JPH106018A - Resistance spot welder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the response speed and to attain highly accurate pressing force control by giving the necessary pressing force by the elasticity of secondary arm itself or a servo mechanism or a spring between the pressing mechanism and the secondary arm. SOLUTION: In a resistance spot welder, the positioning is controlled by a servo motor 10 and deflecting quantity of the second arms 11, 12 being elastic bodies is controlled by this motor to adjust the pressing force. In the secondary arms, a function as a secondary conductor for supplying welding current to a material to be welded and a function as the elastic body for giving a prescribed pressure to the material to be welded are integrally provided. By this constitution, since the pressing force is adjusted by physical coefficient of elasticity at the tip part side of the second arms having further small mass, the response speed is improved and the high accurate pressing force control is attained because the pressing force adjustment is executed by easily controlable positioning control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance spot welding machine for energizing an object to be welded via a secondary arm which can be arbitrarily positioned by a servo mechanism or a mechanical stopper.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional resistance spot welding machine having a pressurizing mechanism, which is an embodiment of a welding machine for adjusting the pressing force by controlling the torque of a servomotor. Servo motor for adjustment. Reference numeral 2 denotes a ball screw that converts a rotary motion into a linear motion.
Reference numerals 3 and 4 denote arm holders supported by the ball screw and the main body. Reference numerals 5 and 6 denote secondary arms having high rigidity and little deflection. Reference numerals 7 and 8 denote electrodes for sandwiching the object to be welded, applying a pressing force to the welded portion, and energizing the electrode. Reference numeral 9 denotes a spot welding machine main body.

FIG. 9 shows an embodiment of a conventional resistance spot welding gun. Reference numeral 21 denotes a rigid arm capable of withstanding a predetermined pressing force.
Reference numeral 22 denotes a rotation stopper guide for the pressure cylinder rod. 2
Reference numeral 3 denotes a pressurizing cylinder. 24 is a cylinder rod. Reference numerals 25 and 26 denote electrode tips for holding the workpiece and applying a pressing force to the workpiece and energizing the workpiece.

In this type of conventional resistance welding machine, a secondary arm and an electrode are generally driven by an actuator such as an air, hydraulic or electric motor to apply pressure, and after the application, the pressure of the same actuator is adjusted. To obtain a predetermined pressure.

In this case, the secondary arm is generally made of an electric conductor such as a copper alloy or aluminum. Although there are restrictions such as weight and thickness, the electric resistance is as low as possible.
It has been said that the higher the strength, the better.

For example, when the pressure control is performed by air, the pressure is adjusted by adjusting the air pressure applied to the pressurizing cylinder, or when the electric servo is used, by controlling the torque.

[0007]

However, when the pressing force is directly controlled by the actuator as described above, the compression of the air, the delay of the servo response, etc., and the friction and the prying inside the pressurizing mechanism, etc., occur. Due to the influence, the work to be softened and settled in the early stage of energization,
Even if the pressure at the tip of the electrode tip changes due to disturbances such as the electrodes being forcibly expanded due to the thermal expansion of the weld in the middle stage of energization, a sufficient pressure response speed has not been obtained for them.

[0008] Conventionally, in a pressurizing device using an air cylinder, a spring is sometimes inserted into a pressurizing mechanism for the purpose of improving the response of a pressing force. However, they are not designed to perform arbitrary pressure control in combination with arbitrary positioning control.
The pressure control itself has been performed by an actuator such as an air cylinder. Accordingly, the spring merely improves the electrode follow-up against the disturbance by a fixed spring constant, and cannot always perform a desired arbitrary pressure control.

On the other hand, the secondary arm of the spot welding gun is generally made of an electric conductor such as a copper alloy or aluminum. Since it also has the role of receiving and supporting, it must have enough rigidity to withstand the applied pressure and not to bend easily. This inevitably leads to an increase in size and weight, which requires a robot with a larger payload to hold the gun, increases the burden on the operator who operates the gun, and increases the cost of copper alloys and other expensive materials. There are problems such as the need for many materials and the disadvantage of cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been made in consideration of the elasticity of a secondary arm itself or the elasticity of a spring provided between a servo mechanism or a pressurizing mechanism and a secondary arm. The present invention provides a resistance spot welding machine that achieves improved pressure response characteristics by applying a predetermined pressure to a welding spot.

According to another aspect of the present invention, the protrusion of the pressurizing cylinder or the servo pressurizing unit is fixed at an arbitrary position by a positioning control device using a stopper or a servo, and the position is adjusted to be pushed by a desired amount. Provided is a resistance spot welding gun in which the secondary arm of the gun is reduced in size and weight by applying a predetermined pressure to the workpiece by the elasticity of the secondary arm itself. The technical measures taken are listed below.

[0012]

According to a first aspect of the present invention, there is provided a resistance spot welding machine comprising: a servo mechanism capable of arbitrarily positioning a secondary arm and an electrode by air, hydraulic pressure, or electric servo; The present invention is characterized in that the function as a secondary conductor for supplying a welding current to an object to be welded and the function as an elastic body for applying a predetermined pressing force to the object to be welded are integrated. Compared to the conventional method that performs delicate pressing force control on the entire pressurizing mechanism with a large mass, the pressing force is adjusted by the physical elastic coefficient on the tip side of the secondary arm with a smaller mass. In addition, the response speed can be greatly improved, and the pressure can be adjusted by the positioning control, which can more easily control the fluctuation due to the disturbance of the pressure, so that the pressure can be controlled with high accuracy.

According to a second aspect of the present invention, in the above-described resistance spot welding machine, instead of the servo mechanism capable of arbitrarily positioning, a push-off pressure mechanism that does not perform positioning control and a secondary arm are abutted and stopped. It is characterized by using a movable mechanical stopper. As a result, the same operation and effect as those of the first aspect can be obtained even in the push-off pressure mechanism that does not use the positioning control by the servo.

According to a third aspect of the present invention, the secondary arm of the resistance spot welding machine is made of a highly rigid material instead of an elastic body, and a spring is provided between the servo mechanism and the secondary arm. . Thus, even in a pressing mechanism that does not use an elastic body for the secondary arm, the same operation and effect as those of the first aspect can be obtained.

According to a fourth aspect of the present invention, the secondary arm of the resistance spot welding machine is made of a highly rigid material instead of an elastic body, and a spring is provided between the pressing mechanism and the secondary arm. did. As a result, the same function and effect as those of the second aspect can be obtained even in a push-off mechanism that does not use the positioning control by the servo and that does not use the elastic body in the secondary arm.

According to a fifth aspect of the present invention, the armature current of the servo motor of the resistance spot welding machine is monitored to detect the torque value moment by moment, and when the detected torque value exceeds a predetermined value, the electrode is welded. The system is characterized in that it detects that it has come into contact with an object, and pushes in a predetermined distance from that position to perform positioning. As a result, the deflection of the spring, which is installed between the secondary arm of the elastic body or the pressurizing mechanism and the secondary arm, that is, the fluctuation of the pushing amount is corrected even for the electrode tip that is worn during repeated welding. ,
The same functions and effects as the first and third aspects are obtained.

The invention of claim 6 is characterized in that the contact of the electrode of the resistance spot welding machine with the workpiece is detected by a contact sensor instead of the torque detection of the servomotor. Thus, even if a contact sensor is used instead of the means for detecting the torque value of the servomotor, the same operation and effect as those of the fifth aspect can be obtained.

As described above, according to the main configuration of the present invention,
During pressurization, the pressurizing mechanism side is fixed by positioning control during pressurization, and the necessary pressing force is set by the elasticity of the secondary arm itself or the servo mechanism or between the pressurizing mechanism and the secondary arm. With a configuration in which the pressure is applied by a spring, a drastic improvement in response speed to fluctuations due to disturbance of the pressing force can be achieved.

According to a seventh aspect of the present invention, in the resistance spot welding gun, there is provided a positioning control device using a stopper or a servo for fixing a protruding allowance of the electrode pressurizing cylinder at an arbitrary position, and is provided on the secondary arm of the welding gun. By integrating the function as a secondary conductor that supplies welding current to the workpiece and the function as an elastic body that applies a predetermined pressing force to the workpiece, the secondary arm is reduced in size and weight. .

That is, during the pressurization, the pushing force of the pressurizing cylinder or the servo pressurizing unit is stopped by a stopper or a servo positioning control device installed at a position where the secondary arm is depressed by a predetermined amount. The secondary arm is fixed at that position, and the pressing force required for welding is given by the elasticity of the secondary arm itself which has been depressed, thereby achieving a significant reduction in the size and weight of the secondary arm.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of a welding machine according to the present invention, in which a servomotor performs positioning control, thereby controlling a deflection amount of a secondary arm which is an elastic body to adjust a pressing force. Reference numeral 10 denotes a servo motor for performing positioning control so that a predetermined pressing force is obtained by bending the secondary arm. Reference numerals 11 and 12 denote elastic secondary arms. Hereinafter, FIG.
The same components as those of the conventional apparatus are denoted by the same reference numerals, and detailed description thereof will be omitted.

Next, FIG. 2 shows another embodiment in which the position control is performed by moving a mechanical stopper by using an air cylinder to obtain the same effect as the embodiment of FIG. That is, the positioning control is performed by the air cylinder 13 and the mechanical stopper 14 by the pressurizing mechanism using the mechanical stopper 14 according to the present invention shown in FIG. 2, thereby controlling the deflection amount of the secondary arm 11 which is an elastic body. To adjust the pressing force. In this embodiment of the welding machine, the cylinder 13 deflects the holder 3 of the secondary arm until it hits the mechanical stopper 14 to obtain a predetermined pressing force. The position of the mechanical stopper 14 can be arbitrarily changed.

FIG. 3 shows a state where the pressing force is zero in the pressing force adjustment by the mechanical stopper 14 of FIG. In the embodiment using the mechanical stopper 14 shown in FIG. 3, in a state where the upper and lower electrodes 7 and 8 are in contact with each other, the upper secondary arm 11 has not yet reached the mechanical stopper 14 and the pressing force is zero. The state is shown. In this state, the gap between the holder 3 of the secondary arm and the mechanical stopper 14 still corresponds to the set pressure value.

FIG. 4 shows a state where a predetermined pressing force is applied in the pressing force adjustment by the mechanical stopper 14 of FIG. 3 shows a state in which the upper secondary arm 11 is deflected and abuts against the mechanical stopper 14 from the state of FIG. Although not shown in FIGS. 3 and 4, the upper and lower electrodes 7 and 8 are used in the actual welding operation.
Needless to say, the workpiece is interposed between them.

Further, in FIG. 4, the upper and lower secondary arms 11, 1
2 are used so as to bend evenly. For example, the lower secondary arm 12 is made sufficiently rigid and the upper secondary arm 12 is made rigid. The pressing force may be applied only by the elasticity of the elastic member 11. In addition, both the secondary arms 11 and 12 have sufficient rigidity, and the secondary arm 11 and the pressurized cylinder rod 1
5 (FIG. 2) or secondary arm 11 and ball screw 2
A structure may be adopted in which a spring is inserted between (FIG. 1) and integrated, and a pressing force is applied by the elasticity of the spring.

As described above, the resistance welding machine of the present invention performs the positioning control, not the conventional pressing force control. Regardless of whether it is air, hydraulic, or electric motor, positioning control is generally easier than pressure control.

For example, when the pressure control is performed by air in the conventional method, the air pressure applied to the pressurizing cylinder is adjusted, but in the positioning control of the present invention, the air pressure is always fixed to the maximum. The adjustment of the pressing force can be adjusted based on the position at which the electrode hits the work to be welded, from which the secondary arm of the elastic body is bent and pushed further.
At this time, the pressure applied to the workpiece is proportional to the amount of deflection if the secondary arm is within the elastic limit at which plastic deformation does not occur. The operation is exactly the same when the secondary arm is made of a high-rigidity material instead of the elastic body and a spring is installed between the pressing mechanism and the secondary arm.

That is, the pressing force is set by the pushing amount and the elastic coefficient of the secondary arm, and the maximum pressing force is determined by the air pressure and the plastic deformation limit of the secondary arm.
The pressing force can be appropriately changed by exchanging the secondary arm itself or by bending the secondary arm and further pushing the secondary arm, that is, the pushing amount.

In general, since the secondary arm is not replaced frequently, the secondary arm is designed to cover the range of the required pressing force when the specification is determined, and the pressing force is adjusted by changing the pushing amount. In order to change the pushing amount, for example, automatic positioning may be performed by servo control, or may be performed by changing the position of a mechanical stopper to which a secondary arm is attached. The position adjustment of the mechanical stopper may be performed manually or automatically.

In this manner, the entire pressurizing mechanism having a large mass can be controlled by the secondary arm having a smaller mass as compared with the conventional system in which the pressure control of air or hydraulic pressure or the delicate pressure control is performed by the servo mechanism. The response speed is greatly improved by adjusting the pressing force by the physical elastic coefficient on the tip side, and high-precision pressing force control is possible by adjusting the pressing force by positioning control, which is easier to control. Become.

The electrode tip gradually wears as the welding point is repeated. There are two methods for correcting the fluctuation of the pushing amount due to the wear.

First, when the welding is not performed, the moving stroke is detected by a sensor installed outside from time to time, or by performing an empty pressurization that sandwiches the work to be welded. In this method, the amount of wear is calculated in comparison with the dimensions of the electrode tip, and in the subsequent welding work, the positioning point of the secondary arm is corrected by the amount of wear.

Second, the positioning control is not performed at the absolute position.
Detects the position where the electrode contacts the workpiece in the process of driving the electrode, and adopts the distance from which the secondary arm is depressed, that is, the pressing force setting value for pre-inputting the pushing amount How to As a method of detecting the contact between the electrode and the workpiece, the armature current of the servomotor is monitored, the torque value is detected every moment, and when the detected torque value exceeds a predetermined value, the electrode is welded. This is done by detecting contact with an object or by using an externally installed electrical or mechanical contact sensor.

FIG. 6 shows an embodiment of a resistance spot welding gun according to the present invention using a resilient arm and a stopper for fixing the protrusion of the pressure cylinder to an arbitrary position. The same components as those of the conventional welding gun are denoted by the same reference numerals. 2
Reference numeral 2 denotes a detent guide for the pressure cylinder rod. 23
Is a pressurizing cylinder. 24 is a cylinder rod. 2
Reference numerals 5 and 26 denote electrode tips that clamp the workpiece and apply pressure to the workpiece and energize the workpiece. Reference numeral 27 denotes a stopper for fixing the protrusion of the pressurizing cylinder at an arbitrary position. Reference numeral 28 denotes a thin elastic arm.

In this embodiment, the stopper is installed coaxially with the rotation preventing shaft of the pressure cylinder rod. However, it is possible to restrict the protrusion of the target pressure cylinder and prevent the pressure cylinder from protruding. If so, it may be installed anywhere.

FIG. 7 shows a state in which the protrusion of the pressurizing cylinder of the gun shown in FIG. 6 is extended until the electrode comes into contact with the workpiece. There is still a distance to the stopper.

FIG. 8 shows a state in which the elastic arm is pressed down from the state shown in FIG.

In order to realize the present invention, the pressing mechanism performs positioning instead of the conventional pressing force control. For example, when pressure control is performed by the conventional method, the torque is adjusted by the air pressure applied to the pressurizing cylinder or by servo control. However, in the positioning method according to the present invention, the air pressure is always fixed to the maximum. The pressure is adjusted based on the position at which the electrode hits the workpiece, and can be adjusted according to the distance from which the secondary arm is bent and pushed further. At this time, the pressure applied to the workpiece is proportional to the amount of deflection if the secondary arm is within the elastic limit at which plastic deformation does not occur.

That is, the pressing force is set by the pushing amount and the elastic coefficient of the secondary arm itself, and the maximum pressing force is determined by the air pressure or the maximum torque and the plastic deformation limit of the secondary arm. The pressing force can be appropriately changed depending on the distance that the secondary arm is bent and pushed further after the electrode comes into contact with the workpiece, that is, the pushing amount. The secondary arm is designed so that the elastic limit covers the required pressure range at the time of specification specification, and the pressure is adjusted by changing the pushing amount. The pushing amount is changed by changing the position of a stopper against which the secondary arm is abutted. The position of the stopper may be adjusted manually or automatically. In the case of servo control, the positioning point is changed by a program.

In this way, the secondary arm according to the present invention only needs to be thick enough to obtain the required pressing force as compared with the conventional gun arm which is assumed not to bend. Can greatly reduce the thickness, size, and weight. Since the protrusion of the pressurizing cylinder or the servo pressurizing unit is regulated by the positioning control by the stopper or the servo, the secondary arm is not excessively bent and bent or bent. Also, compared to the conventional method in which the entire pressurizing mechanism with a large mass is delicately controlled by air pressure or torque control by servo control, the physical elastic coefficient at the tip end of the secondary arm with a smaller mass is compared to the conventional method. Accordingly, the effect that the pressurization response speed is improved because the pressurizing force is controlled is also obtained. Further, the air pressure or torque adjusting mechanism is not required, and the material of the secondary arm can be reduced, which is advantageous in cost.

It should be noted that the electrode tip gradually wears as the welding point is repeated, which causes a problem that the pushing amount of the secondary arm changes, and a predetermined pressure cannot be obtained. For example, in the case of a gun having a low usage rate incorporated in a multi-welding machine, the wear amount is not so large, and a new electrode tip may be periodically replaced before the wear progresses. If the wear rate cannot be ignored due to the high usage rate, such as with a robot gun, the number of weldings is counted and the wear amount of the electrode tip is calculated from the empirical value, or the wear amount of the electrode tip is measured by an external sensor. Is detected, and the stopper position is adjusted manually or automatically by that amount to keep the pushing amount constant. In the case of servo control, the same operation and effect can be obtained by changing the positioning point by a program.

[0042]

As described above, according to the resistance spot welding machine of the present invention, the pressurizing mechanism is fixed by the positioning control during pressurization, and the necessary pressurizing force is adjusted by the elasticity of the secondary arm itself or the servo. By applying a spring provided between the mechanism or the pressurizing mechanism and the secondary arm, the entire pressurizing mechanism with a large mass can be delicately controlled by air or hydraulic pressure adjustment or servo mechanism. Compared to the conventional method, the pressure is adjusted by the physical elastic coefficient on the tip side of the secondary arm, which has a smaller mass, so that the response speed can be greatly improved.
High-precision pressure control is possible because the pressure is adjusted by the positioning control, which is easier to control even with the fluctuation of the pressure due to disturbance.

According to the resistance spot welding gun of the present invention,
In the reverse concept of conventional resistance spot welding guns, pressurizing cylinders or servo pressurizing units pressurize the protruding force during pressurization, and a stopper or servo installed at a position where the secondary arm is depressed by a predetermined amount. The secondary arm is made thinner and more compact by stopping it by the positioning control device and fixing it at that position, and applying the pressure required for welding by the elasticity of the secondary arm itself that is depressed. Weight and weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of a pressing mechanism using an elastic secondary arm according to a first embodiment of the present invention.

FIG. 2 is an explanatory view of the principle of a pressing mechanism using a mechanical stopper based on an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a state where a pressing force is zero in the pressing force adjustment by the mechanical stopper of FIG. 2;

FIG. 4 is a schematic diagram showing a state in which a predetermined pressing force is applied in the pressing force adjustment by the mechanical stopper in FIG. 2;

FIG. 5 is a schematic diagram showing a case where a pressing force is adjusted by torque control of a servomotor in a pressing mechanism of a conventional electric resistance spot welding machine.

FIG. 6 is an overall external view of a resistance spot welding gun using an elastic secondary arm according to a second embodiment of the present invention.

FIG. 7 is a second embodiment of the present invention, in which a protruding margin of a pressurizing cylinder of a gun is extended until an electrode comes into contact with a workpiece.

FIG. 8 shows a second embodiment of the present invention, in which a predetermined pressure is applied to the workpiece by bending the elastic arm until it hits a stopper.

FIG. 9 is an overall external view of a conventional resistance spot welding gun.

[Explanation of symbols]

 1 ··· Torque control servo motor 2 ··· Ball screw 3 ··· Arm holder 4 ··· Arm holder 5 ··· Secondary arm 6 ··· Secondary arm 7 ··· · Electrode 8 ··· Electrode 9 ··· Body 10 ··· Position control servo motor 11 ··· Elastic secondary arm 12 ··· Elastic secondary arm 13 ··· Air cylinder 14 ··· Mechanical stopper 22 ··· Detent guide 23 ··· Cylinder 24 ··· Cylinder rod 25 ··· Electrode tip 26 ··· Electrode tip 27 ··· Stopper 28 .... Elastic arms

Claims (7)

[Claims] In a resistance spot welding machine, a servo mechanism capable of arbitrarily positioning a secondary arm and an electrode by air, hydraulic pressure, or electric servo is configured, and a welding current is supplied to the workpiece to the secondary arm. And a function as an elastic body for applying a predetermined pressing force to a workpiece to be welded. 2. The resistance spot welding machine according to claim 1, wherein a push-off pressure mechanism that does not perform positioning control and a secondary arm are abutted and stopped, instead of the servo mechanism that can be arbitrarily positioned. A resistance spot welding machine characterized by using a movable mechanical stopper. 3. The resistance spot welding machine according to claim 1, wherein the secondary arm is made of a highly rigid material instead of the elastic body, and a spring is provided between the servo mechanism and the secondary arm. Characterized resistance spot welding machine. 4. The resistance spot welding machine according to claim 2, wherein the secondary arm is made of a highly rigid material instead of the elastic body, and a spring is provided between the pressurizing mechanism and the secondary arm. A resistance spot welder characterized by: 5. The resistance spot welding machine according to claim 1, wherein the armature current of the servomotor is monitored and its torque value is detected every moment, and the detected torque value becomes larger than a predetermined value. A resistance spot welding machine characterized by detecting that an electrode has come into contact with an object to be welded, and pushing in a predetermined distance from that position for positioning. 6. The resistance spot welding machine according to claim 5, wherein the contact of the electrode with the workpiece is detected by a contact sensor instead of the torque detection of the servomotor. 7. A resistance spot welding gun is provided with a positioning control device by a stopper or a servo for fixing a protrusion of an electrode pressurizing cylinder at an arbitrary position, and a welding current is applied to a workpiece to be welded on a secondary arm of the welding gun. A resistance spot welding gun that reduces the size and weight of the secondary arm by integrating the function as a secondary conductor that supplies the pressure and the function as an elastic body that applies a predetermined pressure to the workpiece.