what is the resolution of the servo motor positioning？----20151117

[Thunder laser - Tom]

Hi, what is the resolution of the servo motor positioning? I understand laser focus limits useful resolution to 500 dpi (or 1000 dpi with HR head), but I am interested to learn about servo resolution in terms of steps/mm
Thanks
Matt

Answer:
Hi Matt
The smallest position is 0.0791mm for the resolution of servo motor
Now our laser controller is set to 7.91(micron) length/step(per pulse) for servo resolution.
So when the controller send a pulse to the driver/motor, the motor will moves 0.0791mm distance.
But the laser head does move by the belt to pull it, and the motor is assemble a gear that it can be fited with the belt
The belt and gear exsits a little bit gap, so sometimes the moving distance has a little error due to they have a little gap while moving

For summary, the movement of the laser head for a single step is 0.0791mm, with some variation for belt stretch, backlash, gear tolerance, etc.

Hope it will be help for you

[Matthew]

0.0791 mm gives 321 dpi resolution. If the normal head gives 0.1mm line width, don't you just end up with a gap between lines when using HR head with its 0.05mm dot size?

[Thunder laser - Tom]

Hi Matt
Yeah, 0.0791 mm gives 320 dpi resolution,
The standard head gives 0.1mm dot size that is the "original" size of the laser beam, if it lasers into the surface of material, it will not only 0.1mm size
But we make the engraving job, that the laser dots are overlap on the material surface.
Then the HR head will gives a 0.05mm dot size that is also the original size of the laser beam.
So no, the gap between lines is 0.7(the smallest gap) even if using the HR head with moving for y-axis or x-axis.

[Thunder laser - Tom]

Hi Matt
Sorry i wrote it wrong with the gap between lines is 0.7mm(the smallest gap)
It should be 0.007mm(7.91um) for the smallest gap with moving for y-axis or x-axis

Also the smallest moving step is about 0.00791(7.91um), not 0.0791, sorry
So it should gives 3200DPI resolution, sorry i sent the wrong data to you bofore
Now i corrected it for you

[Matthew]

OK, this makes much more sense to me.

I am having two issues right now:

1) Focus. I cannot seems to achieve 0.1 line width. In the attachment PIC1 you can the line widths at various focus points. 6mm is best, but it's still very wide at about 0.2mm. I'm using the normal (non HR) lens that is spec'd for 0.1mm dot diameter. I am running fast (500mm/sec) and very low power (20-30%). But as you know laser power isn't very reliable below 20%.

2) Line spacing. In PIC2, you can see a 5x5 mm box that I drew in RDCAM. In this test, I had the scan interval set to 0.1mm. The box size is confirmed to be 5x5mm. A 5x5 box with 0.1mm scan I would expect to have 50 scan lines. But here you can clearly see there are just 26 scan lines. This suggests that the scan interval is actually 0.2mm instead of 0.1.

I have a similar problem with a bitmap (see PIC3). I import a bitmap that is 28 pixels tall and the resolution is specified at 254 DPI (254/0.1mm scan). With scan interval set to 0.1, the finished size is correct at 2.8mm, but you can see again that the scan interval appears to be delivering 0.2mm/step. That is, the bitmap is constructed with 15 scan lines instead of the expected 28 scan lines.

So, my questions are thus:

1) What dot size should I expect in anodized aluminum with the stock lens with perfect focus?
2) When I have scan interval set to 0.1mm, I would expect each pass to cover 0.1mm. That does not seem to be the case. What does the scan interval setting actually mean?

Thanks!

[Thunder laser - Tom]

Hi Matt
Thank you for your reply
For your two issues
1. Focus. yeah, our website that write the standard lens can lasers a 0.1mm width dot, but this is testing after a kind of special equipment, if the laser beam is shoot into the material, it will be burn and be enlarged on the surface, laser beam is likely a flame. it will burning the surface of material, so you can't get it 0.1mm width really on the material.
In the meantime, its width is difference with different material, for example, Anodized Aluminum and wood, you can make a test.
2. 5X5mm box, you set the interval to 0.1mm, so you get 26 can lines are right, why i said that right?
1. i assume the line is 0.1mm,
2. the interval(the gap) is also 0.1mm.
so 5mm/(0.1+0.1)=25 lines
you should understand what is the interval, it meant that the distance of both lines, so you did not add the interval for 5mm length.

For your Bitmap, 28/254 * 25.4 =2.8mm, set the interval to 0.1, the laser will gives you 15lines that is right. as i proved.

[Matthew]

OK, so the line width is 0.2mm on anodized aluminum with the normal lens, and that is as you expect.

On the same material, will an HR lens make a dot size that is half of the normal lens? In other words, can I expect a 0.1mm line in anodized aluminum using HR lens (compared to normal) with everything else being the same?

Also, does the software always assume the line width is the same as the interval width? That is, if you enter 0.05mm for the interval with an HR lens, then lines are drawn 0.1 apart?

[Thunder laser - Tom]

Matt
In the theory, On the same material, with HR lens makes a dot size that is half of the normal lens
But different material that will gets a different actual result
The second questions, it is not the same
For example, if we cut 0.1line in wood using HR lens, it will not the same with the anodized aluminum
Also, does the software always assume the line width is the same as the interval width?
No, the interval width is a distance that the motor does movement, but it will may difference if the laser beam shoots into different material.
The laser cuts a line that it's the laser beam width on the material surface. but the real interval width is a distance that motor does movement

[Matthew]

OK, so basically the motor will move 2X of the interval setting always, is that right? So if interval setting is 0.075mm then the lines will be 0.15 mm apart. Or, if interval is set to 0.2mm, then lines will be 0.4mm apart. Is that right?

[Thunder laser - Tom]

Matt
The motor will move the interval setting always, then add the laser line width, so you can only see that 5x5mm only gets 26 lines
The laser lines are not the same with the interval, for some material, they are the same, but for material, the laser lines will bigger than the interval
As i said before, the laser will makes a different laser line widths for different material, do you understand? because of the laser beam will burning the material.