[Swiss]

Hi all,

I was just curious to know if anyone has used either linear brushless motors, or linear stepper motors in their projects? For examples these:

Linear brushless: http://www.aerotech.com/uk/products/...ar_motors.html
Linear stepper: http://www.acpd.co.uk/cobra-linear-steppers.html

I was just wondering if anyone had any comments of their usefulness for CNC.

thanks

Hugo

[Gizmot]

Hi all,

I was just curious to know if anyone has used either linear brushless motors, or linear stepper motors in their projects? For examples these:

Linear brushless: http://www.aerotech.com/uk/products/...ar_motors.html
Linear stepper: http://www.acpd.co.uk/cobra-linear-steppers.html

I was just wondering if anyone had any comments of their usefulness for CNC.

thanks

Hugo

never heard of anybody

seems like the main problems are controlling the motor, cost and strong magnetic field.

[Swiss]

seems like the main problems are controlling the motor, cost and strong magnetic field

The motors are basically brushless motors, so a normal brushless motor driver can be used (I think).

Cost is certainly a big issue, as these motors are still quite expensive. But, being a home build, the price for the machine still comes in at a lot less than a similarly speced commercial machine.

I hadn't thought about the magnetic field though. Is the field a lot stronger with these motors? What problems might it cause?

Hugo

[Swiss]

I just spoke to the company that sells the linear motors. They say the motors are frequently used for CNC applications. They also supply drive electronics, so control isn't a problem. The only problem is the price. Alltogether, for 3 axes, two motors per axis, encoders, electronics and software, it comes to more than £10,000! *ouch* Still, that would make the whole machine less than we paid for our Emco 105.

Hugo

[Garfield2]

Yeah, I've got an old style one that I drove with my PICStep drivers a few years ago. It was quite strong but it would really only be suitable for very light engraving.

http://www.fromorbit.com/content/pic...linear-stepper

Alan.

[Gizmot]

I just spoke to the company that sells the linear motors. They say the motors are frequently used for CNC applications. They also supply drive electronics, so control isn't a problem. The only problem is the price. Alltogether, for 3 axes, two motors per axis, encoders, electronics and software, it comes to more than £10,000! *ouch* Still, that would make the whole machine less than we paid for our Emco 105.

Hugo

control is not a problem... if you have the money

Control may be a problem for cheap guys using EMC2...
Most linear motors use a scale or glass linear encoder, wich is kind of expensive.

What I would love to do is develop a GPS style feedback system that use a cheap TGV (the train) style of linear motor. Next step would be to start my own machine tool business and crush the competition

btw, do you have any specifications on that £10000 quotation?

[Swiss]

btw, do you have any specifications on that £10000 quotation?

It was for six BLMC-92 motors, four CP-30 amplifiers, three Renishaw 1um linear encoders, CNC Control software, firewire cables.

The motors are 65.9N continuous, and 263.7N peak. I would like to use two per axis.

Specs for the motors: http://www.aerotech.com/products/motors/blmcspecs.html
Specs for the amplifiers: http://www.aerotech.com/products/amps/nd.html
Specs for the encoders: http://www.renishaw.com/en/9802.aspx
Specs for the software: http://www.aerotech.com/products/con.../a3200smc.html

Hugo

[RICHARD ZASTROW]

Hugo, If you're into spending money, try this: http://calinear.com/products.htm

Dick Z

[Swiss]

http://calinear.com/products.htm

Holy moly. Those are some awesome looking motors, strong too. The only thing is that they are a bit massive. Still, I might get a quote to see how they compare to the Aerotech ones.

Hugo

[RICHARD ZASTROW]

Hugo, FYI look at http://www.advancedmotion.net/pdf/servo1.pdf

They combine hydro/pnuematic (gas spring?) with linear tube motor. Think of counter-balanced vertical (Z-axis) application.

Just another EXPEN$IVE idea.

Dick Z

[Swiss]

Richard,
those are really nice looking actuators. Actually, I think we met the guys from that company when we were building a VR chair a few years ago. I'm going to ask them for a quote too.

Just another EXPENSIVE idea.

I'm not just looking to spank loads of money. We don't have much. I'm trying to save my company money. Next time we buy a milling machine, I'd like to show them that they can have a better, more reliable and less expensive one if we assemble it ourselves, rather than buying one. These components seem expensive, but when you add it all together, it comes to less than the low end Emco we have now.

Hugo

[RICHARD ZASTROW]

Hugo, I was only trying to do the Disney "imagineering" thing. I know those are expensive items. What if you counter-acted or assisted less expensive electric devices with pneumatic cylinders?

I've done that by using rather small ballscrews/nuts and counter-balancing with air cylinders & remote air reservoirs. The system also prevented power-off falling of the rather heavy vertical axis. It's a little bit of a balancing act but it does work.

Another reason or motive besides cost is I want to use off-the shelf, readily available components so my client/customers can have a replacement part available in case of failure. They wouldn't appreciate waiting for a non-standard part while their production is shut down.

Dick Z

[Swiss]

What if you counter-acted or assisted less expensive electric devices with pneumatic cylinders?

Well, I was thinking of counterbalancing the weight of the Z axis with a couple of long springs (so the force doesn't change too much as the axis moves). I thought cylinders might have some friction or stiction.

Richard, what are you using them for? Got any pics?

Hugo

[NEATman]

Swiss-
I've designed several gantries using linear motors, and air bearings with Renishaw or heidenhain linear scales for processing LCD panels.
(http://www.cnczone.com/gallery/showp...n/name/NEATman)
Thier performance is incredible if properly applied. It is only improved when used with air bearings, as the only point of contact in the whole system is the tube carrying the air pressure to the bearings and the cables to the motors & encoders. Truly massive motors are available if you are willing to spend the money. On some machines we water cooled the coils to get more performance out if them. The typical moving masses were on the order of 30 lbs (on the pneumatically counter balanced Z axis) to 4000 lbs on a huge lower axis. One excelent trick to counterbalancing the Z axis is to use some anti-stiction air cylinders from Airpot:
http://www.airpot.com/beta/html/exhibit31.html
These bleed some air, but are in essence air bearing cylinders. Combine this with a precision SMC regulator that is self-relieving (to evacuate the air on the down stroke) and you have an efficient counterbalance.
http://www.smcetech.com/CC_catalogs/smc/pdf/ir.pdf
You will need air pressure to the system at all times, or the Z axis mass will cause the servoloop to overcurrent and crash. I would suggest biasing the air counterbalance so the payload moves up if you loose servoloop, otherwise you get a nice guillotine! Also, put a reserve tank with a one way inlet valve and a low pressure switch on it to shut down the system if you loose pressure. An extra saftey would be an air cylinder Z axis brake with spring extend and air retract. Size the spring so that it will overcome the air pressure when it gets to a level a few PSI above the safe pressure level required to counterbalance the Z. Be sure to notify the controller if this happens, or you may smoke a motor coil.

As far as motor vendors, I had used the round style tube motors, Kollmorgen linear motors, Baldor linear motors, and a motor from indonesia that I can't recall the name of - good quality and low pricing.
Linear motor vendors:
http://www.thomasnet.com/nsearch.htm...sec=prodsearch

The thing that will really blow the budget is the magnet tracks. Plus, they can be dangerous! keep anything ferrous away! Also, don't get your wallet too close either, as the gauss levels are between 4000 and 6000 inside the tracks and can easily erase credit card magnetic strips. It only takes about 1000 gauss to erase a card.

These motors will work with common three phase brushless drives.

I hope this helps.
NEATman

[Swiss]

NEATman,

that's great. It's an awesome looking machine. Much cooler than what I have in mind for mine. I'm glad someone has used these motors, because I was beginning to think they might not actually be suitable, since no one else had used them.

I like the idea of non-stiction air cylinders. But I think at the moment, I'm stuck on the idea of using normal steel springs because they're cheap, and zero friction, and definitely bias them to more uplift, as you say.

Any more pics of your lovely gantry?

Hugo

[NEATman]

Hugo-
I probbably have more pictures somewhere. I'll have to take a look. Maybe some of a much larger system as well.

Take a look at this:
http://www.danaherprecision.net/Down...ure_120407.pdf
and this:
http://www.danaherprecision.net/Spec...Page.aspx?ID=5

This was really cool to see run:
http://www.danaherprecision.net/Spec...Page.aspx?ID=8
A bit of math required to work out the commanded position, but it's kind of like a flat hexapod.

Also, here is a great design guide for anything mechanical:
http://www.danaherprecision.net/MotionHandbookPage.aspx

How much Z travel do you need? I have a spare Z axis (or three) from a similar machine with about 4" to 5" of travel. It's completely stripped except for THK rails and two aluminum plates, but it might get you that far.

NEATman

[Swiss]

NEATman,

is that "NEATman" as in "NEAT Rotary Motor Mount" ? Thanks for those links. Yes that flat hexapod looks lovely. I love those kind of things. This is my favourite one: http://www.prsco.com/rotopod.html

I have a spare Z axis

Wow, that is a very generous and tempting offer. I was actually aiming for about 12" travel. But still, very tempting. Listen, let me do some CAD and see if it's enough. Maybe we could swap one for a robot finger? http://www.shadowrobot.com/hand/overview.shtml

Hugo

[NEATman]

Hugo-
NEAT as in New England Affiliated Technologies - I worked there for 8 years. After a few years it was taken over by Danaher, and it has since become all corporate.

The flat hexapod is an XY stage with a partial rotary axis. It is being tested for up to 10g's of acceleration and nanometer resolutions. It's sick to see it move at those speeds!

I would gladly swap one of these stages for one of those fingers Cool! - Heck, I may even be able to find a linear motor and encoder to fit the Z stage (I need to rummage through my pile...) I knew of a co-worker who had salvaged several motors and tracks from a smaller system - Baldor I think. I've already sent him a message to see if he still has any left. If I had the room there was one complete XY system with about 1 meter x 1 meter of travel with linear motors & glass scales - it was dumped upside down in a dumpster. It was obsolete - but would have made a fun project. Probbably $50k in parts alone. I couldn't salvage anything from it, as it was several thousand mounds of granite crushing all of the good parts.

NEATman

[Swiss]

Argh. It pains me to think of such a nice machine being thrown away.

Wow, I'm really excited about the prospect of getting my hands on a linear motor.

[Xerxes]

If you need a low cost linear motor, you can build it yourself. It consists just magnets, iron and copper coil. The most expensive parts are magnets, which may cost few bucks a piece.

I have built a small one for testing, see this thread:
http://cnczone.com/forums/showthread...tor#post245555