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Accurate method of Linear motion cont...

:: EPE Chat Zone ­:: ­Radio Bygones Message Board :: » EPE Forum Archives 2010 - » Archive through 02 October, 2014 » Accurate method of Linear motion control required « Previous Next »

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noel
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Username: noel

Post Number: 146
Registered: 06-2005

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Posted on Thursday, 31 July, 2014 - 04:31 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hello all,
I have an application whereby I need to move a 10 gram weight in one axis in precise increments. The increments need to be 0.1mm or less, speed of travel is not critical - 1 or 2mm per second and the range of travel needs to be 15mm or more.

Ideally the position would be controlled with a voltage signal input (e.g. 0 to 10V over the position range), but im open to other methods.

What's the easiest way to achieve this ? Is there anything off-the-shelf that I could use with a little modification ?

Any suggestion would be appreciated.

Thanks - Noel
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mikehibbett
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Post Number: 1609
Registered: 04-2005


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Posted on Thursday, 31 July, 2014 - 06:11 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Is this for a 'one off' project? If so, I would suggest using a CD or DVD drive mechanism, as used here:

http://www.instructables.com/id/Pocket-laser-engraver/
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web: mjhdesigns.com twitter: mikehibbett
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joe
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Posted on Thursday, 31 July, 2014 - 06:25 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Or you could look at a linear actuator.

http://www.robotshop.com/en/actuators.html

Joe
My projects, technical info and ramblings at www.hobbyelectronics.net/
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mikeb
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Post Number: 1099
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Posted on Thursday, 31 July, 2014 - 06:43 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Do you mean +/- .1mm? – that’s +/- 4 thou in old money, that’s not easy to get repeatedly and reliably.

Do you have any electronics/mechanics background? Of course it’s a trade off between quality/cost/project time.

If you do not build/buy the mechanics to the highest standards, you will never get the repeatable accuracy you have specified – be warned.

You need all the mechanics, a stepper motor/belt drive, polished guide rails and bearings and most importantly, an accurate 0.00mm reference point (normally a simple little opto sensor but don’t be deceived – the mechanics and positional repeatability need to be excellent). The carriage should support 10g no problems.

You then need an interface to the stepper motor (lots of boards available), a power supply, an interface to the zero datum sensor and finally some method of managing the whole process (ie moving left/right, speed, sensing datum, backlash control and overrun, and an interface to you) – this is normally some sort of computer (PC or micro). I write my own control software so I can handle just about any need I have. Flexibility here is essential, because once your machine is working, you will want it to do something that was not envisioned.

All positional systems suffer from inexact mechanics and these result in tiny discrepancies between the command position and actual position. Your controller needs to add some pulses to compensate for these errors and this is handled during setup. Setting up your system requires some moderate precision engineering measuring instruments – dial gauge, micrometer.

My advice is to look at peoples homemade CNC projects on the web. Build mechanics well, with good parts and get help from a good model engineer if you can snag one (model steam train clubs are full excellent engineers).

You could build a prototype using the carriage from an old inkjet printer, but this would only serve to show you what the problems are – you will probably need something better engineered that this.
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bowden_p
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Post Number: 343
Registered: 01-2006

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Posted on Thursday, 31 July, 2014 - 07:49 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Noel,
Is this any use for your application? It is a stepper motor with a threaded shaft that moves throught the motor body. A single step of the motor advances the shaft by 0.01mm, so I guess that the shaft mechanics are quite precisely made.
http://www.technobotsonline.com/stepper-motor-21ncm-200-steps-rev-threaded-shaft.html
You can find a spec under the "Downloads" tab.

The site also has other mechanical parts you may need of the MakerBeam/OpenBeam type - as mikeb outlines above.

With regards, Paul.

(Message edited by bowden_p on 31 July, 2014)
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noel
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Post Number: 147
Registered: 06-2005

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Posted on Friday, 01 August, 2014 - 10:27 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Thank you all for you suggestions.

Mikehibbitt: It is indeed a one-off, work related project.
Joe: thanks for the link - I will have a look though this website
mikeb: many thanks for your experienced tips. to answer your questions as you list them: I meant the movement resolution needs to be 0.1mm or better, that said, and although not as critical, repeatability would probably need to be around +/-0.1.
My background: I am a mechanical engineer, with experience in electronics and PIC programming. The project application is work related and owing to time constraints I'm looking for a solution with the minimum amount of work involved.
Bowden_P: very interesting link- thanks - this look like a good solution

Noel.
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mikeb
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Post Number: 1100
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Posted on Friday, 01 August, 2014 - 11:04 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Ahh ... excuse the lecture on mechanics then noel.

Well done Bowden_p - I was looking for this device on my websites and could not find it - I think that my have possibilities.

I have used www.motioncontrolproducts.co.uk a lot.
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mikeb
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Post Number: 1101
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Posted on Friday, 01 August, 2014 - 11:09 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

I have just noticed that the above company has a 14mm linear motion stepper.
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bowden_p
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Post Number: 344
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Posted on Friday, 01 August, 2014 - 12:10 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Hi Mike,
That's an interesting link. I too am looking for a simple linear solution - closing some contacts in a linear fashion.

Do you know the difference between a captive and a non-captive linear stepper?
(With apologies to Noel's thread.)

With regards, Paul.
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mikeb
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Post Number: 1103
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Posted on Friday, 01 August, 2014 - 02:20 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Well raised - its important to Noel I think ....

I was wondering if it was about whether motor stays still and the thread moves or Vicky verky.

It feels like they are the same thing, until I realised a thread needs to somehow be held captive if you want the motor to be stationary and the threaded bar to be ejected - otherwise the threaded bar would simply rotate (I think).

Thats the solution Noel wants but it perhaps needs a telephone call to check with supplier.
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externet
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Username: externet

Post Number: 200
Registered: 05-2005


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Posted on Monday, 11 August, 2014 - 05:04 pm:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Motion is done with motor ang gearing, controlled by interfacing a----> http://www.robotroom.com/Caliper-Digital-Data-Port.html
Abolish the deciBel !
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alec_t
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Username: alec_t

Post Number: 809
Registered: 03-2009

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Posted on Wednesday, 24 September, 2014 - 11:44 am:   Edit Post Delete Post Print Post    Move Post (Moderator/Admin Only)

Have you considered a piezo motor, such as this?

http://www.piezomotor.com/products/linear/ll10/

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