An injecting method of physical damping to haptic interfaces based on FPGA

Abstract

Abstract:In this paper, an injecting method of physical damping to haptic interfaces is proposed. For injecting adjustable physical damping, time-domain passivity controller is implemented in hardware level with FPGA. Noise free velocity signal can be estimated with T-method. Instead of force command from the virtual environment, directly measured current signal with Hall sensor is used for calculating more accurate energy flow. The entire time-domain passivity control scheme is implemented with several different control routines inside FPGA, and through this hardware implementation, noisy behavior of the conventional software based time-domain passivity controller can be significantly removed.

FPGA based time domain Passivity Observer and Passivity Controller

“…The detection logic to get the current position and direction is shown in table I. The elapsed time is measured between each successive pulses which can be used in velocity calculation [13]. In this PO/PC application, the elapsed time counter is masked since it is not necessary in the simplified scheme.…”

“…To remove the noise behavior, reference energy following and new algorithm which ignore the produced energy near zero velocity has been proposed [19]. In our previous research [13], FPGA was tested to solve several issues on software based damping injection method including the noise behavior.…”

“…The PO/PC module is updated irregularly only when the encoder pulse is detected by the counter module. The reference current was used for energy calculation instead of measured motor current [13] to avoid the measured signal noise. …”

“…In [13], FPGA based hardware implementation of the time-domain passivity controller was introduced to solve several issues on software based damping injection. The noise behavior of the conventional software based time-domain passivity controller was significantly removed through this hardware implementation.…”

“…Thanks to the fast sampling rate and parallel processing of FPGA, it is possible to capture every single encoder pulse while running separate control loops simultaneously. In [13], we used measured motor current to estimate more accurate energy flow. But there was some drawback like measured…”