Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1993-07-07
1995-09-05
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856813, 31856822, 318626, B25J 1300
Patent
active
054481449
DESCRIPTION:
BRIEF SUMMARY
FIELD OF ART
This invention relates to a method and apparatus for controlling a robot wherein the torque of a servo motor is transmitted to a robot arm by way of a speed reducer, and more particularly, to the holding of a load while the robot is in a stopped condition.
BACKGROUND OF THE INVENTION
Particularly among industrial robots, there are some which utilize hydraulics as drive means thereof. However, the robots generally employ servo motors and the torque of the servo motors is usually transmitted to a robot arm by way of a speed reducer.
Meanwhile, in the teaching playback robot, the plurality of points on a path along which the robot arm passes are preliminarily taught and, at the time of playback, the robot is controlled by an interpolation of teaching points so that the robot arm moves along the path from one teaching point to another teaching point.
Conventionally, when the robot moves from one teaching point to another teaching point, once the robot reaches a target point, the robot is stopped without considering the conditions of the loads applied to the respective shafts of the robot.
Therefore, it is often the case with any one of the robot shafts that when the movement of the arm from one teaching point to another teaching point is in a direction to lift a load, the robot shaft is stopped in the load lifting condition even after the completion of the movement.
FIG. 1 exemplifies such a movement, wherein numeral 1 indicates a first shaft, numeral 2 indicates a second shaft, numeral 3 indicates a third shaft and capital letter W indicates a load. In FIG. 1, when the respective shafts move from positions shown with a solid line to positions shown with a hyphenated line which represents subsequent teaching points, the second shaft 2 moves in a direction to lift the load W and is stopped in the load lifting condition. Here, no brake means is provided for maintaining the stopped condition.
If the drive system of the above shafts comprises a servo motor 4, a speed reducer 5 and an arm 6 comprised of any desired shafts, the transmission of the torque from the servo motor 4 to the arm 6 is expressed as follows.
Meanwhile, the torque transmission from the load W to the servo motor 4 is expressed as follows.
As described previously, since the normal efficiency .eta. (<1) is the inverse of the reverse efficiency .eta.'(<1), the load applied to the servo motor 4 for driving the shaft greatly differs between a case (a) in which the arm is moved in a load lifting direction and then is stopped while maintaining the load lifting condition and a case (b) in which the arm is moved while holding the load and then is stopped.
Therefore, in the case (a), the servo motor consumes a considerable amount of electricity and eventually increases the generation of heat which will adversely affect the accurate operation of the motor.
Accordingly, the task to be achieved by this invention lies in stopping the robot under the condition (b), thus reducing the required torque of the servo motor and the generation of heat.
SUMMARY OF THE INVENTION
To solve the above task, the method for controlling the robot according to this invention lies in that, in controlling a robot wherein the robot comprises shafts having one degree of freedom or plural degrees of freedom and a dynamic load is applied to at least one of the above shafts, the shafts being driven by a servo motor via a speed reducer, the improvement is characterized in that the shaft to which the load is applied is moved in a load acting direction and thereafter is stopped.
Furthermore, the apparatus for controlling the robot according to this invention lies in that, in an apparatus for controlling a robot wherein the robot comprises shafts having one degree of freedom or plural degrees of freedom and a dynamic load is applied to at least one of the above shafts, the shafts being driven by a servo motor via a speed reducer, the improvement is characterized in that the controlling apparatus comprises means to judge whether the robot is stopped or not by dete
REFERENCES:
patent: 4555758 (1985-11-01), Inaba et al.
patent: 4591944 (1986-05-01), Gravel
patent: 4980839 (1990-12-01), Souji et al.
patent: 5130632 (1992-07-01), Ezawa et al.
Nishi Masanori
Okamura Kunihiro
Tounai Shuichi
Kabushiki Kaisha Yaskawa Denki
Ro Bentsu
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