Development of Shoulder Mechanism for a Wearable Upper Limb Force-Feedback Device with Pneumatic Artificial Muscles and MR Brakes

We have been developing a wearable force-feedback device using pneumatic artificial muscles and magnetorheological fluid brakes. In a previous study, we confirmed that this device can present the stiffness of a virtual object. However, based on the results of a questionnaire administered during the experiment, we considered that the subjects' awareness of the device's weight suppressed the reality of the VR experience. Therefore, we redesigned the device to reduce the physical burden on the user. From simulation results, we confirmed that this redesign reduced the shoulder joint torque required for flexion and increased the workspace of the force-feedback device. In addition, the torque transmission characteristics of the link mechanism involved in horizontal shoulder motion was tested. We also measured the vertical load applied to the user's hand during horizontal shoulder motion. The results show that the device transmits torque close to the target value in the horizontal flexing direction but does not reach the target value in the horizontal extending direction. We also confirmed that the vertical load during horizontal motion could be reduced by redesigning the device.