laser engraving + hardware

[Robertspark]

Given CNCDrive sell hardware, I was wondering if I could ask a few questions on laser engraving?

I've seen you 1.6W 450nm laser http://www.shop.cncdrive.com/index.php?productID=736

but am curious, what can it do? Can it only engrave (etch / burn) wood and some plastics or is there some limitations in its wattage which can be counteracted by slowing down the feedrate?

I've seen this one for some time on ebay
http://www.ebay.co.uk/itm/Engraving-laser-head-445nm-5W-43mm-aluminium-holder-PSU-CNC-laser-diode/231638465532?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140122125356%26meid%3Dab0dfbced42d4d068932a169bedaf64b%26pid%3D100005%26rk%3D3%26rkt%3D6%26sd%3D231584079211
besides the cost, 43mm dia heatsink and the 43mm aluminium holder, how much different is the 5W at 445nm (same company does many variants, but it gets a little confusing for someone who has just a small interest, but a keen interest to know a little more.

I've read a few websites on laser diodes, and understand the longevity and that they don't like heat etc, but I've never really found a clear guide to what would be best for what? Is there something as too much power, or can you just pwm it down? I would have thought that a 1.6W laser diode with pwm control has a better controllable range than a 5W diode

I was impressed by looking at this image posted on cnczone, and thought I'd ask what does it take (hardware + software + image & quality) to do something like that.


I also saw this and have never known how that is done (and if it requires something different to control the focal distance).


Thanks for your time

Rob

[cncdrive]

Rob,

Laser diodes are controller with current source circuits, this means that the current flow in the diode is controlled around a set value by the regulator/driving circuit.
These circuits are sold with the laser diodes and you can set the value of the electric current you want to flow in the diode and that setting will be your max. power to the diode.
Ofcourse for the different type of diodes can allow different level of current, mostly manufacturers setting the max. on the board with onboard potentiometer and if you turn that up too much will overcurrent and burn your diode, so it is a good idea to leave this potmeter at the factory setting.
The control circuit also have a trigger input which if you driving high it switches the current regulator and therefor the diode on and if you drive it low it switches the current regulator off or vica verse if it has a negative logic.

How the UCCNC makes the control is it has a dedicated laser output which outputs a variable duty cycle PWM signal.
You can connect this PWM to the regulator circuit's trigger input.
The PWM has a fixed frequency of 100kHz, so it changes very fast, much faster than the burning happens, so the workpiece will act as if you burning it with the avarage power, about proportional to the PWM duty cycle.
The duty cycle is the time on/full cycle time ratio in each PWM cycles.
The max duty cycle is defined with value 255, so a 128 value will cause about 50% duty cycle when the PWM is on for the first half cycle and off for the second half of the cycle creating an 50% avarage burning power in the laser diode.

You can switch the laser in the UCCNC with M10 and M11 to on and off.
The M10 has one parameter P, with a range of 0-255 controlling the PWM duty cycle between fully off and fully on.

Also we have a plugin for picture engraving, that plugin reads a picture image, greyscales it and then creating an array with the darkness off each point.
Also there is an option to convert it to black and white image and option to convert it to half tone image.
The plugin does not generate any g-codes, because that would be just a waste of memory as with the array creation method one pixel takes up only one byte space while with creating g-code with unicode characters every letter requires 2 bytes, so the code for large images could eat up even hundreds of megabytes of memory while with the array creation it needs a much smaller memory size.
So, this array is then sent to the motion control API and it generates motion using a constant feedrate on the rows, so the machine can run very smooth, no vibration and what is changing between the points is only the PWM duty cycle, but the feedrate is constant.