Request for input on potential firmware configurations for an SLS printer
Greetings,
I have been working with FDM printers for over a year now; maintaining converted XYZ daVinci’s, converting a pair of CTC dual extruder MakerBot clones to Repetier firmware on a RAMPS 1.4 Board, and currently fitting a RigidBot with an insulated enclosure and replacing the extruder and hot end. I am now in the design stages of a much larger project, an SLS printer.
The Printer will have the following features:
- 4040
extrusion Frame
- A 40W
CO2 Laser
- Mirrors
attached to an X-axis saddle and Y-Axis carriage to direct the beam through a
focusing lens onto the print bed
- Temperature
controlled bed by 140W 24V Kapton heater
- Temperature
controlled enclosure by heater coils
- 210x210x210
mm3 Print Volume
- 0.1mm Layer Height
- 0.1x0.1
mm2 X-Y Resolution
- 50mm/s
scan speed
- Ball-Screws
(1204s) attached to NEMA 23 stepper motors running at 4x micro-steps (5.0um/micro-step,
200micro-steps/mm) for X-Y Movement
- NEMA
23 are used in X-Y axis for potential servo replacement in future
- Off
board Stepper Drivers for X-Y Axis Steppers running at 24V
- Supported
Linear Rails (SBR12s) for X-Y guidance
- Trapezoidal
thread screws (TR10x2s) attached to NEMA 17s running at 8x micro-steps (1.25um/micro-step)
for reservoir and Z-axis build platform movement
- 8mm
rods for reservoir and Z-axis build platform guidance
- Roller
to distribute powder
- Roller
Rotational Speed controlled by a NEMA 17 stepper
- Roller
attached to saddle riding along the same rails as the X-axis saddle
- Roller
saddle linear speed done by belt/pulley system attached to a NEMA 17 Stepper
- 5 sets of Max and Min limit switches (X, Y, and Z axis, reservoir, roller saddle)
The layer change process will go as follows:
- Laser will be disabled
- X-Axis saddle will home to the X-Axis max limit switch
- Y-Axis carriage will home to the Y-Axis max limit switch
- Z axis will lower by layer height
- Reservoir will raise required amount
- Roller rotation will be enabled
- Roller saddle linear movement will move powder from reservoir, over print bed, and then any amount of roller powder left will fall into an overflow bin. If moved to far will hit max roller saddle limit switch
- Roller rotation will reverse direction
- Roller saddle returns home to min roller saddle limit switch
Here are a few of the issues I have run into so far in this design. Any input in these area would be most welcome.
- Laser power output is controlled via a PWM signal sent to the laser power supply. Rough calculations put the energy requirements per 0.1x0.1 mm² pixel around 17J. What would be the best way to keep the same energy on a x-y pixel no matter the x-y velocity?
- Is there an in depth explanation on the Laser mode in the Configuration Tool, particularly regarding how to use “E override”?
- What would be the best way to program the Reservoir, Roller rotation, and Roller Saddle linear movement?
- As the Reservoir and Roller Saddle need max and min limit switches, can each be declared as an independent axis (V,W)?
- If not, could the Reservoir and Roller Saddle be set to different extruder tools and use the jam detection as limit switches?
- The leading edge or the Roller will need to rotate at a controllable tangential speed in relation to the print bed. [ (rev/s * 2pi rad/rev * roller radius) ± roller saddle velocity]. I’m thinking that a unique M-code would be best (M-XXX LLL) would look at velocity of the roller saddle and move at an LLL relative tangential velocity. So whenever the roller saddle move, the roller rotates at a calculated speed. Would this be the best way to go about this or am I overthinking it.
- Will a Mega base board be fast enough to control this setup or should a Due board with logic lever converters be used?
I’m currently in the process of drafting up a CAD model of the printer with a BOM. Tentative
first design revision to be ready by the end of next week (2017-03-10).
Thanks for any input that can be provide.
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