Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
2000-02-18
2001-10-09
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S160000, C700S249000, C700S251000, C700S254000, C700S257000, C700S259000, C700S260000, C700S264000, C701S009000, C701S015000, C701S019000, C701S023000, C318S568100, C318S568110, C318S568130, C318S568150, C318S568190, C318S573000, C414S729000
Reexamination Certificate
active
06301525
ABSTRACT:
TECHNICAL FIELD
The present invention relates to controlling and correcting the spatial location of the positioning head of a robot. In the following, the term “robot” also covers machine tools of NC type, for instance, since in certain applications the present robot acts as a numerically controlled machine tool.
BACKGROUND ART
According to Patent specification SE 8502327-3 (452 279) a robot with a positioning head, the robot comprising at least three setting devices which can be extended and shortened in longitudinal direction, is already known. Each setting device is secured in a fixed frame via a first joint so that each setting device is pivotable in all directions in relation to the frame. Each setting device is also attached at one end in a movable positioning head via a second joint. A rigid arm is also joined to and emanates from the positioning head between the setting devices, the arm being radially guided but axially displaceably journalled in a universal joint relative to and rigidly connected to the frame.
A similar robot is also known in which the setting devices are secured in a displaceable runner via a first joint, the runner being secured in a fixed frame, so that each setting device is pivotable in all directions in relation to the frame. The joint is thus indirectly secured in the frame.
These known robots are controlled by each setting device being provided with a motor to extend or shorten the setting device. Control is effected by the setting devices being controlled linearly to a predetermined location of the positioning head or the positioning head being controlled along a predetermined pattern of movement. There is thus no control of the set location of the positioning head, which means that the influence of force and temperature on the setting devices, joints, positioning head, etc. results in a difference between the desired set point and the actual position.
This difference between set point and actual position is unsatisfactory and leads to reduced accuracy in the use of the robot.
OBJECT OF THE INVENTION
The object of the present invention is to increase the accuracy of a robot of the type described above.
SUMMARY OF THE INVENTION
This object is achieved by arranging a feedback control system to supplement the existing control system. Characteristic of the invention is first that the existing control system and the feedback control system indicate the coordinates of the positioning head in different coordinate systems. Secondly, the sensors of the feedback control system are placed for measurement on a part which is movable in the robot and accompanies its movement, but which is free of tension. The part is thus not influenced by temperature or force.
The invention thus relates to a control system for a robot, which robot comprises at least three setting devices which can be extended or shortened in the longitudinal direction. Each setting device is secured in a fixed frame via a first joint so that each setting device is pivotable in all directions in relation to the frame. Each setting device is attached at one end in a movable positioning head via a second joint. A rigid arm is joined to, emanates from the positioning head and is arranged between the setting devices, the arm being radially guided but axially displaceably journalled in a universal joint relative to and rigidly connected to the frame. Each setting device is provided with a length sensor LS
1
, LS
2
, LS
3
, said sensors forming a part of a control system S
1
for controlling the location (X, Y, Z) of the positioning head in the work space of the robot. The control system thus cooperates with a feedback control system R
2
arranged to correct the location (X, Y, Z) of the positioning head in the work space. The control system S
1
and feedback control system R
2
operate in accordance with different coordinate systems.
The invention also relates to a method for controlling the location of the positioning head of a robot, wherein
a) a control system controls the positioning head in accordance with a cartesian coordinate system,
b) a feedback control system senses the location of the positioning head in accordance with a spherical coordinate system,
c) a coordinate transformation is performed of the location of the positioning head from the spherical coordinate system to the cartesian coordinate system,
d) the deviation obtained between set point and actual position in the cartesian coordinate system is added to the previous set point of the positioning head, thus producing a new set point
e) the location of the positioning head is altered to this new set point,
f) steps a)-e) are repeated to achieve continuous control of the set point.
REFERENCES:
patent: 4163183 (1979-07-01), Engelberger et al.
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patent: 4543635 (1985-09-01), Joo et al.
patent: 4732525 (1988-03-01), Neumann
patent: 4790718 (1988-12-01), Vickers
patent: 5797191 (1998-08-01), Ziegert
patent: 5813287 (1998-09-01), McMurtry
patent: 5987726 (1999-11-01), Akeel
patent: 6043621 (2000-03-01), Newmann
patent: 452279 (1987-11-01), None
patent: 509505 (1999-02-01), None
Zannatha et al., Position and Differential Kinematic Neural Control of Robot manipulators: A Comparison Between Two Schemes, 1993, IEEE, pp. 479-484.*
Vaccaro et al., A Joint-Space Command Generator for Cartesian Control of Robotic Manipulators, 1988, IEEE, pp. 70-76.*
Lee et al., External Sensory Feedback Control for End-Effector of Flexible Multi-Link Manipulators, 1990, IEEE, pp. 1796-1802.
Cuchlinski Jr. William A.
Marc McDieunel
Neos Robotics AB
Ostrolenk Faber Gerb & Soffen, LLP
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