JP2003071571A - Control device for spot welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grasp exactly the dotting position for spot welding, and on the basis of the grasped dotting position, welding condition is selected. SOLUTION: Between a jig 100 and a stationary side electrode 132 of a welding gun 130, voltage is applied, and when the stationary side electrode 132 is brought into contact with a vehicle body frame W, currents flowing in respective jig posts 100a-100i are detected. And on the basis of the ratios of the currents flowing in respective jig posts 100a-100i, the contact position of the stationary electrode, i.e., dotting positions are detected. When the dotting position is the previously stored dotting position, the welding condition of the dotting position is selected and the spot welding is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding control apparatus which accurately grasps a spot welding spot position and selects welding conditions based on the grasped spot welding position.

[0002]

2. Description of the Related Art Conventionally, for example, when spot welding a frame of an automobile, welding conditions vary depending on the area of the frame. Therefore, as disclosed in Japanese Utility Model Laid-Open No. 63-29684, a proximity sensor, a photoelectric sensor, etc. The detection means detects the area of the frame where the welding gun is located, selects the welding condition according to the detected area, and performs spot welding under the selected welding condition.

[0003]

However, when the narrow areas having different welding conditions are adjacent or continuous, it is difficult to install the detecting means for detecting the welding gun. If it is installed by force, the area where the welding gun is present may be erroneously detected, and appropriate welding conditions may not be selected.

Further, since the detecting means must be provided on the moving path of the welding gun during spot welding, it may adversely affect the operability of the welding gun and may deteriorate the workability.

Further, even if the detection means can accurately detect the area where the welding gun is present (different from the welding point position), the welding point cannot be detected up to the spot welding spot position. Even if it is out of position, it cannot be detected.

Further, since the detecting means detects the welding gun in area units, it is possible to manage the work order for each area, but it is not possible to manage the work order for each dot position.

The present invention has been made in view of the conventional problems as described above, and spot welding for accurately grasping the spot welding position of spot welding and selecting welding conditions based on the grasped spot welding position. It is intended to provide a control device.

[0008]

[Means for Solving the Problems] In order to solve the above problems,
In order to achieve the object, a spot welding control apparatus according to the invention of claim 1 has a plurality of supporting means for supporting a work, a welding gun for spot welding the work, and an electrode of the welding gun for the work. When the electrode of the welding gun is brought into contact with the work, the voltage applying means for applying a voltage to the closed circuit consisting of the welding gun, the work, the plurality of supporting means, and the path leading to the welding gun, which is formed when they are brought into contact with each other. To
Current detecting means for detecting a current flowing through each of the plurality of supporting means, and contact position calculating means for calculating a contact position of the electrode of the welding gun with respect to the workpiece based on the current flowing through each of the plurality of supporting means. And are included.

A spot welding control apparatus according to a second aspect of the present invention is the spot welding control apparatus according to the first aspect, wherein the contact position calculating means is based on a ratio of currents flowing through the plurality of supporting means. The contact position, which is the spot welding position of spot welding, is calculated.

A spot welding control apparatus according to a third aspect of the present invention is the spot welding control apparatus according to the second aspect, further comprising a welding point position storage means for storing a welding point position of the spot welding of the work, And a spot position alarming means for issuing an alarm when the spot welding spot position calculated by the contact position calculating means deviates from the spot welding spot position stored in the spot position storing means. .

A spot welding control apparatus according to a fourth aspect of the present invention is the spot welding control apparatus according to the second aspect, further comprising welding condition storage means for storing welding conditions for each spot welding spot position. Welding condition selecting means for selecting the welding conditions based on the spot welding position of the spot welding calculated by the contact position calculating means, and a welding current to the welding gun for spot welding under the selected welding conditions. And a welding current supply means.

A spot welding control apparatus according to a fifth aspect of the present invention is the spot welding control apparatus according to the third aspect, further comprising welding sequence storage means for storing a welding sequence at a welding point position where spot welding is performed. A welding sequence alarm means for issuing an alarm when the spot welding spot position calculated by the contact position calculating means is not a spot welding position according to the welding sequence.

[0013]

As described above, according to the present invention,
Since the spot welding position of spot welding can be accurately grasped, it is possible to always select appropriate welding conditions. Further, since it is not necessary to provide a sensor for grasping the welding point position of the welding gun, the operability of the welding gun is not deteriorated and the workability is improved.

Further, when an attempt is made to perform spot welding at a spot position deviating from the regular spot position, or when the spot position is not a spot position according to the welding sequence, an alarm is issued. High welding quality can always be maintained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the spot welding control apparatus according to the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an overall view of a spot welding apparatus for performing spot welding on a vehicle body frame (workpiece) by an operator manually operating a spot welding gun. Based on this figure, the general operation of this spot welding apparatus will be described.

The jig 100 includes a plurality of jig posts (supporting means) 100a to 10a for supporting the vehicle body frame W.
0i is attached. The body frame W is placed on these jig posts 100a to 100i and is firmly fixed by a clamp (not shown). Each of the jig posts 100a to 100i has a toroidal coil (current detection means) 110a to 11 for detecting a current.
0i is attached. At least three toroidal coils are enough, but in this embodiment, they are attached to all jig posts. These toroidal coils 1
10a to 110i are connected to a spot welding control device (voltage applying means, contact position calculating means) 120. A spot welding gun (welding gun) 130 manually operated by an operator is connected to the spot welding control device 120.

The spot welding control device 120 applies a DC voltage of, for example, about several volts between the spot welding gun 130 and the jig 100. When the worker brings the fixed-side electrode 132 of the spot welding gun 130 into contact with the spot position of the vehicle body frame W for spot welding, the spot welding control device 120, the fixed-side electrode 132 of the spot welding gun 130, and the vehicle body frame W. , Jig post 100
a to 100i, jig 100, spot welding control device 12
A closed circuit reaching 0 is formed. Therefore, jig post 1
A current according to the distance from the hitting point flows through each of 00a to 100i. Each jig post 100a-1
The current flowing through 00i is the toroidal coil 110a.
~ 110i detected. Each toroidal coil 1
The current values detected by 10a to 110i are output to the spot welding control device 120. The spot welding control device 120 obtains the coordinates of the spot position from the ratio of these current values, and the coordinates coincide with the preset coordinates of the spot position or fall within the allowable welding position tolerance centered on the coordinates. If there is, the welding condition set at the spot position is selected. Worker is spot welding gun 1
By operating the welding switch 134 provided at 30, the spot welding position can be spot welded under the selected welding conditions. On the other hand, when the coordinates of the hitting point position deviate from the preset coordinates of the hitting point position by more than the welding position tolerance allowable range, the spot welding control device 1
20 gives an alarm. Further, even when the welding point position is a welding point position different from the predetermined welding sequence, regardless of whether the welding point position is within the welding position tolerance allowable range of the predetermined welding point position. Then, an alarm is issued from the spot welding control device 120.

FIG. 2 is a block diagram showing a schematic configuration of the spot welding control device 120 according to the present invention. The spot welding control device 120 includes an A / D conversion unit 210, a storage unit 220, a calculation processing unit 230, an equipment control unit 240, an alarm unit 250, and a power supply unit 260.

The A / D converter 210 converts the current value detected by the toroidal coils 110a to 110i from analog to digital. In the figure, one A / D
Although only the converter is shown, the number of toroidal coils is actually provided.

The storage unit 220 stores the coordinates of each welding point position of spot welding, the allowable welding position tolerance centering on the coordinates, the welding conditions at each welding point position, the welding sequence of the welding point positions, and the type of the body frame to be the work. I remember each one. The coordinates of each spot position of spot welding are two-dimensional coordinates of X and Y, and the welding position tolerance allowable range is set for each spot position. The welding conditions include the welding current, welding time and pressure at the welding point, the welding position tolerance tolerance range, and the like. The welding sequence of the spot positions is as follows:
Second, the welding point position of this coordinate is the second, and the welding order is for each welding point position where spot welding should be performed in order.

The storage unit 220 is a dot position storage means,
It functions as a welding condition storage means and a welding order storage means.

The arithmetic processing section 230 includes an A / D conversion section 210.
Each toroidal coil 110a-11 converted by
Based on the current value of 0i, the ratio of the current values is obtained, and the coordinates of the spot position where spot welding is to be performed are obtained from the ratio. The reason why the coordinates of the dot position are determined from the ratio of the current values is that the actual measurement value directly affects the environment of the site, and stable detection accuracy can be obtained regardless of the environment of the site. Because.
Further, the detection accuracy is improved by learning the current ratio and the coordinates of the hit point position. The method of obtaining the coordinates of the hit point position will be described in detail later. Then, the coordinates are stored in the storage unit 2.
If any of the welding point positions stored in 20 matches or is within the allowable welding position tolerance centered on the coordinates, the welding condition set for that welding point position is selected. Then, when the welding order of the welding point position is the welding point position that matches the welding order stored in the storage unit 220, the selected welding condition is adopted. On the other hand, when the welding sequence of the welding point position is different from the welding sequence stored in the storage unit 220, for example, even though the welding spot position is the tenth welding spot position, the welding sequence stored in the storage unit 220. Therefore, at the 13th spot position, the welding sequence is different, so the selected welding condition is not adopted.

The coordinates of the obtained hitting point position are stored in the storage unit 22.
When the welding position tolerance allowable range of the coordinates of any of the welding point positions stored in 0 is exceeded, the welding condition cannot be selected, so the welding condition is not selected.

The calculation processing section 230 functions as a contact position calculation means, a welding condition selection means, and a welding current supply means.

The equipment control unit 240 inputs the welding conditions selected by the arithmetic processing unit 230, and when the welding switch 134 is operated (ON), the welding gun 13 is operated under the welding conditions.
0 and the welding timer 136 are operated. Welding gun 130
Applies a welding current defined by the welding conditions between the electrodes, and a welding timer 136 counts the time for applying the welding current for the welding time defined by the welding conditions.

The alarm unit (spotting position alarming means, welding sequence alarming means) 250 has the coordinates of the welding point positions obtained by the arithmetic processing unit 230 coincident with the coordinates of any of the welding point positions stored in the storage unit 220, or If the welding position tolerance around the coordinates is not within the allowable range, or if the welding sequence at the welding point position is different from the welding sequence stored in the storage unit 220, an alarm is issued.

The power supply section (voltage applying means) 260 is used for the spot welding gun 13 except during spot welding.
An alternating voltage of, for example, about several volts is applied between the fixed electrode 132 of 0 and the jig 100.

Next, the operation of the spot welding control apparatus according to the present invention will be described in detail based on the flowcharts of FIG. FIG. 3 is a flowchart showing the operation of the spot welding control device according to the present invention.

First, the worker sets the body frame (work) W to be spot-welded to the jig post 1 of the jig 100.
Placed on 00a-100i, each jig post 100a-1
Body frame W with clamp attached to 00i
Is firmly fixed (S1).

As shown in FIG. 1, the worker moves the spot welding gun 130 to the first hitting point position (S).
2).

The operator brings the fixed-side electrode 132 of the spot welding gun 130 into contact with the first welding point position and positions it at the welding point position (S3).

When the fixed electrode 132 comes into contact with the hitting point of the vehicle body frame W, the power source 260 and the spot welding gun 1
A closed circuit including the fixed-side electrode 132 of 30, the vehicle body frame W, the jig posts 100a to 100i, the jig 100, and the power supply unit 260 is formed. Therefore, the jig post 100a-
A current for position detection according to the distance from the hitting position flows in each of 100i (S4).

The current flowing through each jig post 100a-100i is detected by the toroidal coils 110a-110i (S5).

The A / D converter 210 inputs the current detected by each of the toroidal coils 110a to 110i and digitizes the analog current value into a digital value (S6).

The arithmetic processing section 230 includes an A / D conversion section 210.
Each toroidal coil 110a-11 converted by
Based on the current value of 0i, the ratio of the current values is numerically processed, and the coordinates of the spot position where spot welding is to be performed are obtained from the result of the numerical processing (S7).

When the operator operates the welding switch 134 of the spot welding gun 130, a welding start signal is output to the equipment control section 250 (S8).

The arithmetic processing unit 230 determines whether the obtained coordinates of the welding point position match the coordinates of any of the welding point positions stored in the storage unit 220 or are within the allowable welding position tolerance centered on the coordinates ( Whether or not the welding position is correct) is also considered in consideration of whether or not the welding sequence of the welding position is the welding position that matches the welding sequence stored in the storage unit 220. If the accuracy of hitting point detection is indicated by a correct answer rate, in the case of continuous hitting point detection, a correct answer rate of about 80% was obtained in the experiment (S9).

If the coordinates of the obtained hitting point position are the coordinates of the correct hitting point position (S9: YES), the arithmetic processing section 230 selects from the welding conditions stored in the storage section 220 for that hitting point position. The set welding conditions are selected (S10).

The equipment control unit 240 spot-welds the welding point position based on the selected welding condition. That is, the welding time is set in the welding timer 136 in order to flow the welding current for the welding time determined by the welding condition, and the welding current determined by the welding condition is set between the electrodes sandwiching the vehicle body panel. Shed. Welding timer 136
When the welding time is up, the supply of welding current is stopped and spot welding is completed (S1).
1). Note that while the welding current is flowing, the power supply unit 260
The application of voltage to the jig 100 and the fixed-side electrode 132 due to is stopped.

On the other hand, when the coordinates of the obtained hitting point position are not the coordinates of the correct hitting point position, or when the coordinates of the hitting point position cannot be found because the current cannot be detected (S9: NO), equipment control unit 240
Outputs a welding position defect signal to the alarm unit 250, and the alarm unit 250 issues an alarm. By this alarm, the operator confirms that the spot welding position at which spot welding is about to be performed is out of the predetermined spot welding position and that the spot welding position is different from the predetermined welding sequence. Can be known (S1
2).

In this case, even if the operator operates the welding switch 134, only the alarm sounds and the spot welding gun 130 itself does not operate. Therefore, spot welding is performed at a welding point position deviated from a predetermined welding point position. Will not be performed, and spot welding will not be performed at a welding point position that does not follow a predetermined welding sequence. Further, since the vehicle body panel is not pressed by the electrodes of the spot welding gun 130 before the spot welding, the panel deformation can be prevented.

Next, a process for determining which position of the vehicle body panel W the fixed-side electrode 132 of the spot welding gun 130 is in contact with, that is, a process for determining a hitting point position will be described. FIG. 4 is a flowchart showing the processing for obtaining the hit point position. This flowchart is a subroutine flowchart for explaining in detail the processing of S7 of the flowchart shown in FIG.

In the processing shown in this flow chart, the coordinates of the hitting point position are obtained by using the known MTS (Mahalanobis Taguchi system) method. First, based on the design drawing, the vehicle body panel W (assembled state) to be spot-welded is mapped to a mapping area on a computer prepared in advance (S21). Next, as shown in FIG. 5, the coordinates of the respective intersections of straight lines (lattice lines) drawn in a lattice pattern on the mapping area are determined. This intersection is the coordinate Aij (Xi
j, Yij). Here, i and j have shown the row number and the column number. Similarly, as shown in FIG. 5, the coordinates of the intersection of each grid line and the outline of the vehicle body panel W are obtained. This intersection is the coordinate Bij (Xij, Yij) of the end point. Next, the welding point position (welding point) stored in advance in the storage unit 220 and the welding position tolerance allowable range D centered on the coordinates of the welding point position are mapped as shown in FIG. The coordinates of the position are obtained, and the welding position tolerance allowable range D of each welding point position is converted into coordinates (S22).

Next, the fixed side electrode 132 of the spot welding gun 130 is actually brought into contact with each other at each coordinate grid point, each end point, each welding point position, and the welding position tolerance permissible range D of each welding point position, and at that time, the toroidal coil 110a. The current value detected by ~ 110i is digitized and stored. The measured number n of the current value at this time is 3 which is the number of toroidal coils.
It is desirable that the number is twice or more. In the case of the present embodiment, since the toroidal coils are provided at nine places, it is desirable that the number of measured current values is 27 or more (S23).

From the current value obtained by the above measurement, M
Create reference space data based on the TS method. Then, the data is standardized to create a database. That is, each coordinate grid point, each end point, a normal welding point position within each welding position tolerance allowable range, and a current value of each toroidal coil at each point are stored in a database. in this way,
The reason why the current values at points other than the current value relating to the dot position are also stored in the database is to improve the calculation position accuracy of the dot position (S24).

Next, the Mahalanobis distance based on the MTS method is calculated. The Mahalanobis distance can be calculated by the following formula (S25).

[0047]

[Equation 1]

In the above equation, D ² is the Mahalanobis distance, a is the inverse matrix of the standard space data, and
I is the actual measurement value of the current detected by each toroidal coil, K is the number of toroidal coils (9 in this embodiment), m is the average value of the actual measurement value of the current detected by each toroidal coil, σ is the standard deviation, and the subscript i and j indicate the rows and columns of the inverse matrix a (in the present embodiment, i is the number of items, that is, the number of toroidal coils, and j is the number of data n).

Then, in order to use the optimum data among the data detected by the toroidal coil, FIG.
Create an experimental design example as shown in. No. in the figure. Indicates the number of experiments, and I1 to I7 indicate the current values detected by the seven toroidal coils. In this embodiment, nine toroidal coils are provided as shown in FIG. 1, but in this experimental design example, the current values of seven toroidal coils are described. This is to explain the contents of the invention in an easy-to-understand manner, and the current values of the nine toroidal coils are actually used (S26).

Next, the fixed side electrode 132 is intentionally brought into contact with a position distant from the coordinates (position on the design drawing) of the predetermined hitting point position, and the current value detected by each toroidal coil at that time, The distance from the hit point position at that time is measured (S27).

Then, from the distance between the current value detected by each toroidal coil and the hitting position at that time, S
The / N ratio is calculated (S28).

A factor-effect diagram as shown in FIG. 7 is created based on this S / N ratio, and if there is a toroidal coil that is not necessary for determining the coordinates of the hitting point, the current value detected by that toroidal coil is excluded. . That is, the current value to be removed is set to the second level in FIG. 6 (S29).

Then, the Mahalanobis distance is obtained, and the distance is set as a threshold value (S30). By performing the above processing on all the above points, a database for obtaining the hitting point position based on the ratio of the currents flowing in the toroidal coils is created.

As described above, since it is possible to detect in real time which coordinate of the workpiece the fixed side electrode of the welding gun is in contact with, it is possible to perform spot welding even if the spots are densely packed in a very narrow place. The welding point position can be accurately grasped, and appropriate welding conditions can always be selected. In addition, an alarm is issued when a spot welding is attempted at a spot position deviating from the regular spot position, or when the spot position is not a spot position according to the welding sequence. It is possible to force the operator to spot weld the welding point positions in a predetermined order, and always maintain high welding quality. By detecting the excess and deficiency of the number of welding points, so-called human error can be completely eliminated. The dot position is calculated using information processing methods such as the neuro method and the MTS method based on the ratio of the current flowing through each jig post, so the measured values may vary slightly due to fluctuations in the power supply voltage and other fluctuation factors. You can get it accurately even when you do. Further, since it is not necessary to provide a sensor for grasping the welding point position of the welding gun, the operability of the welding gun is not deteriorated and the workability is improved.

[Brief description of drawings]

FIG. 1 is an overall view of a spot welding apparatus that performs spot welding on a vehicle body frame by an operator manually operating a spot welding gun.

FIG. 2 is a block diagram showing a schematic configuration of a spot welding control device according to the present invention.

FIG. 3 is a flowchart showing the operation of the spot welding control device according to the present invention.

FIG. 4 is a flowchart showing a process for obtaining a hit point position.

FIG. 5 is a diagram for explaining each coordinate grid point, each end point, each welding point position, and a welding position tolerance allowable range of each welding point position.

FIG. 6 is a diagram showing an example of an experimental design using an orthogonal table.

FIG. 7 is a factorial effect diagram created from the S / N ratio from the relationship between the current value detected by the toroidal coil and the coordinates of the hit point position.

[Explanation of symbols]

100 ... jig, 100a-100i ... jig post, 110a to 110i ... Toroidal coil, 120 ... Spot welding control device, 130 ... Spot welding gun, 132 ... Fixed side electrode, 134 ... Welding switch, 136 ... Welding timer, 210 ... A / D converter, 220 ... storage unit, 230 ... Arithmetic processing unit, 240 ... Equipment control unit, 250 ... alarm unit, 260 ... power supply section, W ... Body frame.

Claims (5)

[Claims] 1. A plurality of supporting means for supporting a work, a welding gun for spot welding the work, a welding gun, a plurality of work guns, which are formed when electrodes of the welding gun are brought into contact with the work. Voltage applying means for applying a voltage to a closed circuit consisting of a supporting means and a path leading to the welding gun, and a current for detecting a current flowing through each of the plurality of supporting means when the electrode of the welding gun is brought into contact with a workpiece. A spot welding control device comprising: a detection unit; and a contact position calculation unit that calculates a contact position of the electrode of the welding gun with respect to the workpiece based on a current flowing through each of the plurality of support units. 2. The contact position calculating means calculates the contact position, which is a spot welding position of spot welding, from the ratio of the currents flowing through the plurality of supporting means, respectively. Spot welding control device. 3. A spot welding position storing means for storing a spot welding spot position of the workpiece, and a spot welding spot position calculated by the contact position calculating means are stored in the spot welding position storage means. The spot welding control device according to claim 2, further comprising: a welding point position alarm means for issuing an alarm when the welding position is out of the welding point position. 4. Further, welding condition storage means for storing welding conditions for each spot welding spot position, and welding conditions for selecting the welding condition based on the spot welding spot position calculated by the contact position calculator. 3. The spot welding control device according to claim 2, further comprising a selection unit and a welding current supply unit that supplies a welding current to the welding gun to perform spot welding under the selected welding conditions. 5. A welding sequence storage means for storing a welding sequence of spot welding positions for spot welding, and a spot welding spot position calculated by the contact position calculating device is not a spot welding position according to the welding sequence. The spot welding control device according to claim 3, further comprising: a welding sequence alarming means for issuing an alarm at times.