JP2004090020A - Method for controlling servo motor driven spot welding gun with equalizing mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a high-speed operation, to drastically reduce the cost, and to improve the reliability and the operability. <P>SOLUTION: A servo motor driven spot welding gun has an equalizing mechanism 3 in which the pressurizing operation and the equalizing operation in a gun body 2 are performed by respective exclusive servo motors 4 and 11. Since each servo motor is controlled as each shaft of a robot, to make possible synchronous control with other shafts of the robot. The output torque of the motor 11 for the equalizing operation is controlled to have a desired value without going through steps even during the operation of other shafts according to the spot welding attitude of the gun. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to control of a spot welding gun driven by a servomotor provided with an equalizing mechanism between a robot arm and a welding gun body.
[0002]
[Prior art]
Conventionally, a servo motor driven spot welding gun having an equalizing mechanism in which a pressurizing operation and an equalizing operation in a gun body are respectively driven by dedicated servo motors is disclosed in, for example, JP-A-9-70671. It is known as such.
[0003]
[Problems to be solved by the invention]
By the way, in the case of the above-described conventional example, the two-axis operation (the pressurizing operation and the equalizing operation of the gun body) is not controlled synchronously with the positioning operation of the gun body by the robot. The positioning operation cannot be performed at the same time. For example, as shown in FIG. 4, the gun body is moved to the vicinity of the work 18 'by the robot, and finally the welding fixed position is changed from the state (1) to the fixed welding position (2). This is until the upper and lower electrodes 5 'and 7' are positioned at the upper and lower positions of the work 18 '. Then, after a current for setting a required pressurizing torque or a torque for weight balance is set to each motor, both motors are driven and the electrodes 5 'sequentially approach the work 18'. 7 'slowly rises to the state of (3), and the electrode 7' stops, but the electrode 5 'continues to descend and contacts the work 18' to the state of (4), and the electrode 5 ' By pressurizing the side, the gun body is equalized to the state (5) in which the work 18 'is sandwiched between the electrodes 5' and 7 '. As described above, since the pressurizing operation and the equalizing operation of the gun body are respectively continuous operations, it takes a long time from the electrode opening state to the electrode pressing. Also, during the operation of approaching the lower electrode 7 'to the work 18', the driving force of the motor for equalizing operation is set in advance to a weight balance force corresponding to the welding position of the gun. When the balance force is small, the acceleration force is also small, and as a result, it takes time to start up. From the above, it is difficult to increase the speed of gun control.
[0004]
Further, since the control device for the two axes must be prepared separately from the control device for the robot, the cost increases. Further, at the time of teaching operation, since the robot has to position the gun body and have two teaching pendants for the two axes, teaching is troublesome.
There are problems such as.
[0005]
The present invention has been made in view of such problems of the prior art, and its object is to expect high-speed operation, significant cost reduction, improvement in reliability and operability, and the like. An object of the present invention is to provide a control method of a servo motor driven spot welding gun with an equalizing mechanism.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a control method of a servo motor driving spot welding gun with an equalizing mechanism according to the present invention is characterized in that the pressurizing operation and the equalizing operation in the gun body are each driven by a dedicated servo motor, Each servo motor is controlled as one axis of the robot, thereby enabling synchronous control with the other axes of the robot, and the output torque of the equalizing motor is adjusted in accordance with the strike position of the gun. The torque is controlled steplessly even during the operation of the other shaft.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a robot arm, and an equalizing mechanism 3 is disposed between the robot arm 1 and the welding gun main body 2. The welding gun main body 2 is connected to the robot arm 1 via the equalizing mechanism 3. Will be connected to
[0008]
The welding gun body 2 has a movable arm 6 driven by a pressurizing servomotor 4 having an electrode 5 at the tip and a substantially C-shaped fixed arm 8 having an electrode 7 at the tip. Are formed, and constitute a C-type spot welding gun as a whole.
[0009]
The equalizing mechanism 3 includes a bracket 9 fixed to the robot arm 1, a groove 10 in which the welding gun body 2 can slide, and an equalizing servomotor 11 fixed to the bracket 9. And a lead screw 13 screwed into a nut 12 fixed to the gun body 2.
[0010]
Numeral 14 is a nut fixed to the movable arm 6, and a lead screw 15 from the servomotor 4 is screwed thereto. Reference numerals 16 and 17 denote connection terminals for supplying a welding current to the work 18 via the electrodes 5 and 7, which are connected to output terminals of the welding transformer 19.
[0011]
An encoder input signal 20 corresponding to the position of the pressurizing shaft and an encoder input signal 21 corresponding to the position of the equalizing shaft are output from the encoders provided with the servomotors 4 and 11, respectively. The robot controller 22 inputs the desired pressurization control motor output signal 23 and the equalization control motor output signal to the respective servo motors 4 and 11 from the robot controller 22. 24 is transmitted to control the current of both servomotors 4 and 11.
[0012]
Further, an encoder input signal 25 corresponding to the position of the robot arm 1 from the robot arm 1 is input to the robot controller 22, and the robot controller 22 outputs a desired position to the robot arm 1 from the desired position. , The robot arm position control signal 26 is transmitted to control the robot arm 1 (normal six-axis control).
[0013]
A welding timer 27 is operated by a control signal 28 from the robot controller 22. The primary current of the welding transformer 19 is controlled by a welding current control signal 29 from the welding timer 27. It is controlled.
[0014]
In the above-described C-type spot welding gun, when the welding gun main body 2 is moved by the robot arm 1, the welding gun main body 2 itself needs to be fixed to the robot arm 1; The welding arm body 2 is moved to a fixed welding position by the robot arm 1 in FIG. 2 in a state immediately before the gun is pressed between (1) and (2). Then, the servo motor 11 has a current value set in advance during teaching. At the time of teaching, the current in the servomotor 11 is measured first, and the posture and the state of gravity balance of the welding gun body 2 can be determined from the magnitude and polarity of the current. That is, the current value at that time indicates a torque balanced with the gravitational force applied to the welding gun body 2, and the polarity thereof is determined by the direction of the pressing direction of the electrode 5 with respect to the horizontal plane. The gravity referred to here is the gravity acting on the portion related to the load of the servo motor 11 other than the robot arm 1, the bracket 9 and the servo motor 11 in FIG. Note that the teaching described here includes teaching by simulation performed on a computer screen in addition to teaching by actually moving a robot and a gun.
[0015]
Then, based on this data, the pressing force (approximately 0 to 20 Kg) allowed for the work 18 is calculated, and the current of the servo motor 11 is set to the calculated value. At this time, the set current and its direction are "measured current-work allowable current (current corresponding to the pressing force allowed for the work) when the pressing direction of the electrode 5 is upward with respect to the horizontal plane. In the counter-working direction ", and when the pressing direction is downward with respect to the horizontal plane," measurement current + working allowable current in the working direction "is obtained.
[0016]
As described above, both servomotors 4 and 11 are driven while the movement of the welding gun body 2 by the robot arm 1 is continued, and the movable arm 6 and the electrode 5 are worked by the servomotor 4. The electrode 7 approaches the work 18 rapidly (2) due to the movement of the servomotor 11 and the other axis of the robot body. Since the electrode 5 comes into contact with the work 18 and thereafter, the electrode 7 also applies a pressing force to the work 18 by the reaction force of the pressing force of the servomotor 4, so that both electrodes are applied. The control operation of the gun, in which the contact time of the workpieces 5 and 7 with the work 18 is remarkably reduced, becomes a high speed operation. Since the weight of the welding gun body 2 is balanced by the servomotor 11, the deformation of the work 18 during the pressurizing operation can be almost completely prevented.
[0017]
FIG. 3 is a schematic configuration diagram of an X-type spot welding gun suitable for carrying out the present invention. In this embodiment, a robot arm 41 is connected between the robot arm 41 and the welding gun body 42 by a support bracket 44 having a welding transformer 43.
[0018]
In the welding gun body 42, an upper arm 46 having an electrode 45 at the tip and a lower arm 48 having an electrode 47 at the tip are pivoted about a main shaft 49 to constitute an X-type spot welding gun. .
[0019]
At the rear upper part of the upper arm 46, the distal end of the pressing shaft 51 of the pressing drive unit 52 driven by the pressing servo motor 50 and having the pressing shaft 51 at the distal end is connected by a connecting pin 53. Being pivoted. The lower arm 48 integrally extends further rearward and upward from a position pivoted on the main shaft 49 to form a swing arm 54 for equalizing, and a rear end of the swing arm 54 is formed by the rear end of the swing arm 54. The pressure drive unit 52 is pivoted on a side portion by a connection pin 55.
[0020]
The distal end of the drive shaft 57 of an equalizing drive unit 58 driven by an equalizing servomotor 56 and having a drive shaft 57 at the distal end is pivoted at a middle portion of the swing arm 54 by a connecting pin 59. ing. An equalizing drive unit support bracket 61 is disposed on the mounting member 60 of the robot arm 41, and a tip of the equalize drive unit support bracket 61 is connected to a side portion of the equalize drive unit 58 by a connecting pin 62. The equalizing drive unit 58 is supported by the robot arm 41 by the drive unit support bracket 61.
[0021]
The servomotors 50 and 56 are controlled in the same manner as the servomotors 4 and 11 in the aforementioned C-type spot welding gun, and the detailed control circuit is substantially a C-type spot welding gun. The description is omitted because it is the same as that of the welding gun.
[0022]
Also, in this X-type spot welding gun, when the welding gun body 42 is moved by the robot arm 41, the welding gun body 42 itself needs to be fixed to the robot arm 41. The robot arm 41 moves the welding gun body 42 to a fixed welding position. In FIG. 2, the state immediately before the pressurization is applied between (1) and (2). Then, the servo motor 56 has a current value set in advance at the time of teaching. At the time of teaching, the current in the servomotor 56 is measured first, and the current value to the servomotor 56 is set based on this data. Note that the teaching described here includes teaching by simulation performed on a computer screen in addition to teaching by actually moving a robot and a gun.
[0023]
In this manner, both the servomotors 50 and 56 are driven while the movement of the welding gun body 42 by the robot arm 41 is continued, and the upper arm 46 and the electrode 45 are moved by the servomotor 50 to the work 18. And the electrode 47 rapidly approaches the work 18 by the swing of the swing arm 54 caused by the operation of the servomotor 56 and the other axis of the robot body (2). After the electrode 45 comes into contact with the work 18, the electrode 47 also applies a pressing force to the work 18 by the reaction force of the pressing force of the servomotor 50. The control operation of the gun in which the contact time of the workpieces 45 and 47 with the work 18 is remarkably reduced becomes a high-speed operation. Since the weight of the welding gun body 42 is balanced by the servo motor 56, the deformation of the work 18 during the pressurizing operation is almost completely prevented. That is, the same control as that of the welding gun body 2 and the electrodes 5 and 7 in the C-shaped spot welding gun is performed on the welding gun body 42 and the electrodes 45 and 47.
[0024]
【The invention's effect】
As described above, in the present invention, each servomotor is controlled as one axis of the robot, thereby enabling synchronous control with the other axes of the robot, and the output torque of the equalizing operation motor. Is controlled steplessly to a desired torque even during the operation of the other axis according to the hitting posture of the gun, so that high-speed operation of the gun control becomes possible, and the control device of each servomotor is controlled. It is not necessary to prepare the robot separately from the robot controller, and the cost is reduced. Since teaching to each servomotor is performed according to the positioning of the gun body by the robot, the teaching is easy. In addition, the present invention provides a control method for a servo motor driven spot welding gun with an equalizing mechanism, which can be expected to achieve high-speed operation, significant cost reduction, and improvement in reliability and operability.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a control method for a servomotor driven C-type spot welding gun with an equalizing mechanism according to the present invention.
FIG. 2 is an explanatory diagram of movement of both electrodes in a control method according to the present invention.
FIG. 3 is a schematic side view of an X-type spot welding gun suitable for applying a control method of a servo motor driven spot welding gun with an equalizing mechanism according to the present invention.
FIG. 4 is an explanatory view of movement of both electrodes in a conventional example.
[Explanation of symbols]
1,41 Robot arm 2,42 Welding gun body 3,52 Equalizing mechanism 4,50 Servo motor for pressurizing operation 5,7,45,47 Electrode 11,56 Servo motor for equalizing operation 22 Robot control ―La

Claims (1)

In a servo motor driven spot welding gun having an equalizing mechanism in which a pressurizing operation and an equalizing operation in a gun body are respectively driven by dedicated servo motors, each of the servo motors is one of robots. By being controlled as an axis, synchronous control with other axes of the robot is possible, and the output torque of the equalizing motor is stepless even during the operation of the other axis in accordance with the gun's hitting posture. And a servo motor driven spot welding gun control method with an equalizing mechanism, characterized in that the torque is controlled to a desired torque.

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