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 to
0.02". OUT position is not critical, as long as it is about 3" away
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
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.
18 years ago