Digital Arm Controls Five Joints

A new upper-limb prosthesis allows amputees to control movements of five joints, while competitive solutions permit control of only three joints.

The Boston Digital Arm also provides amputees with more flexibility and capability. Developed by Liberating Technologies (Holliston, MA, USA), the arms owes its performance and integration to digital signal controllers developed by Texas Instruments (TI, Houston, USA), called TMS320C2000. Until recently, upper limb prostheses were based on analog controls, meaning that a user relied solely on upper-arm muscle movements to control the prosthetic device. The power that the gripper exerted was controlled by a single predefined limit.

"We selected TI's C2000 controllers because they provide vastly superior abilities to generate pulse width modulated (PWM) signals for the most efficient method of driving the DC motors that are used in prostheses. One TI digital signal controller gives us the ability to drive five motors, expandable to nine with an add-on module,” commented Bill Hanson, president, Liberating Technology.

The Boston Digital Arm is controlled by signals generated from one or more of the user's noninjured upper-limb muscles. Operational amplifiers and instrumentation amplifiers from TI detect, condition, and amplify the signals generated by the muscles. The C2000 controller then examines the strength of the signals and determines how much voltage to send to motors in the elbow, wrist, and hand. The device uses five PWM outputs to drive each motor, making it possible to go beyond the traditional arm, wrist, and hand motion to provide shoulder movement without working shoulder muscles. An enhanced capability also allows the prosthetic arm to swing instead of hanging stiffly while the user walks. Software enables the wearer to interface with the prosthesis in many ways.






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Liberating Technologies