Linear Positioning using Stepper Motor

[abicash]

Hello

This forum has always been helpful and i am happy to be a part of it!

This time i require some pointers/ideas/ ready-to-use-projects for a Positioning system, the brief will be explained below.

A linear shaft has to be positioned at a max distance of 2 meters +/-2 microns.
I am contemplating using a stepper motor with micro-stepping to achieve this.
But as is always , there is a simpler method which someone has already worked on.
Can someone point out various methods to do this.I will share more information after a response

Thanks and regards

 

[jpanhalt]

Just to clarify... Do you mean ±2 microns or ±2mm? If you have a shaft that is 2 meters long, thermal changes could well exceed the former level of precision.

John

 

[MikeMl]

Just to clarify... Do you mean ±2 microns or ±2mm? If you have a shaft that is 2 meters long, thermal changes could well exceed the former level of precision.

Maybe he could use the stepper to get close, and then heat/cool the rod to get to the final position?

 

[abicash]

Maybe he could use the stepper to get close, and then heat/cool the rod to get to the final position?

Hi friends

Thanks for replying

My email account does wonders. All forum messages landed up in spam. I saw the messages today , hence replying late

Returning to the problem at hand...

I wanted to know what schemes and hardware is available to achieve the result. My target would be to get a 2 micron accuracy ,but in the end would accept whatever accuracy is feasible without utilising unwieldy methods (cooling shaft)
I am trying to retrofit a shearing machine.Currently the guys manually set the lead screw within 50 microns so that the blade is set, and then operate.

I am planning to apply a stepper motor to the currently used handle mechanism and get a feedback from a linear encoder to correct errors.
Can you guide me in this direction?

Thanks and best regards

 

[jpanhalt]

You might be able to get within 50 micron with a ball screw and appropriate design. Here are ball screw precision limits. Errors are in microns; lengths are in mm.

C0 is the highest class made, and would still not meet the 2 micron specification. However, if you go to a more common C3, you might get an acceptable level of precision. Precision ball screws will often come with a chart showing actual lead errors for each screw. You can use that information to improve your precision. A precision of 50 microns (0.001") is much more easily attained.

How often does the blade have to be set? What method is being used to get 50 micron accuracy at 2 meters? How much force is going to be needed? Do you have a budget?

John

 

[misterT]

I am planning to apply a stepper motor to the currently used handle mechanism and get a feedback from a linear encoder to correct errors.

What kind of forces are needed to move the thing. And what kind of sensor are you planning to use to achieve 2 micron accuracy (inductosyn maybe)?

 

[abicash]

Hello Guys

Thanks for the inputs
1)Forces needed to move the thing : Currently it's being moved by a rotary mechanical handle (driven manually-by hand) on a lead screw
2)There are so many options for a sensor that now i am not sure what to use...Maybe you can throw in some standard mechanisms
3)"How often does the blade have to be set? What method is being used to get 50 micron accuracy at 2 meters? How much force is going to be needed? Do you have a budget?"
-- Its being used in a workshop to shear metal sheets.So i guess duty is quite frequent.These guys use a scale to measure and the handle to move in positive or negative direction.Force is less than 5kgcm (it can be freely moved by hand,without an effort)
The entire budget is not more than USD 2000.00 (two thousand dollars) which will include the intelligence (i/o from a microcontroller) and the entire assembly

 

[KMoffett]

You might consider using DRO scales as the sensor: **broken link removed**

Ken

 

[misterT]

1)Forces needed to move the thing : Currently it's being moved by a rotary mechanical handle (driven manually-by hand) on a lead screw

That does not say anything about the forces involved. A stepper motor may be too weak to move the thing.

2)There are so many options for a sensor that now i am not sure what to use...Maybe you can throw in some standard mechanisms

There are not many options if you want 2 micron resolution. Inductosyn is about 0.001mm accurate.

 

[jpanhalt]

That could be a very tight budget, if you go with ground, precision ball screws of that length. One thing I am lacking is a good mental image of what you are trying to do. My experience with shears is that the blade is set to a specific gap tolerance so that it avoids interference with the other blade and provides a proper shearing action. A fairly wide range of material thicknesses can be cut without changing the blade settings.

Your description makes it sound as if the blade(s) are being set for cutting different sizes of material. In my experience, sizes are set with various stops, not the position of the blade. Is the blade being adjusted because there is a wide variety of materials and thicknesses being sheared every day?

Directly to your question and for that budget, I think I would focus on making the manual adjustment easier rather than trying to make the adjustment automatic. For example, modern digital readouts and linear scales for machine tools can be obtained for about that much money and would facilitate adjustment.

John

Edit: Just saw Ken's post (#8). We are talking about the same thing.

 

[JimB]

Abicash

Do you REALLY mean 2 micron ??

1 micron = 1x10-6 metres (ie 0.000001 metre or 0.001 milimetre)

On a SHEARING machine ??

Unless this is something VERY special, the surface finish of the cut will be very much worse than 2 micron.

JimB

 

[abicash]

Dear Friends

This is to inform that your inputs were well received
Re-thinking on concept

 

[tunedwolf]

I have to agree with JimB here, having worked on and designed upgrades to various machines over the years, including large rotary driven guillotines, the accuracy that you hope to achieve (2 micron) is less than the actual roughness of the material at the cut edge. Most machines I have worked on have a reposition accuracy of 0.025mm, and that's on a good day using precision ground ballscrew mechanisms and top notch Panasonic servos What material are you cutting that requires such accuracy?

 

[atferrari]

High accuracy ball screws are a costly thing.