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

The aim of this work is to conceptualize, design and develop a device to assist the sit-to-stand (STS) motion for disabled and elderly. The device assists the human to stand up from sitting position along the natural trajectory of STS motion. Both human and device are assumed to be functioning fully in the sagittal plane. The natural trajectory of armpit is found for the STS motion using a motion capture system. The coordinates are projected onto a sagittal plane passing through the ankle. A four-bar mechanism is synthesized with four-position motion generation using Burmester curve theory. Assuming quasi-static motion, forces on joints at different time steps are found out. Finite element analysis (FEA) is carried out to determine the required cross section of the links of the structural components of device. Material and dimensions of STS device components are selected, and the device is fabricated. Final experiments of STS device with human show that while using the device, the ground reaction force (GRF) of the human during STS motion decreases by approximately 25%, thereby indicating a reduction in effort of the human for STS by the same order.