JP2635760B2 - Inverter type spot resistance welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an inverter type spot resistance welding machine for spot resistance welding a work, and more particularly, a power semiconductor element constituting an inverter circuit of the welding machine. The present invention relates to an inverter-type spot resistance welding machine in which a power semiconductor element is prevented from being destroyed by monitoring a period of time in a conductive state.

BACKGROUND OF THE INVENTION A resistance welding machine, for example, sandwiches a pair of workpieces between a pair of electrodes, generates a Joule heat by applying a welding current between the electrodes, and relatively presses the electrodes. This is a device for joining works. The resistance welding machine is
Since no welding rod or the like is required for joining, the joining method is excellent in work efficiency.

In this case, the joining method by resistance welding requires an extremely large welding current as compared with, for example, an arc welding joining method or the like, so that the welding transformer tends to be large and heavy. Therefore, this has been pointed out as a difficulty in attaching to an arm portion of a welding robot or the like.

Therefore, recently, in order to reduce the size of the welding transformer, a direct current is once converted into a high-frequency alternating current under the action of the power semiconductor element, and the high-frequency alternating current is supplied to the welding transformer to reduce the pressure. Inverter-type spot resistance welding equipment, which is supplied to a welding gun arm after being converted into a direct current again or using a rectifier, has begun to be adopted. The reason for converting to high-frequency AC is that the welding transformer can be made relatively small and lightweight by utilizing the fact that the cross-sectional area of the transformer core constituting the output transformer is inversely proportional to the frequency of the high-frequency AC.

In the inverter-type spot resistance welding machine configured as described above, there is a constant demand for increasing the supply current and reducing the size of the apparatus. Thereby, a large current can be supplied even when welding a material having a high thermal conductivity, such as a steel plate having a material having a different melting point, such as a plated steel plate, or an aluminum plate.

By the way, an inverter circuit used in this type of device is provided with a protection means for preventing a power semiconductor element such as a power transistor constituting the circuit from being damaged by heat or the like. Conventional protection means, for example,
As disclosed in JP-A-57-113776, JP-A-62-064274, etc., a semiconductor comprising an inverter circuit provided with an overcurrent detecting means or a temperature-sensitive element or a thermal resistance element is included. A general method for detecting abnormal heating of the element has been used.

However, when using these safeguards,
Since the detection speed is low, there is an inconvenience that the actual power consumption value with respect to the rated power of the semiconductor element must be small, in other words, the margin must be set large. Further, in the conventional inverter circuit, the transistor is operated within a continuous rated value (DC rated value). For example, even if the base circuit operates abnormally and the transistor remains conductive, the thermal limit is not exceeded. If so, the inverter circuit is designed so that destruction can be avoided. For this reason, it is necessary to previously set the operation value lower than the continuous rated value, and as a result, there is an inconvenience in the use of supplying a large current in a resistance welding machine or the like.

[Object of the Invention] The present invention has been made in order to overcome the above-described disadvantages, and monitors a time period during which a semiconductor element constituting an inverter circuit is in a conductive state, thereby making the semiconductor element a continuous rated value or more. It is an object of the present invention to provide an inverter-type spot resistance welding machine which can be used with a current of less than and can supply a large current to a workpiece.

Means for Achieving the Object In order to achieve the above object, the present invention provides an inverter-type spot resistance welding machine having an inverter unit that performs switching operation of a semiconductor element to convert DC to AC. A base drive circuit for operating the element at a switching current value equal to or higher than a continuous rated value; and a timer circuit for measuring a conduction time of the semiconductor element, wherein the timer circuit sets an allowable conduction time of the semiconductor element in a counter section. A setting unit to perform, a counter unit for measuring the conduction time, and a signal for stopping the driving of the inverter when the measurement time reaches the conduction time when the set conduction time is compared with the measurement time. And means for performing the following.

[Embodiment] Next, a preferred embodiment of an inverter type spot resistance welding machine according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing a schematic configuration of an inverter type spot resistance welding machine according to the present embodiment. The inverter type spot resistance welding machine basically converts a three-phase alternating current output from the three-phase alternating current power supply 20 into a direct current, and converts the direct current output from the converter 22 into a predetermined high frequency alternating current. An inverter unit 24, an output transformer 28 which is a welding transformer for transforming a voltage output from the inverter unit 24, and a semiconductor device connected in a full-bridge type constituting the inverter unit 24, for example, a power transistor 36a It comprises a base drive circuit 30, a control circuit 32, and a timer circuit 40 for supplying a pulse-width-modulated base current to the base circuit 36d. In this case, the value of the base current supplied from the base drive circuit 30 is set to a value sufficient for the collector current to be equal to or higher than the continuous rated value (DC rated value).

The timer circuit 40 includes an AND gate 41, an oscillator 42, a counter 44, and a set value 46. The timer circuit 40 is the conduction time calculated by operating the counter 44 on the basis of the timing gate signal T _m in synchronization with the conduction time of the transistor to be supplied to the transistors 36a to 36d through the base drive circuit 30 from the control circuit 32 If the conduction time is equal to or longer than a predetermined time preset in the setting unit 46, the output signal Toff is output to force the base current supplied from the base drive circuit 30 to each of the transistors 36a to 36d. It operates so as to be electrically non-conductive.

Further, the converter section 22 includes a rectifier diode stack 34a, a reactor 34b, and a capacitor 34c, and the output transistor 28 includes a primary coil 52, a transformer core 54, a secondary coil 56, and a center tap 57. Furthermore, the secondary coil 56 is a rectifier 31a, is connected to one end of 31b, the rectifier 31a, a center tap 57 of the common connecting terminal and the output transformer 28 and 31b the other end of the workpiece W _a, clamping the W _b Connected to the welding electrodes 58a and 58b.

The inverter type spot resistance welding machine according to the present embodiment is basically configured as described above. Next, the operation and effect thereof will be described.

First, the work 7W _a, together with W _b is sandwiched by welding electrodes 58a and 58b, the initial pressure is made. In this state, the three-phase AC output from the three-phase AC power supply 20 is converted to DC by the rectifier diode stack 34a constituting the converter unit 22, the reactor 34b and the capacitor 34c,
This direct current is introduced into the inverter unit 24.

On the other hand, the base drive circuit 30 receives a timing gate signal T _m (see FIG. 2A) from the control circuit 32 and has a base current sufficient to drive the full-bridge transistors 36a to 36d constituting the inverter section 24. Is supplied to each of the transistors 36a to 36d, and the transistors 36a to 36d are sequentially turned on / off at a predetermined timing. Thereby, the direct current introduced into the inverter unit 24 is converted into an alternating current.

The output AC of the inverter unit 24 is introduced into the primary coil 52 of the output transformer 28 and is transformed to induce a predetermined AC in the secondary coil 56. The alternating current induced in the secondary coil 56 is a rectifier
After being rectified by 31a, 31b, welding electric discharges 58a, 5a are transmitted from the common connection point and the center tap 57 of the output transformer 28.
The workpieces W _a and W _b are supplied via 8b.

By the way, as described above, the transistors constituting the inverter unit according to the related art are designed to operate within the continuous rated value range, and if the output signal from the base drive circuit corresponds to the conductive state. Level, so that even if the transistor remains conductive, the inverter circuit is not destroyed within thermal limits. For this reason, it is necessary to set the actual power to be used to be smaller than the continuous rated value, so that it is not suitable for applications such as welding machines that supply a large current.

In view of the above, the present inventor has found that in a spot resistance welding machine, the time during which a current is applied between welding electrodes (usage rate) is considerably smaller than the operation time of the apparatus. For example, in the case of welding aluminum material, We focused on the fact that the energizing time to the electrode was 15 cycles (for example, 0.3 sec), and the ratio of the energizing time to the operating time of the welding apparatus itself including the movement of the electrode and the work was about 10%. Also, assuming that the inverter circuit performs switching operation at 800 Hz,
The time when the transistor on one side of the inverter is in the conductive state is 0.625 msec at the maximum, and the transistor is in the non-conductive state for more time. In addition, it is known that in a semiconductor element such as a power transistor, when a continuous element is used as a switching element such as an inverter circuit, a large energizing current can be obtained. Therefore, in the inverter circuit used in the spot resistance welding machine, the semiconductor element can be used with a switching current value larger than the continuous rated value. However, in this case, if the switching operation is stopped and the semiconductor element remains conductive, there is a possibility that the semiconductor element may be broken, and a protection circuit for the inverter is required to avoid this inconvenience.

The timer circuit 40 is provided for this purpose, and the base circuit 30
Among the current signals (base drive signals) supplied to the transistors 36a to 36d through the transistors 36a to 36d
When the timing gate signal T _m in synchronization with the conduction time of the input, the high level period AND gate 4, corresponding to the conduction time
1 is energized, the output pulse S ₁ of the oscillator 42 (see FIG. 2 b) passes through the AND gate 41 and is introduced into the counter 44 as a signal S ₂ (see FIG. 2 c), and the counter 44 performs a counting operation. To start. The conduction time of the transistors 36a to 36d under the action of the counter 44 is the measurement, when the measured conduction time exceeds a preset time setter 46 (see time t ₁ point), the timer circuit 40 An output signal Toff is output (see FIG. 2d). Here, the output signal Toff is input to the base drive circuit 30, and forcibly cuts off the base current supplied to the transistors 36a to 36d. Therefore, when the conduction time of the transistors 36a to 36d exceeds the set time, the transistors 36a to 36d are forcibly turned off and do not break down.

The counter 44 starts counting at the rising edge of the timing gate signal T _m, counting at the falling edge portion is reset with ends.

In the above embodiment, the transistor is controlled based on the base drive signal output from the base drive circuit 30.
Although the time corresponding to the conduction state of 36a to 36d was detected, the present invention is not limited to this. As shown in FIG. 3, a current detecting means 60 including a Hall element or the like is interposed on the output side of the inverter unit 24, The output signal of the current detection means 60 is waveform-shaped by a waveform shaping circuit 62 to a level at which the AND gate 41 can operate, and
By supplying the voltage to the gate 41 and the RESET terminal of the counter 44, the actual conduction time of the transistors 36a to 36d can be monitored. As another embodiment, as shown in FIG. 4, two current detecting means 60 shown in FIG. 3 are interposed on the input side of the inverter unit 24 and the output signal of the waveform shaping circuit 62 is output from a multiplier or the like. timer circuit 40 in the electronic switch 64 is switched on the rising edge of the timing gate signal T _m
The same operation can be performed even if the configuration is such that the conduction time is measured by using.

[Effects of the Invention] As described above, according to the present invention, a timer circuit that monitors the conduction time of a semiconductor element constituting an inverter circuit is provided, and when the semiconductor element is in a conduction state for a predetermined time or more, The transistor is forcibly turned off. For this reason, it is possible to use the semiconductor element constituting the inverter section in the switching rated range, and it is possible to use the semiconductor element in the switching rated range by 2 to 3 times as compared with the conventional continuous rated value.
A welding machine capable of supplying twice the current can be obtained.

As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. Of course.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of an inverter type spot resistance welding machine according to the present invention, FIG. 2 is an explanatory diagram of the operation of the welding machine, FIG. 3 and FIG. It is a lineblock diagram showing other embodiments of a welding machine. 22 converter section, 24 inverter section 28 output transformer 30 base drive circuit, 32 control circuit 36a-36d transistor, 40 timer circuit 41 AND gate, 42 oscillator 44 …… Counter, 46 …… Setting device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuo Kobayashi 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (72) Makoto Suzuki 1-1-10-1 Shinsayama, Sayama City, Saitama Honda Engineering (56) References JP-A-62-134683 (JP, A) JP-A-62-148091 (JP, A)

Claims (1)

(57) [Claims] 1. An inverter type spot resistance welding machine having an inverter section for switching a DC to an AC by switching a semiconductor element, and a base drive circuit for operating the semiconductor element at a switching current value equal to or higher than a continuous rated value. A timer circuit for measuring the conduction time of the semiconductor element, the timer circuit comprising: a setting section for setting a permissible conduction time of the semiconductor element in a counter section; and a counter section for measuring the conduction time. Means for comparing the permissible conduction time with the measurement time and outputting a signal for stopping the drive of the inverter when the measurement time reaches the permissible conduction time. .