JP4375671B2 - Robot seam welding method and apparatus - Google Patents

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 portion. 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.

  As a system for automated seam welding of automobile fuel tanks and the like, robot seam welding equipment, in which a robot is added to the seam welding machine, has become the mainstream. In such a device, a robot grips a workpiece (such as a fuel tank), holds a workpiece flange between a pair of electrode wheels provided in a seam welder, and reproduces an operation program taught by a robot controller. By moving the robot, the flange of the workpiece is continuously fed between the electrode wheels and welded.

  In the robot seam welding apparatus of the type described above, the control system for driving the articulated robot and the control system for driving the electrode wheel are independent. Therefore, in order to synchronize both operations, there is a problem that high-speed and precise control is difficult due to the influence of transmission delay between control systems.

Further, such a robot seam welding apparatus has a problem when welding a workpiece curved in a three-dimensional shape.
For example, in the curved welded part of the workpiece 15 as shown in FIG. 4, the upper and lower lengths of the workpiece 15 are different depending on the plate thickness W of the workpiece. When welding the curved portion, if the upper and lower electrode wheels 17a and 17b are rotated at the same speed, a difference occurs between the moving speed at which the electrode wheel is moved with respect to the workpiece 15 and the rotation speed of the electrode wheel, and the difference in speed between them. For this reason, a tensile force acts on the workpiece surface, and cracks occur at the welded point.
In order to solve this problem, it is desirable to control the upper and lower electrode wheels at different speeds.

To deal with these problems, a robot is not used, but a single numerical control device controls the electrode wheels and the workpiece feed mechanism, and drives the upper and lower electrode wheels at different speeds. There has been proposed a seam welder that follows and welds a three-dimensional welding locus (see, for example, Patent Document 1).
In this proposal, rotation control of the electrode wheel is performed by programming. However, when using a robot, the rotation control of the electrode wheel is added so that the robot automatically accelerates or decelerates at the corner of the workpiece. Creating a program takes a lot of man-hours.
JP-A-10-99972

  It is an object of the present invention to provide a robot seam welding method and apparatus capable of accurately controlling the operation of a robot and a welding machine with a relatively simple configuration and preventing cracks in a curved welded portion. And

  In the robot seam welding method according to the present invention, the workpiece to be welded held by the articulated robot is sandwiched between a pair of stationary electrode wheels, the electrode wheels are rotated, and the position of the workpiece to be welded taught in advance is determined. The robot performs seam welding on the workpiece by passing a welding current through the electrode wheel while periodically instructing the robot to move the workpiece along the welding line. In this method, the articulated robot and the electrode wheel are operated synchronously, and the movement distance of each electrode wheel on the workpiece is calculated based on the command position to the robot which is periodically calculated, and this movement distance is met. The electrode wheel is rotated at a speed.

  A robot seam welding apparatus according to the present invention for carrying out the above method includes an articulated robot that grips an object to be welded, a pair of stationary circular electrode wheels, and a control that controls the operation of the robot and the electrode wheels. Including units. 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 by passing a welding current through the electrode wheel while moving the workpiece along the welding line. In this device, the control unit operates the robot and the electrode wheel synchronously, obtains the moving distance of each electrode wheel on the workpiece based on the periodically calculated command position, and at a speed corresponding to this moving distance. The electrode wheel is rotated.

  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 method and apparatus of the present invention described above operate the robot and the electrode wheel in synchronization. Therefore, both can be controlled at high speed and accurately. Moreover, the movement distance of each electrode ring on a to-be-welded object is calculated | required periodically, and an electrode ring is rotated at the speed according 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. This apparatus has an articulated robot 1, a stationary seam welder 6 attached to the articulated robot 1, and a control unit 8 that controls the operation of the robot and the welder.
In FIG. 1, the control unit 8 is displayed so as to be attached to the outside of the robot and the welding machine, but the control unit may be a robot control device built in the robot body.

  The articulated robot 1 includes a workpiece gripping device 2 for gripping the workpiece 5 at the tip thereof. The workpiece gripping device 2 includes a C-shaped frame 3 having one outer end attached to the tip of the robot, and workpiece gripping members 4a and 4b each having a rotation mechanism that are respectively attached to both inner ends of the C-shaped frame. Become. The workpiece gripping members 4a and 4b are movable so as to approach or move away from each other by a cylinder mechanism or the like (not shown), and grip the workpiece 5 by closing the workpiece 5 therebetween.

The seam welding machine 6 has a pair of circular upper electrode wheel 7a and lower electrode wheel 7b arranged opposite to each other, and these electrode wheels are driven to rotate by a separate electric motor via a speed reducer and a drive shaft. Is done. The motor that drives the electrode wheels 7 a and 7 b is controlled by the control unit 8.
Further, the upper electrode wheel 7a is configured to be movable so as to be pressed against the lower electrode wheel 7b by a pressurizing device (not shown) such as an air cylinder mechanism. By this operation, the workpiece is moved between the electrode wheels 7a and 7b. Hold it.

Next, seam welding work in the apparatus of this embodiment will be described.
Prior to this work, the control unit 8 stores an operation program created by teaching the robot 1 so that the workpiece 5 moves along a welding locus in which the flange surface to be welded is applied to the electrode wheels 7a and 7b. At this time, as shown in FIG. 2, straight lines a-a ′ to tangent to the workpiece welding line L (set on the lower surface of the flange of the workpiece 5 in the illustrated example) connecting the rotation centers of the electrode wheels 7 a and 7 b. The robot 1 is taught by setting the movement trajectory of the workpiece 5 so that cc 'is always orthogonal. This operation program includes numerical data including position information for operating the robot, data for controlling the start and end timing of welding, welding speed, welding conditions, and the like. Further, the thickness W of the flange of the workpiece 1 to be welded is stored in the control unit 8 in advance.

The welding operation is performed by reproducing the operation program stored in the control unit 8.
When the work 5 is held by the work gripping device 2 and a work start command is input to the control unit 8, the articulated robot 1 moves based on the operation program, and the work 5 is moved to the electrode wheels 7 a and 7 b of the seam welding machine 6. The flange surface of the workpiece 5 is inserted between the electrode wheels 7a and 7b which are conveyed and opened. Next, under the driving of the pressurizing mechanism described above, the electrode wheel 7a is pressed toward the electrode wheel 7b, and a pressurizing operation is performed with a pressurizing force suitable for welding to sandwich the flange surface of the workpiece 5, whereby the electrode wheel 7a and 7b are at the start position of the welding operation.

  When this pinching operation is completed, the control unit 8 outputs a welding signal and a welding condition signal to the seam welding machine 6, and at the same time, the articulated robot 1 starts moving at a predetermined welding speed, and the electrode wheels 7a, The rotation of 7b is also started. Thus, seam welding of the flange surface of the workpiece 5 is performed, and when the articulated robot 1 moves to the welding end position, the control unit 8 stops the welding signal and stops the articulated robot and the electrode wheel. Thereafter, the electrode wheel 7a is opened, and the work 5 that has been welded is taken out from between the electrode wheels 7a and 7b to complete the operation.

During the reproduction of the operation program described above, the control unit 8 calculates a command position to the robot 1 at regular intervals and commands the servo control device of the robot, and the servo command device drives the robot 1.
At each fixed cycle, the control unit 8 determines the contact position B2 (FIG. 3) between the stationary electrode wheel 7b and the flange lower surface of the workpiece 5 based on the command position for the robot, Is calculated and stored as a position on the coordinate system set to. Further, based on the plate thickness W of the workpiece 5 stored in advance, a position A2 that is separated from the contact position B2 by the plate thickness W on a straight line connecting the rotation centers of the electrode wheels 7a and 7b is calculated in the same manner as B2. And stored as the contact position of the electrode wheel 7a on the pressure side.

  At this time, a first coordinate system in which one coordinate axis is made to coincide with a straight line connecting the rotation centers of the electrode wheels on a position where the electrode wheels come into contact with each other at the time of pressurization in advance, for example, a first coordinate system made to coincide with the Z axis. The coordinate system is defined, and the physical positional relationship between the position where the electrode wheels contact each other and the robot is set. When the first coordinate system is made to coincide with the Z axis, the position B2 is expressed as (0, 0, 0) in the first coordinate system, and the position A2 is expressed as (0, 0, W). The By projecting this coordinate position onto the second coordinate system set at the arm tip, the position B2 and the position A2 can be obtained as positions on the coordinate system set at the arm tip.

At the same time, the control unit 8 simultaneously measures the distance dB between the contact position position B1 between the electrode wheel 7b stored in the previous cycle and the lower surface of the workpiece flange and the currently calculated position B2, and the electrode wheel 7a stored in the previous cycle and the workpiece. The distance dA between the contact position A1 with the upper surface of the flange and the position A2 calculated this time is obtained.
These distances dA and dB are the amount of movement of the electrode wheels 7a and 7b on the outer circumference, that is, the amount of movement of the workpiece 5 on the flange surface.

The control unit 8 calculates a rotation amount commensurate with the calculated movement amounts dA and dB, and instructs the drive motor as a rotation command for the electrode wheels 7a and 7b. The above process is repeated during the operation of the robot from the start to the end of welding.
In this way, even when welding a work part curved in a three-dimensional shape, each electrode wheel 7a, 7b is driven at a rotation corresponding to the movement distance on the work 5, 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 amount of wear of the electrode wheel is known, a rotation command corresponding to the wear can be created based on the current rotation radius of the electrode wheel and the amount of movement on the workpiece.

1 schematically shows a robot seam welding apparatus according to an embodiment of the present invention. FIG. Schematic for demonstrating the welding locus | trajectory taught to the robot of the apparatus of FIG. The schematic for demonstrating rotation control of the electrode wheel by the control unit of the apparatus of FIG. The schematic for demonstrating the problem by the conventional robot seam welding apparatus.

Explanation of symbols

1 Articulated robot 2 Work gripping device 5 Workpiece
6 Seam welding machine 7a, 7b Electrode wheel 8 Control unit A1, A2, B1, B2 Contact position dA, dB Movement distance L Welding line W Thickness of workpiece

Claims (3)

A workpiece to be welded held by an articulated robot is sandwiched between a pair of stationary electrode wheels, these electrode wheels are rotated, and the position on the welding line of the workpiece to be welded is instructed periodically to the robot to be welded. In a robot seam welding method for performing seam welding of an object to be welded by passing a welding current to an electrode wheel while moving an object along the welding line,
The articulated robot and the electrode wheel are operated synchronously, and the moving distance of each electrode wheel on the workpiece is calculated based on the command position to the robot that is periodically calculated, and the electrode is moved at a speed corresponding to the moving distance. A robot seam welding method characterized by rotating a ring.   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 for gripping the workpiece, a pair of stationary circular electrode wheels, and a control unit for controlling the operation of the robot and the electrode wheels. The welding line is memorized, the work piece is sandwiched between the electrode rings, these electrode rings are rotated, the position on the memorized welding line is periodically commanded to the robot, and the work piece is moved along the welding line. However, in the robot seam welding equipment that performs seam welding of the work piece through the welding current through the electrode ring,
The control unit controls the operation of the robot and the electrode wheel in synchronism, obtains the movement distance of each electrode wheel on the workpiece based on the periodically calculated command position, and at a speed corresponding to the movement distance. A robot seam welding apparatus characterized by rotating the electrode wheel.

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