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  1. #21
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    Quote Originally Posted by DanielG View Post
    You'd be surprised at how high performance a rack and pinion system can be. We usually used rack and pinion for the long x-axis. With two servo motors working together, you can get very high speeds and accuracy. We'd run Renishaw scales the full length for secondary feedback and the controls guys would comp each rack segment as well as the joints between rack segments.
    Any idea of how "fine" the comp was done? Every 10"? 1"? Finer values at the joint, then back to a larger pitch?


    At low speeds, the two servos fight each other to eliminate backlash. At higher speeds, they'll work together so you can use smaller servo motors. There is a constant torque offset between the master and slave servos.
    I've had similar thoughts on driving rotary axis with this method, so anything you'd like to share on practical application would be welcome.

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    Quote Originally Posted by Milland View Post
    I've had similar thoughts on driving rotary axis with this method, so anything you'd like to share on practical application would be welcome.
    For rotary axes, Pfauter definitely and maybe Liebherr are doing this on hobbers. Instead of using one large worm/wormgear, they use two smaller ones with servos that fight each other.

    I'm not so sure this is great for cutting large-pitch teeth over a long lifespan, but they are doing it no matter what I think

    Should be a fair amount of info at their website, or you could try to get more out of Rochester. (Not Jack Benny's Rochester, the one in New York.)

    Anyway, the system is in commercial use by an esteemed company, so you're not entirely Gyro Gearloose.

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    Quote Originally Posted by DanielG View Post
    ......You'd be surprised at how high performance a rack and pinion system can be. We usually used rack and pinion for the long x-axis. With two servo motors working together, you can get very high speeds and accuracy. We'd run Renishaw scales the full length for secondary feedback and the controls guys would comp each rack segment as well as the joints between rack segments. At low speeds, the two servos fight each other to eliminate backlash. At higher speeds, they'll work together so you can use smaller servo motors. There is a constant torque offset between the master and slave servos.
    I was part of a crew installing a biggish HBM back in the early 90s that used a dual servo rack and pinion drive with Heidenhain segmented scales. 38 feet of travel so at that time rack and pinion was the only practical method. Not fast though, maybe 400 IPM. It worked well for that application. The column was pretty huge. Y axis was 13 feet and used a screw but again, relatively slow travels.

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    Quote Originally Posted by Vancbiker View Post
    I was part of a crew installing a biggish HBM back in the early 90s that used a dual servo rack and pinion drive with Heidenhain segmented scales. 38 feet of travel so at that time rack and pinion was the only practical method.
    Wouldn't that be a good place for the laser optical measuring systems ? I remember those at like $10,000 an axis way back when, but the length of the axis shouldn't matter, so in your case, 38', it could even be cheaper ? And more accurate ?

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    Quote Originally Posted by Vancbiker View Post
    I was part of a crew installing a biggish HBM back in the early 90s that used a dual servo rack and pinion drive with Heidenhain segmented scales. 38 feet of travel so at that time rack and pinion was the only practical method. Not fast though, maybe 400 IPM. It worked well for that application. The column was pretty huge. Y axis was 13 feet and used a screw but again, relatively slow travels.
    This article has some good picture of a pair of AFP machines with rack and pinion X and ballscrew Y and Z. I want to say that it was 2000ipm. Needless to say, they switched to linear motors after this one.

    https://www.compositesworld.com/arti...commercial-jet

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    Quote Originally Posted by Milland View Post
    Any idea of how "fine" the comp was done? Every 10"? 1"? Finer values at the joint, then back to a larger pitch?


    I've had similar thoughts on driving rotary axis with this method, so anything you'd like to share on practical application would be welcome.
    For a linear axis, the first thing is to get the rack as good as possible. Set your linear rail straight first using either an interferometer or a string line and camera. You then attach an indicator to a bearing car and run the indicator over a pin set between teeth. They make magnetic pins for this purpose so they stay put; they're well worth the money. I had to align a bunch of aluminum gear segments last year and keeping the pins in place sucked. Once the rack segment is set, you start on the next one, setting the gap using a pin and indicator as well.

    In general, the tooth-tooth spacing will be much more consistent within a rack segment than between segments. You'd have a straight line comp for the rack segment, and then another short straight line comp section for the joint. The comp points were, IIRC, about an inch from the end of each rack segment (on Mod 6 rack). Keep in mind that if we needed more accuracy, we would add a scale for secondary feedback, so the comp of the primary feedback just had to be "good enough"

    For linear axes, we used either a Fanuc 30i or a Siemens 840D.

    I've done a few dual-drive rotary axes, They were low precision, so we didn't really care about accuracy, just not having backlash when we went over center. Because the motors take out the backlash, we were sometimes able to save money and use a less expensive industrial gearbox. Turns out there is one size of Bosch servo motor that has the same bolt pattern as an IEC frame motor. This saved a few thousand dollars buying Bonfiglioli rather than Wittenstein Alpha. We also didn't have to be very precise about setting the center distance between the slewing ring and the pinion. We set it a little on the high side and the servos took out the backlash.

    For controls on the rotary axis, we used both Bosch and a Siemens Technology PLC. If any ever suggests using a Siemens Technology PLC, I highly recommend running away quickly.

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    Quote Originally Posted by EmanuelGoldstein View Post
    Wouldn't that be a good place for the laser optical measuring systems ? I remember those at like $10,000 an axis way back when, but the length of the axis shouldn't matter, so in your case, 38', it could even be cheaper ? And more accurate ?
    Possibly a good application. I have never worked with a machine that used that type system. I have used laser interferometers for checking accuracy and setting comp tables. Pretty sweet, but not hardy enough for a full time position loop. Dirty retro-reflector mirror and down it goes.

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    Thanks, but i need a complete machine, not just the linears.

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    These are all very innovative and interesting approaches from all of you professional work masters, but not very helpful to my topic

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    Quote Originally Posted by Vancbiker View Post
    I have used laser interferometers for checking accuracy and setting comp tables. Pretty sweet, but not hardy enough for a full time position loop. Dirty retro-reflector mirror and down it goes.
    I remember something about putting the light beam and mirror in tubes or otherwise protecting it for this exact reason ...

    Quote Originally Posted by Moldmaster
    not very helpful to my topic
    This is the internet. You don't own it.

    p.s. If you call yourself a master, then you have enough experience and knowledge to make your own decisions.

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    Quote Originally Posted by Moldmaster View Post
    Hello everyone. Im a mold/parts manufacturer, looking for a new ,value for money machine.
    My best candidates are:
    Doosan DNM 5700
    Hyunday KF5600
    YCM NSV106AMS

    All of them include mold package

    what do you think?
    Not bad choices. I'm a little biased as I used to work for Doosan, but the DNM is a tremendous value for the money. Full contact spindle, Fanuc control, motors, and drives, thru spindle coolant, optional hi-pressure coolant. Nice, heavy, fine grain castings, chip augers. The optional mold package gives a few extra goodies to the control and the 15k spindle option means you can cook pretty good. Super value that will make you money.

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    Thank you Douglas. Does the mold package on the doosan includes a change of the screw to a different ( more dense) type of screw or just controller modifications? The doosan is the only machine with grease lubrication while the others use oil and air spray, does it has any cons?

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    Quote Originally Posted by Moldmaster View Post
    What benefits do you get from the Siemens? I heard they're better on 5 axis ,but on 3/4 axis? I think fanuc is cheaper and more reliable
    Personal preference. I leverage the more advanced Siemens programming language to do a bunch of automation, tool management, data logging, etc... that couldn't really be replicated on a FANUC. No doubt the latter is more robust if you are just looking do dump code out of CAM and run it though.

    With YCM the pricing for a Siemens 828D was about the same as a FANUC.

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  19. #34
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    Roughly fifteen grand for a wheel mold, in case you want to go into the biz.
    As an aside, I would imagine that wheel mold would be at least $150k, if made in the USA or Europe??

    10 times the cost of making it in China....

    No wonder they have taken such a large chunk of the world's mold and die work.

    ToolCat

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    Like Daniel - we have a fair amount of experience with linear motors on machine tools as well as other equipment.

    The largest machine we provided controls for was a 5-Axis gantry milling machine - roughly 135,000 lbs in X with 100 ft of travel - this was a contra-torque rack and pinion machine done in 1997 . . . it was the slowness of the machine with the inefficiency of the contra-torque on the X-Axis (4 motors) that convinced us to look at linear motors going forward.

    Newer machines are lighter (closer to 80klbs on the X-Axis) capable of 1/4 G accelerations with rapids to 4 m/sec. The speeds and accelerations are actually limited to how much damage that you want to inflict upon the cables and hoses in the energy chain. Heidenhain scales and laser tracker used to comp the machine every 10 inches on a cubic pattern. CNC had sag compensation as well as volumetric compensation combined. Motors are water cooled - thermal stability is not a problem.

    janicki2.jpg

    You can see the two contra-torque Y-Axis servo motors on either side of the Z-Axis mast. X-Axis on this machine is also driven with contra-torque servo motor arrangement.

    We started out with contra-torque designs on the X-Axis on earlier machines and then went to linear Bosch motors in 2003 starting with a Delta Tau CNC and then shifting to the 840D which can handle contra-torque and linear motors just fine with the S120 drives. Our main customer for this work took it in-house in about 2005 and they have been huge fans of Siemens with all of their machines since. They were a big reason why we embraced Siemens for our own machines as well as our other customers machines which led to us becoming a Siemens Solution Partner.



    You can see the bearing housings on the side of the wrist for one of the contra-torque motor assemblies in this image.

    We have also deployed roughly 200 linear motors in the glass container industry - attractive force between magnet and motor is over 1000 lbs and we upsized the linear bearings to react this force. We started out with Anorad but they went to crap after being purchased by Rockwell . . . we now use Bosch linear motors exclusively but control them with Siemens drives and controls.

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  22. #36
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    Just wanted to mention the KAAST VF Mills as a value for your money machine. And they have some in stock in philly!
    KAAST Machine Tools | High quality machine tools

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    Quote Originally Posted by Moldmaster View Post
    Thank you Douglas. Does the mold package on the doosan includes a change of the screw to a different ( more dense) type of screw or just controller modifications? The doosan is the only machine with grease lubrication while the others use oil and air spray, does it has any cons?

    I currently work for Doosan. And Douglas is a thoroughly knowledgeable associate. Aside from the 15K spindle, the mold package includes AICC2 with 600 block look ahead, nano smoothing and jerk control. All the things you would likely need to make molds. I built injection molds for 20 something years and I have tested our machines. The below pic was cut on a DNM5700S at IMTS2018.

    mold-core.jpg

    As for axis designation, as someone mentioned, there is a rule. A axis always rotates along the X axis. B axis always rotates along the Y axis and the C axis always rotates along the Z axis.

    Paul
    Attached Thumbnails Attached Thumbnails 20190109_102816.jpg   mold-core.jpg  

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  25. #38
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    Quote Originally Posted by LockNut View Post

    As for axis designation, as someone mentioned, there is a rule. A axis always rotates along the X axis. B axis always rotates along the Y axis and the C axis always rotates along the Z axis.

    Paul
    Sure, but when you have a C axis knuckle and the final rotary axis rides in it, what sets the designation for that last axis? I'd guess where it homes, but if C is 360* then it could home anywhere the builder set it to.

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    Quote Originally Posted by Moldmaster View Post
    Thank you Douglas. Does the mold package on the doosan includes a change of the screw to a different ( more dense) type of screw or just controller modifications? The doosan is the only machine with grease lubrication while the others use oil and air spray, does it has any cons?
    The ballscrews are the same. The Mold Maker option is mostly updated control software. Memory, lookahead, nano-smoothing, etc. The grease packed lubrication never was an issue when I worked there. The only time spindles came back was when someone crashed. There's also a data server option for the control you may be interested in.

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    Quote Originally Posted by Moldmaster View Post
    Hello everyone. Im a mold/parts manufacturer, looking for a new ,value for money machine.
    My best candidates are:
    Doosan DNM 5700
    Hyunday KF5600
    YCM NSV106AMS

    All of them include mold package

    what do you think?
    we are just setting up our 5700S doosan, sold our vf3/4 in favor of it. heard lots of good things about them.


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