A محرك متدرج مغناطيسي دائم (PM) is a type of stepper motor that uses permanent magnets to create a rotating magnetic field for motion. These motors are electromechanical devices that convert electrical pulses into small mechanical movements, resulting in precise control over position and speed without a feedback system, which makes them open-loop control stepper motors.
الأساسيات
PM stepper motors are known for their simplicity, reliability, and accuracy. They create a strong magnetic field, resulting in higher torque generation compared to other stepper motors. PM stepper motors ensure high torque at low speed, which makes them ideal for applications requiring fine movements and precise positioning. The direction of rotation depends on the polarity of the phase currents.
المكونات الرئيسية
A PM stepper motor consists of several key components:
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الجزء الثابت: The stationary part with multiple windings around its circumference made of insulated copper wire. The configuration of the stator winding includes several poles, which may vary and depend upon the motor’s design, affecting the motor’s speed and torque. The stator consists of a series of electromagnetic coils. When an electric current passes to the stator, it creates a magnetic field that interacts with the permanent magnet of the rotor and causes the rotor to rotate. The stator typically has two or more phases, each consisting of a pair of coils.
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دوّار: The rotating part made up of permanent magnets arranged in cylindrical or disk shapes with alternating north and south poles. This arrangement creates a magnetic field that interacts with the stator’s magnetic field, causing the rotor to rotate at a specific angle1. The rotor consists of a permanent magnet. A rotor also consists of teeth or grooves to improve the performance of the motor. The teeth on the rotor provide more surface area to the magnetic field of the stator to interact with the rotor and help to increase the torque of the motor.
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المحامل: Placed at the end of the rotor to support its rotation and reduce friction, ensuring smooth rotation at a specific angle to achieve accuracy.
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Encoder: An electrical feedback device attached to the motor to provide feedback on the rotor’s position, enhancing movement and ensuring accuracy in operation.
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السكن: Provides protection and support to internal components and is made of durable materials like aluminum or steel to accommodate bearings.
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Shaft: A cylindrical rod connected to the rotor that transfers the rotational movement to the external device using electrical signals.
Working Principle
The working principle of a PM stepper motor is based on the magnetic attraction and repulsion between the stator windings and the rotor’s permanent magnets. Electrical pulses are sent to the stator windings in a specific sequence by the motor’s encoder. Each pulse energizes a particular set of windings, creating magnetic fields with defined north and south poles. The rotor’s permanent magnets align with the magnetic field produced by the stator winding, causing the rotor to rotate in a specific direction. By sequentially energizing the stator windings, the rotor moves from one position (angle) to the next position (angle), called steps. The speed and direction are controlled by adjusting the frequency and sequence of the current based on the encoder’s feedback. The most common step angles are 7.5° and 15°.