Revolutionary Linear Drive System - Page 2


View Poll Results: What is your prefered high precision linear drive system?

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  • Ball Screws

    159 64.11%
  • Rack And Pinion

    33 13.31%
  • Linear Motor

    21 8.47%
  • Lead Screw

    22 8.87%
  • Nexen's Roller Pinion System

    12 4.84%
  • Other

    15 6.05%
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Thread: Revolutionary Linear Drive System

  1. #21
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    pinion gear systems suffer most from lack of contact area. A single line of contact under less than ideal lubrication will always lend it's self to a short "high precision" service life.

    Ball screw systems would represent multiple point contact. The stress strain (deflection) values would be an interesting comparison.

    CalG



  2. #22
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    There are no long wearing aluminum chain sprockets on the countershafts of modern motorbikes.

    The rear sprockets have many teeth in play at once.

    Just to compare systems



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    I recently came across this thread, and it caught my attention. A rack and pinion system that accurate and efficient has got to have potential, right? So I got a few quotes on this system for a machine I am building (a VMC).

    Comparable in price to ball screw? My a**!... If your still reading this thread and are interested in RPS, expect to shell out about $3500/per axis (36" axis, 700-900ipm, 2500/lb expected max dynamic load)... and that price is before before you get into all the little things (mounting brackets etc.) Building a decent scale 3-axis machine with this system, expect to spend $12,000 (roughly my whole budget for this project) in power transmission...

    What a joke... On the bright side they say its good for 30million hits lol...

    Well, I just figured if anybody else bumped into this thread I might save you some time...



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    if pins are stationery, then they are sliding on teeth..
    and if so then I have doubt about how much is it resist wear..

    the good side of, always at least two teeth connecting..

    compared with pinion and rack, pinion has an evolvens surface, what is not same like an arc..

    bicycle chains has "rolling pins" in the chain.. and certain way they are not sensitive for a minimal backlash


    I wouldn't compare with ballscrews.. I would be very much interesting for the first haas mill using this system instead ballscrews

    a plotter or a printer, wheres no load, there mightbe used, but those are working with timingbelt very well..



  5. #25
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    Default Re: Revolutionary Linear Drive System

    Quote Originally Posted by Miksak View Post
    I recently came across this thread, and it caught my attention. A rack and pinion system that accurate and efficient has got to have potential, right? So I got a few quotes on this system for a machine I am building (a VMC).

    Comparable in price to ball screw? My a**!... If your still reading this thread and are interested in RPS, expect to shell out about $3500/per axis (36" axis, 700-900ipm, 2500/lb expected max dynamic load)... and that price is before before you get into all the little things (mounting brackets etc.) Building a decent scale 3-axis machine with this system, expect to spend $12,000 (roughly my whole budget for this project) in power transmission...

    What a joke... On the bright side they say its good for 30million hits lol...

    Well, I just figured if anybody else bumped into this thread I might save you some time...
    A few months back I stumbled across a pair of Nexen roller pinions on Ebay and bought them for $180 each. Two weeks later I picked up two planetary gearboxes for $225 each.
    A few hours on a friends lathe and we made some adapters to mount the pinions to the gearboxes.

    A few hours in AutoCAD and I was able to generate the tooth profiles for the rack. I'm going to cut the racks from 3/4" phenolic plate. Cost for the rack will be about $100 total. I'm building a 4x8 router, and will use the roller pinions to drive the gantry.
    Cost will be about $1000 + servos, or about $2000 with a pair of 400 servos.

    I've seen a few other pinions on Ebay for a similar price. If you can get the rack made, you can use this system without spending a ton of money. Still not cheap, but not $12,000 either.

    Gerry

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    Default Re: Revolutionary Linear Drive System

    Hi, I have to wonder if the plot was lost at the beginning of this thread or along the way, but certainly at the end of it.

    The whole purpose of the Nexen rack type drive (re-post #1) was to offset the cumulative "inaccuracy" of a ball screw longer than about 9" and at the same time add in the anti backlash property which is a highly desirable feature on it's own.

    That is to say, while ball screws are the preferred drive for almost all CNC equipment, the cumulative inaccuracy for anything longer than 9" makes pitching over long distances a question of tolerance.

    That applies to anything that moves by rotary or linear incrementation , EG a leadscrew, rack and pinion etc where the pitch is only as good as the machine and environment that produced it and subsequently the environment that it eventually works in........Sahara desert or Artic Circle etc.

    So, now having bought a roller pinion, the next step is to make a rack!!!!!!!!

    I think that if you have a controlled environment and materials you might make an accurate rack to fit the roller pinion, but it won't be accurate to any known standards unless you are in the business of making accurate equipment to standards that are accurate....IE Metric or Imperial that have definite dimensions over a set distance.

    It will be interesting to find out how you made/make the rack and to what tolerances you worked to........just getting a rack to mesh with the roller pinion is ludicrous if you think it will be more accurate than a long ball screw.

    Perhaps I'm wrong and the roller pinion is a more smoother drive than just a plain involute gear type pinion meshing with a conventional involute profile rack, and I seem to think that the Nexen roller pinion's main attributes were that it was "almost" backlash free....or something like that.

    I would have to say that if the backlash free part is the real attribute, then the long distance accuracy can be sacrificed completely in favour of positional accuracy at any point along the way if not from end to end, otherwise a plain rack and pinion will do the same job.

    In all drives the backlash problem is one that won't go away unless money is a big part of the equation.
    Ian.



  7. #27
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    Default Re: Revolutionary Linear Drive System

    ian

    I think Gerry only wanted to answer for the price issue..
    he has another topic where he showing the nexen roller.. I was also confused little, and I was thinking don't see posts..

    accuracy and backlash can be solved with linear scales..

    these topics about cnc router.. where 0.02 mm or 0.001 in is perfect..

    some of very popular router manufacturer states their precision is 0.15 mm or 0.0075 in...
    due the rack n pinion ,,,

    I like to think that Gerry has acces for that router he makes the rack with, possible more accurate..

    a ""regular"" vmc might no capable to making H7 tolerance.. parts are grounded or bored..

    in theory we can chase absolute accuracy, however it will be out of our capability..



  8. #28
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    Default Re: Revolutionary Linear Drive System

    As Victor pointed out, my post was basically just saying you could build a roller pinion driven machine for far less than $12000. No it won't be as accurate as it would be had I spent $12000.

    I think that if you have a controlled environment and materials you might make an accurate rack to fit the roller pinion, but it won't be accurate to any known standards unless you are in the business of making accurate equipment to standards that are accurate....IE Metric or Imperial that have definite dimensions over a set distance.
    Since I'm building a router, incredible precision is not really needed.
    For my application, I don't think it's as difficult as you say. The rack teeth for the pinions I have are 25mm on center. If I cut the rack so that the pinion rolls along (meshes) properly, and the teeth are 25mm on center, than it should be very accurate for my application. ± a few thousandths isn't critical for me, as long as it's repeatable.


    It will be interesting to find out how you made/make the rack and to what tolerances you worked to........just getting a rack to mesh with the roller pinion is ludicrous if you think it will be more accurate than a long ball screw.
    No, I don't think it will be more accurate than a long ballscrew. But I'll be cutting it on a machine with a long ballscrew, although the rack will be made in short sections (24-36").
    However, the cost will be a fraction of the two 10' long screws I'd need.


    Perhaps I'm wrong and the roller pinion is a more smoother drive than just a plain involute gear type pinion meshing with a conventional involute profile rack, and I seem to think that the Nexen roller pinion's main attributes were that it was "almost" backlash free....or something like that.
    According to Nexen's claims, yes, you're wrong.
    " Actually, the RPS is exceptionally smooth, rivaling the best classes of ball screws and linear motors. This is achieved with the engineered profile, causing the roller to spin at all times. "

    They claim Backlash free. The pinion is preloaded into the rack to achieve this. At least two of the rollers are always in contact with the rack, preventing backlash. This will of course be somewhat dependent on the accuracy of my rack.

    Last edited by ger21; 05-25-2014 at 02:28 PM.
    Gerry

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  9. #29
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    Default Re: Revolutionary Linear Drive System

    I like as accuracy questions always coming up..

    lets take a look on this..

    even it not so visible, companies who making tapemeasure or any other measuring equipment they are using at least one etalon..
    so very much two tapemeasure even from different brands will shows same 8 feet..

    we, the enduser don't have a whole lot option to measuring at home 8 feet..
    any tapemeasure we will buy they will be accurate as much we can see the ticks.. that is way less accuracy that an ordinary caliper even can do..

    and if so, then really doesn't matter how accuracy fluctuating along 8 feet.. we simply can not measure..

    let see an example.. if have to cut an 8 feet long part along 2 inches dia holes distributed to each 6 in, and I make a similar part where same way plugs on a part, then my both part will match.. since I copied the error..

    it might don't match to another part that made on another router..

    in a very good situation, one might has a 24 in caliper.. everything over 24in cost a fortune if anyway one has..

    and cutting a cabinet side... 1/16 deviances really doesn't matter.. so for home using ballscrew, acmescrew or rack n pinion will work with same efficiency..

    ================================================== ==============================

    aligning segments after each other.. some positioning holes can be drilled in the segments, or simply making a negative of the segments will ensure the accuracy..

    if router will be as accurate as 8 feet match to the tick on the tapemeasure, then we can say on one inch it is precise as much as 0.001 or 0.002 in.. within, 1 inch..

    Last edited by victorofga; 05-25-2014 at 01:54 PM.


  10. #30
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    Default Re: Revolutionary Linear Drive System

    Hi I quite agree that accuracy is as you need it, but going to the extent of making a rack to suit the NEXEN pinion and not having the ability to produce it to an accuracy of whatever you use to measure the final overall length is another whole different aspect.

    Why use the NEXEN pinion in the first place when conventional rack and pinion is off the shelf and probably more accurate due to the machinery that produced it, even if it was a production item and produced to a tolerance that dictated the price range per length.

    The only reason to use it is probably because it has backlashless properties that override any lack of accuracy for a home brew.

    In 99% of all big machined jobs on routers the overall accuracy is not all that important.......it isn't important if you don't need it to be .02mm accurate from end to end over a length of 8 feet, but it is quite easy to make it accurate over a length of 1 foot at any place along that 8 feet.

    Many years ago I worked for a firm that on one job needed 10 pieces of rack, each 3 feet long, and they were cut on a planer miller....something like a very big gantry router but it was a planer for cutting metal.....the milling aspect was achieved with a milling head in place of the normal tools that cut the job as it moved under the tool point.

    The point is, the overall rack length of 30 feet was as accurate as the combined sections laid end to end and pitched apart on each of the ends, but the overall length was not an issue for the exact pitch from tooth one to the last tooth of the entire length.

    If the NEXEN pinion can mesh with the rack and be able to accommodate any pitch errors tooth to tooth, then some form of springing will be needed.

    Unless you can maintain the rack profile both in the making and using of, (the rollers will try to reform the rack), then the exercise will be time consuming for no apparent gain.

    As a matter of interest.....how will the rack profile be generated?

    The slots are across the material so that cuts out using a profile cutter like as in a horizontal mill.

    If the cutter is shaped like an end mill, but to the tooth flank profile so that the vertical spindle can be used to cut the teeth....rapid wear will make the cutter useless unless it is carbide, and that's a whole different ball game....finding someone to regrind a carbide end mill to your profile without supplying a projection chart.

    It will be interesting to see how the rack is going to be made.
    Ian.



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    Default Re: Revolutionary Linear Drive System

    ian

    it is simpler, than it looking..

    first thing first...
    Gerry making the rack on a machine that is considerably precise..
    means anywhere in the workare cut a 100x100 mm square it will be in a tolerance like 0.05 mm

    first need some testcut... like cutting 2x2 inches square and that can be measured with caliper or micrometer..

    or measuring the machine on 4-8 feet length.. the router he using for cut this that has a precision..

    making the rack...
    the nexen roller ... I guess exactly same dia rollers... measure one, and measure two..

    of these you have the dia and the distance between rollers..

    now you lay out in autocad two circle as the rollers dia... from the frist circle center make an arc starting at the second circle quadrant..

    from here a simple mirroring and trimming will make one teeth..

    multiple as much need...

    ===================================

    let say he lays out all part at time on the table, and cut all part at time..
    from there simply need to mount on the frame..

    if theres any doubt, then simply he can lay off an alu bar make positioning holes into like in the segments and together mount on the machine..

    or make a negative of teeh like 8-12 teeth and with this gauge mount at the proper distance the segments..

    what ever way, BUT.. copy the used router accuracy..

    this way any point will be same accurate.. if some square rail used then distance between roller and rack can be kept relatively simple without tensioning..

    virtually here chain is rolled up onto a wheel and sprocket layed out as a rack.. same geometry than any sprocket-chain pair..



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    Default Re: Revolutionary Linear Drive System

    Gerry,

    Have you made this yet? I've be interested to hear how the phenolic holds up.



  13. #33
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    Default Re: Revolutionary Linear Drive System

    No, and it's probably going to be at least a year before I have it working.

    Gerry

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  14. #34
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    Default Re: Revolutionary Linear Drive System

    Hi, I have to ask, what is the prime purpose for using the NEXEN roller sprocket if it doesn't maximise the accuracy the NEXEN design for linear travel

    If you already had a NEXEN roller sprocket and wanted to put it to good use, that would be feasible, but buying one in without the main item, the rack, is a puzzle..

    It can't be the overall price as it will cost approx. $1,000 or so to get it to completion, and that without any form of accuracy you can rely on.

    I think it's a wow thing, where the NEXEN roller is being used as a novel way to move a carriage from A to B, but you could do that with conventional rack and pinion for far less cost and time.

    But as I don't want to rain on someone else's parade, it will be interesting to see how the package turns out.
    Ian.



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    Default Re: Revolutionary Linear Drive System

    It won't cost me any more than rack and pinion. I paid $360 for the pinions, and the rack will cost me $50 in materials.
    My original plans were to use a ServoBelt system, but the Nexen system was a lot easier to do than the servobelt.

    My hope is that I can machine the rack accurately enough to be every bit as accurate as standard rack and pinion, with all the advantages of the Nexen RPS system.
    Smoother motion.
    No lubrication.
    Quieter
    Higher load capacity
    No backlash

    After I make the rack, I'll throw a test axis togther to test the smoothness and accuracy of the rack. If it doesn't work, I'll sell the pinions and go back to the ServoBelt. Using the gearboxes I purchased will now make the Servobelt system nuch easier to implement.

    Gerry

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  16. #36
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    Default Re: Revolutionary Linear Drive System

    Hi
    I'm currently experimenting with a DIY RPS style linear drive system that eventually I plan to use on the x axis of a cnc router.

    I also plan to scale the track profile down a little and use it to create a large format 3D printer (500mm x 500mm area) maybe use some type of durable plastic for the rack

    I'm using inexpensive cam followers that are supported only on one side. (I'm not sure if this will stand the test of time but if it works it will be a relatively cheap solution)

    The machined protoype rack shown in the photos is aluminium and rebated so that the THK linear rail can be precisely positioned.
    I machined everything on my CNC Sieg X3 so I'm currently limited to a 400mm rack although I'm hoping I can just add racks together like the Nexen system.

    The geared Nema 17 stepper motor and THK SHS20 Linear rail are not really well suited, its just all I had lying around.

    I would like to know if anyone here has already made a similar DIY system.
    I haven't yet hooked it up to a driver but it seems to move very smoothly by hand.


    Revolutionary Linear Drive System-img_0255-jpgRevolutionary Linear Drive System-img_0256-jpgRevolutionary Linear Drive System-img_0257-jpgRevolutionary Linear Drive System-img_0258-jpg



  17. #37
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    Default Re: Revolutionary Linear Drive System

    Hi, quite a nifty way of doing it.......I have to ask how long the aluminium rack will last before backlash becomes an issue.

    Aluminium tends to have a one way migration under load, as opposed to Nylon etc which has some resilience to surface indentation and will spring back to it's original shape.

    You won't get wear on the flanks as such, but the pressure on the aluminium even with rollers rotating will indent the ally and give you backlash.

    As you have the ability to machine the rack you could explore more durable materials as you don't want to go re-machining racks too often.....just my two pennoths worth.
    Ian.



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    Default Re: Revolutionary Linear Drive System

    Thanks for your comments Ian. I reckon your right about the aluminium ultimately resulting in backlash issues.
    I was thinking the same thing.

    If this prototype works then I'll definitely be looking at more durable materials for the rack.

    Any suggestions on suitable materials are most welcome.

    Do you reckon aluminium would hold up to low load applications such as in a 3D printer?

    Another thing I'm unsure about is: the Cam followers I'm using contain needle bearings so they can withstand fairly high radial loads but I think the geared stepper motor contains ball bearings to support the rotating shaft. I'm wondering if they would need to be changed over to needle bearings too otherwise they might wear too quickly.

    Cheers

    Nikki



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    Default Re: Revolutionary Linear Drive System

    Hi, running rollers on the aluminium will probably not wear as such due to it being a rolling action and as a printer only moves a small load wear may not be a factor as opposed to the ability to move the table with a replaceable drive system home grown.

    You could coat the flanks of the aluminium teeth with some epoxy resin if it could be laid on thin enough and that could be a solution to actual abrasion wear from the impact of the rollers,.....hard chroming comes to mind if it can be done on aluminium.

    Not being in the field of rack and pinion drives per se, I would have to hypothesise that materials for the rack must be able to be cut without resorting to hardening, grinding and other exotic finishing techniques.

    So carbon fibre also comes to mind as a material that can be cut with a router etc, but I think plain Nylon type plastics will fit the bill more fully as they will not actually wear away from impact forces, being resilient, so you also get a sound deadening factor when rapid driving.

    The reverse of the design you have is to make the rack with the rollers and the pinion from plastic etc.......it's probably easier to cut a pinion than to cut and fit a series of rack segments.....pitching the rollers on a long rack would be easy peasy.

    This is only a suggestion for thought as I'm not sure if the acceleration and deceleration forces of a gear tooth shape driving on a roller rack will give you the same effect as a regular rack and pinion with involute gear forms......it may give you a rhythmic undulation along the way.......but this is probably the same for the original design.
    Ian.



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    Default Re: Revolutionary Linear Drive System

    Hi Ian, I just hooked up some power earlier and tested the prototype.

    After testing it for only 5 mins I can see signs of the aluminum wearing.
    It is also much louder than I thought it would be. I think I'll try Nylon next as per your suggestion.

    If I can find some smaller Cam followers I'm going to scale it all down and use some 9mm or 12mm linear rails.
    Nothing in this current prototype is really sized correctly. The whole design is not very forgiving, if anything is slightly out of alignment it won't run properly.
    I reckon these systems call for extreme precision, I wonder If spring loading the rack and roller pinion together would work?

    I too thought the reverse design you mentioned, was the ideal solution, (better to replace a worn plastic gear than a whole rack) but I spent a few hours on CAD investigating this option a while back and came to the conclusion that its impossible. I thought that it would work in the same manner as a chain and a sprocket, but when I tried to design it in CAD I couldn't design something that would work.
    I think the issue is that a chain wraps around a sprocket, when a sprocket moves the chain is constantly changing form, having the rollers positioned in a straight line means that you can't get any rolling motion.
    If you have an example of a design that works in this manner, I'd love to see it, I agree this would be a much better solution but I'm not sure it is possible.

    I should probably start a separate post rather than hijacking this one.
    Here is a video of it in action.

    Nikki




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