Introduction
Power Supplies
It’s likely that you all at least have a general sense of what a power supply is. A Power Supply is the electrical power source for the 3D Printer that provides energy for all of the electronics – motors, heaters, sensors, etc. There’s nothing realllly special to note about power supplies except for the following:
Can I get hurt by a Printer’s Power Supply?
Probably not. Of course the input from the wall is 120VAC which CAN hurt you (even kill you in the right conditions), but the supply on most printers doesn’t exceed 24VDC. That said, short circuits can get hot and either singe your skin or burn your house down.
Why Doesn’t the Bed & Extruder Always Heat Up At the Same Time?
Heaters can pull a lot of energy both from the power supply and through the control electronics. The energy is greatest when the heater first starts up, so to reduce stress on the supply and control electronics, only one heater is set at a time.
A conservatively tuned heater’s response might look something like this:
Stepper Motors
Stepper Motor’s are the main mode of actuation for 3D Printers. They are inexpensive yet highly reliable motors that can accurately control their angles. The rotating part of stepper motor (the rotor) consists of a permanent magnet, and the stationary (the stator) consists of multiple electromagnetic coils. Turning on the proper coil in the stator will cause a small change in rotation of the output shaft – this discrete change is called a step. The relationship is as follows:
[math]ChangeInAngle=DegreesPerStep\times NumberOfSteps[/math]
Let’s take a look at how these things work:
There are several different shapes and sizes of steppers, which are usually classified by their NEMA form factor. For steppers, the form factor only indicates the frame size of the motor, and actually has no bearing on the torque or speed rating of the motor. Typically RepRap printers use NEMA 17 motors. Almost every printer, regardless of the deposition method, uses stepper motors to move the axes, and in some way control the end effector’s operation.
Steppers are open loop control systems
Heaters
By far the most common mode of heating with electronics is resistive heating. Put a current through a wire, the wire gets hot. Put more current through the wire, the wire gets even hotter. Twinkle twinkle little star, power equals I squared R. Meaning:
[math]P=I^2R[/math]
Where P is the amount if power dissipated by the resistor, I is current, and R is resistance. Typically the duty cycle of the current source is adjusted (How much time it is on vs. off) to modulate the energy input to the heating element. It should be noted that a printers control electronics use some sort of transistor (or solid state relay in large cases) to modulate the current source.
Temperature Sensors
Heating systems in 3D Printers are always closed loop control systems. An example of what the system may look like is:
RepRap printers almost always use thermistors as their measurement mechanism – they’re devices that change their resistance as temperature changes. They’re inexpensive, but not linear (meaning their accuracy changes among different temperature ranges) which can some times be annoying to deal with in programming.
If you ever work with some wild custom / high temperature printers, you might run into devices called thermocouples. Endure this corporate video that explains them:
Here’s a quick “hack” for thermocouples that might just save your skin one day.
Fans
Fans are usually used for one of two purposes on a 3D Printer.
- Ventilation – On some printers the fumes generated by the process can be a little janky – so we use fans to pump (and hopefully filter) out fume-containing air, and pump in clean air. I had to set up a ventilation system with my metal 3D Printer project because the process certainly generated some concerning fumes.
- Cooling – Sometimes underestimated, cooling is an important aspect of FDM printers. Usually, you want your filament to cool as quickly as possible so it does not deform. In addition, fans are used on the cool-end part of extruders to ensure that your filament doesn’t start melting up stream and causing clogs.
Control Electronics
The control electronics for low cost 3D printers is usually pretty straight forward. It consists of a core microcontroller (very commonly an ATMEGA 2560, which is also found on the Arduino Mega) that connects to motor drivers, heater controllers, and sensors. There are all sorts of generic boards that exist for RepRap printers, the most common being the RAMPs (RepRap Arduino Mega Pololu Shield) board, which plugs directly into an Arduino Mega.