JP2001030083A - Welding equipment and welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely know an expansion magnitude of a nugget only by measuring an extent of the movement of an actuator. SOLUTION: In a welding equipment where an electrode tip 12A mounted on the tip of a welding gun arm 11 is moved by an actuator 18 and a welding is carried out while a welded work 1 is being pressurized, a storage circuit 26 which storages a static friction force required to begin a movement of the actuator 18, an CPU 21 which controls the actuator 18 so as to pressurize the welded work 1 with a generated force of the actuator 18 which is a summation of a welding pressurizing force and the static friction force at a primary pressurizing time, and thereafter to decrease the generated force of the actuator 18 by an amount of twice the static friction force before the beginning of the welding, and an encoder 19 which measures the amount of movement of the actuator 18, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding apparatus and a welding method, and more particularly, to a welding apparatus capable of detecting an expansion amount of a nugget from a moving amount of an actuator for pressing a member to be welded in resistance welding. And welding methods.

[0002]

2. Description of the Related Art Conventionally, in resistance welding represented by spot welding, as a method for judging the quality of the resistance welding in real time (during welding), the amount of expansion of a formed nugget is detected. .

[0003] The amount of expansion of the nugget is detected by measuring the amount of movement of an actuator that operates a welding gun. This is because the amount of movement of the actuator can be easily obtained from the value of the encoder attached to the actuator, and there is no need to separately install a pressure sensor or the like on the welding gun. It is because it is excellent.

[0004]

However, when the amount of expansion of the nugget is detected from the amount of movement of the actuator as described above, the force for pushing up the welding gun arm due to the thermal expansion of the nugget causes the rigidity of the welding gun arm and the movement of the actuator to start. The nugget expansion cannot be detected accurately because the arm does not move at all, or even if it moves, the response slows down until a force greater than the static friction force is applied because it is canceled by the necessary static friction force etc. There was such a problem.

Accordingly, an object of the present invention is to provide a welding apparatus and a welding method capable of accurately detecting the expansion amount of a nugget only by measuring the movement amount of an actuator.

[0006]

The object of the present invention is achieved by the following means.

(1) An actuator moves an electrode tip attached to the tip of a welding gun arm, and presses a member to be welded with the electrode tip to perform welding while pressurizing a member to be welded. Static friction force storage means that stores the force, at the time of initial pressurization, pressurizes the member to be welded as a force obtained by adding the static friction force to the welding force, and before welding starts, Actuator control means for controlling the actuator so as to reduce the generated force of the actuator by twice the static friction force, and movement amount measurement means for measuring the movement amount of the actuator,
A welding apparatus comprising:

(2) The static friction required for the actuator to start moving in a welding device that performs welding while moving the electrode tip attached to the tip of the welding gun arm by the actuator and pressing the member to be welded with the electrode tip. A static frictional force storage means for storing a force, and at the time of initial pressurization, pressurizing the member to be welded by making the generated force of the actuator higher than a force obtained by adding the static frictional force to a welding pressure, and thereafter starting welding. Before, the actuator control means for controlling the actuator so as to reduce the generated force of the actuator to a force obtained by subtracting the static friction force from the welding pressure, and a movement amount measuring means for measuring the movement amount of the actuator, A welding apparatus comprising:

(3) The static friction required for the actuator to start moving in a welding device that performs welding while moving the electrode tip attached to the tip of the welding gun arm by the actuator and pressing the member to be welded by the electrode tip. A static friction force storing means storing a force, an actuator control means for controlling the actuator so that the generated force of the actuator increases or decreases by the static friction force centering on a welding pressure after the welding is started; and A moving amount measuring means for measuring a moving amount of the actuator;

(4) A moving amount for measuring the moving amount of the actuator in a welding apparatus for performing welding while moving an electrode tip attached to the tip of a welding gun arm by an actuator and pressing a member to be welded by the electrode tip. Measuring means for increasing or decreasing the force generated by the actuator at the time of initial pressurization by an arbitrary force equal to or greater than the static frictional force required for the actuator to move around the welding force, and measuring the increase / decrease force The actuator is controlled such that the movement of the actuator measured by the means is gradually reduced until it stops, and after the welding is started, the generated force of the actuator is maintained at the increasing / decreasing force at the time when the movement of the actuator stops. A welding device comprising: an actuator control unit.

(5) In the welding device, the static friction force is such that the force generated by the actuator is gradually increased from zero in the positive direction, and the movement amount measuring means detects that the actuator has started moving. The generated force of the actuator is stored as a positive static friction force, the generated force of the actuator is gradually increased from zero in the negative direction, and the movement amount measuring unit detects that the actuator has started moving. The force generated by the actuator is stored as a negative static friction force, and the average value of the positive static friction force and the negative static friction force is stored in the static friction storage means. .

(6) In the welding method in which the electrode tip attached to the tip of the welding gun arm is moved by the actuator and welding is performed while the member to be welded is pressed by the electrode tip, the force generated by the actuator at the time of initial pressurization Pressurizing the member to be welded as a force obtained by adding a static friction force necessary for the actuator to start moving to the welding pressure, and after the pressurization, the force generated by the actuator is twice the static friction force. And reducing the generated force of the actuator by twice the static frictional force, and then starting welding, and measuring the amount of movement of the actuator after the start of welding. Characteristic welding method.

(7) In the welding method in which the electrode tip attached to the tip of the welding gun arm is moved by the actuator and welding is performed while the member to be welded is pressed by the electrode tip, the force generated by the actuator during the initial pressurization Pressurizing the member to be welded with a force higher than the sum of the welding force and the static friction force required for the actuator to start moving; and, after the pressing, the force generated by the actuator, And reducing the force to a force obtained by subtracting the static friction force, and the generated force of the actuator,
After reducing the force to a generated force obtained by subtracting the static friction force from the welding pressure, a step of starting welding, and a step of measuring a movement amount of the actuator after the start of the welding, comprising: Method.

(8) In the welding method in which the electrode tip attached to the tip of the welding gun arm is moved by the actuator and welding is performed while the member to be welded is pressed by the electrode tip, the force generated by the actuator is determined by the welding force. Increasing and decreasing the amount of static friction required for the actuator to start moving around, pressing the member to be welded, starting welding, and measuring the amount of movement of the actuator after the start of welding. Characteristic welding method.

(9) In the welding method in which the electrode tip attached to the tip of the welding gun arm is moved by the actuator and welding is performed while the member to be welded is pressed by the electrode tip, the force generated by the actuator during the initial pressurization is obtained. Is increased or decreased by an arbitrary force equal to or greater than the static friction force required for the actuator to start moving around the welding pressure, and pressurizes the member to be welded, and the amount of movement of the actuator is measured. Until the welding, the step of gradually decreasing the increase and decrease of the generated force of the actuator, and after starting the welding, starting the welding while maintaining the increase and decrease of the generated force of the actuator at that time, and Measuring the amount of movement of the actuator.

(10) In the welding method, the static friction force gradually increases the force generated by the actuator from zero in the positive direction, and reduces the force generated by the actuator when the actuator starts to move in the positive direction. Storing the frictional force, and gradually increasing the generated force of the actuator in the negative direction from zero, and storing the generated force of the actuator at the time when the movement of the actuator is detected as a negative static friction force. Stages and
Calculating an average value of the positive-direction static friction force and the negative-direction static friction force.

[0017]

According to the present invention described above, the following effects can be obtained for each claim.

According to the present invention as set forth in claims 1 and 6,
During initial pressurization, the force generated by the actuator is increased by the static friction force, and the force generated by the actuator is reduced by twice the static friction force at the stage before welding. The force equivalent to the static friction force has been removed from the force that presses the member, and the actuator becomes easier to move.Then, when the nugget is thermally expanded, the welding gun arm is pushed up without being affected by the static friction force. be able to. Therefore, this is accurately reflected on the movement amount of the actuator, and the expansion amount of the nugget can be accurately detected.

According to the second and seventh aspects of the present invention,
At the time of initial pressurization, the member to be welded is pressed with an arbitrary force higher than the sum of the force generated by the actuator and the welding force plus the static friction force, and the static friction force is calculated from the welding force at the stage before welding. Since the generated force of the actuator was gradually reduced until it became the subtracted force, the force equivalent to the static friction force was removed from the force applied by the actuator to the welded member during welding. Since the actuator becomes easy to move, the welding gun arm can be pushed up without being affected by the static friction force when the nugget is thermally expanded. Therefore, this is accurately reflected on the movement amount of the actuator, and the expansion amount of the nugget can be accurately detected.

According to the third and eighth aspects of the present invention,
Since the generated force of the actuator during welding is increased or decreased by the static friction force centering on the welding pressure, when the generated force of the actuator increases, the actuator becomes easier to move by the increased force when the nugget contracts, Conversely, when the force generated by the actuator decreases,
When the nugget is inflated, the actuator becomes easier to move by the amount of the reduced force. The amount of contraction and the amount of expansion can be accurately detected.

According to the present invention as set forth in claims 4 and 9,
At the time of initial pressurization, the generated force of the actuator is increased or decreased by an arbitrary force greater than the static friction force centering on the welding pressure, and this increasing / decreasing force is gradually reduced until the movement of the actuator comes to a standstill. Since welding is performed while maintaining the force, when the generated force of the actuator increases during welding, when the nugget contracts, the actuator becomes easier to move by the increased force, and conversely, the generated force of the actuator decreases When the nugget is expanded, the actuator becomes easier to move by the reduced force when the nugget is inflated. , The amount of contraction and expansion of the nugget can be accurately detected. Further, according to the present invention, since the exact static friction force may not be known, the effect of the static friction force can be easily eliminated by the operation.

According to the fifth and tenth aspects of the present invention, the force generated by the actuator is gradually increased from zero in the positive direction, and the force generated by the actuator at the time when the actuator starts moving is obtained as a positive static friction force. On the other hand, the generated force of the actuator is gradually increased in the negative direction from zero, and the generated force of the actuator at the time when the actuator starts to move is obtained as a negative static friction force, and the obtained positive static friction force and negative static friction force are calculated. Since the average value is the static friction force, an accurate static friction force can be obtained with a simple operation.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

Embodiment 1 FIG. 1 is a block diagram showing the overall configuration of a welding device according to the present invention.

This welding device comprises a welding gun 10 and a control device 20. The welding gun 10 comprises a welding gun arm 11,
It comprises electrode tips 12A and 12B, a servomotor 18 (hereinafter simply referred to as a motor), and an encoder 19. On the other hand, the control device 20 includes a CPU 21, a servo control circuit 22, a movement amount detection circuit 24, a current control circuit 16, and a storage circuit 26. A power supply circuit 15 is connected to the electrode chips 12A and 12B.

The welding gun arm 11 is moved up and down by a motor 18 as an actuator.
The electrode tip 12A attached to the tip of the member 1 presses the member 1 to be welded with a predetermined welding pressure required for welding by the generated force (torque) of the motor 18. An encoder 19 is attached to the motor 18 as a movement amount measuring means, and the encoder 19 measures the movement amount (rotation amount) of the motor 18.

The motor 18 is controlled by a servo control circuit 22 that operates based on a command from the CPU 21.

The movement amount detection circuit 24 calculates the movement amount of the motor 18 measured by the encoder 19
2 to determine the amount of movement of the electrode tip 12A. The amount of movement of the electrode tip 12A is determined based on the encoder output value at the time when a predetermined pressing force is applied after the electrode tip 12A abuts on the workpiece 1 at the time of initial pressurization (before starting welding), as a reference position The value when the output value of the encoder changes is subtracted therefrom to obtain the value. In addition, there are various other methods such as setting a reference position separately and subtracting an encoder output value from the reference position.

The amount of movement of the electrode tip 12A obtained here is sent to the CPU 21, where the size of the nugget is detected from the amount of movement of the electrode tip 12A, and the quality of welding is determined. The movement amount of the electrode tip 12A is fed back to the servo control circuit 22 for controlling the position of the motor 18.

The storage circuit 26 stores the motor 1 determined in advance.
It stores the static friction force (details described later) necessary for the 8 to start moving, welding conditions (welding pressure, welding current, energizing time), and the like. Therefore, welding is performed under optimum welding conditions based on the information stored in the storage circuit 26.

The outline of the welding operation by this welding apparatus is as follows.
A and 12B are pressed with a predetermined welding pressure, and in this pressed state, the power supply circuit 1 is instructed by the current control circuit 16.
From 5, a welding current is supplied to both electrode tips 12A and 12B, and welding is started. When welding is started, a nugget starts to be formed at a welding point on the member 1 to be welded, and the member is melted and thermally expanded. At this time, if the force due to the expansion of the nugget is larger than the welding pressure, the electrode tip 12A is pushed up. Thereafter, when the power supply to the electrode tips 12A and 12B is stopped, the nugget contracts. By repeating the expansion and contraction for a predetermined time (welding time), an appropriate nugget is formed, and the welding is completed. Electrode tip 12A due to expansion or contraction of the nugget during this welding
Is measured by the encoder 19 as the movement amount (rotation amount) of the motor 18.

When the electrode tip 12A is pressed against the member 1 to be welded and the torque of the motor 18 is increased, the welding gun arm 11 bends due to its rigidity. It comes to rest in a state where it is balanced with the deflection. When welding is started in this state, the amount of bending of the welding gun arm 11 increases momentarily due to thermal expansion of a nugget formed on the member 1 to be welded. At this time, the balance between the pressing force and the deflection becomes unbalanced, and the electrode tip 12A is pushed back until the balance is balanced. However, the force due to the thermal expansion of the nugget
If the arm 8 is weaker than the static friction force necessary to start moving, the motor 18 does not start moving because the bent arm does not extend beyond the static friction force, and therefore the thermal expansion of the nugget is performed by the encoder 19. , The movement of the electrode tip 12A cannot be detected.

Further, even if the force due to thermal expansion is stronger than the static friction force required for the motor 18 to start moving, it becomes a force to bend the arm until this force becomes stronger than the static friction force. When the bent arm is extended, the motor 18 moves and the encoder 19 controls the electrode tip 12.
It is detected as the movement amount of A. Therefore, in this case, the electrode tip 12A detected by the encoder 19
Will be delayed from the time when the nugget is actually expanded.

The static frictional force obstructing the measurement of the expansion of the nugget varies depending on various factors.
The static friction force is, for example, the mass of a movable member such as the motor 18 and its rotating shaft, the welding gun arm 11, the electrode tip 12A, and the attached encoder 19, the sliding resistance with the member supporting the welding gun arm 11, It changes depending on the viscosity of oil applied (or filled) to the mechanical components. Of these, the weight of the movable members is known because the weight of those members is known, so that it is possible to predict to some extent the static friction force resulting therefrom. However, it is difficult to accurately predict the sliding resistance and the oil viscosity in advance because the sliding resistance and the oil viscosity change due to time changes, environmental temperature, and the like.

Therefore, in this embodiment, first, the static friction force is detected in advance.

FIG. 2 is a flowchart showing a procedure for detecting the static friction force.

The detection of the static friction force is performed by the CPU 21 executing a program for detecting the static friction force. First, according to a command from the CPU 21, the torque F of the motor 18 is set to 0 (S1), and the torque F of the motor 18 is gradually increased in the forward direction (the direction in which the electrode tip 12A descends).
(S2).

Then, the movement of the motor 18 is monitored by the encoder 19, and it is detected whether or not the motor 18 has started moving (S3). Here, if the movement of the motor 18 is not detected (S3, No). Returning to step S2, the motor 18
Continue to increase the torque F. On the other hand, if the movement of the motor 18 is detected (S3, Yes), the torque F at that time is stored as the positive static friction force Fp (S4).

Subsequently, the torque F of the motor 18 is set to 0 again (S5), and thereafter the torque F of the motor 18 is gradually increased in the negative direction (the direction in which the electrode tip 12A rises) (S6).

Then, the movement of the motor 18 is monitored by the encoder 19, and it is detected whether or not the motor 18 has started moving (S7). Here, if the movement of the motor 18 is not detected (S7, No). Returning to step S6, the motor 18
Is increased. On the other hand, if the movement of the motor is detected (S7, Yes), the torque F at that time is stored as the negative static friction force Fn (S8).

Subsequently, the average (Fp + Fn) / 2 of the stored positive static friction force Fp and negative static friction force Fn is obtained and stored in the storage circuit 26 as the static friction force Fs (S9).

The detection of the static friction force is most preferably performed every time before the start of welding. However, this may reduce the operating efficiency of the welding process. May be performed before welding or when tip dressing is performed.

Next, a description will be given of a welding procedure for accurately detecting the expansion amount of the nugget using the static friction force Fs obtained as described above.

FIG. 3 is a flowchart showing a welding procedure according to the first embodiment.

First, in response to a command from the CPU 21, the electrode tip 12A is lowered at a predetermined speed, and the torque of the motor 18 is set to the welding pressure + static friction force as the initial pressurization to apply the workpiece 1 to the welding. Press (S11). At this time, the electrode tip 12A comes into contact with the member 1 to be welded, and when a predetermined pressing force is applied, the member 1 to be welded and the electrode tip 12B come into contact with each other. Stand still in a balanced state.

Here, the welding pressure has a relationship as shown in the following equation (1).

Welding pressure = electrode pressure = motor torque−static friction force (1) Therefore, in order to apply a prescribed welding pressure to the member 1 to be welded, the torque of the motor 18 must be at least the welding pressure. + It is necessary to set the static friction force.

Specifically, for example, a welding pressure of 200 k
gf, if the static friction force is 10 kgf,
From the above equation (1), the torque of the motor 18 is required to be 210 kgf.

For this reason, in the first embodiment, the torque of the motor at the time of the initial pressurization is set to the welding pressure + the static friction force as in step S11.

Subsequently, the torque of the motor 18 is reduced by the amount obtained by doubling the static friction force (S12).

Here, the force of pushing back the electrode tip when the nugget expands during welding (expansion force of the nugget).
And the motor torque have a relationship as shown in the following equation (2).

The expansion force of the nugget = motor torque + static friction force (2) Therefore, when the expansion force of the nugget reaches the specified welding pressure, the stationary motor starts to move.
It is necessary to set the torque of the motor 18 to welding force minus static friction force.

In the present embodiment, the motor 18
In this case, the torque of the motor 18 is defined as welding welding force−static friction force, so that the torque of the motor 18 is calculated by subtracting the static friction force from the motor torque at the time of initial pressing, as described in step S12. It is the power reduced by double.

Thereafter, from this state, the electrode tips 12A,
Electricity is supplied under the welding conditions stored in the storage circuit 26 during 12B to start welding (S13). Encoder 1 during welding
9 to monitor the movement amount of the motor 18, the movement amount detection circuit 24 determines the movement amount of the electrode tip 12A (S1).
4). As a result, when the nugget thermally expands, the torque of the motor 18 has already been removed by the static friction force as described above, so that the electrode tip 12A is pushed up when the expansion force of the nugget exceeds the welding pressure. , Motor 1
8 moves. Therefore, after the welding is started, the expansion amount of the nugget can be accurately detected from the movement amount of the encoder 19.

Thereafter, when a predetermined welding time has elapsed, the welding gun is opened and all the processes are terminated (S15).

Embodiment 2 In Embodiment 2, the initial pressing force is set to an arbitrary force equal to or higher than the static friction force as the welding pressing force.

In the second embodiment, the construction of the welding apparatus is the same as that of the first embodiment, except that the welding procedure is different from that of the first embodiment. Therefore, description of the configuration of the welding device is omitted. In the second embodiment, the static friction force detected in the same manner as in the first embodiment is used.

FIG. 4 is a flowchart showing a welding procedure according to the second embodiment.

This welding procedure is performed by the CPU 21 executing a program for welding. First, C
The PU 21 instructs a torque of the motor 18 higher than (welding pressure + static friction force), and thereby initially pressurizes the member 1 to be welded (S21). The motor torque at this time is
An arbitrary pressing force may be used as long as the member to be welded 1 is not deformed, and for example, a force approximately twice the welding pressing force may be used.

Subsequently, the torque of the motor 18 is gradually reduced (S22), and whether or not the torque of the motor 18 becomes a force obtained by subtracting the static friction force from the welding pressure (welding pressure-static friction force). Is determined (S23). If the torque of the motor 18 is not equal to (welding pressure-static friction force) (S23, No), the process returns to step S22. on the other hand,
If the torque of the motor 18 = (welding pressure−static friction force) (S23, Yes), the storage circuit 2 is stored in the electrode chip.
Electricity is supplied under the welding conditions stored in No. 6 to start welding (S24).

After the welding is started, the movement amount of the motor 18 is monitored by the encoder 19, and the movement amount detection circuit 24 obtains the movement amount of the electrode tip 12A (S25).

Thereafter, when the welding is completed, the welding gun is opened and all the processes are completed (S26).

As described above, in the second embodiment, the member to be welded 1 is pressurized with an arbitrary motor torque that is stronger than the force obtained by adding the static frictional force to the welding pressure as the initial pressurization. Since the torque is reduced until it becomes (welding pressure-static friction force), a force corresponding to the static friction force is released. Therefore, when the electrode tip 12A is pushed up due to the thermal expansion of the nugget, when the force becomes larger than the welding pressure, the motor 18 is immediately turned on.
, And the expansion amount of the nugget can be detected with high accuracy without a response delay due to the effect of static friction.

<< Embodiment 3 >> In Embodiments 1 and 2 described above, the embodiment focuses on detecting the thermal expansion of the nugget. However, Embodiment 3 is applicable not only to the expansion but also to the contraction of the nugget. The present invention eliminates the influence of the static friction force and can accurately detect the amount of expansion and contraction of the nugget.

In the third embodiment, the configuration of the welding device is the same as that of the first embodiment. Therefore, description of the configuration of the welding device is omitted. In the third embodiment, the static friction force detected in the same manner as in the first embodiment is used.

FIG. 5 is a flowchart showing a welding procedure according to the third embodiment.

This welding procedure is performed by the CPU 21 executing a program for welding. First, C
The PU 21 instructs the torque of the motor 18 to be the welding pressure, and thereby initially pressurizes the member 1 to be welded (S31).

Subsequently, a dither signal is added to the torque command value of the motor 18 so that the torque increases or decreases by a force corresponding to the static friction force with the welding pressure as a center value (S3).
2). At this time, the value detected in the same manner as in the first embodiment is used as the static friction force.

Then, in a state where the dither signal is added, the electrode tip is energized under the welding conditions stored in the storage circuit 26 to start welding (S33).

After the welding is started, the movement amount of the encoder 19 is monitored, and the movement amount detection circuit 24 obtains the movement amount of the electrode tip 12A (S34).

Thereafter, the welding gun is opened when the welding is completed, and all the processes are completed (S35).

As described above, in the third embodiment, the dither signal is added to the welding pressure as a center value so that the torque of the motor 18 is increased or decreased by a force corresponding to the static friction force. When the torque of the nugget is weakened by the static friction force due to the dither signal, the response due to the thermal expansion of the nugget is correspondingly increased. Therefore, it is possible to accurately detect both expansion and contraction of the nugget.

<Embodiment 4> In Embodiment 4, similarly to Embodiment 3, it is possible to accurately detect the amount of expansion and contraction of the nugget. However,
The fourth embodiment differs from the third embodiment in that a value of the static friction force is not required.

Since the configuration of the welding device is the same as that of the first embodiment, the description is omitted.

FIG. 6 is a flowchart showing a welding procedure according to the third embodiment.

This welding procedure is performed by the CPU 21 executing a program for welding. First, C
The PU 21 instructs a torque of the motor 18 to be a welding pressure, and thereby initially pressurizes the member 1 to be welded (S41).

Subsequently, a dither signal is applied so that the torque of the motor 18 is increased or decreased with a force greater than the static friction force, with the welding pressure as a central value (S42). The static friction force used here may be an approximate value and does not require an accurate value.

At this time, since the applied dither signal is stronger than (welding pressure + static friction force),
Micro-vibration in both positive and negative directions. If the motor does not vibrate at this time, the applied torque of the motor does not exceed (welding pressure + static friction force), so that the torque is further increased.

Subsequently, the value of the dither signal is gradually reduced (S43).

Subsequently, the motor 1
It is determined whether or not the motion of Step 8 has stopped (S44). Here, if the movement of the motor 18 is not stationary (S44,
No), the process returns to step S43 to continue reducing the dither signal. On the other hand, if the movement of the motor 18 is stationary (S4
4, Yes), the dither signal applied at this time is maintained (S45), and the electrode tip is energized under the welding conditions stored in the storage circuit 26 to start welding (S4).
6). Therefore, during welding, the torque of the motor 18 remains applied with the dither signal at the time when the motor 18 stops.

After the start of welding, the movement amount of the encoder 19 is monitored, and the movement amount detection circuit 24 obtains the movement amount of the electrode tip 12A (S47).

Thereafter, the welding gun is opened when the welding is completed, and all the processes are completed (S48).

As described above, in the fourth embodiment, the dither signal is added to the welding pressure as the center value at the time of initial pressurization so that the torque of the motor 18 is increased or decreased by a force stronger than the static friction force. However, this is gradually reduced until the motor stops, and welding is performed while adding a dither signal at the time when the motor stops, so that the force equivalent to the static friction force at that time is reduced from the motor torque. When the electrode tip is pushed up by the expansion of the nugget or conversely, the electrode tip is lowered by the torque of the motor due to the contraction, the motor 18 is moved. Can be detected with high accuracy.

Although the embodiments to which the present invention is applied have been described, the present invention is not limited to these embodiments. For example, in each of the embodiments, a welding device using a servomotor is shown as an actuator, but instead, an oil cylinder or an air cylinder may be used. In such a case, as a movement amount measuring unit, A gauge is used to measure the amount of piston return and return.

[Brief description of the drawings]

FIG. 1 is a drawing schematically showing a welding apparatus to which the present invention is applied.

FIG. 2 is a flowchart illustrating a procedure for detecting a static friction force according to the first embodiment.

FIG. 3 is a flowchart showing a welding procedure according to the first embodiment.

FIG. 4 is a flowchart showing a welding procedure according to a second embodiment.

FIG. 5 is a flowchart showing a welding procedure according to a third embodiment.

FIG. 6 is a flowchart showing a welding procedure according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... welding gun, 11 ... welding gun arm, 12A, 12B ... electrode tip, 18 ... servo motor, 19 ... encoder, 20 ... control device, 21 ... CPU, 24 ... movement amount detection circuit.

Claims (10)

[Claims] 1. A welding apparatus for performing welding while moving an electrode tip attached to a tip of a welding gun arm by an actuator and pressing a member to be welded by the electrode tip, wherein a static friction force required for the actuator to start moving is provided. A static frictional force storage means storing, at the time of initial pressurization, pressurizing the member to be welded as a force obtained by adding the static frictional force to the welding force, and before starting welding, Welding comprising: actuator control means for controlling the actuator so as to reduce the force generated by the actuator by twice the static friction force; and movement amount measurement means for measuring the movement amount of the actuator. apparatus. 2. A welding apparatus in which an electrode tip attached to a tip of a welding gun arm is moved by an actuator and welding is performed while pressing a member to be welded by the electrode tip, wherein a static friction force required for the actuator to start moving is provided. And a static frictional force storing means for storing the frictional force, and at the time of initial pressurization, pressurizing the member to be welded by making the generated force of the actuator higher than a force obtained by adding the static frictional force to the welding pressure, and thereafter before starting welding An actuator control means for controlling the actuator so as to reduce the generated force of the actuator to a force obtained by subtracting the static friction force from the welding pressure, a movement amount measurement means for measuring a movement amount of the actuator, A welding apparatus comprising: 3. A welding apparatus for performing welding while moving an electrode tip attached to a tip of a welding gun arm by an actuator and pressing a member to be welded by the electrode tip, wherein a static friction force required for the actuator to start moving. A static frictional force storage means storing the following; an actuator control means for controlling the actuator so that the generated force of the actuator increases or decreases by the static frictional force around a welding pressure force after the welding is started; and the actuator. A moving amount measuring means for measuring a moving amount of the welding. 4. A welding apparatus for performing welding while moving an electrode tip attached to a tip of a welding gun arm by an actuator and pressing a member to be welded by the electrode tip, wherein a movement amount of the actuator is measured. Means for increasing or decreasing the force generated by the actuator at the time of initial pressurization by an arbitrary force equal to or greater than the static friction force required for the actuator to move around the welding pressure, and calculating the increase / decrease force by the movement amount measuring means. The actuator that controls the actuator so as to gradually reduce the movement of the actuator measured by the method until the movement stops, and to maintain the force generated by the actuator after the start of welding to maintain the increasing / decreasing force when the movement of the actuator stops. And a control means. 5. The static friction force increases the force generated by the actuator in a positive direction gradually from zero, and the force generated by the actuator when the movement amount measuring means detects that the actuator has started moving. Is stored as a positive static friction force.The generated force of the actuator is gradually increased in the negative direction from zero, and the generated force of the actuator at the time when the movement amount measuring means detects that the actuator has started to move is stored. The static friction force is stored as a negative static friction force, and an average value of the positive static friction force and the negative static friction force is stored in the static friction storage means. The welding device according to any one of the above. 6. A welding method in which an electrode tip attached to a tip of a welding gun arm is moved by an actuator, and welding is performed while pressing a member to be welded with the electrode tip. Pressing the member to be welded as a force obtained by adding a static friction force required for the actuator to start moving to the welding pressure, and after the pressing, the generated force of the actuator is twice as much as the static friction force. Reducing the force generated by the actuator by twice the static friction force, and then starting welding; and measuring the amount of movement of the actuator after the start of welding. And welding method. 7. A welding method in which an electrode tip attached to the tip of a welding gun arm is moved by an actuator, and welding is performed while pressing a member to be welded with the electrode tip. Pressurizing the member to be welded with a force higher than the static friction force required for the actuator to start moving to the welding pressure; and, after the pressing, the force generated by the actuator from the welding pressure. A step of reducing the force generated by the actuator to a force obtained by subtracting the static friction force from the welding pressure, and then starting welding; and a step of starting the welding. Measuring the amount of movement of the actuator afterward. 8. A welding method in which an electrode tip attached to a tip of a welding gun arm is moved by an actuator, and welding is performed while pressing a member to be welded with the electrode tip. A step of increasing / decreasing the static frictional force required for the actuator to start moving to the center and starting welding while pressing the member to be welded, and measuring a movement amount of the actuator after the start of welding. And welding method. 9. A welding method in which an electrode tip attached to a tip of a welding gun arm is moved by an actuator and welding is performed while pressing a member to be welded with the electrode tip. Pressurizing the member to be welded by increasing or decreasing by an arbitrary force equal to or greater than the static friction force necessary for the actuator to start moving around the welding pressure, measuring the amount of movement of the actuator, and stopping the actuator Until gradually decreasing the increase / decrease of the generated force of the actuator, and after starting the welding, starting the welding while maintaining the increase / decrease of the generated force of the actuator at that time; and Measuring the amount of movement of the actuator. 10. The static friction force comprises: increasing the force generated by the actuator gradually from zero in the positive direction, and storing the force generated by the actuator at the time when the actuator starts moving as a positive static friction force. And gradually increasing the generated force of the actuator in the negative direction from zero, and storing the generated force of the actuator at the time of detecting that the actuator has started to move as a negative static friction force; and The welding method according to any one of claims 6 to 9, wherein the welding method is obtained in advance from a step of calculating an average value of the static friction force and the negative static friction force.