Improved Haptic Fidelity via Reduced Sampling Period With an FPGA-Based Real-Time Hardware Platform

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’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.

Experimental study on the stability of an impedance-type force-feedback architecture based on an augmented-state observer for a haptic system under time delay using a LMI approach

“…29,38 This factor is also related to the fidelity of the haptic system. 39 The results of Koul et al 40 have allowed the implementation of higher virtual stiffness at a higher sampling rate. According to Ruspini et al, 41 a sampling rate of at least 1 kHz is required in order to achieve stability and smooth rendering about realistic objects or surfaces for a force-feedback haptic system.…”

Haptic communication system using FPGA and real-time network framework

“…In the haptics, the FPGAs are used to improve the performance of the control system [7] The authors have applied the FPGAs to a multi degrees-of-freedom haptic system in order to reduce sampling periods for a bilateral control system based on acceleration control [8]. The sampling period is important to achieve wide band force sensing and high performance bilateral control system.…”