CNC Laser Engraving 8bit Shades of Grey 445nm

[VDX]

... this application is '2.5D' with 8bit-height data to support the finest details of up to 2000dpi (maybe up to 4000dpi) of the flat top ... but is capable of 3D too, if fed with the right height-field data

Viktor

[JJWMACHINECO]

... this application is '2.5D' with 8bit-height data to support the finest details of up to 2000dpi (maybe up to 4000dpi) of the flat top ... but is capable of 3D too, if fed with the right height-field data

Viktor

Are you interpreting your DPI by the pulsing of your laser, because that calculates to .0005" per pulse if you are. Is your laser's focal point 12.7 Microns, or are they overlapping each other at 2000 DPI?

[VDX]

... no, it's the pixel-size/-distance - for engraving with a CO2-laser it's a pixel diameter (and laser spot diameter too) of 25.4 microns for 1000dpi, the fiber-laser can be beam-expanded+focussed down to 12 microns for 2000dpi resolution (or even down to 6 microns for 4000dpi).

The CNC-drivers resolution is even finer, so the software calculates the step count between two laser shots to get the raster resolution ...

Viktor

[SVP]

I read topic twice and still can't understand difference between TTL and analog drivers. I read manual for flexmod p3, spec for many drivers from ebay and found nothing concrete

If you use TTL input and you driver work in "blink" mode you diode just blink 10000 or more times per second, right ? As many time diode light, as darker image/dot you receive.

If you use analog input what to do driver ? Same ? Blinks very fast ?
Or driver send to diode current proportional to input voltage ?
for example
for 1V at input driver send to diode 100ma
for 2V input - 200ma
for 5V - 500ma
?
At this way diode should be always on, but "burn power" changes for every point .

I can't understand why people care about input signal and don't care about output

[VDX]

... there are different driver techniques to get variable power on a spot.

- analogue = diode output power varies according an analogue input signal - sounds great, but needs a precise calibrating process to get a proportional burning effect over the complete regulating range and moving speeds.

- analoque controlled PWM = the input signal is analogue, the output will be a pulsrate with a constant frequency and varying pulse-lengths - sounds really good too, but the fixed frequencies are mostly in the stepping range, so can interfere and cause inhomogenities when engraving fine details.

- TTL = the laser is simply set ON or OFF according to the voltage level of an input pin ... simply controlling for cutting lines, but not so good for engraving fine shaded details.

There are some other (more application specific) driving methodes, but they weren't so common as the three above and often 'internal developed' know-how, not meant for public disclosure.

I'm driving my lasers with a special 'analogue adjustable' PWM modification to get better precision ...

Viktor

[SVP]

Thanks for info.

Then analogue technique(with some calibration) how i understand best choise ?

May be you can give advice how i can choose driver with this type of control ?
I see many drivers andall contain same SMD components, only price and description differs, but i not found spec/description any information about output, only about input.

for example i cannot understand difference between 10$ drivers

http://www.ebay.com/itm/Analogue-Las...item3cfe966785

http://www.ebay.com/itm/445-450nm-1W...item4d3364a6e7

and 30+

http://www.ebay.com/itm/450nm-2W-Blu...item3cf65c80c9

https://innolasers.com/shop/index.ph...t_loop_monitor
etc

And i have absolutly no idea how understand where analogue output used

[VDX]

... can't say anything about the drivers without a proper datasheet.

A 'pure' analogue driver is only usefull, when you manage to calibrate the effective power into a perfect linear dependancy to moving speed ... otherwise you'll get inhomogenous engraving/burning when accelerating, so you won't be able to get good results with fast moving speeds.

Best would be a pretty fast (~1MHz) PWM driver with analogue input - this is much easier to adjust for speed and acceleration ...

Viktor

[SVP]

> ... can't say anything about the drivers without a proper datasheet.
Same situation, but in datasheet for FlexModP3 i also not found this information.

May be someone else can give me advice/direct link to proper driver with analog OUTPUT please ?

> A 'pure' analogue driver is only usefull, when you manage to calibrate the effective power into a perfect linear dependancy to moving speed ...
> otherwise you'll get inhomogenous engraving/burning when accelerating, so you won't be able to get good results with fast moving speeds.

Hmm... what kind of calibration needed ?
I think about current/output power calibration. (if you sent to laser 100ma and you receive 0.1w power, then if you send 1000ma you can receive not 1w but 2w or more). This calibration not looks really hard. Yes its not linear but can be easy checked(burn some 5x5mm square with different ma and choose 8-16-256 different). Calibration table can be filled and not hard script can be writen for adjust power.

You mean problem with syncronization XY and diode power, right ?
As i understand if i take almost any CNC system(i have moderate expirience with CNC lathe/mills) and just use g-code where XY give me position and Z(or A) give me power i not need think about moving speed and syncronization between XY and Z.
Speed almost always constant (if constant speed mode ON), in trajectory angle good CNC add some radius movement for maintain constant speed.

What wrong here ?

***
What difference between TTL and "analogue controlled PWM" in you scheme ?
TTL just on-off-on-off, its clear.
PWM "the output will be a pulsrate with a constant frequency and varying pulse-lengths" - looks same ?
Difference only in frequency ? (1MHz for fast pwm) ?

[VDX]

>
Speed almost always constant (if constant speed mode ON), in trajectory angle good CNC add some radius movement for maintain constant speed.

... this is true for constant speeds without acceleration/decceleration at start/stop.

But for most CNC's this are the start/stop-speeds with around 10-20mm/s max only! -- with acceleration and nonlinear calibration to get constant burning regardless of actual speed you can engrave with up to 200mm/s on a rigid gantry with servo motors.

This 'nonlinear calibration' is pretty complex and many companies can't do it correct, so they simply limits the speeds for engraving compared to plain cutting.

I'm using a special hardware-PWM-mode inside my laser-drivers which 'automatically' adjusts the effective output power to the stepping rates of the motor-drivers, so the software can simply switch the laser ON/OFF without any fuzz with analog or PWM controlling

What difference between TTL and "analogue controlled PWM" in you scheme ?
TTL just on-off-on-off, its clear.
PWM "the output will be a pulsrate with a constant frequency and varying pulse-lengths" - looks same ?
Difference only in frequency ? (1MHz for fast pwm) ?

Normal PWM is a constant frequency with adjusting the ON time for the analog input -- low analog input voltage results in shorter pulses, compared to the pulsing frequency ... higher analog input voltage elongates the ON time until max, so the laser will be ON continuous.

Problems occures, when the pulsing frequency is nearby or in the range of the motor stepping frequencies or the processing time of short line segments - then you'll get impredictible burning results ... so better use PWM frequencies much higher than the clocking/stepping frequencies of your machine.

For my machines it's roughly 30-80kHz stepping frequencies, so >200kHz PWM frequencies for controlling the laser needed ...

Viktor

[SVP]

> ... this is true for constant speeds without acceleration/decceleration at start/stop.
Its true almost always if you use proper motors and setup.
If you use "constant speed" option, milling machine not stop at angles, instead it software
create small radius at angle and maintain speed. (If you use "exact stop" you machine stop
after every line and have better precise, but speed not constant).

200mm/s really nice speed, but i think power of laser diode(1-2W) not enough for speed 10meter per minute.
CO2 better for fast speeds (10m/minute and more)

My target for first iteration near hobby speed (20-30mm/s). I plan use really old CNC chassis for this evaluation,
but i can use 100-200w servo motors and new electronic.

>I'm using a special hardware-PWM-mode inside my laser-drivers which 'automatically'
>adjusts the effective output power to the stepping rates of the motor-drivers,
>so the software can simply switch the laser ON/OFF without any fuzz with analog or PWM controlling

Its really good solution, but i not ready to design PCB for one-two engravers and try to purchase something from market.
But as i see i need sacrifice my needs, because typical datasheets contains nothing about type of control

PS. I reread documentation for FlexMod P3 and now 90% or so sure about "true analogue" control inside this driver.
Not all 100% clear, but i try this driver for first iteration. UPDATED: No way to purchase FlexMod as i see, i found
many topics concerning problem with availability /distributor. Still looking replacement.