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Hard Drive-like Linear Motors (Posistioning Questions)

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LAN_403

Ash Small

Fri Apr 12 2013, 10:52PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I think I've a ZIP drive in the shed (I still have one somewhere) but I've no idea what the shipping cost would be.

Patrick

Fri Apr 12 2013, 10:59PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

TY, Ash hold on to it please, I may need it.

the laser weighs 9 grams
the optical components would weighs 7-ish grams.
the whole Carbon fiber - balsa frame would be 10 or less grams, with coil.
bearing weighs less than 3 grams.

im seeing this as much more do-able now, than the full rotating VCR head thing...

EDIT: im putting some CAD drawings together, so I can show you all what im thinking as far as the magnet-armature geometry goes.

EDIT: it draws more current one way, and less the other, 1.2 amps vs 4.4 amps, It gets scorching hot in 2-3 seconds as would be expected, with a 9V battery.

If I maximize, turn count, coil current, magnet strength... and minimize, gap distance and moving mass, I should have a situation favoring high speed and force. right? what about loop area, should I increase that too? I think so..

Carbon_Rod

Sat Apr 13 2013, 08:56AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

A low cost galvo scanning assembly, optics, and closed loop driver is less than $150 on ebay.
Having built these, I can certainly tell you the smaller moving magnet type is easier to control.

PM sent

Patrick

Sat Apr 13 2013, 05:22PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carbon_Rod wrote ...

Having built these, I can certainly tell you the smaller moving magnet type is easier to control.

Wait - wait, please elaborate, so the coil would be stationary and the magnet would move? does it take two static coils then?

Carbon_Rod

Sun Apr 14 2013, 07:44AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

If you really need to build one, than there are many versions of this galvo unit around:

*do not copy the position encoder on this link as it is poorly designed.

The mass of the optics and galvo will often set the limit of the scan rate.
These are fine for drawing patterns with a laser, but too unstable for LIDAR work....

Patrick

Sun Apr 14 2013, 03:44PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carbon_Rod wrote ...

If you really need to build one, than there are many versions of this galvo unit around:

the circuit looks like a cool idea, but the flimsy mechanical cap looks like crap...

I was planning to copy the hard drive type of galvo, with a IR stripe position encoder.

there would be 2 IR transistors, 1 IR LED, so there would be two tracks, one to activate the laser, the second to count 5 degrees at a time.

Patrick

Thu Apr 18 2013, 04:31AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

When I was a child I had a programmable car-bot, it was programmed by black and white dots, a black marker was used to fill in sections on a special card. this card was attached to a spinning table, and via IR it was read while the bot was moving about.

I would like to use two ir detectors, and a single IR LED to count the positions coarsely that the linear motor has moved. does any one know how well partitions work for blocking unwanted light? and ive looked throough google and the Robot Builders Bonanza but just saw the simple stuff. is it possible to do barcode-like position detection in this way?

Carbon_Rod

Thu Apr 18 2013, 09:25AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Large encoder discs don't solve this type of problem very well. The cheap rotary magnetic sensors are usually good to 20 to 50kHz, and a differential polarized micro positioning sensor is not common equipment.

You could mechanically sweep something like a $99 DLR130K, but usually people use piezoelectric tilting mirror platforms for steering optics in 2D scanners. I seem to recall someone successfully read the numeric output off the LCD driver pins.

Cheers,

lightlinked

Thu Apr 18 2013, 08:42PM

Registered Member #2087 Joined: Tue Apr 21 2009, 08:32AM
Location:
Posts: 115

would a laser show galvo scanner work for your application? i think you can get one from china for less than $100. they have closed loop feed back and you can get an idea of the accuracy just by looking at some laser animation demos. non animation aerial scanning lasers commonly use stepper motors

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