Improved haptic fidelity via reduced sampling period with an FPGA-based real-time hardware platform
O'Malley, Marcia K.
Master of Science
The challenge of displaying stiff virtual walls in a haptic interaction is the inspiration for this document. The fidelity of their implementation necessitates high virtual stiffness integrated with passive device behavior. An energy-based approach to system passivity for a unilateral, virtual spring is derived. The work addresses the issue of sampling rate; derivations reveal that increasing control loop rates can increase achievable displayed stiffness. The objective is to directly minimize the computational period of the haptic rendering loop for a unilateral virtual spring by employing a hardware platform that utilizes a Field Programmable Gate Array (FPGA) device to handle high-speed data acquisition and low-level control executions directly on hardware. A dedicated real time (RT) execution target coupled to the FPGA is proposed to manage higher-level, deterministic operations necessary for virtual wall implementation in software. The proposed FPGA/RT platform is interfaced with the PHANToM Premium 1.0 commercial haptic manipulator and achieves control loop rates 20 times faster than those executed by its default hardware platform. Experimental findings validate the improved performance of virtual spring rendering. The FPGA/RT platform successfully displays virtual stiffness that far exceeds the passive range of the PHANToM's commercial hardware platform.
Electronics; Electrical engineering; Mechanical engineering