E3 - Dot Burn Time (Finding Speed and Power for Photo Engraving)
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- Опубликовано: 29 сен 2024
- If you have difficulties engraving a photo as you expect...
If the settings you found do not deliver an acceptable engraving...
If your engraved photo seems to be overexposed (bright areas all around)...
... watching this video will help you to find the right speed and power for engraving.
Step 1: Test File (Dots-Lines Pattern)
Step 2: Speed and power settings
Step 3: Investigation
Step 4: Evaluation
Step 5: Conclusion
Step 6: Next Improvement
Following this method and also watching the next episode, one will be able to engrave photos on different materials systematically. One can expect to get the photo engravings similar to the digital version.
Each material requires a specific time after being exposed to a pulse of the laser to reveal an engraved mark. This time is found, as an example, like:
Pixel size: 0.1 mm
Engraving Speed: 3000 mm/m (50 mm/s)
Pulse per pixel: 2 ms
The pulse per pixel for each material can be employed to find an approximate speed for engraving a photo with other pixel sizes (LPIs).
Link to get the Pattern with different pixel sizes, Lightburn file and the ribbon of the gradient of grey: www.intocrafts...
1- Import the test file
2- Set the DPI
3- Choose Threshold as Image Mode
4- Select Pass-Through (Cut/Layer Settings)
Link to next episode (Adjusting the photo LEVELS to compensate overlaps): • E4 - Photo Black Level...
Keywords: Photo Engraving, Dither, Jarvis, Lightburn, Atomstack, X20 Pro, Blue Laser, Photo, Image, Engraving
Can provide a link to the first test file you displayed?
www.intocrafts.dk/files/E1.zip
Hi
Thanks for the attribution. As you know all my test work was done on a CO2 glass tube laser where the mechanism of producing dots is more of a balancing act between power, speed and the response time of ther HV power supply. You have no such issues with the diode laser becuse it is all electronic and driven by PWM.
I note you change the speed and power for your test patterns and see differences in dot size. You have done great job of bringing peoples attention to the 1pixel = 1 dot principle and your images on wood are pretty good. However I think you can do even better. Let me explain. I think you have only a single focal lenght lens that you can use , althouhg I have seen diode lasers where you can choose between two lenses. Lenses are not the creatures we can read about in ALL text books. They do not have a FIXED focal point. The focal point changes with speed,power and material and that is one of the tricks you are missing. Try 6000mm/min speed and 550% power just as an example. Look at the row of dashes on the top of your pattern and adjust the FOCUS until you get the thinnest line. Only when you have done this should you start concentrating on the single bottom line dots. BUT before you spend time experimenting with this, read on.
I Ihave a 30 watt RF CO2 machine that works with PWM. I originally failed to undestand many things about PWM technology and my first attempts to create small dots rapidly was total rubbish. even though I was adjusing the focus perfectly for the speed. Your diode laser is the same in that it can only output a singe power Say 10 watts if that's its rating.. Whenever it's on it delivers 10 watts so there is no variation in beam characterestic as with a glass tube machine. The qualituy of a diode beam is pretty poor M2 number and that is why it is wonderfully suited to engraving but pretty inefficient at cutting. Here are the two major factors that allowed me to do photo replication at 1000mm/s
Your pattern is at present 254ppi or 10 pixels per mm . So if you run nat 6000mm/min that is 100mm/s. and because each mm is 10 pixels and you are attempting to make 1burn dot=1 pixel. you are trying to burn 10x100 =1000 dots per second. This if you set your PWM frequency to 1khz then you will be providing 1 pulse per pixel. Once you have this factir correct you can then start changing the dot size by changing thre %power (ie. the exposure time per pulse). This will give you amzing control over the dot size. I feel sure you will be able to drive your machine to its speed limit if you adopt this simple set of rules ie 1pixel=1dot=1 pulse. IF you can achieve reliable single dot size then you will never need to "adjust" your picture to suit the macines capabilities.
Let me know how succeesful this method is for you
Best wishes
Russ
ps this is a 508ppi image done with the Norton white tile idea but I use 100% titanium dioxide rather than paint. This is on a glass tube CO2 laser at 200mm/s but I have recently found out I can run at 800mm/s on my RF machine.. So there's lots of scope for you if you can change your PWM frequency accurately ruclips.net/video/TVgmoN1wljs/видео.html
Hi Russ
Such an honor to receive your comments and inputs. I enjoy watching your videos.
By the way, my diode laser head has a defined pulse frequency (1kHz), which I have found it limiting the speed (considering 1ms per pulse in addition to the time for each dot to be marked on the material).
For instance for wood I have this time per pixel to be around 2 ms and tile 3.5 ms and so forth.
I have not got the chance to try your suggestion for increasing speed and power for a chosen DPI and readjust the laser head to get the thinest line.
Honestly I did not expect that lasers focal length may change by speed.
@@intoCraftsDK
As I mantioned previously , there is no intention to criticise your work because what I know is done with a CO2l aser (and quite a bit of 1 micron fiber laser. work also).
You are one of VERY few diode users people that are trying to understand how to get better by results by a logical process of understanding. Unfortunately there is no way for you to see how your beam is actually performing, only by the results of your work, I have been able to understand how laser beams and lenses interact because 10.6 micron light has a great effect on acrylic where it acurately tells me how the light intensity is damaging material. Regradless of the length of the light waves, the way that lenses treat laser beams will remain constant (and not the same as normal light) because laser beams always have a Gaussian INTENSITY distribution. To be honest, the diode laser beam quality is a poor match for this ideal distribution but intensity profile is still sufficiently intense at the beam centre to create the same sort of lens/beam relationship. Sadly you cannot change your lens to see all the effects I see. You imagine, your lens has a fixed focal point because normal light has UNIFORM intensity lightwaves whereas the laser lightwaves are of variable INTENSITY and that creates properties that optical engineers never consider. Their goal is to transmit images not use light energy to vapourise material....big difference.
The diode laser has some advantages over CO2 and even fiber lasers. The fact that the beam conforms poorly to the Gaussian ideal intensity distribution means it is what I call a "blunt" beam. On a CO2 glass machine it is possible to get a blunt beam by tuurning the power down really low BUT the10.6 micron light is much better at damaging organic materials that the 450nm light from the diode laser. This means it is still very difficult gfor the CO2m laser to scorch wood and leather. The CO2 beam, even when soft, is always trying to cut. Whereas the diode laser is not only "blunt" but it is far less efficient at damaging organic materials because of inefficient energy absorption. Coupled this with the very low power you are limited to and that means you have the perfect engraving tool that is abysmal at cutting.
You say that you are limited to 1000 Hz so in reality that means your best quality will come from making sure you set the product of resolution and speed to match your frequency. Ideally you are looking for 1 dot per cycle . Lets say your smallest dot is 0.15mm then you have 7 dots per mm. That means your image must be set to 25.4mm/0.15mm= 170ppi . 7 dots per mm x speed must ideally be exactly 1000 (Hz). Thus 1000/7= 143mm/s or in your case 8580mm/min. I hope this makes sense. . With your laser you have no control,of power. it is always 10 watts(say). All you can do is change the change the duty cycle with your %power control. This is the feature tha you should play with to achieve a good dot size More power= bigger do, Thus its a balancinbg act for you to get sufficient exposure time (with %power ) but at the asme tme decrease power to get the ideal dot size. . IF you can ever achieve a 0.1 dot then your image resolution can be 25.4/0.1=254ppi. 0.1 dots =10dots/mm . If youbare limited to 1000Hz then your speed now must be 1000/10 =100mm/s or 6000mm/min.
This data comes from my work with the RF laser that operates by PWM . However, I have a variable frequency up tp 20KHz to play with. I totally failed to get quality photo replication until I discovered that the key was making 1 dot per cycle .
Out of interest the middle row of dots in you pattern are non functional with the diode laser. With a CO2 laser there is a response time for the high voltage to build after every switch off event . This big middle row gap is designed to help define the speed . Too fast and some of these dots will not be burnt.
Keep up your great work for the diode community. I look forward to seeing your results.
Best wishes for the New Year
Russ
Can I resize the dot image larger too check better details? I need to engrave using passthrough?
Yes, you can resize them and choose passthrough. Insert the one for 0.08 mm, scale down to half to get a test file for 0.04 mm, or scale-up to double for 0.16 mm, and so on.
But consider the resolution of your laser engraver. For instance, if it is 0.01 mm, resize the test file in a way that you get 0.08, 0.07, …, 0.04 mm line intervals.
Can I make this test without a microscope?
Yes, I am using a magnifier even down to 0.05-0.04 mm line intervals. Though, it depends on the magnification factor/level of the magnifier.
Since you used image, what image mode setting did you use in Lightburn? I'm assuming Jarvis because that is what you used for the photo example shown at the beginning of the video?
Hi Greg,
For some unknown reasons, sometimes Lightburn mixes up with dithering this small file. Please
1- import the test file
2- set the interval
3- choose Threshold and Passthrough
@@intoCraftsDK Thank you!
@@gpowanda and in general, I use Jarvis and some specific cases with an IR laser (1064 nm and 0.03 mm beam size), I have used Newsprint.
Jarvis works fantastic for all photo engravings, just the correct parameters should be found.