Almost all 3D printers use stepper motors to locate their axes. Their job is to accurately locate the print head and build the surface, and measure the filament when the filament is extruded from the hot end.
Once you understand a simple fact, how they accurately control the shaft feed and speed is easier to grasp:. As the name implies, stepper motors do not rotate as traditional motors do. Instead, they move steppers repeatedly with small fixed increments, which appear in the naked eye as the motor rotates continuously.
The size of each step is determined by the motor. The power behind these steps comes from the stepper motor driver. In the next article, we will introduce the operation of this amazing technology.
Stepping motors simulate continuous rotation by performing separate fixed steps. From the time of manufacture, these steps are part of the structure of stepping motor.
Separation of a circle
The built-in stepping value of the motor is called the stepping angle of the motor. The stepping angle of the motor can reach 90 degrees, which means that the motor will rotate 360 degrees in four steps. However, the more typical stepping angle is 1.8 degrees, which means that 200 steps (360/1.8) are needed to complete the rotation.
Stepping angle is obtained by the placement of motor coils and the construction of magnetic poles in the rotor. This is why the stepping angle of the motor will not change after assembly. In this YouTube video, you can see the animation simulation of the structure and operation of the stepper motor.
Stepping motors are composed of independent coils called phases. They produce a constantly changing electromagnetic field, which is "chased" by permanent magnets in the rotating motor shaft. When each phase is electrified in turn, the poles of the rotor jump or align with them step by step. Therefore, by exciting the phase in proper order, the shaft looks like a normal motor. It's just that the motor doesn't turn. It's trampling. Each step is a fixed degree, which is determined by the structure of the motor as described earlier.
If it is known that it takes 200 steps to rotate the motor 360 degrees, and the motor is connected to a guide screw with a spacing of 1 mm (1 mm conductor rotating each time), each step of the motor moves the shaft forward by. 005 mm. Therefore, the number of steps required to reach the exact position can be easily calculated without feedback.
The number of steps required for calculation is managed by the controller. Then the work that drives these steps is left to the stepping driver.
The complexity of stepper motor drivers varies. Modern drivers can be combined with many different types of stepper motors. Users can usually configure specific motor configurations at installation time. But in general, stepping motor driver is relatively simple equipment.
Stepper motor drivers can be as simple as a dozen components. The following figure depicts a driver like this. According to the original configuration, the work of the component is to respond to the step command pulses from the machine controller and convert them into the correct switch mode needed to drive the stepping motor. This mode excites the phase in proper order and drives the motor in one direction or another at a time.
The type and size of stepper motor seems infinite. In order to adapt to this situation, most modern stepping motor drivers can adapt to different motor types.
The main factors to consider when choosing stepper motor driver are the required torque and precision. Torque is a factor of stepping motor size. Here, the driver must have the ability to generate the step current required by the motor. Accuracy requires small steps or gear systems. Choosing compatible stepping angle motor and micro-step driver is the key part of the equation. Instructables user Fernando Koyanagi has a very interesting discussion on driver design.
The last point is that all stepping motors run in STEPS. It is necessary to generate steps in the correct order and size so that the axis can reach its target position. The motor will advance at the same step angle with each pulse.
Stepper motor drivers must generate these pulses in the proper order of magnitude and phase, so that the driven shaft can be used as a fine tuned vehicle. If we think that the machine controller is the GPS of the vehicle, then the driver must be the engine.