Last week I picked up my test socket from Rich, at Diablo Prosthetics & Orthotics, fitted with the i-Limb hand. Since this is my first myo-electric hand we are still experimenting with the socket design and electrode placement, so it’s still early days.
The test socket Rich built is pretty cool, it’s clear plastic so you can see all of the wires and motor inside (the final socket will be carbon fiber). As well as the i-Limb hand we’re trying out an Otto Bock wrist rotator unit as well, this allows me to rotate the hand 360 degrees (that should freak people out over Halloween).
The socket has two electrodes inside that are in touch with my skin, these pick up the electrical activity when I contract my muscles. If I contract one muscle the hand opens, if I contract the other the hand closes. The speed of the hand is proportional to how hard I contract the muscle. If I contract both at the same time the wrist rotates instead, depending on which one I contract the hardest, the wrist rotates one way or the other…this will take a bit of practice as you can imagine!
The fingers/thumb on the hand are independently driven, each has it’s own motor. Sensors feedback the force exerted by each finger so, although my control is limited to opening/closing the hand, each finger moves independently allowing the hand to grasp irregular shaped objects. I can also rotate the thumb manually from the side of the hand to over the palm, thus changing the grip pattern from making a fist to grasping a bar, for example.
The whole thing is pretty heavy, at least to what I’ve been use to. It weighs 3lbs in total, about half is the hand and the other is the socket. Next week I’m going back to see Rich to change the position of the electrodes and see if we can get a better fit with the socket and liner. We’re trying to use a liner with a lock pin, as per my current arm. The challenge is we have to cut holes in the liner for the electrodes, this reduces the ability for the liner to keep the socket snug on my stump…this is an unusual approach for a myo arm, but if we can get it to work the benefit is the socket doesn’t restrict my elbow movement.