I have been saying and living (!) all along that a detailed functional analysis necessarily precedes successful prosthetic design.
It also precedes successful design anywhere else. Apple recently revealed the iPad. But listen to how Steve Jobs explains what they did: they analysed what was wrong with existing solutions and then designed and built their new device to specifically fill that niche. And so those of you that kept trucking by extending the old prosthetic design metaphor (build it from cheap crap, make it look neat and sell it for millions to non-disabled company or insurance representatives): go and study and do a detailed functional analysis first. The deeper and more detailed, the more extensive and unforgiving, the better.
But now let us see what Steve Jobs can teach us about that:
Obviously Steve gets it wrong soon with his iPad evangelizing - my netbook is absolutely great, slow, light, cheap and has a very long battery life, it runs PC software which in fact is great - so it does exactly what I want it to do. No way an iPad would be of help. Besides, Steve and his friends at Apple still violate Telecommunications Act Section 255 so they should have plenty to do until they fixed that mess. But Steve's means to arrive at that conclusion - by seeing what is not good about existing parts - is the way to do it. That is where I think he completely nailed it.
How do we apply that to prosthetic arms that allow for gripping and holding items, most notably the ones operated by myoelectric switches or cable control?
We already have industrial looking out-of-the-machine as well as humanoid-looking replicate skin type looks. But as in eyewear, we now want armwear.
Some key questions:
- Does the device - particularly the operative terminal device / gripper - look great?
- Does the device - particularly the operative terminal device / gripper - look functional rather than just being functional?
- Is the device - particularly the operative terminal device / gripper - robust and sturdy enough?
- Cleaning the device - particularly the operative terminal device / gripper?
The specific grip/s or function/s available determines many other aspects (see below).
If I can get a non slip grip at the right angle, it saves me stress, inefficient force, subsequent overload and probably skin sores. The cleverer the design, the better the overall outcome.
Things do relate here.
Some key questions:
- ADL/grip benchmark inventory for an average or specific person including all grips required for opening food containers, operating zippers, holding a wallet?
- Speed of reaction of the grip or hand/hook mechanism?
- Duration and conditions of operation of the functional (open/close) parts (e.g., my cable controlled arm works 24/7 practically without any recharge or greade/oil lubrication)?
The amount of grip force used can be minimal if surface and shape interact sensibly with the object that I want to grip or manipulate.
But also, brute grip force at times is simply necessary.
- Can grip force be set to adequate levels for any given task?
- Is too little or too much grip force a problem?
- How can the design be improved to get by with less grip force?
- Is the design too fragile to work with sufficient weight?
Overload, imbalance, posture
At the end of a day, the total of pain and overload accumulates in my elbows, shoulders, neck and back.
- How does the terminal device and its grip angles force me into certain postural restrictions?
- How does the prosthesis including the angles and mount of the gripper/terminal device limit my elbow or shoulder motion? Extend elbow, flex elbow and check.
- What muscles are overused and why?
- Has the gripper / terminal device at all been tested for long enough a duration and what all has been done during that time?
- Do I have to schlepp with me a lot of other trinkets or is the prosthesis self contained: harness? battery pack? external control switches? How much drama is necessary to get that puppy going?
At the end of the day, slip, sweat and what all happens underneath the prosthetic socket determines my quality of life.
- Can the material, particularly of the gripper / terminal device, be kept clean? How?
- Does the prosthesis slide off the arm and when and how often does it do that?
The overall stress that I run up also includes failure of function, failure to look acceptable and so on.
- Field test in the USA and Canada?
- Field test in Switzerland and Germany?
- Field test in Russia?
- Field test in China?
- Field test in Turkey?
- Field test in Saudi Arabia and Egypt?
- Field test in South Africa?
- Field test in Brazil and Argentina?
- Field test in Mexico and Haiti?
- Field test in all other countries?
Field test does not mean sitting in office and waiting / pondering. It means to go out where the sweat happens and do a detailed documentation. It means painstaking attention to detail of open/close/grip as well as wrist mount mechanisms.
After that we should have a pretty good idea about what works and what does not. Where tests cannot be done, results should be approximated - so you can in fact test a prosthetic arm at 40 degrees Celsius without air condition and hard work outside without travelling far away. You just have to do it.