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  1. #1
    Join Date
    May 2019
    Posts
    21

    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
    Join Date
    Dec 2013
    Posts
    5717

    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
    Join Date
    May 2019
    Posts
    21

    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
    Join Date
    Dec 2013
    Posts
    5717

    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
    Join Date
    May 2019
    Posts
    21

    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
    Join Date
    Dec 2013
    Posts
    5717

    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
    Join Date
    May 2019
    Posts
    21

    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
    Join Date
    Dec 2013
    Posts
    5717

    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
    Join Date
    Sep 2006
    Posts
    6463

    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
    339

    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
    Join Date
    May 2019
    Posts
    21

    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
    Join Date
    Dec 2013
    Posts
    5717

    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

  13. #13
    Join Date
    May 2019
    Posts
    21

    Re: Linear Motion Breaking

    So the positional accuracy has to be exact as possible really, I just dont think that a rack and pinion would be accurate enough even though being much more simple. It is to be used as a disengageable Z axis, this is so that I can drive multiple objects on the same ball screw. For example, I have a nut on the ball screw with a housing that is able to attach to a housing below and above it (possibly using electromagnets / servos) and then is able to freely drive it up and down. It is then able to disengage with the object it is moving able to hold its exact vertical position on a linear shaft right next to the ball screw.

  14. #14
    Join Date
    Dec 2013
    Posts
    5717

    Re: Linear Motion Breaking

    Cost increases as a function of the cube of 1/ the required accuracy. So +/- 1 mm is easy and cheap to attain, +/- 0.001mm is comparatively expensive and difficult.

    A clamping device that is attached to the truck and grabs the rail would be the best solution. That has the fewest number of moving parts, just a simple screw or cam applied clamp.
    Jim Dawson
    Sandy, Oregon, USA

  15. #15
    Join Date
    May 2019
    Posts
    21

    Re: Linear Motion Breaking

    I need an accuracy of about +/- 0.05 mm hence why I think a rack would not work.

    -- Sorry just realised, I probably dont actually need a postion accuracy that high for each section to be held in, only for the ball screw to move in. Therefore a rack system could work, the only limitation is that it has to be able to be electronically controlled, the locking and unlocking that is.

  16. #16
    Join Date
    Sep 2006
    Posts
    6463

    Re: Linear Motion Breaking

    A sketch....my kingdom for a sketch...…..do a sketch in MS paint...….uh oh....I see you are posting with a mobile device....phone or IPAD....sketch on a piece of paper and photograph it with your mobile whatever......one picture is worth a thousand words.

    But, of course you already have in post # 1.....that is a vertical running linear rail and a bearing block......how to stop the bearing block at a precise position......what moves the bearing block?

    If the bearing block is moved with a ball screw and driven by a stepper motor you can position the ball nut (and bearing block) very precisely.....on a 1605 ball screw the nut moves 5mm per turn and the stepper rotates in 200 steps per revolution.

    You can move the bearing block up and down very precisely but you need to know where it is at the moment of stopping......a digital read out perhaps?
    Ian.

  17. #17
    Join Date
    May 2019
    Posts
    21

    Re: Linear Motion Breaking

    Here are some scsreenshots of some SolidWorks that I just did quickly. The ball screw would be connected to a stepper motor and the linear shaft is fixed to an outer frame (not pictured) the top and bottom linear bearings hold a frame each(cannot rotate) and need to be moved up and down using the ballscrew nut housing. The ballscrew nut housing is able to lock and unlock using servos(not pictured) into the top and bottom housings and then pull them up and down. The problem which I am asking about is how I should lock the top and bottom linear bearings to the linear shaft electronically whilst they are not being moved.

  18. #18
    Join Date
    May 2019
    Posts
    21

    Re: Linear Motion Breaking

    Also I'm not to sure what it means by mobile device because I am on a desktop computer.

  19. #19
    Join Date
    Dec 2013
    Posts
    5717

    Re: Linear Motion Breaking

    The drawing helps. What I have done in the past where I needed to move more than one device on a single rail similar to what you are doing is to use a servo or stepper and ball screw for each device. In my case it was saw blade arbors in a gang rip saw, but the same principle applies. That way you know exactly where each device is at and no monkey motion trying to connect and disconnect the ball nut from the individual slides. Balls screws and steppers/servos are cheap, designing and fabricating brakes and disconnect devices is going to be expensive.
    Jim Dawson
    Sandy, Oregon, USA

  20. #20
    Join Date
    May 2019
    Posts
    21

    Re: Linear Motion Breaking

    In this design I would quite like to have it on the same ballscrew but thanks for the idea.

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