Locus correcting method for industrial robots

• US 5,276,777 A
• Filed: 10/07/1991
• Issued: 01/04/1994
• Est. Priority Date: 04/27/1988
• Status: Expired due to Fees

• Current Assignee: Fanuc Ltd (Fanuc Corporation)
• Original Assignee: Fanuc Ltd (Fanuc Corporation)
• Inventors: Hara, Ryuichi
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): DAVIS, GEORGE B
• Application Number:
  US07/770,789
• Time in Patent Office: 820 Days
• Field of Search: 395/87, 395/86, 395/93, 219/124.34
• US Class Current: 700/252
• CPC Class Codes: G05B 19/42 Recording and playback systems, i.e. in which the programme is recorded from a cycle of operations, e.g. the cycle of operations being manually controlled, after which this record is played back on the same machine
• CPC Class Codes: G05B 19/425 Teaching successive positions by numerical control, i.e. commands being entered to control the positioning servo of the tool head or end effector
• CPC Class Codes: G05B 2219/36417 Programmed coarse position, fine position by alignment, follow line, path adaptive

Abstract

The robot is started after a groove line of a workpiece to be welded is taught to the robot as a target movement locus for the distal end of a welding torch, by using a fixed coordinate system. A control unit of the robot calculates a position (Pi) of an individual interpolation point in the fixed coordinate system in accordance with data specified in a program (S5), and successively calculates corrected positions Pi'"'"' (Xi Σxr'"'"', Yi Σyr'"'"', Zi Σzr'"'"') of respective interpolation points by using a cumulative value of correction amounts (S8). The correction amounts are obtained through transformation of an output of a visual sensor, representing a deviation of a current moving position of the torch from the groove line in a predetermined coordinate system defined by the current position and a current moving direction of the torch end, into a correction amount in the fixed coordinate system. In accordance with the result of a second transformation of the corrected positions Pi, individual axes of the robot are controlled such that the torch end is moved sequentially to the corrected positions (S9), to thereby move the torch end along the target locus. The correction is carried out each time the position of the workpiece is moved.

Claims

1. A locus correcting method for an industrial robot, comprising the steps of:

(a) teaching a target movement locus for a work point of a robot, using a fixed coordinate system;

(b) periodically detecting an error between a current moving position of the work point and the target movement locus, using a predetermined coordinate system defined by the current moving position and a current moving direction of the work point to define an error vector;

(c) transforming the error vector defined in the predetermined coordinate system into a correction amount in reference to the fixed coordinate system; and

(d) correcting the current moving position of the work point using the correction amount.

2. The locus correcting method according to claim 1, wherein the predetermined coordinate system has an origin coinciding with the current moving position of the work point, a first coordinate axis extending in the current moving direction of the work point, a second coordinate axis extending in a direction perpendicular to the target movement locus taught in step (a), and a third coordinate axis perpendicular to the first and second coordinate axes.

3. The locus correcting method according to claim 2, wherein detection of the error in said step (b) is carried out using a sensor having a field of view covering at least the current moving position of the work point and part of the target movement locus.

4. The locus correcting method according to claim 1, wherein said correcting in said step (d) comprises the steps of:

(d1) performing an inverse conversion on a corrected position of the work point to determine operating conditions of individual axes of the robot for achieving the corrected position; and

(d2) driving movement of the robot along the individual axes in dependence upon the operating conditions determined in step (d1).

5. The locus correcting method according to claim 4, wherein detection of the error in said step (b) is carried out using a sensor having a field of view covering at least the current moving position of the work point and part of the target movement locus.

6. The locus correcting method according to claim 1, wherein detection of the error in said step (b) is carried out using a sensor having a field of view covering at least the current moving position of the work point and part of the target movement locus.

7. An apparatus for correcting an actual movement locus of a robot relative to a workpiece, the robot having a fixed coordinate system, said apparatus comprising:

locus definition means for defining a target movement locus of a work point of the robot relative to the workpiece;

a sensor system to periodically generate an error vector, representing an error between a current moving position of the work point and the target movement locus, in a work point coordinate system defined by the current moving position and a current moving direction of the work point;

a processing unit, operatively connected to said locus definition means and said sensor system, to transform the error vector in the work point coordinate system into a correction amount in reference to the fixed coordinate system of the robot; and

an axis controller, operatively connected to said processing unit, to control movement of the work point of the robot in dependence upon the target movement locus and the correction amount.

8. An apparatus as recited in claim 7,

wherein said locus definition means comprises:

a teaching pendent for producing signals indicating the target movement locus of the work point when the workpiece is in a predetermined orientation in the fixed coordinate system; and

a memory, operatively connected to said processing unit and said teaching pendant, for storing robot control data indicating the target movement locus in dependence upon the signals produced by said teaching pendant.

9. An apparatus as recited in claim 7, wherein said locus definition means comprises a memory, operatively connected to said processing unit, for storing robot control data indicating the target movement locus.

10. An apparatus as recited in claim 7, wherein the robot has an arm, and

wherein said sensor system comprises a television camera mounted on the arm of the robot.