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Hard Drive-like Linear Motors (Posistioning Questions)

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Patrick

Thu Apr 11 2013, 09:58PM

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

In relation to my LIDAR thread, im finding the use of linear motors unavoidable. I plan to buy or make similar devices for rapid radial positioning, (very much like a HD head platter thingie) Ive done the random searching of google, but im wondering how (if the magnetic field is uniform) how position detection is done?

is it done by reading some physically placed format bits on the platter?

I don't need um or nm precision, I must avoid cogging which is why im avoiding normal steppers (even with microstepping).

I must have light mass and very fast swings, 120 degrees in 0.5 seconds or there abouts.

any help would be appreciated.
-Patrick

HD pic

This HD is the one you guys here on the forum help me rescue data off of, after a fall... it will now live for a new purpose, id like to get the arm to move back and forth if possible through some "manufacturer un-approved modifications" hehehe I feel like an evil super villain ...

...

Thu Apr 11 2013, 10:06PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

They use the tracking info on the hard drive platers, sadly.

You might want to look into the galvos used by laser show people, they use a mixture of optical and capacitive feedback depending on the required precision/bandwidth.

elm has a good article on it

Patrick

Thu Apr 11 2013, 10:22PM

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

... wrote ...

They use the tracking info on the hard drive platers, sadly.

You might want to look into the galvos used by laser show people, they use a mixture of optical and capacitive feedback depending on the required precision/bandwidth.

elm has a good article on it

wooo hooo, this was exactly the explantion I needed, that article really explains it! TY

Patrick

Thu Apr 11 2013, 10:32PM

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

There appears to be a spring to return the Arm-head to its park position... that may be useful...

EDIT: can I use a normal round neo magnet, then a piece of metal to shape the field like an arc? or do I need the special hard shaped ones?

I have lots of the round magnets, that's why I ask, would rather not buy specific magnets just for this one purpose.

Dr. Slack

Fri Apr 12 2013, 07:33AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

PM sent

Erlend^SE

Fri Apr 12 2013, 05:05PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Able to find a Zip-Drive or LS120?

They use linear motors like you seek.
LS120 also seems to use some kind of media-independent feedback.

Patrick

Fri Apr 12 2013, 05:33PM

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

Erlend^SE wrote ...

Able to find a Zip-Drive or LS120?

They use linear motors like you seek.
LS120 also seems to use some kind of media-independent feedback.

I dont know anyone in this day and age who still has one those lying around though...

Patrick

Fri Apr 12 2013, 06:41PM

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

I have new pics:

in the above pic, im thinking of grinding into the surface of that gold flex print, to gain direct access to the armature, which is quiet beautiful, I don't want to wreck it. id start with 1.5 volts, and add wiegt to the head tip, then check speed and force.

Erlend^SE

Fri Apr 12 2013, 07:23PM

Registered Member #1565 Joined: Wed Jun 25 2008, 09:08PM
Location: Norway
Posts: 159

Looks like a good start
b.t.w. I would keep the magnet in place as much of the time as possible, due to possible magnet weakning.

The original driver is probably powered from 5V (or of 12V if 3.5" HDD)

As for position, some integrator( or was it derivative) circuits may get quite accurate in making the assembly follow a signal.
You can even "find" the position from the drive-signal using that route.

b.t.w. the winding, one section is within down-going field and the other section is in up-going field.

The field must be as wide as the movement.

PM me if you want me to help you more with it.

Patrick

Fri Apr 12 2013, 10:45PM

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

ok some pics here:

minor problems, big success.

first cut in those two wires, whit and blue only, saw minor movement with 1.5 v, found 2.2kohms. decided to remove the external PCB, found 1.7kohms, so then I cut the flex print entirely, soldered in the the armature itself, found 4.4 ohms.

at 4.4 ohms I get fast moderate force with a 1.5 "D" cell battery. with 2 D's I get better faster movement, tapping a 9V should put in a dangerously hot current for the thin wire, buts its fast and forceful!

im thinking this is the method to traverse 120 degrees in 0.5 to 0.3 seconds... with the laser module and linear sensor array the only components being rotated.

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