Augmenting Virtual Reality Terrain Display with Smart Shoe Physical Rendering: A Pilot Study.

Haptic terrain rendering is limited in existing Virtual Reality (VR) systems. This article describes integration of the Smart Shoe (SS) for physical terrain display with the TreadPort VR system. The SS renders both gross sloped terrain and subtle sensations of stepping on small objects or uneven surfaces. The TreadPort projects terrain on the floor and the SS renders terrain that the user steps upon via motion tracking. The research is motivated towards eventually providing gait training for people with Parkinson's Disease (PD), hence this work presents a pilot study evaluating haptic terrain rendering with healthy elderly and PD participants wearing the SS within the TreadPort. Uneven cobblestone surfaces are rendered by the SS as the participant steps on their graphical representation in VR. While posthoc analysis shows the study is underpowered, kinematic and spatiotemporal results derived from motion capture data demonstrates kinesthetic response (e.g., increased maximum ankle angle and minimum toe clearance, reduced minimum ankle angle and knee angle) provided by the SS. Questionnaire data shows increased VR realism and difficulty walking on cobbled terrain using SS rendering. Thus, results indicate that the integrated haptic system demonstrates promise in potential gait training for PD in future work.

Optimizing Fingernail Imaging Calibration for 3D Force Magnitude Prediction.

This paper discusses the optimization of a fingernail imaging system for predicting fingerpad force. The effects of lighting coloration, calibration grid, and force prediction model on the registration process and force prediction accuracy of fingernail imaging are investigated. White and green LEDs are found to produce statistically similar effects on registration error and force prediction results across all three directions of force. Two calibration grids are implemented, with no statistically significant difference in either registration or force prediction between the Cartesian and cylindrical grid designs. Of the five force prediction models investigated, a principal component regression model based on the pixel intensity eigenvectors estimates the force with the greatest accuracy. This EigenNail Magnitude Model simultaneously estimates force in all three directions with RMS error with 95 percent confidence interval of 0.55 ± 0.02 N (7.6 percent of the full force range). These results indicate a set of optimal parameter choices for the calibration of a fingernail imaging system.

A Full Body Steerable Wind Display for a Locomotion Interface.

This paper presents the Treadport Active Wind Tunnel (TPAWT)-a full-body immersive virtual environment for the Treadport locomotion interface designed for generating wind on a user from any frontal direction at speeds up to 20 kph. The goal is to simulate the experience of realistic wind while walking in an outdoor virtual environment. A recirculating-type wind tunnel was created around the pre-existing Treadport installation by adding a large fan, ducting, and enclosure walls. Two sheets of air in a non-intrusive design flow along the side screens of the back-projection CAVE-like visual display, where they impinge and mix at the front screen to redirect towards the user in a full-body cross-section. By varying the flow conditions of the air sheets, the direction and speed of wind at the user are controlled. Design challenges to fit the wind tunnel in the pre-existing facility, and to manage turbulence to achieve stable and steerable flow, were overcome. The controller performance for wind speed and direction is demonstrated experimentally.

Kinesthetic Force Feedback and Belt Control for the Treadport Locomotion Interface.

This paper describes an improved control system for the Treadport immersive locomotion interface, with results that generalize to any treadmill that utilizes an actuated tether to enable self-selected walking speed. A new belt controller is implemented to regulate the user's position; when combined with the user's own volition, this controller also enables the user to naturally self-select their walking speed as they would when walking over ground. A new kinesthetic-force-feedback controller is designed for the tether that applies forces to the user's torso. This new controller is derived based on maintaining the user's sense of balance during belt acceleration, rather than by rendering an inertial force as was done in our prior work. Based on the results of a human-subjects study, the improvements in both controllers significantly contribute to an improved perception of realistic walking on the Treadport. The improved control system uses intuitive dynamic-system and anatomical parameters and requires no ad hoc gain tuning. The control system simply requires three measurements to be made for a given user: the user's mass, the user's height, and the height of the tether attachment point on the user's torso.

Investigation of the Treadport for gait rehabilitation of spinal cord injury.

The goal of this study is to compare the effect of training by the University of Utah's Treadport versus a conventional treadmill on gait improvement of spinal-cord-injury (SCI) patients. Four incomplete SCI subjects who had reached a rehabilitation plateau were selected to have training first on the treadmill and then the Treadport. Spatiotemporal and gait parameters were utilized to make a comparison between the two training conditions. Overall, the results demonstrated statically significant improvements in most of the spatiotemporal as well as some of the gait parameters during training with the Treadport relative to the traditional treadmill.

Predicting fingertip forces by imaging coloration changes in the fingernail and surrounding skin.

This paper presents an external camera method for measuring fingertip forces by imaging the fingernail and surrounding skin. A 3-D model of the fingernail surface and skin is obtained with a stereo camera and laser striping system. Subsequent images from a single camera are registered to the 3-D model by adding fiducial markings to the fingernail. Calibration results with a force sensor show that the measurement range depends on the region of the fingernail and skin. A generalized least squares model is developed to predict fingertip force given coloration changes, and results for normal and shear force measurement are presented.