My workgroup is interfacing some equipment on an optical bench. We have three small elements (lenses and filters) that need to be moved, on command from a computer, in or out of the optical path. The elements are on ball-bearing linear slides, movement is horizontal, and it only takes a few ounces of force to move them. All the off-the-shelf actuators that I have found so far are very pricy, and overkill for what we need. Our requirements are minimal:
a) IN position can be set by a hard stop, and must be repeatable to0.02". OUT position is not critical, as long as it is about 3" away from IN.
b) No need for proportional control or stopping at intermediate positions between IN and OUT.
c) Transit time is not important: 10 seconds or less.
d) Ideally, each actuator would be controlled by one or two TTL control lines from our interface.
After some googling and brainstorming, I can think of a couple of designs. A motor and leadscrew is the obvious starting point. A small DC motor could be driven in both directions by an H-bridge, plus a couple of transistors or logic gates to handle the polarity switching, limit switches to stop the motor at each end, maybe a flip-flop to keep track of the current state.
Or I could use a stepper instead of a DC motor. HSI has small steppers with integral leadscrews:
I found a nice stepper driver chip (Allegro 3967):
It needs only two TTL control lines: one selects direction, the other counts pulses. Perhaps with a stepper, I would not need the limit switches.
Other solutions were considered. Solenoids might be too violent, pneumatic gizmos too complicated. An R/C hobby servo uses proportional control, but it could be rewired as a bang-bang. I even thought about scavenging the tray actuator from a compact disk drive.
Any other ideas? Thanks in advance.