Kinesthetic Force Feedback and Belt Control for the Treadport Locomotion Interface

Abstract

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.

Speed adaptation and acceleration ripple suppression of treadmill user system using a virtual force moment balance model

“…Figure 1 shows a force moment balance kinetic model of TUS (Hejrati et al, 2015). By taking the human body as a mass point, a basic kinematic equation of TUS can be described by…”

“…Recently, ground reaction force (GRF) of the treadmill is introduced to reflect the user’s intention of accelerating or decelerating, and the treadmill velocity is then updated by using the GRF. For example, a mechanical tether that is attached to the user’s body is used to measure the GRF during the treadmill walking (Christensen et al, 2000; Hejrati et al, 2015; Zitzewitz et al, 2007). But the force produced by the mechanical tether leads to a hard restriction for the user’s natural motions and an extra disturbance for the immersive sense in virtual environments, which is highly undesired for the user.…”

The Treadport: Natural Gait on a Treadmill

“…The proctor of the experiment used the phrase, "at your normal pace," to describe how subjects should walk for each collection session. Unlike self-selected speed on ordinary treadmills, self-selected speed on the Treadport is attained by walking over the belt and attaining a steady-state walking pattern, as described in Hejrati et al (2015).…”

“…The Treadport has been analyzed for enhancing the naturalness of virtual reality walking from three different perspectives: (1) perception of walking (which controller values create the most natural walking experience for the users) as discussed in Hejrati et al (2015); (2) walking functions (attaining any desired self-selected speeds (normal, fast, jogging, backward), maintaining walking speed during steady-state walking, and naturally changing speed) as described in Hejrati et al (2015); and (3) biomechanics of walking. This article is concerned with the final aspect, and it shows that subjects have similar biomechanics on the Treadport and overground in 13 of 14 gait parameters.…”

“…Even with the presence of optical flow, Plotnik et al (2015) found that subjects naturally selected slightly different speeds on the treadmill than overground. The Treadport uses a unique natural speed-selection strategy with a balancing kinesthetic force, as described in Hejrati et al (2015).…”