Total control

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.

If an amputee had limited use of the upper arm muscles, however, he or she may have been unable to use prosthesis or may only have been able to benefit from a fraction of its capabilities.

The power that the gripper exerted was controlled by a single predefined limit, meaning that the same amount of force used for lifting a heavy object would also be applied for holding an egg or a child’s hand.  Also, traditional artificial limbs were limited to controlling only three joints one at a time – the elbow, wrist and hand.

When developing its Boston Digital Arm upper limb prosthesis, Liberating Technologies identified the inflexibility of the control system as the primary limiting factor in upper limb prosthetic performance.

“When we developed our system we considered both microcontrollers (MCUs) and digital signal controllers,” said Bill Hanson, president, Liberating Technology.