servo's not suitable for engraving?

[Rob Bul]

Hi All,
I have bought a big 150W Chinese laser (2,10mtr x 1.60 mtr, 82" x 63")
I'm new to this all and learning every day. ;) However, now i have a problem and i'm confused by the answer i got from my supplier.:confused:
When i want to engrave a text, there is a possibility in lasercut 5.3 to choose the option "bi-directional". Using this i get a ghost image (see photo). My supplier says it is not possible to engrave bi-dir. with my machine because it has servo motors installed. :confused::eek: She also says this is always the case with chinese systems and they can not solve this problem in a short term. Now the main reason for buying this machine was i want to produce big engravings. Doing this in only one direction will cost a lot of time. What should i do? Is there anybody out there who can shine a lite on this??
Thanks!!

Rob


187297

[Scott Shepherd]

I don't know why they would say that, Epilog and Trotec both us servo motors and both engrave in all directions. So if it's "servo" related, it's on their end, not because servos don't do it.

[Rodne Gold]

Its not a servo/stepper problem, its a software problem , there should be a "backlash" setting which will allow bidirectional engraving.
However the machine you bought , saize and power wise , was designed primarily for cutting and not engraving , so if your supplier cant offer a solution for the bidirectional issue , you will have to live with it and use the machine primarily for cutting and slow engraving. The 150w glass tubes are not very good for engraving anyway, they have a large spot size and there are issues with preionization and low current firing.
You can try another control board for your machine ... retinaengrave , both software and a control board, not sure whether it will work with servo motors and your tube but ask em- $1000 or so
www.fullspectrumengineering.com (http://www.fullspectrumengineering.com) supply the system.
http://www.fullspectrumengineering.com/RetinaEngrave.html

[Chuck Stone]

She also says this is always the case with chinese systems and they can not solve this problem in a short term.

I can't say for certain, but this sounds like something that might exit the back end
of one of our bovine friends.
It sounds like a driver problem to me, not anything related to servo motors.
The servo motors don't control when the laser beam is fired, the software and laser
controller do that. And I'm 100% certain that not all Chinese lasers work that way.

[Rodne Gold]

The engravers I have orderd , with steppers , do bidirectional and have tuning functions in software to line up alternating lines

[Gary Hair]

My supplier says it is not possible to engrave bi-dir. with my machine because it has servo motors installed.

My Explorer has a servo for the X axis and it seems to engrave just fine. If you look closely at EVERY inkjet printer out there, they all have servo motors moving the printhead back and forth - somehow they have overcome the "impossible" task of bidirectional printing and have been doing it for quite a few years.

Time to find a new vendor.

Gary

[Rob Bul]

Thanks to all of you. I knew a 150w is not really suitable for engraving but i didn't know this had to do with the size of the dot.
I don't think the supplier can solve this on a short term so i will have to live with it.
Engraving text is reasonable, i'm not sure yet on how a photo would turn out. It would be nice to engrave the globe on a big sheet but i'll stick with smaller items first ;-)

Rob

[Dan Hintz]

You can try another control board for your machine ... retinaengrave , both software and a control board, not sure whether it will work with servo motors and your tube but ask em- $1000 or so
www fullspectrumengineering supply the system.
I have continually found the owner of FSE to be very impressed with himself and his capabilities (he has posted here on several occasions with serious attitude). I have been wholly unimpressed with any work that has come out of his machines... the images he posted (and gloated about) from his machines was worse than anything I had seen before. I believe Mike Null took part in that thread before it was canned for advertising on his part, and he wasn't impressed, either.

[paul mott]

I have continually found the owner of FSE to be very impressed with himself and his capabilities (he has posted here on several occasions with serious attitude). I have been wholly unimpressed with any work that has come out of his machines... the images he posted (and gloated about) from his machines was worse than anything I had seen before. I believe Mike Null took part in that thread before it was canned for advertising on his part, and he wasn't impressed, either.

I share Dan's views on this 100% and I would observe extreme caution if dealing with FSE.

Paul.

[Rodne Gold]

I have no knowledge of the co , just came upon it in my searches , thanks for the heads up. At any rate , on further reading , their system wouldn't work on a servo laser.
Rob , what brand of laser do you have , what control board does it use ? Leeto? What type of tube do you have , a Reci ? (10 month 8000 hr tube) or a stock one?
I'm surprised that they used servo motors in your system as they are generally more expensive than steppers and the only advantage in your system would be very high speed cutting? Was this system originally made for material or fabric processing?
As far as I can gather , apart from spot size , the issue with the more powerful tubes is that they have to be sort of energised and then fired at low amperages for engraving and this seems difficult , they also need Pulse Width modulation (PWM) control to engrave well - I'm not at all certain what all this means tho.
I ordered an 80w machine and a 60w and according to my suppliers the 60w smaller machine will be faster and much better than the 80w larger machine for engraving.
do you have anything like a "backlash" setting in your drivers?

[Dan Hintz]

As far as I can gather , apart from spot size , the issue with the more powerful tubes is that they have to be sort of energised and then fired at low amperages for engraving and this seems difficult , they also need Pulse Width modulation (PWM) control to engrave well - I'm not at all certain what all this means tho.
I know you'll be bumping up against this issue more and more as you order some of the bigger machines you've considered, Rodney. I covered spot size in previous threads (the larger the tube, the harder it is to get a good beam quality, i.e., the beam starts to slip away from a Gaussian distribution). To give more detail... all of the tubes use PWM. Once energized, tubes need a bit of time before they fire (on the order of milliseconds). If you're moving a carriage at 75ips, you could move several hundredths of an inch before the laser actually fires. To avoid this delay, you pre-ionize the tube by providing a very short duty cycle PWM (a.k.a., a "tickle" charge)... not enough to get it to fire, but enough to keep it on the edge of firing. When you're ready for the tube to fire, you increase the duty cycle of the PWM pulse. For large tubes, the amount of power needed for pre-ionization gets quite large, and the line between tickle and fire gets fuzzy.

[paul mott]

I know you'll be bumping up against this issue more and more as you order some of the bigger machines you've considered, Rodney. I covered spot size in previous threads (the larger the tube, the harder it is to get a good beam quality, i.e., the beam starts to slip away from a Gaussian distribution). To give more detail... all of the tubes use PWM. Once energized, tubes need a bit of time before they fire (on the order of milliseconds). If you're moving a carriage at 75ips, you could move several hundredths of an inch before the laser actually fires. To avoid this delay, you pre-ionize the tube by providing a very short duty cycle PWM (a.k.a., a "tickle" charge)... not enough to get it to fire, but enough to keep it on the edge of firing. When you're ready for the tube to fire, you increase the duty cycle of the PWM pulse. For large tubes, the amount of power needed for pre-ionization gets quite large, and the line between tickle and fire gets fuzzy.

Unfortunately not all tubes use PWM and not all tubes use a 'tickle pulse'. Although perhaps true for RF excited tubes, the DC excited tubes, found in the low price end of the China import machines, use a much different technique. The DC excited tube operates by providing a high voltage trigger pulse (around 18,000 Volts) to start the plasma discharge (reducing once the arc has been struck) then controlling the current flow through the tube. Unfortunately they may not fire reliably at low current settings (below 7mA or so). Once fired they can maintain the plasma discharge at low currents but it is this initial hit and miss startup which causes low power operational problems. Some controllers provide a 'pseudo tickle pulse' but because they are not using true PWM, it is of limited effect when compared with the performance of an RF excited tube.

Paul.

[Dan Hintz]

Paul,

You're right, I should have been more specific. It's not PWM in the true sense of the acronym for glass tubes, but the operation is similar, in a manner of speaking. Instead of pumping from 0% power to 100% power, there is a minimum DC bias (the tickle, if you will) and the pulse "width" is increasing/decreasing amplitude of the bias... it's a non-zero-passing PAM (pulse amplitude modulation), so to speak. It takes some finite time to build up the minimum DC bias (the tickle), so you keep it running like that so you're on the edge of ionization.

[Chris S Martin]

Hi Everyone Just to let you know I did buy a laser thru FSE it is not really their laser. I bought a 60W laser thru them. I had more troubles learning LaserCut 5.3 and Corel. The laser seem to be a pretty nice machine. Here is some stuff I have done with the machine. Sorry about the pics some were take with my droid. http://www.sawmillcreek.org/images/misc/pencil.png

[Dan Hintz]

Chris,

Can we get a better shot of the last one (Fightin' Irish and Ohio State)? It may be just the pic, but I see a lot of line width variance, something I came to expect from pictures of items run through a FSE machine...

[Chris S Martin]

Dan it is the pic. I took it with my Droid. Not sure what you mean by line variance. The images were not the greatest to begin with. If you want a better pic I can give you one of the OSU but the Irish I gave away to a friend.

[Peter Odell]

at what speed are you engraving at try slowing it down and cut the power about 10 and see if that don't do the trick

[Mike Null]

Chris

If the school logos weren't vector images then that would explain the irregular lines. I have yet to see a great bitmap of the Ohio State logo. Since my kids and grandkids went to school there I've tried a number of solutions, none of which totally pleased me.

Go Bucks!

[Dan Hintz]

http://www.sawmillcreek.org/attachment.php?attachmentid=187447&stc=1&thumb=1&d=1300651360
The non-painted line between the two painted lines of the 'O'... very irregular. The 'E' is better, but still not completely clean. It could very well be from a poor bitmap, as Mike suggested.

The far right-hand side of the leprechaun's arms is missing colorfill... I'm not sure if that's due to poor colorfill, poor engraving, or poor picture.

The pictures are blurry or too distant to make any definitive statement.