I'm experimenting with a device for tuning piano strings. It attaches to the piano's tuning pins and turns them slightly by applying a torque impulse. It is a semi-automatic process, handled by a human operator.
- Operator presses a piano key, control system records the tone and calculates the frequency error. (The set frequency is known.)
- The control system calculates the required size of the torque impulse.
- The device applies the torque impulse.
- The operator presses the key again. If pitch error is still large, repeat from 1.
The change in frequency caused by a torque impulse is a function of the impulse size and the current frequency of the string.
I'm now going to design a control system for this. So far I've found that it probably is a Markov process, since it is not time dependent and not depends on previous states. But what could be a suitable control method for this application?