Improved haptic fidelity via reduced sampling period with an FPGA-based real-time hardware platform (IMECE)

TitleImproved haptic fidelity via reduced sampling period with an FPGA-based real-time hardware platform (IMECE)
Publication TypeConference Proceedings
Year of Conference2007
AuthorsSevcik, KS, Kopp, E, O'Malley, MK
Conference NameASME International Mechanical Engineering Congress and Exposition, Proceedings
Volume9 PART B
Pagination1335 - 1342
Conference LocationSeattle, WA, United States
KeywordsComputer operating systems; Damping; Field programmable gate arrays (FPGA); Multitasking; Real time systems; Virtual reality

Impedance based haptic interfaces face inherent challenges in displaying stiff virtual environments. Fidelity of a virtual environment is enhanced by stiff virtual walls combined with low damping and passive behavior of the interface. However, the stiffness of virtual walls displayed on an impedance based interface is limited by the damping inherent in the controller, the sampling rate of the control loop, and the quantization of the controller's position. Attempting to display a stiffness larger than this limiting value destroys the passivity of the interface, leading to active controller behavior and eventually closed loop instability. We propose a method of increasing the fidelity of a PHANToM Premium 1.0 commercial haptic interface by controlling it via a Field Programmable Gate Array (FPGA) both alone and with a Real Time Operating System (RTOS) control system. This custom controller enjoys several benefits over the standard control achieved via a proprietary control card in a Multitasking OS, including reduced system overhead and deterministic loop rate timing. The performance of the proposed FPGA/RTOS controller compares favorably with the performance of an FPGA/Multitasking OS controller. The FPGA/RTOS controller achieves control loop rates an order of magnitude greater than that of the proprietary controller, allowing virtual walls to be displayed with greatly increased stiffnesses, while retaining the passivity and low damping of the PHANToM interface. Copyright © 2007 by ASME.

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