JP2006082087A - Method and apparatus for robot seam welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for so called robot seam welding, by which method cracks, etc. on curved welded portions can be surely prevented, and which apparatus has a comparatively simple structure. <P>SOLUTION: In the method for the robot seam welding, the seam welding operation for a workpiece is carried out such that the workpiece 7 is gripped by a pair of electrode rings 3, 4 mounted on an articulated robot 1, and the welding current is supplied to the electrode rings while turning and moving the electrode rings along a preliminarily indicated welding line L of the workpiece by periodically giving the commands for the positions on the preliminarily indicated welding line L to the robot. In this method, the moving distances dA, dB of the respective electrode rings on the workpiece are determined based on the periodically calculated commanded positions A1, A2, B1, B2, and the electrode rings are turned at a speed corresponding with the moving distances. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a seam welding (hereinafter referred to as robot seam welding) method and apparatus using an articulated robot, and more particularly to a robot suitable for an object to be welded (hereinafter referred to as a workpiece) having a three-dimensionally curved welding line. The present invention relates to a seam welding method and apparatus.

  In seam welding, welding is performed by continuously applying a welding current between the electrode wheels while pressing the workpiece with a pair of rotating electrode wheels and moving the workpiece in accordance with the rotation of the electrode wheels. Such seam welding is suitable for joining containers that require airtightness, and is used, for example, in the manufacture of fuel tanks for automobiles.

Seam welding is automated using a robot. In general, a robot grips a workpiece and is configured to perform welding on a stationary seam welder having a pair of electrode wheels by moving the workpiece along the welding line.
On the contrary, there is a seam welding apparatus in which a welding head composed of an electrode wheel and a pressurizing device is mounted on a robot and moved along a fixed workpiece to perform welding (see, for example, Patent Document 1). This configuration is advantageous because the robot can move freely up and down, left and right, and it is easy to weld a three-dimensionally curved portion on the workpiece.
JP-A-9-234666

However, the seam welding apparatus as described above has a problem when welding a workpiece that is curved three-dimensionally.
For example, in the curved welded part of the workpiece 7 as shown in FIG. 3, the upper and lower lengths of the workpiece differ depending on the plate thickness W of the workpiece. When welding this curved part, if the upper and lower electrode wheels are rotated at the same speed, there is a difference between the moving speed at which the electrode wheel is moved relative to the work and the rotation speed of the electrode wheel. Tensile force acts on the surface, and cracks occur at the weld point.

In order to solve such a problem, it is desirable to control the upper and lower electrode wheels at different speeds.
Although not an apparatus using a robot, it has been proposed to control the upper and lower electrodes of a seam welder at different speeds (see, for example, Patent Document 2). In this proposal, rotation control of the electrode wheel is performed by programming. However, when a robot is used, a program that adds rotation control of the electrode wheel is used to automatically accelerate and decelerate the robot at corners. It takes a lot of man-hours to create.
Japanese Patent Laid-Open No. 10-99972

  An object of the present invention is to provide a robot seam welding method and apparatus capable of reliably eliminating a difference in speed of electrode wheels at a curved welding site and preventing cracking of a welded portion with a relatively simple configuration. And

  In the robot seam welding method according to the present invention, a workpiece is sandwiched between a pair of electrode wheels mounted on an articulated robot, the electrode wheels are rotated, and the position on the welding line of the workpiece to be previously taught is indicated to the robot. The workpiece is seam welded through a welding current while periodically moving the electrode wheel along the welding line. This method is characterized in that a moving distance of each electrode ring on the workpiece is obtained based on a command position calculated periodically, and the electrode wheel is rotated at a speed corresponding to the moving distance.

A robot seam welding apparatus according to the present invention for carrying out the above method includes an articulated robot, a pair of circular electrode wheels mounted on the articulated robot, and a control unit for controlling the operation of the robot and the electrode wheels. Including. The control unit memorizes the weld line of the workpiece to be taught in advance, sandwiches the workpiece with the electrode ring, rotates the electrode ring, and periodically instructs the robot on the stored position on the weld line. The workpiece is seam welded through a welding current while moving the electrode wheel along the welding line.
In this apparatus, the control unit further memorizes the thickness of the workpiece, obtains the movement distance of each electrode wheel on the workpiece based on the command position periodically calculated, and the electrode at a speed corresponding to the movement distance. It is characterized by rotating a ring.

  Preferably, the weld line is set on one surface of the workpiece, and the contact position of the electrode ring on the other surface of the workpiece is determined as a position away from the weld line by the thickness of the workpiece.

The above-described method and apparatus of the present invention periodically obtains the moving distance of each electrode wheel on the workpiece and rotates the electrode wheel at a speed corresponding to this distance. Therefore, even in the case where there is a difference in the moving distance of each electrode wheel in a three-dimensionally curved welding site, the rotational speed of each electrode wheel is changed according to the moving distance, the conventional tensile force is eliminated, and welding is performed. Defects such as cracks can be prevented.
Since such processing can be performed by using a command value obtained from the reproduction of the movement route taught to the robot, the present invention has a simple configuration without greatly changing the conventional system, and therefore is relatively There is an effect that the welding quality can be improved reliably and inexpensively.

Next, the present invention will be described based on embodiments shown in the accompanying drawings.
FIG. 1 shows a robot seam welding apparatus according to an embodiment of the present invention, which controls an articulated robot 1, a welding head 2 attached to the wrist of the robot 1, and the operation of the robot and the welding head. And a control unit 8.
Although the control unit 8 is displayed outside the robot 1 in FIG. 1, the control unit may be built in the robot body.

The welding head 2 includes a pair of circular pressure-side and fixed-side electrode wheels 3 and 4 that are arranged to face each other, motors 5 and 6 that rotationally drive the respective electrode wheels, a speed reducer and a drive shaft that connect the electrode wheels to the motor. In addition, a pressurizing mechanism (not shown) such as an air cylinder is provided to press the pressurizing side electrode ring 3 toward the fixed side electrode ring 4 so as to sandwich the workpiece between the electrode wheels.
Further, a welding transformer (not shown) is also included in the welding head 2, but this transformer may be installed outside the welding head. A welding machine (not shown) that controls the welding current is also placed outside the robot.

The control unit 8 has a built-in welding work program including work welding conditions and welding parts. When a work start command is issued, this program is executed to control the operation of the robot 1 and the welding head 2. To do.
In the welding operation, the robot 1 moves the welding head 2 to position the stationary work 7 (FIG. 3) between the electrode wheels 3 and 4. Next, under the driving of the pressurizing mechanism described above, the electrode wheel 3 is pressed against the electrode wheel 4 on the fixed side, and the work 7 is sandwiched between both electrode wheels. In this state, the electrode wheels 3 and 4 are rotated in opposite directions by driving the motors 5 and 6, and the robot 1 moves the electrode wheels 3 and 4 along the welded portion of the workpiece 7 in accordance with the rotation. At the same time, a welding current is applied to the electrode wheels 3 and 4 from the above-described welding machine, and a desired portion of the workpiece 7 is melted and seam welded.

Next, the work program of the control unit 8 and its processing will be described.
In the control unit 8, the position of contact of the fixed electrode wheel 4 with the workpiece 7 is registered as the tool tip (TCP) of the articulated robot, and the coordinate system at the tool tip is set as shown in FIG.
For a workpiece 7 having a plate thickness W as shown in FIG. 3, a weld line L is set along one surface (the lower surface in the illustrated example) of the workpiece. The movement trajectory of the robot 1 is taught so that a straight line I connecting the rotation centers of the electrode wheels 3 and 4 is orthogonal to the welding line L, and a work program for welding is created. By teaching in this way, the tip of the tool becomes a contact point with the workpiece 7 of the fixed-side electrode wheel 4, and the position separated from the tool tip in the Z direction by the thickness W of the workpiece in the tool tip coordinates is the pressure-side electrode. This is the contact point of the wheel 3 with the work 7. Since the tool tip speed of the robot 1 is equal to the welding speed, the welding speed is taught as the tool tip speed. The control unit 7 stores the thickness W of the workpiece 7 in advance.

When reproducing the taught work program, the control unit 8 calculates a command position for commanding the servo control unit of the articulated robot 1 at regular intervals.
At the same time, based on the calculated command position, the tool tip position A2 (contact position of the fixed electrode wheel 4) and the position B2 (pressurization side) separated from the tool tip at the tool tip coordinate by the plate thickness W of the workpiece 7 in the Z direction. The contact position of the electrode ring 3 is obtained. These positions are compared with the same fixed-side electrode wheel contact position A1 and pressure-side electrode wheel contact B1 calculated in the previous cycle to determine the distance dA between A2 and A1, and the distance dB between B2 and B1. The distance dA is the amount of movement of the fixed-side electrode wheel 4 on the workpiece 7, and the distance dB is the amount of movement of the pressure-side electrode wheel 3.

  The control unit 8 calculates a rotation amount commensurate with the movement amount calculated as described above, and instructs the servo motor as a rotation command for the electrode wheels 3 and 4. Thus, even in the case of welding a work part curved in a three-dimensional shape, each electrode wheel 3, 4 is driven at a rotation corresponding to the movement distance on the work, without causing the tensile force as described above, Good seam welding without cracks can be performed.

Although the present invention has been described based on the illustrated embodiments, the present invention is not limited to this specific form, and various modifications can be made to the form described within the definition described in the appended claims. Or the present invention may take other forms.
For example, the wear amount may be detected and taken into the control unit 8 in preparation for wear of the electrode wheel. With such a configuration, since the wear amount of the electrode wheel is known, a rotation command commensurate with the wear can be created based on the worn rotation radius and the movement amount of the workpiece.

1 schematically shows a robot seam welding apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a tool tip coordinate system set in the control unit of the apparatus of FIG. 1. The schematic for demonstrating rotation control of the electrode wheel by the control unit of the apparatus of FIG.

Explanation of symbols

1 Articulated Robot 2 Welding Head 3, 4 Electrode Wheel 7 Workpiece
8 Control unit A1, A2, B1, B2 Command position dA, dB Travel distance L Welding line W Thickness of workpiece

Claims (3)

The work piece is sandwiched between a pair of electrode wheels mounted on an articulated robot, the electrode wheels are rotated, and the position of the work piece on the weld line taught in advance is periodically commanded to the robot so that the electrode wheel is moved. In the robot seam welding method for performing seam welding of the workpiece through the welding current while moving along the welding line,
A robot seam welding method characterized in that a moving distance of each electrode wheel on a workpiece is obtained based on a periodically calculated command position, and the electrode wheel is rotated at a speed corresponding to the moving distance.   2. The method according to claim 1, wherein the weld line is set on one surface of the workpiece, and the contact position of the electrode ring on the other surface of the workpiece is separated from the weld line by the thickness of the workpiece. Robot seam welding method to be calculated as a position. An articulated robot, a pair of circular electrode wheels mounted on the articulated robot, and a control unit for controlling the operation of the robot and the electrode wheels, the control unit is configured to weld a workpiece to be welded in advance. The wire is memorized, the work piece is sandwiched between the electrode wheels, the electrode wheels are rotated, the position on the memorized welding line is periodically commanded to the robot, and the electrode wheel is moved along the welding line while welding. In robot seam welding equipment that performs seam welding of workpieces through electric current,
The control unit further memorizes the thickness of the workpiece, obtains the moving distance of each electrode wheel on the workpiece based on the periodically calculated command position, and rotates the electrode wheel at a speed corresponding to the moving distance. A robot seam welding apparatus characterized by

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