i need something like a solenoid which can generate 0 to 30 pounds of
linear force. it needs to be easily controllable, i.e. have a
proportionate response to voltage or current as it will be used in a
closed loop system.
i think solenoids are ruled out because they dont generate force in a
nice proportionate way to voltage/current? am i wrong about that?
it also needs to be fast responding, i.e. 0 to 30 pounds in less than
100ms
hmm a solenoid does sound like the right thing..but why do i think
they are on/off?
You have not mentioned how far it has to travel. If it is just a few
milli-meteres its one thing, if it is a foot, it's quite another.
Furthermore, the mass you need to push will be important in the response
time.
You are correct about solenoids, they are non-linear devices who's force is
a strong function of the distance pulled in as well as current in the coil.
However, they can provide the high forces in the range you require and are
cheap.
One possibility is to use a solenoid, either a pusher or a puller depending
on the direction you want with feedback from a force sensor to linearize and
control the force. You did mention closed loop. A simple strain gauge force
transducer or load cell provides the the force sensing feedback. This is
applied to an ampifier to deliver current to the solenoid. A Pulse Width
Modulation scheme, PWM, may be in order to keep power dissipation in check.
As mentioned in other posts, a voice coil actuator would probably be the
best, though expensive choice. Force can be quite linear over a moderate
throw distance and the direction depends on the polarity of the drive
current. Lower mass makes it fast compared to a solenoid. Feedback can also
be applied here to improve performance.
A piezo electric (ceramic) transducer would probably be the cheapest way to
do it but the throw distance is very short. But, it can be very fast.
Ultrasonic tranducers work this way.
Yet another way is the linear induction motor. Basically it is like a
transformer with a shorted single turn secondary free to move. AC current in
the primary causes the shorted secondary to repel away. Forces can be vary
high. Depending on design, mass can be relatively low, but accurate force
would have to be controlled with feedback. Throw distance can be as long as
you want. Maglev trains work on this principle.
A small DC or other motor working on a ball screw, jack screw or rack and
pinion may be the simplest and and relatively cheap method of getting the
motion you want. With proper design, the speed reqirement can probably be
met. Again throw distance must be considered in determining speed, motor
size and gear ratios.