Industrial robots have been widely used in many fields such as automobile manufacturing due to their advantages of high repeatability, good reliability and strong anti-harsh environment.The widespread application of industrial robots is an effective means for automobile enterprises to realize automatic production, improve product quality and production efficiency, save labor and manufacturing costs, and enhance industrial competitiveness.

China's industrial robot manufacturing industry started from the seventh five-year Plan in the 1980s. With the support of the "863" program of the National science and Technology research project, China's robot industry has made a big leap from scratch after more than ten years of development, production and application.At present, from the perspective of China's industrial robot market, the weight of imported industrial robots is relatively large. Compared with foreign brands, the gap between domestic robots in terms of trouble-free running time, positioning accuracy, positioning speed and accuracy retention is mainly reflected in the substandard technology of core components.Bearing, as a key component of industrial robots, has great influence on the key performance indexes of robots, such as running stability, repeated positioning accuracy, turning accuracy and working reliability.

Characteristics and classification of industrial robot bearing

The development of modern industrial robots tends to be light, which requires the supporting bearing to have more light structure.Because the bearings to meet the industrial robot in limited installation space host, the precision and the carrying capacity of bearing stiffness and friction torque performance requirements, choose standard general bearing is very difficult to meet this requirement, pursuit of shape and thin wall bearing limit of size, with light weight, small volume, high precision, long life and other excellent properties, can solve this problem well.

Industrial robot bearings, accurately called industrial robot bearings, mainly include: thin-wall ball bearings, cross cylindrical roller bearings, harmonic reducer bearings.Most of them adopt non - standard, multi - scroll design principles.

1. Thin wall bearing with equal section

Different from ordinary bearings, the cross section of each series of this kind of bearing is mostly square, and the size is designed to be fixed (see Figure 1) : In the same series, the cross section size is unchanged, and it does not increase with the increase of the inside diameter, so it is called equal section thin-wall bearing.The equal section thin-walled ball bearing includes the series of thin-walled four-point contact ball bearing, the series of thin-walled angular contact ball bearing and the series of thin-walled deep groove ball bearing, which are mostly used in the waist, elbow and wrist of industrial robots.In the case of the same inner diameter size, thin-walled ball bearings with equal section contain more steel balls than standard rolling bearings, so as to improve the internal force distribution of the bearing, reduce the elastic deformation at the contact point between the ball and the channel, and improve the bearing capacity.

2. Thin-wall crossed cylindrical roller bearing

Thin-walled cross roller bearing internal structure of the roller are arranged 90 ° vertically cross each other, with a single bearing can bear radial force at the same time, the bidirectional interaction of axial force and overturning moment, with intervals between roller holder or the isolation piece, can prevent the each other between the tilt or roller of roller mill, effectively prevent the increase of the friction torque (see figure 2).In addition, the structure of vertical cross arrangement of rollers can avoid the locking phenomenon of rollers;At the same time, because the inner and outer ring of the bearing is a segmented structure, the clearance can be adjusted, even if the pressure is applied, higher rotation accuracy can be obtained.Thin-walled cross roller bearings are mainly used for robotic arms, critical robot shoulders, waist, hips and so on due to their light structure and good performance.

3.RV reducer bearing

RV reducer also known as precision bearing reducer, it is widely used in industrial robots because of its small size, strong impact resistance, large torque, high positioning accuracy and many other advantages.For RV reducer, the shape and structure of bearing and precise positioning are the key factors of compact structure, excellent rigidity and precise transmission. RV reducer bearings include a variety of thin-wall bearing series and cylindrical roller cage assembly series (see Figure 3).

4. Harmonic reducer

Harmonic reducer is a wave generator to generate controllable elastic deformation of the flexible wheel, the use of flexible bearing controllable elastic deformation to transfer motion and power, its characteristics are compact structure, high motion accuracy, high transmission ratio, used for small and medium torque of the robot joint.Flexible bearing is the core component of harmonic reducer. It can meet the requirement of high reduction ratio through elastic deformation of bearing. Moreover, the life of harmonic reducer mainly depends on the life of flexible bearing (see Figure 4).With the elastic deformation of the flexible bearing, it can bear not only cyclic stress load but also alternating stress load.
Development status of industrial robot bearings
Industrial robot bearing, as one of the key supporting parts of industrial robots, is still a relatively weak link in China.The existing national standards for bearings cannot meet and guide the design, production and inspection of industrial robot bearings.

Luoyang hk company over the years has been committed to research and development of industrial robots bearing, has been formed cross roller bearing, crossed cylindrical roller bearing, harmonic reducer wheel bearing series products of the three major categories, products from 20 mm to 1000 mm diameter in the inner diameter, from P5 to P2 level can manufacture precision, can fully meet the needs of the industrial robot makers.

Bearing company in industrial robot research and production practice, to make the industrial robot bearing production standardization, seriation, has compiled the industrial robot with harmonic reducer bearing samples, sample cross roller bearing, crossed roller wheel bearing samples, made the product technical standard, the standard demonstration, quality and technical supervision for the record by experts, to fill the domestic blank, and in line with international standards.
Currently, luoyang hk specializing in industrial robot bearing research and development, accumulated over the years production and sales of various bearing nearly 100000 sets of robots, are exported to Europe and the United States, Japan, Korea, Singapore, China, Taiwan and other countries and regions, as well as several domestic engaged in the industrial robot and the parts development and production of enterprises, scientific research units to provide ancillary products and technical support services.

Key technologies of bearings for robots

(1) Precise control technology of negative clearance of thin-wall bearing.Industrial robot bearings are required to run smoothly and have an appropriate starting friction torque, so there should be an appropriate amount of negative clearance during bearing production and assembly.Bearing a negative clearance is too large or too little directly affect the noise, vibration and service life of bearing, due to the robot with thin wall bearing inner and outer ring with thin wall thickness, adopts load loading method in measuring clearance, easily lead to deformation of ring, the amount of negative clearance is very difficult to control, need to use special processing and assembling method and technique, and using the special assembly tools.

(2) Precise control of assembly height of thin-wall angular contact ball bearing.The robot has compact structure and precise installation space, which requires high deviation in bearing assembly and strict control of similar bearings abroad.Because the wall thickness of thin-wall angular contact ball bearing ring is very small, it is easy to generate deformation, and the accuracy of each dimension is difficult to be precisely controlled. Besides, it is difficult to strictly control the size selection of inner and outer rings and rolling body, resulting in excessive assembly deviation after bearing assembly.Therefore, in order to realize the precise control of the thin wall angular contact ball bearing assembly and even achieve the purpose of universal matching, special groove position design, grinding process formulation, precise selection and so on must be carried out on the bearing, and meanwhile the grinding process of increasing the bearing protrusion quantity must be increased.

(3) Precise assembly technology of thin-wall bearing.Due to the ultrathin wall thickness and poor stiffness of the special robot series precision bearing, the common assembly method and mold are adopted, which can easily deform when the mating sleeve is heated.Therefore, in order to realize precision of thin wall bearing assembly, to the finished product of the indicators, must be used for thin wall bearing assembly size selection, formulation and special assembly assembly process, mold and accessories to strict matching good bearing ring grinding, detailed and strict assembly process, and develop special equipment set of tools and accessories, so as to ensure the accuracy of bearing assembly.

(4) Non-contact measurement technology of inner and outer diameter of thin-wall bearing ring.Thin wall bearing ring wall thickness is very thin, precision turning and grinding are needed to achieve the required tolerance, and thin wall bearing ring profile parameter measurement accuracy is high, the traditional detection methods, such as the standard of bearing outside diameter measurement using D913 instruments, measurement of torsional spring table with 0.001 request has the certain load, but the load table people as it is difficult to precise control, directly affect the diameter measurement precision of thin wall ring, unable to meet the needs of detection.Therefore, it is necessary to study the measurement method of inner and outer diameter of thin-wall bearing ring. Based on the non-contact optical precision measurement technology, a set of special measuring instrument for outer contour of thin-wall bearing ring is developed by integrating the relevant technologies such as active vision of motion computer, image processing, precise motion control and computer control.

(5) Bearing comprehensive performance test technology based on robot working conditions.In order to check and evaluate the performance, life and reliability of the robot bearing, it is necessary to carry out simulation test or sampling test in batch production before installation to ensure the bearing performance is stable and reliable.Due to the particularity of robot bearing structure, it is necessary to develop special bearing test rig, and working condition of simulated experiment, the detection of bearing vibration, temperature, load, speed, friction torque and rotation accuracy, such as performance, according to the purpose and use requirements of form a complete set of robot, formulate corresponding test specification, quantity and the time limit stipulated by complete life test, and the test after all tests before the data were analyzed with the experiment, to assess the use of performance, bearing life and reliability of whether meet the requirements.

Industrial robot is a new kind of high-tech intelligent machine which can replace some artificial industrial production.As a robot in industrial production, its requirements can be described in three words: fast, accurate and stable.
For the current robot production technology, fast and accurate are easier to do, and if it is fast and stable at the same time to achieve accurate, it is relatively difficult.
Here is a definition of a word: industrial robot repeated positioning accuracy -- industrial robot repeated a certain action (generally 10-20 times), the average deviation from the planned position is its repeated positioning accuracy, generally need to be measured by laser interferometer.

(edit：admin)