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Thread: X-y-z ultra cheap micro mirror mount based on Nd Magnets

  1. #1
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    Default X-y-z ultra cheap micro mirror mount based on Nd Magnets

    Hi All,
    As always, want to share crazy ideas:

    For those (like me) who have not milling skills also no milling hardware…what about neodymium magnets to fix optics?
    Just theorising on this:

    These are 10x10x2mm magnets, 1kg pull force!! and only at 1/2usd aprox each. There are lots of sources on internet,
    for instance:
    http://www.superimanes.com/bloques-p...-10-10-02.html
    (sorry, this is a spanish site)

    The idea, is to glue thin 1-2mm metal ferro-magnetic sheet (iron) over typical aluminium baseplate in order to have free-movement in all optic supports that ‘moves’ over it..

    So, just glueing optic element to magnet, and also glueing another magnet to iron support base (ferro-magnetic metal pivot, for example: 10x10x20mm size)
    In order to have a mirror or pbs etc support. Better with 2components Artic thermal glue for better thermal stabilisation.

    Theory advantages:

    -Free optics ‘run’ movement/position along baseplate
    -X-Y and Z optics orientation
    -Easy replacing optics
    -really small footprint mirror mount (no "L" shape fixing foot)
    -On traditional flex-mount supports for example, we can't access to mount screw after a PBS is glued. With this 'magnetic' mount, you can reposition ALL axis cube & and ALL axis cube support, after glueing.
    -No need to drill /mill, so easy and fast
    -really cheap mirror mount: 2usd each!
    -While knife edging: With prism mirrors, for example, you can move xyz mirror position near and far field. All movements on all axys are possible.

    These little neodymiun magnets have a lot of force, 1 Kg pull, so optics should be really hard fixed. Also, magnetism on this magnets is hundreds years permanent.
    On the other side, maybe, it could difficult to adjust far-field by hand….don’t know

    So, what do you think, is a crazy idea? or could work? how we could improve this idea?

    Thank you!!

    Jordi

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    Last edited by jors; 11-07-2014 at 05:10.

  2. #2
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    Hi Jordi,

    might work. Have already tried something similar. But the biggest issue is that the magnets and metal plates do influence each other. When rotating one of them the other might also turn :-(...

  3. #3
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    Oh!! I see. So, could be interesting to know what is the minimum distance where the mounts are not affected each-other...this is an obvious problem specially on knife edging, where mounts are really near side by side... have to experiment on this
    Last edited by jors; 11-07-2014 at 04:06.

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    The idea is not a bad one. It will have to be used in conjunction with other means of moving and aligning the optics. Ferromagnetic material tends to be soft and somewhat un-flat. The optical elements can be quickly brought into an approximate position, but because of stiction/slip the final adjustment will need to be made with more traditional translators or flex mounts. On the other hand, the softness of the ferromagnetic material will probably mean that a strong magnet. once placed will remain in position despite accelerations and changes in orientations.

  5. #5
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    Quote Originally Posted by planters View Post
    The idea is not a bad one. It will have to be used in conjunction with other means of moving and aligning the optics. Ferromagnetic material tends to be soft and somewhat un-flat. The optical elements can be quickly brought into an approximate position, but because of stiction/slip the final adjustment will need to be made with more traditional translators or flex mounts. On the other hand, the softness of the ferromagnetic material will probably mean that a strong magnet. once placed will remain in position despite accelerations and changes in orientations.
    Thanks Planters, Mojo, for your thoughts.
    Maybe, fine far-field position could be possible by the help of electronic-kind pliers thus avoiding the fact of possible (but sure as you pointed) 'abrupt magnet slip jumping' due metal to metal friction (this is 1kg force on just 10x10mm!!).
    Or, just making hole and rotating with an allen key
    Click image for larger version. 

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    Last edited by jors; 11-07-2014 at 05:08.

  6. #6
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    I worked on a professional laser that used ~60 optics first on tiny mounts. Mounts were constrained by slots on the baseplate. These slots ran along the optical axis of the laser.There were fold mirrors at the end of each slot, so the laser was compact.

    The idea was each optic was professionally machine aligned at the factory and can be moved at will. Revision two, probably inspired by customer complaints, caused each mount to no longer be magnetic and now had a pin on the base that dropped into a grid of holes in the slots. The lid was stiffened and held the mounts from escaping, but did not rest on the mounts. Again the idea was the CNC was so precise that nothing untoward would ever occur.

    Everything was good until you consider elements that have to rotate around the beam axis, like collimator lenses in diodes or waveplates. So they widened the acceptance angle on the non-linear optics crystals, resulting in the need for fantastic amounts of pump beam power, and massive amounts of realigning the pump every time something rotational moved.

    It can be done, but all optics need CNCed mounts, you need to constrain at least one axis of motion, and one good drop in shipping........ The above laser was shipped with ALL optics removed except the fold mirrors. If inverted, all the optics fell a mm or so until caught by the lid. This was never shipped assembled, A Factory engineer had to build the laser on site*.

    Net result, great if you don't mind readjusting the axis frequently. Pins were far better then magnets.

    To Do this, to align the optics to the mounts, you need a test jig and a autocollimator. Then a multiaxis jig to hold the optics till the glue dries. In some cases you need to order the optics with precise amounts of wedge etc.

    All low cost optics have at least some tiny amount of wedge, the question is how much do they really have?

    One thing to think about is kinematics. It takes three points to define a plane. Other thing to think about is how much warp occurs in a baseplate that has not been through a Blanchard Grinder for flatness.

    *(interferometer guided CNC was used, CNC machine was probably better part of 1 Million Dollars. CNC guy was a wizard, he did pattern artwork using the few toolmarks left in the aluminum.)

    The above are widely regarded as some of the best lab lasers in the world. However magnets left the design early. I'm pretty sure the company hobby was Chess, not soccer.

    --------------------------------------------------------------------
    Commercial optics mounts on switchable Magnetic bases exist. But having used them, you do need to touch up the positioning frequently. They are not used on baseplates that are moved around town. They are used on very flat baseplates that have been surface ground, otherwise they subtly move with time. If you place two of them together they do interact until the lever that turns the internal magnet down into the base is turned. These mounts have soft iron pieces or laminated iron pieces that guide the magnetic flux from the other side of the magnet to just where you want it.

    Usually we use them when aligning, not for day to day work.
    ---------------------------------------------------------------

    Again, its not a bad idea. It has been used commercially. It requires a great deal of thought for the implementation. However most people soon switch back to the classic grid of threaded holes.

    Go to www.thorlabs.com and have a look around.

    Steve
    Last edited by mixedgas; 11-07-2014 at 05:44.
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  7. #7
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    Quote Originally Posted by mixedgas View Post
    I worked on a professional laser that used ~60 optics first on tiny mounts. Mounts were constrained by slots on the baseplate. These slots ran along the optical axis of the laser.There were fold mirrors at the end of each slot, so the laser was compact.

    The idea was each optic was professionally machine aligned at the factory and can be moved at will. Revision two, probably inspired by customer complaints, caused each mount to no longer be magnetic and now had a pin on the base that dropped into a grid of holes in the slots. The lid was stiffened and held the mounts from escaping, but did not rest on the mounts. Again the idea was the CNC was so precise that nothing untoward would ever occur.

    Everything was good until you consider elements that have to rotate around the beam axis, like collimator lenses in diodes or waveplates. So they widened the acceptance angle on the non-linear optics crystals, resulting in the need for fantastic amounts of pump beam power, and massive amounts of realigning the pump every time something rotational moved.

    It can be done, but all optics need CNCed mounts, you need to constrain at least one axis of motion, and one good drop in shipping........ The above laser was shipped with ALL optics removed except the fold mirrors. If inverted, all the optics fell a mm or so until caught by the lid. This was never shipped assembled, A Factory engineer had to build the laser on site*.

    Net result, great if you don't mind readjusting the axis frequently. Pins were far better then magnets.

    To Do this, to align the optics to the mounts, you need a test jig and a autocollimator. Then a multiaxis jig to hold the optics till the glue dries. In some cases you need to order the optics with precise amounts of wedge etc.

    All low cost optics have at least some tiny amount of wedge, the question is how much do they really have?

    One thing to think about is kinematics. It takes three points to define a plane. Other thing to think about is how much warp occurs in a baseplate that has not been through a Blanchard Grinder for flatness.

    *(interferometer guided CNC was used, CNC machine was probably better part of 1 Million Dollars. CNC guy was a wizard, he did pattern artwork using the few toolmarks left in the aluminum.)

    The above are widely regarded as some of the best lab lasers in the world. However magnets left the design early. I'm pretty sure the company hobby was Chess, not soccer.

    --------------------------------------------------------------------
    Commercial optics mounts on switchable Magnetic bases exist. But having used them, you do need to touch up the positioning frequently. They are not used on baseplates that are moved around town. They are used on very flat baseplates that have been surface ground, otherwise they subtly move with time. If you place two of them together they do interact until the lever that turns the internal magnet down into the base is turned.

    Usually we use them when aligning, not for day to day work.
    ---------------------------------------------------------------

    Again, its not a bad idea. It has been used commercially. It requires a great deal of thought for the implementation. However most people soon switch back to the classic grid of threaded holes.

    Go to www.thorlabs.com and have a look around.

    Steve
    Wow! is a pleasure to be here with so many experts. Thanks Steve

  8. #8
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    Those magnetic fixtures could make a nice lab setup. On my first tour in the '70's I had a projector with a magnetic beam table that was built on stage every night. A Coherent krypton laser was placed on a table with a steel plate at the output and the optical mounts with magnetic bases holding mirrors and beam splitters were assembled and aligned in front of the laser. This was before the FDA - BRH or variances. New York state, however, already had strict regulations and license requirements for laser use. They made me put a box over the beam table at Madison Square Gardens (my first housing!) to stop the scatter and stray beams. After that, all my projectors had optical breadboards, fixed optics and metal housings. These advancements made for a faster, easier setup and satisfied the FDA-BRH who were beginning to take a close look at lasers in entertainment and requiring labels, interlocks, emission indicators, shutters, reporting and variances. We were learning to travel with delicate lab lasers. The trail was littered with broken plasma tubes.
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  9. #9
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    I am NO expert in this area BUT I remember reading about magnets and galvo scanners
    ......they should NEVER be close to one another--- I am sure Steve or another can explain this better than I can, if indeed I am correct.

    good luck hak

    btw

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  10. #10
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    Mag field is a concern close in with some galvos.

    Its strong for about one magnet diameter and then falls off as the cube of the distance. (1/r^3)

    Hak is right, It is a concern, but one that can be designed out with care.

    Steve
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