Multi-DOF equalization of haptic devices for accurate rendering at high frequencies

Previous work has shown that high frequency content is important for realistic haptic feedback, while stability considerations limit the ability of closed-loop control to effectively generate high frequencies. Open-loop playback of high frequencies offers a promising way to generate rich contact transients and textures, but complex high frequency dynamics cause distortion. This paper explores the equalization and dynamic decoupling of multi-DOF haptic devices for accurate open-loop playback. Toward this end, a user study is performed to determine the frequency limit of human force direction sensitivity at 35Hz. This information together with experimental system identification techniques is used to develop a strategy for equalization in different frequency bands. Finally, MIMO equalization is accomplished through online simulation of the system model under the control of an LQR tracking controller.