Development of a Universal Exercise Robot based on Torque and Impedance Control

Currently, there exists passive exercise machines/equipment that are either single-pose or general-purpose, each having its own advantages and disadvantages. This paper explores a concept of an active exercise robot, named “Johnson Machine”, capable of providing both the advantages of general-purpose and single-pose exercise machines. Johnson Machine can apply an adjustable resistive force of up to 100 N onto the handlebar in any direction within an 80-cm radius of a 2-DoF (Degree of Freedom) plane. It can simulate virtual objects such as weights, springs, dampers, as well as a combination of these objects, and can limit itself onto a 1-DoF path, enabling isolation exercises. The two built-in potentiometers allow for the easy variation of both the resistive forces' magnitude and direction. An exercise safety zone and an emergency switch are implemented as saftey features of Johnson Machine. The two current controlled motors that provides the end-effector force, along with gravitational and frictional compensations are derived using the Lagrangian approach. Finally, this exercise robot is able to experimentally provide resistive forces of up to 74.45 N (8 kg) and demonstrate both general-purpose and single-pose functions by assisting in several exercises such as the squat, bench press, shoulder press and the Lat-pulldown.