A novel six-bar mechanism for executing motion trajectories of sit-to-stand transformation in a multifunctional mobility assist device

This paper presents a novel six-bar Sit-to-Stand (STS) linkage mechanism integrated in a multi-functional assistive device¹, that helps improve mobility of individuals with lower extremity weaknesses. The six-bar linkage follows the J-shaped trajectory of the shoulder-joint and maintains orientation of the supporting bar for the comfort and ergonomics. An overall goal was to design a device that is comfortable to the user during STS transformation, compact, light-weight, portable and one that requires minimum number of external actuators. By following the natural posture and movement of certain joints, a biomechanically correct STS motion is achieved. A natural motion ensures minimum stresses on joints and muscles and if the user can move their legs, they can undergo ambulation therapy and stimulate functional neural pathways. Dynamic analysis is done on the mechanism to design a frame and to select actuators for lifting a person weighing 300lbs. The device was tried by individuals with lower extremity weaknesses and the results showed that it lifts users well and also helps balance and stabilize them during ambulation.