Monitoring/Controlling Stepper output for Laser Engraver
Jim Fouch
Posts: 395
I bought a laser engraver about 5 months ago and can't leave it well enough alone...
I want to be able to see the exact position of the laser head. Similar to how most CNC machines do. Right now you have to eyeball where you are going to start a job. I want to use the propeller to monitor the signals going to the stepper motor controller for each of the 3 axis. There are two outputs for each, Direction & Step. It looks like the fastest it send steps is about 15 microseconds.
My thoughts are to place a propeller in line between the embedded system and the stepper motor controllers. I think I should have plenty of time·using pasm to read the inputs, calculate position, and send outputs to the controllers when I just·want to monitor. Then when I want to control the steppers myself, I will·simply ignore the inputs from the embedded system and create my one.
Some may ask why in the world·would I want to dig into a perfectly working system this way.... Well I want to create a system for measuring objects. A laser engraver is thought of as only an output device. But with the other hardware there, a measurement system could easily be made. My thoughts are to place a small camera on the laser head and use a Propeller backpack to place a cross hair in the center of the video and position information. As the user moves from position to position the location of each reference point can be precisely calculated.
My machine has a working area of ~ 27" x 14" x 8" so a full size laptop could be placed inside and measured.
One neat thing I've found out is the device is USB based and is located about 15 feet away from the PC I use to control it. They have a USB dongle that the PC software needs to see to operate. Without the dongle, the whole laser is pretty much a boat anchor. So, instead of keeping the dongle in the PC, I placed a usb hub inside the laser and plugged the dongle & the laser into the hub. Now when I put a USB Prop Proto board for this project, I'm able to program & open a terminal with the Prop Board without removing it from the laser.
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Jim Fouch
FOUCH SOFTWARE
I want to be able to see the exact position of the laser head. Similar to how most CNC machines do. Right now you have to eyeball where you are going to start a job. I want to use the propeller to monitor the signals going to the stepper motor controller for each of the 3 axis. There are two outputs for each, Direction & Step. It looks like the fastest it send steps is about 15 microseconds.
My thoughts are to place a propeller in line between the embedded system and the stepper motor controllers. I think I should have plenty of time·using pasm to read the inputs, calculate position, and send outputs to the controllers when I just·want to monitor. Then when I want to control the steppers myself, I will·simply ignore the inputs from the embedded system and create my one.
Some may ask why in the world·would I want to dig into a perfectly working system this way.... Well I want to create a system for measuring objects. A laser engraver is thought of as only an output device. But with the other hardware there, a measurement system could easily be made. My thoughts are to place a small camera on the laser head and use a Propeller backpack to place a cross hair in the center of the video and position information. As the user moves from position to position the location of each reference point can be precisely calculated.
My machine has a working area of ~ 27" x 14" x 8" so a full size laptop could be placed inside and measured.
One neat thing I've found out is the device is USB based and is located about 15 feet away from the PC I use to control it. They have a USB dongle that the PC software needs to see to operate. Without the dongle, the whole laser is pretty much a boat anchor. So, instead of keeping the dongle in the PC, I placed a usb hub inside the laser and plugged the dongle & the laser into the hub. Now when I put a USB Prop Proto board for this project, I'm able to program & open a terminal with the Prop Board without removing it from the laser.
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Jim Fouch
FOUCH SOFTWARE
Comments
I've always wanted to play with a Laser Engraver. Team it up with a good rasteriser and you could go into interesting architecture.
"See this block of concrete? Well we'll turn it into an apartment block". "And then the residents pass down this corridor, through the rotating knives"..
Using the device for point scanning would be a great application if you could do it without slicing your laptop into tiny pieces. Far more accurate than the ball-contact scanners conventionally used in converted X-Y tables.
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Life may be "too short", but it's the longest thing we ever do.
The laser should be even better, and with out the chance of loosing position.
Yeah, with·an output of 50W, it could do a real job on laptop. I'll have to be more·careful not to run the·head into an object·and scratching it.
Some people use these to·engrave pictures/artwork into their·electronic devices like laptops and iPhones. One of the reasons, I really want to position the·head·prior to running a job. Having a design·an 1/8" off on a $400 cell·phone·can make for a bad day...
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Jim Fouch
FOUCH SOFTWARE
A simple digitizer for a flat surfaces is an arm with two joints and two encoders, easy on the propeller.
I like the idea of hacking the laser cutter, I have one at work and would definitely consider it.
Graham
Could you use a drill press laser pointer to find the start of your job?
http://www.woodcraft.com/Product/2005475/16259/Drill-Press-Laser.aspx
You could always use the Propeller to turn it off/on
Jim
It already has one, but it's not very accurate. When you raise/lower the table it moves the red dot laser. Also when you're cutting a clear material, it's hard to see the actual location.
My idea is to have the camera in a fixed location in reference to the actual laser. This offset can be programmed into the software to offset the job. This way you will always be certain where the job will begin to cut.
I'll try to upload some pictures of the project·tonight.
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Jim Fouch
FOUCH SOFTWARE
Graham
I also use the electrical tape and a quick zap method of alignment [noparse]:)[/noparse]
Graham
I haven't found any issues with getting a job precisely aligned using the red dot pointer. I always set up the print driver to align the job to the top-left corner of the page. If I'm engraving on, say, a 6" x 6" tile, I'll make sure to include an outline of it in the drawing, but invisible so it doesn't cut. That way I can set the red dot to where the X and Y stops intersect and slide the tile against them. With that method, I get perfect alignment every time.
-Phil
For $6K it's a lot cheaper than others on the market. So far I'm pretty happy with it. I'm sure I'd get better service/support if it was one from the US, but I can only budget so much for this kind of thing.
I saw the Epilogs when I was CES last year and that's where I got the idea of getting a laser engraver. It's the most useful tool I have ever bought. Great for making brackets and enclosures. I've been working with cutting different rubber products. Most people buy these for an engraving business. I'm using it more for prototyping of products and such. I'm soon to enlist the help of the wife to start running the machine. So far she doesn't like it much because it stinks up the house.....lol (Yes I have an exhaust fan installed to blow most of the stink at the neighbors.
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Jim Fouch
FOUCH SOFTWARE
What kind of material are you using to make things like brackets? Is it something you can bend into shape, or do you join multiple pieces? If the latter, how do you join them?
Ditto the smell. With the exhaust fan running, everything is fine until you open the lid; then, peeeww! I guess, if I weren't so impatient, I could wait to open the lid until the fumes have been evacuated...
Like you, I don't know how I survived so long without one of these machines!
-Phil
I'm mostly using Acrylic that I can heat and bend. It cuts so nicely with a laser. I've tried some fiber reinforced plastic, but it soots up a bit too much. I've got some delrin, but haven't cut it yet.
I'm controlling the exhaust fan with the propeller (pun intended, lol) so it comes on when a job starts and runs for a minute or so to clear the smoke. The way the machine was build, the exhaust runs all the time. I'm also going to use the prop to display the coolant temp.
The prop is so well suited for this kind of thing. I will use one of Rays 4.3" touch screen to make a control/display for the system. The default UI that came with the unit leaves a lot to be desired.
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Jim Fouch
FOUCH SOFTWARE
Delrin cuts very nicely. I was hoping to be able to score thin sheets of it with the laser so I could bend them cold; but that didn't pan out, since they tend to crack along the score. Ditto the laminates. I've tried both glass-filled epoxy and paper-filled phenolic. They both ash up rather badly.
I assume you've been warned against cutting PVC or any other chlorinated materials, right? The fumes are not only extremely toxic, but highly corrosive. Epilog voids their warranty if the machine has been used on PVC.
-Phil
I found a good deal on some magnetic sheets, and tried to cut it today and that doesn't work too well. It creates a dust that magically sticks to all the metal/steel parts...lol
I've use Santoprene rubber with very good results. I've found. I bought 4-5 different kinds of rubber sheets for making my own gaskets and rubber washers.
For the acrylic, I use a solvent to weld the parts together and it works very quickly and make a pretty strong part. It dries 100% clear. Only problem with acrylic is it is somewhat brittle and can't be used for a high stress part. I make robotic camera mounts and this laser will work great for making the small parts for that.
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Jim Fouch
FOUCH SOFTWARE
The Santoprene tip is a good one. Thanks!
-Phil
To echo what Graham was talking about, automated manufacturing equipment, like SMT pick and place machines, often uses a fiducial camera to determine the position of a board within the machine. The board would have two or more fiducial markings, or fiducials, in known locations at opposite sides of the board. The fiducials are designed to be easy to find the center of by analyzing the image with software. They are usually a reflective disk inside a larger non-reflective disk. The camera is attached to the head and has a known offset from the functional part of the head. (e.g. the laser or a pick and place nozzle)
Using a fair amount of trigonometry, you can measure the position of the fiducials relative to the working area of the machine, and determine the location and rotation of the board within the work area. This makes it so that all of the operations are repeatable, and you can take a half-finished board out of the machine, then load it back in later to finish it. The hardest part would be the machine vision software to recognize the fiducials. I know the Propeller can handle it, and I think Phil has done some other neat machine vision examples that would be worth looking at.
The pick and place machine that we have takes an 8-bit gray-scale image of the fiducial, then converts it to a 2-bit image based on a user-settable threshold, to classify every pixel as reflective or non-reflective. It then removes all clusters of pixels under a specified size and fills in any gaps of pixels under another specified size. This means that if the threshold was set to five, any pixel will only be considered reflective if it is part of a contiguous group of five or more pixels that are also reflective. It then finds the center of the remaining reflective pixels, and considers that the center of the fiducial. The center is the point where a quarter of the reflective pixels are up and to the left, a quarter are up and to the right, a quarter are below and to the left, and a quarter are below and to the right. It works quite reliably, especially if you can control the lighting to get the best contrast possible.
We have an older pick and place machine that has stepper motors instead of brushless servos. Even though it could count steps to measure the position of the head, it uses a linear glass encoder to be absolutely sure the readings are accurate. It also uses the encoder to double check the position that the motor should be at to detect motor errors. The screw or belt that drives the axis can also have irregularities that wouldn't show up if it only counted steps.
These machines are ridiculously accurate though, so counting the steps may be more than enough accuracy for your needs. I have used our pick and place machine's fiducial camera to measure ultra-fine pitched pad sizes on circuit boards that we were evaluating. If you do want a second opinion on the position of the head, you can add an encoder to the motor shaft for more accuracy.
Keep us up to date on your project, it looks really interesting.
-- David Carrier
P.S. I bought a Ninja 250R in October, and I really enjoy it.
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Jim Fouch
FOUCH SOFTWARE
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Jim Fouch
FOUCH SOFTWARE
For now, I'm going to write the driver to simply send the position back to the PC using a serial terminal. Later I'll add an LCD display.
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Jim Fouch
FOUCH SOFTWARE
after further thought, how accurate has this engraver been for you? the reason i ask is that those red, green and white wires coming back into the side of the controller board, im just wondering if those were intended for encoder inputs, tied directly to the mechanics of the x, y and z of the equipment. seeing that and the way they were wired up, makes me think that the encoders were removed and the feedback pulses are just taken from the output of the controller. yes it would work, but what happens if the belt jumps a tooth or somesuch?
What is the accuracy of this cutter in the XY plane?
Cheers!
paul rowntree
Yes, there are no encoders. It simply HOPES that everything works. It's been pretty accurate. The samples that I cut have been with with .01" and since the laser is about .01", I'd say it's pretty good. On a CNC machine feed back is way more important because you're touching the material and encountering resistance. The laser is never touching the material and as long as you don't overpower the steppers, you *SHOULD* always be where you think you are. Could be one of the reasons this is $6K and other 50W lasers are $12K-$15K.
Paul,
I'd have to look up the specs say .0004", but the laser is .01" wide so it's hard to say. Also remember depending on the material, there is some melting involved. So .0004" would be hard to prove. They normally rate them at .001", which is somewhat misleading.
I also have a small CNC router that I use, but Haven't turned it on since I got the laser about 5 months ago.
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Jim Fouch
FOUCH SOFTWARE
www.fullspectrumengineering.com/co2laser.html
We use a digital isolator that can take 5v or 3.3v inputs·and even include a 40pin socket for the Propeller on our control board.
We're coming out with a full blown Propeller Windows driver but still some time before it's done that allows you to directly print from Windows.
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