JPH0242304B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an electrostatic storage type resistance welding machine. The contact resistance of the workpiece is thereby measured, and then the actual welding current is corrected to an appropriate value based on the measured contact resistance and energized to quickly and reliably perform resistance welding. This invention relates to a control device for a precision electrostatic storage type resistance welding machine.

The controllable energization time of a conventional electrostatic storage type resistance welding machine is, for example, in the case of an AC type, when the frequency of the commercial AC power source is 60Hz, the set time unit is 16ms.
In the case of a general electrostatic storage type resistance welding machine, the time is in units of 1 to 10 ms. The reason why the welding time is unavoidably long is that the rise time of the supplied welding voltage is long, and if an attempt is made to shorten the welding time, stable welding cannot be achieved. However, as can be foreseen, when welding takes such a long time, there is a good chance that the diffusion of excess heat into the workpiece will cause adverse effects such as discoloration, deformation, and distortion of the workpiece.

Therefore, in a resistance welding machine, it is naturally possible to detect the welding resistance between the welding electrodes in advance and control the welding time based on this. This type of prior art is disclosed in Japanese Patent Publication No. 61-29829. According to this method, a weak and constant direct current that does not cause welding of the welding material through the welding electrode,
For example, by supplying a discharge current from a separately provided capacitor to the welding part and measuring the voltage between both welding electrodes at that time, the contact resistance value between the welding electrodes can be determined from the following equation.

R=V/I R: Resistance value between electrodes V: Voltage between electrodes I: Constant DC current However, as disclosed, the contact resistance determined by this method is based on a weak current, specifically 100A. Because it is necessary that the current is below
This current cannot scatter and eliminate the slight oxidation of the electrode tip of the resistance welding machine and the oxides, dirt, etc. on the surface of the workpiece. Therefore, the increase in contact resistance caused by these factors is included as an error. This increment value can be more than twice the contact resistance for electrodes and workpieces that are free of oxides and dirt, and in this case it is no longer necessary to set the actual welding current based on the preliminary measured contact resistance. This resulted in the disadvantage that a complete welding action could not be performed and stable and effective welding could not be performed. To avoid this inconvenience, clean the electrode tip of the resistance welder and the workpiece before measuring the contact resistance.
Alternatively, there are drawbacks such as the need to remove the coating member covering the workpiece, which is inefficient.

Furthermore, the conventional electrostatic energy storage type resistance welding machine control device as shown in the above-mentioned Japanese Patent Publication No. 61-29829, and the conventional electrostatic energy storage type resistance welding machine as shown in Japanese Patent Publication No. 61-29828. In the welding machine control device, it has been pointed out that there are drawbacks such as a significant increase in manufacturing costs due to the structure in which a special DC power supply device is required for contact resistance measurement.

The present invention has been made in order to overcome all of the above-mentioned disadvantages, and it is possible to generate a welding current in microseconds and apply the welding current for a very short period of time in advance to apply the welding current to the workpiece. It is an object of the present invention to provide a control device for an electrostatic storage type resistance welding machine that can always perform stable welding by removing members and the like and then performing actual welding.

In order to achieve the above object, the present invention comprises an electrostatic energy storage capacitor whose negative electrode side is substantially connected to one end of the workpiece, a positive electrode side of the electrostatic energy storage capacitor which is connected to a collector terminal, and an emitter follower circuit in which a plurality of transistors are connected in parallel, the emitter terminals of which are connected to the other end of the work; a first amplifying means for inputting a voltage applied to both ends of the work; a second amplification means whose output side is connected to the base terminal of the emitsuta follower circuit; The amplifying means is characterized in that it forms a load return loop.

Next, a preferred embodiment of a control device for an electrostatic storage type resistance welding machine according to the present invention will be described in detail with reference to the accompanying drawings.

First, FIG. 1 shows a circuit block configuration of an embodiment of the present invention.

In FIG. 1, reference numeral 10 indicates an AC primary power source, which is connected to both ends of the input terminal of a power transformer 12. In FIG. One of the output terminals of the power transformer 12 is connected to the anode of the rectifying element 14.
The cathode of No. 4 is connected to the positive terminal of the electrostatic storage capacitor 16. The electrostatic energy storage capacitor 16
The negative terminal of is connected to the other output terminal of the power transformer 12, and charges are accumulated at both ends of the electrostatic storage capacitor 16 based on the above connection. On the positive electrode side of the electrostatic energy storage capacitor 16, there is a voltage buffer means 22, which is a plurality of parallel-connected transistor emitter follower circuits that also perform a switch function.
Connected to the collector terminal of An emitter terminal of the voltage buffer means 22 is connected to one electrode 24a of the welding electrode 24. The other electrode 24b of the welding electrode 24 is connected to the negative electrode of the electrostatic storage capacitor 16 via a shunt resistor 20 whose value has been accurately measured in advance. Reference numeral 26 indicates a workpiece (object to be welded) to be superimposed, and a welding electrode 24
It is held between a and 24b.

Next, the voltage across the welding electrodes 24a, 24b is applied to the input of a first operational amplifier 40 as a first amplifying means, and the output side of the operational amplifier 40 is applied to a second operational amplifier 40 as a second amplifying means. It is connected to one first input terminal of the amplifier 38 and to a first switch 54b in switching means 54, for example an analog switch. The switching means 54 is controlled to open and close by the calculation control section 30.

On the other hand, the analog output of the D/A converter 36 that receives the output signal from the arithmetic control section 30 is introduced into the other input terminal of the second operational amplifier 38 .
This analog output is an output applied to a preset welding voltage. The output side of the second operational amplifier 38 is connected to the base terminal of the voltage buffer means 22. In this way, when the buffer means 22 is in an active state, the first operational amplifier 4
0, the second operational amplifier 38 and the buffer means 2
2 is in a closed loop state, and at this time, welding electrode 2
The polarities of the respective operational amplifiers 38 and 40 and the buffer means 22 are configured so that a negative feedback effect is applied to make the voltage between the two voltages equal to the output voltage of the D/A converter 36.

Furthermore, the voltage across the shunt resistor 20 is fed to a third operational amplifier 52, the output of which is connected to a second switch 54a in the switch means 54. A common terminal of each switch 54a, 54 of the switch means 54 is connected to an A/D converter 56. One output side of the A/D converter 56 is a voltage storage means 6 for storing the voltage value between the welding electrodes 24.
Connected to 2. The storage means 62 is, for example,
Consists of RAMIC.

Next, the output side of the storage means 62 is connected to the arithmetic control unit 30, and the value thereof is read by the arithmetic width unit 30. The other output side of the A/D converter 56 is a storage means 5 for storing a current value determined from the resistance value of the shunt resistor 20, whose value has been accurately measured in advance, and the voltage value across the shunt resistor 20.
8 is connected. Therefore, one output of the current storage means 58 is connected to one input side of a comparator 60, and a reference current setting digital switch 50 is connected to the other input side of the comparator 60.
The output side of the comparator 60 is connected to be input to the calculation control section 30.

Therefore, the differential voltage that is the output of the comparator 60 is read by the arithmetic control section 30. The current storage means 5
The other output side of 8 is directly connected to the calculation control section 30, and its current value is read. Arithmetic control unit 30
The voltage value and current value read in are displayed on the display device 66 via the calculation control section 30. The display device 66 is composed of, for example, an LED.

In addition to the welding configuration described above, the calculation control section 30 includes a digital switch 68 for contact resistance measurement, a time setting digital switch 70 for contact resistance measurement, a digital switch 34 for setting actual welding voltage, and a digital switch 32 for setting actual welding time. and a correction factor setting digital switch 64 are connected to each other. The arithmetic control section 30 includes an input/output control section (not shown), an arithmetic section, a CPU for judgment processing, and a timer to perform desired operations.

The control device for the electrostatic storage type resistance welding machine according to this embodiment is basically configured as described above, and its operation and effects will be explained below using FIGS. 1 to 4. do.

First, as a first step, the operation of determining the actual welding voltage and actual welding time will be explained. in this case,
It is assumed that the electrostatic energy storage capacitor 16 is always charged to a desired voltage through the AC power supply 10, the power transformer 12, and the rectifying element 14. In such a state, in order to determine the optimum values of the actual welding voltage and actual welding time, after the test work 26 is held between the electrodes 24, the digital switch 34 for setting the actual welding voltage and the digital switch 34 for setting the actual welding time are switched. Set the switch 32 appropriately. The setting value of the digital switch 34 for setting the actual welding voltage is determined by the calculation control section 3.
0 to the voltage setting D/A converter 36. The D/A converter 36 converts the digital setting value into an analog voltage value, and this analog voltage is supplied to the workpiece under test 2 through one input of the operational amplifier 38 and the voltage buffer means 22.
6. The voltage across the workpiece 26 is detected by a first operational amplifier 40, and the output thereof is fed back to the other input of the second operational amplifier 38. In this case, if a voltage difference occurs between the inputs of the second operational amplifier 38, that is, the set input voltage and the workpiece 2
If the voltages across the workpiece 26 are not equal, the output voltage of the voltage buffering means 22 is further adjusted, so that the set input voltage and the voltage across the workpiece 26 are adjusted by performing a so-called negative feedback function. Make equal. However, the feedback loop formed by the second operational amplifier 38, voltage buffer means 22, and first operational amplifier 40 is an analog signal loop and can be operated at extremely high speed. According to experiments, using the voltage buffer circuit described later, approximately
It was possible to obtain a rise time t _r and a fall time t _f of about 20 μs or less (see Figure 2).

Next, the voltage buffer means 22 is substantially, as shown in FIG. 1, a plurality of emitter fabric circuits connected in parallel, each having a base, an emitter, and a collector connected to each other. In particular, by selecting a transistor with a small base-to-emitter junction capacitance, it is possible to operate the transistor as a high-current, high-speed voltage follower. Second
In the experimental example shown in the figure, approximately 120 transistors selected in this way were connected in parallel. However, in this case, the impedance of the shunt resistor 20 and the capacitor 16 for storing electrostatic energy related to the large current path flowing through the workpiece 26 are selected to have sufficiently low values.

On the other hand, when the switch means 54 receives a signal from the contact resistance measurement voltage setting digital switch 68 or the actual welding voltage setting digital switch 34, the switch 54b side is closed by the control signal from the calculation control section 30. The voltage applied to both ends of the workpiece 26 appearing in the output of the operational amplifier 40 is stored in the voltage storage means 62 through the A/D converter 56, and is also displayed on the display device 66 through the calculation control section 30 for confirmation. That will happen.

Next, the calculation control section 30
A timer (not shown) is set in , and the time period for which the signal is energized to the D/A converter 36 is controlled.

The sample work 26 is actually welded by the above procedure. After measuring and confirming the tensile strength, nugget shape, etc. of this welded test workpiece 26, and repeating trial and error on the test workpiece 26 according to the above procedure several times until a stable welding condition was obtained, the most stable Obtain the actual welding voltage and actual welding time related to welding.

Next, as a second step, the contact resistance of the workpiece is measured prior to actual welding, and the contact resistance measurement voltage setting digital switch 68 and the contact Time setting digital switch 70 for resistance measurement
The operation and effect when activated will be explained.

When operating the contact resistance measurement voltage setting digital switch 68 and the contact resistance measurement time setting digital switch 70, the digital values of the actual welding setting digital switches are set to 0 so that they are not operated. Next, a new sample workpiece 26 is set to be held between the welding electrodes 24. Then, turn on the voltage setting digital switch 6 for contact resistance measurement.
The voltage value in step 8 is set to the same value as the actual welding voltage value obtained in the previous step. Further, the time of the contact resistance measurement time setting digital switch 70 may be set to a value of 1/10 to 1/20 of the actual welding time obtained in the previous procedure based on experience. When the voltage setting digital switch 68 for contact resistance measurement and the time setting digital switch 70 for contact resistance measurement are selected, the switch means 54 receives a command from the calculation control section 30, and the switch 54a side is connected. Based on these setting operations, the D/A converter 36 outputs an analog voltage for contact resistance measurement in the same procedure as the previous procedure based on a command from the arithmetic control section 30. Then, a voltage equal in phase to this voltage is supplied to the workpiece 26, the current passing through the workpiece 26 is detected via the shunt resistor 20, and the third operational amplifier 52, the switching means 54, the A/D converter 56 and the current memory are detected. The current is introduced into the arithmetic control section 30 via the means 58, and a current value corresponding to the contact resistance is displayed on the display device 66. However, this current value for contact resistance measurement is determined by the D/A converter 36, the second operational amplifier 38, the voltage buffer means 22, the first operational amplifier 40, and the second operational amplifier 3.
Since it is controlled by the closed loop of 8, as mentioned above, it is possible to flow a large current in μs units, which scatters and eliminates oxides on the electrode tip of the resistance welding machine, oxides, dirt, etc. on the surface of the workpiece. It is possible to measure contact resistance accurately. Furthermore, after repeating the second procedure, the average current value related to the measured contact resistance is set in the reference current setting digital switch 50.

Next, a current correction factor (for example, 30%) is determined from the distribution of this contact resistance, and is stored in the arithmetic control section 30 by the correction factor setting digital switch 64.

Next, the welding voltage setting sequence including the contact resistance check is performed by the voltage setting digital switch 68 for contact resistance measurement, the time setting digital switch 70 for contact resistance measurement, the digital switch 34 for setting the actual welding voltage, and the digital switch 32 for setting the actual welding time. Set using . For example, as shown in FIG. 3, this is to generate a contact resistance check voltage B, 2V in this embodiment, prior to the actual welding voltage A.

Therefore, actual welding is performed based on the preparations described above. That is, the workpiece 26 is placed between the welding electrodes 24.
, and activate the operation start switch 150. Based on this switch operation, first, the preliminary current is set to 500A (ampere), for example, based on the above-mentioned Fig. 3.
A voltage B is supplied to the workpiece 26 by the operation of the arithmetic and control unit 30 in order to cause a current to flow therethrough. That is, D/A
The voltage B may be output from the converter 36 to the second operational amplifier 38. However, if the current that actually flowed through the workpiece 26 was 400A,
The current value of 400A is temporarily stored in the current storage means 58 through the third operational amplifier 52, and the stored value of 400A is stored in the calculation control unit 30 within the correction factor setting range (±30% in the setting of this embodiment). ) to determine whether the current value is within ). Based on this judgment, a corrected digital signal corresponding to (500/400)×2V is supplied to the input of the D/A converter 36 so that an actual current of 500 A flows through the work 26. This takes place after the rest period t ₂ of FIG. As a result, the actual voltage between t3 and the voltage supplied to the workpiece ₂₆ becomes 2.5V, allowing a current of 500A to flow as an actual welding current.
In this setting, for example, if there is no workpiece 26 between the welding electrodes 24, when the preliminary current flows, the value will normally be at least 30% of 500A, and this is outside the range of correction, so the calculation control unit 30, the actual voltage A is not generated. That is, the output voltage value of the D/A converter 36 is set to zero value so that the welding current becomes zero value. This effect is particularly important in order to prevent damage to the welding electrode and to be economical.

As described above, according to the present invention, welding current can be controlled in μs units. This allows the necessary amount of current to flow through the workpiece in an extremely short period of time, which prevents heat from spreading around the welding point and generates the required amount of heat in the required area. becomes possible. In the end, discoloration and distortion of the workpiece due to excess heat can be prevented. Furthermore, in the conventional control device for an electrostatic storage type resistance welding machine, it was impossible to prevent the negative effects of heat diffusion during this time due to the long rise time of the current. The control device for a power storage resistance welding machine has a very short start-up and fall time, which gives it the great advantage of being able to supply the necessary current from the beginning of welding. In addition, if there is a material mixed in that could cause an explosion when welding current is applied, such as an oxide film attached to the workpiece, it is possible to prevent this explosion by using the correction function. Therefore, there is no need to worry about damaging the welding electrode. Furthermore, while conventional control devices for electrostatic storage type resistance welding machines require a DC power source to measure contact resistance, the present invention is configured so that contact resistance can be measured using the same circuit as for actual welding. Therefore, the circuit itself is further simplified.

As described above, according to the control device for an electrostatic storage type resistance welding machine according to the present invention, it is possible to achieve high-quality, high-speed welding, and to be economical.

Although the present invention has been described above with reference to a preferred embodiment, the present invention is not limited to this embodiment. Of course, various improvements and changes in design are possible without departing from the gist of the invention.

[Brief explanation of the drawing]

Fig. 1 is a circuit block diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a waveform diagram of welding voltage according to the invention, and Fig. 3 is a waveform diagram for explaining the operation of an embodiment of the invention. be. DESCRIPTION OF SYMBOLS 10... AC primary power supply, 12... Power transformer, 14... Rectifying element, 16... Capacitor for electrostatic storage, 20... Shunt resistor, 22... Voltage buffer means, 24... Welding electrode, 26... ... Workpiece, 30 ... Arithmetic control section, 32 ... Digital switch for setting actual welding time, 34 ... Digital switch for setting actual welding voltage, 38, 40, 52 ... Operational amplifier, 54 ... Switch means, 56 ... …A/D
Converter, 60...Comparator, 62...Voltage storage means, 64...Digital switch for setting correction factor, 6
6... Display device, 68... Voltage setting digital switch for contact resistance measurement, 70... Time setting digital switch for contact resistance measurement, 150... Operation start switch.

Claims (1)

[Scope of Claims] 1. An electrostatic energy storage capacitor whose negative electrode side is substantially connected to one end of the workpiece, whose positive electrode side is connected to a collector terminal, and whose emitter terminal is connected to the workpiece. an emitter follower circuit in which a plurality of transistors connected in parallel are connected to the other end; a first amplification means for inputting the voltage applied to both ends of the work; and an output of the first amplification means set in advance. a second amplifying means whose output side is connected to the base terminal of the emitsuta follower circuit, the emitsuta follower circuit, the first amplifying means, and the second amplifying means having an output applied to a welding voltage as an input signal; A control device for an electrostatic storage type resistance welding machine characterized by forming a negative feedback loop. 2. A control device for an electrostatic storage type resistance welding machine according to claim 1, wherein the first amplification means and the second amplification means are operational amplifiers. 3. The control device according to claim 1 or 2, which is an electrostatic energy storage type resistance welding machine in which a shunt resistor for current measurement is inserted between the negative electrode side of the electrostatic energy storage capacitor and the workpiece. Control device. 4. In the control device according to claim 3, the value of the preliminary current applied to the contact resistance of the workpiece measured based on the shunt resistance for current measurement is outside the predetermined range of the preset reference current value. control of an electrostatic storage type resistance welding machine having a comparator and an arithmetic control unit that controls a preset welding voltage to a value that makes the welding current zero when the welding current is zero. Device.