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HomeNewsWhat is the difference between stepper motor and normal motor?

What is the difference between stepper motor and normal motor?

2019-11-13
Electric motor
A motor is a device that converts electrical energy into mechanical energy. It uses a coiled coil (that is, a stator winding) to generate a rotating magnetic field and acts on a rotor (such as a squirrel-cage closed aluminum frame) to form a magnetoelectric rotational torque. The electric motor is divided into a direct current motor and an alternating current motor according to the use of the power source. The electric motor in the electric power system is mostly an alternating current motor, and may be a synchronous motor or an asynchronous motor (the stator magnetic field speed of the motor and the rotational speed of the rotor are not kept at the synchronous speed). The motor is mainly composed of a stator and a rotor, and the direction of the force-carrying wire in the magnetic field is related to the direction of the current and the direction of the magnetic induction line (the direction of the magnetic field). The working principle of the motor is that the magnetic field acts on the current to force the motor to rotate.
Basic structure
1. The structure of a three-phase asynchronous motor consisting of a stator, a rotor and other accessories.
(1) Stator (still part)
1, the stator core
Function: A part of the magnetic circuit of the motor and the stator windings placed on it.
Structure: The stator core is generally formed by laminating and laminating a silicon steel sheet having an insulating layer on the surface of 0.35 to 0.5 mm thick, and a uniformly distributed groove is punched in the inner circle of the core for embedding the stator winding.
There are several types of stator core slots:
Semi-closed groove: The efficiency and power factor of the motor are higher, but the winding and insulation are more difficult. Generally used in small low voltage motors.
Semi-opening groove: It can be embedded with molded windings, and is generally used for large and medium-sized low-voltage motors. The so-called forming winding, that is, the winding, can be placed in the groove before being insulated.
Open type slot: used to embed the formed winding, the insulation method is convenient, mainly used in high voltage motors.
2, stator winding
Function: It is the circuit part of the motor, which is connected to three-phase alternating current to generate a rotating magnetic field.
Structure: It is made up of three identical windings in which the space is separated by 120° electrical angles and symmetrically arranged. The respective coils of these windings are respectively embedded in the slots of the stator according to certain rules.
The main insulation items of the stator windings are as follows: (to ensure reliable insulation between the conductive parts of the windings and the core and reliable insulation between the windings themselves).
(1) Insulation to ground: insulation between the stator winding and the stator core.
(2) Phase-to-phase insulation: insulation between stator windings of each phase.
(3) Turn-to-turn insulation: insulation between turns of each phase stator winding.
Wiring in the motor junction box:
There is a wiring board in the motor junction box. The six wire ends of the three-phase winding are arranged in two rows, and the three terminal blocks in the upper row are numbered 1 to 1 (U1), 2 (V1), and 3 from left to right. (W1), the three wiring posts in the lower row are numbered 6 (W2), 4 (U2), and 5 (V2) from left to right. Connect the three-phase windings to a star connection or a delta connection. All manufacturing and maintenance should be arranged according to this serial number.
3, the base
Function: Fix the stator core and the front and rear end caps to support the rotor, and play the role of protection and heat dissipation.
Construction: The base is usually cast iron, the large asynchronous motor base is usually welded with steel plate, and the base of the micro motor is made of cast aluminum. There is a heat dissipation rib on the outer surface of the closed motor to increase the heat dissipation area. The end caps of the protective motor have ventilation holes at both ends, so that the air inside and outside the motor can be directly convected to facilitate heat dissipation.
(2) Rotor (rotating part)
1. Rotor core of three-phase asynchronous motor:
Function: As part of the magnetic circuit of the motor and placing the rotor windings in the core slot.
Construction: The material used is the same as that of the stator. It is made of 0.5 mm thick silicon steel sheet and laminated. The outer surface of the silicon steel sheet is punched with evenly distributed holes for the rotor winding. The inner core of the silicon steel sheet that is behind the stator core is usually used to punch the rotor core. Generally, the rotor core of a small asynchronous motor is directly press-fitted on a rotating shaft, and the rotor core of a large and medium-sized asynchronous motor (with a rotor diameter of 300 to 400 mm or more) is pressed against the rotating shaft by means of a rotor bracket.
2. Rotor winding of three-phase asynchronous motor
Function: Cutting the rotating magnetic field of the stator generates induced electromotive force and current, and forms electromagnetic torque to rotate the motor.
Construction: divided into squirrel cage rotor and wound rotor.
(1) Squirrel-cage rotor: The rotor winding consists of a plurality of bars inserted into the rotor slots and two end rings of the ring. If the rotor core is removed, the entire winding is shaped like a squirrel cage, so it is called a cage winding. The small cage motor adopts a cast aluminum rotor winding, and is welded by a copper strip and a copper end ring for a motor of 100 KW or more.
(2) Wire-wound rotor: The wound rotor winding is similar to the stator winding, and is also a symmetrical three-phase winding, which is generally connected in a star shape, three outgoing heads are connected to the three collecting rings of the rotating shaft, and then passed through the brush and the outer Circuit connection.
Features: The structure is more complicated, so the application of the wound motor is not as extensive as the squirrel cage motor. However, through the collector ring and the brush, additional components such as resistors are inserted in the rotor winding circuit to improve the starting and braking performance and speed regulation performance of the asynchronous motor. Therefore, equipment that requires smooth speed regulation within a certain range, such as Cranes, elevators, air compressors, etc. are used above.
(3) Other accessories for three-phase asynchronous motor
1. End cap: support function.
2. Bearing: Connect the rotating part and the moving part.
3. Bearing end cover: protect the bearing.
4. Fan: Cool the motor.
Precautions
(1) Before disassembling, use compressed air to blow off the surface dust of the motor and wipe off the surface dirt.
(2) Select the working location where the motor is disassembled and clean up the site environment.
(3) Familiar with the structural characteristics of the motor and the technical requirements for maintenance.
(4) Prepare the tools (including special tools) and equipment needed for disintegration.
(5) In order to further understand the defects in the operation of the motor, an inspection test can be performed before disassembly in case of conditions. To this end, the motor is loaded with a load test, and the temperature, sound, vibration, etc. of each part of the motor are inspected in detail, and the voltage, current, speed, etc. are tested, and then the load is disconnected, and a no-load inspection test is performed separately, and the test is performed. Record current and no-load loss.
(6) Cut off the power supply, remove the external wiring of the motor, and make a record.
(7) Test the insulation resistance of the motor by using a megger with a suitable voltage. In order to compare the insulation resistance value measured at the time of the previous inspection to determine the change trend of the insulation of the motor and the insulation state, the insulation resistance value measured at different temperatures should be converted to the same temperature, generally converted to 75 °C.
(8) Test the absorption ratio K. When the absorption ratio is greater than 1.33, it indicates that the motor insulation is not damp or the degree of moisture is not serious. In order to compare with the previous data, the absorption ratio measured at any temperature is also converted to the same temperature.
What is the difference between a stepper motor and a normal motor?

1, system common sense: Stepper Motor and Stepper motor driver constitute a stepper motor drive system. The performance of the stepper motor drive system depends not only on the performance of the stepper motor itself, but also on the advantages and disadvantages of the stepper motor driver. Research on stepper motor drives has been carried out almost simultaneously with the study of stepper motors.

2. System Overview: A stepper motor is an actuator that converts electrical pulses into angular displacement. When the stepper motor driver receives a pulse signal (from the controller), it drives the stepper motor to rotate a fixed angle (called the "step angle") in a set direction, and its rotation is at a fixed angle. Run step by step.

3. System control: The stepping motor cannot be directly connected to DC or AC power supply, and a dedicated driving power supply (stepping motor driver) must be used. The controller (pulse signal generator) can control the angular displacement by controlling the number of pulses 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, thereby achieving the purpose of speed regulation.

4. Use: Stepper motor is a kind of special motor for control. As an actuator, it is one of the key products of mechatronics. With the development of microelectronics and computer technology (the performance of stepper motor driver is improved), stepping The demand for electric motors is increasing. The stepping motor has no accumulating error in operation accuracy, making it widely used in various automatic control systems, especially open-loop control systems.

5, stepper motor according to the structure classification: stepper motor is also called pulse motor, including reactive stepper motor (VR), permanent magnet stepper motor (PM), hybrid stepper motor (HB).

(1) Reactive stepping motor: also called inductive, hysteresis or magnetoresistive stepping motor. The stator and the rotor are made of soft magnetic material. The large magnetic poles evenly distributed on the stator are equipped with multi-phase excitation windings, and the small teeth and slots are evenly distributed around the stator and the rotor. After the power is applied, the torque is generated by the change of the magnetic permeability. Generally three, four, five, six phases; can achieve large torque output (high power consumption, current up to 20A, high driving voltage); small step angle (minimum 10'); power off There is no positioning torque; the internal damping of the motor is small, and the single-step operation (when the pulse frequency is very low) has a longer oscillation time; the starting and running frequency is higher.

(2) Permanent magnet stepping motor: Generally, the rotor of the motor is made of permanent magnet material. The stator made of soft magnetic material has multi-phase excitation windings. There are no small teeth and slots around the stator and rotor. After energization, permanent magnets are used. The stator current magnetic field interacts to produce torque. Generally two-phase or four-phase; small output torque (less power consumption, current is generally less than 2A, driving voltage 12V); large step angle (such as 7.5 degrees, 15 degrees, 22.5 degrees, etc.); Holding torque; low starting and running frequency.

(3) Hybrid stepping motor: also called permanent magnet reactive type, permanent magnet induction type stepping motor, which combines the advantages of permanent magnet type and reactive type. There is no difference between the stator and the four-phase reactive stepping motor (but the two magnetic poles of the same phase are opposite, and the N and S polarities of the windings on the two magnetic poles must be the same), and the rotor structure is complicated (the inner part of the rotor is cylindrical forever) Magnet, soft magnetic material on both ends, with small teeth and grooves around). Generally two or four phases; positive and negative pulse signals must be supplied; output torque is larger than permanent magnets (less power consumption); step angle is smaller than permanent magnets (typically 1.8 degrees); Positioning torque; high starting and running frequency; it is a stepping motor that is developing rapidly.

6, the basic parameters of the stepper motor:

(1) Inherent step angle of the motor: It indicates the angle at which the motor rotates every time the control system sends a step pulse signal. The motor is given a step angle value when it leaves the factory. For example, the 86BYG250A motor gives a value of 0.9°/1.8° (0.9° for half-step operation and 1.8° for full-step operation). This step angle It can be called 'motor inherent step angle', it is not necessarily the actual step angle when the motor is working, and the actual step angle is related to the driver.

(2) The number of phases of the stepping motor: refers to the number of coil groups inside the motor. Currently, two-phase, three-phase, four-phase, five-phase stepping motors are commonly used. The number of phases of the motor is different, and the step angle is also different. Generally, the step angle of the two-phase motor is 0.9°/1.8°, the three-phase is 0.75°/1.5°, and the five-phase is 0.36°/0.72°. Increasing the number of phases in a stepper motor can improve performance, but the structure and drive power of the stepper motor are more complicated and the cost is increased.

(3) Holding torque (HOLDING TORQUE): Also called maximum static torque, it is the maximum torque applied to the energized stepping motor shaft under the rated quiescent current without continuous rotation. It is one of the most important parameters of a stepper motor. Usually, the torque of the stepping motor at low speed is close to the holding torque. Since the output torque of the stepping motor is continuously attenuated with the increase of the speed, the output power also changes with the increase of the speed, so the holding torque becomes one of the most important parameters for measuring the stepping motor. For example, when people say that a 2N.m stepping motor is a stepping motor that maintains a torque of 2N.m unless otherwise specified.

(4) Step accuracy: It can be expressed by positioning error or by step angle error.

(5) Moment angle characteristic: The recovery torque of the stepping motor rotor after leaving the equilibrium position changes with the deviation of the rotation angle. The relationship between the static torque of the stepping motor and the offset angle is called the moment angle characteristic.

(6) Static temperature rise: When the motor is stationary, the maximum number of phases in the specified operation mode is the rated quiescent current, and the temperature rise is achieved when the temperature is stable.

(7) Dynamic temperature rise: The motor runs at no load under a certain frequency and works according to the specified running time. The temperature rise reached by the motor after the running time is called dynamic temperature rise.

(8) Torque characteristics: It indicates the relationship between the motor torque and the excitation current at the time of single-phase energization.

(9) Starting moment frequency characteristic: The relationship between starting frequency and load torque is called starting torque characteristic.

(10) Operating moment frequency characteristics / inertia frequency characteristics: slightly

(11) Lifting frequency time: refers to the time required for the motor to rise from the starting frequency to the highest operating frequency or from the highest operating frequency to the starting frequency.

(12) DETENT TORQUE: refers to the moment when the stator locks the rotor when the stepping motor is not energized. DETENT TORQUE has no unified translation method in China and is easy to misunderstand; the rotor of reactive stepping motor is not permanent magnet material, so it does not have DETENT TORQUE.

7, some features of the stepper motor:

(1) The stepping motor has no accumulation error: the accuracy of the general stepping motor is 3-5% of the actual step angle, and does not accumulate.

(2) When the stepping motor is in operation, the pulse signal is alternately applied to each phase winding in a certain order (the ring winding in the driver controls the winding to be powered off and on).

(3) Even with the same stepping motor, the torque frequency characteristics are quite different when using different driving schemes.

(4) Stepper motor is different from other motors, its nominal rated voltage and rated current are only reference values; and because the stepping motor is powered by pulse, the power supply voltage is its highest voltage, not the average voltage, so stepping The motor can operate beyond its rated range. However, the selection should not deviate too far from the rated value.

(5) The maximum temperature allowed by the appearance of the stepping motor: If the temperature of the stepping motor is too high, the magnetic material of the motor will be demagnetized first, resulting in a torque drop and even out of step. Therefore, the maximum temperature allowed by the motor surface should depend on the magnetic material of different motors. Demagnetization point; in general, the demagnetization point of magnetic materials is above 130 degrees Celsius, and some even up to 200 degrees Celsius, so the external temperature of the stepping motor is completely normal at 80-90 degrees Celsius.

(6) The torque of the stepping motor will decrease with the increase of the speed: when the stepping motor rotates, the inductance of each phase winding of the motor will form a back electromotive force; the higher the frequency, the larger the back electromotive force. Under its action, the motor decreases with increasing frequency (or speed), resulting in a drop in torque.

(7) The stepping motor can run normally at low speed, but if it is higher than a certain frequency, it cannot be started, accompanied by howling.

The stepping motor has a technical parameter: the no-load starting frequency, that is, the pulse frequency that the stepping motor can start normally under no-load conditions. If the pulse frequency is higher than this value, the motor cannot start normally, and lost or blocked may occur. In the case of load, the starting frequency should be lower. If the motor is to be rotated at a high speed, the pulse frequency should have an acceleration process, that is, the starting frequency is low, and then rise to a desired high frequency (the motor speed is increased from a low speed to a high speed) at a certain acceleration.

(8) The four-phase hybrid stepping motor is generally driven by a two-phase driver. Therefore, the four-phase motor can be connected to two phases by series connection or parallel connection. The series connection method is generally used in the case where the motor speed is low. In this case, the required output current of the driver is 0.7 times of the motor phase current, so the motor generates less heat; and the connection method is generally used in the case where the motor speed is high (also called high speed connection). Method), the required driver output current is 1.4 times of the motor phase current, so the motor generates a large amount of heat.

(9) The power supply voltage of the hybrid stepping motor driver is generally a wide range (for example, the power supply voltage of the IM483 is 12 to 48 VDC), and the power supply voltage is usually selected according to the operating speed and response requirements of the motor. If the motor has a higher operating speed or a faster response, the voltage is higher, but note that the ripple of the supply voltage cannot exceed the maximum input voltage of the driver, otherwise the drive may be damaged.

(10) The power supply current is generally determined based on the output phase current I of the driver. If a linear power supply is used, the power supply current can generally be 1.1 to 1.3 times that of I; if a switching power supply is used, the power supply current can generally take 1.5 to 2.0 times that of I.

(11) When the offline signal FREE is at a low level, the current output from the driver to the motor is cut off, and the motor rotor is in a free state (offline state).

In some automation equipment, if the motor shaft (manual mode) is required to be directly powered while the drive is unpowered, the FREE signal can be set low, the motor can be taken offline, and manually operated or adjusted. After manual completion, set the FREE signal high to continue automatic control.

(12) Adjust the direction of rotation of the two-phase stepper motor after power-on in a simple way. Simply swap the A+ and A- (or B+ and B-) wires of the motor and the driver.

8, some features of the stepper motor driver:

(1) An ASIC that constitutes a stepper motor driver system:

A pulse distributor integrated circuit: such as PMI8713 (three/four phase), PMM8723 (four phase), PMM8714 (five phase), etc. of Sanyo Company.

B Controller integrated circuit including pulse distributor and current chopping: such as L297 (four-phase) and L6506 (four-phase) of SGS.

C Driver integrated circuits containing only power drives (or current control, protection circuits): such as MTD1110 (quadrature chopper drive) and MTD2001 (two-phase, H-bridge, chopper drive) from Japan's New Electric Industrial Co., Ltd.

D Drive controller ICs including pulse distributor, power drive, current control and protection circuits, such as SAA1042 (four-phase) from MOTOROLA and UCN5804 (four-phase) from ALLEGRO.

(2) Overview of [Segment Drive":

Concept: The method of subdividing [the inherent step angle of the motor" into several small steps is called subdivision driving. The subdivision is realized by the driver precisely controlling the phase current of the stepping motor, independent of the motor itself. The principle is that the stator current phase current does not rise to the first position, and the power phase current does not drop to zero at one time (the winding current waveform is no longer an approximate square wave, but an N-order approximate step wave), then the stator winding current The resultant magnetic field forces the rotor to have N new equilibrium positions (forming N step angles).

The latest technology development: domestic and international research on subdivision drive technology is very active, high-performance subdivision drive circuit can be subdivided into thousands or even any subdivision. At present, it is possible to make the stepped angle of the subdivided uniform by the complicated calculation, greatly improve the pulse resolution of the stepping motor, reduce or eliminate the oscillation, noise and torque fluctuation, and make the stepping motor more "Class servo" feature.

The effect on the actual step angle: When there is no subdivision driver, the user mainly chooses the stepping motor with different phase numbers to meet his requirements for the step angle. If a subdivision driver is used, the user can change the actual substep angle by simply changing the number of subdivisions on the drive. The effect of the 'phase number' of the stepper motor on changing the actual step angle is almost negligible.

The relationship between subdivision technology and the accuracy of stepping motor: The subdivision technology of stepping motor is essentially an electronic damping technology. Its main purpose is to reduce or eliminate the low frequency vibration of stepper motor and improve the running precision of the motor. An add-on feature of the technology. After the subdivision, the resolution of each pulse is improved when the motor is running, but whether the running accuracy can reach or approach the pulse resolution depends on other factors such as the subdivision current control accuracy of the subdivision driver. The accuracy of subdivision drivers from different manufacturers may vary greatly; the larger the number of subdivisions, the more difficult it is to control.

The true subdivision has a relatively high technical and process requirements for the drive, and the cost will be higher. Some domestic drivers use [smooth" processing of the motor phase current to replace the subdivision, which belongs to [false subdivision". [Smoothing" does not generate microsteps, which will cause the motor torque to drop. The true subdivision control will not only cause the motor torque to drop, but the torque will increase.