Method of controlling robot for use in arc welding

• US 5,624,588 A
• Filed: 08/17/1995
• Issued: 04/29/1997
• Est. Priority Date: 08/22/1994
• Status: Expired due to Term

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Ikeda, Yoshitaka, Terawaki, Fumikazu
• Primary Examiner(s): SHAW, CLIFFORD C
• Application Number:
  US08/515,989
• Time in Patent Office: 621 Days
• Field of Search: 219/124.34, 219/125.11, 901/42
• US Class Current: 219/124.34
• CPC Class Codes: B23K 2101/06 Tubes
• CPC Class Codes: B23K 9/1272 Geometry oriented, e.g. beam optical trading

Abstract

A robot supports a welding torch for use in arc welding of a cylindrical welding object. The welding object is rotated about an axis and is controlled by a robot controller. The robot is operated to track the welding torch along a calculated welding line to continuously position the welding torch along the welding line. A reference circle is formed by rotation of one point on the welding object. A coordinate system is set with a center corresponding to the center of the reference circle. A laser sensor detects a point on the welding line, and the detected point is stored by using a distance r from a center O of the work coordinate system and a z-coordinate value z. As the cylindrical welding object is rotated by an angle θ corresponding to an interval between the position detected by the laser sensor and a calculated second position, the welding torch is moved to a position to coincide with the second position.

Claims

1. A method for controlling a welding robot system including an industrial robot, a robot controller which outputs control signals to control the robot, a welding torch supported by a distal end of the robot, cylindrical welding object rotating means driven in response to the control signals of said robot controller, and a laser sensor to detect a welding line on said welding object, said method comprising the steps of:

(a) rotating a first point on the welding line of said cylindrical welding object in response to control signals from said robot controller and at a predetermined angular velocity to form a reference circle having a center position, and determining a position of said welding torch with respect to the center position;

(b) detecting a second point on said welding line with said laser sensor during rotation of said welding object and calculating position data which corresponds to the second point;

(c) calculating a time when said second point will reach the position of said welding torch from the angular velocity of the welding object and the calculated position data of the second point;

(d) calculating a future position of said second point during rotation about the center position of said reference circle; and

(e) moving the welding torch to the calculated future position at the calculated time, thereby executing welding line tracking of said robot.

2. A method of controlling a robot according to claim 1, wherein the center position of the circle in the step (a) is set as a coordinate origin of an orthogonal three axes coordinate system including said circle as a plane along a first-axis and a second-axis.

3. A method of controlling a robot according to claim 2, wherein the position data of the second point includes a distance measurement from the origin of said orthogonal three axes coordinate system to the detected point, and a third-axis value from the detected point.

4. A method for controlling a welding robot system including an industrial robot, a robot controller which outputs control signals to control the robot, a welding torch supported by a distal end of the robot, a roller which rotates the cylindrical welding object in response to the control signals of said robot controller, and a laser sensor which detects a welding line on the welding object, said method comprising the steps of:

rotating a first point on the welding line of said cylindrical welding object in response to control signals from the robot controller at a predetermined angular velocity to form a reference circle having a center position and determining a position of said welding torch with respect to the center position;

detecting a second point on said welding line with said laser sensor during rotation of said welding object and calculating position data corresponding to the second point;

calculating a time when said second point will reach the position of said welding torch from the angular velocity of the welding object and the calculated position data of the second point;

calculating a future position of said second point during rotation about the center position of said reference circle; and

moving the welding torch to the calculated future position at the calculated time.

5. A method for controlling a robot arm which performs arc welding with a robot controller, comprising the steps of:

(a) (a-1) positioning a cylindrical object for rotation about a rotating axis,

laying a robot tool center point on a first specific point of said object, and

obtaining coordinate value data corresponding to said first specific point on a world coordinate system,

(a-2) repeating sub step (a-1) to obtain coordinate value data of second and third specific points on the world coordinate system,

(a-3) creating an equation which represents a reference circle passing through each of the first, second, and third specific points;

(b) setting a work coordinate system in the robot controller in which first and second orthogonal axes lie on a plane of said reference circle and a third axis extends perpendicularly through the center of the circle to define an origin;

(c) storing position data of the specific points in the robot controller on the work coordinate system which corresponds to a value of the rotating axis at a predetermined period, by using a laser sensor attached to a distal end of a robot arm, while rotating the object about the rotating axis at a predetermined speed;

(d) obtaining a detected position on the work coordinate system of a welding point to be welded by said laser sensor based on the position data stored in said step (c);

(e) calculating an incremental amount of rotation about the rotating axis which is required for said welding point to reach a distal end of a welding torch, based on the obtained position data, the position of the distal end of the welding torch, and the point of the origin of the work coordinate system; and

(f) causing the distal end of the welding torch to aim at the position which is obtained by rotating said detected point by an angle corresponding to said incremental amount about the origin of said work coordinate system.

6. A method of controlling a robot to weld a rotating object, comprising:

(a) obtaining the shape of the rotating object from at least three points about the circumference of a circle corresponding to said object;

(b) welding the object while rotating the object at a predetermined speed;

(c) detecting position data about the circumference of the circle during step (b); and

(d) performing weld line tracking from the detected position data during a predetermined period, the shape of the rotating object obtained in step (a), and the predetermined rotating speed.