Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1987-12-02
1990-03-13
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318632, 318567, 31856816, 901 9, 901 15, 364513, G05B 501
Patent
active
049085590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a robot control apparatus for servo-controlling various drive means by calculating, on-line, the torque command of a robot arm on the basis of the motion equation of a manipulator.
Horizontal articulated-type robots of the kind shown in FIG. 4 have recently come into use on factory assembly lines and the like. A robot of this type comprises a post 1, a first arm 2, a second arm 3, a hand 4, a joint shaft 5, a cable 6, a base 11 and covers 22, 32. When the arms and the hand are driven by servomotors (not shown) to grip a workpiece and perform other motions, a torque command for the robot arms is calculated on-line by a microcomputer for servo-control based on a manipulator motion equation, whereby each of the drive means is servo-controlled.
The drive torque of a servomotor used for robot arm drive is determined as a function of the weight of the workpiece gripped by the hand and inertia determined by the length of the arm. However, the torque necessary for motion when the workpiece is being gripped differs from that when the workpiece is not being gripped. Accordingly, the operator provides a control unit with inputs indicative of whether the robot arm is gripping a workpiece, the weight of the workpiece, etc., and the control unit calculates inertia by computing complicated simultaneous equations, thereby commanding a drive torque of the servomotor. Consequently, the operation for commanding the drive torque of the servomotor is troublesome and the processing performed by the control unit is complicated. In order to compute other parameters such as control current during execution of this processing, a considerable high-speed processing capability is required.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the foregoing problems and its object is to provide an inexpensive robot control apparatus capable of shortening the processing time required for torque calculation and of executing highly precise control without interfering with other processing for current control and the like.
The robot control apparatus of the present invention is constituted as follows: Specifically the invention is characterized by having a servomotor for driving a manipulator through the intermediary of a robot arm, arithmetic means for computing drive torque of the servomotor in accordance with a motion equation, memory means for executing a computation, with regard to an inertia term included in the motion equation, at a predetermined period greater than a drive torque computation period in dependence upon the position of the robot arm, and for sequentially updating and storing the results of this computation, and control means for performing feed-forward compensation of the servomotor based on the motion equation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an embodiment of the present invention;
FIG. 2 is a schematic diagram of a horizontal articulated-type robot;
FIG. 3 is a flowchart illustrating an example of operation; and
FIG. 4 is a partially exploded perspective view of a horizontal articulated-type robot.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram of the invention, in which a represents an input unit, b a CPU (central processing unit), and c a sensor provided on a robot hand for sensing that the robot hand has gripped a workpiece. For example, a weight sensor provided between the robot hand and wrist can be used as the sensor.
Further, d denotes a servocontrol circuit, e a servomotor for drive along each axis of the robot, f a pulse coder for detecting the rotational angle of the servomotor, and g a tachogenerator for detecting the rotational speed of the servomotor.
A method of commanding torque for the servomotor e by means of the robot control apparatus of the invention will now be described. The horizontal articulated-type robot shown in FIG. 4 can be expressed by a simplified diag
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Iwamoto Takashi
Kurakake Mitsuo
Sakamoto Keiji
Fanuc Ltd
Ip Paul
Shoop Jr. William M.
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