Electricity: motive power systems – Limitation of motor load – current – torque or force
Patent
1994-12-01
1998-03-31
Cabeca, John W.
Electricity: motive power systems
Limitation of motor load, current, torque or force
318601, 318632, G05B 101
Patent
active
057342423
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a force control method which applies force to a controlled system, and controls the applied force, in machine tools, robots and industrial machines.
DESCRIPTION OF THE RELATED ART
In industrial machines, when employing force control, which not only applies force to a controlled system but also controls the applied force, it has conventionally been a common practice to hydraulically control the force applied to the controlled system by oil pressure of a hydraulic cylinder. In the case of a deburring robot for removing a burr with a robot, the force for pressing the deburring tool mounted on the distal end of the tool's wrist against the work is controlled during the deburring operation. In such a deburring robot, a drive source for driving various axes such as robot's arms and the like comprises a hydraulic cylinder, a servo motor and the like. In the case where the drive source comprises the servo motor, a force sensor is used for executing the aforesaid force control. More specifically, the force sensor is mounted on a distal end portion of a machine against which the controlled system is pressed, and the force detected by the sensor is fed back so that a detected value is controlled to agree with a target value.
In the case where force feedback control is carried out using a force sensor, the stability and reliability of the force control depend on the stability and reliability of the used force sensor. Thus, the higher the stability and accuracy of the used sensor, the higher the accuracy of the available force control. In general, however, the reliability of the force sensor is low as compared with that of a position detector used in conventional servo motor control, and the accuracy of force control is also low as compared with that of position/velocity control. Further, the force sensor is too expensive to be used in low-priced devices. Furthermore, there is a problem that the installation of the force sensor is difficult. In the case where force control is to be carried out with a motor, the use of force sensor is indispensable; however, the use of the force sensor causes the above-mentioned problems. This, therefore, necessitates the use of a hydraulic cylinder. These problems are the factors that have prevented the change of the drive source from the hydraulic drive source to electric drive source.
SUMMARY OF THE INVENTION
An object of the present invention is to easily execute force control with a motor, but without using a force sensor. Another object of the present invention is to provide force control of the motor according to disturbance load estimated.
In a method according to the present invention, a disturbance load torque applied to a motor is estimated by a disturbance estimation observer, and the estimated disturbance load torque is fed back to effect feedback control, by making the estimated disturbance load torque correspond to a force command value which is a target value. Therefore, the estimated disturbance load torque is controlled so as to correspond to the target value. Further, when the estimated disturbance load torque approximates to an actual load torque, the actual load torque is controlled to a target value.
The disturbance estimation observer estimates a disturbance load torque based on a torque command value commanded to the motor, an actual velocity of the motor and the like. Thus, in the case where the motor is not subjected to any reactive force from the controlled system, for the reasons such that the controlled system to which a torque is to be applied is absent, or that the controlled system shifts its position when subjected to a torque, the estimated disturbance load torque will not reach the target value, thereby assumedly causing the motor to rotate excessively seeking the target value. In such a case, a value obtained by adding the product of the velocity of the motor and the predetermined coefficient to the estimated disturbance load is used, as the feedback value of the force, for the feedback co
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patent: 4993715 (1991-02-01), Nakamura et al.
patent: 5101145 (1992-03-01), Rehm
patent: 5374684 (1994-12-01), Koren et al.
Cabeca John W.
Fanuc Ltd.
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