JPH07102467B2 - Electric pressure control method and device for resistance welding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a low-speed, high-torque DC electric motor as a method of pressurizing an object to be welded by a resistance welding machine such as a spot welding machine and a projection welding machine, and when pressurizing, that is, restraining the electric motor. The present invention also relates to an electric pressurization control method and device capable of controlling a necessary pressing force in a wide range.

[0002]

2. Description of the Related Art Conventionally, a pressurizing device for a resistance welding machine has mainly used an air pressure or a hydraulic cylinder, but not only requires an air pressure source and a hydraulic pressure source, but also makes it difficult to sensitively change the applied pressure. is there.

On the other hand, in recent years, in welding machines, welding current,
By controlling the waveform, time, etc., the welding conditions are optimized, the quality is improved, and the productivity is improved. Both of the analog and digital control methods are performed by electric signals, but it is an important issue in terms of system configuration that only the pressure device requires an air pressure source and a hydraulic pressure source.

On the other hand, when an electric motor is used as the actuator of the pressurizing device, it is considered that both a DC electric motor and an AC electric motor can be put into practical use. It is in a restrained state, that is, at a rotational speed of zero or close to it. Therefore, a large restraint torque is required because the necessary pressing force is output even when the electric motor is stationary.
Further, when the movable electrode is fed out and pulled up other than when pressure is applied, the operation must be performed as fast as possible in order to obtain workability. At this time, the electric motor is required to rotate at full speed.
The problem with the electric pressurizer is that the required torque is output even from zero revolutions to full revolutions even at zero revolutions, and torque control must be relatively fast even when the applied pressure changes due to thermal expansion of the weld. I have to.

Now, in the permanent magnet type DC motor, when the terminal voltage V, the field magnetic flux Φ, the rotation speed N, the armature current I _a , the armature circuit resistance r _a , and K are constants, the output torque T is (1 ) Formula is shown. T = KΦ / 1.027r _a (V−KΦN) (1) Furthermore, the output torque T _s when N = 0 is restricted is given by the formula (2). T _s = KΦV / 1.027r _a = K ^' I _a・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (2)

From this equation, the torque T _s is proportional to the armature current I _a even when restrained. Actually, a mechanical loss torque component from the electric motor to the movable electrode exists in the armature current I _a , but since this component has a constant value, it is necessary to control the armature current in order to control the pressing force. It is clear that wide range control is possible.

[0007]

Next, it is said that the torque of an inexpensive and maintenance-free induction motor is inversely proportional to the frequency f and proportional to the square of the terminal voltage. However, the induction motor is used as a variable speed motor. If used, there is a problem with the controller. Particularly, the restraint torque control requires an independent and complicated control law of the magnetizing current component and the torque generating component from the current vector of the induction motor. That is, although it is the vector control method, the control device such as the temperature correction of the winding and the countermeasure against the torque vibration at the low speed is more expensive than the control device of the DC motor, and in this sense, there is a problem in maintenance. There is primary frequency control as a variable speed control method for the induction motor. This is so-called V / f constant control, but the speed control range is limited, and torque control during restraint is difficult.

[0008]

The present invention solves the above-mentioned problems, and the concrete means is to weld an object to be welded by passing a pressing force and an electric current necessary for welding through opposing electrodes. In the resistance welding machine, a direct or rotary type DC electric motor is used as a pressure source for the electrodes, and the rotational movement is converted into a linear movement through a ball screw screw or the like.
The present invention is characterized in that the restraint torque at the time of pressurization is detected from the armature current of the electric motor and the feedback control is performed to control the pressing force in a wide range.

As a device for implementing the above system, a circuit for converting an AC voltage into a DC voltage in an electrode pressurizing device of a resistance welding machine using a direct-current or rotary DC motor as an electrode pressurizing source. And a DC chopper circuit for dividing the DC voltage converted by this circuit to form a waveform for driving an electric motor, an armature current detector for detecting an armature current Ia of the electric motor, and from this detector A pulse width modulation circuit that controls the pulse width so that the detected value of the pulse width follows the value set in the torque setting device in advance, and a chopper drive circuit that drives the switching element of the chopper circuit with the pulse width signal from this pulse width modulation circuit. The pressure of the electrode is controlled by the current feedback control loop having the following.

[0010]

According to the method and apparatus of the present invention, the DC motor as an actuator of the electric pressurizing device can detect the pressing force, that is, the restraint torque by the armature current, and the armature current control means can also rotate forward and backward. The DC chopper circuit, the chopper drive circuit, the pulse width modulation circuit, and the armature current detection circuit that enable the structure make the structure simple and inexpensive to manufacture, and the pressing force can be precisely and automatically controlled over a wide range. Stable welding results are obtained.

[0011]

EXAMPLES Next, examples of the present invention will be described. FIG. 1 is a block diagram of a stationary resistance welding machine. Reference numeral 1 is a welding machine main body having a welding transformer and a thyristor switching circuit (contactor) for controlling a welding current. A few
Is an electrode for welding an object to be welded, generally 2 is a movable electrode,
3 is a fixed electrode. Reference numeral 4 represents an electric actuator for pressurization. Reference numeral 5 is an electric pressure control device of the present invention.

FIG. 2 is a sectional view specifically showing the internal structure of the pressurizing electric actuator 4. Reference numeral 30 is a guide case provided at the tip of the upper arm of the resistance welding machine. Reference numeral 31 is a pressure ram which is vertically guided in the guide case. A ball screw nut 32 is provided on the upper portion of the pressure ram. Reference numeral 33 is a ball screw screw that is screwed into the screw hole of the ball screw nut, and passes through a bearing 35 provided inside a pressurizing drive bracket 34 that is bolted to the upper part of the guide case and passes through the coupling 3
It is connected to the electric motor 37 via 6. The pressurizing electric actuator 4 is a permanent magnet type DC electric motor which has a relatively low rotational speed and generates a high torque, and a ball screw screw directly connected to the electric actuator 4 makes a linear movement, that is, a vertical movement of the movable electrode 2. I do.

Next, FIG. 3 shows an embodiment of the most preferable electric pressure control device for specifically implementing the method of the present invention, and shows an electric circuit mainly including a bidirectional DC chopper. Further, FIG. 4 shows a graph for explaining the relationship between the rotation speed N and the torque T, that is, the armature current I _a . In FIG. 3, 8 is generally a single-phase AC input, and of course three-phase AC may be used. 9
May be through a rectifying transformer in a diode bridge circuit. The DC voltage output from the diode bridge circuit 9 is divided by the capacitors 10 and 11.
Reference numerals 12 and 13 denote semiconductor switching elements, for which bipolar transistors, IGBTs, MOSFETs, etc. are used.
A low speed, high torque DC motor 14 is provided at an intermediate point between the semiconductor switching elements 12 and 13 and the capacitors 10 and 11.
Are connected.

If the semiconductor switching element 12 is on and the semiconductor switching element 13 is off, a current flows from the capacitor 10 through the semiconductor switching element 12 and the DC motor 14 to the midpoint between the capacitors 10 and 11.

Next, when the semiconductor switching element 12 is off and the semiconductor switching element 13 is on, the current flows from the capacitor 11 to the DC motor 14 and then to the semiconductor switching element 13 in the opposite direction. This circuit is a bidirectional DC chopper circuit 22. Further, the magnitude of the current can be varied from 0 to the maximum value that can be allowed by the chopping width of the semiconductor switching elements 12 and 13, that is, the pulse width modulation circuit 19 (PWM).

The armature current I _a is measured by the armature current detector 15,
For example, it is detected by Hall CT or the like and amplified by the amplifier 16. The current setting signal corresponding to the torque setting value is given from the setter 17, and the difference 18 between the setter 17 and the amplifier 16 is given.
Becomes a pulse width by the pulse width modulation circuit 19, and the semiconductor switching element 12 or the semiconductor switching element 13 is operated via the pulse amplifier 20 which drives the semiconductor switching elements 12 and 13.

The electrical circuit of FIG. 3 is a current feedback control loop. The current flowing through the DC motor 14 is the setting device 1
It goes without saying that the torque setting signal given from 7 is faithfully followed. Basically, the DC motor 14 continues in both the rotating state and the restraining state, but in reality, as can be seen from the equations (1) and (2), the output torque of the motor is low during the upward and downward movements of the movable electrode 2. You may In other words, the detected value of the armature current Ia is small, and the setter 17 and the amplifier 16
The difference 18 with the difference becomes large, and the DC motor 14 rotates at a voltage value close to the terminal voltage of the capacitor 10 or the capacitor 11. In the case of the DC motor 14, the rotation speed is proportional to the terminal voltage V. Therefore, the original torque control is automatically performed while the object to be welded is pressed between the electrodes 2 and 3.

I ₁ , I ₂ , and I _{3 in} FIG. 4 show the operating characteristics when the torque setting signal is changed, and the number of revolutions of the DC motor 14 is N≈V. The speed can be controlled by changing the speed.

As described above, by adopting the DC motor as the actuator of the pressurizing device, the pressing force can be controlled easily and in a wide range by a simple electric control device.

In order to make the portion surrounded by the dotted line 21 in FIG. 3 into a digital circuit, if the amplifier 16 on the output side of the armature current detector 15 is an AD converter, it becomes a direct digital controller. It is also easy to configure.

[0021]

As described above, according to the method of the present invention, as compared with the conventional method in which the induction motor is used as the pressurizing electric actuator of the resistance welding machine, by using the high torque low speed DC motor, the torque control device can be used. Is simple and practical from the point of view of price, and the electric control device can be easily realized in both analog and digital types. Further, in the device of the present invention, the shock to the object to be welded at the time of pressurizing the electrode can be eliminated, and the electrode can be constantly pressed by the soft touch regardless of the material and the rigidity of the object to be welded, and the responsiveness of the electrode operation is accelerated. It is possible to obtain precise effects on workability and weldability, such as precise control of pressurizing operation in conjunction with welding conditions such as welding current, waveform, and time. Realized the control.

[Brief description of drawings]

FIG. 1 is a side view showing an appearance of a stationary resistance welding machine.

FIG. 2 is a detailed cross-sectional view showing the internal configuration of the electric pressing actuator of the present invention.

FIG. 3 is an electric circuit diagram showing an example of an electric pressurization control device for carrying out the method of the present invention.

FIG. 4 is a graph showing the relationship between the rotational speed N and the torque T under the control of the present invention.

[Explanation of symbols]

 2 electrodes 3 electrodes 4 electric actuator for pressurization 5 electric pressurization control device 9 diode bridge circuit 12 semiconductor switching device 13 semiconductor switching device 15 armature current detector 16 amplifier 17 setting device 19 pulse width modulation circuit 20 pulses Amplifier (chopper drive circuit) 22 DC chopper circuit

Claims (3)

[Claims] 1. A resistance welding machine, in which a pressing force and an electric current required for welding are applied to an object to be welded through opposed electrodes, using a direct-current or rotary type DC electric motor as a pressure source of the electrodes, and a rotary motion. Is an electric pressurizing method in which a linear motion is converted via a ball screw screw or the like, the restraint torque at the time of pressurization is detected from the armature current of the electric motor, and this is feedback-controlled to control the pressurizing force. An electric pressure control method characterized by the above. 2. A resistance welding machine, which applies a pressure and a current required for welding to a workpiece through opposing electrodes, uses a direct or rotary type DC motor as a pressure source for the electrodes to electrically drive the resistance welding machine. In the pressure method, a high DC voltage is applied to the electric motor when the electrode is opened and closed, and the electrode is switched to a low voltage while the electrode is approaching or pressing the workpiece, and the armature current flowing through the electric motor uses a chopper. An electric pressurizing control method characterized in that the polarity is switched at a high frequency by PWM control to perform an average value control of pressurizing torque. 3. An electrode pressing device for a resistance welding machine, which uses a straight or rotary type DC electric motor as a pressure source for the electrode,
A circuit that converts an AC voltage into a DC voltage, a DC chopper circuit that divides the DC voltage of the circuit to form a waveform for driving the electric motor, and that can rotate forward and backward, and detects an armature current of the electric motor. Armature current detector, a pulse width modulation circuit for converting the difference between the output value of the armature current detector and the value preset in the torque setting device into a pulse width, and the chopper circuit with the pulse width signal. An electric pressurizing control device for a resistance welding machine in which an electric force is controlled by an armature current feedback control loop having a chopper drive circuit for driving a switching element.