Design and Development of a Locomotion Interface for Virtual Reality Lower-Body Haptic Interaction

TL;DR

ForceBot addresses VR locomotion by enabling natural lower-body interaction across varied terrains using two planar gantries delivering 2 DoF per foot. It combines an admittance controller with a walking algorithm to produce treadmill-like motion, under a 1,000 Hz EtherCAT-based framework and open-source IHMC software for real-time pHRI. VR integration is achieved through Unity via WebSocket, linking force-velocity control to avatar motion and terrain height, with dynamic walking velocity estimation. Experimental results show stable force-to-motion coupling, manageable delays, and successful VR terrain realization, indicating a scalable platform for lower-body haptic VR research and development.

Abstract

This work presents the design, build, control, and preliminary user data of a locomotion interface called ForceBot. It delivers lower-body haptic interaction in virtual reality (VR), enabling users to walk in VR while interacting with various simulated terrains. It utilizes two planar gantries to give each foot two degrees of freedom and passive heel-lifting motion. The design used motion capture data with dynamic simulation for ergonomic human-robot workspace and hardware selection. Its system framework uses open-source robotic software and pairs with a custom-built power delivery system that offers EtherCAT communication with a 1,000 Hz soft real-time computation rate. This system features an admittance controller to regulate physical human-robot interaction (pHRI) alongside a walking algorithm to generate walking motion and simulate virtual terrains. The system's performance is explored through three measurements that evaluate the relationship between user input force and output pHRI motion. Overall, this platform presents a unique approach by utilizing planar gantries to realize VR terrain interaction with an extensive workspace, reasonably compact footprint, and preliminary user data.

Figures (21)

• Figure 1: A concept sketch of the presented locomotion interface alongside the actual device. The locomotion interface features two linear gantries, a pair of foot platforms, and a base frame.
• Figure 2: Motion capture marker positions to obtain walking motion data for dynamic simulation.
• Figure 3: The simulated motor torque and rotation speed that are based on motion capture data of walking. Right: Simulated motor torque for walking motion. Left: Simulated motor RPM for walking motion.
• Figure 4: A detailed composition of the planar gantry system. The gantry actuates X and Z-axis motion to provide 2 DoF for each foot, featuring linear rails (Model HMRB-18, OSPE32-BHD by Parker), motors (Model R88M-1L2K030TS2 by Omron), gear reducers (Model RX90, PV90 by Omron), and a connection point for the foot platform.
• Figure 5: The overall foot platform design contains a support frame made of T-slotted aluminum extrusion, a PLA foot platform base, TPU foot straps, a force/torque sensor (Model MINI-58 by ATI), and a force sensor board. A user's foot is attached to the platform through TPU straps and hook-and-loop fasteners. A rubber dampening layer is implemented in between the foot platform and force sensor to reduce the negative effect of a stiff force sensor.