low cost linear motion with feedback

[eganders]

I have an application where I have to move a 3 lb object in a 3 ft
cubic space. I am not looking at high performance or high accuracy.
It can take as much as 30 seconds to traverse the 3 ft distance and
the accuracy could be no better than 0.020 or 0.050 inch (possibly the
spec could be even looser). The position must be able to be repeated and I want to know where I am remotely, so I need some crude feedback.

Linear actuators would appear to be the best solution, but I am
finding that they are hundreds or even thousands of dollars. The
product I want to build will have to cost no more than $2,000 for a 3
axis device with controller, overhead and profit.


What is it in a linear actuator that costs so much that you could not
build a low cost version using a threaded rod, servo or stepper motor
and an extruded frame for a lot less?


Does anyone know of a linear actuator that can provide the kind of
performance I am looking for for a couple hundred dollars?

[sp1nm0nkey]

Why not use a stepper? You'll know where you are unless you skip steps. Just make sure it doesn't skip steps and you'll be hunky dory.

Otherwise, use a Johnson motor (the cheap crap kind) and a gearbox, and a piece of acetate with light and dark printed on it attached to the shaft. Put two IR sensors on it that are out of phase with the pattern, and close the loop with a microcontroller and an h-bridge. If you need any details explained let me know. With that and a lead screw (cheap threaded rod or something) you should be able to do a lot. If you have a 30 tpi lead screw, and a pattern that has 6 sections (3 dark, 3 light), you should be able to meet your requirements no problem. That's more or less how computer printers do it, only they use belts (which might be a good solution too instead of a lead screw).

But seriously reconsider steppers.

[Khalid]

sp1nm0nkey
Could u through some more light on"Otherwise, use a Johnson motor (the cheap crap kind) and a gearbox, and a piece of acetate with light and dark printed on it attached to the shaft. Put two IR sensors on it that are out of phase with the pattern, and close the loop with a microcontroller and an h-bridge. If you need any details explained let me know"


I will be very happy if u further describe the method/working principle along with some construction details.

Best Regards

[Al_The_Man]

You did not mention whether you need to do variable positioning or just fixed point to point?
if P to P. Then you could consider limit switch positioning and AC stepper motor fed from 120vac, you can pick these up at giveaway price on ebay, they do not need a stepper controller.
The are capable of immediate start stop, and are very accurate for this kind of app.
And if you just need indication that you are in posistion, this could be done with a light/lED indicator, or an encoder and Red Lion counter.
The details of what you want to do are a bit vague on what degree of sophistication you need.
Al.

[eganders]

I understand your descriptions and agree that I could design the components instead. Ultimately I expect to be building low production quantities of these and was hoping that a linear actuator/controller combination might exist in the marketplace so I don't have to redesign the wheel. I have designed high speed line printers and automotive sensors in my career, so I could build one of these. However, I don't want to find (as I have in the past) that a simple, low cost solution exists that I could use out-of-the-box. Ideally, I would like to have 3 linear actuators, 2 of which would be on an X-Y base and the 3rd that would travel vertically from this X-Y base (call this the Z axis). I would need to control the three with a controller that would be programmed from a computer program I would write for the specific application I have in mind. (I can't divulge the purpose of this device at this time incase there are patent issues). I need to be able to represent the position by an icon on the program and be able to return to that position (by storing the X-Y-Z coordinates).

[eganders]

I need to correct an error I made about the length of the actuators. They need to be 1 ft each, not 3 ft. It is a 1 cu ft space.

I need to be able to position a 3 lb (may be 1 to 3 lb) object within that 1 cu ft space. I need to store the postion and be able to return to that position. The accuracy requirement is 0.02 to 0.05 inch. I would like to store several positions and that can be done by controlling the system through a computer program. So I need a controller that can be commanded through an RS232 or USB port. The time it takes to traverse the volume is not important, it can take many seconds.

The bottom line is that the end product cannot be more than $2,000 to $3,000 including material, overhead and profit. The volume will be in the couple of thousands of units.

The problem I have is that I can't seem to get to the price point no matter what the specifications are. I may be able to relax one or more of the specs if I can get somewhere near the price I am looking for.

[ahren]

I would check out intelligent actuator: http://www.intelligentactuator.com/. They have some fairly low cost systems that might squeak in under your budget. Other than that, you're likely looking at a custom build. In that case, things will be a little tougher, as small requirements (interface specs, material requirements, etc.) will quickly eat into your budget. I used to do custom automation (and still do to a certain degree) -- PM me if this is something you'd like to investigate further.

Ahren
www.cncrouterparts.com

[ahren]

Oh, another good bet is IMS for low cost systems:

http://www.imshome.com/

You could potentially combine these with parts from my system to make what you want. I'll be releasing a complimentary linear motion system to go with the motor and bearing mounts already on my site next week. With that, you could build the system you want, and probably be under $2000. I could do some of the assembly work for you as well, so the overall system was nearly "off the shelf" when shipped to you.

Ahren
www.cncrouterparts.com