JP2708361B2 - How to create electrode tip wear control data - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for creating electrode tip wear amount management data for managing the wear amount of each electrode tip constituting a resistance welding machine.

[0002]

2. Description of the Related Art A resistance welding machine for automatically performing a welding operation by sequentially moving a welding gun mounted on a robot to a plurality of welding points of a workpiece has been widely used. In this type of resistance welding machine, a plurality of welding operations are performed on the work by sandwiching each welding point position of the work with a pair of electrode tips, and a dressing operation is performed on the electrode tips for each desired number of welding points. In addition, a loss (abrasion) due to wear or cutting occurs in the electrode tip.

Therefore, in order to manage the amount of wear of the electrode tip, the closed position of the welding gun when an unused electrode tip is attached, that is, the degree of opening is stored, and a preset value is set based on the degree of opening of the welding gun. When it is detected that the amount of wear has been reached, a signal indicating the replacement time of the electrode tip is output, and the operation of replacing the electrode tip is performed.

[0004]

By the way, a pair of electrode tips are mounted on the welding gun, and these electrode tips have different wear amounts due to impact at the time of pressurization or application of welding current. There are many. Further, when one of the electrode tips comes off, only the electrode tip on the side from which the electrode tip has come off is replaced with a new electrode tip, and the other electrode tip is reused during the wear.

Therefore, the setting of the replacement time of the electrode tip corresponds to the amount of wear until one of the electrode tips reaches the wear limit at the earliest time. The other usable electrode tip must also be replaced. If the other usable electrode tip is continuously used, the other electrode tip continuously used before reaching the next limited replacement time exceeds the wear limit, and a sufficient pressing force can be obtained. This is because there is a problem that the cooling water does not exist or the cooling water hole is reached. As a result, it has been pointed out that each electrode tip cannot be used efficiently.

SUMMARY OF THE INVENTION The present invention has been made in order to eliminate such a problem, and it is possible to reliably and easily manage the amount of wear of each electrode tip and to efficiently utilize each electrode tip. It is an object of the present invention to provide a method of creating wear amount management data for an electrode tip, which can perform the method.

[0007]

In order to achieve the above object, the present invention provides a resistance welding machine for performing a welding operation by closing an electrode tip corresponding to a welding point of a workpiece.
A method for preparing a wear amount management data for managing a wear amount of the electrode tip, comprising: a step of setting a wear limit value and a first replacement wear value of the electrode tip in advance; After performing the dressing operation of the electrode tip, the amount of wear of the electrode tip is reduced to the first level.
Generating a first replacement signal for the electrode tip when the replacement replacement wear value is reached, and using the actual wear amount of the electrode tip before replacement and the number of dressings or welding spots at that time. Generating a change characteristic of the amount of wear of the electrode tip with respect to the number of times of use, and setting a use number limit prediction value of the electrode tip corresponding to the wear limit value based on the change characteristic. When,
Calculating a second replacement wear value from the change characteristic corresponding to an intermediate value between the set use count limit predicted value and the use count at the first replacement, and calculating the second replacement wear value. The first replacement wear value is changed and newly set, and the electrode tip after replacement is sequentially subjected to each of the above-described steps based on the second replacement wear value to set a new use frequency limit predicted value. And when the new use count limit prediction value is the same as the previous use count limit prediction value, the process corresponds to an intermediate value between the new use count limit prediction value and the use count in the second replacement. Calculating a third replacement wear value from the change characteristic and sequentially performing the above-described steps.

Each of the above steps is sequentially repeated a predetermined number of times, and when the use count limit predicted value updated each time changes, the minimum number of use times of the use count limit predicted values is changed. It is preferable to use a marginal predicted value.

Further, the above-mentioned steps are sequentially repeated a predetermined number of times, and when the use count limit predicted value updated each time changes, the number of times is obtained from the latest updated N times measurement results. It is preferable to adopt the lower limit of the 3σ (standard deviation) limit as the use count limit predicted value.

[0010]

In the electrode tip wear amount management data creating method according to the present invention, when the electrode tip wear amount reaches the first replacement wear value, the actual wear amount and the number of times of use of the electrode tip are detected, A change characteristic of the amount of wear of the electrode tip is created, and based on the change characteristic, a predicted value of the number of times of use of the electrode tip is set. Next, a second value is set based on an intermediate value between the use count limit predicted value and the use count at the time of the first replacement.
The replacement exchange wear value is set, and the usage count limit predicted value is newly set and updated according to the same procedure. If the updated use count limit predicted value is the same as the previous use count limit predicted value, the above procedure is repeated. As a result, it is possible to easily obtain an extremely accurate use limit prediction value, and it is possible to use the electrode tip efficiently, and to reliably prevent problems such as using the electrode tip beyond its wear limit. can do.

On the other hand, when the usage count limit prediction value updated each time changes, the minimum usage count limit prediction value or the lower limit of the 3σ limit obtained from the latest N measurement results is updated. By setting the number of times of use as the predicted value of the number of times of use, it is possible to reliably prevent the electrode tip from being used beyond the wear limit.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a method for preparing data for managing the amount of wear of an electrode tip according to the present invention.

FIG. 1 is a block diagram showing the overall configuration of a resistance welding machine 10 for carrying out the method of the present invention. The resistance welding machine 10 includes a welding gun 12 and the welding gun 1
2 is attached to the tip of the arm of the robot (not shown). A transformer 16 is mounted on the bracket 14, and a pair of upper and lower gun arms 20, 2
2 is swingably supported.

Electrode tips 24 and 26 are detachably attached to the tips of the gun arms 20 and 22, respectively.
A pair of output terminals of the transformer 16 are connected to 0 and 22 via an ounce copper plate (not shown). Gun arm 20
A pressurizing cylinder 28 is fixed to the rear end side. One end of a connecting piece 32 is engaged with a rod 30 extending downward from the pressurizing cylinder 28, and the other end of the connecting piece 32 is connected to a gun arm 22 via a pin 34. And the first link piece 36. The first link piece 36 engages with the second link piece 40 via the pin 38, and the pin 38
You will be guided to 2. The second link piece 40 is connected to the gun arm 20.
At the rear end.

The pressurizing cylinder 28 includes a pneumatic servo circuit 44.
The pneumatic servo circuit 44 includes a servo valve 48 controlled by a servo amplifier 46 and a regulator 52 controlled by a driver amplifier 50. The pressurizing cylinder 28 has a pressure sensor 54 for detecting the pressing force of the welding gun 12 from the pressure in one of the chambers, and the gun arm 2 based on the displacement of the rod 30.
An opening sensor 56 for detecting the opening of 0 and 22 (the distance between the electrode tips 24 and 26) is provided. The opening degree sensor 56 is composed of, for example, a magnetic potentiometer including a magnetic scale attached to the rod 30 and a pickup coil.

The gun arm 2 detected by the opening sensor 56
The opening degrees of 0 and 22 are input to the electrode wear amount calculating means 60 via the A / D converter 58. The amount of wear (amount of wear) of each of the electrode tips 24 and 26 calculated by the electrode wear amount calculating means 60 is input to a CPU 62 constituting a pressure controller 63, and the CPU 62 From the respective wear amounts, a change characteristic straight line (described later), which is wear amount management data of the electrode tips 24 and 26, is created.

A signal from the pressure sensor 54 is input to a CPU 62 via an A / D converter 61,
The CPU 62 supplies a pressure command signal and a pressure setting signal to the servo amplifier 46 and the driver amplifier 50 via the D / A converters 64 and 66. CPU62
Is a read-only memory (hereinafter referred to as ROM) 68 in which programs for controlling the opening degrees and pressures of the gun arms 20 and 22 and creating a change characteristic line are stored.
And welding condition data corresponding to each of the hitting positions, that is, the welding current and the energizing time, the pressing force, the opening set value corresponding to the thickness of the work W at the hitting position, and the opening of the gun arms 20 and 22 after welding. A readable / writable memory (hereinafter, referred to as a RAM) 70 for temporarily storing data such as the degree, and a wear limit setting means 72 for presetting a wear limit of each of the electrode chips 24 and 26 are provided. .

A setting signal for the welding current and the energizing time is transmitted from the CPU 62 to the transformer 16 via the energizing control circuit 74, so that the electrode tips 24 and 26 are energized at a predetermined current value for a predetermined time. The CPU 62 receives an input of a determination signal of the hitting position from the robot controller 76,
From 70, welding condition data corresponding to the hitting position at which the welding gun 12 arrives is read. Robot controller 7
The welding controller 82 is communicable with the pressure controller 6 and the pressure controller 63.

In the resistance welding machine 10 configured as described above, a change characteristic straight line (wear amount management data) of the electrode tips 24 and 26 is created based on the wear amount management data creation method according to the present embodiment. While controlling the wear amount of the electrode tips 24 and 26, the work W
2 and 3 will be described with reference to the flowcharts of FIGS.

First, the unused electrode tips 24, 26 are mounted on the gun arms 20, 22, and the wear limit P of the electrode tips 24 and the wear limit Q of the electrode tips 26 are inputted to the wear limit setting means 72. It is, is set as the wear limit P content 1st exchange amount of wear of the electrode tip 24 (1st exchange wear amount) S ₁ to premature wear (see steps S1 and Figure 4).

When the arrival of the welding gun 12 at the standby position is confirmed by a signal from the robot controller 76, a pressure command signal is input from the CPU 62 to the servo amplifier 46 via the D / A converter 64. For this reason, air is supplied to the pressurizing cylinder 28 and the gun arm 2
The pins 0 and 22 swing (close) in synchronization with each other in a direction approaching each other with the support shaft 18 as a fulcrum. At the time of this idling, the opening degree sensor 56 detects the displacement of the rod 30 from the gun arms 20 and 2.
The opening is detected by the CPU 62 via the A / D converter 61, and the opening is stored in the RAM 70 as a reference opening (steps S2 and S3).

[0022] Then, in step S4, after the number of welding operations initialization performed by N _W and dressing number N _D is reset, the welding operation is started (step S
5). That is, when the signal from the robot controller 76 confirms that the welding gun 12 has reached the welding point of the workpiece W via a robot (not shown),
The welding condition data corresponding to this welding point is stored in RAM7.
It is read from 0. Then, a pressurizing command signal is input from the CPU 62 to the servo amplifier 46 via the D / A converter 64, and a pressure setting signal is input to the driver amplifier 50 via the D / A converter 66, and the servo valve 48 Pressurizing cylinder 2 via
Air is supplied to 8. Thereby, the gun arm 20,
22 starts the closing operation.

When the electrode tips 24 and 26 of the gun arms 20 and 22 hold the work W, the pressure for holding the work W is increased based on the signal output from the CPU 62, and the initial pressurization is started. The initial pressurization is performed for a predetermined time. At this time, a setting signal of the welding current and the energization time is transmitted from the CPU 62 to the energization control circuit 74, and a current is applied between the electrode tips 24 and 26 at a predetermined current value for a predetermined time, and welding is performed at a predetermined welding point of the workpiece W. Done.

[0024] welding at the predetermined welding point is finished, the welding spot number N _W is +1 (step S6), and the updated welding point number N _W is compared with the set number of RBI required dressing (Step S7). Here, if it is determined that dressing is necessary (YES in step S7), the process proceeds to step S8, and the electrode tips 24 and 26 are performed.
Dressing operation is performed, the dressing number N _D is +1 (step S9).

After the dressing, the amount of wear of the entire electrode tips 24 and 26 is automatically detected from the opening of the welding gun 12 (step S10).
The total wear amount is the first replacement wear amount S ₁ (wear limit amount P)
Is reached (YES in step S11),
A first exchange notification alarm (first exchange signal) is output (step S12). Further, the opening before the replacement of the electrode tip 24 and the opening after the replacement of the electrode tip 24 are detected through steps S13 to S15.

That is, before the replacement, the welding gun 12 is closed and the electrode tips 24 and 26 are hit, and the opening of the welding gun 12 at this time is detected (step S13), and the electrode tips 24 and 26 are detected. When the pre-replacement remaining wear amount C ₁ is detected from the wear limit remaining amounts P ₁ and Q ₁ (see FIG. 5), the pre-replacement remaining wear amount C ₁ is stored in the RAM 70. Then, the electrode tip 24 is exchanged for an unused electrode tip 24 (step S14), the welding gun 12 is closed, and the unused electrode tip 24 and the used electrode tip 26 are blanked, and the welding is performed. The opening of the gun 12 is detected (step S15).

As a result, as shown in FIG. 6, the remaining wear amount C ₂ (= P + Q ₁ ) after replacement is detected, and the remaining wear amount C ₁ before replacement is subtracted from the remaining wear amount C ₂ after replacement. While the actual amount of wear Y _U (= P-P ₁ ) of the electrode tip 24 is calculated, the remaining amount of wear C ₂ after replacement is subtracted from the remaining amount of wear S ₀ when not in use, so that the electrode tip 26 has a smaller amount of wear. the actual amount of wear _{Y L (= Q-Q 1} ) is calculated (step S15).

Here, the amount of wear of the electrode tips 24 and 26 increases substantially in proportion to the number of welding points and the number of dressings. Since the dressing operation is performed every time the welding operation reaches a certain number of points, the electrode tips 24, 26
Can be expressed by a relational expression only of the number of times of dressing (the number of times of use), as shown by the following equation (1).

Electrode tip wear = T _CNT (number of dressings) × δ (coefficient) (1) In equation (1), δ is the number of dressings on the horizontal axis and the amount of electrode tip wear on the vertical axis. Is a coefficient corresponding to the slope of the change characteristic straight line. Therefore, in order to obtain a change characteristic line between the number of times of dressing of the electrode tip 24 and the electrode tip 26 and the amount of wear thereof, the inclination δ _U of the change characteristic line of the electrode tip 24 and the electrode tip 2
The slope δ _L of the change characteristic line of No. 6 is calculated by the following equation (2).
What is necessary is just to calculate from Formula (3).

Δ _U = amount of wear Y _U / T _CNTM (2) δ _L = amount of wear Y _L / T _CNTM (3) (However, T _CNTM is obtained when the amounts of wear Y _U and Y _L are obtained. Thus, as shown in FIG. 7, change characteristic lines H _U and H _L between the number of times of dressing of the electrode tip 24 and the electrode tip 26 and the amount of wear are obtained (step S17). In this case, since the wear limit amounts P and Q of the electrode tips 24 and 26 are set in advance, the estimated dressing times (use count limit predicted values) corresponding to the replacement time of the electrode tips 24 are set.
T _CNTU and the predicted dressing count (use count limit predicted value) T corresponding to the replacement time of the electrode tip 26
_{The CNTL} can be predicted and set from the following equations (4) and (5) (step S18).

T _CNTU = P / δ _U (4) T _CNTL = Q / δ _L (5) Next, it is determined whether or not the number of replacements of the electrode tip 24 is the first time (step S 19). If it is determined that this is the first time (YES in step S19), step S
Proceed to 21. For the sake of simplicity, the procedure for creating management data for the electrode chip 24 will be described in detail below.

That is, as shown in FIG. 8, the estimated dressing number T corresponding to the wear limit amount P of the electrode tip 24.
When _CNTU is set, the prediction dressing number T dressing number T _CNT1 of the electrode tip 24 at the time of exchanging the first time
_An intermediate value T _CNT2 with _CNTU is calculated, and a wear amount corresponding to the intermediate value T _CNT2 on the change characteristic line H _U , that is, a second replacement wear amount S ₂ is calculated (step S21).

Furthermore, welding point speed and the dressing of times about the electrode tip 24, which is exchanged is reset (step S22), and 2nd replacement wear amount S ₂ as a reference, step S5 to step from step S23 the newly set Proceeding to S17, a new change characteristic line H _U is created. Then, based on the new change characteristic line H _U , a predicted dressing number T _CNTU corresponding to the time when the electrode tip 24 is replaced is calculated (step S18).

Here, since the electrode tip 24 is the second replacement (NO in step S19), step S2 is performed.
Proceeding to 0, the predicted dressing count T _CNTU calculated this time
Is compared with the previously calculated estimated number of dressings T _CNTU, and if they are determined to be the same (step S
(YES in 20), the process proceeds to step S21. In step S21, intermediate values T _CNT3 dressing number (median) T _CNT2 and the predicted dressing number T _CNTU of the two changes at the electrode tip 24 is calculated, the change characteristic line H _U
, The amount of wear corresponding to the intermediate value T _CNT3 , that is, the third replacement wear amount S ₃ is calculated.

Then, from step S22 to step S2
3, the management data is created in accordance with a predetermined program, and while the welding work of the work W is performed by the welding gun 12, the electrode tips 2 are formed in accordance with the management data.
The amount of wear is managed at 4, 26.

On the other hand, in step S20, the current calculation
Predicted dressing count T_CNTUAnd the last calculated
Number of dressing times T_CNTUIs determined to be different
(NO in step S20), the predetermined program ends.
It is determined whether or not it has occurred (step S24). Predetermined professional
When the gram is not completed (NO in step S24),
In step S25, the first replacement wear amount S₁Is set again
Next change characteristic line H _UIs performed.

[0037] Incidentally, work of creating the variation characteristic line H _U is performed by a desired number of times, when each time different prediction dressing number T _CNTU 9 was obtained, the prediction dressing number T _CNTU in step S26 The calculation work is performed by, for example, first and second methods described below. That is, the first method, in the different prediction dressing number T _CNTU, earliest wears adopted predicted dressing number T _CNTU to exchange notified alarm when reached the predicted dressing number T _CNTU this minimum value is output To be controlled. This is for surely preventing the wear amount of the electrode tip 24 from exceeding the wear limit amount P. Next, the second method is to take the 3σ (standard deviation) limit of the average change characteristic line H ′ _V obtained by the latest updated N measurements, and to calculate the average predicted dressing count T corresponding to the lower limit. ' _CNTU -3σ is adopted. This makes it possible to effectively secure the safety of the electrode tip 24.

As described above, in the present embodiment, the wear amount management data of each of the electrode tips 24 and 26 is created while actually performing the welding operation and the dressing operation on the work W via the electrode tips 24 and 26, and By managing the amount of wear of each of the electrode tips 24 and 26 in accordance with the amount management data, an effect is obtained in which the replacement time of each of the electrode tips 24 and 26 can be accurately predicted and set.

Moreover, the time for replacing the electrode tips 24, 26
Dressing count T corresponding to _CNTUIs a single measurement
And not obtained from the operation, as shown in FIG.
First measured wear value S₁, 2nd replacement wear
S_TwoAnd the third replacement wear amount S_ThreeAs soon as possible
Measurement several times while approaching the wear limit P
It is set by performing a calculation. Therefore,
Precisely and reliably predict when to replace pole tips 24 and 26
And the amount of wear of the electrode tips 24 and 26 can be reduced.
Even if different, each electrode tip 24, 26 has its own wear
It is possible to utilize it to the limit efficiently.

On the other hand, as shown in FIG. 9, when the different prediction dressing times T _CNTU calculated every time, earliest abrasion predicting dressing number T _CNTU or N times the mean change characteristic line H 'of _U, By taking the lower limit change characteristic line H ′ _U −3σ of the 3σ limit and adopting the average predicted dressing number T ′ _CNTU −3σ corresponding to this, there is an advantage that the safety can be improved.

Further, it is determined whether or not the total wear amount of the electrode tips 24 and 26 has reached the first replacement wear amount S ₁ , the second replacement wear amount S _2, the third replacement wear amount S _{3, and the} like. Can be automatically detected from the opening of the welding gun 12. Thus, if the replacement work of the electrode tips 24 and 26 is performed by the automatic replacement device, a remarkable effect is obtained that the entire welding process including the management work of the electrode tips 24 and 26 can be easily performed.

If the number of times of dressing calculated according to the replacement time does not become an integer, a process of rounding down the decimal point is performed in consideration of safety. Although the wear amount of the electrode tips 24 and 26 is represented by a relational expression of only the number of times of dressing, the number of welding points may be adopted as the number of times of use instead of the number of times of dressing.

[0043]

According to the electrode tip wear amount management data creating method of the present invention, when the electrode tip wear amount reaches the first replacement wear value, the actual wear amount and the number of times of use of the electrode tip are detected. Then, a change characteristic of the amount of wear of the electrode tip is created, and a use count limit predicted value of the electrode tip is set. Next, a second replacement wear value is set based on an intermediate value between the usage count limit predicted value and the usage count at the first replacement, and a usage count limit predicted value is newly set according to the same procedure. . If the newly set use count limit predicted value is the same as the previous use count limit predicted value, the above procedure is repeated. As a result, the replacement wear value is successively updated by approximating the wear limit value, so that an extremely accurate use count limit predicted value can be easily obtained, and the electrode tip can be used efficiently, and Problems such as using the electrode tip beyond its wear limit can be reliably prevented.

On the other hand, when the usage count limit prediction value updated each time changes, the minimum usage count limit prediction value or the lower limit value of the 3σ limit obtained from the latest updated N measurement results is used. By setting the number of times of use as the predicted value of the number of times of use, it is possible to reliably prevent the electrode tip from being used beyond the wear limit.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a resistance welding machine that performs a method of the present invention.

FIG. 2 is a flowchart for explaining the method of the present invention.

FIG. 3 is a flowchart for explaining the method of the present invention.

FIG. 4 is an explanatory diagram of an initial state of an electrode tip in the method of the present invention.

FIG. 5 is an explanatory view showing a state where the amount of wear of the entire electrode tip reaches a wear limit in the method of the present invention.

FIG. 6 is an explanatory view showing a state in which one electrode tip is replaced in the method of the present invention.

FIG. 7 is a graph showing the relationship between the amount of electrode tip wear and the number of dressings in the method of the present invention.

FIG. 8 is an explanatory diagram of a change characteristic straight line in a case where the number of predicted dressings is the same each time in the method of the present invention.

FIG. 9 is an explanatory diagram of a change characteristic straight line when the number of times of prediction of dressing is different each time in the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Resistance welding machine 12 ... Welding gun 20, 22 ... Gun arm 24, 26 ... Electrode tip 28 ... Pressurizing cylinder 44 ... Pneumatic servo circuit 54 ... Pressure sensor 56 ... Opening sensor 60 ... Electrode wear amount calculation means 62 ... CPU 63 ... pressure controller 72 ... wear limit setting means 76 ... robot controller 82 ... welding controller H _U, H _L ... change characteristic line P, Q ... wear limit amount

Claims (3)

(57) [Claims] 1. A method for producing wear amount management data for managing a wear amount of an electrode tip in a resistance welding machine which performs welding work by closing an electrode tip in accordance with a welding point of a workpiece. A step of presetting a wear limit value and a first replacement wear value of the electrode tip; and performing a welding operation using the electrode tip and a dressing operation of the electrode tip. Generating a first replacement signal for the electrode tip when the replacement wear value is reached; and the actual wear amount of the electrode tip before replacement and the number of times of use, which is the number of dressings or welding spots at that time. Detecting the change in the amount of wear of the electrode tip with respect to the number of times of use, and the number of times of use of the electrode tip corresponding to the wear limit value based on the change characteristic. Setting a number limit predicted value; and calculating a second replacement wear value from the change characteristic corresponding to an intermediate value between the set usage count limit predicted value and the number of uses in the first replacement. By changing the second replacement wear value to the first replacement wear value and newly setting the same, and sequentially performing the above-described steps on the electrode tip after replacement based on the second replacement wear value. Setting a new use count limit predicted value, and when the new use count limit predicted value is the same as the previous use count limit predicted value, setting the new use count limit predicted value and the second replacement time A method of calculating a third replacement wear value from the change characteristic corresponding to an intermediate value with the number of times of use, and sequentially performing each of the above-described steps, characterized by comprising the steps of: 2. The method according to claim 1, wherein each of said steps is sequentially repeated a predetermined number of times, and when the use count limit predicted value updated each time changes, said use count limit predicted value is changed. A method for creating electrode tip wear amount management data, wherein a minimum value of the usage limit prediction value is adopted. 3. The method according to claim 1, wherein each of the steps is sequentially repeated a predetermined number of times, and when the use count limit predicted value updated each time changes, the latest update N times. 3. A method for preparing electrode tip wear amount management data, wherein a lower limit value of a 3σ (standard deviation) limit obtained from the measurement result is used as a predicted value of a use frequency limit.