**Introduction to Stepper Motors**
A stepper motor is an electromechanical device that converts electrical pulse signals into angular or linear displacement. It receives a sequence of pulses as input and produces corresponding incremental movement or stepping motion. In normal operation, it has a fixed number of steps per revolution, and when running continuously, its rotational speed is directly proportional to the frequency of the input pulses, independent of voltage fluctuations or load changes. Due to its compatibility with digital control, it is ideal for use with microcomputers.
**(1) Types of Stepper Motors**
There are three main types of stepper motors:
(1) **Variable Reluctance (VR) Stepper Motor**: These have a simple structure, low cost, and small step angles, but poor dynamic performance.
(2) **Permanent Magnet (PM) Stepper Motor**: They offer higher torque and better dynamic performance, but larger step angles.
(3) **Hybrid (HB) Stepper Motor**: Combining the advantages of both VR and PM motors, hybrid steppers provide smaller step angles, higher torque, and excellent dynamic performance. They are considered the most advanced type of stepper motor and are sometimes referred to as permanent magnet induction steppers.
**(2) Working Principle of Stepper Motors**
Figure X1 shows a schematic of a three-phase reactive stepper motor. The stator has six evenly spaced magnetic poles at 60° intervals, with windings connected to phases A, B, and C. The rotor has 40 teeth, each spaced 9° apart. The stator also has five teeth on each pole, matching the rotor’s tooth pitch. Because the number of teeth on the stator and rotor are different (30 vs. 40), a misalignment occurs. When phase A is energized, the rotor aligns with the stator teeth, and when phase B is activated, the rotor rotates by 3° due to reluctance torque. Repeating this process in the order A→B→C→A causes continuous clockwise rotation. Changing the sequence to A→C→B→A reverses the direction. This mode is known as single three-phase operation, with a step angle of 30°. Other modes like double three-phase or six-phase reduce the step angle further.
The step angle can be calculated using the formula:
θb = 360° / (N × Er)
Where N is the number of phases, and Er is the number of rotor teeth.
**(3) Characteristics of Stepper Motors**
- Stepper motors require pulse signals to operate; without them, they remain stationary.
- They can start and stop instantly, making them ideal for precise control.
- By changing the pulse sequence, the direction of rotation can be easily reversed.
**How the L298N Drives a Motor**
In a stepper motor driver module, the TLP521 optocoupler provides isolation and interference resistance. The L297 chip controls the motor’s direction via high/low signals on pin 17, while pin 18 serves as the stepping clock input. Pin 19 selects between full-step and half-step modes. Pin 10 enables/disables the motor. The L298N contains four logic drivers and a high-voltage, high-current dual H-bridge to control forward and reverse motion. Diodes are used for freewheel protection, and a 7805 voltage regulator supplies 5V to the controller and the L298N chip. However, prolonged use may cause overheating, leading to instability.
**Key Features of L298N**
- Chip: L298N Dual H-Bridge DC/Stepper Motor Driver
- Operating Voltage: 4.5–5.5 V
- Motor Power Supply: 5–35 V DC
- LED indicator for power status
- PCB Size: 4.4 x 5.0 cm
- Max Output Current: 2A (peak 3A)
- Max Output Power: 25W
- Freewheel protection diodes included
- Can control two DC motors or one 2-phase 4-wire/6-wire stepper motor
- Supports reversing and parallel connection for higher current
**L298N Stepper Motor Program**
[Images of circuit diagrams and code examples are available to illustrate the setup and programming of the L298N for controlling a stepper motor.]
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