On the drive of ball screw

Mechatronics technology is an inevitable trend in the development of machinery industry, and has broad technological prospects. The ball screw pair is a new type of transmission mechanism developed to meet the requirements of Mechatronics mechanical transmission system. It consists of ball screw, ball nut (component) and ball ball. It can turn the rotation motion into a straight motion, or turn the straight motion into a rotating motion. The ball screw is not only the core functional component of all kinds of CNC equipment, but also the important general parts of capital intensive and technology intensive in the field of machinery industry. In linear drive family, ball screw pair is a product with wide application and high degree of industrialization.

The present situation of the ball screw in China

China's rolling functional components industry is not concentrated in production, the product is single, and the gold content is low. There is no famous brand in the world, which has become the bottleneck of the development of CNC machine tools in China. At present, there are 50 rolling functional components manufacturing enterprises in China (excluding Taiwan), 3 research institutes and universities, and 3 affiliated enterprises. There are 48 enterprises producing ball screw, with annual output value of up to 650 million yuan. There are 6 enterprises to produce rolling linear guide (4 of them produce ball screw), with annual output value of up to 150 million yuan. Among the 50 enterprises, there are only 6 enterprises with large production scale, complete equipment, large output and many varieties, and the enterprises lack strategic research on the user market, the work of industrial technology development can not keep up with the requirements of the development of the situation, the core competitiveness of the enterprises is not strong, and the new ability is poor. The main gap between China's rolling functional components industry and foreign countries is that the level of professional production is not high, the information management is lagging behind, the process of industrialization is slow, and the individualized service can not keep up. The gap between the medium and low grade products and similar products abroad is smaller or basically flat, but the production efficiency is far lower than that of foreign countries. The high performance, high-grade products and NSK, THK, INA and other well-known enterprises have a clear gap, which has become a bottleneck restricting the development of high-end CNC machine tools.

Two. The structure and innovation of the ball screw pair

1. moderately increasing the lead Pn and thread head number of ball screw pair is the best choice for achieving high speed.

In 1989, China completed the "75" of the big guide ball screw pair, and the spiral lift angle of the large guide ball screw has been produced in mass production with the angle of >9 degree to 17 degrees. However, because of the heredity of the transmission chain error of thread grinder, the larger the lead is, the better the lead precision is.

2. to improve the ball

In high speed motion, the spin speed, the speed of the rotation and the centrifugal force of the ball are all very large, and the impact of the ball and the reverse mechanism on and out of the ball are also great. There are four ways to solve this problem: by optimizing the ball chain calculation, the ball diameter is properly reduced; hollow ball is used, and hollow ball ball screw can be used to effectively reduce the moment of inertia and improve the speed of the screw, and the ball arrangement is changed to a large and small interval in the ball chain; silicon nitride is used. Porcelain ball。

3. for ball added maintainer

After the ball screw is added to the ball screw, the direct friction between the ball body is avoided, and the effect of quiet, smooth running, long lubrication period, high speed, durability and so on is realized.

4. hollow strong cold

In high speed operation, the thermal deformation of the screw shaft is one of the sources of machining error. In order to improve the rigidity of the system, heat can also be generated in the pre stretching of the screw shaft. The effective way to solve the heat problem is to pass the coolant into the hollow screw inside for forced circulation cooling, which also helps to reduce the inertia of the high speed operation and increase the twist rigidity of the screw shaft.

5. improve the structure of ball nut

(1) improve the way of pre load and carry out dynamic control on preload Fp. In order to maintain the stiffness and accuracy of the ball screw pair in full range, the Fp must not be lost and the dynamic pretightening torque Tp is constant.

(2) when the ball enters and reverses the mechanism, it will repeat the Brinell effect, that is, Brinell impact loss. Therefore, the optimum design of the loop reverse mechanism should be made for the high speed requirements: the optimization of the inner loop reverse structure and the curve parameters of the return bead, and the soft landing of the ball in the cycle with high oil and high density fiber antifriction material, and the use of the high strength thick wall alloy material, the radius of curvature, the radius of curvature, and the ratio of the curvature of the outer circulation guide tube. The tube wall and tube tongue are strengthened, and the coordinate positions of the reverser and the guide tube on the ball nut body are optimized.

(3) other measures for vibration reduction and noise reduction are as follows: anti noise casing is arranged around the ball nut body.

6. actuation of double motor drive for ball screw

A servo motor is used to drive the ball screw shaft, and the other servo motor drives the ball nut supported by the bearing in the opposite direction, so that the feed speed of the table can be almost doubled.

7. change the driving mode

When the stroke of the screw is very long, the screw drive mode of "screw rotation of screw rod" can be changed into "screw screw fixed, nut side turning and moving" nut driving mode.

8. improvement of friction characteristics of ball screw pair

The use of a coating on the thread raceway, the reverse channel of the ball and the surface of the steel ball can reduce the friction torque by about 10% at high speed, and obviously reduce the abrasion of the steel ball to the thread raceway during the "slip" process of the non pure rolling and prolong the service life.

Three, the development trend of ball screw pair

In the future, the ball screw vice president will develop in the direction of large scale, heavy load and precision. The development of ball screw pair and its innovation in all aspects can realize the high speed of mechanical device, which provides convenient conditions for the development of mechatronics technology. Mechatronics technology will become the leading role of the machinery industry in twenty-first Century, which will bring significant economic and social benefits.