When you say linear rotary actuator, I am assuming that you mean a mechanism
that  converts linear motion into rotary or vice versa; and you have a
feedback mechanism about the motion. If you want to hold position and  you
are talking about  standard closed loop position  control. A brush or
brushless (brush is easier) motor with the encoder as a feedback element in
a PI or a PID loop should do it. Microchip has an app note on it's web site
dealing with the implementation of PID control on a PIC. Good luck
Madhu

> Hey everyone.
>
> Recently I obtained a very sophisticated piece of equipment. A linear
rotary
> actuator with an optical quadrature decoder for feedback. In other words:
a
> harddrive arm. I thought of making a foot control pedal with it, to be
built
> into a MIDI controller pedal with preset buttons. The tilt is just about
> right, and the optical encoder has amazing resolution. The idea is to have
> the pedal assume its last stored position for each preset, and to provide
> mechanical resistance when moved by the user.
>
> I guess I'll hook up the "voice coil" to a PWM-controlled H-bridge. The
> encoder has TTL outputs. So I'm not worried about hardware. But how would
I
> go about the software, to have the maximum counter torque, but also a
> position hold, when the pedal is left alone? Anybody know any links to
this
> kind of motion control? I'm using a PIC16F874-04
>
> Thanks,
> Joris.

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