Project: Laser Cutter (CNC)

[Jerry]

Ever since TechShop went under one of the things that you found was really useful was a laser cutter. We had two different ones. An Epilog Helix 45W machine and a Chinese built Rabbit with a 80 watt laser. The chinese made machine was actually pretty good. Not as polished as the Epilog but in some ways was actually superior.

So I decided to build one. Not going to start from scratch though. At my friends surplus store two Hamilton Starlet Microlab fluid handling robots showed up. Its kind of a light duty gantry robot that can do repetitive tasks. A company that builds electron microscopes and FIB machines had bought these to try and automate loading wafers into a SEM. Didnt work out. So they are basically brand new. Here is a video of one:



He had it for a couple months and there was zero interest in it. The software is proprietary and you have to go to them to take a class before they will even sell you the software. Even the company that made it would only offer a pittance for it. The other day it hit me that it would be perfect for a laser cutter. Its completely servo driven. Maxon motors throughout. Rexroth slides on the Y and Z axis and THK on the X. Travel in X and Y is a little more than 36" x24"



Pic of the main board. Uses dual Infineon processors. Nice 41v, 15A Astec power supply.


The encoder for the X axis, magnetic, .01mm resolution.


The Y and Z axis. The Y uses a little pancake style brushless motor from Maxon. 30W, 40v or so. It is coupled to a spinning nut that drives it along the leadscrew. The lead screw looks to be 7 starts, 1/2" per turn, 1/4" teflon coated.


I got a couple servo drives off ebay. They are made by Elmo. Pretty neat little drive, they will run either brushed or brushless motors and you can control them with step and direction pulse inputs in positioning mode. They also have dual loop support so you can have a encoder on the motor and a linear encoder on the axis.

[Jerry]

Today I got wheels mounted on the base this afternoon and gutted the old electronics that I cant use.

Mach3 can handle cutting but it does not do well with raster engraving. G-Code is just not capable doing it efficiently since it needs to vary the beam power (PWM or analog signal to the laser power supply). There are ways to do it but you get huge code that runs slow. There are a couple options. There is the controller used in the majority of the Chinese machines, the Leetro MPC6515. Its what was on the Rabbit we had at techshop. Worked OK, software was kind of klunky but did a good job. It outputs step and direction signals to the stepper drivers and controls the laser. Has a whole lot more I/O that isnt used.

There are two new controllers out there now, another Chinese one, looks similar to the old one, this is supposed to be a new replacement for the MPC6515:

http://www.lightobject.com/4-Axis-DSP-C ... -P321.aspx

There is another one made here in the US. They did the hardware and software. Looks promising (about 2/3rds down the page):

http://www.fullspectrumengineering.com/ ... 2-40w.html

There is one more, and open source controller that used an XMOS uC. But I have not seen any activity since March on the project.

http://www.buildlog.net/cnc_laser/xmos_controller.php

[Doug Coulter]

Do you think this thing is going to have the angular stability to allow the laser to be a bit away from the substrate without that making trouble?
Or are you just going to put the head real close to the work?

All ways have some play after all. I've worked with rabbits -- basically a fast Z-80, and a bear to program as you have to deal with their
preconceived notion of a real time opsys, and theirs sucks. PIC's have hardware PWM and it takes one assembly instruction to update the pulse width, or two
if you want full resolution. And there we get my opsys, which at least is a lot more flexible, but it's a job of work to do anything really complex from
scratch no matter the uP you use. Here we tend to put the heavy lifting into easy to write code on a PC and let the uP just do the realtime stuff
as the PC tells it to - kind of divide the problem up in such a way that the uP takes moderately high level commands (so the communication bandwidth
doesn't have to high with such low latency) and the PC generates those commands. In other words, use each for what it does the best.

[Jerry]

The lens is fixed focus so you either bring the work up to the lens or bring the lens down to the work. I have been looking at using the existing z slide to move the lens up and down to the work but that will add more mass to the cutting head. So what I will probably end up doing is making a motorized shelf that moves up and down. That's how most of the commercial machines do it, optically simpler.

Rabbit is the name of the Chinese brand of laser cutter, not the processor it uses. The controllers usually use a texas instruments dsp to control everything. I have no interest in building my own controller. Hardware is one thing, then you have to deal with software that takes your files and allows you to do what you want with it.

[Doug Coulter]

I had kind of guessed that -- when working with such big functional blocks you can't really get down to the level of detail it takes to
write custom software -- for a one-off. Unless that's going to be a life-hobby, and in your case, I kinda doubted that one, too much other
interesting stuff to get on with!

[Jerry]

Plus I couldnt do it if I wanted to!

I dont know the hardware or programming any where near well enough to even attempt something like this. Plus there are others doing the heavy lifting so no sense in reinventing the wheel.

Got notice my servo drives shipped today. Need to figure what I am going to do for feedback on the Y axis. I have a heidenhain enclosed linear scale but if I use it I will loose a couple inches of travel. I am looking at using one of the strip type instead.

Need to go through all my surplus optics stuff, I know i have some mirror mounts in there someplace.

[Jerry]

The servo drives showed up last week and I am now trying to figure out just how I want to do this. I had though of making a lifting table for the Z axis but now I am thinking of just putting the optics on the existing Z axis on the gantry. My only worry is the little Y axis motor will not have enough oomph, its only 30W. Ill just keep things light and see what happens. I can always throw in a small DC PM motor if I am not happy.

One thing of note. I will never use Steppers again if I dont have to. The price of PM servo drives has dropped to a point where they are completely in line with steppers. The drives from http://cncdrive.com are a good example.

Also trying to figure out what I want for a controller. The Rabbit we had used the MPC6515. It was not that bad but the software sucked eggs. There were always little issues in importing files. Once you got it in it was pretty decent and had a few advantages over the epilog software. But I am mostly looking at the controller from Full Spectrum. That looks right now to have the most promise. Though I have been around the block with new hardware that never lived up to expectations (Gecko G100, SmoothStepper).

I am probably going to install a 40W tube in the top of the machine and wrap the beam along the outside to the gantry. Since I believe the length of the tube is longer than the longest dimension of the enclosure I will probably have to install it diagonally. I have a bunch of kinematic mirror mounts lying around waiting for something like this and some real light ones that will be perfect for the flying head.

I think the next thing I really need to do is sit down and lay out boards that breakout the 30 pin flat cables that it uses to get power to the X axis encoder and up to the gantry. Also need to find a source of the FFC cables, 1mm pitch, 8 conductor, 40" Long.

Heres a pic of some of the controls. The two servo drives, Fuse holders, SSR and timer for the exhaust fan and some auxiliary relays.



Here are some of the mirror mounts I have:

[Jerry]

Getting some things slowly sorted out. I got some silicone rubber insulated high flex wires that will feed the Z axis and Y axis motors and encoders. They have micro D connectors on the end but I can work with that. I have a couple spare cable sets so I can use one for the connectors on the end. Lucky for me the cables have one female and one male. Otherwise I would have to replace the connectors are these guys are almost $100 each!


Micro D connectors by macona, on Flickr


I got the encoder for the Y axis today. Heidenhain LS403 series scale and reader. This is an exposed scale so there will be no friction resistance like the normal enclosed glass scales. That little motor is going to need all the help it can get. The scale outputs a 1v peak to peak quadrature sinusoidal analog signal. I happen to have one of the Heidenhain sine to ttl interpolator boards which converts the signal to something I can use. I am not sure what the multiplication factor is with the board I have, guess I will find out! The sensor head also has magnetic limit switches built in which is pretty cool. The scales are used. Hoping one is still good. The encoder strips mount in an aluminum rail that is glued to the machine. This allows removal for replacement or cleaning. Heres the data sheet on the linear encoders:

http://www.heidenhainweb.com.ar/bajando ... 522421.pdf


Heidenhain Scale by macona, on Flickr

[Jerry]

Got the boards laid out. I attached screen shot of each of them

The main board breaks out the two 30 pin FFCs coming from the gantry and utilizes the existing linear encoder on the X axis. It also has a relay that will kill motor power to the servos in an estop condition and also can either kill power to the laser power supply or drop the enable line. The board uses mostly .1 spaced connectors except for a couple phoenix style connectors on the higher power section. The board is also meant to support different encoders for the Y axis with connection for an interpolation unit. Jumpers will bypass those connectors if it is not needed. The board is 4"x4"

The arm board takes the two 30 pin cable and breaks them out to two 16pin IDC right angle connectors. One for the Y encoder and one for the Y motor, Z mot, Z enc, and limits. The connection for Y motor and halls are grouped in the connector in case a fixed Y motor is mounted to the gantry itself. There is also a 8 pin FFC connector for the light bar that is on the machine already. The board is 1.77x 4"

The shuttle board has the DB-15 for the heidenhain encoders I have. Also a 8 pin connector for other encoders. Connectors with power for Y and Z homes are there. as well as a spare connector if we want to replace that little brushless motor with a brushed type. Also a connector for the existing maxon motor on the Z axis. Board is 2x2.5"



main board by macona, on Flickr




arm board by macona, on Flickr




shuttle board by macona, on Flickr

[Doug Coulter]

Very pretty Jerry! Good to see this one coming along, it's going to be fun. I always get more excited about adding some new capability than merely refining one I had already myself.
Not sure if that's the way I should be, but I am. What PCB layout software did you use?