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Author Topic: Optical Registration Mark Reading With Mach3  (Read 17738 times)

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Offline stirling

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Re: Optical Registration Mark Reading With Mach3
« Reply #20 on: January 29, 2014, 11:47:59 AM »
Am I correct in thinking that the non-linear distortion is introduced when the print is affixed to the substrate? i.e. every piece will be "differently non-linear"?

OR

Is the non-linearity introduced at the print stage i.e. A batch will be non-linearly distorted with respect to the original but the individuals within a batch will be identically distorted?
« Last Edit: January 29, 2014, 11:50:15 AM by stirling »
Re: Optical Registration Mark Reading With Mach3
« Reply #21 on: January 29, 2014, 12:53:04 PM »
Ian,

I would very much like to pick up where you left it at that conversation and I promise I won't disappear any day soon.

To address the question of the distortion here's a more in-depth view.

The technology that we use, and most others do is solvent inkjet printing. What basically happens in the printing process is that a piezo-electronic printhead shoots tiny droplets of ink pigment in an acetone solvent. The solvent "burns" into the material and leaves sort of a relief into which the pigment gets into and gets stuck there.

The printing process itself doesn't necessarily stretch the material, we are talking about self-adhesive vinyl here since it will be applied to a rigid substrate, but it leaves it susceptible to the stretching during application since the vinyl is much softer now.

If you leave the vinyl to gas off for 24 hours or so the ink will dry, the solvent gases will fume out and the stretching effect from the solvent is mostly gone.

The other stretching though comes from the mechanical forces that it endures during application to the rigid substrate.

If you have never seen solvent vinyl without the liner on it is almost rubery.

This is what the application looks like - http://www.youtube.com/watch?v=-u4TxTBU80g#t=51

As you can see the vinyl is quite stretchy so the distortion really depends on the direction you are applying the vinyl in. There may be some distortion in other directions as well but I think that it would mostly go in the direction of the application.

Now in this industry when you are doing serial cutting either via punching as is done in offset or via hand you leave some bleed. Bleed is basically some extra space or color around the image which is a tolerance so that if the cutting misses a bit that you don't get a white part there.

This image explains it perfectly:





To see just how much of a real-world problem the distortion really is tomorrow I'm gonna do a few prints, apply them straight out of the printer, ungassed, to a substrate and try cutting them based on a single cross-marker and then we can proceed from there.

Am I correct in thinking that the non-linear distortion is introduced when the print is affixed to the substrate? i.e. every piece will be "differently non-linear"?

OR

Is the non-linearity introduced at the print stage i.e. A batch will be non-linearly distorted with respect to the original but the individuals within a batch will be identically distorted?

The majority of the distortion would happen during application but I have reason to believe that either each or at least some of the pieces would be differently distorted. The reason for this assumption is that the distortion (stretching) is a result of mechanical forces applied on the vinyl during application. So for example you could apply some parts with less force and you could maybe pull a bit harder on a certain part and that could cause the distortion to increase on that part but not on the others.


Here is one thing I don't understand though, optical registration of print marks and cutting based on them is nothing novel in our industry. Pretty much any plotter cutter you buy has this option, even those shabby Chinese ones so it can't be that hard...I mean we are talking about a $500 or so and they cut the printed vinyl without fail every single time.

Here is an example of how that works - http://www.youtube.com/watch?v=jV1v8dRdsn4#t=158

It prints 4 of these marks (the black dots) total, one on each corter of the print then the cut head scans each dot and based on those it starts contour cutting the print based on the vectors you defined in your design software.

Same goes for the Zund and iCut system. You have to print these reg marks out and the camera scans these and based on them it cuts the print, no matter the distortion.

What I can't understand is how do they account for the distortion based on those registration marks ?

Demonstration of how the iCut system works - http://www.youtube.com/watch?v=s3MeHLluzC0

An even more impressive example, an iCut system on a laser cutter - http://www.youtube.com/watch?v=F4OLzJsakag
That must be less than a millimeter in precision and from the description:

"Printed signs, displays or POS materials can be cut on an individual basis using laser technology and i-cut®. The cutting line therefore follows the exact printed specification. With other methods, slight distortions of the printed design create unsatisfactory results. However, i-cut® is an intelligent, easy to use system which recognizes any distortions in the printed design. No matter whether it is a linear or non-linear distortion or a rotation, the cutting path is adjusted automatically and dynamically. The cutting lines therefore always perfectly match the printed design on both flexible and rigid materials."

EDIT: Added the iCut demo
« Last Edit: January 29, 2014, 01:06:07 PM by xxtoni »
Re: Optical Registration Mark Reading With Mach3
« Reply #22 on: January 30, 2014, 02:22:02 PM »
I didn't have time to perform the cut tests today but will do so early tomorrow so it doesn't get away.

Tweakie (hopefully you're still following this) the 2 laser setup to get a crosshair seems a bit daunting to me because of the need to angle them and well...use 2 lasers.

Would a single laser like this work or am I missing something important ? - http://www.ebay.com/itm/New-650nm-5mW-Laser-Cross-Module-Diode-w-driver-/260839502067?pt=LH_DefaultDomain_0&hash=item3cbb3ef0f3
Re: Optical Registration Mark Reading With Mach3
« Reply #23 on: January 30, 2014, 04:17:20 PM »
Nevermind I mixed something up.

Just re-read Tweakie's post. I thought that you used two lasers for getting the cross instead of one. Mea Culpa.
Re: Optical Registration Mark Reading With Mach3
« Reply #24 on: February 01, 2014, 02:19:35 PM »
Why don't you use microscope camera, it is much easier to pin-point marks?
Optical Registration Mark Reading With Mach3
« Reply #25 on: February 02, 2014, 02:38:22 PM »
Look at the sheet cam forum.   It looks like Les is working on an idea that will do this.   It uses a camera to trace edges and the exports that.   

Steve


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Re: Optical Registration Mark Reading With Mach3
« Reply #26 on: March 07, 2014, 08:31:43 PM »
Resurrecting a dead thread here...

We have several newer CNC machines and one old multicam which I converted to mach 3 when the factory controller electronics crapped out.  As we use it less and less, we have decided to make it a print/cut only machine.  We already do this successfully on routed substrates in conjunction with our flatbed printer with very accurate results.  We have print/cut thousands of dibond boards by just dropping them on the bed and using the stops we machined in as fences to align the board.  Fast, easy and accurate. 

I just purchased a Donek drag knife and want to start cutting our roll substrates on the machine.  When un-mounted, the distortion is fairly linear over a distance of less than 12 feet (our bed is 5'x10' anyways).  So the stretch and rotate work arounds that already exist will work just fine.  What we really want to do is automate the registration mark detection vs using a web cam or pointer.

Like the OP, we have a Mimaki vinyl cutter with registration mark detection which works very well.  The system works like this:  It has a light/dark edge detecting camera/sensor and two "L" shaped marks of between 10mm and 40mm long and 1-3mm wide are printed at the corners of the print.  Mind you, all this system does is address skew (rotation) and stretch.  The operator positions the sensor in the corner of the L and begins the automatic routine.  The camera scans approximately 80mm left and upon hitting the edge of the line, returns to its starting point and then travels 80mm up to find the horizontal line.  This gives the machine an origin corner so to speak.  It then travels along the X axis until it hits the edge of the next horizontal line for the upper corner mark.  It relies on the marks length and the operator loading the media vaguely straight to insure that it intercepts it.  If the media is too skewed, it will miss the mark and fail, but you have to be incredibly lazy to load it that far off.  Upon finding the horizontal edge, it advances a few mm forward and then finds the vertical edge and thus is able to divine the top corner inline with its new found origin corner (confusing I know, but when you see it it is simple).  It returns to the first corner and runs the same routine on the y axis.  Ultimately, by finding the coordinates of the 3 outer corners of the file, it can calculate linear stretch and skew and the job begins.  This system is pretty bullet proof.

I think many of us could benefit from a collaborative effort to get a system like this working in mach 3.  The commercial turn key options are obnoxiously expensive for the quality of the machines.  Compare what you get with an Esko or Zund vs a Biesse for the same money. 

Here are my thoughts on potential solutions:

Create a stand alone arduino based edge detecting camera.  When edges are located, have it simply go +5 feeding an input to your mach 3 interface (we use one the CNC 4 pc boards and its very easy to IO from, I think it's the C32?).  There is a healthy repository of open source machine vision type projects in the arduino community and it would entirely divorce the edge finding logic from the PC piece and mach 3.  Thus, all it would take is a simple macro that responded to the input from the arduino based edge finding sensor.

My other thought is to run in parallel on the PC a basic piece of machine vision software and use a sort of virtual IO to do the same as above. 

Am I just crazy or is this imminently doable?

Offline Tweakie.CNC

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Re: Optical Registration Mark Reading With Mach3
« Reply #27 on: March 08, 2014, 03:02:05 AM »
I think it is a brilliant suggestion Eforer and it could become a very useful plugin for Mach3.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Optical Registration Mark Reading With Mach3
« Reply #28 on: March 09, 2014, 01:21:56 AM »
I should have the sensor mounted up and on the machine early next week. Does anyone want to help me with the macro?
Re: Optical Registration Mark Reading With Mach3
« Reply #29 on: March 12, 2014, 06:35:13 PM »
I have the sensor board working well, meaningful output difference as it passes over a reg mark and I am lighting up an output based on some simple evaluation of the incoming data.  I'm ready to start playing with a Macro.  Is there a way to make a sort of development environment so that I don't have to mess about on my mach 3 installation out in the machine shop?