JP2900773B2 - Spot welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot welding method for assembling a work by a welding robot, and more particularly to a spot welding method for easily positioning a work to be welded.

[0002]

2. Description of the Related Art Spot welding has advantages such as a high welding speed and relatively easy automation, and is widely used as a method for assembling works such as panel parts constituting an automobile body. . FIG. 8 is a plan view showing an example of an assembly stage for performing such an assembly operation, and FIG. 9 is a side view showing a gauge post installed on the assembly stage. As shown in FIG. 8, a gauge post 101 on which the workpiece W is placed is installed on the assembly stage 11. Then, as shown in FIG. 9, a clamp member 103 for clamping the work W placed on the gauge post 101 is attached to the gauge post 10. The clamp member 103 has a clamp arm that can be opened and closed by a driving means such as an air cylinder 105.
Is closed (moved to the position shown by the solid line) to fix the work W. Further, a locate pin 109 for positioning a workpiece W to be placed is attached to some of the gauge posts 101. The locating pins 109 are attached to position the workpiece W to be placed at two positions, and a locating hole (not shown) formed in the workpiece W is fitted to the locating pins 109. Positioning is being performed.

Therefore, as shown in the flowchart of FIG. 10, when spot welding the work W, when the work W is first carried into the assembly stage 11, the gauge post is inserted into the locating hole formed in the work W at the same time. 1
The work W is supported by the gauge post 101 while the locating pin 109 formed at 01 is fitted (step 1). When the work W is placed on the gauge post 101, the clamp arm 1 is subsequently moved by the air cylinder 105.
07 is driven to fix the work W at a predetermined position by the clamp arm 107 (step 2). After fixing the workpiece W in this manner, a welding gun (not shown) for spot welding (not shown) is positioned at a predetermined position, and
The work W is pinched by a pair of welding tips (not shown) of the welding gun to perform spot welding (step 3). When the welding is completed, the pair of welding tips are separated from each other, and when the next work is carried in, the process returns to step 1 again to repeat the same operation. As described above, when performing spot welding, the work W is fixed by the clamp member 103 around the welding point.

As described above, in the conventional spot welding method, spot welding is performed with the periphery of the spot welding position fixed by the clamp member.

[0005]

However, when the work W is fixed in this manner, when spot welding is performed by the welding robot, the welding gun of the welding robot does not contact the gauge post 101 or the clamp member 103. Operation must be controlled. As a result,
Since these members are moved to a desired position while avoiding these members, the movement of the welding robot becomes extremely complicated, and therefore, the welding operation time is lengthened. This means that the number of points that can be welded within a certain period of time decreases, and if the predetermined spot welding work cannot be performed within the tact time in the body assembly work, the assembly stage must be increased. The problem arises. Also, as a worker, the moving path of the welding robot becomes complicated, so that the teaching work becomes complicated. Further, since a large number of clamp members need to be manufactured for each work, the assembly cost of the vehicle body increases. Further, since the gauge surface 111 of the gauge post 101 is used as a clamp member, there is a possibility that the gauge surface 111 is worn and the positioning accuracy of the vehicle body is reduced.

The present invention, which has been made in view of the above problems, has a small number of clamp members, the movement of a welding robot is simple, spot welding can be performed quickly, and a welding gun arm is used as a member for fixing a work. An object of the present invention is to provide a spot welding method.

[0007]

According to the present invention, there is provided a spot welding method comprising: an assembly stage provided with a gauge post on which a workpiece to be welded is placed and a locating pin for positioning the workpiece; The work placed on the assembly stage is clamped and welded by the fixed welding tip and the movable welding tip which can be moved forward and backward by the servo motor with respect to the fixed welding tip, and the welding gun welds the workpiece to the work. A spot welding method to be performed, wherein the servomotor is driven to move the movable welding tip forward, and the movable welding tip and the fixed welding tip cooperate to move the movable welding tip to the work placed on the assembly stage. Positioning the work and fixing the work before welding, and forming the work by welding. Is characterized by a step of calculating a correction value a according to the measurement value with measuring the assembling accuracy of body parts used for correction of the position of the welding of the welding gun.

[0008]

In the spot welding method having such features, when a work is placed on the assembly stage, the welding gun is first moved to a predetermined position. When the welding gun moves to a predetermined position, the servomotor is driven to move the movable welding tip forward, and the movable welding tip and the fixed welding tip position and fix the work. Thus, before welding the work, the work is fixed in advance by the movable welding tip and the fixed welding tip. Subsequently, current is supplied between the movable welding tip and the fixed welding tip to weld the work fixed to the two welding tips. Also, after welding is completed, the assembly accuracy of body parts is measured.
A correction value of the welding gun position at the time of welding is calculated based on the measured value. When the welding position of the welding gun is corrected based on this correction value, spot welding is performed at a more suitable position.

[0009]

Next, an embodiment of the present invention will be described with reference to the drawings. Note that the same reference numerals as those already used are assigned to the assembly stage and the work. FIG. 1 is a schematic perspective view showing an example of a spot welding apparatus used when assembling an automobile body, and FIG. 2 is a state in which a welding robot performs spot welding on a work supported on an assembly stage. FIG. FIG.
FIG. 3 is a plan view showing an assembly stage on which a work is placed.

As shown in FIG. 1, the spot welding apparatus includes an assembly stage 1 for supporting a workpiece W to be welded.
1 and a welding robot R for welding the work W. The welding robot R has a pedestal 13 attached to a base (not shown), and the pedestal 13 is provided with a swivel 15 that can swing in the direction of arrow J1. A robot shaft 17 is mounted on the revolving base 15 so as to be swingable in the direction of arrow J2. And this robot axis 17
, A robot shaft 19 is mounted so as to be swingable in a direction indicated by an arrow J3 and rotatable in a direction indicated by an arrow J4. At the tip of the robot shaft 19, a servo gun, that is, a welding gun 21 is attached so as to swing freely in a direction indicated by an arrow J5 and freely rotate in a direction indicated by an arrow J6.
Therefore, the robot R shown in FIG. 1 has a function of a total of six axes.

The welding gun 21 has a C-shaped gun arm 23. The gun arm 23 has a fixed electrode, that is, a fixed welding tip 25, and a movable welding part for welding the workpiece W in cooperation with the fixed welding tip 25. An electrode, ie, a movable welding tip 27 is provided. The movable welding tip 27 is moved forward by the servomotor 29 toward the fixed welding tip 25, and welds the work W. The operation of the servomotor 29 for operating the movable welding tip 27 and the operation of the aforementioned six axes are controlled by the robot control panel 31 shown in FIG.

FIG. 2 is a side view showing details of the gun arm shown in FIG. As shown, gun arm 2
3 has a drive rod 33 to which the movable welding tip 22 is attached at the tip. The drive rod 33 is supported by a bearing 35 attached to the gun arm 23 so as to be able to move forward and backward in the direction of arrow A, and is screwed to a nut of the gun arm 23 at a thread formed on the outer periphery. I have. The nut portion 37 is connected to a pulley 39 attached to a servomotor spindle attached to the gun arm 23 via a timing belt 41 as shown in the figure. Therefore, by driving the servo motor 29 to rotate the nut portion 37, the drive rod 33 screwed to the nut portion 37 can be moved forward and backward.

Further, by moving the driving rod 33 forward, a work is previously performed before spot welding is performed between the movable welding tip 27 attached to the tip of the driving rod 33 and the fixed welding tip 25 facing the movable welding tip 27. Since W is fixed, it is not necessary to attach a clamp member for fixing the work W around the welding point to the assembly stage 11. That is, the assembly stage 11
Can be simplified. Therefore, the number of clamp members installed on the assembly stage can be minimized, so that the cost required for the assembly equipment can be reduced, and the manufacturing cost of the product can be reduced. Further, the welding tips 25, 27 for fixing the workpiece W in this manner.
Next, spot welding is performed by supplying electric power from a power supply (not shown).

On the other hand, an assembly stage 1 for supporting the workpiece W
1, a gauge post 4 having a gauge surface 43 on which a workpiece W is placed, as shown in FIGS.
5 are installed. The assembling stage 11 of the present embodiment includes:
This is a stage for assembling a work W constituting the rear side of the vehicle body. As shown, a seat cross member W1, a center cross member W2, left and right rear side members W3 and W3, and left and right extension rear side members W4 and W4 are assembled. Have been. In this embodiment, the number of the gauge posts 45 supporting such a work W is ten, and a locate pin 47 is installed on each of the gauge posts 45. The work W placed on the assembly stage 11 is positioned at two places by such a gauge post 45. In the present embodiment, the number of the locate pin 47 for positioning the extension rear side member W4 is one. However, the work clamp member 49 described later has a shape corresponding to the shape of the work. It does not rotate, and the rotation of the work is also prevented by the adjacent work. Of course, two may be provided. Further, when the work W is relatively large or has a complicated shape, a gauge post having no locating pin may be provided to support the work W.

In the assembly stage 11 of this embodiment, clamp members 49 are provided by the number of which fix the work W to be placed at two places. In particular,
In the spot welding apparatus of the present embodiment, twelve clamp members 49 are provided for six works W. The work W can be stably supported on the assembly stage 11 by the clamp member 49 until the spot welding is performed. That is, when performing spot welding,
Since spot welding is performed in a state where the workpiece W is fixed in advance by the two welding tips 25 and 27 of the welding robot R, it is not necessary to install a clamp member 49 at each welding point. What is necessary is just to install the minimum clamp member. As a result, the cost required for the assembly equipment can be reduced, and the manufacturing cost of the product can be reduced.

As the clamp member, for example, a pair of clamp arms that can be opened and closed by driving means such as an air cylinder can be used. In this case, by closing the clamp arm, the work is held and fixed in a stable state. Alternatively, the gauge surface of the gauge post may be used as one of the arms. In this case, the workpiece is fixed by opening and closing the other clamp arm.

Next, the operation of the spot welding apparatus according to the present embodiment will be described with reference to the flowchart shown in FIG.
First, when the workpiece W is carried into the assembly stage 11, the locating pin 47 attached to the gauge post 45 is fitted into a locating hole (not shown) formed in the workpiece W, and the gauge surface of the gauge post 45 is fitted. The work W is placed on the work 43. Thereby, the work W is positioned on the assembly stage 11. When each work W is carried in and positioned, each clamp member 49 installed on the assembly stage 11 is operated to fix each work W (step 1). When the positioning and fixing of the work W are completed in this way, the welding robot R controlled by the control panel 31 is moved to position the fixed welding tip 25 fixed to the gun arm 23 below the welding point (step). 2). When the positioning of the fixed welding tip 25 is completed, the driving rod 33 is moved forward to the fixed welding tip 25 side, and the fixed welding tip 25 and the movable welding tip 27 at the tip of the driving rod 33 cooperate. Then, the work W is pressurized (step 3). This pressurizing operation is a clamp operation. As described above, since the workpiece W is clamped by the gun arm 23 of the welding robot R before performing the spot welding, it is not necessary to install the clamp member 49 for fixing the position close to each spot welding point on the assembly stage 11. . When the clamping of the workpiece W by the gun arm 23 is completed, a current is applied between the welding tips 25 and 27 to perform spot welding (step 4). These operations are repeated to perform spot welding to assemble the vehicle body.

Further, in the spot welding apparatus of this embodiment,
The method includes a step of performing position correction of a welding point using position correction data generated based on assembly accuracy measurement data measured off-line (step A).
In this position correction step, spot welding position data used for robot operation control is corrected as needed.

Hereinafter, the process of creating data necessary for correcting the position of a welding point will be described in detail with reference to FIGS. 5, 6 and 7. FIG. 5 is a schematic perspective view of a measuring device for measuring the assembling accuracy of the assembled work, FIG. 6 is an enlarged perspective view showing measuring points and spot welding points, and FIG. It is a flowchart shown. As shown in FIG. 5, first, the assembled body parts W are placed on a post 53 installed on a surface plate 51, and the layout machine 5 on the surface plate 51 is placed.
5, measurement points A to F in three directions of X, Y and Z
Each time, the deviation amount (measured value) ΔAx, from the standard points A0 to F0
ΔAy, ΔAz to ΔFx, ΔFy, ΔFz are measured, respectively. Then, the data indicating the measured shift amount is transmitted to a calculating means such as a personal computer (not shown) (step A).
1).

In the personal computer, based on the read deviation amount,
The correction amount (correction value) of the involved spot welding point P is calculated (step A2). Specifically, in the personal computer, a function f of the deviation amount of the measurement point and the correction amount of the spot welding position is prepared in advance, and by using this function f, the correction amount is calculated based on the measured deviation amount. Calculated quickly. For example, X of the n-th welding point by the welding gun 21
The direction correction amount Pnx is calculated by the following equation (1).

Pnx = f (ΔAx) Expression (1) This function f is an existing method used for data correction. In the present embodiment, a function f called a contribution rate is calculated by focusing on a point closer to the deviation amount as the correction amount of the spot welding point closer to the measurement point is calculated. The amount is calculated for each direction (see FIG. 6). Note that this is a simple explanation of the method of calculating the correction amount, and in practice, other auxiliary functions such as compensation for the deviation of the reference point itself are used in combination.

The created correction amount Pn is added to the position data before correction, and the corrected position data is created (step A3). The created position data is transmitted to the controller of the welding robot, that is, the control panel 31, and is used for controlling the destination position of the gun arm 23 during the subsequent assembling work. When the position of the gun arm 23 is corrected in this manner, the assembly accuracy of the work W is improved.

[0023]

As described above, according to the present invention, the number of clamp members to be set on the assembly stage can be minimized, so that the cost required for the assembly equipment can be reduced and the manufacturing cost of the product can be reduced. be able to. Also, when the number of clamp members is reduced, the number of members that hinder the operation of the welding robot is reduced, so that the operation of the welding robot can be simplified and the welding time can be shortened. In addition, the operation of teaching the operation of the welding robot becomes easy. Furthermore, since the work is fixed by the welding gun,
Even if the gauge surface is worn, the positioning accuracy of the work during the welding operation does not decrease. And since it has a means for correcting the positioning position of the welding robot, the welding robot can be moved to a position corresponding to the shape of the assembled work, so that spot welding can be performed at a suitable position. .

[Brief description of the drawings]

FIG. 1 is a schematic perspective view illustrating an example of a spot welding apparatus according to an embodiment.

FIG. 2 is a side view showing a state where spot welding is being performed on a work supported on an assembly stage by a welding robot.

FIG. 3 is a plan view showing an assembly stage on which a work is placed.

FIG. 4 is a flowchart showing an operation sequence of the spot welding apparatus according to the embodiment.

FIG. 5 is a schematic perspective view of a measuring device for measuring the assembling accuracy of assembled body parts.

FIG. 6 is an enlarged perspective view showing a measurement point and a spot welding point.

FIG. 7 is a flowchart showing an assembly accuracy measuring step.

FIG. 8 is a plan view showing a conventional assembly stage.

FIG. 9 is a side view showing a gauge post installed on a conventional assembly stage.

FIG. 10 is a flowchart showing an operation sequence of a conventional spot welding apparatus.

[Explanation of symbols]

11: assembly stage, 21: welding gun, 2
3: Gun arm, 25: fixed welding tip, 27: movable welding tip, 31: robot control panel, 45: gauge post, 47: locate pin, 49: clamp member, R: robot, W: work.

Claims (1)

(57) [Claims] An assembly stage provided with a gauge post on which a workpiece to be welded is mounted and a locating pin for positioning the workpiece, and a workpiece mounted on the assembly stage are fixed to a fixed welding tip and a fixed welding tip. A spot welding method in which welding is performed on the workpiece by a welding gun that presses and welds with a movable welding tip that is movable forward and backward by a servomotor with respect to the welding tip, wherein the servomotor is driven to move the movable tip. A step of moving a welding tip forward and positioning and fixing the work before welding is performed on the work placed on the assembly stage by cooperation of the movable welding tip and the fixed welding tip. Welding between the movable welding tip that fixes the work and the fixed welding tip to weld the work. Measuring the assembling accuracy of the body parts formed by welding the workpiece, and calculating a correction value used for correcting the position of the welding gun at the time of welding according to the measured value. And spot welding method.