I am attempting to construct a syringe pump using a linear actuator similar to the following
The main reasons I am attempting to make the linear actuator rater than buying one is cost and the ones I have seen are too fast for my needs.I need the arm to move at a rate of ~500um/sec.
As already mentioned, a threaded rod (in a stainless steel alloy that agrees with auto-claving if that's applicable) and driven from a geared down DC motor would be much better than a stepper.
A rod with 1mm pitch should then turn at 30RPM, to get the wanted 500Ám/s.
With a worm gear in between the motor and the rod, a worm wheel with 60 to 100 teeth will get it into a range of 1,800RPM to 3,000RPM, which agrees well with a lot of small (and dirt cheap) DC motors.
A 10 segment shaft encoder on the motor will, with a gearing of 100:1, give you 1000 pulses each shaft revolution, which, in an ideal world, would mean a pulse each Ám, but a cheap threaded rod will likely not be that
perfect. Still, compared to how cheap it can be made, it's extremely good and in any case, can be made with more precision than you likely need (you didn't add the acceptable tolerances though).
For the best precision, you should run it one way only (until done with whatever dosing job at hand), as going back and forth, the backlash will introduce some (small) errors.
A linear actuator is build on the same principles, just with less gear reduction.
Now here are my questions:
1.Do you guys know where I can find/purchase a motor that has range of 1-10RPMs.
2.I am attempting to use a steeper motor from an old scanner, will this fulfil the requirements?
3.To control the speed of the motor would a voltage regulator be effective?
1. I'd prefer a worm gear (as this is self locking) and a cheap DC motor. Any irregularities in motor poling will more or less vanish, as each complete turn nullifies it, so only the last uncomplete revolution may cause (extremely small) offsets and this divides with the gear factor. A stepper set up for direct rotation of the shaft will be more irregular.
Not sure if you just want a constant feed speed in a single run.
2. Don't. Other people already told you of the added complexity and depending on how you wanna use it, be aware that steppers needs ramping up and down of the speed, to keep it from loosing steps.Further, you'd need to limit current, as a motor used on a 12V system may in reality be eg. a 5V motor using a current limit method to make it step faster.
While I don't know your abilities in programming and tuning of control loops, I know you'll get better result from a DC motor, with the least amount of needed experience in mechanics, electronics and programming.
3. To control the speed of a DC motor, Pulse Width Modulation (PWM) is far superior.
To control the speed of a stepper, you just clock the changes at the needed rate (with a careful eye on the dynamics of the motor).
Since you only need to change the direction of the motor once in a single syringe emptying, you don't need an H-bridge for a DC motor, as the PWM can be made with a single transistor and a manual switch (or a relay) can change the direction.