JP3733438B2 - Control method and control apparatus for electric servo resistance welding apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control method and a control device for an electric servo resistance welding apparatus. More specifically, the present invention relates to a control method and a control device for an electric servo resistance welding apparatus in which excessive current supply to a joint is prevented.
[0002]
[Prior art]
Conventionally, in spot welding by a robot, an electric servo resistance welding apparatus (hereinafter referred to as a servo gun) that operates in synchronization with the robot has been used. In this servo gun, spot welding is performed by controlling the welding current, the applied pressure, the welding time, and the like based on the teaching data.
[0003]
However, in the control of the conventional servo gun, as described in JP-A-7-32160, the welding current value during welding is constant, and the time is also constant at each spot welding position. Therefore, the following problems have arisen.
[0004]
Materials to be welded, such as steel plates, have a slight difference in the respective parts to be welded even if the surface state is the same part, and the composition is also slightly different. Therefore, when spot welding is performed for a certain welding time, the welding time may be excessive or insufficient depending on the degree of difference in the surface state and the like. If the welding time is excessive or insufficient, a desired nugget is not formed, which may result in poor welding. That is, if the welding time is appropriate, a nugget N as shown in FIG. 9 is formed. If the welding time is too short, the penetration becomes shallow as shown in FIG. If it is not formed and the welding time is too long, dust is generated in the nugget N as shown in FIG. In addition, an excessive current increases the temperature of the electrode and causes the life of the electrode to be shortened.
[0005]
Japanese Patent Laid-Open No. 9-168867 proposes a resistance welding machine control device in which energization is stopped when a required nugget is directly input and the nugget grows into the required nugget. In such a control device, there is a problem that a required nugget must be input for each welding and the work is complicated. It is also unclear how to stop energization.
[0006]
[Problems to be solved by the invention]
The present invention has been made in view of the problems of the prior art, and provides a control method and a control device for an electric servo resistance welding apparatus in which excessive current supply is prevented from being supplied to a joint without inputting a required nugget. The purpose is that.
[0008]
[Means for Solving the Problems]
The control method of the electric servo resistance welding apparatus of the present invention is a spot welding control method using the electric servo resistance welding apparatus, and reduces the welding current to the nugget formation current when the growth of the nugget is completed, Then, the welding current is set to zero after a predetermined time has elapsed.
[0010]
In the control method of the electric servo resistance welding apparatus of the present invention, for example, the time when the increase in the encoder value of the servo gun is finished is set as the time when the growth of the nugget is finished, or the rate of change of the encoder value of the servo gun becomes negative. Or the time when the growth of the nugget ends.
[0012]
The control apparatus for an electric servo resistance welding apparatus according to the present invention is a spot welding control apparatus using an electric servo resistance welding apparatus, the control apparatus comprising a welding current value command means and a state detection means, When it is determined by the state detection means that the nugget growth has been completed, the welding current value command means reduces the welding current to the nugget formation current , and then the welding power source is turned off after a predetermined time has elapsed.
[0014]
In the control device for the electric servo resistance welding apparatus of the present invention, the growth of the nugget has been completed due to the end of the increase in the encoder value of the servo gun, or the rate of change in the encoder value of the servo gun has become negative. It is said that the growth of the nugget has ended.
[0015]
[Action]
Since the present invention is configured as described above, it is possible to prevent an excessive welding current from being supplied after the nugget is formed at the joint. As a result, an excessive temperature rise of the welding electrode due to excess current is prevented, so that the life of the welding electrode is extended.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described based on an embodiment with reference to the accompanying drawings, but the present invention is not limited to the embodiment.
[0017]
Embodiment 1
A control device (hereinafter simply referred to as a control device) 1 for a servo gun G according to Embodiment 1 of the present invention is shown in a block diagram in FIG. 1, and this control device 1 turns on / off a welding power source 2 of the servo gun G. The welding instruction means 11 for instructing and the state detection means 12 for detecting the state of the workpiece W from the change of the encoder value of the encoder 4 of the servo motor 3 are provided as main means. As shown in FIG. 2, the control device 1 including the units 11 and 12 includes an input / output interface, a ROM, a RAM, a clock, and the like centered on the CPU. This is realized by storing the corresponding program.
[0018]
Next, the state detection of the workpiece W by the state detection means 12 will be described. Since the welding command means 11 is the same as that conventionally used for spot welding by the servo gun G, its detailed description is omitted.
[0019]
When the welding pressure of the servo gun G and the welding current are set to predetermined values and spot welding of the workpiece W is performed, the workpiece W is heated and thermally expanded, and a nugget N is generated. The generated nugget N expands during the formation process. As a result, the interval between the workpieces W increases. The speed at which this interval increases depends on the amount of heat supplied to the workpiece W, and the amount of heat supplied depends on the surface state of the workpiece W. That is, if the surface condition is bad, the speed is high, and conversely if the surface condition is good, the speed is low. On the other hand, since the pressurizing force of the servo gun G is maintained at a predetermined value during spot welding, the encoder value of the encoder 4 that measures the displacement of the servo motor 3 changes correspondingly as the interval of the workpiece W increases. To do. That is, the tip (upper electrode) 5 of the servo gun G driven by the servo motor 3 is pushed back by an amount corresponding to the increase in the interval between the workpieces W, and the encoder value of the servo motor 3 changes accordingly (see FIG. 3). ). Therefore, if the rate of change per unit time of the encoder value (hereinafter referred to as encoder speed) is detected, the degree of thermal expansion of the workpiece W and the growth of the nugget N, that is, the state of the workpiece W can be known. it can.
[0020]
Next, spot welding of the steel sheet W by the control device 1 configured as described above will be described with reference to FIGS. 3 and 4. FIG. 3 schematically shows the time change of the encoder value, and FIG. 4 schematically shows the time change of the welding current value.
[0021]
(1) A power-on command is sent from the welding command means 11 to the welding power source 2.
[0022]
(2) The welding power source 2 supplies a predetermined current to the servo gun G.
[0023]
(3) The steel plate W is spot welded by the servo gun G.
[0024]
(4) The encoder value after the start of spot welding is sent to the control device 1. This encoder value may be continuously sent from the start of pressurization of the servo gun G.
[0025]
(5) The state detection means 12 determines whether or not the growth of the nugget N has been completed based on the change in the input encoder value.
[0026]
(6) When the state detection means 12 determines that the growth of the nugget N has been completed, the welding command means 11 instructs the welding power source 2 to turn off the power based on the determination result.
[0027]
(7) The welding power source 2 turns off the welding current in response to the instruction from the welding command means 11.
[0028]
As described above, in the first embodiment, when the growth of the nugget N is finished, the welding current is turned off and the supply of the welding current to the steel plate W is stopped. This prevents the nugget N from getting dusty. In addition, since the supply of excess current is prevented, power saving is achieved, and the temperature rise of the electrodes 5 and 6 is prevented more than necessary, thereby extending the life of the electrodes 5 and 6.
[0029]
In this case, the welding power source 2 may be turned off when the growth rate of the nugget N becomes negative.
[0030]
Embodiment 2
A control device 1A according to the second embodiment of the present invention is shown in a block diagram in FIG. 5, and this control device 1A is a modification of the control device 1 according to the first embodiment. The welding current value commanding means 14 for commanding the current value to the welding power source 2 of the servo gun G is provided.
[0031]
Hereinafter, the spot welding of the steel sheet W by the control device 1A configured as described above will be described with reference to FIGS. 3 and 6.
[0032]
(1) The power-on and welding current command values are sent from the welding current value command means 14 to the welding power source 2.
[0033]
(2) The welding power source 2 supplies the commanded current to the servo gun G.
[0034]
(3) The steel plate W is spot welded by the servo gun G.
[0035]
(4) The encoder value after the start of spot welding is sent to the control device 1A. This encoder value may be continuously sent from the start of pressurization of the servo gun G.
[0036]
(5) The state detection means 12 determines whether or not the growth of the nugget N has been completed based on the change in the input encoder value.
[0037]
(6) When the state detection means 12 determines that the growth of the nugget N has been completed, based on the determination result, the welding current value command means 14 instructs the welding power source 2 to reduce the welding current to a predetermined value. This predetermined value is, for example, 4 (t) ^0.5 (nugget forming current). Here, t is a plate thickness (unit: mm).
[0038]
(7) The welding current value command means 14 instructs the welding power source 2 to turn off the power after a predetermined time has elapsed. This predetermined time is a time for the nugget diameter to recover to the reference value when, for example, dust occurs. The specific value is determined by a welding test or the like.
[0039]
(8) The welding power source 2 turns off the welding current in response to an instruction from the welding current value command means 14.
[0040]
As described above, in the second embodiment, when the growth of the nugget N is completed, the welding current is reduced to a predetermined value, and after a predetermined time has elapsed, the welding power source 2 is turned off, and the welding current to the steel plate W is reduced. Since the supply is stopped, the nugget N is prevented from being dusted due to the excessive welding current being supplied to the steel plate W. In the second embodiment, the welding current is reduced to a predetermined value when the growth of the nugget N is completed, and the welding power source 2 is turned off after a predetermined time has elapsed. Even if the state detection means 12 erroneously determines that the growth of the nugget N has been completed at the time of occurrence, there is an advantage that sufficient bonding strength can be obtained because the current is supplied until the nugget diameter is recovered.
[0041]
In this case, the welding current may be reduced to a predetermined value when the growth rate of the nugget N becomes negative.
[0042]
Embodiment 3
A control device 1B according to the third embodiment of the present invention is shown in a block diagram in FIG. 7, and this control device 1B is a modification of the control device 1 according to the first embodiment, and replaces the welding command means 11. The welding current value command means 16 for commanding the current value to the welding power source 2 of the servo gun G is provided.
[0043]
Hereinafter, spot welding of the steel sheet W by the control device 1B configured as described above will be described with reference to FIGS. 3 and 8. FIG.
[0044]
(1) The power-on and welding current command values are sent from the welding current value command means 16 to the welding power source 2.
[0045]
(2) The welding power source 2 supplies the commanded current to the servo gun G.
[0046]
(3) The steel plate W is spot welded by the servo gun G.
[0047]
(4) The encoder value after the start of spot welding is sent to the control device 1B. This encoder value may be continuously sent from the start of pressurization of the servo gun G.
[0048]
(5) The state detection means 12 determines whether or not the growth of the nugget N has been completed based on the change in the input encoder value.
[0049]
(6) When the state detecting means 12 determines that the growth of the nugget N has been completed, based on the determination result, the welding current value command means 16 instructs the welding power source 2 to reduce the welding current to zero at a constant speed. To do. This constant speed is, for example, a speed that becomes zero at a set energization time, and is specifically determined by a welding test or the like.
[0050]
(7) The welding power source 2 reduces the welding current to zero at a constant speed in response to an instruction from the welding current value command means 16.
[0051]
Thus, in this Embodiment 3, since the welding current is reduced to zero at a constant speed when the growth of the nugget N is completed, the nugget N is prevented from being dusted by the excessive welding current to the steel sheet W. Is done. In the third embodiment, since the welding current is reduced to zero at a constant speed when the growth of the nugget is completed, the welded portion can be gradually cooled as compared with the first and second embodiments. There is an advantage.
[0052]
In this case, when the growth speed of the nugget N becomes negative, the welding current may be reduced to zero at a constant speed.
[0053]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to obtain an excellent effect of preventing an excessive current from being supplied to the junction. In addition, since no excessive current is supplied to the joint, generation of dust due to the excessive current is prevented, and an excellent effect that the temperature of the welding electrode is prevented from being increased more than necessary and the life of the welding electrode is extended can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram of a control device according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram of an electrical configuration of the control device.
FIG. 3 is a graph schematically showing temporal changes in encoder values.
FIG. 4 is a grab schematically showing a temporal change in welding current in Embodiment 1 of the present invention.
FIG. 5 is a block diagram of a control device according to a second embodiment of the present invention.
FIG. 6 is a grab schematically showing a temporal change in welding current in the second embodiment of the present invention.
FIG. 7 is a block diagram of a control device according to a third embodiment of the present invention.
FIG. 8 is a grab schematically showing a temporal change in welding current in the third embodiment of the present invention.
FIG. 9 is a schematic view of a nugget when the welding time is appropriate.
FIG. 10 is a schematic view of a nugget when the welding time is short.
FIG. 11 is a schematic diagram of a nugget when the welding time is too long, and shows how dust is generated.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Control apparatus 11 Welding command means 12 State detection means 14, 16 Welding current value command means 2 Welding power supply 3 Servo motor 4 Encoder 5 Upper electrode, tip 6 Lower electrode, Tip G Servo gun N Nugget V Cavity W Welded material, steel plate

Claims (7)

A method for controlling spot welding using an electric servo resistance welding apparatus, wherein the welding current is reduced to a nugget forming current when the growth of the nugget is completed, and then the welding current is set to zero after a predetermined time has elapsed. A control method of an electric servo resistance welding apparatus characterized by the above.  2. The control method for an electric servo resistance welding apparatus according to claim 1, wherein the time point when the increase of the encoder value of the servo gun is finished is set as the time point when the growth of the nugget is finished.  2. The control method for an electric servo resistance welding apparatus according to claim 1, wherein the time point when the rate of change of the encoder value of the servo gun becomes negative is the time point when the growth of the nugget is finished. A control device for spot welding using an electric servo resistance welding device, wherein the control device comprises a welding current value command means and a state detection means,
When it is determined by the state detection means that the nugget growth has ended, the welding current value instruction means reduces the welding current to the nugget formation current , and then the welding power source is turned off after a predetermined time has elapsed. Control device for electric servo resistance welding equipment. 5. The control device for an electric servo resistance welding apparatus according to claim 4 , wherein the growth of the nugget is finished when the increase of the encoder value of the servo gun is finished. 5. The control apparatus for an electric servo resistance welding apparatus according to claim 4 , wherein the growth of the nugget is terminated when the rate of change of the encoder value of the servo gun becomes negative. An electric servo resistance welding apparatus comprising the control device according to claim 4, 5 or 6 .

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