Fundamental Hardware Knowledge of 3D Printers

(Purely Informative, Please Share)

2015-5-04

Core Tip: For us as consumers and users, choosing a printer that fits both functionality and price is the most important. Whether to spend 2000 yuan to DIY an open-source printer or 20000 yuan to buy a ready-made CUBE is a personal choice. We do not need to argue about this; what we need to do is understand the various types of printers, know their advantages and disadvantages, so we can make the best choice.

Currently, there are various types of 3D printers available for purchase on Taobao, which can be quite overwhelming. In my opinion, the principles and technologies used in these printers are fundamentally similar. However, as merchants, they will inevitably include some advertising elements for the products they sell (which is understandable). For us as consumers and users, choosing a printer that fits both functionality and price is the most important. Whether to spend 2000 yuan to DIY an open-source printer or 20000 yuan to buy a ready-made CUBE is a personal choice. We do not need to argue about this; what we need to do is understand the various types of printers, know their advantages and disadvantages, so we can make the best choice.

1. Basic Knowledge

1) The 3D printer consists of the following components:

1) Body Frame: The body frame is the biggest difference among various printers. There is a principle that must not be violated: structural rigidity! Most printers primarily use triangular or rectangular shapes as the basic structure. Since the printer operates with the X and Y axes constantly moving, to ensure the printer’s accuracy, the impact of the nozzle’s momentum on the body should be minimized. The solution is to reduce the nozzle’s mass and increase the body’s rigidity. The advantages and disadvantages of various body structures will be discussed in detail later in this article.

2) Mechanical Axes

The mechanical axes are the components that enable XYZ axis movement, mainly consisting of three types:

Rectangular Coordinate Type: The XYZ axes are perpendicular to each other, with the XY axes typically positioned by a synchronous belt connected to a stepper motor, while the Z axis is controlled by a lead screw.

Triangular Claw Type: The mathematical principle is similar to the rectangular coordinate type, using Cartesian coordinate principles. The XY axes are mapped to the positions of three claws using trigonometric functions.

Servo Rotation Type: The mathematical principle used for the XY axes in this type is based on polar coordinates (if you don’t understand, see the explanation below). Unlike Cartesian coordinates, the control program has completely different code.

Theoretically, regardless of whether it is Cartesian or polar coordinates, the representation of a point in space is the same, meaning that the printing accuracy of these printers is consistent. There is no difference in quality between polar and Cartesian coordinate systems (don’t be misled by merchants!).

3) Control Circuit

The basic structure of the control circuit consists of a microcontroller, stepper motor drivers, control for the nozzle and heated bed using MOSFETs, and various external interfaces.

There are currently two main types of microcontrollers:

1) Using Arduino MEGA open-source hardware as the base component, with specific parameters available here. An integrated circuit board is added outside the microcontroller to include stepper motor drivers, MOSFETs, and other peripheral circuits. The main representatives are Ramps and Ultimaker. The advantage of this design is reduced maintenance costs, as the control board is divided into core, expansion, and driver boards, allowing for easy replacement of damaged parts. Additionally, Arduino MEGA has abundant resources, and its expansion capabilities are greater than those of ATMEGA644P and ATMEGA1284 chips. The downside of this design is the high initial investment cost and larger size compared to a single control board (which is self-explanatory, as adding an expansion board increases both size and cost!).

2) Directly using AMTEL ATMEGA644P, ATMEGA1284, etc., to integrate the microcontroller and control circuit into one board. The main representatives are: Sanguinololu, Printrboard, GEN6, Melzi. The advantage of this design is its smaller size and slightly lower initial cost compared to the first type. The downside is that maintenance is more difficult, and those without a certain level of electronic repair knowledge and experience may struggle. For beginners, the likelihood of being able to repair this type of board is almost zero.

4) Nozzle and Heated Bed

The nozzles are mainly divided into two types:

One is the J-head;

The J-head is lightweight and suitable for structures with high precision requirements or weak mechanical axis load capacities (triangular claw type uses this). Additionally, it is relatively inexpensive on various platforms.

The other is the Budaschnozzle

This type of nozzle has both active and passive cooling methods, with the MK7 nozzle using an active cooling structure. Machines from Makebot and Reprappro typically use this nozzle structure as the default.

Of course, there is no inherent superiority or inferiority between these two structures; it is only a matter of suitability. When DIYing, we can recombine based on our actual needs.

5) Extruder: The extruder is mainly divided into direct drive extruders, gear extruders, and liquid extruders.

We commonly use direct drive and gear extruders:

Gear Extruder: A stepper motor drives a small gear that turns a larger gear to extrude filament. The advantage of this setup is that the current and parameter requirements for the stepper motor are not too high, and the use of gears for reduction increases the extrusion force. The downside is that this setup is more complex and can be a bit troublesome to maintain.

Direct Drive Extruder: The stepper motor directly connects to an extrusion wheel for filament extrusion. This requires a stepper motor with a higher torque. The advantage of this structure is its simplicity and ease of maintenance, but it is not suitable for long-distance extrusion (when the distance between the nozzle and extruder is long, some printers try to reduce the weight of the nozzle for better precision, which may require placing the extruder on the body and using PTFE tubing as a conduit between the nozzle and extruder. In this case, a gear extruder is preferable).

6) Power Supply: Generally, ATX power supplies (computer power supplies), switch-mode power supplies, or Xbox360 203W power supplies are used. You only need to consider whether the power supply is within 12-24V and has a current rating above 8A. The maximum power consumption components of the entire printer are the nozzle and heated bed, so it is best to choose a quality computer power supply or switch-mode power supply. These can usually be found in local electronics stores, typically priced under 100 yuan.

2. Mathematical Knowledge of Motion Control in 3D Printers

Cartesian Coordinate System:

The Cartesian coordinate system is a general term for both rectangular and oblique coordinate systems. The two axes intersect at the origin, forming a planar affine coordinate system. If the units of measurement on the two axes are equal, this affine coordinate system is called a Cartesian coordinate system. A Cartesian coordinate system with two axes perpendicular to each other is called a Cartesian rectangular coordinate system; otherwise, it is called a Cartesian oblique coordinate system. The Cartesian coordinates represent the position of a point in space but differ from rectangular coordinates, as the two can be converted into each other.

Polar Coordinate System:

A coordinate system consisting of a pole, polar axis, and polar radius in a plane. A point O is fixed in the plane, called the pole. A ray Ox is drawn from O, called the polar axis. A length unit is then defined, usually with angles measured counterclockwise as positive. Thus, the position of any point P in the plane can be determined by the length ρ of the segment OP and the angle θ from Ox to OP. The ordered pair (ρ, θ) is called the polar coordinates of point P, denoted as P(ρ, θ); ρ is called the polar radius of point P, and θ is called the polar angle of point P. When restricted to ρ≥0 and 0≤θ<2π, every point in the plane except the pole O has a unique polar coordinate. The polar radius of the pole is zero, with the polar angle being arbitrary. If the above restrictions are removed, every point in the plane has infinitely many sets of polar coordinates. Generally, if (ρ, θ) is the polar coordinate of a point, then (ρ, θ+2nπ) and (−ρ, θ+(2n+1)π) can also serve as its polar coordinates, where n is any integer. Some curves in the plane have simpler equations when expressed in polar coordinates. For example, the polar coordinate equation of a circle centered at the origin with radius r is ρ=r, and the polar coordinate equation of an equiangular spiral is ρ=aθ. Additionally, the three different conic sections: ellipse, hyperbola, and parabola can be represented by a unified polar coordinate equation.

Conversion between Polar and Cartesian Coordinates:

To convert between polar coordinates and the Cartesian coordinate system (rectangular coordinate system), the two coordinates ρ and θ in the polar coordinate system can be converted to Cartesian coordinates using the following formulas: x=ρcosθ

y=ρsinθ

From the above two formulas, we can determine how to calculate the polar coordinates from the Cartesian coordinates x and y.

θ=arctan(y/x) (x ≠ 0)

In the case of x=0: if y is positive, then θ=90° (π/2 radians); if y is negative, then θ=270° (3π/2 radians).