There have been many attempts made to re-create human anatomy through mechanical means. The human body however, is so complex that it is very difficult to duplicate even simple functions. Robotics and electronics are making great strides in this field, of particular interest are limbs such hands, arms, and legs.
In order to reproduce human extremities there are a number of aspects that must be considered:
- The gripping force required to manipulate different objects (eggs, pens, tools)
- The motion capabilities of each joint of the hand
- The ability to feel or touch objects (tactile senses)
- The method of controlling movement within the limb
- Emulating real human movement (smoothness, and speed of response).
Many different solutions have been proposed for this problem, some include using "muscles" controlled by air pressure, piezoelectric materials, or shape memory alloys. Shape memory alloys mimic human muscles and tendons very well. SMA's are strong and compact so that large groups of them can be used for robotic applications, and the motion with which they contract and expand are very smooth creating a life-like movement unavailable in other systems.
Creating human motion using SMA wires is a complex task but a simple explanation is detailed here. For example to create a single direction of movement (like the middle knuckle of your fingers) the setup shown in Figure 1 could be used. The bias spring shown in the upper portion of the finger would hold the finger straight, stretching the SMA wire, then the SMA wire on the bottom portion of the finger can be heated which will cause it to shorten bending the joint downwards (as in Figure 1). The heating takes place by running an electric current through the wire; the timing and magnitude of this current can be controlled through a computer interface used to manipulate the joint.
There are still some challenges that must be overcome before robotic hands can become more commonplace. The first is generating the computer software used to control the artificial muscle systems within the robotic limbs. The second is creating large enough movements to emulate human flexibility (i.e. being able to bend the joints as far as humans can). The third problem is reproducing the speed and accuracy of human reflexes.
The wires in such robotic hands are modeled through simple experiments. The first link takes you to a video clip showing one of these simple experiments in action. The next link is demonstration of how the interactive applet modeling this experiment works, while the third link goes to the applet itself. Finally, the fourth link is to a game involving an SMA wire in the context of the experiment you have just seen.
