Volume 26 Issue 1 - Publication Date: 1 January 2007
Special Issue: The 12th International Symposium on Robotics Research
Wave Haptics: Building Stiff Controllers from the Natural Motor Dynamics
N. Diolaiti Stanford Telerobotics Lab and AI-Robotics Lab, Stanford University, Stanford, CA 94305, USA, G. Niemeyer and N.A. Tanner Stanford Telerobotics Lab, Stanford University, Stanford, CA 94305, USA
Haptics, like the fields of robotics and motion control, relies on high stiffness position control of electric motors. Traditionally, DCmotors are driven by current amplifiers designed to hide their electrical dynamics. Meanwhile encoder-based position feedbackcreates virtual springs. Unfortunately this cancellation-replacement approach experiences performance limits due to sensor quantization, discretization, and amplifier bandwidths.
An alternate approachis presented, noting the inherent inductor-resistor dynamics of the motor are beneficial to the haptic task. Two main insights are followed, which may be utilized independently or preferably in combination. First, the electrical inductance L can serve as a stiffness, providing a natural sensorless coupling between the virtual environment and the user. Second, the electrical resistance R can create a natural wave transformation, providing a robust computer interface between the discrete and continuous time domains. The resulting analog circuit implements a simple voltage drive and can achieve higher stiffness than traditional approaches, especially in the frequency range where human users are most sensitive. Aprototype 1-DOF system has been implemented and confirms the promise of this novel paradigm.
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