HAPI Bands: A haptic augmented posture interface

In the instruction of motor tasks, feedback from a teacher in the form of visual demonstration, aural directives, or physical guidance enhances student performance and facilitates motor learning. When the teacher's guidance is not available, or visual and aural cues are not appropriate, a wearable presentation of haptic feedback that mimics the teacher's touch is an alternative solution. We present HAPI Bands, a set of user-worn bands instrumented with eccentric mass motors that provide vibrotactile feedback for guidance of static pose. Joint misalignment from a target pose is corrected for 15 degrees of freedom (DOFs) of the upper-body. HAPI Bands uses a low-cost range camera, the Microsoft Kinect, and related software to measure the 3D position of a user's joints in space. We developed a novel algorithm that computes 6-DOF joint pose by integrating Kinect position sensing with orientation data from body-mounted accelerometers. Accuracy of the system's sensing was measured against Optotrak data, resulting in average joint biases of approximately 2.33°, 7.13°, and 7.48° for torso, shoulder, and elbow joints, respectively, with an average static RMS measurement error of 0.59°. In a user study, haptic feedback was found to be as effective as visual feedback in reducing endpoint error in 1-DOF movements of the torso and arm. Future work is planned to evaluate the HAPI Bands system in realistic applications and explore guidance of dynamic motion trajectories.