MakerBotControlSystem
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Contents |
MakerBot: Control System Design, Implementation and Characterization
Time to brush off some of that rusty old control system design knowledge I once majored in.
Goals
My goals will be to:
- Describe the MakerBot thermal, electrical and mechanical system in terms of a state-space model.
- Model said system using the GNU Octave free open-source software (FOSS) suite of tools.
- Design test and measurement criteria and data to generate a set of parameter estimation functions to calibrate the control system model.
- Generate discrete-time state-space octave model.
- Implement discrete-time algorithm using microcontroller or DSP (as required).
The Model
Controllable Parameters
Extruder
- Heater On/Off (PWM control code)
- DC Motor Voltage (PWM control code)
- Nozzle aperture diameter (fixed)
- Incoming filament diameter (fixed)
X Axis
- Stepper Velocity (step rate)
Y Axis
- Stepper Velocity (step rate)
Z Axis
- Stepper Velocity (step rate)
Observable Parameters
Extruder
- Relative Nozzle Temperature (thermistor ADC code)
- Closed loop
- Calibrated Nozzle Temperature (thermocouple based digital thermometer)
- Open loop
- Incoming filament position (with encoder wheel/sensor)
- Closed loop
- Incoming filament travel (callipers)
- Open loop
- Outgoing filament diameter (callipers)
- Open loop
- Outgoing filament length (callipers)
- Open loop
- Outgoing filament mass (scale)
- Open loop
- Possibly closed loop with build platform integrated weight cells.
X Axis
- Endstop activation
- Closed loop
- Position (ruler)
- Open loop
Y Axis
- Endstop activation
- Closed loop
- Position (ruler)
- Open loop
Z Axis
- Endstop activation
- Closed loop
- Position (ruler)
- Open loop
Variable Definition Table
Subsystem | Variable | Units | Description |
---|---|---|---|
Global | Tra | Celcius | Room Ambient temperature |
Subsystem | Variable | Units | Description |
---|---|---|---|
Build Platform | Vbp | Volts | Build Platform, PWM generated voltage through nichrome |
Tbp | Celcius | Build Platform temperature, ADC sampled thermistor | |
Tbc | Celcius | Build Chamber temperature, ADC sampled thermistor |
Subsystem | Variable | Units | Description |
---|---|---|---|
Extruder | Vem | Volts | Extruder Motor, geared DC, PWM generated voltage |
θwe | Degrees | Rotational Extruder displacement of drive motor shaft. | |
Veh | Volts | Extruder Heater, PWM generated voltage through nichrome | |
Ten | Celcius | Extruder nozzle temperature, ADC sampled thermistor | |
Dif | mm | Input Filament diameter, entering extruder | |
Def | mm | Exiting Filament diameter, emerging from nozzle | |
Den | mm | Exit Nozzle diameter |