Transradial Prosthesis Based on Wireless Mioelectronic Bracelet: design of the Sensing Electronic System and Hand Movements Control

Prosthesis is a complex medical device which needs to be adapted to the specific individual requirements. A good prosthesis is based on reliable and simple interaction of its mechanic and electronic parts with the user; it is controlled by small electrical signals generated by muscle contractions (myoelectric signals) and measured with electrodes placed on the skin. In this research work, the designed and realized prosthesis (Fig. 1a) is equipped with sensors and actuators that simplify and aid the hand movements. The myoelectric signals are detected through the MYO bracelet which integrates the Electromyography (EMG) electrodes and an Inertial Measurement Unit (IMU) based on InvenSense MPU-9150 IC; all these data are sent wirelessly by MYO bracelet to the control electronics for activating one DC motor for handling the five fingers and two servomotors for wrist [1]. Unlike conventional prostheses that use five motors one for each finger, in designed prosthesis a mechanism based on rigid and compact toothed wheels is exploited; the wheels apply constant forces, not dependent on fingers position thus transmitting movement to all fingers. Also, use of a single motor allows to obtain a lighter and less expensive prosthesis, battery energy savings and larger space for control electronics housing. The realized driving/control electronic unit handles the different prosthesis sections (Fig. 1b); it acquires data from five resistive force sensors and five LM35 temperature sensors, each couple for finger, it drives two Futuba S3305 servo-motors for wrist movement and one Maxon DCX 19 S DC motor for fingers movement. Also, the Arduino-based control unit receives data, wirelessly from MYO bracelet through bluetooth low-energy MYO unit, by using the HM11 module that integrates SoC Texas Instruments CC2541 chip (Fig 2a) and it exchanges data with the Raspberry Pi board (placed into proper case with LCD display, Fig. 2b) by USB serial cable [2]. The Raspberry board collects data from sensors and, through a WiFi connection, sends them on cloud to a dedicated web server; it also manages the touch-screen 3.5” LCD getting user-friendly interface in order to handle different aspects of the prosthesis such as autonomy, sensors data displaying, wireless connectivity. Performed experimental tests (Figs. 3, 4) show that realized electronic system (firmware developed in Arduino IDE) allows to correctly detect the different data provided by sensors and by the EMG MYO electrodes and to drive the employed DC and servo motors [3]. Data related to physical and myoelectric parameters from IMU, EMG MYO electrodes and from temperature and pressure (force) sensors are displayed on PC terminal via USB connection for verifying the correct system operation (Fig. 4a) and, through the Raspberry Pi board, same data are sent on cloud in order to be monitored by the orthopedic staff (Fig. 4b).