JPS61253189A - Pressurizing device for resistance welding machine - Google Patents

Abstract

PURPOSE:To control freely the stop position of an electrode tip and the pressurizing force thereof by driving an electric motor to move and pressurize the electrode. CONSTITUTION:Materials to be welded are fixed and the electric motor 11 is driven to rotate a screw shaft 12 in a prescribed direction thereby feeding a ball screw 13 screwed thereto. A cylinder rod 14 fixed to the screw 13 is thereby fed to lower the electrode down to the prescribed position. The motor 11 stops revolving in this state but the motor 11 is constituted to generate the prescribed torque even during the stoppage by a control device and therefore the electrode presses eventually the materials to be welded under the prescribed force. Welding is thereafter executed by conducting electricity to the electrode and after the specified holding time is taken upon the conduction, the motor 11 is run backward to rise the electrode. The welding is thus completed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressurizing device for a resistance welding machine, and more particularly to a pressurizing device for a resistance welding machine whose driving source is an electric motor.

[Conventional technology]

Usually, resistance welding is carried out by sandwiching the object to be welded between electrodes provided with a pressure mechanism and passing a large current through a secondary circuit of a welding transformer connected to the electrodes.

A pneumatic or hydraulic cylinder has been used as the pressurizing device.

[Problem that the invention seeks to solve]

However, the conventional pressurizing device uses a pneumatic or hydraulic cylinder, and pressurizes with a constant force as long as the cylinder rod is constant, so it was necessary to change it according to the welding conditions.

Therefore, when welding objects of different thickness using a spot welder, which is an example of a resistance welder, there is a problem in that it is necessary to change the pressurizing force, which is very time-consuming.

In addition, resistance welding usually requires energization time within 0.1 to 0.2 seconds, and conventionally, the electrode pressure is applied using an air cylinder, etc., so the response is poor and the energization time is within 0.1 to 0.2 seconds. It was difficult to change.

Therefore, it may be difficult to perform accurate welding in accordance with the object to be welded.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a pressurizing device for a resistance welding machine that can change the electrode pressurizing force with a simple operation and has good responsiveness in accordance with the energization time. do.

[Means to solve problems]

A pressurizing device for a resistance welding machine according to the present invention that achieves the above object includes:
The object to be welded is pressurized with opposing electrodes equipped with a pressure mechanism,
In a resistance welding machine that performs welding by passing a current through the electrode to the workpiece, the pressurizing mechanism is screwed into an electric motor and a screw shaft connected to an output shaft of the electric motor, and the screw shaft. A ball screw, a cylinder rod fixed to the ball screw, and a control device that rotationally drives the motor and controls the torque when the motor is stopped, and controls the movement and pressurization of the electrode. It is constructed by being driven by an electric motor.

Here, the resistance welding machine refers to a spot welding machine, a seam welding machine, a projection welding machine, etc., and the electric motor refers to a motor driven by electric power, and therefore a DC motor or a motor connected to an inverter. This includes AC motors (including induction motors), pulse motors, etc.

Further, although the control means varies depending on the type of electric motor, the control device is configured to include at least means for changing the rotational speed of the electric motor and means for controlling the torque when the electric motor is stopped. I need to be there.

Therefore, open loop control may be used, but feedback control may also be used in which a rotary encoder is connected to the motor and the rotation and torque of the motor are controlled in accordance with the output of the rotary encoder.

[Function] Next, the function of the pressure device of the resistance welding machine according to the present invention will be explained.

First, with the object to be welded fixed, the electric motor is driven to rotate the screw shaft in a predetermined direction and feed the ball screw to be screwed together. This sends the cylinder rod fixed to the ball screw and lowers the electrode to a predetermined position.

In this state, the electric motor stops rotating, but since the electric motor is configured by the control device to generate a predetermined torque even when stopped, the electrodes are exposed to a predetermined force. This means that you are pushing the workpiece.

After this, welding is carried out by applying electricity, but in this case as well, if necessary, the electric motor is controlled to control the torque.
The pressure may be changed in some cases.

Then, after a certain holding time has elapsed after energization, the electric motor is reversed to raise the electrode and finish welding.

Note that in a welding machine in which the lower electrode is also driven by an electric motor to move the lower electrode up and down, it is further possible to determine the position of the electrode according to the height of the object to be welded.

〔Example〕

Next, an embodiment embodying the present invention will be described with reference to the attached drawings to provide an understanding of the present invention.

Here, FIG. 1 is a sectional view of an electric cylinder constituting a pressure device for a resistance welding machine according to an embodiment of the present invention, and FIG. FIG. 3, a side view of the spot welding machine, is a schematic circuit diagram of a control device for controlling the pressurizing mechanism used in the above embodiment.

As shown in FIG. 1, a pressurizing mechanism 10 constituting a pressurizing device for a resistance welding machine according to an embodiment of the present invention includes an upper electric motor 11 and a pressurizing mechanism 10 connected to the electric motor 11. It has a screw shaft 12, a ball screw 13 screwed onto the screw shaft 12, a cylinder rod 14 fixed to the ball screw 13, and guide rods 15 and 16 provided on both sides of the cylinder rod 14. It is composed of These will be explained in detail below.

In this embodiment, the electric motor 11 is composed of a three-phase induction motor, and a rotor encoder (not shown) is disposed on the shaft of its rotor, so that the number of revolutions of the electric motor 11 can be measured. .

A coupling 1 is attached to the output shaft 17 of this electric motor 11.
A Fuji shaft 12 is connected via 8.

The upper end of this threaded shaft 12 is rotatably fixed to the upper housing 20 via a bearing 19, and the threaded portion 21 has a ball inside and the sliding portion reduces friction by rolling the ball. ball screw 1
3 are screwed together, and the ball screw 13 can be moved linearly by the rotation of the screw shaft 12. A cylinder loft 14 is fixed to the ball screw 13, and a guide rod 1 is attached to the cylinder loft 14.
A guide 22.23 having a linear bearing or the like is slidably fitted to the cylinder rod 14, and the cylinder rod 14 is configured to move linearly.

Further, the lower housing 24 is also provided with a guide 25 having a linear hair ring or the like to hold the cylinder loft 14.

A hole 26 is provided in the upper part of the cylinder rod 14, and the screw shaft 12 can be inserted into the hole 26 up to a certain length.

Next, we will explain about a subosol [F welding machine] which is an example of a resistance welding machine using this pressure mechanism.As shown in FIG.
A guide protector 28 in which is housed is attached, and an electric cylinder 10 constituting a pressurizing mechanism according to an embodiment of the present invention is provided on the upper part of the guide block 28. An electrode holder portion 29 connected to a secondary circuit of a welding transformer (not shown) is attached to the lower part of the guide block 28.

Note that this electrode holder portion 29 is electrically insulated at the mounting portion of the guide block.

A chip holder 30 is attached to this electrode holder part 29 and holds an electrode chip 31, which is an example of an electrode.

On the other hand, a pressure mechanism 33 similar to that attached to the upper arm 27 is attached to the lower arm 32, and the structure is such that an electrode tip 34, which is an example of an electrode, can be moved up and down by rotation of the electric morph. In this case, the electric motor used in the lower pressurizing mechanism needs to be stopped with a predetermined signal, so it is preferable that the motor is equipped with a brake.If not, it should have a predetermined holding torque. It is preferable to adopt one that has The secondary conductor of the welding transformer connected to the upper electrode holder part 29 and the lower electrode holder part 35 is made of a sufficiently flexible material, so that the electrode holder part 29 and 35 are free. It has a structure that allows it to be moved up and down. Further, in the figure, 35a indicates a control device of the welding machine, and 35b indicates a foot switch that sends a signal to start welding.

Next, a control device that drives this pressurizing mechanism 10 (or 33) will be explained.

As shown in FIG. 3, a control device 36 constituting a pressurizing mechanism according to an embodiment of the present invention includes three-phase AC power supplies R, S, and T.
A rectifying section 37 connected to the rectifying section 37, a capacitor part 38 connected to the rectifying section 37, an inverter section 39 for converting DC power into AC, and a control section 40 for controlling the inverter section 39. It is composed of Hereinafter, these will be explained in detail. The rectifier section 37 is constituted by a three-phase bridge rectifier circuit, and surge absorbers 41, 42, and 43 made of varistors are attached to each input.

The rectifier 37 rectifies the three-phase alternating current to become a direct current, which is connected to a capacitor part 38 via a protective resistor 44 for preventing rush current, and is configured to supply reactive current. An inverter section 39 is connected to 38 to convert direct current to alternating current.

As shown in the figure, this inverter section 39 is constituted by a transistor inverter, and generates alternating current by sequentially turning on the transistors, which is controlled by the PWM signal command of the CPU 45, which performs the central processing of the computer. This is done by the received Heas driver circuit 46.

On the other hand, this CPU 45 has predetermined RA, M47 and RO.
M48 is connected to the display 50 which shows the operating status etc. through the interface circuit 49, and the above-mentioned CPU.
A keyboard 51 for inputting commands to the electric motor 45 is connected to the output of a low-return encoder 52 directly connected to the electric motor 11.

Note that the power source 53 is for sending electricity to the control section.

Next, the operation and usage method of the pressure device of the resistance welding machine according to the above embodiment will be explained.

First, the lower part of the electrode holder 3 according to the height of the object to be welded.
5 and the position of the electrode chip 34 fixed thereto is determined, and the position is entered manually using the keyboard 5I. in this case,
The lower electrode tip 34 is manually adjusted to a height of 2 or more in accordance with the position of the electrode holder part 35, and the lower electrode tip 34 is adjusted to a height corresponding to the welding position.
It is also possible to adjust the position of.

In this state, the pressurizing force of the upper pressurizing mechanism 10 is adjusted, and this pressurizing force is adjusted by controlling the torque of the electric motor 11. To explain this torque control in detail, the torque T of the induction motor is expressed as in the following equation.

Here, p = number of poles, f = frequency, m = number of phases of the -th winding,
V,=-secondary voltage, S=slip, r,=-resistance of next-side circuit,
r, = resistance of the secondary circuit converted to the primary circuit, X, =
-Next side leakage reactance, xz = primary side converted value of secondary leakage reactance with respect to the power supply frequency at the time of restraint.

From the above equation, it can be seen that when the slip S is constant, the torque T is inversely proportional to the frequency r and proportional to the square of the voltage 1. Therefore, if the object to be welded is pressurized, the tip of the electrode tip 30 will come into contact with the object to be welded and the electric motor 11 will stop. This can be done by controlling the

That is, the rotational speed of the induction motor is detected by a rotary encoder 52 (described later), the frequency and voltage (or current) of the inverter section 39 controlled by the CPU 45 are determined, torque is calculated, and the difference is calculated by comparing it with a set value. The torque can be controlled by detecting the difference and then issuing a command from the CPU 45 to cancel the difference.

Therefore, by programming a torque value that matches the welding conditions, the static torque can be controlled and welding can be performed under appropriate conditions.

This is because when welding multiple points under different welding conditions, the welding current can be easily adjusted by changing the roll call angle of the cylinder (not shown) connected in series with the welding transformer. The resistor 54 provided within the capacitor is for detecting current, and welding can be performed under the specified welding conditions.
As a result, the current of the motor is detected, the rotation speed of the electric motor 11 is measured using the signal from the low-resolution encoder 52, and the PWM signal sent to the CPU is changed according to the setting conditions, The frequency and voltage of the inverter section 39, which is the final output, are controlled.

In the above embodiment, the pressure mechanisms 10 and 33 are attached to the upper arm 27 and the lower arm 32, respectively, to change the heights of the upper electrode tip 30 and the lower electrode tip. Also good. In particular, if the lower pressure mechanism is the electric cylinder according to the above embodiment, the position of the electrode tip can be changed depending on the welding height of the object to be welded, and the electric cylinder can be used as the upper pressure mechanism. If the lower part is a fixed electrode tip, welding conditions can be controlled to apply pressure depending on the welding location.

〔Effect of the invention〕

The present invention is configured as described above, and since an electric motor is used as the pressurizing mechanism for the welding part, the stop position of the electrode tip and the pressurizing force thereof can be freely controlled. Therefore, it is possible to obtain a pressure that matches the welding conditions of the workpiece, and when the pressure mechanism according to the present invention is adopted for the lower electrode tip, the height of the electrode tip can be adjusted according to the welding height. can be set freely, resulting in extremely high workability.

Furthermore, when performing a large number of resistance welds with a small number of automatic welding machines, a single gun can control multiple positions and pressures, so the automatic welding machine can be configured with a small number of parts.

Furthermore, when the present invention is applied to welding round bars, wires, etc., the crushing height can also be adjusted by adjusting the pressure applied during welding.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an electric cylinder constituting a pressure device for a resistance welding machine according to an embodiment of the present invention, and FIG. ) A side view of the welding machine, and FIG. 3 is a schematic circuit configuration diagram of a control device for controlling the pressurizing mechanism used in the above embodiment. [Explanation of symbols] 1], ----1 electric motor, 2-- shaft, 13-- ball screw, 14- cylinder rond, 36--1 control device, 39--111- inverter. part (inverter)

Claims (2)

[Claims] (1) In a resistance welding machine that performs welding by pressurizing a workpiece with opposing electrodes equipped with a pressure mechanism and passing a current through the electrodes to the workpiece, the pressurization mechanism is connected to an electric motor. A screw shaft connected to the output shaft of the electric motor, a ball screw screwed to the screw shaft, a cylinder rod fixed to the ball screw, and a control for rotationally driving the motor and controlling torque when the motor is stopped. A pressurizing device for a resistance welding machine, characterized in that the electrode is moved and pressurized by driving the electric motor. (2) The pressurizing device for a resistance welding machine according to claim 1, wherein the electric motor is an induction motor, and the induction motor is driven via an inverter.