Design and Walking Algorithm of a Foot-Pad Omni-directional Locomotion Interface

This paper proposes a novel foot-pad omni-directional locomotion interface, establishes planar walking algorithm for it in detail. The proposed locomotion interface allows users walking omni-directionally in a virtual environment, which can improve users’ immersion characteristic significantly. The established walking algorithm explains the relation between the motion of foot-pads and the position of ankles, during walking straight or turning. At last, draw a criteria which can be used to decide walking straight or turning. Introduction Locomotion interface (LI) has been widely used in immersive virtual reality system. LI creates a sense of walking in a virtual environment (VE), without damaging the sense of distance and orientation during walking, while a user’s true position is maintained in the real word [1]. The main existing locomotion devices can be classified into four types [2]: foot-pad, robotic tiles, treadmills, sliders. Foot-pad is one of the best approaches to create sense of walking on uneven surface. University of Utah developed a foot-pad LI, named BiPort [3], with two large manipulators driven by hydraulic actuators, which is too expensive to be applied. Rosten [4] developed a similar device “Whole Body Display” at the Cybernet Systems Corporation, which is too large to be located inside a laboratory. Iwata [5] developed “Gait Master” which consists of two 6-DOF platforms mounted on a turntable. While the available stride distance is too small to allow normal walking and the user’s feet are attached to platform by straps, which limit both feet motion. Schmidt [6] developed a new solution “Haptic Walker” comprising two programmable foot platforms with permanent foot-machine contact, which limits the relative turn motion between feet and platforms. Yoon [7] [8] [9] developed a Virtual Walking Machine which consists of two 4-DOF platforms mounted on a 3-DOF parallel manipulator turntable and proposed a symmetric walking cancellation algorithm and planar curved path walking algorithm. However details to control the motion of foot-pads are not shown. This paper presents the design of foot-pad-based omni-directional LI and describes the planar walking algorithm including walking straight line and turning in detail. Design of the LI The hard core elements of the foot-pad-based omni-directional LI are two 2-DOF manipulators mounted on a turntable. The actuator of the manipulator is foot-pad that can simulate omni-directional surface on which user can walk naturally. The LI consists of four parts as shown in Figure1 (a). Part one is a turntable which traces user’s walking direction momentarily. Part two are two linear guideways. One of them is used to make one foot-pad to trace swing foot, while another is used to move user back. Part three are two auxiliary turntables which can work with the turntable to trace user’s foot angles. Part four are two pads which support user just as road surface during walking. 4th International Conference on Machinery, Materials and Computing Technology (ICMMCT 2016) © 2016. The authors Published by Atlantis Press 1175 (a) Physical configuration (b) Kinematics model of right pad Fig.1 Design of the LI As shown in Figure1 (b), O is the center of the LI. The current center position of foot-pad in the dynamic coordinate system is defined P(x, y), while in static coordinate system is defined P(X, Y). Given α is the rotation of turntable, whose radius is R0. y is the displacement of foot-pad on the linear guideway whose length is Lmax. θ is rotation of foot-pad, whose relative rotation to the turntable is β. The position and posture can be defined as: