Basic Principle of stepper motor

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Basic Principle of stepper motor

1. stepper motor is an open-loop control component that converts an electrical pulse signal into an angle displacement or linear displacement. In the case of non-overload, the speed and stop position of the motor only depend on the frequency and number of pulses of the pulse signal, and is not affected by the load changes. That is, a pulse signal is added to the motor, the motor turns a step angle. The existence of this line of relations, coupled with stepper motor only periodic errors without cumulative errors and other characteristics. It makes it easy to use stepper motors to control speed and position. Although the stepper motor has been widely used, the stepper motor cannot be used normally like a common DC motor. It must be a control system consisting of a double ring pulse signal and a power drive circuit. Therefore, it is not easy to make good use of stepper motor. It involves many professional knowledge such as machinery, motor, electronics and computer.
At present, there are indeed many manufacturers producing stepper motors, but there are very few manufacturers with professional and technical personnel who can develop their own stepper motors. Most manufacturers have only one or two people, no basic device is connected. It is only in a blind imitation stage. This causes a lot of trouble in product selection and use. In the above cases, we decided to use a wide range of induction sub-type stepping motor as an example. Describe its basic working principles. It is expected to help users in selecting, using, and improving the entire machine.

Ii. Working Principle of induction child Stepping Motor
(1) Principle of reactive stepping motor: the working principle of reactive stepping motor is relatively simple. The following describes the principle of three-phase Reactive stepping motor.

1. structure: the rotor of the motor is evenly distributed with many small teeth. The stator teeth have three excitation winding obstacles, and their geometric axes are staggered with the Rotor Tooth axis. 0, 1/3 Tib, 2/3 Tib, (the distance between the adjacent two Rotor Tooth axis is indicated by the pitch), that is, a is aligned with tooth 1, and B and tooth 2 are staggered to the right by 1/3 Gb/s, C and tooth 3 are staggered to the right by 2/3, and A' is aligned with tooth 5. (a' is A, and tooth 5 is tooth 1) The following is the Expansion Diagram of the stator:

2. Rotation: If the phase is energized and the B and C phases are not energized, the tooth 1 is aligned with a due to the magnetic field (the rotor is not subject to any force below ). If B is connected to electricity, when A and C are not powered, tooth 2 should be aligned with B. At this time, the rotor shifts to the right over 1/3 Gb/s, And the offset between tooth 3 and C is 1/3 Gb/s, offset between tooth 4 and a (Percentile-1/3 percentile) = 2/3 percentile. If C is connected to electricity, A and B are not powered, and tooth 3 should be aligned with C. At this time, the rotor is shifted to the right over 1/3 Gb/s, and tooth 4 is aligned with a Offset of 1/3 Gb/s. For example, if the phase is powered on, the B and C phases are not powered on, the tooth 4 is aligned with A, and the rotor is shifted to the right over 1/3 Gb/s, which passes through the power-on status of A, B, C, and a respectively, the tooth 4 (that is, the first tooth of the tooth 1) is moved to the phase, and the rotor of the motor turns right over a tooth margin. If you continuously press a, B, c, ...... Power-on: the motor rotates to the right at 1/3 Gb/s per step (per pulse. For example, press A, C, B, ...... Power-on, the motor will reverse.
It can be seen that the position and speed of the motor are in a one-to-one correspondence between the Electric Conducting times (number of pulses) and the frequency. The direction is determined by the conductive sequence. However, for considerations such as torque, stability, noise, and angle of reduction. The A-AB-B-BC-C-CA-A is often used in this conductive State, so that the original step 1/3 degrees change to 1/6 degrees. Even through different combinations of Two-Phase currents, the 1/3 Gb/s is changed to 1/12 Gb/s and 1/24 Gb/s, which is the basic theoretical basis for motor Subdivision Driving. It is not difficult to launch: The Motor Stator has m-phase excitation winding resistance, and its axis is offset by 1/m, 2/m, and so on with the Rotor Tooth axis ...... M-1. And the conductive motor can be controlled by a certain phase sequence-this is the physical condition for the stepper motor to rotate. As long as this condition is met, we can theoretically manufacture any phase stepper motor. For cost and other considerations, the market is generally dominated by two, three, four, and five phases.
3. torque: Once the motor is powered on, a magnetic field will be generated between the stator and the stator. When the rotor and the stator are staggered at a certain angle, the production force F is proportional to (D Ratio/d θ ).

The magnetic flux density = Br * s BR indicates the magnetic density, and s indicates the magnetic conductivity area. F is proportional to L * D * Br. L indicates the effective length of the core, d indicates the rotor diameter. BR = N · I/RN · I indicates the number of turns of the excitation winding resistance (current multiplication turns) r indicates the reluctance. Torque = force * radius torque is proportional to the effective volume of the motor * number of turns * magnetic density (only linear state is considered). Therefore, the larger the effective volume of the motor, the larger the number of turns of the excitation, the smaller the air gap between the stator and rotor, the larger the motor torque, and vice versa.

(2) Induction substepping Motor

1. Features: compared with the traditional reactive stepper motor, the rotor is equipped with a permanent magnet to provide soft magnetic material working points, the stator excitation only needs to provide a variable magnetic field and does not need to provide the energy consumption of the magnetic material work point. Therefore, the motor has high efficiency, low current, and low fever. Due to the existence of permanent magnet, the motor has a strong back potential, and its own damping effect is better, so that it is relatively stable during operation, low noise, low frequency vibration. The induction sub-stepping motor 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. (Must be driven by Bipolar voltage), but not reactive motors. For example, four-phase, eight-phase operation (A-AB-B-BC-C-CD-D-DA-A) can use two-phase eight-shot operation mode, it is not difficult to find that the condition is c =
, D =. the internal winding of a two-phase Motor is exactly the same as that of a four-phase Motor. A small-power motor is generally directly connected to a two-phase Motor, while a larger-power motor flexibly changes the dynamic characteristics of the motor for ease of use, the external wiring is usually eight leads (four-phase). In this way, both the four-phase Motor and the two-phase Motor winding can be used in series or in parallel.

2. Classification induction sub-type stepper motor in phase numbers can be divided into two phase Motor, three phase Motor, four phase Motor, five phase Motor and so on. The seat number (outer diameter of motor) can be divided into: 42byg (byg is the serial number of the induction sub-type stepping motor), 57byg, 86byg, 110byg, (International Standard ), for example, 70byg, 90byg, and 130byg are all domestic standards.

3. Term Phase Number of the static indicator of the stepping motor: produces the number of exciting coils of different pole N and S magnetic fields. Commonly used M representation. Number of beats: the number of pulses required to perform periodic changes in the magnetic field, or the number of pulses required for the conducting state to be expressed as N, or the number of pulses required for the motor to turn a pitch angle. Taking a four-phase Motor as an example, there are four phase four beat running mode that is AB-BC-CD-DA-AB, four phase eight beat running mode that is A-AB-B-BC-C-CD-D-DA-A. step angle: corresponds to a pulse signal, and the rotation angle of the motor rotor is expressed by θ. θ = 360 degrees (number of rotor teeth J * Number of running beats). Take the conventional second-and fourth-Phase Motor with 50-tooth rotor teeth as an example. The step range of the Four-shot operation is θ = 360 degrees/(50*4) = 1.8 degrees (commonly known as the whole step ), the step range of the 8-beat operation is θ = 360 degrees/(50*8) = 0.9 degrees (commonly known as half-step ). Positioning torque: when the motor is not powered on, the locking torque of the motor rotor (caused by the harmonic and mechanical error of the magnetic field tooth) Static torque: the motor under the rated static electricity, when the motor does not rotate, the locking torque of the motor shaft. This torque is used to measure the size (geometric size) of a motor and has nothing to do with the driving voltage and power supply.
Although the static torque is proportional to the number of electromagnetic exciting turns and is related to the air gap between the fixed tooth rotor, it is not advisable to excessively reduce the air gap and increase the excitation turns to increase the static torque, this will generate heat and mechanical noise of the motor.

4. stepper motor dynamic indicators and terminology:

1. Step angle accuracy: the error between the actual value and the theoretical value of each step angle of the stepping motor. %: The error/Stride Angle * 100%. The value of the number of running beats is different. The four beats should be less than 5%, and the eight beats should be less than 15%.

2. Out-of-step: the number of steps during motor operation, which is not equal to the theoretical number of steps. This is called a missing step.

3. offset angle: If the Rotor Tooth axis line is offset from the angle of the stator tooth axis line, there must be an offset angle in the motor operation. The error caused by the offset angle cannot be solved by subdivided driving.

4. Maximum no-load start frequency: the maximum frequency that a motor can start directly without loading in a certain drive type, voltage, and rated current.

5. Maximum no-load running frequency: the maximum speed of the motor without load in some drive mode, voltage and rated current.

6. Running moment frequency characteristics: the curve of the motor's output torque and frequency measured under certain testing conditions is called the running moment frequency characteristics, which is the most important of many dynamic curves of the motor, it is also the fundamental basis for motor selection. As shown in


Other features include inertial Frequency Characteristics and startup frequency characteristics. Once the motor is selected, the static torque of the motor is determined, but the dynamic torque is not. The dynamic torque of the motor depends on the average current (rather than the static current) of the motor during operation. The larger the average current, the larger the motor output torque, the harder the motor's frequency characteristic. As shown in:

Among them, curve 3 has the largest current, or the highest voltage; curve 1 has the smallest current, or the lowest voltage. The intersection of curve and load is the maximum speed point of load. To increase the average current, increase the driving voltage as much as possible, and enable a motor with a small inductance and large current.

Video on stepper motor: http://v.ku6.com/show/D27Cp7CBcf6zr3_u.html