MAINTEX - a professional DC motor, gear motor, step motor & brushless motor manufacturer

Industry Knowledge

Explore stepper motors: the working principle and classification of stepper motors

Writer: admin Time:2020-06-17 16:17 Browse:

The stepper motor is an open-loop control motor that converts electrical pulse signals into angular displacement or linear displacement. It is the main execution element in modern digital program control systems and is widely used. In the case of non-overload, the speed and stop position of the motor only depend on the frequency and pulse number of the pulse signal, and are not affected by the load change. When the stepper driver receives a pulse signal, it drives the stepper motor according to The set direction turns a fixed angle, called "step angle", and its rotation runs step by step at a fixed angle. The amount of angular displacement can be controlled by controlling the number of pulses, so as to achieve the purpose of accurate positioning; at the same time, the speed and acceleration of the motor rotation can be controlled by controlling the pulse frequency, so as to achieve the purpose of speed regulation.

23.jpg


The stepping motor is an induction motor. Its working principle is to use an electronic circuit to supply DC power when it is converted into components. The multi-phase sequential control current is used to supply power to the stepper motor so that the stepper motor can work normally. The driver is a multi-phase timing controller that supplies power to the stepper motor in time-sharing. Although stepper motors have been widely used, stepper motors cannot be used like ordinary DC motors or AC motors under normal conditions. It must be composed of a double ring pulse signal, power drive circuit, etc. to form a control system before it can be used. Therefore, it is not easy to use a stepper motor well, it involves many professional knowledge such as machinery, motor, electronics and computer. Stepper motor is one of the key products of electromechanical integration as an actuator. It is widely used in various automation control systems. With the development of microelectronics and computer technology, the demand for stepper motors is increasing day by day, and has been applied in various national economic fields.


  Main categories


Stepping motor can be divided into reactive stepping motor (Variable Reluctance, VR), permanent magnet stepping motor Permanent Magnet (PM), hybrid stepping motor (Hybrid Stepping, HS), single-phase stepping There are many types of input motors, flat stepping motors, etc., among the stepping motors used in China, reactive stepping motors are the main ones. The operation performance of the stepper motor is closely related to the control mode. From the perspective of its control mode, the stepper motor control system can be divided into the following three categories: open-loop control system, closed-loop control system, and semi-closed-loop control system. Semi-closed-loop control systems are generally classified as open-loop or closed-loop systems in practical applications.


  Reaction type: There are windings on the stator, and the rotor is composed of soft magnetic materials. The structure is simple, the cost is low, and the step angle is small, up to 1.2°, but the dynamic performance is poor, the efficiency is low, the heat is large, and the reliability is difficult to guarantee.


  Permanent magnet type: The rotor of the permanent magnet stepper motor is made of permanent magnet material, and the number of poles of the rotor is the same as that of the stator. It is characterized by good dynamic performance and large output torque, but this motor has poor precision and large step angle (generally 7.5° or 15°).


  Hybrid type: Hybrid stepper motor combines the advantages of reactive and permanent magnet type, its stator has multi-phase winding, the rotor uses permanent magnet material, and the rotor and stator have multiple small teeth to improve the accuracy of step torque. It is characterized by large output torque, good dynamic performance, small step angle, but complex structure and relatively high cost.


   According to the windings on the stator, there are two-phase, three-phase and five-equal series. The most popular is the two-phase hybrid stepper motor, which accounts for more than 97% of the market share. The reason is that it is cost-effective and works well with the subdivision driver. The basic step angle of this kind of motor is 1.8°/step. After being equipped with a half-step driver, the step angle is reduced to 0.9°. After being equipped with a subdivision driver, the step angle can be subdivided up to 256 times (0.007°/micro step). Due to friction and manufacturing accuracy, the actual control accuracy is slightly lower. The same stepper motor can be equipped with different subdivided drivers to change the accuracy and effect.


  Method of choosing


  Stepper motor and driver selection method:


   Judge how much torque is needed: Static torque is the selection step


   One of the main parameters of the motor. When the load is large, a high torque motor is required. When the torque index is large, the motor shape is also large.


  Judgment of motor running speed: When the rotation speed is high, the motor with larger phase current and smaller inductance should be selected to increase the power input. And use higher power supply voltage when selecting the driver.


  Select the installation specifications of the motor: such as 57, 86, 110, etc., mainly related to the torque requirements.


  Determine the requirements for positioning accuracy and vibration: determine whether and how many subdivisions are required.


  Select the driver according to the motor current, subdivision and supply voltage.


  Fundamental


  working principle


   Usually the rotor of the motor is a permanent magnet. When current flows through the stator winding, the stator winding generates a vector magnetic field. The magnetic field will drive the rotor to rotate an angle, so that the direction of the pair of magnetic fields of the rotor is consistent with the direction of the magnetic field of the stator. When the stator's vector magnetic field rotates by an angle. The rotor also turns an angle with the magnetic field. Each time an electric pulse is input, the motor rotates an angle to advance. The angular displacement it outputs is proportional to the number of pulses input, and the speed is proportional to the pulse frequency. Change the winding energization sequence, the motor will reverse. Therefore, the rotation of the stepper motor can be controlled by controlling the number of pulses, the frequency, and the energizing sequence of each phase winding of the motor.


  Principle of fever


   Usually see all kinds of motors, there are iron core and winding coil inside. There is resistance in the winding, and loss will occur when energized. The loss is proportional to the resistance and the square of the current. This is the copper loss we often say. If the current is not a standard DC or sine wave, harmonic loss will also occur; the core has hysteresis The eddy current effect will also produce losses in the alternating magnetic field, its size is related to the material, current, frequency, voltage, which is called iron loss. Both copper loss and iron loss will be expressed in the form of heat, which affects the efficiency of the motor. Stepper motors generally pursue positioning accuracy and torque output. The efficiency is relatively low, the current is generally large, and the harmonic content is high. The frequency of the alternating current also changes with the speed. Therefore, the stepper motor generally has a heating situation, and the situation is more than the general. The AC motor is serious.


  Main structure


  Stepper motor is also called stepper. It uses electromagnetic principles to convert electrical energy into mechanical energy.


  People started using this motor as early as the 1920s. With the increasing popularity of embedded systems (such as printers, disk drives, toys, wipers, vibrating pagers, robotic arms and video recorders, etc.), the use of stepper motors has also begun to surge. Whether in industrial, military, medical, automotive, or entertainment industries, as long as an object needs to be moved from one location to another, the stepper motor will definitely come in handy. Stepper motors come in many shapes and sizes, but regardless of shape and size, they can be classified into two categories: variable reluctance stepper motors and permanent magnet stepper motors.


  Stepper motor is driven by a group of coils wound on the stator slot of the motor. Normally, a wire wound in a coil is called a solenoid, and in a motor, the wire wound on a tooth is called a winding, coil, or phase.


  Stepping motor acceleration and deceleration process control technology


Because of the wide application of stepper motors, more and more researches on the control of stepper motors have been conducted. If the step pulse changes too fast during startup or acceleration, the rotor will not follow the change of the power-on signal due to inertia, resulting in blockage. Spin or out-of-step may cause over-step when stopping or decelerating for the same reason. In order to prevent stalling, out-of-step and overstep, and to increase the working frequency, the stepping motor should be controlled for speed up and down.


   The speed of the stepper motor depends on the pulse frequency, the number of rotor teeth and the number of beats. Its angular velocity is proportional to the pulse frequency, and it is synchronized with the pulse in time. Therefore, in the case of a fixed number of rotor teeth and running beats, the desired speed can be obtained by controlling the pulse frequency. Since the stepper motor is started by its synchronous torque, the starting frequency is not high in order not to lose the step. Especially as the power increases, the rotor diameter increases, the inertia increases, and the starting frequency and the maximum operating frequency may differ by as much as ten times.


  The starting frequency characteristic of the stepper motor prevents the stepping motor from directly reaching the operating frequency when starting, but there must be a starting process, that is, gradually increase the speed from a low speed to the operating speed. When stopped, the running frequency cannot be immediately reduced to zero, but there must be a process of high speed gradually decreasing to zero.


The output torque of the stepper motor decreases with the increase of the pulse frequency. The higher the starting frequency, the lower the starting torque and the poorer the ability to drive the load. It will cause a step out when starting, and an overshoot will occur when stopping. To make the stepper motor reach the required speed quickly without losing steps or overshooting, the key is to make the torque required for acceleration in the acceleration process not only make full use of the torque provided by the stepper motor at each operating frequency, but also This torque cannot be exceeded. Therefore, the operation of the stepper motor generally goes through three stages of acceleration, uniform speed, and deceleration, requiring the acceleration and deceleration process to be as short as possible and the constant speed time as long as possible. Especially in the work that requires quick response, the running time from the start point to the end point is the shortest, which requires the shortest process of acceleration and deceleration, and the highest speed at constant speed.


Scientists at home and abroad have conducted a lot of research on the speed control technology of stepper motors, established a variety of acceleration and deceleration control mathematical models, such as exponential model, linear model, etc., and designed and developed a variety of control circuits on this basis. , Improves the motion characteristics of stepper motors, popularizes the application range of stepper motors, exponential acceleration and deceleration takes into account the inherent torque frequency characteristics of stepper motors, which can not only ensure that stepper motors do not lose steps in motion, but also give full play to the motor The inherent characteristics of the motor shorten the speed of acceleration and deceleration, but it is difficult to achieve due to the change in the load of the motor. Linear acceleration and deceleration only consider the relationship between the angular velocity of the motor in the load capacity range and the pulse, which is not proportional to the fluctuation of the power supply voltage and the load environment. The characteristics of the change, the acceleration of this speed-up method is constant, the disadvantage is that the characteristics of the output torque of the stepper motor with speed change are not fully considered, and the stepper motor will lose synchronization at high speed.


   Stepping motor subdivision drive control


Stepper motors are limited by their own manufacturing process. For example, the size of the step angle is determined by the number of rotor teeth and running beats, but the number of rotor teeth and running beats is limited, so the step angle of the stepper motor is generally large and is Fixed, stepping resolution is low, lack of flexibility, vibration at low frequency operation, noise is higher than other micro motors, making physical devices prone to fatigue or damage. These shortcomings make the stepper motor can only be used in some occasions with lower requirements. For higher requirements, only closed-loop control can be adopted, which increases the complexity of the system. These shortcomings seriously limit the stepper motor as an excellent open loop Effective use of control components. Subdivision drive technology has effectively overcome these shortcomings to a certain extent.


  Stepper motor subdivision drive technology is a drive technology developed in the mid-1980s that can significantly improve the comprehensive performance of stepper motors. American scholars first proposed the stepping motor step angle subdivision control method at the annual meeting of the incremental motion control system and devices in the United States. In the following 20 years, the stepping motor subdivision drive has been greatly developed. It gradually developed to a fully mature one in the 1990s. The research on the subdivision drive technology in my country is almost the same as that in foreign countries.


   reached a great development in the mid-1990s. Mainly used in industrial, aerospace, robot, precision measurement and other fields, such as photoelectric theodolites for tracking satellites, military instruments, communications and radar, etc., and the wide application of subdivision drive technology makes the number of motor phases not limited by the step angle , Which brings convenience to product design. At present, in the subdivision driving technology of stepper motors, chopping constant current drive, pulse width modulation drive of the instrument, and constant rotation and constant current drive control of the current vector are used, which greatly improves the running accuracy of the stepper motor and makes the stepper motor In the field of medium and small power applications, it is developing in the direction of high speed and precision.


Initially, the control of the phase current of the stepper motor is realized by hardware. Usually, two methods are used, which are multi-channel power switch current power supply and current superposition on the winding. This method makes the power tube loss less, but due to the circuit The number is large, so there are many devices and the volume is large.


The pulse signal is superimposed first, and then linearly amplified by the power tube to obtain a ladder-shaped current. The advantage is that there are few devices used, but the power tube consumes large power and the system power is low. If the tube works in the nonlinear region, it will cause distortion. The shortcomings of these two methods have rarely been adopted.


Introduction of Maintex stepper motor: 24BYJ28-089 stepper motor reducer


Model Item Item Specification Spec

24BYJ28-089 Rated Voltage 5VDC

Phase 2

Reduction Ratio 1/36

Step Angle 11.25°

Exciting Method 1-2

DC resistance Direct-current Resistance 38Ω±10% (25°C)

No-load pull-in Frequency ≥350Hz

No-load pull-out Frequency ≥500Hz

Pull-in Torque ≥40mN.m (5VDC, 400Hz)

Positioning torque Detent Torque ≥30mN.m

Insulation Resistance ≥50M Ω 500VDC

Dielectric Strenght 600VAC

Insulation Class B

Noise Noise ≤40dB

Friction Torque Friction Torque 39.2-196mN.m

Terminal Specifications Terminal Spec 4P*1.25


700 24BYJ28-089.jpg

24BYJ28-089-1.png


Scan the qr codeClose
the qr code