@article {101, title = {Improved Haptic Fidelity via Reduced Sampling Period with an FPGA-Based Real-Time Hardware Platform }, journal = {ASME Journal of Computing and Information Science in Engineering}, volume = {9}, number = {1}, year = {2009}, note = {
Improved Haptic Fidelity Via Reduced Sampling Period With an FPGA-Based Real-Time Hardware Platform
Marcia K. O{\textquoteright}Malley, Kevin S. Sevcik, and Emilie Kopp, J. Comput. Inf. Sci. Eng. 9, 011002 (2009), DOI:10.1115/1.3072904


}, month = {03/2009}, abstract = {

A haptic virtual environment is considered to be high-fidelity when the environment is perceived by the user to be realistic. For environments featuring rigid objects, perception of a high degree of realism often occurs when the free space of the simulated environment feels free and when surfaces intended to be rigid are perceived as such. Because virtual surfaces (often called virtual walls) are typically modeled as simple unilateral springs, the rigidity of the virtual surface depends on the stiffness of the spring model. For impedance-based haptic interfaces, the stiffness of the virtual surface is limited by the damping and friction inherent in the device, the sampling rate of the control loop, and the quantization of sensor data. If stiffnesses greater than the limit for a particular device are exceeded, the interaction between the human user and the virtual surface via the haptic device becomes nonpassive. We propose a computational platform that increases the sampling rate of the system, thereby increasing the maximum achievable virtual surface stiffness, and subsequently the fidelity of the rendered virtual surfaces. We describe the modification of a PHANToM Premium 1.0 commercial haptic interface to enable computation by a real-time operating system (RTOS) that utilizes a field programmable gate array (FPGA) for data acquisition between the haptic interface hardware and computer. Furthermore, we explore the performance of the FPGA serving as a standalone system for communication and computation. The RTOS system enables a sampling rate for the PHANToM that is 20 times greater than that achieved using the \“out of the box\” commercial hardware system, increasing the maximum achievable surface stiffness twofold. The FPGA platform enables sampling rates of up to 400 times greater, and stiffnesses over 6 times greater than those achieved with the commercial system. The proposed computational platforms will enable faster sampling rates for any haptic device, thereby improving the fidelity of virtual environments.

}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/101-JCISE\%20proof\%20FINAL\%202-09.pdf}, author = {O{\textquoteright}Malley, M.K. and Sevcik, Kevin S. and Kopp, E} } @proceedings {082211289621, title = {Improved haptic fidelity via reduced sampling period with an FPGA-based real-time hardware platform (IMECE)}, volume = {9 PART B}, year = {2007}, note = {

Real Time Operating System (RTOS) control system;Proprietary control card;

}, pages = {1335 - 1342}, address = {Seattle, WA, United States}, abstract = {

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{\textquoteright}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 {\textcopyright} 2007 by ASME.

}, keywords = {Computer operating systems, Damping, Field programmable gate arrays (FPGA), Multitasking, Real time systems, Virtual reality}, attachments = {https://mahilab.rice.edu/sites/default/files/publications/56-IMECE2007-42085.pdf}, author = {Sevcik, Kevin S. and Kopp, E and O{\textquoteright}Malley, M.K.} }