http://en.wikipedia.org/wiki/Linear_actuatorprobably the best way - You could make one fairly easily.
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For what it's worth, linear actuators of this sort are one classic design for hospital "infusion pumps", since -- especially if the motor is geared down -- they can be controlled fairly precisely.(I spent a year doing equipment repair in a hospital. One of the regular tasks was to make sure those pumps dispensed EXACTLY at the rate they were supposed to.)
A critically and scary responsible job, when you understand there are medicines which become a poison in the wrong dose. Shown is a micro-liter pulse solenoid dispenser.Every need has multiple interesting possible solutions. A
Yep. The art of engineering is that of picking the _best_ solution, where "best" is defined by the specific job you're trying to accomplish and usually involves conflicting goals.Actually, I was surprised just how low-tech the infusion pumps were at the time ( decades ago) -- until I realized that the goal was to to produce a device that was almost "too simple to fail". Though there was one design flaw I'd have changed, given my druthers -- not a problem under normal use, but an opportunity for users to make a mistake.One of the nice things about this application, by the way, is that -- unlike other uses of leadscrews -- the critical operation is all in one direction, so mechanical hysterisis when the gear train reverses really doesn't become an issue.
+1. I've used exactly that method in the past, in both fluid delivery (via a hypodermic syringe in fact) and in mechanical positioning. A linear actuator such as the one shown uses a screw drive to ensure precision delivery of the fluid, where N turns of the shaft results in X linear distance.
you could probably build your own linear motor with a servo modified for continuous rotation, or gear motor spinning a long bolt or screw tapped through a block of wood or plastic riding on some sort of rail.
you can get a servo motor used in rc cars and add a lever and linkage. use geometry and circles to figure out the required length of the arm on the servo to get full throw of the plunger. there are also linear actuators which could be used but are not as abundant as rc servos.
Trouble with that method is you get variable pressure on the syringe, and a non linear relationship between angle and linear position.
Im just impressed how people decipher slip speak :)