Just Noticeable Differences for Joint Torque Feedback During Static Poses

Joint torque feedback is a new and promising means of kinesthetic feedback for providing information to a person or guiding them during a motion task. However, little work has been done in determining the psychophysical parameters of how well humans can detect external torques. In this study, we determine the human perceptual ability to detect kinesthetic feedback at the elbow during all possible combinations of preload torques and test stimulus torques, with the elbow in a static posture. To accomplish this, we constructed an exoskeleton for the elbow providing joint torque feedback. The device is designed to convey 0.54 Nm of stall torque for up to 120 seconds via a semi-rigid sleeve structure. Using this device, we assessed perception capability using the Interweaving Staircase Method. We found that users could detect average torques of 0.14-0.18 Nm in the extension or flexion directions with no preload. When a preload of 1.27 Nm was applied, this increased to 0.25-0.27 Nm for when flexion stimuli were applied, and 0.180.3 Nm when extension stimuli were applied, depending on the preload direction.