Matrix Heating Element Design: Advice Needed

[depthfish]

Hi, I'll cut to the chase: I've been designing a project that uses a series of MCUs and such, in order to control a series of systems. The device is ment to run from a standard 120 V wall outlet, has a few motor controls, a piston control, but problematically also needs a heating element that is controlled.

The heating element needs to be of size 10cm x 10cm, and have a 32x32 resolution, to be able to heat to between 400-1000 F. It is ment to be so that if a picture of 32x32 resolution is given to it, in black and white it can burn the image onto a medium without any moving parts.

Currently, I've come up with a few designs, but they all have problematic statistics on them. There will be 1 MCU used for each row, for a total of 32 MCUs, and each MCU will have to output a high output constantly for 3-4 minutes during the burn process, at the specified pixel positions, meaning potentially many pixels per MCU at once.

The wire being used for heating is Nichrome(NiCrA) that will heat up to 400-1000 F at Amperages between 2.9 and 5.6.

This has, led to many problems, so my question is, does anyone have any advice, or think they could deduce a design that would work under these conditions, or potentially an alternative for burning a pixel image into a medium within 3-4 minutes, within those heat parameteres.


Thank you for your help, thank you a lot!

 

[anorlunda]

ping @Baluncore can you help with this spring cleaning question?

 

[Baluncore]

There are two real difficulties here;
1. Total power must be available from 120V outlet.
2. The complexity of 32x32=1024 discrete parallel channels.

A 120V single phase outlet rated to 15 amp is limited to 1.8 kW.
If all pixels were on, each element would be limited to only 1.8 watt.
I would question if a 3x3 mm square element could be heated sufficiently with only 2.4 watt.
Each element measures 3mm x 3mm and requires between 2.9 and 5.6 A for 3 minutes.
1.8 watt at say 4 amps, suggests an element voltage of only 0.45 volts.
There is no spare power so the element current must be regulated very efficiently.
The voltage is so low that each channel will require a mosfet based switching regulator with a synchronous mosfet rectifier.
Since connection resistance will vary, the current to each element should be regulated, not the voltage.

Consider 32 identical circuit boards. Each with an MCU to control 32 switching current regulators. The work involved in the assembly of the equipment will be very significant. Every operation will need to be repeated 1024 times.
If the heating elements were mounted on the edge of the PCB then each PCB would need to be thinner than 3mm, which will be very difficult to achieve. Between 33 and 64 connections will be required between elements and the PCB.

I would not take on the above project as I believe it is not economically achievable.

Now, 7 years later, a simple solution, (with moving parts), is now available for less than $1000.
It is a small 3D engraver, fitted with a laser to do the heating.