Hollow cup motor (Micro coreless motor) is a special DC motor. Traditional DC motor is widely used in industrial production, household appliances, transportation and other fields, composed of two core parts of the stator and rotor, the stationary part of the DC motor is called the stator, the main role of the stator is to generate a magnetic field, composed of the frame, main magnetic pole, reversing pole, end cap, bearing and brush device. Commonly used stator magnet materials include Ndfeb, Samarium cobalt, aluminum nickel cobalt and ferrite. The part that rotates during operation is called the rotor, and its main role is to produce electromagnetic torque and induced electromotive force, which is the hub of DC motor for energy conversion, so it is usually called the armature, which is composed of rotating shaft, armature core, armature winding, commutator and fan.
The hollow cup motor breaks through the structural form of the traditional DC motor in structure, using a no-core rotor, and its armature winding is a hollow cup coil, similar in shape to a water cup, so it is called "hollow cup motor". Hollow cup motor belongs to DC, permanent magnet, servo micro motor. This novel rotor structure makes the hollow cup motor have the following excellent characteristics: ① Energy-saving characteristics: core-free design completely eliminates the power loss caused by the formation of eddy currents in the iron core, and the energy conversion efficiency is very high, the maximum efficiency is generally more than 70%, and some products can reach more than 90% (iron core motors are generally 70%); (2) Control characteristics: fast starting and braking, fast response, mechanical time constant less than 28 milliseconds, some products can reach less than 10 milliseconds (core motors are generally more than 100 milliseconds); The speed can be easily adjusted sensitively under the high speed running state in the recommended operating area; (3) Drag characteristics: The operation stability is very reliable, the fluctuation of speed is very small, as a micro motor, its speed fluctuation can be easily controlled within 2%; ④ Lightweight characteristics: compared with the same power core motor, its weight and volume are reduced by 1/3-1/2, and the energy density is greatly improved. The core indicator of the hollow cup motor is the power density, that is, the ratio of the output power to the weight or volume. The rotor without iron core eliminates eddy current and hysteresis loss at the molecular end and improves the energy conversion efficiency. Reduced weight and volume at the denominator end.
The brush is an important component of the brushed motor, responsible for conducting the current between the rotating parts and the stationary parts. Because it is more made of graphite, it is also called carbon brush. In the ordinary DC motor, in order to keep the rotor rotating, the rotor current direction needs to be changed in real time, so the commutator and carbon brush need to be used. The brushless motor cancels the mechanical brush commutation mode, so the rotor position needs to be detected to complete the electronic commutation. There are two common ways to obtain rotor position information: (1) sensorless control mode, when the motor is running, the rotor position is determined by the measurable variable fed back by the motor; The position sensor control mode, the motor rotor position is directly detected by the position sensor inside the motor. Commonly used position sensors are Hall sensors, photoelectric encoders, rotary transformers and so on. Hall sensor detection accuracy is not high, but the price is low; The photoelectric encoder and rotary transformer position detection is accurate and the error is small, and they are generally used for high-performance control systems, such as magnetic field orientation control and direct torque control.
Hollow cup motor according to its structure can be divided into brush and brushless two kinds. ① Brushed hollow cup motor (also known as DC brushed coreless motor, rotor without iron core) : The use of mechanical brush commutator, generally by the shell, soft magnetic material inner stator, permanent magnet stator, hollow cup rotor armature composition. When the hollow cup brush motor is energized, the winding has current through, generating torque, the rotor begins to rotate, if the rotor turns to a specific Angle, the brush uses the mechanical commutator to change the direction of the current, so that the output torque direction is unchanged, the rotor continues to rotate. Because the hollow cup brush motor uses the brush commutation, there is a certain relative friction during the operation of the motor, which will produce noise, electric spark, and reduce the service life of the motor. Generally domestic "hollow cup motor" generally refers to brush motor; ② brushless hollow cup motor (also known as DC brushless slotless motor, stator without iron core) : The use of electronic commutation, generally by the shell, soft magnetic materials, insulating materials and hollow cup armature composed of the stator and permanent magnetic steel rotor. The hollow cup brushless motor connects different windings to the circuit by controlling the on-off of electronic components to achieve the effect of reversing. This commutation mode makes the hollow cup brushless motor have the characteristics of high efficiency, small torque fluctuation, high service life, compact structure, easy maintenance and so on.
1.2. Core barrier: winding process
The process flow of hollow cup motor is complex, and the processing difficulty is far more than that of ordinary DC slotted motor. Taking the DC slotless motor of Dingzhi Technology (that is, its hollow cup motor products) as an example, from the front coil winding, middle bearing, mandrel, support ring and other core parts installation, to the rear cover installation and circuit board welding line, etc., involving nearly 30 processes, the complexity is far more than ordinary DC slotted motors. Coil production needs to go through the process of enameled wire - winding - heating shaping - wire stripping, connecting the common wire - coil installation and so on.
Among them, coil manufacturing is one of the core processes of hollow cup motor. Coreless self-supporting windings are made of so-called enameled wire, which is an insulated copper wire with a coat of paint on the outside. In the manufacturing process, the paint of adjacent wires is fused together by applying pressure and temperature. Proper bonding (tape or fiberglass) can further improve the strength and shape stability of the winding, which is especially important under high current loads.
The production technology of hollow cup motor coil is mainly divided into three categories according to the forming method of coil: 1) manual winding. Through a series of complex processes, including pin insertion, manual winding, manual wiring and other steps to produce. 2) Winding production technology. The winding production technology is semi-automatic production, the enameled wire is first sequentially wound to the main shaft with a diamond-shaped cross-section, and it is removed after reaching the required length, and then flattened into a wire plate, and finally the wire plate is wound into a cup-shaped coil. Taking a winding hollow cup as an example, the manufacturing process can be roughly divided into the following steps: (1) Winding of hexagonal wire billet coil: it is carried out on the inclined winding group winding machine; ② The wire blank coil is pasted with two pieces of shaped pressure sensitive tape, demoulding to be flattened; ③ Flattening: the shape plate is inserted into the wire blank coil, and the coil is flattened, and then sent to the flattening machine to flatten and become a flat wire blank. Shape with a bamboo scraper. Cut off the excess tape, leaving only one hitch, the hitch should be left on the slightly raised side of the flat strand, so that the reel can form a row; ④ Coil: the flat wire blank is fed into the coil of the hollow cup coil machine, so that the wire blank is connected to the end, and the tape is pasted on the surface of the wire blank head to become the hollow cup coil; ⑤ Coating epoxy shaping: After coating epoxy adhesive, put it in the oven for curing and shaping. 3) One molding production technology. The winding machine winds a enameled wire to a spindle according to the law through the automation equipment, and takes off the coil after winding into a cup, forming at a time, and does not require multiple processes such as rolling and flattening, with a high degree of automation.
Overseas winding process developed early, the degree of automation is higher than domestic. The domestic mainly adopts winding production, the process is more complicated, the labor intensity of workers is large, can not complete the coil with thicker wire diameter, and the scrap rate is high. Foreign countries mainly use one-time wound production technology, high degree of automation, high production efficiency, coil diameter range, good coil quality, tight arrangement, motor types, good performance. The hollow cup motor can be divided into straight wound, saddle shape and inclined wound according to the winding method. In 1958, Dr.F. F. aulhaber (von Haber) of Germany developed the inclined winding coil winding technology, and obtained the patent technology of the inclined winding of the rotor coil of the hollow cup motor in 1965. Germany, Switzerland, Japan and other hollow cup motor development earlier, in the winding process has accumulated rich experience. Among the three leading hollow cup motors in the world, Swiss Maxon mostly uses straight wound shape and saddle shape, and German Faulhaber and Swiss Portescap mostly use inclined wound shape. The process of straight-wound winding is more complicated, and it is mostly used for long winding structures, often made of multiple winding. Saddle shape can reduce coil thickness, reduce magnetic air gap effectively on high power density motor, increase the length of cutting magnetic field, and make better use of stator magnetism; Oblique winding developed earlier, relatively simple winding, tight wiring, suitable for large batch production.
Winding is the core technical barrier of hollow cup motor. ① Design link: overseas three main technology originated in the 1960s, the domestic hollow cup motor started late, less research, lack of combination of material subdivision grade, rotor cup type to optimize the motor, lack of systematic forward design, lack of customized requirements of system drive scheme configuration and product design capabilities; ② Processing link: Compared with the traditional brushless motor, brush motor, servo motor, the structure of the hollow cup motor belongs to the toothless groove structure, there is no fixed groove, all enameled wire is suspended winding, there is no internal support, it is very difficult in the process, and the early yield is low. In terms of winding accuracy, the precision requirements of hollow cup motors are higher than those of traditional motors. The hollow cup motor itself is small in size, and the tolerance for error is lower than that of ordinary permanent magnet motors and stepper motors, and the processing accuracy directly affects the stability of the magnetic field. The difference of wire thickness and winding turns makes the winding resistance value, starting current, speed constant and other motor parameters have great differences. Because of this, domestic manufacturers need to improve the precision, yield and automation in the production and processing links. Compared with overseas, China is also relatively weak in terms of winding equipment. Winding equipment can be divided into automatic and manual non-automatic equipment. Compared with overseas, the degree of automation of winding equipment in China is relatively low. The world's leading manufacturers of winding equipment include Meteor of Switzerland, Tanaka Seiki Co., Ltd. of Japan, and Hitote Mechanical Engineering Co., LTD. Domestic enterprises are still in a relatively vacant state in terms of equipment, and they purchase more Japanese winding equipment, with prices ranging from hundreds of thousands to millions. The relatively representative companies in China include Zhongspecial Technology, Dongguan Taili Electronic Machinery Co., LTD., Qinlian Technology, Kunshan Cook and so on.
1.3 Downstream applications: The characteristics of the hollow cup motor determine the downstream application scenario
The hollow cup motor belongs to the micro motor, and the upstream raw materials are similar to the raw materials of the micro motor, including copper, steel, magnetic steel, bearings, plastics, etc. Hollow cup motor was originally used in aviation, aerospace, military and other cutting-edge industries, in recent years, its application gradually expanded to civilian industries, such as medical devices, consumer electronics, power tools, industrial automation and other scenarios.
The different performance of the hollow cup motor corresponds to its application in different fields: 1) the characteristics of small size, light weight, and large power to volume ratio make it suitable for areas with high weight requirements, such as various types of aircraft, etc., which can minimize the weight of the aircraft; It is also widely used in various consumer electronic products, such as electric toothbrushes and portable electric fans. 2) The characteristics of rapid starting and braking and extremely fast response make it suitable for areas that need to achieve fast automatic control, such as missile direction adjustment with high control performance requirements, high-rate optical drive follow-up, highly sensitive equipment, industrial robots, etc. 3) The characteristics of high energy conversion efficiency and long running time make it suitable for all kinds of fields requiring energy saving and battery life, such as portable instruments and field work equipment.
Humanoid robot opens a new blue ocean of hollow cup motor applications. According to the latest development of Optimus, a humanoid robot released by Tesla, each hand includes six drives and 11 degrees of freedom, two drives for the thumb and one drive for each of the other four fingers, and the hand can carry up to 20 pounds. The hand joint module is mainly composed of hollow cup motor, precision planetary reducer, ball screw and sensor. The hollow cup motor enables the finger to have the ability to move, the precision planetary gearbox enables the manipulator to position more accurately and use more flexible, the encoder provides high-precision position feedback and speed feedback of the hand, and the sensor enables the robot to have human-like perceptual function and reaction ability. According to Musk, the number of humanoid robots in the future will exceed the number of humans, and it is expected to reach the level of 100 billion units in the long term. Hollow cup motor is the mainstream technical solution of robot hand with high certainty. Humanoid robots use 6 hollow cup motors per hand, considering the end situation, humanoid robots are expected to reach the level of one billion units, if the mass production of humanoid robots landing, will pull hollow cup motor related enterprises revenue growth.
