Linear motor control

[zohonie]

Hi,

I recently bought anUltraMotion linear actuator with a 24v dc servomotor:

http://www.ultramotion.com/products/bug.php
I would like to extend and retract the rod continuously for upto 24 hours. I would also like to control the frequency and distance of travel. The actuator comes with adjustable limit switches to control the travel distance. what I need help with though is figuring out how to control its speed and direction. It would be best if I can do this with analog circuit. Please be as specific as possible as I'm very new to think kind of work. Thank you very much.
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[mstacho]

Analog circuits are typically not recommended, since they can really badly waste energy.  If you're set on doing it with an analog circuit, though, you may need to be a bit more specific: do you want to be able to physically set the controls, and then turn it on, or will you be setting it up through a computer (which would require extra work and you should probably just do it digitally anyway :-P).

Does your motor come with the precision linear potentiometer?  That would make things a lot easier for you.  In fact, it looks like you bought the version with a servo attached...servos allow you to just specify their position and off they go, but you have to do it digitally.  Can you be more specific about all the options you have on your actuator?

If you didn't get the servo version (so you'll have to do the control yourself), my best advice would be to get a microcontroller with a Pulse-Width Modulation (PWM) output attached to a motor control board (many such boards and microcontrollers exist that are pre-built for you so you don't have to do much in the way of soldering.

[Soeren]

Hi,

Analog circuits are typically not recommended, since they can really badly waste energy.

Sounds like you're confusing terms like "analog" and "linear"?
Analog or digital has nothing to do with the efficiency of a circuits - digital is just analog driven to the extremes (voltage-vise).
SMPSU's amongst others are analog.

[...] In fact, it looks like you bought the version with a servo attached...servos allow you to just specify their position and off they go, but you have to do it digitally.

Not all servos are R/C servos!
R/C servos has been analog up until around the last decade or so and can still be used with analog circuitry!

However, the mentioned actuator has not got a servo motor, but instead a regular DC motor, according to the link.

[...] my best advice would be to get a microcontroller with a Pulse-Width Modulation (PWM) output attached to a motor control board [...]

A microcontroller could be used, but is not what the OP want, so must be considered gross overkill and a bad solution.
A simple circuit, digital or analog is all that's needed, so please don't scare the OP suggesting a microcontroller solution.

[Soeren]

Hi,

[...] what I need help with though is figuring out how to control its speed and direction. It would be best if I can do this with analog circuit.

Do you know the current draw of the motor, running as well as stall?
That's a parameter we need to know, at least an approximation.

[mstacho]

I stand corrected. 

[nickc]

The limit switches on a linear actuator are meant to be wired into a motion control system so they don't really control the distance just prevent damage to the motor and screw.  The controller shuts the motor down when the limit is tripped so you don't run the actuator into the hard stop.   
If you are new to this kind of work and you are doing this for work(not for fun), it would much cheaper, faster and better to buy a motor controller from the same company. 

[Soeren]

Hi,

The limit switches on a linear actuator are meant to be wired into a motion control system so they don't really control the distance just prevent damage to the motor and screw.

If the OP decides that the limit switches are going to be used for controlling the limits of travel and fashions a controller using them, then they will be controlling the distance in that particular project.