Abstract
A power assist chair helps the user to stand up. The force directly acts on the user and soft actuation is important. In this study, a virtual spring is proposed to realize the soft actuation. The seat is pushed up with a pneumatic cylinder so that assist force is controlled to be proportional to the seat angle. This leads to spring characteristics. Combination of a proportional pressure-reducing valve and a single rod cylinder is the key to realize the virtual spring characteristics. With its control, the seat behaves like a spring, and the spring constant and the pre-compression can be adjusted by the control.
