New Machine Build- Linear Servo Motor Guru Please Help

[protomate]

Hello all,
I am in the process of trying to gather any knowledge I can on design and build of a cnc linear motor driven raster/vector laser table. If possible, maybe a router will work too. I have gathered several aerotech linear motors. After some discussion with Aerotech I am still kind of confused as to which drives would be best linear or pwm, and how to size them. I do have water cooling systems for these, so I can imagine they can be run pretty hard. For laser work, i won't touch the force. If I run them with ones system moving the gantry i will see 100lb rms, and around 500lbs peak. Double that if I use 2 systems for one axis. I think this shouldn't have a problem with a high speed spindle 20k and a 1/8" cutter? Also, I am unclear what type of linear encoder system might be cheapest and best to arrive at working precision of .0001" or so. The best I have figured for a chasis is a granite surface plate, but I wondered if an optical table might be ok from a flatness standpoint? I also read a little about pouring your own granite type material for a machine base on this forum.
Any ideas/cheap solutions/ thoughts would be greatly appreciated.
Thanks again

[mike_Kilroy]

whew! heavy duty stuff!!!! then scare us all of asking for a guru!! none of us want to step into that role! but a lot of us will give our opinions I supply approx 300 axes of this type linear servo motor/drive per year so will take a stab at it....

take ur questions/comments sequentially,....

I am in the process of trying to gather any knowledge I can on design and build of a cnc linear motor driven raster/vector laser table. If possible, maybe a router will work too. I have gathered several aerotech linear motors. After some discussion with Aerotech I am still kind of confused as to which drives would be best linear or pwm, and how to size them.

you do NOT want linear motors **EDITED - I MEANT LINEAR DRIVE AMPLIFIERS** for this project;; aerotech will push linear drives since that is a big part of their business IMO for coordinate measurement machines, where they measure not .0001" but rather .0000005" - pwm noise can make machne building harder - not impossible as we do it daily - but harder. linears get hot, are big, expensive, not nice. use std pwm servo drive for running these motors.

next how to size?? the linear motors have a CONTINUOUS AMP RATING- simply pick ur drive cont amp rating to match! aerotech motors are often 230v rms ac motors; so do not use 460 on them or they will break. so 230 or 120v ac depending on motor rating. pick that way.

I do have water cooling systems for these, so I can imagine they can be run pretty hard.

some of their motors do have air/water slots in them for cooling to get more CONTINOUS AMP ratings - dont go there unless u need to. water is nasty corrosive stuff in time. if u must, blow air threw the holes.... best to keep away from both IMHO.

For laser work, i won't touch the force.

I do not know what this means.....

If I run them with ones system moving the gantry i will see 100lb rms, and around 500lbs peak. Double that if I use 2 systems for one axis. I think this shouldn't have a problem with a high speed spindle 20k and a 1/8" cutter?

If I were sizing such a system, I would ask you how much thrust force is required to push that 20krpm spindle with 1/8: cutter along the axis? You tell me and I then pick the thrust motor required...... in this case, is it less than your 100# available? or 200 if u use 2? being gantry I assume you will put one linear motor on each side to push in synch?

Also, I am unclear what type of linear encoder system might be cheapest and best to arrive at working precision of .0001" or so.

all linear encoders will easily do 1/10,000" consider Newall Electronics - Digital Readout (DRO) and Linear Encoders for unique perhaps beneficial feedback thing....

The best I have figured for a chasis is a granite surface plate, but I wondered if an optical table might be ok from a flatness standpoint? I also read a little about pouring your own granite type material for a machine base on this forum. Any ideas/cheap solutions/ thoughts would be greatly appreciated.

I am electrical not mechanical so have no clue on this

my 2 cents

[protomate]

I took a look at the encoder companies site. Very impressive. Great innovation and durability. I also looked at US Digital. From what I gather, as long as you can stay within 34" they have a setup to I think get you with quadrature to .0002" sensor and scale for under $100. Seems like a real value. Unfortanatly for this project my needs are over that length range.
When I made reference to "laser work", I do work with Yag, co2, and some Ktp laser cutting, engraving, and rapid prototyping. Main goal for the linear servos is to achieve a HD engraving resolution. With digital cameras now into ultra high resolution range, the laser should be able to transfer the image at a much higher range then what is available. I have the lasers, need a fast, accurate transport to match.
Not sure of the exact force required at this time to push the spindle yet. The objective is a series of shallow passes, at high feed and spindle to lessen the rigidity requirement, improve heat dissipation, and ultimately improve precision of parts produced. Already done, just wish to have it in my shop.

[jlnading]

Originally Posted by protomate I took a look at the encoder companies site. Very impressive. Great innovation and durability. I also looked at US Digital. From what I gather, as long as you can stay within 34" they have a setup to I think get you with quadrature to .0002" sensor and scale for under $100. Seems like a real value. Unfortanatly for this project my needs are over that length range. When I made reference to "laser work", I do work with Yag, co2, and some Ktp laser cutting, engraving, and rapid prototyping. Main goal for the linear servos is to achieve a HD engraving resolution. With digital cameras now into ultra high resolution range, the laser should be able to transfer the image at a much higher range then what is available. I have the lasers, need a fast, accurate transport to match. Not sure of the exact force required at this time to push the spindle yet. The objective is a series of shallow passes, at high feed and spindle to lessen the rigidity requirement, improve heat dissipation, and ultimately improve precision of parts produced. Already done, just wish to have it in my shop.

Go to this web site http://www.candcnc.com/ and ask to join the forum, I think Tom can help you, Jeff.