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  1. #1
    Member
    Join Date
    May 2019
    Posts
    19

    Linear Motion Breaking

    Hello,

    I have searched the forums however haven't found any applicable results. Basically I need a device which will be able to hld the exact position of a linear bearing on some linear rod(part of a Z axis). Attached is a rough picture of it. I have thought about possibly having a small electromagnet however am not sure how to apply it so that the bearing would keep its exact location on the linear rail. I have seen some devices that have springs and micro electromagnets with friction plates but cost £100 +. The device would have no need to have a holding force more than ~ 20k however the lower the cost the better. Any help regarding this issue would be greatly appreciated.

  2. #2

    Re: Linear Motion Breaking

    Normally the position holding is done at the device driving the axis. Example; a brake on the Z axis motor.

    I guess it would be possible to add a small electromagnet on a bracket attached to the bearing block. Maybe something like this https://www.ebay.com/itm/55-LB-Elect...4AAOSwfVpYpfn4
    Jim Dawson
    Sandy, Oregon, USA

  3. #3
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    Join Date
    May 2019
    Posts
    19

    Re: Linear Motion Breaking

    Hi Jim,

    Thanks for your reply, I am aware of stepper motor brakes etc... however in this application it is needed on the bearing / housing around the bearing itself, I was looking at electromagnets like the one you suggest however am not actually sure how I could apply it, what would it actually pull towards. If it was just a steel plate on the side, the linear bearing would still be able to move upwards and downwards. If you then had a series of steel plates as part of the frame around the linear rod, it would not allow for the exact position of the linear bearing to be kept, instead just locked to one of the plates.

  4. #4

    Re: Linear Motion Breaking

    Well I guess the steel plate would be mounted solid to the frame and the electromagnet would be fixed to the bearing or Z carriage.

    Maybe something like a bicycle wheel brake or even a disk brake type system could work also. The bicycle wheel brake could actually grab the rail. The disk brake could grab a piece of steel to the side of the carriage.

    In any case the moving part would need to be solidly fixed to the bearing block.
    Jim Dawson
    Sandy, Oregon, USA

  5. #5
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    Join Date
    May 2019
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    19

    Re: Linear Motion Breaking

    I prefer the idea of the electromagnet due to the need for building 8 of these, probably making it the more effective route.I was getting confused before due to thinking that there would have to be a sizeable gap between the mounted steel plate and the bearing, meaning that the bearing would still be able to 'slide' up and down whilst the electromagnet is powered, making it useless. However, if the gap was only a couple of mm then it would lock the bearing in place, how would I be able to stop it slipping however???

  6. #6

    Re: Linear Motion Breaking

    I would have the magnet basically rubbing on the steel plate. You could let the magnet float a bit axialy, but keep it solidly positioned radially. That way, the magnet would solidly contact the steel plate and friction would keep things in place.
    Jim Dawson
    Sandy, Oregon, USA

  7. #7
    Member
    Join Date
    May 2019
    Posts
    19

    Re: Linear Motion Breaking

    Would the holding force due to friction be the same as the holding force of the magnet??? Also is there any other way that I could do this for example have it so that it is braking until the magnet is powered then it is able to move freely. I.e. i can turn the power off and it will keep its position.

  8. #8

    Re: Linear Motion Breaking

    Yes, sort of. Really the holding force is rated as a direct pull, but due to the nature of the application, the force on the magnet would be sideways. But it would be pretty close.

    Holding with power off would be a spring application, then the magnet would release the brake. This is the way normal motor brakes work. In that case you would want a spring applied brake that slides along a plate, then the magnet would release it

    A bicycle disk brake caliper that was spring applied and released by a small air cylinder might work well. Going to require a little engineering.
    Jim Dawson
    Sandy, Oregon, USA

  9. #9
    Gold Member
    Join Date
    Sep 2006
    Posts
    6374

    Re: Linear Motion Breaking

    Hi, you could mount a rack, parallel to the linear rail, and have a pinion meshed with it attached to the linear bearing block, then apply a brake to the pinion activated by an electro magnet to remove the braking force when you want to move the linear bearing block or whatever it's attached to.

    However, KISS...….I think a solenoid brake, attached directly to the linear bearing block, activated by an electro magnet and impacting on the linear rail, would be a simpler solution.
    Ian.

  10. #10

    Join Date
    Aug 2019
    Posts
    295

    Re: Linear Motion Breaking

    As Jim rightly pointed out the breaking will need to be carried by the driving unit, if accurate positioning & holding is what's required.
    Any 3rd force applied to your rotating assembly will put it off, at least in 1dof, regardless of how engineered it is or mounted.

  11. #11
    Member
    Join Date
    May 2019
    Posts
    19

    Re: Linear Motion Breaking

    Thank you for your replies, The rack is a good idea however I can't imagine it giving the sort of positional accuracy that I require. I have done a bit more research and was wondering if it would be possible to use a system similar to this : https://www.youtube.com/watch?v=NDSj0KV6OvU so there is a hinge at the back of two parts which are each about a semicircle with a inner diameter just smaller than the outer diameter of the linear shaft(wouldn't be rotating as in the video), there is then a spring pulling the two semicircles together and locking them to the shaft. A small electromagnet(or push/pull solenoid) then pushes the small lever to disengage the two semicircles. Would this be possible and if so what would I make the two semcircles out of??? What materials would I line them with to cause the most friction with the steel shafts??? And also, how would I manufacture the assembly, would it be viable just to 3d print it seeing as how the shaft would not have an outer diameter larger than ~ 20mm and also there would be no need to hold anymore than 10kg really???, Max

  12. #12

    Re: Linear Motion Breaking

    The one question that has not been asked or answered here is what positional accuracy is required of the brake? Also a better understanding of the actual application would be helpful to me.
    Jim Dawson
    Sandy, Oregon, USA

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