Programmable mechanical compliance in actuation is desirable for human interaction tasks and important for producing biomimetic motion, particularly for robots designed for use in domestic settings. In this paper, the equilibrium point (EP) hypothesis is proposed and implemented as a new strategy for controlling programmable compliance. The primary objective of this work is to design and demonstrate a simple robot control strategy that can potentially be used by assistive robots to learn and execute compliant interaction tasks from human demonstrations. A 2-DOF planar manipulator activated by McKibben actuators was constructed for the purpose of demonstrating the application of the EP hypothesis on an inexpensive robotic platform, such as might be used in domestic applications. The equilibrium angle and stiffness of each of the joints on the manipulator can be independently programmed. The results presented herein show stable and satisfactory tracking behavior during free motion, interaction, and transition tasks for a robot control system inspired by the EP hypothesis and implemented with a linear proportional-integral (PI) control strategy.
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