A CUSTOMIZABLE AND RESPONSIVE MECHANISM FOR A CHAIR TO ASSIST DURING ALL PHASES OF STAND-TO-SIT AND SIT-TO-STAND MANEUVERS

Most of the assistive chairs do not provide support during the body-extension and stabilization phases of sit-to-stand maneuver because they only pivot about a horizontal axis. And there is limited scope for customization to individual's needs. To address this, we present a mechanism that combines a compliant hinge mechanism with a linkage that includes a gas-spring. The compliant hinge mechanism uses open-circular cross-section shells that bend and twist to provide customized torque-angle characteristics with negative stiffness and bistability features. By adding a linkage with a gas-spring, the mechanism in this work is designed such that it provides the necessary support right from the intent to rise until the last phase of stabilizing in the standing position. Similar full support is provided for the stand-to-sit maneuver. Furthermore, the mechanism is responsive entirely by virtue of the compliant hinge mechanism and the gas-spring, and without using any sensors or external actuation. This completely mechanical device with two degrees of freedom allows the users to control the trajectory of the hip joint to their comfort and ability. Additionally, the envelope of trajectories of the seat that slides vertically and rotates about a horizontal axis can be mass-customized to ergonomic parameters of the population. We present the concept, customization features, kinetoelastic analysis, prototyping, and preliminary testing. We illustrate the efficacy of the mechanism through EMG data.