Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1987-02-25
1990-02-06
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856819, 364513, 901 47, G05B 1942
Patent
active
048990957
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a robot control system in which a predetermined task is executed by teaching a robot a position (hereafter referred to as "TCP") of a distal end of a working member (tool) mounted on a wrist of the robot.
When parts are assembled by using an industrial robot, it is necessary for prescribed parts to be repeatedly supplied to a set position at a predetermined timing by a parts feeder, which supplies the parts automatically. However, parts delivered in a flow by a conveyor belt, or the like, cannot always be accurately supplied to the same position every time. Accordingly, an offset for the TCP that has already been taught for the hand must be corrected by reading, via a TV camera, or the like, position information relating to the part to be manipulated, and feeding the information into the robot each time.
In such cases, in accordance with the prior art, an amount of rotational correction obtained from a sensor such as a camera is calculated in terms of displacement of the a rotational angle with regard to three basic axes of a hand vector. The tool offset at a taught position, serving as the origin of the correction, is corrected by a G45 preparatory code for a position rotating correction.
The position information sent to a robot from the sensor side is data indicative of an angle defined by a workpiece gripping direction vector, obtained by data processing on the sensor side, and a predetermined axis, e.g. the Xs axis, of the sensor coordinate system. Meanwhile, a robot calculation control unit stores the sensor coordinates upon converting them into data in the robot coordinate system. Consequently, when a rotational correction is performed which brings a unit vector (reference vector) in the direction of a predetermined axis, e.g., the Yt axis, of the tool coordinate system into coincidence with a gripping direction vector, of the workpiece, which of the Xt, Yt and Zt axes of the tool coordinate system the rotational correction will be performed about differs each time a workpiece is supplied. Moreover, control data, stored in the robot, regarding the sensor coordinate system, and control data in the tool coordinate system, for deciding the feedback data of the robot control unit, are both processed upon being converted into data indicative of the fundamental coordinate system of the robot. As a result, calculating the amount of rotational correction which brings the reference vector into coincidence with the gripping direction vector is very complicated.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the foregoing points and an object is to provide a robot control system capable of performing a tool position correction by simple processing based on position data received from a sensor.
A robot control system according to the present invention is adapted to execute a task at a predetermined position upon correcting a tool position offset of a robot, based on information indicative of the position of a workpiece. The robot control system includes a sensor arranged on a Z axis perpendicular to a coordinate plane (X-Y plane) parallel to a surface on which the workpiece rests, the coordinate axes of the sensor being fixed; and a robot calculation control unit for calculating an amount of rotational correction of a tool with regard to the sensor coordinate axes, from position information based on a vector indicating the gripping direction of the workpiece sensed by the sensor. If a rotational angle is determined from a projection of the gripping direction vector and the tool is subjected to a rotational correction with regard to the sensor coordinate axis (Zs, axis perpendicular to the surface on which the workpiece rests), then the tool position offset can be corrected even if the gripping direction vector of the workpiece is not parallel to the surface on which the workpiece rests.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view of the X, Y and Z coordinate axes illustrating a rotational correction of a tool vector a
REFERENCES:
patent: 3804270 (1974-04-01), Michaud et al.
patent: 4017721 (1977-04-01), Michaud
patent: 4105925 (1978-08-01), Rossol et al.
patent: 4373804 (1983-02-01), Pryor et al.
patent: 4380696 (1983-04-01), Masaki
patent: 4706000 (1987-11-01), Kishi et al.
Karakama Tatsuo
Kishi Hajimu
Sakakibara Shinsuke
Fanuc Ltd
Martin David
Shoop Jr. William M.
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