JP2721952B2 - Control method of spot welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a pressure actuator using a motor as a drive source of an electrode of a spot welding machine by using a signal from a controller of a robot.

[0002]

2. Description of the Related Art It is well known that a pressurizing method using a fluid pressure cylinder or an electric motor is generally used as a pressurizing drive source for electrodes of a resistance welding machine.

Recently, a pressurizing actuator using a motor controls the opening or pressurizing operation of an electrode during movement of a spot welding machine (spot welding gun) based on electrode position information from a control device of a welding robot. System technology has been developed. Prior art related to this is described in, for example, JP-A-5-138366, "Apparatus for controlling tool operation including clamp" and JP-A-5-261560, "Spot welding method and apparatus". Things are known.

In the former system technology, two servo control units for controlling the opening / closing operation of the clamp of the welding gun are provided, one unit for controlling the opening / closing operation of the clamp during welding, and the other unit for controlling the opening / closing operation during welding. The unit controls the opening and closing operation of the clamp while the robot moves the gun, and these two units are switched by electronic switches under the control of sensors.

The latter system technology controls the opening operation or the pressing operation of the welding gun based on the position information of the robot and the position information of the electrodes of the welding gun while the robot is moving the welding gun to the welding position. System.

[0006]

However, in such a conventional servo control system for a spot welding machine, the following problems could not be solved.

In the former case, since the servo control unit and another servo control unit are switched by an electronic switch, it is necessary to develop a new control device and the switching structure is unnecessary.

[0008] Even if an attempt is made to replace the air pressurizing gun with a motor pressurizing gun, the currently used 6-axis robot controller cannot be used. In addition to the development of a new control unit, significant costs such as compensation for resumption of production lines and re-tching due to replacement of the control unit are expected. This has been a major obstacle to increasing the number of motor pressurized guns used.

When one air gun is controlled by two servo control units by switching electronic switches, the control circuit is duplicated and the cost increases.

In the latter case, the robot controller is X
Axis, S-axis, Y-axis, Z-axis, R-axis, and Θ-axis are basically controlled. However, when an electric motor is used for the pressurized actuator of the spot welding gun, the electric motor of the actuator is used. Seven axes were needed for servo control. Therefore, when adding 7 axes to the conventional robot controller, generally, the controller of the current 6 axis robot is largely modified or a controller for 7 axes, which also has a pressing force control function, is used. You have to make a new one, which increases the cost.

[0011] Similarly to the former, even if an attempt is made to replace the air pressurized gun with a motor gun, the current robot control device cannot be used as it is, and this has been an obstacle to increasing the use of the motor gun.

The control device of the robot for controlling the pressing force and the timer device for controlling the welding current are separate independent units, and the control of the pressing force and the welding current is not performed in association with each other.

That is, it has become a barrier in the development of technical fields such as investigation of causes at the time of occurrence of defects, monitoring of nuggets expected in the future, spatterless welding, and energy-saving welding in which pressure and current are synchronously balanced. .

[0014]

SUMMARY OF THE INVENTION The present invention has been developed to solve the above-mentioned problems, and employs the following technical means.

That is, a method of controlling a pressurized actuator using a motor as a drive source of an electrode of a spot welding machine, wherein a control device of the actuator and information in which the welding machine or the workpiece is stored in advance. And a positioning robot controller that reproduces and drives the actuator according to the trajectory based on the trajectory. The actuator controller controls the actuator based on an electrode stroke release signal of the spot welding machine in response to an electrode stroke release signal from the robot controller. Control the stroke of the electrode of the spot welder steplessly .

[0016] Then, the welding start signal from the robot controller to start the pressurizing operation, the welding completion signal robot controller from the control device of the actuator is to start movement of the robot to the next welding position That you did.

Further, during the welding period from pressing of the electrode of the spot welding machine to opening of the electrode, the electrode pressing force by the actuator control device is synchronized with the welding current by the timer device for controlling the switch of the welding power supply. control both in
I will. Technical means.

[0018]

FIG. 1 is a system diagram for implementing the method of the present invention. FIG. 2 is an operation system diagram of the electrode of the present invention.

FIG. 1 shows a known robot body. The robot freely moves along the X, S, Y, Z, R, and Θ axes. 2 is a wrist axis of the joint, and 3 is a robot arm connected to the wrist axis.

Reference numeral 4 denotes a resistance welding machine, which in this case is a C-type spot welding robot gun connected to the wrist shaft at the tip of the robot arm. The gun pressurizing actuator 5 uses a servomotor. It has a fixed-side electrode 7 attached to one end of a gun arm 6 and a movable-side electrode 9 attached to a ball screw 8 as an electrode drive shaft of a pressure actuator 5 attached to the other end of the gun arm.

The robot gun 4 has a guide rod 12 of an equalizing device 11 mounted on a robot support bracket 10 supported by a movable base 13 of the gun body, and an elastic member inserted into the guide rod of the equalizing device. The spring 14 generates a pressing force in the direction of lifting the gun body to balance the weight of the gun body.

Reference numeral 15 denotes a robot control device. The positioning data of each control axis by the handling of the robot is input to this control device. The robot gun is guided to the welding position based on the trajectory information of the positioning data.

Reference numeral 16 denotes a speed detecting means for controlling an appropriate acceleration / deceleration of the electrode. For example, a tacho generator is provided in the pressurized actuator. Reference numeral 17 denotes a means for detecting the position of an electrode, for example, an encoder provided on a pressure actuator together with a tachogenerator.

The speed detecting means 16 can be omitted by calculating the speed by sampling the output of the electrode position detecting means 17 at regular time intervals.

The above-mentioned robot controller 15 controls the robot 6
The signal flowing to the servomotor detector of each control axis is
It has a command function of controlling the load current of the servomotor based on the difference between the feedback and the command value to reproduce and guide the welding gun along the orbit route taught in advance.

Reference numeral 18 denotes a servo control device. This device is fed back with the pressure setting value and the command value by the electrode position setting, the speed from the tachogenerator and the encoder, and the electrode position information one by one, and calculates the difference between the command value and the fetched speed and electrode position one by one. It has an information command function of moving the electrode to a predetermined position at a predetermined speed. The servo controller outputs an electrode opening stroke position confirmation signal to the robot controller, and the robot controller inputs an electrode opening stroke amount instruction signal.

Reference numeral 19 denotes a welding control device including a welding timer for controlling the welding current to the welding gun and a contactor. A welding completion signal is output to the robot controller, and a welding start signal is input from the robot controller.

Next, FIG. 2 shows the movement of the welding gun and the stroke operation of the electrode by the control system according to the present invention.

The robot control device 15 is previously taught information on the movement trajectory of the welding gun by the robot, and the servo control device 18 is set with the electrode opening speed and electrode opening position data of the welding gun.

When an instruction signal of an opening stroke that minimizes each step in FIG. 2 is received from the robot controller 15, the servo controller 18 controls the position of the electrode at the time of opening according to the instruction. At this time, if information on the movement amount and time to the next step is also transmitted and received from the robot controller at the same time, circular interpolation of linear interpolation becomes possible. Needless to say, the instruction signal of the opening stroke amount is given in advance so that the opening operation of the welding gun is performed simultaneously with the movement of the robot. Further, it is of course possible to correct in advance the amount of chip reduction on the pressurized actuator side.

As shown in FIGS. 3A and 3B, the opening stroke of the movable electrode 9 moves to each hit point position with an appropriate stroke that can avoid the interference with a minimum stroke.

At the time of welding, a pressurizing operation is started by a welding start signal from the robot controller, and when welding is completed, the robot is moved to the next welding position by a welding completion signal from the welding controller. During the period from the pressurization signal to the release signal, the servo control device on the gun controls the pressing force and the electrode position, and synchronizes with the welding current with the timer device. In other words, an appropriate pressing force and welding current value are controlled during the nugget generation, and the generation of spatter is suppressed, so that a nugget of a required size can be reliably obtained.

In the present invention, the opening position can be set to the minimum for each hit point, so that the distance between the electrode and the work is kept short and the squeeze time can be set to the shortest. Alternatively, an energizing signal is sent to the timer side simultaneously or in anticipation when the pressurizing force rises to the set value by applying pressure, so that there is almost no delay until energizing.

FIG. 3 shows an embodiment in which the control system for a robot gun described above is applied to a stationary spot welding machine. In this case, the workpiece W is supported so as to move along the orbital path taught in advance by the robot with respect to the electrode position of the spot welding machine 4 whose position is fixed. Since the configuration, function, and operation are basically the same as those of the above-described embodiment, the same reference numerals are given to the same components, and the details are omitted.

[0035]

As described above, according to the control system of the present invention, when controlling the pressurized actuator using the motor of the spot welding machine including the robot gun and the stationary type, the control of the pressurized actuator is performed. A control device and a control device for positioning the robot for driving the welding machine or the work to be welded. Control, and
Information such as speed and position from pressure actuator and timer device
The welding current value from the machine was controlled by considering each other
In spite of the fact that the servo control function of the pressurized actuator and the control function of the robot are separated from the conventional robot controller, switching means such as electronic switches are not required. Since it can be used as it is, significant cost reduction can be realized. In addition, accurate synchronization between electrode pressure and welding current
Control is obtained and welding quality is improved. That is, the conventional
Servo control function for 6-axis robot controller (7th axis)
It is not necessary to add
For proper synchronous control that balances pressure and welding current synchronously
Nugget monitoring and spatter generation during welding
And realize energy saving welding.

[0036]

[Brief description of the drawings]

FIG. 1 is a control system diagram of a spot welding machine showing an embodiment of the present invention.

FIG. 2 is an operation diagram showing an electrode opening position in the control method of the present invention, in which (a) an electrode opening position during movement of the robot;
(B) shows the electrode pressing and electrode opening positions.

FIG. 3 is a schematic view of a stationary spot welding machine showing another embodiment of the system of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Robot main body 14 Spring 2 Wrist axis 15 Robot control device 3 Robot arm 16 Speed detection means 4 Spot welding machine (robot gun) 17 Electrode position detection means 5 Pressurized actuator 18 Pressurized actuator control device 6 Gun arm (Servo control device) 7 Fixed side electrode 19 Welding control device 8 Ball screw W Workpiece 9 Movable side electrode 10 Robot support bracket 11 Equalizing device 12 Guide rod 13 Moving table

Claims (1)

(57) [Claims] 1. A method for controlling a pressurized actuator using a motor as a drive source of an electrode of a spot welding machine, comprising: a controller for the actuator; and information in which the welding machine or the workpiece is stored in advance. how a robot controller for positioning the drive to reproduce the trajectory as the control device of the actuator by the electrode stroke opening signal from the robot controller controls the electrode stroke amount of the spot welder steplessly based In the above, the robot
Pressing operation is started by the welding start signal from the
The robot completes with a welding completion signal from the actuator control unit.
Controller starts moving the robot to the next welding position
And the electrode pressure from the spot welding machine
During the welding period until opening, the control device of the actuator
To control the electrode pressing force by welding and the switch of the welding power source
Control both to synchronize the welding current with the device
Control method of spot welding machine.