip of the shank 16U extending downward from the cylinder 18, and the tip of the shank 16L is attached to the tip of the shank 16L on the gun arm 15 side. Are attached to face the shank 16U and the electrode tip 16a. As the cylinder 18 operates and the shank 16U extends downward, a plurality of stacked workpieces W, for example, workpieces W1 and W2 are pressed between two electrode tips 16a and 16b, and a welding current is applied from the transformer 12 between both electrodes. Supply and perform spot welding.
Further, spot welding guns using an electric motor as a driving source instead of air are also in widespread use. As shown in FIG. 1, a motor 11 controlled by a robot controller 2 is used to drive a movable side through driving units 13 and 14. A series of welding operations are performed in which the electrode tip 16a is moved up and down to pressurize the workpiece W, and a welding current is passed through the transformer 12, and the workpiece can be welded at a high speed.
However, even when spot welding to the workpiece W is completed, as shown in FIG. 7, the electrode tip and the workpiece W adhere in various states (hereinafter referred to as welding) at the welding spot position, and the robot 1 is operated. There was a problem that could not be done.
Specifically, when only the fixed side tip 16b is welded as shown in FIG. 7A, only when the movable side tip 16a is welded as shown in FIG. 7B, or as shown in FIG. 7C. The movable tip 16a and the fixed tip 16b may both be welded. In particular, in the case of a galvanized workpiece, even if a nugget is generated by spot welding, the tip and the workpiece are easily welded, and the robot 1 often stops during the continuous automatic welding.

Therefore, in the conventional method, as shown in FIG. 6, a limit switch 20 for confirming the opening of the tip of the gun is provided on the pneumatic welding gun 17. A member that moves upward in conjunction with the shank 16U when the gun tip is opened activates a limit switch above the cylinder 18 to determine whether the tip of the pneumatic welding gun 17 is normally opened after welding. If it is not opened, it is judged that the electrode tip is welded to the workpiece W as shown in FIG. 7, and the operation of the robot 1 is stopped. Thereafter, the worker uses a tool to peel off the welded portion. It was.
However, although it is easy to detect the welding with the conventional technology, when the welding gun and workpiece are peeled after that, it has been necessary to rely on manual work.

  Therefore, as a method for automatically performing confirmation of welding and separation of the welded portion, there is a method as described in Patent Document 1. That is, based on the welding phenomenon as shown in FIG. 7, it is determined that the welding is detected if the electrical connection between the welding gun 17 and the jig 40 is detected by the welding detection unit 7 in FIG. 6 at the end of welding. In that case, the welding state is released by re-energizing the welding gun 17 at least once.

  As another prior art, in the configuration of FIG. 6, after welding is detected by the welding detection unit 7 in the robot controller 2, air is pressurized again to the welding gun 17, and at the same time, the welding timer 30 is connected from the input / output unit 3. There is a method in which welding is released by operating the robot 1 and rotating the welding gun 17 forward and backward about the vertical axis while supplying a current between both electrodes of the welding gun 17 (see FIG. For example, see Patent Document 2).

JP-A-1-299784 JP-A-6-122077

However, in the method of Patent Document 1, since welding by re-energization is only repeated, depending on the damaged state of the electrode tip, the material and surface state of the workpiece, the welding conditions, etc., both of them are melted to promote further welding. There was a fear.
In the method of Patent Document 2, since the welding gun is pneumatic, it is impossible to appropriately control the electrode pressing force, and the workpiece is easily distorted by rotating the welding gun with a robot while being sandwiched with a high pressing force. It could not be used frequently due to adverse effects such as misalignment of the electrode part of the gun and wear and damage of the electrode.
In view of such problems, the present invention has an object to provide a welding release method and an apparatus thereof that can be realized using existing equipment, without making a new capital investment or remodeling especially for an electric welding gun. To do.

In order to achieve the above object, the present invention is as follows.
The invention according to claim 1 is a robot control method in which a welding gun that drives an electrode by an electric motor is mounted and spot welding is performed by the welding gun, between the workpiece and the electrode after performing spot welding. When it is detected that welding has occurred, the electrode is again pressed against the workpiece with a preset force, and the opening / closing part is energized with a preset current value and energization time. Is rotated by a preset angle around a pressure direction axis, and then a series of operations are performed to try to open the electrode, thereby melting and peeling the weld between the workpiece and the electrode. It is characterized by making it.
According to a second aspect of the present invention, the welding gun is rotated by the preset angle around the axis in the pressurizing direction by the preset angle, and then the welding gun is turned in the reverse direction. From this, it is attempted to open the electrode.
According to a third aspect of the present invention, the welding gun is rotated by the preset angle around the pressurizing direction axis by the preset angle, and then the welding gun is turned back to rotate in the reverse direction. An attempt is made to open the electrode after returning the position of the welding gun to the position at the time of spot welding execution.
The invention described in claim 4 is characterized in that a series of operations at the time of detecting the welding is repeated a predetermined number of times, and the robot is stopped when the welding is not resolved even after the number of times is repeated.
The invention according to claim 5 is characterized in that the direction of the rotation is a direction in which the welding gun does not interfere with an object around the workpiece.
In the invention according to claim 6, the applied pressure of the electrode, the current value to be energized, the energization time, the direction of rotation, the angle of rotation, and the number of repetitions in a series of operations at the time of detection of welding are: It is set for each spot welding spot.
According to a seventh aspect of the present invention, there is provided a robot control apparatus in which a welding gun for driving an electrode by an electric motor is mounted and spot welding is performed by the welding gun. The control apparatus includes a welding timer for energizing the electrode and the welding timer. A central processing unit that controls a robot and an electric motor of the welding gun; and a welding detection unit that detects that welding has occurred between the workpiece and the electrode due to electrical continuity, and the central processing unit includes the welding When welding is detected by the detection unit, the electrode is again pressed against the workpiece with the applied pressure according to a preset applied pressure, current value, energization time, rotation direction, and rotation angle of the electrode, and the opening and closing is performed. And the robot is energized with the preset current value and the preset energization time, and the welding gun is set by the robot around the pressurizing direction axis. After only rotated angle the preset in the direction was carried out a series of operations that attempt to open the electrodes, melting the welding between the workpiece and the electrode, characterized in that to peel.
In the invention according to claim 8, the welding gun is rotated by the preset angle around the pressurizing direction axis by the preset angle, and then the welding gun is turned in the reverse direction. From this, it is attempted to open the electrode.
According to the ninth aspect of the present invention, the welding gun is rotated by the preset angle around the pressurizing direction axis by the preset angle, and then the welding gun is turned back to rotate in the reverse direction. An attempt is made to open the electrode after returning the position of the welding gun to the position at the time of spot welding execution.
According to a tenth aspect of the present invention, the central processing unit is configured such that the pressure applied to the electrode, the current value to be energized, the energization time, the rotation direction, and the rotation angle in a series of operations at the time of detecting the welding. The number of repetitions is stored for each spot welding spot.

According to the present invention, welding can be reliably released without damaging the electrodes of the welding nugget or welding gun formed on the workpiece. In addition, since the robot automatically releases the welding, it is possible to reduce the burden on the operator and improve the production efficiency of the production line.
Furthermore, since each parameter at the time of releasing welding can be easily set and changed, it is possible to deal with various workpieces having different characteristics.

  Hereinafter, the present invention will be described in detail with reference to examples and drawings.

FIG. 1 is a schematic diagram of a system configuration of the present invention. In the figure, 1 is a robot, 2 is a robot controller for controlling the robot 1 and an electric welding gun 10 described later, and 10 is an electric welding gun for spot welding attached to the tip of the wrist of the robot 1. A welding timer 30 supplies a welding current to the electric welding gun 10.
In FIG. 1, the robot 1 and the electric welding gun 10 are drawn separately in order to explain the overall configuration of the present invention, but actually, as shown in FIG. 2, the electric motor is attached to the wrist tip of the robot 1. A welding gun 10 is attached.
Reference numeral 40 denotes a jig for placing the workpieces W1 and W2 to be spot-welded.
In the following description, the workpieces W1 and W2 are collectively referred to as a workpiece W.

A fixed electrode tip 16b is attached to the gun arm 15 of the electric welding gun 10 via a shank 16L, and a movable electrode tip 16a is attached to the movable side opposite to the gun arm 15 via a shank 16U.
The power of the motor 11 attached to the electric welding gun 10 is transmitted to the movable side electrode 16a through the pulley 14 and the ball screw 13, and the movable side electrode 16a opens and closes. Specifically, it moves up and down on the pressure direction line 21.

The operation of the motor 11 is controlled by the gun motor control unit 6 in the robot controller 2. The welding current control of the electric welding gun 10 is performed by the input / output unit 31 of the welding timer 30 that receives a welding command from the input / output unit 3 in the robot controller 2, and the current is supplied from the welding timer 30 to the power source 2. It is sent to the transformer 12 attached to the electric welding gun 10 through the next cables 32 and 33. Further, in order to detect welding after the end of welding, a welding detection unit 7 is provided in the robot controller 2, and the welding detection unit 7 includes a detection line 8 b from the electric welding gun 10 and a jig 40. A detection line 8a is connected.
The central processing unit 4 in the robot controller 2 controls the entire system in accordance with a previously taught procedure, and controls the robot 1, the electric welding gun 10, and the welding timer 30.

From the spot welding at a certain point to the welding release by the system of FIG. 1 will be specifically described along the flow shown in FIG.
First, the robot controller 5 in the robot controller 2 controls each joint axis of the robot 1 in accordance with a command from the central processing unit 4 to operate the robot 1. As the robot 1 moves, the electric welding gun 10 attached to its wrist also moves, and its fixed side electrode 16b arrives at the hit point position SP on the workpiece W, which is the target position, and the variable n (n = 0 or more) Is set to 0 (step 1 in FIG. 3). n will be described later.
Next, the motor 11 is driven by the gun motor controller 6 in the robot controller 2 to move the electrode tip 16a of the movable shank 16U downward and contact and pressurize the workpiece W. Then, the workpiece W is sandwiched at the hit point position SP (step 2 in FIG. 3).

At the same time, the robot controller 2 gives a start command to the input / output unit 31 in the welding timer 30 via a signal line (step 3). Then, the welding timer 30 causes a current to flow through the transformer 12 via the power source secondary cables 32 and 33. In response to this, a current also flows between the electrodes, and spot welding is performed on the workpiece W (step 4).
The welding current and the welding time at the time of spot welding are controlled by the welding timer 30, and when the welding is finished, a completion signal is sent from the welding timer 30 to the input / output unit 3 of the robot controller 2. Upon receiving the completion signal, the robot controller 2 immediately issues a command to move the movable side electrode 16a upward by the gun motor control unit 6, and issues a command to move the electric welding gun 10 downward by the robot control unit 5, An opening operation for releasing the workpiece W is performed. (Step 5).
The spot welding sequence is thus completed. Finally, the welding between the electric welding gun 10 and the workpiece W is determined by confirming electrical continuity with the welding detection unit 7 in the robot controller 2 as described above. (Step 6).
If welding has not occurred, the robot 1 is moved to the next spot position (step 15), and the spot welding sequence from step 1 is performed again.

Below, the process when the welding with the electric welding gun 10 and the workpiece | work W is detected after spot welding execution is demonstrated. These processes correspond to steps 7 to 14 in the flowchart of FIG.
When welding is detected, it is first checked whether or not the number of welding occurrences at that point is equal to or greater than a preset number N (N: natural number) (step 7). The aforementioned n is a variable indicating the number of welding occurrences, and n is incremented in step 13 described later after the welding release operation.
If n> N, that is, if the welding is not solved even after performing the welding release operation N times, the operation of the robot is stopped as an alarm (step 14).
If n ≦ N, the central processing unit 4 stores the position and performs predetermined processing, that is, gun pressurization (step 8), welding timer activation (step 9), and gun rotation control (steps 10 and 11). A series of processes such as opening the gun (step 12) is executed.
Hereinafter, this series of processes will be described in detail.

  First, the position where welding has occurred is stored in the central processing unit 4. Next, the motor 11 of the electric welding gun 10 is driven to move the movable electrode tip 16a at the position before welding to a position where it contacts the workpiece W. At this time, even if the welding of the electric welding gun 10 and the workpiece W is any of the cases shown in FIGS. 7A to 7C, the electric welding gun 10 is appropriately moved in the vertical direction by the operation of the robot. It is possible to make it contact. After moving to the contact position, gun pressure is applied (step 8). Since the movable side electrode 16a is driven by the motor 11, the pressure can be controlled unlike the case of driving by the air cylinder. In the gun pressurization in step 8, the pressure is set to be smaller than the actual spot welding.

Thereafter, the electric welding gun 10 is rotated with respect to the workpiece W around the pressing direction line 21, and there are two rotation directions, clockwise and counterclockwise.
4A and 4B are top views showing the operation of the electric welding gun 10 at the spot position where welding has occurred, and correspond to steps 10 and 11 in the flow of FIG.
FIG. 4A shows the operation of rotating the electric welding gun 10 counterclockwise as viewed from above, and the post of the jig 40 that supports the workpiece W by rotating it in the direction of the arrow in the figure. Interference with 40a is avoided. In FIG. 4B, the electric welding gun 10 is rotated clockwise as viewed from above to avoid the jig post 40a.
In FIG. 4, the robot 1 is omitted for explanation, and only the gun arm 15 is drawn for the electric welding gun 10.
The above-described rotation control means that each axis of the robot 1 is operated according to a command from the robot control unit 5 and the gun arm 15 is moved in a positive or negative direction around the pressing direction line 21 at a preset angular velocity and angle. Control that rotates clockwise or counterclockwise and turns in the opposite direction instantly.
Even during rotation, each axis of the robot 1 is operated to control the posture of the electric welding gun 10, so that the electric welding gun 10 maintains an appropriate angle of attack with respect to the workpiece W.
Furthermore, since the electric welding gun that drives the movable side electrode by a motor is used as described above, the pressure applied to the workpiece W is not the same as that during spot welding as in the air type, and the gun arm 15 A low pressure is set to facilitate rotation.

Prior to pressurization and rotation of the electric welding gun 10, an energization command is output from the robot controller 2 to the welding timer 30 in step 9. As a result, a current flows between the two electrode chips gripping the workpiece W, the welded portion is melted by the Joule heat, and peeling by rotation of the gun arm 15 is further facilitated. At this time, the energization time is set shorter than the rotation time of the gun arm 15 and the current value is set lower than the practical welding current, and the controller 2 controls the welding timer 30 according to the setting.
When the rotation of the gun arm 15 is completed, the opening operation of the electric welding gun 10 similar to step 5 is performed (step 12).
When the series of processes is completed, n is incremented (step 13), and the process returns to step 6 again to check whether the welding has been eliminated.

FIG. 5 shows an example of setting of the rotation direction, the rotation angle, the applied pressure during rotation, the energization time, the energization value, and the number of repetition processing loops, which are the parameters of the welding release process in steps 7 to 11 described above. The “number of repetitions” in FIG. 5 corresponds to N. In this example, if the welding release process is performed three times and the problem is not solved, an alarm is generated in step 14.
Such settings are stored in advance in the central processing unit 4 for each hit point, and can be browsed using a teaching device (not shown) connected to the robot controller 2 and can be changed.

The processing conditions used for releasing the welding as shown in FIG. 5 can be appropriately determined according to the material and surface condition of the workpiece W and other various conditions. However, the processing after the weld nugget has already been generated can be determined. Considering this, the current is lower than the normal spot welding conditions for the workpiece W, and there is no problem with short-time energization. The pressurizing force only needs to be lower than that of spot welding.
As described above, a series of welding release procedures can be repeated up to N times for each striking point, but since a large couple can be given by turning the welding gun at the welding position, it is usually one rotation. The welding can be sufficiently released by the operation.
Therefore, in the reverse rotation of step 11, it is not always necessary to return the posture of the electric welding gun 10 to the posture before starting the forward rotation. For example, after the electric welding gun 10 is rotated 15 ° counterclockwise as viewed from above in step 10, the opening operation of the electric welding gun 10 and welding confirmation are performed when the electric welding gun 10 is rotated 10 ° clockwise. Only when the welding has not been released, the electric welding gun 10 may be further rotated clockwise by 5 ° to return to the original posture, and if the welding has been released, it may be moved to the next hit point. Further, when the electric welding gun 10 is rotated counterclockwise as viewed from above in Step 10, the opening operation of the electric welding gun 10 and the welding confirmation are performed, and the electric welding is performed only when the welding is not released. The welding gun 10 may be rotated clockwise to return to the original posture, and if welding has been released, it may be moved to the next hit point.
Furthermore, the types of welding guns that can make use of this method and apparatus are applicable not only to C type guns as shown in FIG. 1 but also to X type guns (not shown).

The outline of the present invention described above is repeated as follows.
At the spot where the welding has occurred, the motor of the electric welding gun is controlled to bring the electrode into contact with the workpiece with a pressure lower than the pressure applied during normal spot welding, and pressure is applied. The gun is rotated by a set angle around the axis of the electrode tips that are in perpendicular contact with the workpiece, that is, around the pressure direction line and in a direction free of interference. By rotating the gun, a sufficiently large couple can be applied to the welded spot position, and as an auxiliary, a current lower than the practical welding current is applied for a predetermined time so as not to damage the solidified nugget. By doing so, melting of only the surface is promoted with less Joule heat, and the alloyed chip and workpiece are easily separated. Further, the rotation angle at this time does not need to be increased, and may be about 10 to 20 °. Further, the robot controller 2 can set the rotation direction and angle. Such a series of operations is performed at a predetermined number of times (N times) at the maximum, and if welding can be released, the process proceeds to the next welding operation.

  According to the present invention, the workpiece and the electrode tip can be reliably separated without impairing the existing weld nugget. Therefore, production efficiency can be significantly improved compared to the case where the worker stops the robot and performs the peeling work.

  The present invention can be widely applied to spot welding robots equipped with an electric welding gun.

It is a figure which shows the system configuration | structure of this invention. It is a perspective view which shows the mode of the spot welding to the workpiece | work by this invention. It is a flowchart which shows a series of operation | movement from the spot welding by this invention to welding cancellation | release. It is a top view which shows the operation example of the electric welding gun at the time of welding cancellation | release. It is an example of a parameter at the time of welding release. It is a figure which shows the conventional system configuration. It is the side view which explained the welding phenomenon typically.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Robot 2 Robot controller 3 Input / output part 4 Central processing part 5 Robot control part 6 Gun motor control part 7 Weld detection part 8a, 8b Detection line 10 Electric welding gun 11 Motor 12 Transformer 13 Ball screw 14 Pulley 15 Gun arm 16a Movable side electrode 16b Fixed side electrode 16U Movable side shank 16L Fixed side shank 17 Pneumatic welding gun 18 Cylinder 19 Valve 20 Limit switch 21 Pressure direction line 30 Welding timer 31 Input / output unit 32, 33 Power supply secondary cable 40 Jig 40a Jig post W , W1, W2 Work SP RBI

Claims (10)

A control method for a robot that wears a welding gun that drives an electrode with an electric motor and performs spot welding with the welding gun,
After spot welding is performed, when it is detected that welding has occurred between the workpiece and the electrode, the electrode is again pressed against the workpiece with a preset force, and a preset current value and energization are applied to the opening / closing portion. A series of operations are performed in which the welding gun is rotated by a predetermined angle in a predetermined direction around the pressurizing direction axis and then the electrode is opened after being energized with time. A method for controlling a robot, characterized by melting and peeling the weld between the workpiece and the electrode.   After rotating the welding gun by the preset angle about the pressure direction axis, turning the welding gun in the reverse direction and then attempting to open the electrode The robot control method according to claim 1.   The welding gun is rotated by the preset angle around the pressurizing direction axis by the preset angle, and then the welding gun is rotated in the opposite direction to change the attitude of the welding gun when performing spot welding. The robot control method according to claim 1, wherein the electrode is attempted to be released after returning to the posture.   The robot control method according to claim 1, wherein a series of operations at the time of detecting the welding is repeated a preset number of times, and the robot is stopped when the welding is not eliminated even after the number of repetitions.   The robot control method according to claim 1, wherein the direction of the rotation is a direction in which the welding gun does not interfere with an object around the workpiece.   The applied pressure of the electrode, the current value to be energized, the energizing time, the direction of rotation, the angle of rotation, and the number of repetitions are set for each spot welding spot in a series of operations at the time of detection of welding. The robot control method according to claim 1. In a control apparatus for a robot that wears a welding gun that drives an electrode with an electric motor and performs spot welding with the welding gun,
The control device comprises a welding timer for energizing the electrodes, a central processing unit for controlling the electric motor of the robot and the welding gun,
A welding detection unit that detects that welding has occurred between the workpiece and the electrode due to electrical conduction;
When the central processing unit detects welding in the welding detection unit, the electrode is again applied to the workpiece according to a preset pressing force, current value, energization time, rotation direction, and rotation angle of the electrode. Pressurization is performed by applying pressure, the opening / closing portion is energized at the preset current value and the preset energization time, and the welding gun is set by the robot around the axis in the pressurization direction. A robot control apparatus characterized by performing a series of operations of trying to open the electrode after rotating it in the direction by the preset angle to melt and peel the weld between the workpiece and the electrode.   After rotating the welding gun by the preset angle about the pressure direction axis, turning the welding gun in the reverse direction and then attempting to open the electrode The robot control device according to claim 7.   The welding gun is rotated by the preset angle around the pressurizing direction axis by the preset angle, and then the welding gun is rotated in the opposite direction to change the attitude of the welding gun when performing spot welding. The robot control device according to claim 7, wherein the electrode is attempted to be released after returning to the posture.   The central processing unit determines the applied pressure of the electrode, the current value to be energized, the energization time, the direction of rotation, the angle of rotation, and the number of repetitions of spot welding in a series of operations when the welding is detected. The robot control apparatus according to claim 7, wherein the robot is stored for each hit point.

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