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.