1. Definition of coreless motor

Coreless motors are DC permanent magnet servo and control motors, and can also be classified as micro motors. In terms of structure, it breaks through the rotor structure of traditional motors, and adopts an ironless rotor, also called a hollow cup rotor. This novel rotor structure completely eliminates the power loss caused by the eddy current formed by the iron core. Because there is no iron loss, its efficiency is higher than that of ordinary micro DC motors. Its coil is the rotor, which has a small moment of inertia and is easy to control. But without an iron core, the coil of the rotor can only be made very thin, otherwise it will The magnetic flux is lost, so the power of the coreless motor is not large, and the large coreless motor can only achieve a few hundred watts.

2. Coreless motor structure

The hollow cup motor is mainly composed of the rear cover, terminal block, brush end cover, brush, commutator, cup winding (rotor), shaft, gasket, sliding bearing, shell, magnet (stator), flange, and positioning ring. . See the figure below for details. The stator is composed of a permanent magnet, a shell and a flange. The housing provides a constant magnetic field, so that the motor has no iron loss. No soft magnetic teeth. The torque produced is uniform, resulting in smooth operation even at low speeds. At higher speeds, the motor reduces vibration and reduces noise. Rotor with windings and commutator. The windings are connected to the shaft by so-called commutation plates. The coil moves in the air gap between the magnet and the housing. The commutation system uses a pair of precious metal brushes to reduce brush sparking. Reduced brush sparking produces less electromagnetic emissions.

3. Classification of coreless motors

Coreless motors are divided into two types: brushed and brushless. The rotor of the brushed coreless motor has no iron core, and the stator of the brushless coreless motor has no iron core.

The hollow cup DC brushed micro motor adopts mechanical commutation, the magnetic pole does not move, and the coil rotates. When the motor is working, the coil and commutator rotate, and the magnetic steel and carbon brushes do not rotate. The alternating change of the coil current direction is completed by the commutator and brushes that rotate with the motor. During the rotation, the carbon brush will be rubbed, causing wear and tear, and the carbon brush needs to be replaced regularly. When the carbon brush and the coil terminal are switched on and off alternately, electric sparks will occur, which will generate electromagnetic damage and interfere with electronic equipment.

The brushless coreless DC motor adopts electronic commutation, the coil does not move, and the magnetic pole rotates. The brushless coreless DC motor uses a set of electronic equipment to sense the position of the poles of the permanent magnet through the Hall element. According to this perception, the electronic circuit is used to switch the direction of the current in the coil in a timely manner to ensure that the magnetic force in the correct direction is generated. to drive the motor. Because it is self-controlled, it will not add a start winding to the rotor like a synchronous motor with heavy load under variable frequency speed regulation, and it will not cause oscillation and out of step when the load changes suddenly, eliminating the need for coreless DC brushes. Disadvantages of micromotors.

4. Main characteristics of coreless motor

1. Energy-saving characteristics: the energy conversion efficiency is very high, and its maximum efficiency is generally above 70% , and some products can reach above 90% (the iron core motor is generally 70% ).

2. Control characteristics: fast starting and braking, extremely fast response, mechanical time constant less than 28 milliseconds, some products can reach within 10 milliseconds (iron core motors are generally above 100 milliseconds); under high-speed operation in the recommended operating area , It is convenient to adjust the speed sensitively.

3. Drag characteristics: the running stability is very reliable, and the fluctuation of the speed is very small. As a micro motor, the fluctuation of the speed can be easily controlled within 2% .

Five, coreless motor advantages

1. Low starting torque

No hysteresis loss, no cogging effect, very low starting torque. At start-up, usually the bearing load is the only hindrance. In this way, the starting wind speed of the wind generator can be very low.

2. There is no radial force between the rotor and the stator

Since there is no stationary silicon steel sheet, there is no radial magnetic force between the rotor and the stator. This is especially important in critical applications. Because the radial force between the rotor and the stator will cause the rotor to be unstable. Reducing the radial force will improve the stability of the rotor.

3. Smooth speed curve and low noise

There is no grooved silicon steel sheet, which reduces the harmonics of torque and voltage. At the same time, since there is no AC field in the motor , there is no AC- generated noise. Only noise from bearings and airflow and vibration from non-sinusoidal currents are present.

4. High speed brushless coil

When running at high speed, a small inductance value is necessary. A small inductance value results in a low start-up voltage. Smaller inductance values help reduce the weight of the motor by increasing the number of poles and reducing the thickness of the case. At the same time, the power density is increased.

5. Quick response brushed coil

The brushed motor with copper plate coil has a low inductance value, and the current responds quickly to the fluctuation of the voltage. The moment of inertia of the rotor is small, and the response speed of torque and current is equivalent. Therefore, the rotor acceleration is twice that of a conventional motor .

6. High peak torque

The ratio of peak torque to continuous torque is large because the torque constant is constant as the current rises to the peak value. The linear relationship between current and torque enables the motor to produce a large peak torque. With traditional motors, when the motor reaches saturation, no matter how much current is applied, the torque of the motor will not increase.

7. Sine wave induced voltage

Due to the precise position of the coils, the voltage harmonics of the motor are low; and due to the structure of the copper plate coils in the air gap, the resulting induced voltage waveform is smooth. The sine wave drive and controller allow the motor to generate smooth torque. This property is particularly useful on slow-moving objects (such as microscopes, optical scanners, and robots) and precise position control, where smooth-running control is key.

8. Good cooling effect

There is air flow on the inner and outer surfaces of the copper plate coil, which is better than the heat dissipation of the slotted rotor coil. The traditional enameled wire is embedded in the groove of the silicon steel sheet, the airflow on the surface of the coil is very little, the heat dissipation is not good, and the temperature rise is large. With the same output power, the temperature rise of the motor with copper plate coil is smaller.

6. Disadvantages of coreless motor

When the DC motor is in a static state, if one phase of the winding is cut off or the power supply is cut off and the other phase is powered on, the winding will generate two rotating magnetic fields of equal size and opposite directions. The torque generated by the two rotating magnetic fields and the action of the rotor is equal. The directions are opposite, just canceling each other, the starting torque is zero, and the motor cannot start, which is the shortcoming of the coreless motor.

This shortcoming of the coreless motor is a very dangerous failure. When using it, we need to check whether the DC motor is faulty, check whether the power circuit has a circuit breaker, whether there is a fuse, and then check whether each phase of the three-phase winding is damaged. cut-off phenomenon.

7. Application range of coreless motor

Since the coreless motor overcomes the insurmountable technical barriers of the iron core motor, and its outstanding features focus on the main performance of the motor, it has a wide range of applications. Especially with the rapid development of industrial technology, higher expectations and requirements are constantly put forward for the servo characteristics of the motor, so that the coreless motor has an irreplaceable position in many applications.

The application of hollow cup motors has developed rapidly for more than ten years after entering the large industrial and civil fields from the military and high-tech fields, especially in industrially developed countries, and has involved most industries and many products.

1. A servo system that requires quick response. Such as the rapid adjustment of the flight direction of the missile, the follow-up control of the high-magnification optical drive, the fast automatic focus, the highly sensitive recording and testing equipment, the industrial robot, the bionic prosthesis, etc., the hollow cup motor can well meet its technical requirements.

2. Products that require smooth and long-lasting dragging of the drive components. Such as all kinds of portable instruments and meters, personal portable equipment, field operation equipment, electric vehicles, etc., with the same set of power supply, the power supply time can be extended by more than double.

3. All kinds of aircraft, including aviation, spaceflight, model aircraft, etc. Utilizing the advantages of light weight, small size and low energy consumption of the hollow cup motor, the weight of the aircraft can be reduced to the greatest extent.

4. All kinds of household electrical appliances and industrial products. Using the hollow cup motor as the actuator can improve the product grade and provide superior performance.

5. Taking advantage of its high energy conversion efficiency, it can also be used as a generator; taking advantage of its linear operation characteristics, it can also be used as a tachogenerator; coupled with a reducer, it can also be used as a torque motor.

With the advancement of industrial technology, the strict technical conditions of various electromechanical equipment put forward higher and higher technical requirements for servo motors. The scope of application on low-end products such as civilian use is to widely improve product quality. According to relevant statistics, there are more than 100 kinds of civilian products in industrially developed countries that have maturely applied hollow cup motors.

8. Domestic development status of coreless motor

The domestic industry has not yet fully understood the excellent performance of the hollow cup motor, which has hindered the technological progress of electromechanical products in many fields and seriously affected our technical competitiveness with similar foreign products. Many new products developed in China, because the motor performance does not meet the requirements, the overall level of their products has always been far behind similar foreign products, which limits the development and development of many products, such as medical equipment, prosthetics, robots, video cameras, cameras and This phenomenon even exists in some special fields, such as textile machinery and laser measuring instruments. However, due to its complex process, the production of hollow cup motors is far less automated than that of iron core motors, resulting in high production costs, high labor costs, and high requirements for the operator's skill level. Bring many difficulties and restrictions to mass production. The research and development of hollow cup motors in our country has a history of 20 to 30 years, but it has not developed rapidly until later, not only replacing imported products in the domestic market, but also companies have begun to participate in the competition in the international market.