Industrial robots are widely used in manufacturing industries such as automobile manufacturing, electrical equipment production, and food machinery processing. With the increase in labor costs in China, the trend of robots replacing human labor is becoming more and more obvious. The advantages of robots in producing products with good consistency and high assembly precision are also increasingly valued by manufacturers.
Currently, the cost of robots globally is mainly composed of: reducers ( around 35%), servo motors (around 20%) , control systems ( around 15%) , and machining of the robot body ( around 15% ). The global high-end robot market is primarily controlled by a few international robot companies such as ABB , Fanuc , and Kuka , and 75% of the precision reducers used in these robots are manufactured by Japanese companies.
Precision speed reducers used in the robotics industry can be divided into three types: RV speed reducers, harmonic speed reducers, and planetary speed reducers. Their market share is approximately 40% , 40% , and 20% , respectively .
In articulated robots, RV reducers are generally placed in heavy-load positions such as the base, upper arm, and shoulder, while harmonic reducers are generally placed in the forearm, wrist, or hand.
RV reducer is short for Rotary Vector reducer. It was first invented in Japan. It is a new hybrid of traditional cycloidal pinwheel and planetary gear transmission devices. RV reducer has a large transmission ratio ( 30-260 ).
The principle of RV reducers has been public for a long time and is not protected by patents, which is different from what we have always heard. However, Japan still occupies 80% of the RV reducer market, with the main brands being Nabtesco and Sumitomo.
RV reducer structure
The transmission device of the RV reducer consists of two parts: a first-stage involute cylindrical gear planetary reduction mechanism and a second-stage cycloidal pinwheel planetary reduction mechanism, forming a closed differential gear train.
The active sun gear 1 is connected to the input shaft. If the involute center gear 1 rotates clockwise, it will drive the three planetary gears 2, arranged at 120 ° intervals , to revolve around the center gear axis while also rotating counterclockwise. Three crankshafts 3 are fixedly connected to the planetary gears 2 and rotate at the same speed. Two cycloidal wheels 4, with a phase difference of 180 ° , are hinged to the three crankshafts and mesh with a fixed pinwheel. While their axes revolve around the pinwheel axis, they also rotate in the opposite direction, i.e., clockwise. The output mechanism ( i.e., the planetary carrier ) 6 is driven by three pairs of crankshaft support bearings mounted on it, transmitting the rotation vector from the cycloidal wheels at a 1:1 speed ratio. (See diagram below)
RV reducer working principle
The core challenge in manufacturing RV reducers lies in the close coordination of various processes, including: tooth surface heat treatment, machining accuracy, part symmetry, grouping technology, and assembly accuracy. The overall distribution of tolerances in these processes results in product wear and lifespan.
The main domestic RV reducer manufacturers are Nantong Zhenkang and Hengfengtai. Nantong Zhenkang 's annual output reached more than 200 units in 2017. Its products have been tested by many robot manufacturers, including foreign companies such as ABB , KUKA , and FANUC, as well as domestic companies such as EFORT and Estun.
Speed reducers achieve speed reduction through the simple principle that the rotational speed is inversely proportional to the number of teeth, achieved by the transmission between large and small gears. However, to achieve a large transmission ratio, using the commonly seen cylindrical gears would result in a very large gear reducer. So, how can we minimize its size?
Harmonic reducers simply embed gears inside them!
A harmonic gear drive mainly consists of four basic components: a wave generator, a flexible gear, a flexible bearing, and a rigid gear.
Harmonic reducer structure
A harmonic drive reducer is a gear transmission that uses a wave generator fitted with a flexible bearing to cause controllable elastic deformation of a flexible gear, which then meshes with a rigid gear to transmit motion and power. (See diagram below)
Working principle of harmonic reducer
The main technical challenges of harmonic reducers lie in the lifespan of the flexspline and the machining accuracy.
In October 1970 , Hasegawa Gear Co., Ltd. and USM Corporation of the United States reached an agreement, with each party contributing 50% of the capital, to establish Harmonic Drive Systems Inc. at 3-24-13 Minamirokugo , Ota - ku, Tokyo . This company went public in Germany in 2002 and in the United States in 2004 , establishing subsidiaries in Germany and the United States respectively, to handle product sales in Europe and the Americas. Harmonic Drive Systems Inc.'s Japanese, German, and American subsidiaries essentially monopolize the global harmonic drive gearbox market.
China began research and development of harmonic drives in 1961. To date, dozens of companies in China, including Beijing Zhongji Kemei Harmonic Drive Co., Ltd. and Beijing Harmonic Drive Technology Research Institute, are engaged in research and production in this field, and have successively developed various types of harmonic gear transmission devices. Currently, China's manufacturing capacity for harmonic drives is only equivalent to Japan's level in the 1980s. The main problems facing the domestic harmonic drive industry are its small scale, limited product variety, and insufficient research and development personnel and investment.
Currently, there are very few domestic companies that can rival HarmonyNav.
In general, my country's progress in precision speed reducers is constrained by two major areas: materials and precision machining.
