• Question: With prosthetic limbs, how are they designed to move like normal limbs?

    Asked by Amelia to Ejay, Edgars on 7 Jun 2019.
    • Photo: Edgars Kelmers

      Edgars Kelmers answered on 7 Jun 2019:

      I just know the basics. You can have simple mechanical limbs or more complicated limbs with electronic control.

      Leg prostheses are easier to make compared to arms. In simple designs you can use just a hinge joint with attached rod and a shoe. During simple walking you do not use much of your leg muscles. You just swing your leg and when it lands on the ground your upper body moves forward until the moment when you need to swing your other leg. Therefore with a good hinge joint you would not notice if a person does not have his real leg when he is wearing pants.

      Arms are much more complicated. You need to move all fingers, your wrist and elbow. Arm prosthesis are nowhere near as good as natural arms. Most of the arm prosthesis allow only simple movements: clamp or release all fingers and turn a wrist. You would have small motors inside the prosthesis, which you could control with touch sensors or electric signals from your muscles.

    • Photo: Ejay Nsugbe

      Ejay Nsugbe answered on 8 Jun 2019:

      I think Edgar has done a good job of explaining the concept around the mechanical design of prosthetic limbs,now-using an example of an Upper-Limb prosthetic,allow for me to shed some insight on the second stage-which is based around getting man and machine to work in sync-the control of the prosthetic arm as though it was a biological limb.
      I like to chunk this into 3 key phases; the first is the acquisition of the amputees intended limb motion and this involves the recording of an appropriate Electrophysiological signal which contains the relevant information(i.e limb open or close), the second phase is the number crunching and signal processing of the source signal and yields an output machine control signal,in the final stage,this control signal is sent to the prosthetic controller which actuates the prosthetic arm and gets it to open/close as desired.

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