JPH03151175A - Dc resistance welding equipment - Google Patents

Abstract

PURPOSE:To control to stop energizing for members to be welded and to perform pertinent welding by forming a current difference signal corresponding to the resistance value change at the time of energizing the members to be welded from a front edge part current value signal and a rear edge part current value signal. CONSTITUTION:A detection signal S1a corresponding to a switching action signal S1 brought out from an inverter 14 is obtained from a detection part B and the signals are supplied to track hold amplifiers 24 and 26, respectively. Further, signals sent out from a PWM circuit 34 and timing signals St1 and St2 corresponding to the front edge part and the rear edge part of the detection signal S1a by a timing generator 32 are supplied to the amplifiers 24 and 26. By this method, output signals S3 and S4 formed to levels corresponding to a current value of the front edge part and a current value of the rear edge part via resistors R1 and R2 from signals brought out from the amplifiers 24 and 26 are supplied to a logarithmic amplifier 28. By this method, the logarithmic amplifier 28 sends out an arithmetic signal S6 by analog logarithmic processing.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a DC resistance welding apparatus in which indirect measurement of the resistance value of a welded member during energization and energization stop control are suitably performed.

[Prior Art] Recently, DC resistance welding equipment used in welding robots has been equipped to measure changes in voltage between welding electrodes, ultrasonic transmission/reflectance, and welding energy, which is the product of voltage between welding electrodes and time. Equipped with a monitor to do so.

The monitor that measures the voltage between the welding electrodes corresponds to the change in resistance value due to the state of formation of a current-carrying path (nugget), that is, the gradual decrease in resistance value due to local melting of the welded member after voltage application. Measures the voltage change between welding electrodes.

As a result, welding electrodes are pressurized and separated by being fully aware of the temperature rise in the welding part during energization and the cooling state that accompanies the end of energization, producing excellent welding strength and good nuggets without scattering. For example, it is intended to obtain a good welding condition immediately before failure.

[Problems to be Solved by the Invention] However, in the above-mentioned monitoring of the voltage measurement between welding electrodes, the main body of the inverter, converter, etc., and the welding transformer, rectifier, etc. disposed near the welding gun are separated from each other. It is arranged.

As a result, it is common to shorten the distance between the welding gun and the rectifier to prevent conduction loss due to the low voltage and large current that is derived.

Therefore, the connection wire between the welding electrode and the monitor is relatively long, and the voltage change between the welding electrodes is extremely small. For this reason, there are drawbacks such as a decrease in the detection voltage and the superimposition of noise generated during energization, making it difficult to accurately measure the amount of change in the detection voltage.

The present invention has been made in view of the above points, and its purpose is to provide a relatively simple configuration in which a signal having a value corresponding to the energization state of the workpiece to be welded can be indirectly generated from a change in current accompanying the switching operation of the inverter. Another object of the present invention is to provide a DC resistance welding device that can be obtained with high accuracy and can perform appropriate welding by controlling the stoppage of energization to a member to be welded based on the obtained change signal.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the DC resistance welding apparatus of the present invention includes a welding gun which is provided with at least a converter, an inverter, a welding transformer, and a rectifier, and which holds a workpiece to be welded. A DC resistance welding device equipped with: a detection means for sending out a detection signal corresponding to the output waveform of the inverter; and a leading edge/trailing edge for sending out respective current value signals of the leading edge and the trailing edge from the detection signal. a control means for sending a control signal for detecting the leading edge/trailing edge current to the leading edge/trailing edge current detecting means; The present invention is characterized by comprising a calculation means for forming and transmitting a current difference signal corresponding to a change in resistance value during energization of a member to be welded from a value signal.

[Operation] In the above configuration, the current values (L Io ) at the leading edge and trailing edge of the output accompanying the switching operation of the inverter connected to the primary side of the welding transformer and the rectifier connected in series to the secondary side, Combined resistance value R1 of welding gun and workpiece
Voltage e1 intagtance 1 hour t can be expressed as 1°. Here, assuming that the resistance values of the rectifier and welding gun are constant and negligible values, the ratio of current values at the leading edge and the trailing edge, Io/I, is the energy consumed by the workpiece, i.e., the workpiece It corresponds to the value of resistance change due to the formation of nuggets during welding.

As a result, the change in the resistance value of the workpiece to be welded held between the welding guns when energized can be indirectly obtained from the ratio of the current values at the leading and trailing edges of the output (waveform) associated with the switching operation of the inverter. .

[Example] Next, an example of the DC resistance welding apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the overall structure of the embodiment, and FIG. 2 is used to explain the operation of FIG. 1, and is a diagram showing signal processing waveforms and timing.

The example shown in FIG. 1 includes a so-called inverter-controlled power supply section A that includes a welding gun, etc., and a detection section that derives a signal with a value corresponding to an output (waveform) signal accompanying a switching operation of the power supply section A. (Detection means) B and a difference signal calculation section C (front end) that creates current value signals for the leading edge and trailing edge from the signals derived by the sensing section B, and then forms and sends out a current difference signal. A control section D (corresponding to the edge/trailing edge current detection means and calculation means) and a control section D (corresponding to the edge/trailing edge current detection means and calculation means), which creates control signals for the leading edge/trailing edge current detection and also performs closed-loop control of the overall operation, etc. It is roughly composed of (corresponding to the means).

The power supply unit A includes a converter 12, an inverter 14, a welding transformer 16, and rectifiers 18a and 18b.
, 18b, the combined DC El flows to the welding gun 20.
is applied to Furthermore, welding tip 20a of welding gun 20
, 20b, a member to be welded (work) 22 is held between them.

The detection section B employs a current detector such as a toroidal coil, is placed on the connection path between the inverter 14 and the welding transformer 16, and sends out a detection signal S1m corresponding to the switching operation signal S1.

The difference signal calculation unit C generates the detection signal SI. A track-and-hold amplifier 24.26 is supplied with a timing signal 311, SL2 for holding the leading edge as well as a trailing edge of the track and hold amplifier 24.26, and an output signal S3.34 is supplied via connected resistors R, , R2. , and a logarithmic amplifier 28 that sends out an arithmetic signal S6 based on analog logarithm processing.

The control unit is, for example, a welding system controller, and includes switching transistors Trl, Tr2, Tr3,
A base drive circuit 30 that sends a drive signal to T□ (full bridge circuit), a timing generator 32 that sends a timing signal 5LlSSt2, and a base drive circuit 30 that changes the ratio of 0N10FF time while keeping the switching frequency fixed. The so-called fixed frequency pulse modulation method (PW
M). Furthermore, these closed-loop controls are performed, and a welding start command signal Cc is supplied from the arithmetic signal S6 and a setting means/centralized control device such as a computer for FMS that performs full-closed NC control, thereby performing so-called welding sequence control. It has a microprocessor (MPU) 36 equipped with functional means such as a CPU, RAM, ROM, and Ilo.

In addition, the control section contains numerical values/values corresponding to the processing of each section.
A monitor 40 for visually displaying waveforms, and a setting section 42 for issuing instructions for displayed numerical values/waveforms or for issuing control instructions in cooperation with the MPU 36 are provided.

The operation of the above configuration will be explained below (see FIGS. 1 and 2).

Welding start command signal Cc is supplied to MPU36,
First, an instruction to operate the PWM circuit 34 is given.

As a result, a drive signal from the base drive circuit 30 is supplied to the inverter 14, and the entire operation starts. Then, the three-phase 400V is rectified by the converter 12,
Next, the inverter 14 converts it into a pulsed high frequency (AC) switching operation signal SI. Additionally, the alternating current is supplied to a welding transformer 16 and converted to a relatively low voltage, high current, eg, IOV. Subsequently, the rectifier 18a
118b performs double-wave rectification and is combined to create a direct current E1.
is derived.

Then, from the detection unit B, a switching operation signal S derived from the inverter 14 shown in FIG. 2(a),
A detection signal Sla corresponding to this is obtained. Detection signal Sla
are supplied to track and hold amplifiers 24 and 26, respectively. Furthermore, the track and hold amplifiers 24 and 26 include PW
The signal sent from the M circuit 34 is sent to the timing generator 32.
As shown in FIG. 2(a), 0)), the leading edge (current value I) and trailing edge (current value I) of the detection signal S0 are
Timing signals Stl and St2 corresponding to step o) are supplied. This allows the track and hold amplifier 24.26
The signals derived from the second
As shown in Figures (6) and (e), the levels V+ and V corresponding to the current value ■ at the leading edge and the current value Io at the trailing edge
The output signals S5 and S4 formed at 2 are supplied to a logarithmic amplifier 28. As a result, the logarithmic amplifier 28 infects and sends out, as a time T, an arithmetic signal S@ by analog logarithmic processing.

The calculation signal S6 obtained in this way is sent to the rectifier 18a,
18b, the resistance value of the welding gun 20 is constant and negligible, and the portion m shown in FIG. This corresponds to the change in resistance value caused by the formation of nuggets during welding.

The calculation signal S8 is sent to the MPU 3 via a squarer (not shown).
6, and after quantization, it is converted into a digital signal,
It is sampled with the timing signal shown in FIG. 2(f), and its numerical value/waveform is visually displayed on the monitor 40.

As a result, the change in resistance value of the welded member 22 held between the welding tips 20a120b when energized is controlled by the inverter 14.
It is indirectly obtained from the current value I at the leading edge and the current value I0 at the trailing edge of the switching operation signal S of .

Next, referring to these numerical values/waveforms, welding using energy that does not cause failure and provides high strength, that is, a welding tip, is performed on different members to be welded 22 based on experience and experiments. The direct current E applied between 20a and 2Ob is controlled.

In this control, first, the setting unit 42 transmits the energization start/stop timing, energization time, etc. to the MPU 36 via the monitor 40.
Set it in the internal RAM.

Next, for example, a setting means such as a computer for FMS/
The workpiece 22 to be welded is transported/fixed in response to various full-closed NC controls in the production line of the central control device, but subsequently, after the welding gun 20 is pressurized,
The MPU 36 instructs the PWM circuit 34 to send a signal to the base drive circuit 30 based on the set energization start/stop timing or the energization time value.

In this way, a high strength weld is formed without expulsion.

[Effects of the Invention] As understood from the above description, the DC resistance welding device of the present invention has the following effects.

With a relatively simple configuration, a signal having a value corresponding to the energization state of the welded member can be indirectly obtained from a change in the current of the inverter. This eliminates the need for a connecting wire to detect voltage changes between welding electrodes, that is, changes in resistance due to the formation of current-carrying paths (nuggets), which reduces detection voltage drop and noise that occurs when current is applied. The superimposition of is reduced, and the change in resistance value of the welded member when energized can be obtained with high accuracy.

Furthermore, based on the resistance values of different parts to be welded when energized,
It becomes possible to appropriately control the start/stop timing of energization to the welded member or the energization time stop control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the entire embodiment of the DC resistance welding apparatus of the present invention, and FIG. 2 is a diagram showing signal processing waveforms and timing, used to explain the operation of FIG. 1. 12...Converter 14...Inverter 1
6... Welding transformer 18a, 18b... Rectifier 20... Welding gun 22... Welded member 24.26... Track hold amplifier 28... Logarithmic amplifier 30... Base drive circuit 32.・・・
Timing generator 34...PWM circuit 36...Microprocessor 40...Monitor 42...Setting section A...
・Power supply section B...Detection section C...Difference signal calculation section D...Control section R1, R2...Resistor
S la...Detection signal S, , s,... Output signal
s6...Calculation signal S L I SS t2...Timing signal FIG, 2

Claims (2)

[Claims] (1) In a DC resistance welding device that is equipped with at least a converter, an inverter, a welding transformer, and a rectifier, and a welding gun that clamps the workpiece, a detection means that sends out a detection signal corresponding to the output waveform of the inverter; , a leading edge/trailing edge current detection means for transmitting respective current value signals for the leading edge and trailing edge from the detection signal; and a control signal for detecting the leading edge/trailing edge current for the leading edge/trailing edge current detection means. /control means for sending to the trailing edge current detection means; forming and sending out a current difference signal corresponding to a change in resistance value when the welding member is energized from the leading edge current value signal and the trailing edge current value signal; A DC resistance welding device characterized by comprising: calculation means for calculating. (2) In the DC resistance welding device according to claim 1,
A direct current resistance welding device characterized by comprising an energization stop control means that stops energization of a welding gun that clamps a welded member when the value of the current difference signal derived from the calculation means is a preset predetermined value.