(L-451) Development of a Center of Pressure Movement System for use in Virtual Reality

This study focused on the development of the hardware and software needed to implement a center of pressure, and vertical ground reaction force-based movement algorithms, as well as initial testing and system performance monitoring. We also compared different types of motion controls relative to thumb stick controls to test patient response and overall adaptability.  

A Nintendo Wii Fit balance board was disassembled and 3 of the 4 force transducers were attached to the bottom of a wooden platform, with 2x4 lumber rim to reinforce the board and to clearly identify the limits of where the user can stand on the board while wearing a VR headset. Force transducers were connected to an Arduino Uno using HX711 amplifiers. Scales were calibrated and zeroed using the HX711 library in Arduino and then weights from each sensor were sent to Unity using serial communication via USB and the System.IO.Ports library in a C# script. 

A custom scene was development in Unity with a hilly terrain, and player controller with XR support. The movement of the player was set to operate based on user input and the orientation of the headset. Two movement schemes were implemented, one based on thumb stick input for a connected game controller, and one using the absolute value of change in center of pressure position.  

Initial testing resulted in frame rates of ~10 frame per second (FPS) due to delays in communication primarily because of the speed of the HX711 amplifier. The C# script used to receive data from the Arduino was modified to allow the process to be skipped if data from the Arduino was not received for all 3 sensors.  

After modification, the algorithm functioned as intended and was able to run at 60 FPS (see figure 3) and in the initial test authors were able to successfully able to navigate the 3D terrain in the game using either the controller thumb stick or custom balance board (see figure 4). 

Future work will focus on systematic evaluation of immersion and physical activity of these controls by comparing combinations of automatic path thumb stick movement, user-controlled path with thumb stick movement, automatic path with posture-based movement, and user-controlled path with posture-based movement.