An industrial robot is a general-purpose machine equipped with memory devices and end effectors, capable of performing various movements or processes to replace human labor. In production, it typically replaces workers in performing monotonous, frequent, and repetitive long-term tasks, or in hazardous or harsh environments. It can improve production efficiency and product quality, and is an effective solution for enterprises to supplement and replace their workforce.
The current development characteristics of industrial robots are high speed, precision, compact body structure, multiple degrees of freedom, and increased rigidity. Key fields also require heavy loads or fast response times. For example, welding robots in automobile manufacturing mostly have a load capacity between 150-300 kg, while assembly robots in the electronics industry need to respond quickly to parts on the production line.
In the field of mechanical transmission, a speed reducer is an intermediate device connecting the power source and the actuator. Typically, it reduces the speed of high-speed power from motors, internal combustion engines, etc., by meshing a small gear on the input shaft with a large gear on the output shaft, thus transmitting greater torque. Currently, mature and standardized speed reducers include: cylindrical gear reducers, worm gear reducers, planetary reducers, planetary gear reducers, RV reducers, cycloidal pinwheel reducers, and harmonic reducers. Since the 1980s and 1990s, the development of emerging industries such as aerospace, robotics, and medical devices has created a demand for high-performance precision speed reducers with simple and compact structures, high power transmission, low noise, and smooth transmission. Among these, RV reducers and harmonic reducers are two important types of precision speed reducers.
RV (Rot-Vector) reducer
The RV reducer was developed based on the cycloidal pinwheel transmission and features a two-stage reduction and a central disc support structure. Since its introduction to the market in 1986, it has become the go-to reducer for robots due to its advantages such as large transmission ratio, high transmission efficiency, high motion accuracy, small backlash, low vibration, high rigidity, and high reliability.
Harmonic reducer
Harmonic reducers consist of three parts: a harmonic generator, a flexible wheel, and a rigid wheel. Their working principle involves the harmonic generator causing controllable elastic deformation of the flexible wheel, which then meshes with the rigid wheel to transmit power and achieve speed reduction. Depending on the type of harmonic generator, there are cam-type, roller-type, and eccentric disc-type reducers. Harmonic reducers feature large transmission ratios, small overall dimensions, fewer parts, and high transmission efficiency. Single-unit transmission ratios can reach 50-4000, with transmission efficiencies as high as 92%-96%.
Planetary gear reducer
As the name suggests, a planetary gear reducer consists of three planetary gears rotating around a sun gear. Planetary gear reducers are small in size, lightweight, have high load-bearing capacity, long service life, smooth operation, and low noise. They feature power splitting and unique multi-tooth meshing characteristics; they are a widely used industrial product, with performance comparable to other military-grade planetary gear reducers, but at an industrial-grade price, making them suitable for a wide range of industrial applications.
Industrial robots are typically powered by AC servo motors. Since these motors are driven by pulse signals and their speed can be adjusted, why do they still need speed reducers? Industrial robots often perform repetitive actions to complete the same processes. To ensure reliable task completion and process quality, high positioning and repeatability are required. Therefore, improving and ensuring the accuracy of industrial robots necessitates the use of RV reducers or harmonic reducers. Another function of precision reducers in industrial robots is to transmit greater torque. When the load is heavy, simply increasing the power of the servo motor is inefficient; a speed reducer can be used to increase the output torque within a suitable speed range. Furthermore, servo motors are prone to overheating and low-frequency vibration at low frequencies, which is detrimental to the accurate and reliable operation of industrial robots that operate for extended periods and in cyclical processes.
The presence of precision reducers allows servo motors to operate at appropriate speeds, precisely reducing the rotational speed to the required speeds for various parts of the industrial robot, increasing the rigidity of the mechanical body while outputting greater torque. Compared to general-purpose reducers, robot joint reducers require characteristics such as short transmission chains, small size, high power, light weight, and ease of control. Reducers widely used in articulated robots mainly fall into two categories: RV reducers and harmonic reducers.
Compared to harmonic reducers, RV reducers have higher rigidity and rotational accuracy. Therefore, in articulated robots, RV reducers are generally placed in heavy-load positions such as the base, upper arm, and shoulder; while harmonic reducers are placed in the forearm, wrist, or hand; planetary reducers are generally used in Cartesian coordinate robots.
Current Market Status of Gear Reducers
Currently, there are two main types of speed reducers used in robotics: RV reducers and harmonic reducers. In articulated robots, RV reducers, due to their higher rigidity and rotational accuracy, are typically placed in heavy-load positions such as the base, upper arm, and shoulder, while harmonic reducers are placed in the forearm, wrist, or hand. Japan holds a dominant position in high-precision robot speed reducers, with 75% of the global precision speed reducer market currently dominated by two Japanese companies, Nabtesco and Harmonic Drive (commonly known in the industry as RV reducers and harmonic reducers). Reducers for major international robot manufacturers such as ABB, FANUC, and KUKA are supplied by these two companies. Harmonic Drive alone holds a 15% market share in the industrial robot joint sector.
According to industry insiders, the four major international giants purchase a precision reducer for 30,000 to 50,000 yuan, sell it to domestic customers with good relationships for about 70,000 yuan, and to ordinary customers with average relationships for about 120,000 yuan. The cost for domestic enterprises to purchase precision reducers is more than double that of international giants, which shows how big the profit difference is.
In 2013, global shipments of industrial articulated robot reducers reached 730,000 units, a year-on-year increase of 6%. Currently, the global precision reducer market is essentially monopolized by Japan's Nabtesco and Germany's Harmonicadrive. According to an announcement from Shanghai Electric Group, Nabtesco's sales revenue in 2012 was approximately 3 billion yuan, maintaining a stable global market share of 60%.
It's worth noting that Nabtesco of Japan took 6-7 years from proposing the RV type design in the early 1980s to achieving a substantial breakthrough in RV reducer research in 1986; while Nantong Zhenkang and Hengfengtai, the first domestic companies to achieve results, also took 6-8 years. This demonstrates that there are no shortcuts in technology. In other words, the current development level of RV reducers in China is still at the level of Japan in the late 1980s.
According to unnamed sources within the industry, major international robot manufacturers such as ABB, FANUC, Yaskawa, and KUKA all rely on these two Japanese companies for their speed reducers. Furthermore, they have very stringent cooperation conditions with these two companies: users cannot use other companies' products while using these two companies' products, or the partnership will be terminated.
Nantong Zhenkang's annual output last year was over 200 units. Its products have been tested by several robot manufacturers, including international companies like ABB, KUKA, and FANUC, as well as domestic companies such as Eft and Estun. Eft, in particular, has purchased several hundred RV reducer products after testing them.
Core components have long been a constraint on the rapid development of robots in China, making it crucial to achieve the localization of accelerators as soon as possible.
