Development of a Modular Bionic Prototype Arm Prosthesis Integrating a Closed-Loop Control System

An active prosthetic arm is not only dependent on critical factors for clinical use, such as weight or bulk but also needs reliable control inputs for accurate and safe positioning. Particularly with a high level of amputation, light but robust devices are essential. Our concept is composed of a modular system, based on bionic design principles, that is adaptable to the specific level of amputation of an arm. By following three basic rules: proximal weight, flexibility and lightweight but silent operation, it is possible to mimic the weight distribution of a human arm. A custom developed control hardware attached on top (HAT) is based on a Raspberry Pi 3 (RPi3) and holds the ADS1299 that is capable of acquiring sensor and other bioelectrical signals. The motion and position data is gathered using a 9-axis inertial measurement unit. Based on the processed data a control signal is sent to the independent actuator control unit. The use of the RPi3 allows performing complex decisions and control algorithms fast enough for real-time control of the prosthesis actuators. The resulting ranges of motion are 120° for the elbow joint and 270° for the wrist joint. The elbow joint can lift a weight of maximal 3.3 kg with a lever of 30 cm through the entire range of motion within two seconds. The system provides a novel bionic design that allows usage not only for transradial but also transhumeral amputation. The proximal weight distribution and the used materials increase the wearing comfort in daily tasks and mimic to a high extent physiological conditions. Furthermore, the speed of the control system is within the range of the electromechanical delay in the human body which not only is beneficial for control purposes but also increases the acceptance of the prosthesis.