The NTNU Revolute Wrist Device (NRWD): A Kinematically Optimized Externally Powered Wrist Prosthesis

BACKGROUND Many transradial amputees choose not to use a powered wrist unit because the benefits are literally outweighed by its weight, poor cosmesis and control complexity. For those who use a powered wrist, prosupination is typically the only function offered. PURPOSE In a recent study, the functionally optimal axis of rotation was identified for a single degree-offreedom wrist device. A physical device which implements this kinematics is now being built in order to assess its practical properties and actual functional benefits or drawbacks. PROPERTIES OF THE DEVICE The axis of rotation goes through the wrist from a dorsal-lateral position proximally to a ventralmedial (palmar) position distally, forming an angle of 10.7° with the forearm and 6.9° with the sagittal plane. Distally the axis is displaced 18.9° with respect to the 3rd metacarpal and 13.2° with respect to the palmar plane. The device includes a microcontroller with external communication lines configurable as a CAN or I2C bus, or as dual analog inputs and outputs, respectively, for compatibility with commercial terminal devices as well as other experimental systems. The control software is modular, transparent to the communication mode. Several control modes are available, such as on/off and proportional torque, velocity or position. Electromechanical properties are comparable to those of other existing devices.