Precision high resolution machine build


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    Default Precision high resolution machine build

    I'm looking for 1um in 500mm resolution and also accuraries in the order of 1um.
    What does it take to achieve this.
    I was looking for a 3 axis gantry type build, with 500mm x 500mm work area, is that the way to go?

    I have read this forum post exhaustively https://www.cnczone.com/forums/linea...60578-cnc.html

    And from what I gather from that post the minimum requirements are

    1. C1 / C3 ground ball screw with 3mm lead.
    2. Ultra precise encoder 24bit+
    3. AC Servo motors or Linear motors
    4. Good air conditioning
    5. Good measuring equipment

    Also I have read user hanermo's post https://www.cnczone.com/forums/linea...ml#post1656188 and he gives quite interesting advice.

    I have a few questions
    1. Can I get away with C7 rolled ball screw, my thinking is with ultra precise encoder and servo's and maybe a optical linear scale, the controller should be able to accurately position itself even though the screw is inaccurate?
    2. Can I get a off the shelf gantry structure with decent accuracy so that will speed up my build.
    3. For encoder/ linear scale Renishaw Resolute what kind of price range does one expect?
    4. Servors DMM ac servo's ok? I mean with their integrated 16bit encoders? Can steppers do the job, by running it in closed loop mode?
    5. What kind of motion controller / software would I need for achiving these accuracies?
    6. How does the optical linear scale work in conjunction with the integrated servo encoders? I mean does the optical linear scale output go in seperately to the motion controller, and then some software needs to be written for closed loop control?

    Thanks in advance

    Similar Threads:
    Last edited by ZeroBacklash; 10-24-2018 at 05:21 AM.


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    Default Re: Precision high resolution machine build

    Quote Originally Posted by ZeroBacklash View Post
    I'm looking for 1um in 500mm resolution and also accuraries in the order of 1um.
    What does it take to achieve this.
    I was looking for a 3 axis gantry type build, with 500mm x 500mm work area, is that the way to go?

    I have read this forum post exhaustively https://www.cnczone.com/forums/linea...60578-cnc.html

    And from what I gather from that post the minimum requirements are

    1. C1 / C3 ground ball screw with 3mm lead.
    2. Ultra precise encoder 24bit+
    3. AC Servo motors or Linear motors
    4. Good air conditioning
    5. Good measuring equipment

    Also I have read user hanermo's post https://www.cnczone.com/forums/linea...ml#post1656188 and he gives quite interesting advice.

    I have a few questions
    1. Can I get away with C7 rolled ball screw, my thinking is with ultra precise encoder and servo's and maybe a optical linear scale, the controller should be able to accurately position itself even though the screw is inaccurate?
    2. Can I get a off the shelf gantry structure with decent accuracy so that will speed up my build.
    3. For encoder/ linear scale Renishaw Resolute what kind of price range does one expect?
    4. Servors DMM ac servo's ok? I mean with their integrated 16bit encoders? Can steppers do the job, by running it in closed loop mode?
    5. What kind of motion controller / software would I need for achiving these accuracies?
    6. How does the optical linear scale work in conjunction with the integrated servo encoders? I mean does the optical linear scale output go in seperately to the motion controller, and then some software needs to be written for closed loop control?

    Thanks in advance
    If you are serious then a linear motor would be the easiest way to achieve this, I have some that do +/- 1um at 2G

    C7 Rolled Ballscrew never going to happen

    Steppers not possible no matter what you use

    Dmm they do have some other Encoders they are working on, this could be possible if everything else is used Precision Grade Linear Rails C1 Ballscrews all built on Granite

    It gets very complicated when you want duel control of both linear and rotary Encoders which is not necessary when you use a C1 or C3 Ballscrew you would achieve very little by having Linear scales, plus to have a Linear scale with that accuracy would cost more money than the whole machine build

    Mactec54


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    Default Re: Precision high resolution machine build

    Quote Originally Posted by mactec54 View Post
    If you are serious then a linear motor would be the easiest way to achieve this, I have some that do +/- 1um at 2G
    What brand is that, what costs are we looking at for a +/-1um? and what is 2G?

    C7 Rolled Ballscrew never going to happen
    Why is a C7 ballscrew bad, when we have precision servo's with precision encoder. What could go wrong ? and where?

    Steppers not possible no matter what you use
    why? and why would closed loop steppers not achieve this kind of accuracy, repeatability etc. is it due to the inherent construction of the stepper motor?

    Dmm they do have some other Encoders they are working on, this could be possible if everything else is used Precision Grade Linear Rails C1 Ballscrews all built on Granite
    If not DMM then what would you suggest?

    It gets very complicated when you want duel control of both linear and rotary Encoders which is not necessary when you use a C1 or C3 Ballscrew you would achieve very little by having Linear scales, plus to have a Linear scale with that accuracy would cost more money than the whole machine build
    Ok so you are saying either use the rotary mounted encoder or a glass scale encoder. Using both could leed to complications. correct? What is the best way an encoder mounted on the axis on an encoder mounted on the motor?



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    Default Re: Precision high resolution machine build

    Quote Originally Posted by ZeroBacklash View Post
    What brand is that, what costs are we looking at for a +/-1um? and what is 2G?


    Why is a C7 ballscrew bad, when we have precision servo's with precision encoder. What could go wrong ? and where?


    why? and why would closed loop steppers not achieve this kind of accuracy, repeatability etc. is it due to the inherent construction of the stepper motor?


    If not DMM then what would you suggest?


    Ok so you are saying either use the rotary mounted encoder or a glass scale encoder. Using both could leed to complications. correct? What is the best way an encoder mounted on the axis on an encoder mounted on the motor?
    I would say you need to do some research and figure some of this out some of the basic's for your self, you are just wasting peoples time with these questions

    C7 Ballscrews and closed loop steppers not sure why you would be even asking that question 1um

    For servos other than Dmm Yaskawa sigma 7

    Linear motor all the major manufactures make them

    Mactec54


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    Default Re: Precision high resolution machine build

    1 um resolution is easy. ish.
    Accuracy of about 1 um is potentially easy if your motion controller system supports mapped screws and optical glass scales. ish.

    In both cases you need very rigid screws.

    For example my current lathe revisit is going on to servo direct drive, and a 32/5 mm screw. For 270 mm motion.
    And 25 mm hiwin linear guides, heavy preload.

    At issue is not the strength of the guides but the rigidity and repeatability of the system.
    A 32 mm screw is 54 kg of force, per micron, in yield error.

    My screw is C7 from TBI.
    There is probably about 0.05 mm in positioning error, max, in the screw.
    So no-where near single microns.
    But because the screw is extremely rigid, and the linear movement is extremely rigid I get excellent repeatability.
    So small incremental movements of 1 micron are 100% reliable.

    External measurement via 1 micron micrometers and 1 micron electronic dtis proves mechanical resolution and movement.

    So I can cut 1 micron steps into a workpiece I have measured with digital 1 micron micrometers.

    Past:
    But I could not, with 3/4 inch rolled roton ballscrew, and a 30 mm wide HTD8/30 1:2 drive get reliable repeatable results from the whole system running cnc from gcode without manual intervention.



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    Default Re: Precision high resolution machine build

    Steppers are inherently inaccurate to about 1/2 of one step == 400 / turn.
    They get increasingly springy as the resolution goes to smaller angular movements.

    A stepper at 1/10 microstep has about 1/10 the torque at stall, iirc.
    So a 3Nm stepper has 0.3 Nm for 1/2000 angular movement.
    A 3 Nm (cont) ac servo, like on my lathe, has 9 Nm peak torque at 10.000 counts/rev.

    So it is about 5x more accurate, at about 10x more torque vs the stepper at 10 microsteps.

    Another good way to look at it is acceleration.
    At 68 V a Nema 23 3Nm stepper gets to 3000 rpm in about 0.5-1 sec using a good hw pulse engine. A bigger nema 34 stepper is slower.
    A Nema 34 servo gets to 3000 rpm in 20 ms or 0.02 secs.

    Once You get to 1 micron repeatability, and 1 micron mechanical resolution reliably, it is not hard to map out or adjust thermal effects.
    Simply running flood coolant a few degrees above ambient will get you a steady temperature.
    Simply probing tooltips against a fixed probe will get you submicron wear offsets.

    I am using a csmio-ip-s controller on machx sw.
    It is quite expensive, all-in, and the 750W ac servos and 32 mm D screws are not cheap.
    At some point I will add in glass scales, hopefully at 0.1 microns, for feedback.

    I have 3 points.
    It is not hard to make a 1 micron incremental movement reliably from your current tooltip position or controlled point.
    My old steppers, 1:3 HTD 5/18 belt drives, did this, 10 years ago.

    It is quite hard to get reliable repeatable positioning within +/- 1 micron.
    Not accuracy, just repeatability.
    This needs about 2-10x the 1 micron resolution desired, from the motion control system and very high push force and very high rigidity and linearity.

    It is quite hard to map screws or feedback glass scale positioning to the motion control train.



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    Default Re: Precision high resolution machine build

    Quote Originally Posted by hanermo View Post
    1 um resolution is easy. ish.
    Accuracy of about 1 um is potentially easy if your motion controller system supports mapped screws and optical glass scales. ish.
    What kind of motion controller will support that , I currently have a UC400ETH from CNCDrive is that good enough?

    My screw is C7 from TBI.
    There is probably about 0.05 mm in positioning error, max, in the screw.
    So no-where near single microns.
    Can't this kind of error with wiped out with the electronic positioning system. I'm still not getting why we need highly accurate screws. When the encoder + servo can map the movement. I mean when I say go x10.003, y20.005 won't the controller do the necssary jugglery to reach there. as long as the encoder is not given it a feedback the I have reached to target the servo will try to achieve the target position.

    Btw do all modern software operate down to 1um, I mean can I say in gcode go to 0.001 and it will move to that position?

    When we talk of ball screws. Is c0 to c5 ground version and c7 onwards are rolled versions. because that was the impression i got when i read the THK catalogue.



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    Default Re: Precision high resolution machine build

    Quote Originally Posted by hanermo View Post
    Steppers are inherently inaccurate to about 1/2 of one step == 400 / turn.
    They get increasingly springy as the resolution goes to smaller angular movements.

    A stepper at 1/10 microstep has about 1/10 the torque at stall, iirc.
    So a 3Nm stepper has 0.3 Nm for 1/2000 angular movement.
    A 3 Nm (cont) ac servo, like on my lathe, has 9 Nm peak torque at 10.000 counts/rev.

    So it is about 5x more accurate, at about 10x more torque vs the stepper at 10 microsteps.

    Another good way to look at it is acceleration.
    At 68 V a Nema 23 3Nm stepper gets to 3000 rpm in about 0.5-1 sec using a good hw pulse engine. A bigger nema 34 stepper is slower.
    A Nema 34 servo gets to 3000 rpm in 20 ms or 0.02 secs.

    Once You get to 1 micron repeatability, and 1 micron mechanical resolution reliably, it is not hard to map out or adjust thermal effects.
    Simply running flood coolant a few degrees above ambient will get you a steady temperature.
    Simply probing tooltips against a fixed probe will get you submicron wear offsets.

    I am using a csmio-ip-s controller on machx sw.
    It is quite expensive, all-in, and the 750W ac servos and 32 mm D screws are not cheap.
    At some point I will add in glass scales, hopefully at 0.1 microns, for feedback.

    I have 3 points.
    It is not hard to make a 1 micron incremental movement reliably from your current tooltip position or controlled point.
    My old steppers, 1:3 HTD 5/18 belt drives, did this, 10 years ago.

    It is quite hard to get reliable repeatable positioning within +/- 1 micron.
    Not accuracy, just repeatability.
    This needs about 2-10x the 1 micron resolution desired, from the motion control system and very high push force and very high rigidity and linearity.

    It is quite hard to map screws or feedback glass scale positioning to the motion control train.
    Many thanks Hanermo this is very useful, and highly appreciated.
    If I'm getting you correct if I need a +/-1 um reapeatable position, would i need 0.1um glass scales? I see that the typical scales that we get is 5um with a 20um grating pitch and you also get 1um with 20um pitch by paying a bit extra.

    Like I said earlier I still don't understand who is responsible for the repeatable accuracy. I thought its solely the electronic system, servos + controller + encoder. I still don't get what part does the screw have to play in getting a precise position?

    What kind of recommended part list would you suggest for this system. I don't have much load on the axis I will just be mounting a laser, so there are not much forces on the system.



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    Default Re: Precision high resolution machine build

    Quote Originally Posted by mactec54 View Post
    I would say you need to do some research and figure some of this out some of the basic's for your self, you are just wasting peoples time with these questions

    C7 Ballscrews and closed loop steppers not sure why you would be even asking that question 1um

    For servos other than Dmm Yaskawa sigma 7

    Linear motor all the major manufactures make them
    Thanks for the suggestions, truly appreciate it.



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    Default Re: Precision high resolution machine build

    I'm looking for 1um in 500mm resolution and also accuraries in the order of 1um.
    What does it take to achieve this.


    A lot of properly aged cast iron, some very expensive ball screws OR some very expensive linear glass scales, and $100k - $200k to put it all together.
    You will also need to air condition the workshop to 1 C and temp stabilise the cast iron to <1 C (embedded cooling water pipes).

    I still don't understand who is responsible for the repeatable accuracy.
    Which is a warning signal at about 120 db.

    Cheers
    Roger
    PS: Resolution of <1 um is not hard (my machine does that), but accuracy is another matter.



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    Default Re: Precision high resolution machine build

    What kind of motion controller will support that , I currently have a UC400ETH from CNCDrive is that good enough?

    No.
    I think LinuxCNC can do it.
    Possibly the KFLOP and KMotion?
    Other than that, you'd probably be looking at $5000-$10000 for a control that can do it.

    This project is far more complex (and costly) than you think. If it was so easy, others would have done it.

    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Precision high resolution machine build

    Cslabs controllers like the csmpio-ip-s I use on lathe supports secondary feedback via glass scales.

    My lathe has C axis, x, z, for now and the B axis (tailstock) and live tooling are coming.

    Quote Originally Posted by ger21 View Post
    No.
    I think LinuxCNC can do it.
    Possibly the KFLOP and KMotion?
    Other than that, you'd probably be looking at $5000-$10000 for a control that can do it.

    This project is far more complex (and costly) than you think. If it was so easy, others would have done it.




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