A novel locomotion interface with two 6-DOF parallel manipulators that allows human walking on various virtual terrains

Abstract

This paper proposes a novel locomotion interface that can generate an infinite floor with various surfaces and can provide a user with proprioceptive feedback about walking. The interface allows users to experience life-like walking in virtual environments with various terrains. The interface consists of two platforms, each consisting of a three-degrees-of-freedom (3-DOF; x, y and yaw) planar device on which a 3-DOF (pitch, roll and z) footpad is mounted. Alternating current servomotors drive the planar devices to generate rapid motions, while pneumatic actuators drive the footpad devices to generate the impedances required for various virtual terrains, in addition to supporting the user's weight. To simulate natural human walking, the locomotion interface design specifications are based on gait analysis, and each mechanism is optimally designed and manufactured to satisfy these requirements. The locomotion interface allows natural walking (step, 0.8 m; height, 20 cm; load capability, 100 kg; slope, 55 degrees) on various terrains. In addition, a new walking control algorithm is proposed for generating continuous walking on an infinite floor involving various terrains. In this algorithm, each independent platform follows a human foot during the swing phase, while the other platform returns to the home position during the single-limb stance phase. During the double-limb stance phase, the two platforms assume neutral positions to compensate for the offset errors generated by velocity changes. Therefore, this algorithm can satisfy natural walking conditions in any direction. The transition phase between the swing and stance phases is detected using a simple switch sensor system, while human foot motions are sensed using a calibrated magnetic motion tracker attached to the shoe. Actual walking simulations on level ground, slopes, and stairs show that the proposed locomotion interface allows an average person to walk naturally on various virtual terrains in safety, without marked disturbances. This interface has various applications, such as in virtual reality (VR) navigation, rehabilitation, and gait analysis.