JP2000326075A - Resistance welding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease workload of a welder, while ensuring the quality of welding and surely preventing weld defects. SOLUTION: A resistance welding machine is provided with a electrode 2 for passing a welding current to a work for welding and a controller 4 supplying electric power to the electrode 2 via a transformer 3 for welding, corresponding to a set value of welding current. The welding current passing the electrode 2 is detected with a sensor part 7 of a electric current detector 7, and the detected data are fetched by a monitor part 8 and are subjected to A/D conversion. These detected data are taken into a automatic adjusting device 11, and prescribed numbers of the latest detected data are stocked. The automatic adjusting device 11 detects the variation of welding conditions from the detected data of prescribed numbers in stock, and based on the detected result, the controller 4 increases or decreases welding current by adjusting the electric power supplied to the electrode 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding machine for welding a portion to be joined by applying a welding current to a workpiece and heating the workpiece. More particularly, the invention relates to a resistance welding machine which changes a welding current according to a change in welding conditions. The present invention relates to a resistance welding machine having a function of increasing or decreasing.

[0002]

2. Description of the Related Art In a typical resistance welding machine, a portion to be joined is softened or melted by Joule heat generated by applying a welding current to a work made of a metal material, and then a plastic joint is formed. It is to bond the parts by crimping. FIG. 6 shows a schematic configuration of a conventional resistance welding machine 1. An electrode section 2 having a pair of welding electrodes 2a and 2b for supplying a welding current to a work under a pressurized state, and a controller 4 is shown.
Comprising an input voltage e ₁ given voltage e ₂ of the welding electrodes 2a obtained by lowering the, and a welding transformer 3 to be applied to and 2b from.

The controller 4 outputs a voltage e _{1 of} 200 volts supplied from an AC power supply (not shown) to the primary side of the welding transformer 3 for a set time, thereby transmitting the voltage e ₁ through the welding transformer 3. A predetermined power is supplied to the electrode unit 2. The welding current i flowing through the electrode part 2 is determined by the application time T (hereinafter, referred to as “heat value”) of the voltage e ₁ by the controller 4. The operator sets the desired heat value T by using the controller 4. 4 is provided with a setting switch 5.

[0004] For example, in the article manufacturing line, every time the same work is supplied, when the same same spot is sequentially spot-welded, the work and the part to be joined are the same. Is theoretically constant. Thus, by applying the same voltage e ₂ to the electrode portion 2 by the same time, always the same welding current i flows through the workpiece,
The weld quality at the welded location should be constant.

[0005]

However, the cable connecting the electrode section 2 and the welding electrodes 2a and 2b to the welding transformer 3 is heated by the repetition of the welding operation, so that the resistance value of the path through which the welding current i flows is obtained. Changes gradually. Also,
The contact state between each of the welding electrodes 2a and 2b and the work is not always physically the same in actuality, and the electrode shape is worn or deformed with time. Resistance is not always constant. in this way,
As a result of the change in welding conditions at the time of welding, it is difficult to keep the welding current i constant at all times, so that the welding quality at the welded location is not constant.

[0006] In addition, if the welding current i becomes extremely smaller than the optimum set value, the joining becomes insufficient and the welding surface peels off with a small force, while the welding current i becomes extremely larger than the optimum set value. When this happens, the weld surface melts or burns, and in either case, welding failure occurs.

In order to solve the above problem, the conventional resistance welding machine 1 incorporates a current detection device 6 for detecting a welding current i flowing through the electrode portion 2 and monitoring a change in welding conditions. The current detecting device 6 includes a sensor unit 7 composed of a toroidal coil provided in a path through which a welding current i flows, and a monitor that A / D converts and displays a detection value _Ij of the welding current detected by the sensor unit 7. Unit 8. Operator confirms the display of the monitor unit 8, when the detection data I _j of the welding current is changed magnitude relative to the set value,
By manually operating the setting switch 5 of the controller 4, the heat value T is adjusted so that the welding current detection data _Ij approaches the set value.

However, in such an adjusting method,
Since the operator needs to constantly monitor the display on the monitor unit 8, the work load is large, and such monitoring cannot be performed in practice. For this reason, the welding current cannot be finely adjusted to an optimum state, and it is difficult to ensure a constant welding quality and to surely prevent the occurrence of poor welding.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and automatically adjusts a welding current in accordance with a change in welding conditions to ensure a constant welding quality and reliably prevent poor welding. It is an object of the present invention to provide a resistance welding machine in which the work load on the worker is reduced.

[0010]

SUMMARY OF THE INVENTION The present invention relates to a resistance welding apparatus comprising: an electrode section for applying a welding current to a workpiece to perform welding; and a controller for supplying power to the electrode section in accordance with a set value of the welding current. In the machine, current detection means for detecting a welding current flowing through the electrode portion, storage means for stocking a predetermined number of latest detection data detected by the current detection means, and a predetermined number of stock data stored in the storage means Analysis means for detecting a change in welding conditions from the detection data;
Control means for adjusting the power supplied to the electrode portion by the controller based on the detection result by the analysis means to increase or decrease the welding current.

In the invention of claim 2, the analysis means calculates an average value of a predetermined number of pieces of detection data stored in the storage means, and the control means calculates a difference between the average value and a set value of the welding current. After calculating the correction data according to the power, the power is adjusted according to the correction data.

[0012]

When power corresponding to the set value of the welding current is supplied to the electrode portion, the welding current flows through the work and the portions to be joined are welded. The welding current is detected by the current detecting means,
A predetermined number of latest detection data is stored in the storage means. The welding current fluctuates in magnitude depending on the change in welding conditions, and the change in welding conditions is detected by the analysis means from a predetermined number of pieces of detection data stored in the storage means. When a change in the welding conditions is detected, the control means adjusts the power supplied to the electrode unit by the controller to increase or decrease the welding current.

In the resistance welding machine according to a second aspect, the analyzing means includes:
In order to detect a change in welding conditions, an average value of a predetermined number of pieces of detection data stored in the storage means is calculated. After calculating the correction data according to the difference between the average value and the set value of the welding current, the control means performs power adjustment according to the correction data.

[0014]

FIG. 1 shows a schematic configuration of a resistance welding machine 1 according to one embodiment of the present invention, in which a welding portion 2, a welding transformer 3, a controller 4, a current detecting device 6, an automatic adjusting device 1 are shown.
1 and a computer terminal device 12. As shown in FIG. 2, the electrode section 2 has a pair of welding electrodes 2a and 2b for applying a welding current to the work in a pressurized state. A toroidal coil as the sensor unit 7 of the current detection device 6 is mounted on one electrode 2b. In this example,
A welding head having the electrode unit 2 is arranged along an article manufacturing line, and performs spot welding on workpieces supplied one after another by a robot hand, and welds portions to be joined.

The controller 4 includes an AC power supply (not shown).
Without. ) Than 200 volts e ₁Given this
Voltage e₁Is the heat value set by the automatic adjustment device 11
Output to the primary side of the welding transformer 3 for a time corresponding to T
You. The welding transformer 3 receives the input from the controller 4
Secondary side voltage e₁To a predetermined value, and the secondary side voltage e_Two
Is applied between the welding electrodes 2a and 2b,
A predetermined power is supplied to the pole part 2.

The sensor section 7 composed of the toroidal coil constitutes a current detecting device 6 together with the monitor section 8. The current detecting device 6 detects a welding current i flowing through the electrode portion 2.
For detecting a change in welding conditions by detecting the welding current i flowing through the electrode portion 2 by the sensor portion 7 each time welding is performed, and detecting the welding current detected by the sensor portion 7. A / D conversion is performed on the detected data _Ij by the monitor unit 8 and digitally displayed.

Each time welding is performed, the automatic adjustment device 11 fetches the detection data _Ij of the welding current from the monitor 8 of the current detection device 6 one after another, and determines a welding condition based on a predetermined number of latest detection data. After detecting the change, the heat value T is automatically adjusted based on the detection result to increase or decrease the welding current.

FIG. 3 shows a circuit configuration of the automatic adjustment device 11, including a CPU 21 which is a main body of control and calculation, a ROM 22 for storing programs and fixed data, a RAM 23 for reading and writing various data and parameters. And a switch operation unit 24, a display unit 25, a transmission unit 26, and the like. The transmission unit 26 exchanges data and parameters with the computer terminal device 12. The computer terminal device 12 sends a current set value I ₀ ,
Various parameters such as an initial heat value T ₀ , a current upper limit I _max , a current lower limit I _min , a heat step upper limit ΔT _max , and a proportional gain α are set, and the automatic adjustment device 1
This is for taking in the detection data of the welding current from No. 1 and performing various analyses.

The RAM 23 has a work area W for storing welding current detection data, as shown in FIG. 4, in addition to a storage area for storing various parameters. The work area W, the buffer area BF detection data I _j of the welding current obtained in this welding is captured, the n stock area storing n latest detection data I ₁ ~I _n M _{1 to Mn} . For example, in the stock area _Mn , the detection data In of the _n-th welding current obtained in the previous welding is obtained, and in the next stock area _Mn-1 , the data is obtained by the last two weldings (n-1). ) The detection data In _-1 of the welding current is stored.

[0020] When the welding is performed, the detection data I _j from the monitor unit 8 is taken into RAM23 buffer area BF, n number of detection data I ₁ ~I stored in each stock area M ₁ ~M _{n As} shown by an arrow in the figure, _n is sequentially forwarded to the next storage area and overwritten,
Detection data I _j of the buffer region BF is overwritten been moved to the stock area M _n. Thus the n-number of stock area M ₁ ~M _n, always the latest n number of detection data I ₁ ~I _n is stock.

FIG. 5 shows the CPU in the automatic adjustment device 11.
21 shows a flow of control by 21. In the figure, ST indicates each step in the control flow. In ST1 of FIG.
The CPU 21 sets the current set value I ₀ , the initial heat value T ₀ , the current upper limit I _max , the current lower limit I _min , and the heat step upper limit ΔT input from the computer terminal device 12.
various parameters such as _max and proportional gain α
After that, the value j of an internal counter for counting the number of times of welding is reset to zero (ST2).

When a work is set on the electrode section 2, the CP
A welding command is given to U21, and the determination in ST3 is "YE
S ". This welding command is output from a predetermined object detection sensor to the CPU 21 when the workpiece is positioned on the electrode unit 2 in an automatic welding line. If it is not an automatic welding line, when a worker presses a predetermined start switch, a welding command is output to the CPU 21 from the switch.

[0023] If there is the welding command, CPU 21 outputs to the controller 4 the initial heat value T ₀ as a heat value T (ST4). Thereby, the controller 4 applies the voltage e ₁ to the primary side of the welding transformer 3 for a time corresponding to the heat value T, and the secondary side voltage e ₂ is applied to the welding electrode 2 of the electrode unit 2.
By being applied between a and 2b, a welding current i flows through the electrode portion 2 and spot welding is performed on the work. The welding current i is detected by the sensor unit 7 of the current detector 6, the detection data I _j is taken into the monitor unit 8 is A / D converted welding current (ST5). Since the welding current varies depending on the welding conditions, the detection data _Ij reflects the welding conditions at the time of the current welding. CPU 21
Reads the detection data I _j of the digital amount and
3 is written to the buffer area BF.

[0024] In the following ST6, CPU 21 has determined whether detection data I _j is smaller than the current limit I _max, and greater than the current limit value I _min of the welding current. If the determination in ST6 is "YES", it is determined that normal welding has been performed, and the value j of the counter is incremented by 1 (ST7). If the detection data I _j of the welding current upper current limit I _max is greater than or smaller than the current limit value I _min, it is determined that the welding abnormality occurs, an error processing such as issuing an alarm. In this case, the value j of the counter is not incremented.

In the next step ST8, the CPU 21 sets the RAM
The n number of detection data I ₁ ~I _n stored in each stock area M ₁ ~M _n of 23 with overwriting and forward respectively to the next memory area, the detection data I _j in the buffer area BF
Is moved to _n stock areas M _n and overwritten. In the first welding is performed step by treatment ST8, the stock area M _n, each time the detection data I _n by first welding but only been stocked, the welding is repeated, each stock area M _n ~M ₁ is satisfied by detecting data.

In the next step ST9, the CPU 21 determines whether or not the value j of the counter has reached a predetermined average number n, that is, the welding current detection data I _{n to} I ₁ is stored in all the stock areas M _{n to} M _1. Determine if it is stocked. When the counter value j is smaller than the average number n, S
The determination at T9 is “NO”, and the CPU 21 calculates an average value I for j pieces of detection data (ST11).
If the counter value j is equal to or greater than the average number n, ST
The determination of No. 9 is “YES”, and the CPU 21 calculates an average value I for n pieces of detection data (ST10).

In the next step ST12, the CPU 21 calculates a heat step value ΔT by multiplying the difference between the average value I and the current set value I ₀ by a proportional gain α, and then determines whether the calculated value is appropriate, step upper limit value [Delta] T _max is determined whether smaller (ST13). If the judgment is "YES", the process proceeds to ST14, determines whether the mean value or I is current larger than the set value I _0. In addition,
If the heat step value [Delta] T calculated in ST12 is larger than the heat step the upper limit value [Delta] T _max is the heat step upper limit value [Delta] T _max and heat step value [Delta] T (ST18).

When the average value I is larger than the current set value I ₀ , the determination in ST 14 is “YES” and the CPU 21
Subtracts the heat step value ΔT from the current heat value T and sets the calculated value as a new heat value T (ST1
5). If the average value I is equal to or less than the current set value I ₀ ,
The determination in ST14 is “NO”, and the CPU 21 adds the heat step value ΔT to the heat value T, and sets the calculated value as a new heat value T (ST16). Next ST
At 17, the CPU 21 determines whether or not to stop welding. If the determination is "NO", the process returns to ST3 and waits for the next welding command.

In the above embodiment, changes in welding conditions are analyzed by moving average processing.
Other analysis techniques can be employed. In addition, the automatic adjustment device 11 is provided with a mode changeover switch, and by operating the mode changeover switch, an automatic mode in which the optimum heat value T is calculated and output to the controller 4, and the initial heat value T ₀ is always output to the controller 4. You may be comprised so that a through mode etc. may be switched.

[0030]

As described above, according to the present invention, welding current detection data is stocked, a change in welding conditions is detected from the latest predetermined number of the stocked detection data, and the controller determines an electrode based on the detection result. Since the welding current is increased or decreased by adjusting the power supplied to the part, it is possible to automatically adjust the welding current to an optimum value according to changes in welding conditions, and to secure a constant welding quality, Defects can be reliably prevented. Further, since it is not necessary to constantly monitor the welding current while watching the display of the current detection device, the work load on the operator can be greatly reduced.

According to the second aspect of the present invention, an average value of a predetermined number of stored detection data is calculated, and correction data corresponding to a difference between the average value and a set value of the welding current is calculated. Since the power adjustment is performed accordingly, the welding current can be optimized by a simple calculation process.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a resistance welding machine according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a configuration of an electrode unit.

FIG. 3 is a block diagram illustrating a circuit configuration of the automatic adjustment device.

FIG. 4 is an explanatory diagram showing a storage area of a RAM.

FIG. 5 is a flowchart showing a flow of control by a CPU in the automatic adjustment device.

FIG. 6 is a block diagram showing a schematic configuration of a conventional resistance welding machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Resistance welding machine 2 Electrode part 4 Controller 6 Current detection device 11 Automatic adjustment device

Claims (2)

[Claims] 1. A resistance welding machine comprising: an electrode unit for welding by flowing a welding current to a workpiece; and a controller for supplying power to the electrode unit according to a set value of the welding current. Current detection means for detecting a welding current; storage means for storing a predetermined number of latest detection data detected by the current detection means; and a change in welding conditions from the predetermined number of detection data stored in the storage means. A resistance welding machine comprising: analysis means for detecting; and control means for adjusting power supplied to the electrode unit by the controller based on a detection result by the analysis means to increase or decrease a welding current. 2. The analysis means calculates an average value of a predetermined number of pieces of detection data stored in a storage means, and the control means calculates correction data corresponding to a difference between the average value and a set value of a welding current. 2. The resistance welding machine according to claim 1, wherein after calculating the power, the power is adjusted according to the correction data.