Thread: Who knows something about linear actuators?

Originally posted by SuperMatty
Can linear actuators be made to 'step' forward and backward? A guy who was selling one on e-bay said that a standard linear actuator can only extend fully and retract fully, no in between movements. I was wondering if they can be made to do this, or if I need a special kind, and what that kind is

I want an actuator that can be made to step forward say 2 inches, then maybe back 1 inch, then maybe forward 3 inches, back 2, etc do the hokey pokey and turn itself around, etc etc.

I can't help you with your question but here is a good website that might: http://www.selectproducts.com/frameindex.htm

They have different size actuators and other things... Check it out.

Armen

you might have to look into linear stepper acuators. the ones i have seen online appear to be threaded rods that are surounded by a motor and gearing. the rod protrudes from both ends of the device. the motor turns the rod so that it extends or retracts form the body of the unit. they are supposedly very controllable. but with more precise control on the distance you are going to sacrifice speed of the unit. more precise positioning means slower retraction and extension.

or you could use a basic stepper motor with a linage to transform the rotation to linear motion.... i dont know the requirements that you have, but there are options.

and yes, as far as i know, linear actuators are only open or closed. i dont know the specifics of how they work, but thats what i have seen.

~mike

Assuming that the time taken to extend 1 inch is the same no matter how far it has already extended by then you could do it by timing the supply of power.
I dont know if they have to extend fully before they can retract, but I would assume that they could, wouldnt you?

Well...basically for my application, I need a linear actuator that is fast, but can be positioned somewhat accurately within say 1/4". It has to be able to repeat these positions several times, too. So I thought about setting up a timer circuit so that X seconds of power would move the actuator to position 1, etc. But this has its drawbacks in that it may take more or less time for it to move to a certain position, depending on temperature, available power to the device, and things like that. Maybe the best idea would be for me to buy a standard linear actuator that is fast, and then control the power using an LED and a phototransistor, when the actuator comes between them I would know that it has reached its destination and it should stop.

Any other thoughts?

Originally posted by SuperMatty
Well...basically for my application, I need a linear actuator that is fast, but can be positioned somewhat accurately within say 1/4". It has to be able to repeat these positions several times, too. So I thought about setting up a timer circuit so that X seconds of power would move the actuator to position 1, etc. But this has its drawbacks in that it may take more or less time for it to move to a certain position, depending on temperature, available power to the device, and things like that. Maybe the best idea would be for me to buy a standard linear actuator that is fast, and then control the power using an LED and a phototransistor, when the actuator comes between them I would know that it has reached its destination and it should stop.

Any other thoughts?

I dont quite understand what youre trying to do. Linear actuators are basically the same as power window. It needs something to control the power feeding the motor. Are you trying to build a setup that's much like a motorized indash monitor, with the ability to extend fully then ables you to adjust the length 1 by 1? Almost all the linear actuator setups that Ive seen use pressure switch to control the actuator. A timer module is not always reliable due to the fact that sometimes it would take X seconds to completely extend the actuator, sometimes Y seconds depending on the battery voltage, temparture, and load.

Yes, basically, I want to be able to make a circuit so that if I press button 1, it extends to 5 inches if i press button 2, it goes to being extended 2 inches, if i press button 3, it goes to being extended 12 inches, etc.

What is a pressure switch?

I would get it to trigger microswitch limit switches rather than anything optical.
I get the feeling you want to be secret about your application, but it might help if you told us as there might be a better solution than an acutator.

Well here's a hint.
I'm going to attach the actuator to a cable. Then, accurately pulling that cable to different positions will do different things

Originally posted by SuperMatty
Well here's a hint.
I'm going to attach the actuator to a cable. Then, accurately pulling that cable to different positions will do different things

Weight jacking? For racing?

A pressure or limiter switch will probably be the most cost effect way of doing it. You will setup 3 reed or lever type switches at 5", 7" then at 12" each on its own button switch with a relay. When you hit the button switch, the relay will engage the Linear Actuator until it hits the corresponding lever switch witch will disable the actuator.

It will be a "poor man's" stepper actuator. I could probably sketch out a quick diagram to illustrate if it still isn't clear.