Torso Force Feedback Realistically Simulates Slope on Treadmill-Style Locomotion Interfaces

This paper investigates whether torso force feedback on treadmillstyle locomotion interfaces can substitute for treadmill tilt to simulate walking on smooth inclines. The experimental platform is the Sarcos Treadport, whose active mechanical tether can apply horizontal forces to the user to simulate the gravity forces experienced in slope walking. The authors show that users are extremely sensitive to slope while walking, being able to discriminate a 0.5 degree slope change. Comparisons are then made between walking on a tilted treadmill platform versus walking on a level platform but with tether force application. Psychophysical experiments show that users select tether forces that are predicted by the gravity forces, although at The International Journal of Robotics Research Vol. 20, No. 12, December 2001, pp. 939-952, ©2001 Sage Publications a 65% fractional force level. These results demonstrate definitively that torso force feedback can realistically simulate gravity forces during smooth slope walking. KEY WORDS—haptic interfaces, virtual reality, locomotion interfaces, gait, slope walking