(2) Competition pattern: overseas head enterprises dominate, and domestic enterprises are accelerating to catch up

Overseas leading enterprises, the market concentration is high. Hollow cup motor technology is from the German Dr.F. F. Volhaber in 1958 developed inclined winding coil winding technology, started earlier, with the continuous development of production technology, foreign hollow cup coil production technology has been very mature. Most of the foreign countries use a molding technology, the production process of high degree of automation, less human interference, so in improving production efficiency at the same time also improve product quality, reduce production costs, the competitive advantage is obvious, so occupy a larger market share. According to the statistics of QY research in the “Global Coreless DC Motors Market Research Report 2022″, the world’s three leading companies occupied 55.43% of the market share in 2021, and the competitive pattern is highly concentrated.

After catching up with domestic enterprises in recent years, the gap in product performance has been narrowing. Previously, China was not fully aware of the development prospects of hollow cup motors. In recent years, China’s hollow cup development speed is fast, there are more and more manufacturers began to engage in the design and manufacturing of hollow cup motor, the domestic leader Mingzhi electrical appliances can now produce base size 8mm, rated voltage 6V, no-load speed 13500rpm, mechanical constant 6.6ms, Brushed hollow cup motor with maximum continuous torque of 0.60mNm. Compared with the brushed hollow cup motor products of the same base size and rated voltage of Faulhaber, one of the world’s hollow cup taps, there is only a small difference in performance parameters, and the technical gap between domestic and foreign taps is narrowing.

(3) Domestic substitution: The need for humanoid robots to reduce costs is urgent, and domestic substitution has ushered in new opportunities

The key to the popularity of humanoid robots is cost reduction. Musk said at AI Day 2022 that he expects the Optimus to cost less than $20,000 when it eventually goes into production. From the perspective of return on investment, humanoid robots will be more attractive to customers only when they are widely used in housekeeping, rehabilitation, and industrial scenarios, and the cost is lower, so the humanoid robots need to reduce the cost urgently. The domestic hollow cup motor is more cost-effective, and the cost reduction demand brings new opportunities for domestic substitution. Compared with the price of hollow cup motors with similar performance and similar size of overseas manufacturers Maxon and domestic manufacturers Mingzhi Electrical appliances, Maxon products have small advantages in power density and maximum continuous torque, but their price is about 2 times that of Mingzhi electrical products, and Mingzhi electrical products are more cost-effective. Driven by the demand for cost reduction, more and more domestic manufacturers will enter the hollow cup industry, which is expected to duplicate the proven route of cost reduction of auto parts and accelerate the industrialization of humanoid robots.

Three, hollow cup coil design and production

(1) Coil design: Each of the three mainstream designs has its own strengths

Hollow cup motor coils are commonly used in three designs – straight winding, oblique winding, diamond winding.

The diamond winding design is the most material saving and the least power consumption. Liu Minghao compared and analyzed the copper loss of hollow cup motors with different coil designs in Maxwell 3D in “Design of Permanent Magnet DC Brushed Hollow cup Motors”. When the copper loss is stable, the copper consumption of diamond winding is the smallest, followed by oblique winding, and the copper consumption of straight winding is the largest. From the root analysis, the copper consumption of winding copper wire comes from the resistance in the wire. In the case of the same material, the winding span is 180°, because the axial edge distance of the straight winding is longer, the required copper wire size is the longest, so the copper consumption is the largest. The oblique winding is slightly longer than the diamond winding at the corner distance, and the length is close but the copper consumption is slightly greater than the diamond winding, so the diamond winding is the most material saving and the least power consumption.

In terms of winding process, the inclined winding is more suitable for manual winding, the straight winding is second in difficulty, and the diamond winding is more difficult to manually wind, which generally needs to be completed with the help of specific winding machine process equipment. In the process of manual winding, the human error is large, and the multi-sided winding and fixing are more likely to have insufficient precision and deformation, which will reduce the spatial density and shape specification of the winding, which will affect the role of electromagnetic conversion of the winding. The hollow cup motor of the world famous enterprises mostly uses the mechanical diamond winding method. In the previous design, the air gap area in the straight winding is larger, the axial direction of the hollow cup is longer or the rated power of the motor is larger.

(2) coil winding process: “winding type” is easy, “one molding” is better

The key to the production of hollow cup motor lies in the winding method of hollow cup coil. At present, there are two main production methods: winding production and one-time winding production.

1, winding production process

Winding production is mainly composed of four steps: wire feeding, blank coil winding, slab forming and coil forming. The following is an example of the intelligent manufacturing line of high-precision hollow cup coil of a Guizhou enterprise in Liu Qingxing’s Research on Quality Control of Hollow Cup Coil based on Small sample Learning.

Wire feeding: In the process of coil winding, the tension of the enameled wire will affect the degree of loose forming of the blank wire, and have different degrees of influence on the subsequent slab pressing and rolling forming process. Therefore, the servo magnetic damping tensioner is used to control the tension of enameled wire. The magnetic damping tensioner transmits constant torque to the magnetic field generated by the permanent magnet. Blank coil winding: After tension adjustment of tension controller, hollow cup coil winding machine will be enameled wire into a certain number of turns and lead pin number of blank coil. When the enamelled wire is wound to a constant number of turns, the rotation stops. The press plate on the left and right sides flattens the coil on the prismatic coil column. At the same time, the crochet is lifted under the enamelled wire and rotated to form a lead. Repeat the above process, when the number of turns and the number of leads of the blank coil reach the set value, the blank coil is formed.

Slab forming: After forming the slab coil, the hollow cup coil flattening device takes the slab coil from the prismatic coil column, and compels the slab coil into slab through the gluing heating on the fixture and the pressure setting of the fixture, and the slab wire plate is placed on the coil forming assembly for rolling forming.

Coil forming: The fixture moves along the guide rail, the pressed slab is sent to the coil winding device, and the slab is heated and pressurized by four molds and the coil cylinder in the middle, and then the slab is rolled into a coil. By setting the key process parameters such as pressure, temperature and time, the forming quality of the coil can be guaranteed. After coil winding is completed, the hollow cup coil is removed from the coil cylinder and placed on the picture acquisition platform in order to detect its appearance defects.