JP3832731B2 - Welding gun equalizing device and equalizing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an equalizing device for a welding gun, and more particularly to an equalizing device for a welding gun in consideration of thermal expansion of an object to be welded that occurs during energization of a welding current.
[0002]
[Prior art]
In spot welding, which is often used in automobile body welding processes, the welded body is usually held by a welding gun mounted as an end effector of a welding robot, and sufficient pressure is applied to the welded body. Appropriate welding quality is ensured by supplying a welding current.
[0003]
However, the pressure at the time of welding causes a deflection in the gun arm of the welding gun, and the welded body is deformed along with the deflection of the gun arm.
[0004]
As a technique for preventing the deformation of the welded body due to the pressurization, several equalizing apparatuses have been proposed so far.
[0005]
[Problems to be solved by the invention]
However, in the above-described prior art, the deflection of the gun arm is corrected at the time of initial pressurization or release from pressurization after energization of the welding current, and welding is performed due to thermal expansion that occurs during energization of the welding current. The deformation of the body was not taken into consideration, and the deformation of the welded body due to the expansion of the nugget formed during the energization of the welding current was not guaranteed.
[0006]
The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide an equalizing device for a welding gun in consideration of thermal expansion of a welded body that occurs during energization of a welding current. .
[0007]
[Means for Solving the Problems]
  (1) In order to achieve the above object, according to the present invention, a first welding tip displacement detecting means for detecting a displacement amount of a first welding tip attached to one tip of a welding gun, A second welding tip displacement detecting means for detecting a displacement amount of a second welding tip attached to the other tip of the welding gun, and the welding according to the amount of thermal expansion of the welded body during welding current application. An equalizing device having a welding gun position correcting means for giving a command for correcting the position of the gun, wherein the welding gun position correcting means is detected by the first welding tip displacement detecting means. And a displacement amount of the position of the welded portion of the welded body during energization of the welding current is calculated from the displacement amount of the welding portion and the displacement amount of the second welding tip detected by the second welding tip displacement detecting means. ,To offset the displacement,There is provided an equalizing device for giving a command for correcting the position of the welding gun.
[0008]
  The first welding tip displacement detecting means detects the displacement amount of the first welding tip attached to one tip of the welding gun, and the second welding tip displacement detecting means is the other tip of the welding gun. The displacement amount of the second welding tip attached to the part is detected, and the displacement of the position of the welded part of the welded body that causes thermal expansion during welding current energization in the welding gun position correcting means from the detected displacement amount Calculate the quantity,To offset the displacement,By issuing a command for correcting the position of the welding gun, it is possible to correct the position of the welding gun in accordance with the amount of thermal expansion of the welded body during energization of the welding current.
[0009]
(2) In the above invention, although not particularly limited, the first welding tip displacement detection means detects a displacement amount of an actuator for moving the first welding tip provided in the welding gun. Is more preferable.
[0010]
Displacement accompanying the thermal expansion of the welded body that occurs during welding current application in the actuator for moving the first welding tip of the welding gun by the first welding tip displacement detecting means as the displacement amount of the first welding tip. By detecting the amount, it is possible to accurately detect the displacement amount of the first welding tip.
[0011]
  (3) In the above invention, although not particularly limited, the second welding tip displacement detecting means is a strain of a gun arm of the welding gun in the vicinity of the second welding tip.The displacement amount of the second welding tip is calculated fromMore preferably.
[0012]
  The distortion of the gun arm in the vicinity of the second welding tip due to the thermal expansion of the welded body caused by the second welding tip displacement detecting means during welding current energizationTo calculate the displacement of the second welding tipThis makes it possible to accurately measure the displacement amount of the second welding tip.
[0013]
  (4) In the above invention, although not particularly limited, the displacement amount of the position of the welded portion of the welded body calculated by the welding gun position correcting meansIs calculated by the following formulaDisplacement amount of the center position of the welded bodyTCIt is more preferable that
  TC = (TU + TL) / 2
However, in the above formula, TU is the displacement amount of the first welding tip, and TL is the displacement amount of the second welding tip.
[0014]
In the welding gun position correcting means, the displacement amount of the center position of the welded body is used as the displacement amount of the position of the welded portion of the welded body calculated from the first welding tip displacement amount and the second welding tip displacement amount. By calculating, it becomes possible to accurately estimate the displacement of the welded body due to thermal expansion that occurs during energization of the welding current.
[0015]
  (5) In order to achieve the above object, according to the present invention, there is provided an equalizing method for correcting the position of a welding gun in accordance with the thermal expansion of an object to be welded during energization of a welding current. From the displacement amount of the first welding tip attached to the distal end of the welding gun and the displacement amount of the second welding tip attached to the other distal end portion of the welding gun, the welded portion of the welded body during welding current conduction Calculate the displacement amount of the position ofTo offset the displacement,An equalizing method for correcting the position of the welding gun is provided.
[0016]
  From the displacement amount of the first welding tip during the welding current energization and the displacement amount of the second welding tip, the displacement amount of the position of the welded portion of the welded body during the welding current energization is calculated,To offset the displacement,By correcting the position of the welding gun, it is possible to correct the appropriate position of the welding gun in accordance with the amount of thermal expansion of the welded body that occurs during welding current application.
[0017]
(6) In the above invention, although not particularly limited, the displacement amount of the first welding tip is calculated from the displacement amount of an actuator for moving the first welding tip provided in the welding gun. Is preferred.
[0018]
As the displacement amount of the first welding tip, the displacement amount associated with the thermal expansion of the welded body generated during welding current energization in the actuator for moving the first welding tip of the welding gun is accurately detected. It becomes possible to detect the displacement amount of one welding tip.
[0019]
(7) In the above invention, although not particularly limited, it is preferable to calculate the displacement amount of the second welding tip from the distortion of the gun arm of the welding gun in the vicinity of the second welding tip.
[0020]
As the displacement amount of the second welding tip, by detecting the distortion of the gun arm in the vicinity of the second welding tip due to the thermal expansion of the welded body that occurs during the energization of the welding current, it is possible to accurately detect the second welding tip. It becomes possible to measure the amount of displacement.
[0021]
(8) In the above invention, although not particularly limited, the calculated displacement amount of the position of the welded portion of the welded body is:Calculated by the following formulaDisplacement amount of the center position of the welded bodyTCIt is preferable that
  TC = (TU + TL) / 2
However, in the above formula, TU is the displacement amount of the first welding tip, and TL is the displacement amount of the second welding tip.
[0022]
By calculating the displacement amount of the center position of the welded body as the displacement amount of the position of the welded portion of the welded body calculated from the first welding tip displacement amount and the second welding tip displacement amount, welding is performed. It is possible to accurately estimate the displacement of the welded body due to the thermal expansion that occurs during current application.
[0023]
【The invention's effect】
According to the first aspect of the present invention, it is possible to correct the position of the welding gun in accordance with the thermal expansion amount of the welded body during energization of the welding current, and to form the nugget without causing deformation of the welded body. This makes it possible to ensure appropriate welding quality.
[0024]
In addition, it is possible to grasp the thermal expansion amount of the welded body by detecting the amount of displacement generated during energization of the welding current of the first welding tip and the second welding tip attached to the welding gun. The to-be-welded body that is difficult to detect directly by calculating the displacement amount of the welded portion of the to-be-welded body that occurs during energization of the welding current from the displacement amount of the first welding tip and the displacement amount of the second welding tip It is possible to estimate the amount of displacement of the center position of the weld.
[0025]
According to the second aspect of the present invention, the first welding tip displacement detecting means detects the displacement amount of the first welding tip during the welding current energization in the actuator for moving the first welding tip of the welding gun. By detecting the amount of displacement that accompanies the thermal expansion of the welded body that occurs, it is possible to accurately detect the amount of displacement of the first welding tip.
[0026]
  According to the invention described in claim 3, the second welding tip displacement detecting means detects the strain of the gun arm in the vicinity of the second welding tip due to the thermal expansion of the welded body that occurs during welding current application.Calculate the displacement of the second welding tip fromBy doing so, it is possible to accurately measure the displacement amount of the second welding tip.
[0027]
According to the fourth aspect of the present invention, by calculating the displacement amount of the center position of the welded body as the displacement amount of the position of the welded portion of the welded body, the welded body accompanying the thermal expansion that occurs during energization of the welding current is calculated. It is possible to accurately estimate the displacement of the body.
[0028]
According to the fifth aspect of the present invention, it is possible to grasp the thermal expansion amount of the welded body from the displacement amount of the first welding tip and the displacement amount of the second welding tip during welding current energization. Furthermore, it becomes possible to estimate the displacement amount of the center position of the welded portion of the welded body, which is difficult to detect directly. This makes it possible to correct the position of the appropriate welding gun in accordance with the amount of thermal expansion of the welded body during energization of the welding current, so that the nugget can be formed without causing deformation of the welded body. Welding quality can be ensured.
[0029]
According to the sixth aspect of the present invention, as the displacement amount of the first welding tip, the displacement accompanying the thermal expansion of the welded body that occurs during welding current energization in the actuator for moving the first welding tip of the welding gun. By detecting the amount, it is possible to accurately detect the displacement amount of the first welding tip.
[0030]
According to the seventh aspect of the present invention, as the displacement amount of the second welding tip, the strain of the gun arm in the vicinity of the second welding tip that accompanies the thermal expansion of the welded body that occurs during energization of the welding current is detected. Thus, the displacement amount of the second welding tip can be accurately measured.
[0031]
According to the eighth aspect of the present invention, by calculating the displacement amount of the center position of the welded body as the displacement amount of the welded portion of the welded body, the welded object accompanying the thermal expansion that occurs during energization of the welding current is calculated. It is possible to accurately estimate the displacement of the body.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0033]
FIG. 1 is a diagram showing an overall configuration of a welding robot in an embodiment of the present invention, and FIG. 2 is a diagram showing a configuration of a welding gun 10 that is an end effector of the welding robot 1 of FIG. FIG. 3 is a block diagram showing a control configuration in the embodiment of the present invention, and FIG. 4 is a diagram showing a displacement state of the welding tips 13a and 13b and the welded body 15 during welding current conduction. .
[0034]
As shown in FIG. 1, the welding robot 1 in the embodiment of the present invention is, for example, a multi-joint mechanism 2 having N joints in which a plurality of arms are sequentially connected via a joint mechanism, as shown in FIG. Each of which has one welding robot motor 30, 40, 50 so that it can be driven for each joint. Therefore, the multi-joint mechanism 2 includes N welding robot motors 30, 40, 50. Have. The N welding robot motors 30, 40, 50 corresponding to the respective joints are controlled by a welding robot control device 60 as shown in FIG. Further, a welding gun 10 which is an end effector and a welding machine is provided at the distal end portion of the multi-joint mechanism 2, and a welding current feeding cable 3 for feeding welding current from a welding power source (not shown). Is piped to the welding gun 10 via the multi-joint mechanism 2.
[0035]
As shown in FIG. 2, the welding gun 10 includes a gun arm 11, two support members 12a and 12b, two welding tips 13a and 13b, a slide mechanism 14, a welding gun motor 20, and a welding gun encoder. 21 and a strain sensor 22.
[0036]
The gun arm 11 is generally U-shaped as shown in FIG. 2, and a fixed-side welding tip 13b is provided on the distal end side of the lower gun arm 11b of the gun arm 11 via a fixed-side support member 12b. ing.
[0037]
On the other hand, a slide mechanism 14 slidable in the vertical direction (the direction of the arrow in FIG. 2) is attached to the upper gun arm 11 a of the gun arm 11, and the movable portion 14 a of the slide mechanism 14 has a movable side. A movable welding tip 13a is mounted via the support member 12a. The movable-side welding tip 13a and the fixed-side welding tip 13b are mounted so that their central axes coincide with each other and face each other. Further, a welding gun motor 20 which is an actuator for holding the welded body 15 between the welding tips 13a and 13b and applying pressure to the welding tips 13a and 13b is provided at the upper part in the vertical direction. The movable support member 13a is slid through the slide mechanism 14 by driving the welding gun motor 20, so that the interval between the welding tips 13a and 13b can be freely adjusted. The above-described welding current feeding cable 3 is connected so as to feed welding current to the welding tips 13 a and 13 b of the welding gun 10.
[0038]
The welding gun encoder 21 is means for detecting the amount of displacement of the rotational angle of the drive shaft of the welding gun motor 20. Based on the detection of the displacement amount of the rotation angle of the welding gun motor 20, the movable welding tip displacement amount TU, which is the amount by which the movable welding tip 13 a is pushed back by the thermal expansion of the welded body 15 during energization of the welding current. Calculation can be performed accurately. In addition, when the actuator for adjusting the space | interval between the welding tips 13a and 13b of the said welding gun 10 is an air cylinder, to-be-welded during welding current energization by providing position measuring means, such as a displacement meter, in the said air cylinder. It is possible to detect the movable-side welding tip displacement amount TU due to the thermal expansion of the body 15.
[0039]
The strain sensor 22 is a means for detecting the strain of the gun arm 11b accompanying the thermal expansion of the welded body 15 when a welding current is applied, and the lower gun arm in the vicinity of the fixed-side welding tip 13b so that appropriate strain can be detected. 11b. From the strain detected by the strain sensor 22 and the elastic coefficient of the gun arm 11 measured in advance, due to the thermal expansion of the welded body 15 during energization of the welding current, the lower direction is opposite to the direction of pressurization. It is possible to accurately calculate the fixed side welding tip displacement amount TL that is the amount by which the gun arm 11b is pushed back, that is, the amount by which the fixed side welding tip 13b is pushed back. As the strain sensor, a strain sensor composed of a piezoelectric element or crystal, a strain gauge, or the like can be used.
[0040]
Below, based on the block diagram of FIG. 3, the structure of the control in embodiment of this invention is demonstrated.
[0041]
As shown in FIG. 3, the control configuration in the embodiment of the present invention includes a welding robot control device 60, a welding gun position correction device 70, and a welding gun motor 20 provided on the upper gun arm 11 a of the gun arm 11. A welding gun encoder 21 for the welding gun, a strain sensor 22 provided on the lower gun arm 11b, and N welding robot motors 30 provided at each joint of the multi-joint mechanism 2 of the welding robot 1. 40, 50 and N welding robot encoders 31, 41, 51 for detecting the displacement amount of the rotation angle of the drive shaft of each of the N welding robot motors 30, 40, 50. Yes.
[0042]
The welding robot control device 60 is means for controlling the driving of the welding gun motor 20 and the welding robot motors 30, 40, 50, and is provided at each joint of the multi-joint mechanism 2 of the welding robot 1. The driving of the welding robot motors 30, 40 and 50 is controlled, and the position and orientation of the welding gun 10 which is the end effector of the welding robot 1 is controlled. Further, the driving of the welding gun motor 20 provided in the welding gun 10 is controlled, and the clamping and pressurization of the welded body 15 of the welding gun 10 are controlled. Further, the welding robot controller 60 is energized with welding current from the displacement amount of the rotation angle of the drive shaft of each motor 20, 30, 40, 50 detected and transmitted by each encoder 21, 31, 41, 51. The movable side welding tip displacement amount TU which is the displacement amount of the welding gun motor 20 and the position of each joint of the multi-joint mechanism 2 are calculated, and the position of the welding gun 10 which is an end effector is calculated.
[0043]
The welding robot control device 60 is connected to the welding gun motor 20 and each of the welding robot motors 30, 40, 50 so as to be able to transmit a drive command for control, and corrects the welding gun position. The movable side welding tip displacement amount TU calculated in the apparatus 70 is connected so as to be transmitted. Further, it is possible to receive the displacement amount of the rotation angle of the drive shaft of each motor 20, 30, 40, 50 detected from the welding gun encoder 21 and the N welding robot encoders 31, 41, 51, respectively. Furthermore, it is connected so that a position correction command that is a command for correcting the position of the welding gun 10 can be received from the welding gun position correction device 70.
[0044]
The welding gun position correcting device 70 calculates the fixed-side welding tip displacement amount TL from the strain of the lower gun arm 11b detected and transmitted by the strain sensor 22 and the elastic coefficient of the gun arm 11 measured in advance. The displacement amount of the center position of the welded body 15 from the fixed-side welding tip displacement amount TL and the movable-side welding tip displacement amount TU detected by the welding gun encoder 21 and calculated by the welding robot controller 60. This is means for calculating the center position displacement amount TC of the welded body. Furthermore, it is means for transmitting a position correction command for the welding gun 10 to the welding robot control device 60 based on the calculated welded body center position displacement amount TC.
[0045]
The welding gun position correcting device 70 is connected so as to be able to receive the movable welding tip displacement amount TU calculated by the welding robot control device 60, and the strain of the lower gun arm 11 b detected by the strain sensor 22. It is connected so that the information can be received. Further, the welding gun position correction command based on the calculated welded body center position displacement amount TC is connected so as to be transmitted to the welding robot controller 60. The processing for calculating the welding object center position displacement amount TC in the welding gun position correction device 70 will be described in detail later.
[0046]
The N welding robot motors 30, 40, 50 provided at each joint of the multi-joint mechanism 2 are connected so as to receive a drive command from the welding robot control device 60, respectively. One welding robot encoder 31, 41, 51 is provided for each of the robot motors 30, 40, 50. For example, the displacement amount of the rotation angle of the drive shaft of the first welding robot motor 30 is provided. Is detected by the first welding robot encoder 31 so that the information on the rotational angular displacement can be transmitted to the welding robot controller 60, and the drive shaft of the second welding robot motor 40 is connected. The second welding robot encoder 41 detects the rotational angle displacement amount, and is connected so as to transmit the rotational angle displacement amount information to the welding robot control device 60. The N-th welding robot encoder 51 detects the displacement amount of the rotation angle of the drive shaft of the robot motor 50, and is connected so that information on the rotation angle displacement amount can be transmitted to the welding robot control device 60. .
[0047]
The strain sensor 22 is a means for detecting the strain of the lower gun arm 11b as described above, and is connected so that the detected strain of the lower gun arm 11b can be transmitted to the welding gun position correcting device 70.
[0048]
The operation will be described below.
[0049]
First, the displacement state of the welding tips 13a and 13b accompanying the thermal expansion of the nugget 16 formed when a welding current is applied to the welded body 15 will be described. FIG. 4 is a diagram showing the displacement state of the welding tips 13a and 13b and the welded body 15 during energization of the welding current. The thermal expansion that occurs when the rigidity of the upper gun arm 11a and the lower gun arm 11b is substantially equal. It shows the phenomenon.
[0050]
Part (a) of FIG. 4 shows a state in which the welding tips 13a and 13b before the welding current is energized sandwiched and pressed the workpiece 15 having a thickness t1, and the welding current is energized. Therefore, thermal expansion does not occur in the welded body 15. The welded body 15 is composed of two metal plates 15a having substantially the same plate thickness, and the two metal plates 15a are made of the same material.
[0051]
4B shows a state in which the welding tips 13a and 13b sandwich and pressurize the welded body 15 during energization of the welding current. The welded body 15 is shown in FIG. This indicates that the welding current of the welded body 15 is energized and the thermal expansion occurs at the location where the nugget 16 is formed by the generated Joule heat. Due to the thermal expansion occurring in the nugget 16, the thickness of the energized part of the welded body 15 during energization of the welding current, that is, the nugget 16 part of the part (b) in FIG. The thickness t2 is greater than the thickness t1 of the welded body 15 before the welding current is passed. Due to the expansion of the nugget 16 from the plate thickness t1 to the plate thickness t2 during energization of the welding current, the movable welding tip 13a is pushed by the movable welding tip displacement amount TU in the direction opposite to the pressurization, and the fixed welding tip 13b. Is also pushed in the direction opposite to the pressurization by the fixed side welding tip displacement amount TL. Between the parts (a) and (b) in FIG. 4, the welding tips 13 a and 13 b are pushed in the direction opposite to the direction of pressurization due to thermal expansion of the welded body 15 during energization of the welding current. The movable side welding tip displacement amount TU and the fixed side welding tip displacement amount TL are shown.
[0052]
FIG. 5 shows the movable-side welding tip displacement amount TU and the fixed-side welding tip displacement amount TL that accompany the expansion of the nugget 16 of the welded body 15 during energization of the welding current detected by the welding gun encoder 21 and the strain gauge 22. And a welding center position displacement amount TC calculated by a welding gun position correcting device 70 described later. In this figure, the horizontal axis shows the energization time of the welding current, and energization of the welding current is started at time 0 ms. Further, in the displacement amount of the vertical axis, the vertical upward displacement amount of the welding tips 13a and 13b is the positive direction of the vertical axis, and the displacement amount of the movable side welding tip displacement amount TU and the fixed side welding tip displacement amount TL is 0 mm, That is, the origin of the vertical axis is a state in which the object to be welded 15 immediately before energization of the welding current is sandwiched and pressurized. From this figure, the energizing time of the welding current elapses, and the movable welding tip 13a moves in the direction opposite to the pressurization, that is, the vertical axis It can be seen that the fixed side welding tip 13b is pushed in the direction opposite to the pressurization, that is, in the negative direction of the vertical axis. Further, with the thermal expansion of the nugget portion 16 that occurs during welding current application, the positions of the welding tips 13a and 13b are displaced, but the movable side welding tip displacement amount TU and the fixed side welding tip displacement amount TL are not necessarily the same. It is found that the position of the center of the welded body 15 is not constant and is displaced according to these displacements.
[0053]
Further, when the rigidity of the upper gun arm 11a and the rigidity of the lower gun arm 11b are different, the difference between the movable welding tip displacement amount TU and the fixed welding tip displacement amount TL may be particularly large. For example, FIG. 6 is a diagram showing a displacement state of the welding tips 13a and 13b and the welded body 15 when a welding current is applied under the same conditions as in FIG. FIG. 6 is a view in which the welded bodies 15 of the welding tips 13a and 13b before energizing the welding current are sandwiched and pressed, and FIG. 6 (b) shows the welding tips 13a and 13b and the objects to be welded during energization of the welding current. A welded body 15 is shown. Since the portion (a) in FIG. 6 is before the welding current is energized, thermal expansion does not occur in the welded body 15, and the portion (b) in FIG. 6 is thermally expanded due to the energization of the welding current. 6 differs from FIG. 4 in that the fixed-side welding tip is fixed via the fixed-side support member 12b rather than the rigidity of the upper gun arm 11a to which the movable-side welding tip 13a is mounted via the movable-side support member 12a. The lower gun arm 11b to which 13b is attached is strong. In this case, due to the rigidity of the lower gun arm 11b, the lower gun arm 11b is not displaced by the fixed-side welding tip 13b due to thermal expansion, and most of the displacement that occurs due to thermal expansion is The welding tip displacement amount TU. From this figure, it can be seen that the center position of the welded body 15 is significantly displaced upward in the vertical direction due to the difference in rigidity between the upper gun arm 11a and the lower gun arm 11b. Between the parts (a) and (b) in FIG. 6, the movable side welding tip 13 a is pushed in the direction opposite to the direction of pressurization due to the thermal expansion of the welded body 15 during energization of the welding current. The movable body welding tip displacement amount TU and the welded body center position displacement amount which is the displacement amount of the center position of the welded body 15 caused by the difference in rigidity between the upper gun arm 11a and the lower gun arm 11b of the gun arm 11. TC is shown, and the fixed side welding tip displacement TL is not shown because it is substantially equal to zero.
[0054]
As described above, with the thermal expansion of the nugget 16 of the welded body 15 during energization of the welding current, the center position of the welded body 15 moves and the welded body 15 is deformed. It becomes difficult to ensure appropriate welding quality. Therefore, in order to suppress deformation of the welded body 15, the welded body center position displacement amount TC accompanying thermal expansion during energization of the welding current described below is calculated, and welding is performed based on the welded center position displacement amount TC. It is necessary to perform processing for correcting the operation of the robot 1.
[0055]
FIG. 7 is a diagram showing a flowchart of calculation of the welding object center position displacement amount TC and control of the correction operation of the welding robot 1 in the welding gun position correction device 70 and the welding robot control device 60.
[0056]
In step S100 of FIG. 7, the welding robot control device 60 transmits a drive command to the welding robot motors 30, 40, 50 provided at the joints of the multi-joint mechanism 2 of the welding robot 1. The welding robot motors 30, 40, 50 are driven in accordance with the drive command. When the welding gun 10 is positioned at a position where the workpiece 15 can be clamped by this driving, the welding robot control device 60 transmits a drive command to the welding gun motor 20, and the welding gun motor 20 receives the command. And the workpiece 15 is sandwiched between the welding tips 13a and 13b and pressurized with a predetermined pressure.
[0057]
Next, in step S200, the welding robot control device 60 transmits, for example, a welding current energization start command to a welding machine control device (not shown), and the welding machine control device receives the welding power source. Further, the welding current is supplied to the welding tips 13a and 13b, whereby the welding current is supplied to the welded body 15.
[0058]
Next, in step S300, the welding robot controller 60 calculates the movable-side welding tip displacement amount TU from the displacement amount of the rotation angle of the drive shaft of the welding gun motor 20 detected and transmitted by the welding gun encoder 21. Then, the calculated movable welding tip displacement amount TU is transmitted to the welding gun position correcting device 70.
[0059]
Next, in step S400, the welding gun position correcting device 70 calculates the thermal expansion of the welded body 15 from the strain of the lower gun arm 11b transmitted from the strain sensor 22 and the elastic coefficient of the gun arm 11 measured in advance. Thus, the fixed side welding tip displacement amount TL, which is the amount by which the fixed side welding tip 11b is pushed back in the direction opposite to the pressurizing direction, is calculated.
[0060]
Next, in step S500, the welding gun position correcting device 70 calculates the movable side welding tip displacement amount TU calculated and transmitted by the welding robot control device 60 in step S300, the distortion of the lower gun arm 11b and the gun arm in step S400. From the fixed-side welding tip displacement amount TL calculated from the elastic coefficient, the displacement amount of the position of the welded portion of the welded body 15 and the center position of the welded body 15 on the central axis of the welding tips 13a and 13b. The center position displacement amount TC to be welded, which is the displacement amount, is calculated. Here, the welded body 15 is composed of two metal plates 15a having substantially the same thickness, and when both are made of the same material, the respective expansion amounts of the metal plates 15a can be regarded as being substantially equal. Therefore, the center position displacement amount TC of the welded body can be calculated as TC = (TU + TL) / 2. Here, by calculating the displacement amount of the center position of the welded body 15 as the displacement amount of the position of the welded portion of the welded body 15, the displacement amount of the welded body accompanying the thermal expansion that occurs during the welding current conduction is calculated. It is possible to calculate accurately. It should be noted that during welding current application, the pressure applied to the welded object 15 is maintained substantially constant, and the cause of the distortion generated in the welding gun 10 is mostly due to thermal expansion in the nugget portion 16, so By this method, the displacement amount of the welded body 15 due to thermal expansion during energization of the welding current can be calculated with high accuracy.
[0061]
By calculating the center position displacement amount TC of the welded body 15 from the movable side welding tip displacement amount TU and the fixed side welding tip displacement amount TL as described above, the center of the welded portion of the welded body 15 that is difficult to detect directly is calculated. It is possible to estimate the amount of displacement of the position.
[0062]
Next, in step S600, the welding gun position correction device 70 calculates the position of the welding gun 10 by the amount of displacement TC of the welded body center position that has occurred due to thermal expansion in the formation of the nugget 16 calculated in step S500. Control for correction, that is, a welding gun for moving the welding gun 10 in the opposite direction to the direction of displacement of the center position of the welded body 15 due to thermal expansion by the same amount as the center position displacement amount TC of the welded body A position correction command is transmitted to the welding robot controller 60. According to the command, the welding robot control device 60 transmits a drive command to each of the welding robot motors 30, 40, 50, and the welding robot 1 moves the welding gun 10 to a position to be corrected according to the command.
[0063]
In FIG. 8, since the rigidity of the lower gun arm 11b is stronger than the rigidity of the upper gun arm 11a as shown in FIG. 6 described above, the center position displacement amount TC of the welded body is perpendicular to the center axis of the welding tips 13a and 13b. FIG. 8 is a diagram showing an example of correction control of the position of the welding gun 10 by the welding robot control device 60 in step S600 of FIG. 7 when it occurs upward. In FIG. 8, the position of the welding gun 10 before the correction control is performed is indicated by a broken line 10a, and the position 10b of the welding gun 10 after the correction control is performed is indicated by a solid line. The welding center position displacement amount TC vertically upward on the central axis of the welding tips 13a and 13b calculated by the welding gun position correcting device 70 in the step 500 is compared with the welding robot in FIG. The control device 60 for the welding robot 1 has a distance L equal to the absolute value of the welded body center position displacement TC from the welding gun position 10a before the correction control, vertically downward (in the direction of the arrow in FIG. 8). This shows that correction control is performed such that the welding gun position 10b after certain correction control is moved.
[0064]
Returning to FIG. 7, if correction control of the position of the welding gun 10 is performed in step S <b> 600, then, in step S <b> 700, the welding robot control device 60 determines whether or not a predetermined energization time of the welding current has elapsed. I do. In this determination, as long as it is determined that the predetermined energization time has not elapsed (NO in step S700), the processing from step S300 to step S600 is repeated, and displacement occurs at the center position of the welded body 15. Each time the control is performed to correct the displacement, and the position of the welding gun 10 is corrected according to the displacement amount of the center position of the welded body 15, the center position of the welded body 15 can be kept constant. Become.
[0065]
If it is determined in step S700 that the predetermined energization time of the welding current has elapsed (YES in step S700), then in step S800, welding robot controller 60 has welding gun 10 to be welded. A command for releasing the clamping and pressurization of the body 15 is transmitted to the welding gun motor 20, and the welding gun motor 20 is driven according to the command, and the welded body 15 is released from the welding gun 10.
[0066]
Next, in step S900, the welding robot control device 60 transmits a drive command to each welding robot motor 30, 40, 50 so as to move the welding gun 10 to the next welding spot position, and the welding robot according to the command. The motors 30, 40, 50 are driven, and the welding gun 10 is moved to the next spot position.
[0067]
As described above, by repeating the control for correcting the position of the welding gun according to the displacement amount of the center position of the welded body accompanying the thermal expansion of the welded body from the start to the end of the welding current, Accordingly, it is possible to suppress the vertical movement of the center position of the welded body, and to perform nugget formation without deformation of the welded body, and to ensure appropriate welding quality.
[0068]
The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a welding robot in an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of a welding gun that is an end effector of the welding robot shown in FIG. 1;
FIG. 3 is a block diagram showing a control configuration in the embodiment of the present invention.
FIG. 4 is a diagram showing a state of displacement of a welding tip and a welded body during energization of a welding current.
FIG. 5 is a diagram showing the center position displacement amount of the welded body, the movable side welding tip displacement amount, and the fixed side welding tip displacement amount during energization of the welding current.
FIG. 6 is a diagram showing a displacement state of a welding tip and a welded body during energization of a welding current when the rigidity of the lower gun arm is strong.
FIG. 7 is a diagram showing a flowchart of calculation of the displacement amount of the center position of the welded body and correction control of the welding robot in the embodiment of the present invention.
FIG. 8 is a diagram showing an example of correction control of a welding gun when the rigidity of the lower gun arm shown in FIG. 6 in the embodiment of the present invention is strong.
[Explanation of symbols]
1 ... Welding robot
2 ... Articulated mechanism
3 ... Cable for welding current
10 ... Welding gun
10a: Welding gun position before correction control
10b: Welding gun position after correction control
11 ... Gunarm
11a ... Upper gun arm
11b ... Lower gun arm
12a: Fixed support member
12b ... movable side support member
13a ... Movable welding tip
13b ... Fixed welding tip
14 ... Slide mechanism
14a ... Movable part
15 ... Welded body
15a ... Metal plate
16. Nugget
20 ... Motor for welding gun
21 ... Welding gun encoder
22 ... Strain sensor
30: First welding robot motor
31 ... First welding robot encoder
40 ... Second welding robot motor
41 ... Second welding robot encoder
50. Motor for Nth welding robot
51. Encoder for Nth welding robot
60. Control device for welding robot
70 ... Welding gun position correction device
L: Correction movement amount
TU ... Moving side welding tip displacement
TL: Fixed side welding tip displacement
TC ... Center position displacement of welded body

Claims (8)

First welding tip displacement detecting means for detecting a displacement amount of the first welding tip attached to one tip of the welding gun;
Second welding tip displacement detecting means for detecting a displacement amount of a second welding tip attached to the other tip of the welding gun;
An equalizing device having welding gun position correcting means for giving a command to correct the position of the welding gun according to the amount of thermal expansion of the welded body during energization of the welding current,
The welding gun position correcting means detects the displacement amount of the first welding tip detected by the first welding tip displacement detecting means and the second welding detected by the second welding tip displacement detecting means. An equalizing device that calculates the displacement amount of the position of the welded portion of the welded body during energization of the welding current from the tip displacement amount and issues a command to correct the position of the welding gun so as to cancel the displacement amount . The equalizing device according to claim 1, wherein the first welding tip displacement detecting means detects a displacement amount of an actuator for moving the first welding tip provided in the welding gun. 3. The equalizing apparatus according to claim 1, wherein the second welding tip displacement detecting unit calculates a displacement amount of the second welding tip from a distortion of a gun arm of the welding gun in the vicinity of the second welding tip . The displacement amount of the position of the welded portion of the welded body calculated by the welding gun position correcting means is a displacement amount TC of the center position of the welded body calculated by the following equation. The equalizing device according to crab.
TC = (TU + TL) / 2
However, in the above formula, TU is the displacement amount of the first welding tip, and TL is the displacement amount of the second welding tip. An equalizing method for correcting the position of the welding gun according to the thermal expansion of the welded body during welding current energization,
Based on the amount of displacement of the first welding tip attached to one end portion of the welding gun and the amount of displacement of the second welding tip attached to the other end portion of the welding gun, the object to be energized during welding current conduction is determined. An equalizing method for calculating a displacement amount of a position of a welded portion of a welded body and correcting the position of the welding gun so as to cancel the displacement amount . The equalizing method according to claim 5, wherein the displacement amount of the first welding tip is calculated from a displacement amount of an actuator for moving the first welding tip provided in the welding gun. The equalizing method according to claim 5 or 6, wherein a displacement amount of the second welding tip is calculated from a distortion of a gun arm of the welding gun in the vicinity of the second welding tip. The equalizing method according to any one of claims 5 to 7, wherein the calculated displacement amount of the position of the welded portion of the welded body is a displacement amount TC of the center position of the welded body calculated by the following equation .
TC = (TU + TL) / 2
However, in the above formula, TU is the displacement amount of the first welding tip, and TL is the displacement amount of the second welding tip.

Images