JP7335093B2 - welding system - Google Patents

Description

The present invention relates to welding systems.

In a spot welding system in which welding is performed by pressurizing a work to be welded between a movable electrode tip and a fixed electrode tip facing the movable electrode tip, when deformation or cracking occurs in the arm of the spot welding gun, spot welding is performed. The stiffness of the entire gun arm is reduced. Therefore, the amount of elastic displacement of the arm of the spot welding gun increases. Therefore, even if the applied pressure is not changed, there is a possibility that the work to be welded will be pushed in and the welding quality will be degraded. Further, if the cracked arm continues to be used, the crack may progress and eventually break the arm. Therefore, the operator must periodically visually check the condition of the spot welding gun. However, it takes time for an operator to visually check each spot welding gun, and it is difficult for an inexperienced operator to detect a slight plastic deformation or a slight crack.

Furthermore, even if the rigidity of the entire arm of the spot welding gun is not reduced, mechanical parts of the spot welding gun, such as ball screws and bearings, may wear out, and lubricating oil in the mechanical parts may deteriorate. . In such a case, the frictional resistance of the mechanical portion changes.

In such a case, it is necessary to detect the actual pressurizing force generated by the torque command supplied to the servomotor with a pressure sensor and recalibrate the relationship between the actual pressure and the torque command. However, when measuring the applied force with the pressure sensor, the spot welding system must be stopped. Therefore, such calibration work cannot be performed while the work to be welded is being welded.

For these reasons, there is a tendency for the interval between stopping the spot welding system and actually measuring the applied force by the pressure sensor to become long. Therefore, the spot welding system may be operated without recognizing that there is a deviation in the applied pressure, and as a result, the welding quality may be degraded. Also, since pressure sensors are relatively expensive, it is difficult to prepare a large number of pressure sensors.

For this reason, various methods have been proposed to solve these problems in spot welding guns equipped with servo motors. There is a possibility of determining that the welding gun has not deteriorated, and even if the position of the tip of the electrode tip at the time of contact is measured in advance, there is a problem that the tip position of the tip of the electrode is displaced.

Therefore, in order to easily estimate the abnormality of the spot welding gun when the arm of the spot welding gun deforms or cracks, or when the friction changes due to the wear of the mechanism, the reference pressure and the pressure for detection are used. A technique is known in which pressure is applied and an abnormality is determined from the difference, or a pressure deviation is calculated (see, for example, Patent Document 1).

Japanese Patent No. 5638102

However, in the technique according to Patent Document 1, in order to calculate the difference, although the pressing position when pressure is applied with a specific torque (reference pressure force) is used as a reference position for calculation, the same torque Even if pressure is applied with , the reference position may shift by the static friction force. Therefore, an error may occur in the detected pressing force deviation.

Therefore, it is desired to provide a welding system that is less susceptible to the static frictional force and, as a result, has a higher accuracy in estimating the applied force.

One aspect of the present disclosure is a welding system that performs welding by pressurizing a workpiece to be welded between a movable electrode tip driven by a servomotor and a fixed electrode tip facing the movable electrode tip, wherein the movable electrode tip and a command value creation unit that creates a constant reference speed command value and at least one detection pressure command value for the movable electrode tip for pressing the work to be welded between the fixed electrode tip and the reference; A rotational position of the servomotor at the time when the movable electrode tip and the fixed electrode tip come into contact is calculated as a reference position from the current value of the servomotor when the servomotor is driven based on the speed command value. Rotation of the servo motor when the servo motor is driven based on a reference position calculation unit, a rotational position of the servo motor calculated by the reference position calculation unit, and the at least one detection pressure command value a displacement amount deviation calculation unit that calculates a rotational deviation between the position and the position as a displacement amount deviation; and a state determination deviation calculator that calculates a state determination deviation as a state determination deviation from the displacement amount deviation in a state in which it is necessary to readjust.

According to one aspect, it is less likely to be affected by the static friction force, and as a result, the accuracy of estimating the applied force is increased.

It is a figure showing composition of a spot welding system of one embodiment. It is a figure which shows the structure of the robot control apparatus of one Embodiment. It is a figure which shows the determination method of the reference position in one embodiment. It is a figure which shows the determination method of the reference position in one embodiment. It is a flow chart which shows operation of a spot welding system of one embodiment. 4 is a flow chart showing a method of calculating a displacement amount deviation in one embodiment. FIG. 5 is a diagram showing the relationship between a command value of applied pressure and a rotational position in one embodiment; It is a figure which shows the relationship between the deviation for state determination in one Embodiment, and the progress degree of a crack. It is a flow chart which shows operation of a spot welding system of one embodiment. It is a figure which shows the relationship between the pressurization force command value and the reference|standard displacement amount deviation in one Embodiment. It is a figure showing composition of a spot welding system concerning a modification of one embodiment. It is a figure showing composition of a spot welding system concerning other modifications of one embodiment.

A spot welding system will be described below as an example of an embodiment of a robot system according to the present invention with reference to the accompanying drawings. In addition, suppose that the same code|symbol is attached|subjected to the part which is the same or equivalent in each drawing.

(Spot welding system: robot system)
FIG. 1 is a diagram showing the configuration of a spot welding system according to this embodiment. The spot welding system 1 shown in FIG. 1 uses a robot 10 to relatively move a spot welding gun 20 and a work W to bring the spot welding gun 20 into contact with the work W, thereby performing spot welding on the work W. FIG. The spot welding system 1 includes a robot 10 , a spot welding gun 20 , a robot controller 30 that controls the operation of the robot 10 , and a welding gun controller 40 that controls the operation of the spot welding gun 20 .

The robot 10 is, for example, a 6-axis vertical articulated robot, and has a base 11 , a lower arm 12 , an upper arm 13 , and an arm tip 14 . The base 11 is installed on the floor. One end of the lower arm 12 is connected to the base 11 so as to be rotatable about a first axis (vertical axis) J1 and rotatable about a second axis (horizontal axis) J2. One end of the upper arm 13 is connected to the other end of the lower arm 12 so as to be rotatable about a third axis (horizontal axis) J3. On the other end side of the upper arm 13, an arm tip portion 14 is rotatable about a fourth axis J4 perpendicular to the third axis J3 and rotatable about a fifth axis J5 perpendicular to the fourth axis J4. connected to A spot welding gun 20 is attached to the arm distal end portion 14 so as to be rotatable around a sixth axis J6 perpendicular to the fifth axis J5.
The robot 10 is not limited to a 6-axis vertical articulated robot, and may be any other type of articulated robot such as a 4-axis vertical articulated robot as long as the spot welding gun 20 and the workpiece W can be relatively moved. may be

The robot 10 incorporates a plurality of servomotors 15 (only one is shown for convenience) that respectively drive a plurality of drive axes, ie, the first axis J1 to the sixth axis J6. The servomotor 15 is driven by control signals from the robot controller 30 . The position and attitude of the spot welding gun 20 are changed by driving the servomotor 15 .

Hereinafter, the first to sixth axes J1 to J6 of the robot 10 are sometimes referred to as robot axes, and the servo motor 15 for driving these robot axes is also referred to as a robot axis motor.
Also, the first axis J1, the second axis J2 and the third axis J3, which are vertical or horizontal axes, are sometimes called basic axes, and the fourth axis J4, the fifth axis J5 and the sixth axis J6 are called wrist axes. There is also The basic axes J1-J3, which are vertical or horizontal, mainly contribute to the positioning of the arm tip 14 of the robot 10. FIG. On the other hand, the wrist axes J4 to J6 mainly contribute to determining the posture of the arm tip portion 14 of the robot 10 .

The spot welding gun 20 is a so-called C-type spot welding gun. The spot welding gun 20 has a C-shaped gun arm 23 connected to the arm tip 14 and a servomotor 24 for clamping a workpiece. The gun arm 23 has a bar-shaped counter electrode 22 protruding from the end of an L-shaped frame 23 a and a bar-shaped movable electrode 21 protruding to face the counter electrode 22 . The movable electrode 21 and the counter electrode 22 are arranged coaxially. While the opposing electrode 22 is fixed to the frame 23a, the movable electrode 21 is coaxial with the opposing electrode 22 and is relatively movable with respect to the frame 23a.

In the spot welding gun 20, the tip of the movable electrode 21 pushes the tip of the counter electrode 22 and elastically deforms the metal arm to which the tip of the counter electrode 22 is attached, thereby applying the required pressure to the electrode tip. Welding is performed by applying pressure to the workpiece W, which is a workpiece to be welded.

The servomotor 24 is driven by a control signal from the welding gun controller 40 , and the movable electrode 21 approaches and separates from the opposing electrode 22 by driving the servomotor 24 . A work W is held between the movable electrode 21 and the counter electrode 22 in the plate thickness direction, and the work W is spot-welded. The work W is supported by a work support device (not shown).

Hereinafter, the axis of relative movement between the movable electrode 21 and the counter electrode 22 of the spot welding gun 20 is also referred to as the gun axis, and the servo motor 24 that drives the gun axis is also referred to as the gun axis motor.

Each servomotor 15 for the robot axis is provided with an encoder 15a, and the rotation angle of the servomotor 15 about the axis is detected by the encoder 15a. The detected rotation angle is fed back to the robot control device 30 , and the position and attitude of the spot welding gun 20 at the arm tip portion 14 are controlled by feedback control in the robot control device 30 . As a result, the opposing electrode 22 integrated with the frame 23a can be positioned at the sandwiching position of the workpiece W in the plate thickness direction, and the position and attitude of the opposing electrode 22 can be detected from the signal from the encoder 15a.

An encoder 24a is provided to the gun shaft servomotor 24, and the rotation angle of the servomotor 24 about its axis is detected by the encoder 24a. The detected rotation angle is fed back to the welding gun control device 40 , and the feedback control in the welding gun control device 40 can position the movable electrode 21 with respect to the counter electrode 22 . The amount of opening between the electrodes 21 and 22 varies depending on the rotation angle of the servomotor 24. In the present embodiment, the servomotor 24 is set in advance as a reference value. Thereby, the rotation angle from the reference value can be detected by the signal from the encoder 24a, and the opening amount between the electrodes 21 and 22 can be detected.

The robot control device 30 and the welding gun control device 40 each include an arithmetic processing device having a CPU, ROM, RAM, and other peripheral circuits. The robot control device 30 and the welding gun control device 40 are connected to perform signal transmission/reception (communication) with each other.

The robot controller 30 stores operation programs (work programs) and teaching data for the robot 10 and the spot welding gun 20 . The teaching data includes welding point data, which are the positions and attitudes of the robot 10 and the spot welding gun 20 when the workpiece W is spot-welded at many welding points. A work program for automatic operation is created based on this teaching data.

During automatic operation, the robot controller 30 operates the robot 10 according to the work program, controls the position and orientation of the spot welding gun 20 with respect to the work W, and places the work W between the electrodes 21 and 22 . In addition, the welding gun control device 40 operates the movable electrode 21 according to the work program, controls the pressure applied to the workpiece W by the electrodes 21 and 22, and controls the current supplied to the electrodes 21 and 22 according to the work program. Then, spot welding is performed at a predetermined welding spot position.

Before automatic operation, the robot controller 30 detects the contact positions between the electrodes 21 and 22 and the workpiece W when the spot welding gun 20 is closed. Based on this contact position, the robot control device 30 corrects the target position (striking position) in the work program.
The robot control device 30 will be described in detail below.

(Robot control device according to the embodiment)
FIG. 2 is a diagram showing the configuration of the robot control device according to the embodiment. A robot controller 30 shown in FIG. 2 is applied to the robot controller 30 in the spot welding system 1 shown in FIG.

The robot control device 30 includes a control section 31 and a storage section 32 .
The control unit 31 is a part that controls the entire robot control device 30, and reads and executes various programs from a storage area such as ROM, RAM, flash memory, or hard disk (HDD) as appropriate to control the Various functions are realized. The control unit 31 may be a CPU. The control unit 31 includes a reference speed command value creation unit 311, a reference speed command value output unit 312, a detection pressure command value creation unit 313, a torque command value output unit 314, a reference position calculation unit 315, and a displacement amount deviation calculation unit 316. , a state determination deviation calculator 317 , and an abnormality determination unit 318 .
In addition, the control unit 31 includes general functional blocks such as a functional block for controlling the robot control device 30 as a whole and a functional block for communication. However, since these general functional blocks are well known to those skilled in the art, illustration and description are omitted.

Reference speed command value creation unit 311 creates a reference speed command value for spot welding gun 20 that presses the work to be welded between the tip of movable electrode 21 and the tip of counter electrode 22 . More specifically, when moving the tip of the movable electrode 21 with respect to the tip of the counter electrode 22 at a constant speed, a constant speed command value is created as a reference speed.
Note that, hereinafter, the tip of the movable electrode 21 may be referred to as the "movable electrode tip", and the tip of the counter electrode 22 may be referred to as the "fixed electrode tip".

The reference speed command value output unit 312 outputs the reference speed command value created by the reference speed command value creation unit 311 to the gun axis servo motor 24 .

The detection pressure command value creation unit 313 creates at least one detection pressure command value. As will be described later, in the spot welding system 1, the rotational position of the servomotor 24 as a reference position and the rotation of the servomotor 24 when the servomotor 24 is driven based on at least one pressure command value for detection The deviation from the position is calculated as the displacement amount deviation, and the detection pressure command value creation unit 313 creates the detection pressure command value used for the calculation of this displacement amount deviation.

Note that, hereinafter, the reference speed command value creation unit 311 and the detection pressure command value creation unit 313 may be collectively referred to as a “command value creation unit”.

The torque command value output unit 314 converts the detection pressure command value created by the detection pressure command value creation unit 313 into a torque command value using a torque-pressure force conversion table 321 described later, and the converted torque command Output the value to the servo motor 24 .

The reference position calculator 315 calculates the current value of the servomotor 24 when the servomotor 24 is driven based on the reference speed command value, and calculates the current value of the servomotor 24 when the tip of the movable electrode 21 and the tip of the counter electrode 22 come into contact with each other. 24 is calculated as the reference position. Specifically, when the tip of the movable electrode 21 is brought into contact with the tip of the counter electrode 22 , which is the fixed electrode, at a constant reference speed, the reference position calculator 315 detects the disturbance indicated by the current value of the servomotor 24 . The reference position is determined from the rise of torque.

3A and 3B show how the reference position is determined. As shown in FIG. 3A, the disturbance torque increases over time, but the reference position calculator 315 may set the rotational position of the servomotor 24 at the time when the disturbance torque exceeds the threshold as the reference position. Alternatively, as shown in FIG. 3B, a certain threshold may be set, and the rotational position of the servomotor 24 at the minimum point where the disturbance torque begins to change beyond the threshold may be used as the reference position.

The displacement amount deviation calculation unit 316 calculates the rotation position of the servo motor 24 calculated by the reference position calculation unit 315 and the position of the servo motor 24 when the servo motor 24 is driven based on at least one pressure command value for detection. A rotational deviation from the rotational position is calculated as a displacement amount deviation.

The state determination deviation calculator 317 calculates the difference between the displacement amount deviation in a state in which the pressure applied to the work W is adjusted to be able to be exerted normally, and the displacement amount deviation in a state in which the pressure applied to the work W needs to be readjusted. The deviation is calculated as the state determination deviation.

The abnormality determination unit 318 compares the state determination deviation calculated by the state determination deviation calculation unit 317 with a predetermined value, and determines whether or not there is an abnormality in the spot welding system 1 based on the comparison result. . In particular, the abnormality determination unit 318 may determine that the spot welding system 1 has an abnormality when the state determination deviation is greater than a predetermined value.

The warning output unit 319 outputs a warning when the abnormality determination unit 318 determines that the spot welding system 1 has an abnormality. For example, the warning output unit 319 may display the warning on a display device provided inside or outside the robot control device 30 . Further, the warning output unit 319 may output the warning by voice.

The storage unit 32 is, for example, a rewritable memory such as an EEPROM. As described above, the storage unit 32 stores operation programs (work programs) of the robot 10 and the spot welding gun 20, teaching data, and the like. The teaching data includes welding point data, which are the positions and attitudes of the robot 10 and the spot welding gun 20 when the workpiece W is spot-welded at many welding points. The teaching data is input by the teacher using, for example, a teaching operation panel (not shown). Based on this teaching data, a work program for automatic operation is created.

The storage unit 32 also stores a torque-pressure force conversion table 321 for converting the detection pressure command value created by the detection pressure command value creation unit 313 into a torque command value.

(Operation of spot welding system)
FIG. 4 is a flow chart showing the operation of the spot welding system 1. As shown in FIG.

In step S11, a torque-pressure conversion table for the spot welding gun 20 is created. Specifically, pressure is applied between the tip of the movable electrode 21 and the tip of the counter electrode 22 based on a plurality of torque commands T1, T2, . Then, the actual pressure at that time is measured by a pressure sensor (not shown). Based on these measurement results, a torque-pressure conversion table representing the relationship between torque and pressure is created. Note that step S11 may be omitted if the torque-pressure conversion table is created in advance.

At step S12, an initialization program is executed. It is assumed that the initial setting program is executed in a state in which the spot welding gun 20 is adjusted so that it can exert its pressurizing force normally.

In step S13, the displacement amount deviation calculator 316 calculates the displacement amount deviation. FIG. 5 is a flow chart for obtaining the displacement amount deviation. A method of calculating the displacement amount deviation will be described below with reference to FIG.

In step S51, the tip of the movable electrode 21 is moved at a constant speed.

In step S52, when the disturbance torque exceeds the threshold (S52: YES), the process proceeds to step S53. If the disturbance torque is equal to or less than the threshold (S52: NO), the process proceeds to step S52.

At step S53, the rotational position x0 of the servomotor 24 is measured by the encoder 24a. This rotational position x0 is stored in the storage unit 32 as a displacement amount.

In step S54, the workpiece W is pressurized between the tip of the movable electrode 21 and the tip of the counter electrode 22 based on the pressure command value for detection, for example, the pressure command value for detection f1.

In step S55, when the motor current flowing through the servomotor 24 reaches the applied pressure command value f1 for detection (S55: YES), the process proceeds to step S56. If the motor current flowing through the servomotor 24 does not reach the detection pressure command value f1 (S55: NO), the process proceeds to step S55.

In step S56, the rotational position x1 of the servomotor 24 is measured by the encoder 24a. This rotational position x1 is stored in the storage unit 32 as a displacement amount.

In step S57, if it is necessary to perform the same process for the other detection pressure command values f2 and f3 (S57: YES), the process proceeds to step S54. If the same processing is not performed for other detection pressure command values (S57: NO), the process proceeds to step S58.

In step S58, the displacement amount deviation calculator 316 calculates the displacement amount deviation. Specifically, when the displacement amount deviation calculator 316 drives the servo motor 24 based on the rotational position of the servo motor 24 calculated by the reference position calculator 315 and at least one pressure command value for detection. and the rotational position of the servomotor 24 is calculated as a displacement amount deviation.

FIG. 6 is a diagram showing the relationship between the applied pressure command value and the rotational position. The horizontal axis of FIG. 6 represents the applied force command value, and the vertical axis represents the rotational position. As can be seen from FIG. 6, the larger the pressing force command value, the larger the rotational position.

The displacement amount deviation calculation unit 316 calculates the deviation between the rotational position x0 corresponding to the reference applied force command value f0 and the rotational positions x1, x2 and x3 corresponding to the detected applied force command values f1, f2 and f3. Calculate each. That is, as can be seen from FIG. 6, the displacement amount deviation calculator 316 calculates elastic displacement amount deviations d1 (=x1-x0), d2 (=x2-x0), and d3 (=x3-x0).

In FIG. 5, even if the pressurizing operation is performed a plurality of times with respect to one pressurizing force command value, for example, the reference pressurizing force command value f0, and the average value of a plurality of rotational positions x0 is adopted as the official rotational position x0. good. In such a case, the variance of displacement can be reduced.

Further, in step S55, the rotational position of the servomotor 24 is measured when the motor current reaches the pressing force command value. However, the rotational position of the servomotor 24 is sequentially measured at predetermined time intervals, and when the rotational position stops changing, it is determined that the applied force corresponding to the applied force command value has been obtained, and the rotational position at that time is adopted. may

Referring to FIG. 4 again, in step S13, these elastic displacement amount deviations d1, d2 and d3 are stored in the storage unit 32 as reference displacement amount deviations b1, b2 and b3, respectively.

At step S14, the spot welding system 1 is operated based on a normal operation program to weld the workpiece W. As shown in FIG.

Then, when the pressure of the spot welding gun 20 needs to be readjusted, the process proceeds to step S15.
At step S15, a diagnostic program is executed. The diagnostic program may be substantially similar to the initialization program. Accordingly, the displacement amount deviation calculator 316 recalculates the displacement amount deviation as described above.

In step S16, the elastic displacement amount deviations d1', d2', and d3' calculated in step S15 are stored in the storage unit 32 as current displacement amount deviations n1, n2, and n3.

In step S17, the state determination deviation calculator 317 subtracts the reference displacement amount deviations b1, b2, and b3 from the current displacement amount deviations n1, n2, and n3, respectively, to obtain the state determination deviation v1 (=n1-b1), Newly obtain v2 (=n2-b2) and v3 (=n3-b3). Further, when the state determination deviation v1 is larger than the first predetermined value, the process proceeds to step S18. When the state determination deviation v1 is equal to or less than the first predetermined value, the process proceeds to step S19.

Here, FIG. 7 is a diagram showing the relationship between the state determination deviation v and the degree of progress of the crack in the gun arm 23. As shown in FIG. In FIG. 7, the horizontal axis represents the state determination deviation v1 . As shown in FIG. 7, the crack in the gun arm 23 progresses as the state determination deviation v increases. Therefore, when the state determination deviation v1 is larger than the first predetermined value in step S17 of FIG.

In step S18, the warning output unit 319 outputs a warning. In such a case, the operator can stop the spot welding system 1, replace the part of the spot welding gun 20, such as the gun arm 23, or stop the spot welding system 1. is. Therefore, the occurrence of welding defects can be prevented in advance.

In step S19, the state determination deviations v1, v2, and v3 are stored in the storage unit 32 together with the time. Further, the operator displays the stored state determination deviation v1 and the past state determination deviation v1' on a display device (not shown) in sequence or at once. For this reason, when the difference between the state determination deviation v1 and the past state determination deviation v1′ is expected to exceed a second predetermined value described later, the operator must control the spot welding gun 20 , such as the gun arm 23, is replaced early. As a result, deterioration of welding quality in the spot welding system 1 can be prevented in advance, and sudden stoppage of the spot welding system 1 can be avoided.

In step S20, these state determination deviations v1, v2, v3 are compared with the past state determination deviations v1′, v2′, v3′ stored in the storage unit 32, and the state determination deviations v1, v2, If the difference between v3 and the past state determination deviations v1′, v2′, v3′ is greater than the second predetermined value (S20: YES), the process proceeds to step S21. If the difference between the state determination deviations v1, v2, v3 and the past state determination deviations v1', v2', v3' is equal to or less than the second predetermined value (S20: NO), the spot welding system described later Go to 1 additional action.

In step S21, the warning output unit 319 outputs a warning.

FIG. 8 is a flowchart for explaining additional operations of the spot welding system 1 according to this embodiment. Additional acts shown in FIG. 8 may be performed subsequent to the flowchart shown in FIG.

At step S22, the spring constant of the spot welding gun 20 is calculated. The spring constant can be obtained by a known method from the relationship between a plurality of applied force command values used when calculating the reference displacement amount deviation and a plurality of rotational positions. In other words, the spring constant corresponds to the slope of the straight line shown in FIG.

In step S23, the spring constant K obtained in step S22 is multiplied by the state determination deviations v1, v2, and v3 obtained in step S17, respectively, to obtain pressure deviations A1 (=K×v1) and A2 (=K×v2). ) and A3 (=K×v3) are calculated. According to the present invention, when the friction changes due to wear of the mechanism, it is possible to automatically and accurately calculate the applied force deviation that accompanies the change.

Moreover, in this case, the work of measuring the applied pressure using the pressure sensor can be omitted, and the work man-hours required for readjusting the applied pressure can be reduced. Further, in this embodiment, the rotational position of the servo motor 24 of the spot welding gun 20 during pressurization is measured from the encoder 24a to detect the pressurization force deviation. There is no need to add , and it is possible to suppress an increase in facility costs.

FIG. 9 is a diagram showing the relationship between the applied pressure command value and the rotational position. In FIG. 9, the horizontal axis represents the applied force command value, and the vertical axis represents the reference displacement amount deviation. Further, FIG. 9 shows the state determination deviations v1 and v2. As can be seen from FIG. 9, the pressing force deviations A1 and A2 corresponding to these state determination deviations v1 and v2 may be obtained by linear interpolation. The same applies to the pressing force deviation A3 not shown in FIG. In this case, without calculating the spring constant K, the pressure deviation A1 . . . can be calculated.

Referring to FIG. 8 again, in step S24, if each of the pressing force deviations A1 is greater than the third predetermined value (S24: YES), the process proceeds to step S26. Otherwise (S24: NO), the process proceeds to step S25.

In step S25, the pressing force is corrected. That is, the torque command value to the servomotor 24 is corrected or the rotational position command value of the servomotor 24 is corrected so that the pressure deviation A1 . . . becomes zero. This makes it possible to achieve the desired applied pressure and improve weld quality.

In step S26, the pressing force deviation A1 is compared with a fourth predetermined value. The fourth predetermined value is a value greater than the third predetermined value. If the pressing force deviation A1 is greater than the fourth predetermined value, the process proceeds to step S27. Otherwise (S26: NO), the process proceeds to step S28.

In step S27, the warning output unit 319 outputs a warning. Alternatively, the spot welding system 1 may be stopped through a peripheral device (not shown).

In step S28, the pressure deviations A1, . Thereby, the operator can confirm the value of the pressure deviation through the display device. Then, when the applied pressure deviation is large, the operator himself/herself may stop the spot welding system 1 and readjust the applied pressure.

In step S29, the pressing force deviations A1, . . . are stored in the storage unit 32 in chronological order.

In step S30, a plurality of pressure deviations stored in the past are displayed together on the display device. As a result, the operator can grasp that the pressing force deviation is changing rapidly. Further, when the amount of change in the pressure deviation is larger than a predetermined value, a warning may be output to the display device. Further, when the operator expects that the pressing force deviation will exceed the fourth predetermined value in an early stage, the operator may readjust the pressing force in an early stage. In this case, it is possible to prevent deterioration of welding quality.
The process may then proceed to step S14.

(Effect of the first embodiment)
As described above, according to the robot control device 30 and the spot welding system 1 of the first embodiment, the servomotor 24 is controlled so that the movable electrode tip is kept at a constant speed, and when the fixed electrode tip is brought into contact with the Analyze the rise of disturbance torque and acquire the reference position.
Since the measurement of the reference position is calculated from the motor current of the servo motor 24 when the movable electrode tip is operated at a constant speed, it is not easily affected by the static friction force, and the reference position can be measured with high accuracy. As a result, the accuracy of pressurizing force estimation increases. As a result, the abnormality of the spot welding gun 20 can be easily estimated.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Moreover, the effects described in the present embodiment are merely enumerations of the most suitable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the present embodiment.

For example, in the embodiment described above, the spot welding system 1 provided with the C-type spot welding gun 20 was exemplified. However, the features of the present invention are not limited to this and are applicable to spot welding systems with various spot welding guns. For example, as shown in FIG. 10, a so-called X-shaped spot welding gun having a pair of gun arms 26a and 26b that can be opened and closed, and a movable electrode 21 and a counter electrode 22 attached to the tip of each gun arm 26a and 26b. It is also applicable to spot welding systems with

Further, in the above-described embodiment, the spot welding gun 20 is moved relative to the work W by fixing the work W and attaching the spot welding gun 20 to the arm tip portion 14 of the robot 10 . However, the spot welding gun 20 may be moved relative to the work W by fixing the spot welding gun 20 and holding the work W at the arm tip 14 of the robot 10 . For example, as shown in FIG. 11, the spot welding gun 20 is supported by a gun stand 25 installed at a predetermined position, and the workpiece W is held at the tip of the arm of the robot 10 via the robot hand 19, thereby allowing the robot to 10 may be driven to move the work W relative to the spot welding gun 20 to place the work W between the electrodes 21 and 22 .

Also, in the above-described embodiments, the spot welding system was exemplified, but the present invention is not limited to this. A feature of this embodiment is a welding system that performs welding by pressurizing a workpiece to be welded between a movable electrode tip and a fixed electrode tip facing the movable electrode tip, for example, a welding system that performs welding by seam welding, a rivet It is applicable to a control system that performs hitting.

1 spot welding system (robot system)
REFERENCE SIGNS LIST 10 robot 11 base 12 lower arm 13 upper arm 14 arm tip 15 servo motor (driving unit)
15a encoder 20 spot welding gun (processing tool)
21 movable electrode 22 counter electrode 23 gun arm 23a frame 24 servo motor 24a encoder 30 robot control device 31 control unit 32 storage unit 311 reference speed command value creation unit 312 reference speed command value output unit 313 pressure command value creation unit for detection 314 torque Command value output section 315 Reference position calculation section 316 Displacement amount deviation calculation section 317 State determination deviation calculation section 318 Abnormality determination section 319 Warning output section 321 Torque-pressure force conversion table J1 First axis (drive axis, basic axis)
J2 2nd axis (drive axis, basic axis)
J3 Third axis (drive axis, basic axis)
J4 4th axis (drive axis, wrist axis)
J5 5th axis (drive axis, wrist axis)
J6 6th axis (drive axis, wrist axis)
W work (object to be processed)

Claims (4)

In a welding system that performs welding by pressurizing a work to be welded between a movable electrode tip driven by a servomotor and a fixed electrode tip facing the movable electrode tip,
command value creation for creating a constant reference speed command value and at least one detection pressure command value for the movable electrode tip for pressurizing the workpiece to be welded between the movable electrode tip and the fixed electrode tip; Department and
Based on the current value of the servomotor when the servomotor is driven based on the reference speed command value, the rotational position of the servomotor at the time when the movable electrode tip and the fixed electrode tip come into contact is defined as a reference position. a reference position calculator for calculating;
Rotation between the rotational position of the servomotor calculated by the reference position calculation unit and the rotational position of the servomotor when the servomotor is driven based on the at least one pressure command value for detection a displacement amount deviation calculation unit that calculates the deviation as a displacement amount deviation ,
The welding system, wherein the constant reference speed command value is a constant speed command value when moving the movable electrode tip with respect to the counter electrode tip at a constant speed. The welding system calculates the deviation between the displacement amount deviation in a state in which the pressure applied to the work to be welded is adjusted to be normally exerted, and the displacement amount deviation in a state in which the pressure needs to be readjusted. a state determination deviation calculator that calculates a state determination deviation;
2. The welding system according to claim 1, further comprising an abnormality determination unit that compares the state determination deviation with a predetermined value and determines whether or not there is an abnormality in the welding system based on the comparison result. 2. The reference position calculation unit determines the reference position as the rotational position at which a disturbance torque exceeds a threshold when the servomotor is driven based on the pressure command value for detection. Welding system according to claim 2. The reference position calculation unit calculates the rotational position at the time of a local minimum point at which a change in which a disturbance torque begins to exceed a threshold value when the servo motor is driven based on the pressure command value for detection is calculated as the reference position. 3. Welding system according to claim 1 or claim 2, in position.

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