Servo Motor Controller Switching to Force Control
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Solution Overview
Problem
Existing servo motor controllers using the first method face issues with delayed contact between the driving target and subject due to premature selection of velocity commands for force control, leading to mechanical shocks during switching from position control to force control.
Innovation Solution
A servo motor controller that selects the velocity command for position control until the driving target contacts the subject and uses a force threshold to switch to force control, maintaining the force command at an initial value to reduce mechanical shocks by comparing and selecting the smaller velocity command between position and force control, and optionally employing a filter or integrator for smoother torque transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the velocity command for force control is selected when it becomes smaller than the velocity command for position control, then the transition from position control to force control becomes smooth, but the driving target contacts the subject later than expected
Solution Approach 1:
The patent applies preliminary action by correcting the force command to a smaller value before the driving target contacts the subject. This preliminary correction ensures that when the transition to force control occurs, the velocity command for force control is already smaller than the velocity command for position control, enabling smooth transition without delaying contact. The corrected force command is restored to its initial value after the transition completes.
2Ease of operation
If the force command is restored from corrected value to initial value after switching from position control to force control, then the force control can proceed normally, but the velocity command for force control increases steeply causing mechanical shock
Solution Approach 1:
The patent applies beforehand cushioning by correcting the force command to a smaller value before the transition from position control to force control. This preliminary correction cushions against the potential mechanical shock that would occur when restoring the force command to its initial value after switching, as the velocity command for force control starts from a lower value and increases more gradually.
3Loss of time
If the velocity command for position control is selected forcibly until the driving target contacts the subject, then contact timing is maintained, but the transition to force control may cause mechanical shock
Solution Approach 1:
The patent combines forced selection of the velocity command for position control until contact with preliminary correction of the force command before contact. This ensures that contact timing is maintained while the force command is already corrected to a smaller value, preparing for a smooth transition to force control without mechanical shock when the velocity command for force control becomes smaller than the velocity command for position control.
Data Source
AI summary
A servo motor controller comprises: a position command generation unit; a position detection unit; a position control unit that generates a velocity command for position control based on a position command and a position FB; a force command generation unit that generates a force command for instructing force to be applied to a subject by a driving target; a force detection unit; a force control unit that generates a velocity command for force control based on the force command and a force FB; a selection unit that selects one of the position control and the force control; and a storage unit that stores a force threshold. The selection unit selects one of the velocity commands for the position control and the force control of a smaller value. If the force FB is smaller than the force threshold, the selection unit selects the velocity command for the position control.