# Mechanical Design, Control, and Laboratory Test of a Two-Degrees-of-Freedom Elbow Prosthesis

## TL;DR

This paper describes a two-degrees-of-freedom elbow prosthesis prototype and compares two control methods to improve its movement accuracy.

## Contribution

The novel contribution is the use of a sliding mode control with time base generator strategy to achieve biomimetic movement in a 2DOF elbow prosthesis.

## Key findings

- The SMC + TBG control method produced biomimetic angular displacement and velocity patterns.
- The PID control method failed to replicate natural movement patterns effectively.
- The prosthesis demonstrated a range of motion suitable for transhumeral amputees.

## Abstract

This study presents the design and experimental testing of a two-degrees-of-freedom (2DOF) elbow prosthesis prototype designed to replicate the movement patterns of a native or normal human elbow. Two methods of the control of the prosthesis, namely, the proportional–integral–derivative method (PID; a well-established method) and a combination of sliding mode control with a time base generator strategy (SMC + TBG; an advanced method), were compared on the basis of various performance metrics of the prosthesis, as obtained in laboratory tests. Among these metrics were the angular displacement and velocity as a function of time. The mechanical design combined 3D-printed components with custom-designed joints, featuring a worm gear transmission with a crown gear for flexion–extension, enhanced by torsional springs, and a pinion gear with a crown gear for pronation–supination and control. Sensors for voltage and current data acquisition enabled real-time monitoring and control. The prosthesis was tested in the laboratory with a range of motion of 100–120° for flexion–extension, 50° for supination, and 75° for pronation, demonstrating the adaptability of the actuators and validating their autonomy through battery-powered operation. The results showed that control using SMC + TBG resulted in biomimetic patterns for angular displacement and angular velocity of the prosthesis, whereas control using PID did not. Thus, the prosthesis with control provided using an SMC + TBG strategy may have been promised for use by people who have undergone transhumeral amputation.