I'm trying to figure out whether or not we should pursue current-controlled testing or distance. The problem I am running into is that I do not currently have a method to give instantaneous current to the motor. Therefore, when I change the maximum current running through the motor, the speed at which the skin stretch device rotates varies. However, when at the final skin stretch position (there is a limited distance which the device can rotate), the feeling of skin stretch appears to be the same, regardless of current/torque. To summarize into words that make more sense, I can feel the different torque being applied during the rotation, but at the end of the rotation, there doesn't seem to be a difference in sensation. If we knew what response torque/force the skin provided at certain distances of skin stretch, we could easily use torque to control the skin stretch. For example, if 0.5 Nm of torque moved the skin only 1 mm, and to move the skin any further required more torque, we could find a relationship between the torque necessary to move the skin and skin stretch constant/stiffness.

The easy way to apply the skin stretch is to vary the distance, and apply a single, uniform torque each time.

So if that is necessary, we would need an encoder to control the rotational distance of the device.

Questions:

What program do we use?

For testing, we only need a very simple feedback control system where we input our desired rotational distance and use an encoder to read the actual rotational distance. We could probably use Matlab to do this, however Li and I have no experience of setting up a computer, and hooking it up to a device...digital control is not an area we have a lot of experience, most of our controls knowledge is analog.

However, if we want to keep the skin stretch sensation between person to person the same, torque is probably a better way to apply different amounts of skin stretch. For example, if you have very tight skin, and stretch the skin a little bit, because your skin is so tight, you feel a stronger sensation than if you have very loose skin and stretch it the same amount.

If we do that, it would be necessary to measure the torqe...and the motor is current controlled, which correspondes to the torque. But high torques will need a distance control as well, because while the torque threshold for humans is probably high, the skin stretch distance threshold is definitely limited.