This is my first post. I have some limited experience with Arduino, and now I am planning a project as shown here:
The goal is to unwind the wire from the coil with constant tension as soon as I pull the wire in the direction of the red arrow. I want to move the coil so that I have a constant wire tension regardless of pulling speed, coil size etc.
The spring loaded pulley will bring the magnet closer to the hall sensor (A1319) which gives me linear output at any analog pin: the smaller the gap between magnet and sensor the higher the value will be at the pin. This I can translate into RPM of the stepper. As the coil is heavy and in many cases the wire will be pulled rather slow I decided to go with a stepper. I can ramp up and down the stepper with simple ramps using this modified pwm library.
I studied various sources on winders, tension control, dancers etc., and most state that it's possible without measuring the coil diameter, although the diameter changes during unwinding. But in this case I would need to use PID control. I looked into the PID library which seems useful. I understood that winding / unwinding processes are less simple than they look...
What do you think: which approach is most simple and will fill my bill? Should I continue with PID? Is it theoretical possible with such a simple device to get the wire off the coil without breaking it? The coil is up to 8kg, the wire is 0.12mm and breaks at a load of 0.4kg!
(I will provide some code snippets in the following post)
EDIT: check here for improved versions of the diagram.