Position-Based PD Control Design for Hydraulic Robots Using Passive Subsystems in Multi-Time Scales

Woongyong Lee1, Wan Kyun Chung1

  • 1POSTECH

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Regular Papers

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09:55 - 11:10 | Tue 30 May | Room 4011 | TUA1

Actuators 1

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Abstract

A position-based proportional-derivative (PD) controller with inner torque feedback loops can be used as a simple controller to render compliant behaviors to a hydraulic robots. However, using this control framework involves a tradeoff between the stability and performance of the closed-loop system (which includes the external environment) because the joint position sensors and control units (i.e., electrohydraulic servovalves) used in the control are separated (non-collocated) from the robot by their joint flexibility. To effectively overcome this limitation, this paper proposes a joint position-based PD control strategy for constructing an inherently stable and compliant hydraulic robot system. To this end, we use virtual internal leakage to separate the system by frequency into subsystems that include control units (i.e., servovalve), flexible joints, and robot manipulator, respectively. This architecture allows the hydraulic robot to behave as a passive system within its operating frequency region under the guidance of controllers designed to guarantee the stability of the passive subsystems within the respective frequency regions. The proposed approach was verified experimentally.

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Summary

  • Conventional hydraulic robots operate without feedback interconnections.
  • This is because the servovalves used in their actuation systems include non-backdrivable mechanisms.
  • Virtual internal leakage injected into the system decomposes the hydraulic robot into passive subsystems.
  • Stability-guaranteed PD controller with inner-loop torque controller enables to interact passively with unexpected environments.