Stepping Motor

                          Stepping motor

Stepping motor is an open-loop control element that converts electric pulse signal into angular displacement or linear displacement. In the case of non-overloading, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal, but not affected by the load change. When the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle in the set direction, called "step angle", and its rotation is operated step by step at a fixed angle. The angular displacement can be controlled by controlling the number of pulses to achieve the purpose of accurate positioning; At the same time, the speed and acceleration of the motor can be controlled by controlling the pulse frequency to achieve the purpose of speed regulation.

Stepping motor is a kind of induction motor. Its working principle is to use electronic circuits to convert DC power into a time-sharing power supply, and the polyphase timing control current. The stepping motor can work normally only when the current is used to power the stepping motor. The driver is a time-sharing power supply for the stepping motor, and the polyphase timing controller.

Although the stepping motor has been widely used, the stepping motor can not be used as the ordinary DC motor, and the AC motor is used in the conventional way. It can only be used if it consists of a control system consisting of double-ring pulse signal, power drive circuit, etc. Therefore, it is not easy to make good use of stepping motor, which involves many professional knowledge such as machinery, motor, electronics and computer. As an executive component, stepping motor is one of the key products of electromechanical integration, and is widely used in various automatic control systems. With the development of microelectronics and computer technology, the demand for stepping motor is increasing day by day, and it has been applied in various fields of national economy.

Definition Overview

Stepping motor is a kind of induction motor. Its working principle is to use electronic circuit to convert DC power into a time-sharing power supply, and the polyphase timing control current. The stepping motor can work normally only when the current is used to power the stepping motor. The driver is the time-sharing power supply for the stepping motor, and the polyphase timing controller

Although the stepping motor has been widely used, the stepping motor can not be used as the ordinary DC motor, and the AC motor is used in the conventional way. It can only be used if it consists of a control system consisting of double-ring pulse signal, power drive circuit, etc. Therefore, it is not easy to make good use of stepping motor, which involves many professional knowledge such as machinery, motor, electronics and computer.

As an executive component, stepping motor is one of the key products of electromechanical integration, and is widely used in various automatic control systems. With the development of microelectronics and computer technology, the demand for stepping motor is increasing day by day, and it has been applied in various fields of national economy.

Stepping motor is an actuator that converts electric pulse into angular displacement. Generally speaking, when the stepper driver receives a pulse signal, it drives the stepper motor to rotate a fixed angle (i.e., the stepper angle) in the set direction. You can control the angular displacement by controlling the number of pulses to achieve the purpose of accurate positioning; At the same time, you can control the speed and acceleration of the motor rotation by controlling the pulse frequency to achieve the purpose of speed regulation fold.

Classification

There are three types of stepper motors: permanent magnet (PM), reactive (VR) and hybrid (HB). Permanent magnet stepping is generally two-phase, with small torque and volume, and the stepping angle is generally 7.5 degrees or 15 degrees; Reactive stepping is generally three-phase, which can achieve large torque output. The stepping angle is generally 1.5 degrees, but the noise and vibration are very large, which has been eliminated in developed countries such as Europe and America in the 1980s; Hybrid stepping refers to the combination of the advantages of permanent magnet type and reactive type. It is divided into two phases and five phases. The two phase step angle is generally 1.8 degrees and the five phase step angle is generally 0.72 degrees. This type of stepping motor is the most widely used.

Energy-saving transformation

Energy-saving transformation of stepper motor by frequency converter

Features of special inverter for three-phase stepping motor:

■ Low frequency torque output 180%, good low frequency operation characteristics

■ The maximum output frequency is 600Hz, which can control high-speed motor

■ Full range of detection and protection functions (overvoltage, undervoltage, overload), instant power failure and restart

■ Protection functions such as acceleration, deceleration and stall prevention during running

■ Automatic identification function of motor dynamic parameters ensures the stability and accuracy of the system

■ Fast response during high-speed shutdown

■ Rich and flexible input and output interfaces and control methods, with strong versatility

■ Adopt SMT full-mount production and three-proofing paint treatment process, with high product stability

■ The whole series adopts the latest Siemens IGBT power devices to ensure high quality

Basic principle

Usually, the rotor of the motor is a permanent magnet. When the current flows through the stator winding, the stator winding generates a vector magnetic field. This magnetic field will drive the rotor to rotate at an angle, so that the direction of a pair of magnetic fields of the rotor is consistent with that of the stator. When the vector magnetic field of the stator rotates by an angle. The rotor also rotates an angle with the magnetic field. Each time an electric pulse is input, the motor rotates one angle and advances one step. Its output angular displacement is proportional to the number of input pulses, and its speed is proportional to the pulse frequency. Change the sequence of winding energization, and the motor will reverse. Therefore, the rotation of the stepping motor can be controlled by controlling the number and frequency of pulses and the power-on sequence of each phase winding of the motor.

Folding reactive stepping motor

Because the working principle of reactive stepping motor is relatively simple. The following describes the principle of three-phase reactive stepping motor.

1. Structure: The motor rotor is evenly distributed with many small teeth, and the stator teeth have three excitation winding resistances, and their geometric axes are staggered from the rotor tooth axes in turn. 0, 1/3 θ, 2/3 θ, (the distance between the tooth axes of two adjacent rotors is represented by the tooth pitch), that is, A is aligned with tooth 1, B is staggered with tooth 2 by 1/3 θ to the right, C is staggered with tooth 3 by 2/3 θ to the right, A 'is aligned with tooth 5, (A' is A, and tooth 5 is tooth 1) The following is the expanded view of the stator and rotor:

2. Rotation: if phase A is powered on, and phase B and C are not powered on, tooth 1 is aligned with A due to the magnetic field (the same below the rotor is free of any force). If phase B is powered on and phase A and C are not powered on, gear 2 should be aligned with B. At this time, the rotor moves to the right by 1/3 ÷. At this time, gear 3 and C are offset by 1/3 ÷, and gear 4 and A are offset (Δ - 1/3 ÷)=2/3 ÷. If phase C is powered on, phase A and phase B are not powered on, tooth 3 should be aligned with C, and then the rotor moves to the right by 1/3 ÷, and tooth 4 is aligned with A by 1/3 ÷. If phase A is powered on, phase B and phase C are not powered on, gear 4 is aligned with phase A, and the rotor is moved to the right by 1/3 ‰. In this way, the gear 4 (i.e., the front tooth of gear 1) is moved to phase A, and the motor rotor rotates to the right by one tooth pitch. If the power is continuously pressed on A, B, C, A..., the electric machine will rotate to the right by 1/3 ‰ per step (per pulse). If you press A, C, B, A... to power on, the motor will reverse. It can be seen that the position and speed of the motor are in one-to-one correspondence with the number of conductive times (pulse number) and frequency. The direction is determined by the order of conduction. However, due to the consideration of torque, stability, noise and angle reduction. The conductive state of A-AB-BC-C-CA-A is often used, which changes the original 1/3 ÷ to 1/6 ÷ in each step. Even through different combinations of two-phase currents, 1/3 ÷ becomes 1/12 ÷, 1/24 ÷, which is the basic theoretical basis of motor subdivision drive. It is not difficult to deduce that there is an m-phase excitation winding on the motor stator, and its axis is offset from the rotor tooth axis by 1/m, 2/m...... (m-1)/m, 1 respectively. And the conduction can be controlled by positive and negative rotation of the motor according to a certain phase sequence - this is the physical condition of rotation. As long as this condition is met, we can theoretically manufacture any phase of stepping motor. Considering the cost and other aspects, the market generally consists of two, three, four and five phases.

3. Torque: once the motor is energized, magnetic field (magnetic flux) will be generated between the stator and rotor Ф） When the rotor and stator are staggered at a certain angle, force F and (d Ф/ d θ） In direct proportion to its magnetic flux Ф= Br * S Br is the magnetic density, S is the magnetic conductivity area, F is proportional to L * D * Br, L is the effective length of the iron core, D is the rotor diameter, Br=N · I/R N · I is the ampere turns of the excitation winding resistance (current times turns), R is the magnetic resistance. Torque=force * radius torque is proportional to the effective volume of the motor * ampere turns * magnetic density (only considering the linear state). Therefore, the larger the effective volume of the motor, the greater the excitation ampere turns, the smaller the air gap between the stator and rotor, the greater the motor torque, and vice versa.

Folding inductor stepper motor

1. Features

Compared with the traditional reaction type, the inductor type has a permanent magnet added to the rotor in the structure to provide the working point of the soft magnetic material, while the stator excitation only needs to provide the variable magnetic field without providing the energy consumption of the working point of the magnetic material, so the motor has high efficiency, low current and low heat. Due to the existence of permanent magnets, the motor has a strong back EMF and its damping effect is relatively good, which makes it more stable, low noise and low frequency vibration during operation. The inductor type can be regarded as a low-speed synchronous motor to some extent. A four-phase motor can be used for four-phase operation or two-phase operation. (It must be driven by bipolar voltage), but reactive motors cannot. For example, the four-phase and eight-phase operation (A-AB-B-BC-C-CD-D-DA-A) can completely adopt the two-phase and eight-phase operation mode. It is not difficult to find that the condition is C=, D=. The internal winding of a two-phase motor is completely consistent with that of a four-phase motor. Small-power motors are generally directly connected to the two-phase motor, while motors with higher power are often connected to eight leads (four-phase) for convenience and flexibility in changing the dynamic characteristics of the motor, It can be used as a four-phase motor, or as a two-phase motor winding in series or in parallel.

2. Classification

Induction motor can be divided into two-phase motor, three-phase motor, four-phase motor, five-phase motor, etc. According to the frame number (outer diameter of the motor), it can be divided into 42BYG (BYG is the code of the inductor stepper motor), 57BYG, 86BYG, 110BYG, (international standard), while 70BYG, 90BYG, 130BYG, etc. are all domestic standards.

3. Terminology for static indicators of stepping motors

(1) Number of phases: the number of exciting coils that produce different N and S magnetic fields. It is usually expressed in m.

(2) Beat number: the number of pulses or conductive state required to complete a periodic change of magnetic field is expressed in n, or refers to the number of pulses required for the motor to turn over a pitch angle. Take a four-phase motor as an example, there are four-phase four-beat operation mode, namely AB-BC-CD-DA-AB, and four-phase 8-beat operation mode, namely A-AB-BC-C-CD-DA-A.

(3) Step angle: corresponding to a pulse signal, the angular position of the motor rotor is shifted θ express. θ= 360 degrees/(number of rotor teeth * number of running beats), take the conventional two and four phase motor with 50 teeth as an example. The step angle is θ= 360 degrees/(50 * 4)=1.8 degrees (commonly known as full step), and the step angle is θ= 360 degrees/(50 * 8)=0.9 degrees (commonly known as half step).

(4) Positioning torque: the locking torque of the motor rotor itself when the motor is not powered on (caused by the harmonic of the magnetic field tooth shape and mechanical error)

(5) Static torque: the locking torque of the motor shaft when the motor does not rotate under the rated static electricity. This torque is the standard to measure the volume of the motor, and is independent of the driving voltage and power supply. Although the static torque is proportional to the number of electromagnetic excitation ampere turns and related to the air gap between the stator and rotor, it is not advisable to increase the static torque by reducing the air gap and increasing the excitation ampere turns, which will cause the heat and mechanical noise of the motor.