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kind of robot suit that is worn in order to improve physical capability. As we already learned, when someone tries to make a movement, weak electrical signals travel in the nerves and occur in the muscle during a contraction. These weak signals can be detected, measured, and amplified with electrode sensors placed on the skin over the muscles being used. The HAL suit uses this control signal to trigger the control of motors acting at joints on the suit. As a result, the suit is controlled directly based on the commands coming from the person wearing it. So, controllers for the elbow joint motors are triggered from nervous system commands going to the muscles that normally flex and extend the elbow. Cyberdyne Inc. likes to call this a “voluntary control system.” This type of system relies on the users’ intended movements to then amplify those movements by making the robot suit do the appropriate action. An additional layer of control is added using a “robotic autonomous control system,” which is a kind of predictive system that works along with the voluntary triggering. All together, HAL applies a hybrid of the two control modes that provide an almost human-like movement. We will pay more visits to HAL later on in the book.
    This basic concept of hybrid control has also been used by a company called Touch Bionics in their development of a fantastic neuroprosthetic hand. Think back to our medieval “Iron Hand” prosthetic shown in figure 2.4 . Touch Bionics has created a sophisticated robot hand prosthetic that is driven by the normal muscle activation signals for the fingers. It can also be controlled by touch signals taken from pressure sensors. The Touch Bionics 5 finger i-LIMB hand uses inputs that come from the normal muscle signals to open and close the lifelike plastic fingers in the prosthetic. So, it uses the signals that come from muscles in the stump or remaining part of the person’s arm. The i-LIMB hand then can open and close to grasp objects in a way similar to a biological hand (panel A of figure 3.2 ).

    Figure 3.2. Touch Bionics 5 finger i-LIMB hand, which uses inputs that come from muscle signals to open and close the lifelike plastic fingers in the prosthetic. The i-LIMB makes a pinch grip (
A
) and individual “Pro-Digits” can be used for people with partial amputations (
B
and
C
). Courtesy Touch EMAS Ltd.
    ProDigits is an application of this device for people who are missing one or more fingers due to accident or from birth. This device has individually powered and controlled motors for each finger and can be set up to take over for just the fingers needed by the user. This means that a lot more than just an open and closed grip can occur and more dexterous activities can be done, such as pointing with the index finger and typing on a keyboard. These seem pretty simple tasks—and they are if you have an intact hand. But they are not if you don’t. An example of replacing one finger is shown in panel B of figure 3.2 and replacing function for four fingers is shown in panel C. The i-LIMB hand and the ProDigits can be covered in a flexible skin product making it look just like a real biological hand. Or they can be left uncovered. Tony Stark would go for the covered option if he needed one, I think.
Using Nervous System Commands to Control Iron Man
    Now let’s return to Tony Stark—someone with a fully intact body and nervous system—wearing a robotic suit to improve and amplify his normal abilities. If you think this through, you will realize that using the Iron Man suit could occur by tracking the nervous system commands and using them to control the suit. Doing this effectively takes the user’s muscles out of the equation. That is, it creates the same disconnect between nervous system and movement that exists after a spinal cord injury or stroke. We just finished talking about using signals in the nervous system to trigger muscle