Compliant Robotic Biceps Machine for Resistance Training and Upper Limb Rehabilitation

End-effector-based resistance rehabilitation training is widely used to restore motor function in individuals with upper extremity motor dysfunction. Incorporating compliant actuation adds the advantage of working closely with patients while providing inherent safety, adaptability, and accurate force control. This paper presents a proof-of-concept robotic biceps machine equipped with a Series Elastic Actuator (SEA) featuring user-adjustable stiffness. The machine provides resistance training for the biceps muscle by generating various resistance levels throughout the elbow’s range of motion. Additionally, it aids in elbow rehabilitation by generating assistive forces to achieve full range of motion. The design, dynamic modeling, and parameter identification of the system are detailed, with stiffness levels selected based on the desired range and accuracy of torque measurement. The system operates in two primary modes: resistive mode which uses a torque controller, and assistive mode which employs a position controller. To ensure safety, a force sensor is added to the handle to verify that a sufficient grip force is provided by the user. To evaluate the machine’s performance, a pilot experimental protocol, including a demonstration of the machine’s use in assistive mode and resistance training is described. Results demonstrate accurate and responsive behavior, with a Mean Square Error (MSE) in tracking of 1.3 degrees, and maximum error in constant torque tracking of 2.56 N.m.