Design and Development of a Mobile Sit-to-Stand Assistive Device

This work presents the design and development of an assistive device to enable natural sit-to-stand motion for individuals with lower extremity weakness. The device is conceptualized based on the synthesis of a four-bar linkage using the Burmester curve theory, the coupler of which follows the elbow trajectory of the user during sit-to-stand motion. The four-bar mechanism is incorporated in a frame that ensures stability during STS and has multiple support locations for easy and comfortable STS transfer of the user. The STS device is portable and actuated by a pair of battery-operated linear actuators enabled with a switch operated by the user. The STS device is fabricated using extruded aluminium profiles which makes it lightweight, modular for easy assembly, and adjustable to different users. The device is tested on a number of healthy subjects for whom the ground reaction forces (GRF) during STS are compared with and without using the device. Approximately 45% reduction of GRF was noted while using the STS device. Further a dynamics based optimization model was created to calculate the forces at the various support points where the user comes in contact with the STS device. The results of optimization model were compared with an experiment and found to be within 10% of experimental data. The designed and developed STS device has potential of becoming a commercial product.