2021-07-22 00:40:40 +02:00
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# Using PWM tools
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2021-03-26 16:25:09 +01:00
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This document describes how to setup a PWM-controlled laser or spindle
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using `output_pin` and some macros.
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## How does it work?
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With re-purposing the printhead's fan pwm output, you can control
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lasers or spindles.
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This is useful if you use switchable print heads, for example
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the E3D toolchanger or a DIY solution.
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Usually, cam-tools such as LaserWeb can be configured to use `M3-M5`
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commands, which stand for _spindle speed CW_ (`M3 S[0-255]`),
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_spindle speed CCW_ (`M4 S[0-255]`) and _spindle stop_ (`M5`).
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**Warning:** When driving a laser, keep all security precautions
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that you can think of! Diode lasers are usually inverted.
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This means, that when the MCU restarts, the laser will be
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_fully on_ for the time it takes the MCU to start up again.
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For good measure, it is recommended to _always_ wear appropriate
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laser-goggles of the right wavelength if the laser is powered;
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and to disconnect the laser when it is not needed.
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Also, you should configure a safety timeout,
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so that when your host or MCU encounters an error, the tool will stop.
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For an example configuration, see `config/sample-pwm-tool-cfg`.
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## Current Limitations
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There is a limitation of how frequent PWM updates may occur.
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While being very precise, a PWM update may only occur every 0.1 seconds,
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rendering it almost useless for raster engraving.
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However, there exists an [experimental branch](https://github.com/Cirromulus/klipper/tree/laser_tool) with its own tradeoffs.
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In long term, it is planned to add this functionality to main-line klipper.
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## Commands
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`M3/M4 S<value>` : Set PWM duty-cycle. Values between 0 and 255.
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`M5` : Stop PWM output to shutdown value.
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## Laserweb Configuration
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If you use Laserweb, a working configuration would be:
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GCODE START:
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M5 ; Disable Laser
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G21 ; Set units to mm
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G90 ; Absolute positioning
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G0 Z0 F7000 ; Set Non-Cutting speed
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GCODE END:
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M5 ; Disable Laser
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G91 ; relative
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G0 Z+20 F4000 ;
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G90 ; absolute
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GCODE HOMING:
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M5 ; Disable Laser
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G28 ; Home all axis
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TOOL ON:
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M3 $INTENSITY
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TOOL OFF:
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M5 ; Disable Laser
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LASER INTENSITY:
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S
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