This project is creating an add-on to a pediatric body-powered arm that would help children learn to use their prostheses faster. The idea comes from Robert Haag, whose two year old son Michael uses a body-powered gripper. Here’s a video of a typical training session with a physical therapist:
In the video, you can see the adults giving him positive feedback when he does the right thing. This is essential to learning; the quantity, quality, and promptness of feedback directly affect the development of a skill. Rob’s idea is to build a small device that would measure the tension in the cable and make friendly sounds to tell Michael that the gripper is opening and closing. Now, instead of just being in short sessions, the feedback would be instantaneous and constant, hopefully helping him learn faster and better.
Jack Walker, an experienced product design engineer, has volunteered to help with this project. He and Rob are corresponding and we’re publishing the results here. If you want to volunteer or offer suggestions too, please contact us and we’ll put you in the loop.
The device will essentially consist of a sound chip that can play audio samples, a sensor that measures tension on the cables, and possibly some component that sits between them and handles the logic. With the right kind of switch, it might be possible to make the logic mostly mechanical.
Rob has found some sound chips that might work from AGC Sound. Below are pictures of them and Rob’s comments. On the left is the 1301 and on the right is the TAS:
The chips pictured here are samples sent to me by Les Zubli at AGC Sound. They are currently activated by closing the connection. The 1301 is the most attractive because of it’s small size. It’s also the least versatile (oh well, it’s a first prototype, right?) The TAS can be re-recorded by the user. The metal disk on the bottom of the 1301 distributes the sound. If you hold it with your fingers, you can barely hear it. Lay it on a resonator like a table top and it’s sounds nice and loud.
Here are some pictures of Michael’s prosthesis and Rob’s comments:
Ideally the new device would be located close to the hook. Limiting any improvements we make to the terminal end of the device means that more people could take advantage of it without consulting their prosthetist. How much force to close the hook? I’m just a dad, man :) I wouldn’t know how to measure that. Michael’s only two so it can’t be that much, although he’s pinched me a couple of times by accident and it hurts like %$@@^#. It has to be enough pressure to overcome the elastic that holds it open and can still hold something. Hanging three VHS tapes from the shoulder strap seems to be a good threshold. In the future we may want to make that threshold adjustable or make it more than binary (the more strain the louder the sound, for instance).