Development of a Human Assistive Robot to Support Hip Joint Movement During Sit-to-stand Using Non-linear Springs

The literature concerning human assistive robots typically focuses on "wearable" devices, with the aim of reducing the muscular effort required of patients during movements. This paper describes the design of an orthosis for assisting patients during sit-to-atand (STS). The newly developed device generates a hip joint torque and reduces the muscle activity required of the wearer. The device makes use of non-linear springs called stiffness adjustable tendons (SATs), to simulate the behavior of human tendons, and to exploit their ability to store energy when in motion and to return it at a later time. A series elastic actuator (SEA) was adopted to create the device. A position reference is designed to realize an assist control without a force sensor. EMG sensors are used to verify the effective reduction of muscle activity required of the wearer during the STS.