Kinematics Estimation Using a Skin-Adhesive Strain Patch for Shoulder Rehabilitation: A Preliminary Study.

Shoulder kinematics has been required to be estimated using compact sensors to provide visual feedback on joint movements for patients undergoing home rehabilitation due to musculoskeletal diseases, such as stroke. Multiple strain patches have been used for shoulder kinematics estimation, either embedded in tight shirts or attached directly to the skin. However, it is desirable to eliminate the tight shirt while minimizing the number of strain patches for convenient use in home rehabilitation. This study presents a single all-in-one skin-adhesive strain patch that enables shoulder kinematics estimation through placement optimization. At the optimal on-skin position, strains caused by flexion-extension and abduction-adduction movements were generated significantly in different directions. The fabricated all-in-one strain patch measured these strains using embedded sensors oriented accordingly. Moreover, the patch was designed to be lightweight and ultra-thin, allowing for convenient attachment to the skin. Shoulder kinematics estimation using this strain patch was preliminarily evaluated with a subject, demonstrating that shoulder joint angles could be estimated with an average error of 15.8 % of the range of motion for two degrees of freedom. The placement optimization reduced the total number of strain patches required for kinematics estimation, enhancing convenience for daily use.