I. The Rise of Humanoid Robots
In 1927, Westinghouse Electric Manufacturing Company in the United States manufactured the world's first humanoid robot, "Televox". In 1972, Waseda University developed the world's largest humanoid robot, WABOT-1, which was capable of walking on two legs and conversing in Japanese.
In 2000, Honda launched the humanoid robot ASIMO, representing a highly integrated stage in the development of humanoid robot systems, possessing highly refined humanoid movements and artificial intelligence. In 2016, Boston Dynamics launched the humanoid robot Atlas, which has excellent balance and obstacle-crossing capabilities, enabling it to undertake search and rescue missions in dangerous environments.
In 2020, Agile Robotics, an American company, successfully launched Digit, the first commercially available bipedal robot priced at $250,000. It can autonomously select and move boxes in an unattended environment, making it suitable for various applications such as logistics, warehousing, and industry. In 2022, Tesla's humanoid robot debuted at AIDAY, once again sparking a wave of discussion about how humanoid robots can achieve commercialization and mass production.
In contrast, my country's humanoid robot industry started relatively late. In 2000, the National University of Defense Technology independently developed China's first humanoid robot, "Pioneer," which possessed human-like appearance features and could simulate human walking and basic operational functions. In 2018, UBTECH released its first-generation Walker robot, achieving a breakthrough in China's bipedal robot walking capabilities.
In August 2023, Unitree Robotics released the H1, China's first fully functional, full-size general-purpose humanoid robot, with shipments expected to begin around the fourth quarter of this year. In November 2023, the GR-1 Fourier humanoid robot, which appeared alongside the General Secretary, achieved a domestic production rate of over 90% for its chips and components and is currently in small-batch production. On December 1, 2023, Shenzhen UBTECH Robotics Corp. passed its listing hearing and is about to be listed on the main board of the Hong Kong Stock Exchange, becoming the "first listed humanoid robot company."
With the continuous research and development efforts of companies such as UBTECH, Fourier Intelligence, CloudMinds, Unitree Robotics, XPeng, iFlytek, Logic Robotics, and Dreame Technology, as well as research institutions such as Beijing Institute of Technology, Zhejiang University, National University of Defense Technology, Harbin Institute of Technology, and the Institute of Machine Intelligence of Shanghai University of Science and Technology, my country's humanoid robot industry is experiencing a boom in development.
According to the "Analysis Report on Humanoid Robot Technology Patents" released by the People's Daily Online Research Institute, China has filed a total of 6,618 patent applications for humanoid robot technology, leading countries and regions such as Europe, the United States, Japan and South Korea, and ranking first in the world; Chinese company UBTECH ranks first in the world in the number of valid humanoid robot patents.
In October 2023, the Ministry of Industry and Information Technology issued the "Guiding Opinions on the Innovative Development of Humanoid Robots," which pointed out that by 2025, a preliminary innovation system for humanoid robots will be established, breakthroughs will be achieved in a number of key technologies such as "brain, cerebellum, and limbs," and the safe and effective supply of core components will be ensured. Complete robot products will reach international advanced levels and achieve mass production, with demonstration applications in special, manufacturing, and public service scenarios, and effective governance mechanisms and methods will be explored and formed.
The "Opinions" document clarifies the future development direction and key tasks, providing a clear path for the orderly development of the humanoid robot industry, and my country's humanoid robot industry is on the verge of mass production.
II. Riding the wave, focus on high-value components such as planetary roller screws.
Humanoid robots integrate advanced technologies such as artificial intelligence, high-end manufacturing, and new materials, and are expected to become disruptive products following computers, smartphones, and new energy vehicles. They will profoundly change human production and lifestyles and reshape the global industrial development landscape.
Currently, humanoid robot technology is evolving rapidly, becoming a new high ground for technological competition, a new track for future industries, and a new engine for economic development, with great development potential and broad application prospects. GGII believes that as the humanoid robot industry enters the pre-mass production phase, the high-value, high-barrier core component segment of humanoid robots will usher in a period of development opportunities.
Planetary roller screws are a core component of the "limbs" of humanoid robots and a crucial link in my country's breakthrough in key "limb" technologies for humanoid robot industry. Taking Tesla's Optimus robot as an example, the Optimus torso has 28 joints, 14 rotary joints and 14 linear joints. Among them, the linear joints use a total of 14 reverse-type planetary roller screws of three sizes (large, medium, and small), accounting for 13.8% of the total value.
Schematic diagram of planetary roller screw application for humanoid robots
Source: Xinjian Transmission Official Website, compiled by GGII
III. What is a planetary roller screw?
Planetary roller screws convert rotary motion into linear motion. The transmission unit consists of rollers between the screw and the nut. It is composed of a planetary carrier, internal gear ring, nut, rollers, screw, etc. It overcomes the inherent shortcomings of traditional hydraulic transmission devices, such as poor environmental adaptability, low reliability, and poor use and maintenance, and combines the advantages of planetary gear transmission, harmonic gear transmission, ball screw, needle roller bearing and other mechanisms.
By arranging several planetary thread rollers around the main lead screw, the contact surface and force-bearing surface of the lead screw transmission process are greatly increased, thus achieving advantages such as "high load capacity, high efficiency, high precision, and high reliability".
Schematic diagram of the internal structure of a planetary roller screw
Simplified diagram of standard planetary roller screw motion
Source: "Principles of Planetary Roller Screw Motion and Finite Element Analysis", compiled by GGII
Planetary roller screws can be classified into standard planetary roller screws, reverse planetary roller screws, circulating planetary roller screws, differential planetary roller screws, and bearing ring planetary roller screws based on their structural composition and motion relationships. Their respective characteristics and application scenarios are shown below:
Types of planetary roller screws
Data sources: "Precision Analysis and Design of Planetary Roller Screw Transmissions", Xinjian Transmission Product Technical Manual, compiled by GGII
The main difference between planetary roller screws and ball screws is that planetary roller screws use threaded rollers instead of balls to transmit the load. This allows them to withstand higher static and dynamic loads, with a static load capacity three times that of ball screws and a lifespan 15 times longer. They also offer greater rigidity and impact resistance, and can provide higher speeds and greater acceleration.
In addition, planetary roller screws use threaded drives, allowing for a wider range of pitch designs, and the lead of planetary roller screws can be smaller than that of ball screws.
Comparison between planetary roller screws and ball screws
Source: "A Discussion on the Plastic Forming of Planetary Roller Screw Pairs", compiled by GGII
IV. What are the technological barriers of planetary roller screws?
1. Lead screw precision
Planetary roller screw pairs achieve precision transmission through threaded engagement, therefore, a high precision grade of raceway surface roughness is recommended. Simultaneously, planetary gears have relatively small tooth profiles, so to ensure the assembly accuracy of the planetary roller screw pair, the gear pair should also employ a high machining precision grade.
2. Surface heat treatment
The purpose of heat treatment is to improve the material properties and machinability of the components in a planetary roller screw assembly, as well as to eliminate residual stress. Heat treatment processes can be divided into two main categories: preliminary heat treatment and final heat treatment. Preliminary heat treatment aims to improve the screw's machinability, eliminate residual stress, and prepare for final heat treatment; its main processes include tempering, annealing, normalizing, and aging. Final heat treatment aims to improve the surface hardness and wear resistance of the threads.
Due to outdated technology and equipment, improper selection of heat treatment process parameters, etc., the heat treatment quality is poor and the deformation after heat treatment is large. The main damage form of planetary roller screw pairs is contact fatigue wear, and improper heat treatment process will reduce their service life.
Heat treatment methods for different parts of planetary roller screws
Source: "Research on Manufacturing Process and Transmission Performance of Precision Planetary Roller Screw Pairs", compiled by GGII
3. Processing and manufacturing
Planetary roller screws mainly suffer from deformation errors, manufacturing errors, and installation errors. The manufacturing process is crucial for minimizing these errors. The manufacturing process includes errors in thread pitch, thread profile, gear tooth pitch, gear tooth profile, and manufacturing eccentricity, placing extremely high precision requirements on the manufacturing process. The machining steps for planetary roller screws are shown below:
Planetary roller screw machining process
Source: "Research on Manufacturing Process and Transmission Performance of Precision Planetary Roller Screw Pairs", compiled by GGII
Threaded rollers are a crucial component of the transmission system, and their forming process and product quality directly determine the performance of the planetary roller screw. When the planetary roller screw transmission mechanism is operating, multiple threaded rollers share the load, preventing any single roller from failing due to excessive load. As a key part of the planetary roller screw transmission mechanism, the forming process and product quality of the threaded rollers directly determine the assembly quality and performance of the mechanism. Currently, planetary roller screw threads are processed using methods such as rolling (rolling) and grinding (grinding).
Currently, grinding is the main processing method for high-precision ball screw threads. The essence of grinding is that many abrasive grains on the surface of the grinding wheel scratch, engrave and cut the workpiece surface. The high-speed rotating forming grinding wheel of the thread grinding machine performs high-speed cutting on the surface of the workpiece, thereby obtaining higher precision. Taking ball screws as an example, the highest precision that can be achieved by grinding is P1.
Note: According to the national standard GB/T 17587.3—2017 Ball Screw Pairs Part 3: Acceptance Conditions and Acceptance Inspection, ball screws are divided into 7 accuracy grades: 1, 2, 3, 4, 5, 7, and 10, with grade 1 (P1) being the highest grade.
4. Processing equipment
In the production of roller screws, thread grinding machines are key equipment for improving screw accuracy. These mainly include internal thread grinding machines and external thread grinding machines (or integrated turning and grinding machines), and are mostly purchased from countries such as Japan, Europe, and the United States. Delivery cycles are long, and even after the equipment arrives on-site, a commissioning period is still required. Currently, domestically produced grinding machines can meet the machining requirements of mid-range screws with C3-C4 accuracy, but when mass-producing high-end screws (C0-C2), inconsistent output occurs.
Note: C precision grade is the Japanese JIS precision grade standard, which is divided into 6 precision grades: C0, C1, C3, C5, C7, and C10. The variation of C3 within any 300 strokes is equivalent to the domestic P2 precision grade, and C2 is equivalent to the domestic P1 standard.
Comparison between internal thread grinding machines and external thread grinding machines
Source: Dongwu Securities, compiled from publicly available information.
V. Domestic planetary roller screws are in their initial stage, with significant room for domestic substitution.
In 1942, Carl Bruno Strandgren of Sweden first applied for a patent for a circulating planetary roller screw, and in 1954 he applied for patents for standard and reverse planetary roller screws. In 1970, the Swiss company Rollvis began developing planetary roller screws, and the Swedish company SKF also began developing them simultaneously. Foreign planetary roller screw companies, through years of technological accumulation and first-mover advantage, have achieved market dominance. According to relevant data, foreign companies Rollvis, GSA, Ewellix, and Rexroth hold market shares of 26%, 26%, 14%, and 12% respectively in the domestic market, while domestic companies (including Nanjing Craft, Bote Precision, and Taiwan UST) account for only 19%, indicating significant potential for domestic substitution.
Currently, although China has a certain industrial foundation in planetary roller screws, with manufacturers such as Nanjing Craft and Bote Precision Machinery capable of small-scale production, their performance lags significantly behind foreign products, primarily in efficiency, load-bearing capacity, and precision. Overcoming the challenges of core components is a prerequisite for the mass production of humanoid robots in my country. Against this backdrop, domestic companies are continuously entering the planetary roller screw field, promoting domestic substitution and facilitating the mass production process of the humanoid robot industry.
Domestic companies' presence in the planetary roller screw field
Data source: Public information, compiled by GGII
VI. The market potential for planetary roller screws in the field of humanoid robots is vast.
Planetary roller screws have a wide range of downstream applications, mainly including automobiles and new energy, oil and gas, medical devices, optical instruments, construction machinery, robots, automation and machine tool equipment. According to relevant data, the global roller screw market was worth approximately RMB 2.15 billion in 2023.
In the field of humanoid robots, planetary roller screws are mainly used in linear joints, offering advantages such as high load capacity, fast response, small size, low noise, and high precision. According to GGII estimates, the global market demand for planetary roller screws in the humanoid robot sector will reach nearly 18 million units by 2030, with a market size of nearly 13 billion yuan.
Market Size Estimation for Planetary Roller Screws in the Humanoid Robot Field
