Problems with raster engrave

[dadelon]

Every time I try to engrave a raster image it comes out short (squished, distorted). The width of the engraving is fine, but the height is always short. I can make it a little better by increasing the scan interval, but it reduces the quality of the engraving when i do. Vector images come out perfect so I don't think it's a problem with step length. Any ideas?

[lanoph]

Hi,

Can you please upload a picture.

Thanks

[dadelon]

Sure! Here is an example using a checker board pattern.

The border was done by "Frame Cut". The width of the pattern is correct, but the height is short.

I've uploaded the source file as well.

Checkerboard_pattern.png (3.55 KiB) Viewed 4930 times

[twehr]

Try reducing your Y acceleration speed.

It is likely that the y drive is not keeping up (mechanically) with the steps. I have had the same issue in the past.

The reason it does not show up on vectors is that the vectors are made up of hundreds or thousands of steps. Loosing a single step while coming us to speed is not noticeable on a vector, but loosing a single step on a single step instructions means the head did not even move. So if that happens 20% of the time, your image will be about 20% short by the time you get to the end of the scan.

Reducing your Y acceleration will slow the entire processing time, but not to any great amount. And since we are only reducing acceleration speed, it won't have much affect on vector movements, either. Most of the time of a scan is spent doing X movement, so that is the one that needs to be optimized.

[dadelon]

Thanks twehr, I tried your suggestion. I slowed down the Y accel to 10 mm/s with a jump off speed of 1. Unfortunately, it didn't seem to make any difference (aside from processing time being a bit longer). Side by side the two engravings look the same.
I've also tired making the step interval an even multiple of my machine's distance/step but that didn't seem to help either.

[twehr]

Sorry that did not do it for you. Obviously, it is a mechanical issue with the Y axis.

Try slowing down the entire job (just as a test), to say 20-30 mm/sec tops. If that works, try faster and faster till you get the max speed it can handle, then set your y MAX speed to that. (Of course it will affect your vector speeds as well, but you could swap in and out different settings files between vector and scanned runs.)

If you are not able to correct by changing speeds, look at the physical aspects of the y axis - belt wear, toothed pulley wear, etc.

Hope you can find it. Let us know when you do.

[dadelon]

I got it! Turns out it was a problem with my setup. Don't know what I was thinking when I said my interval was an even multiple of my distance per step.
I was working through the exercise of ramping up Acc speeds when I noticed. Everything is working perfectly now with Acc speeds of ~1500mm/s on Y, plenty fast the vector work that I will do. Thanks for your help Tim.

[twehr]

Glad you got it going. (It always seems so simple after you figure it out. )

[maralb]

I got it! Turns out it was a problem with my setup. Don't know what I was thinking when I said my interval was an even multiple of my distance per step.
I was working through the exercise of ramping up Acc speeds when I noticed. Everything is working perfectly now with Acc speeds of ~1500mm/s on Y, plenty fast the vector work that I will do. Thanks for your help Tim.

possible to know the type of resolved problem
I do not succeed to resolve in no way
the designs in raster are not uniforms in height
thanks

[dadelon]

Here's a better explanation (I hope ) of what I did to correct my problem.
First, in my machine config on the Y axis I have a Step Distance on 22.86um. This is the distance that the axis moves for each step of the motor. It's very important that this number is correct and since my machine is home made my number is probably different than yours. Make sure you have the right number for your machine.

To fix my problem I had to make sure that the "Interval" setting for each layer was an even multiple of my Step Distance. With my Step Distance of 22.86um (that's about 0.023mm) an Interval value of 0.046mm works well. 0.092 works pretty good too. Values that don't evenly divide by 0.023mm cause the image to distort along the Y axis.

[twehr]

To fix my problem I had to make sure that the "Interval" setting for each layer was an even multiple of my Step Distance. With my Step Distance of 22.86um (that's about 0.023mm) an Interval value of 0.046mm works well. 0.092 works pretty good too. Values that don't evenly divide by 0.023mm cause the image to distort along the Y axis.

Dennis,

Thanks for posting this. I got your email with the file and will look at what you have posted here, first. While your posted solution makes some sense, I am not sure how that is affected by the different behavior at slow vs fast speeds.

Thanks again!

[maralb]

my problem and on the carrier with many nodes vector
at the end of the cut not to return to precise ground zero
to obtain not aligned mixed designs vector/raster.

possible loss steps

[twehr]

my problem and on the carrier with many nodes vector
at the end of the cut not to return to precise ground zero
to obtain not aligned mixed designs vector/raster.

possible loss steps

Anytime you are doing vectors that cannot return to the same spot, you are losing steps. If the displacement is horizontal, you are losing x steps. If the displacement is vertical, it is losing y steps. If both, then obviously it is in both directions.

If it only happens when doing many very short vectors, then it probably is caused by acceleration speed to high. If it also happens with longer vectors, it is probably the speed you have set.

Try slowing down BOTH acceleration and speed till the symptoms go away. Then increase speed till you get good results with the kind of overall speeds you want. Then start increasing the acceleration till the symptoms return. Then back it off a bit.

If you can't get rid of the symptoms by slowing down the acceleration and the speed, then it is likely your jump off speed is too high. Back that off and see what happens.

In the end, it is just a matter fine tuning these three things in the affected axis to match your physical machine and motors.

Let us know how it works out for you.

tim

[baccus61]

How did you get on with your problem????
Did Tim's advice help.
Wouldn't it be nice if everyone came back and posted whether their answer was correct for others to learn from.
I guess no news is good news on the forums.

Steppers suffer from mid band resonance and the DSP and some stepper drivers go a long way to fix the problem. If you are trying to push it too fast then you will definitely get into trouble. Sometimes if you go faster then the problem goes away but more than likely you will need to go slower. Your steppers probably don't have dampeners on them anyway to help with this problem.
A lot of people see the professionally built European and American lasers and want their laser to go just as fast, and sometimes they can with the DSP, but some machines just won't cut it, so to speak.
I would follow Tim's advice and try slow then increase until you get what you are after.
Rich.

[maralb]

have not resolved the problem the problem is the motors that to insufficient brace to lowland speed.
nobody knows the difference between a motor to 2 Phase and a 3 motor Phase?

I see from the images that nearly all the producers use motor and drive 3 phase, which to be the reason? more precision?

to excuse my language to use the translator