Development trend of the hottest ball screw pair

2022-08-10
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The development trend of ball screw pair

ball screw pair was invented as early as the end of the 19th century, but it has not been applied in practice for a long time, because it is too difficult to manufacture. The first one in the world to use ball screw pairs is the Saginaw branch of general motors, which uses ball screw pairs in the steering mechanism of automobiles. In 1940, the United States began to mass produce ball screw pairs for automotive steering mechanisms. In 1943, ball screw pairs began to be used in aircraft. The emergence of precision thread grinding machine has made a great leap in the accuracy and performance of ball screw pairs. With the development of CNC machine tools and various automatic equipment, the research and production of ball screw pairs have been promoted. Since the 1950s, manufacturers of ball screw pairs have sprung up in industrialized countries, such as warner-beaver and gm-saginaw in the United States; Rotax in the UK; NSK company and TSUBAKI company in Japan. As early as the late 1950s, China began to develop ball screw pairs for program-controlled machine tools and CNC machine tools. For more than 40 years, ball screw pairs have been widely used in machinery, aerospace, aviation, nuclear industry and other fields because of their high efficiency, high precision, high stiffness and other characteristics. Now, the ball screw pair has become the preferred component for mechanical transmission and positioning. The development of ball screw pair is mainly in the following aspects

1 types of ball screw pairs

as the use of ball screw pairs is becoming more and more popular, the field of use is expanding, and there are more and more requirements for ball screw pairs. Ordinary ball screw pairs are far from meeting the use requirements, such as aerospace, small precision testing devices, electronic instruments and semiconductor devices. Basically, micro ball screw pairs with nominal diameter d0 ≤ 12mm and lead ph=0.5 ~ 2.5 mm are required. NSK company in Japan has developed the world's smallest lead micro ball screw pair with nominal diameter d0=4mm and lead ph=0.5mm. Semiconductor plug-in devices and small robots need miniature ball screw pairs with large lead to meet the requirements of high-speed drive

with the development of mechanical products in the direction of high speed, high efficiency and automation, the feed drive speed of industrial robots, CNC forging machines, machining centers and electromechanical integrated automatic machines is constantly improving, and the emergence of large lead ball screw pairs meets the requirements of high speed. Japan NSK company has developed nominal diameter × Lead: 15mm × Colleagues in 40mm and 1 markets often ask themselves to think in an alternate position 6mm × 50mm、20mm × 60mm、25mm × 80mm super large lead ball screw pair, with a fast feed speed of 180m/min

the ball screw pair is classified according to the conventional method, as shown in Figure 1

Figure 1 Classification of ball screw pairs

at present, there is no unified classification of ball screw pairs in domestic and foreign literature, but countries generally classify them according to the following principles. Ordinary ball screw pairs generally refer to nominal diameter d0=16 ~ 100mm, lead ph=4 ~ 20mm, and screw rise angle φ< 9°。

micro ball screw pair refers to the ball screw pair with nominal diameter d0 ≤ 12mm. The ball screw pair with lead pH ≤ 3mm is called micro small lead ball screw pair, and the spiral rise angle φ> The 9 ° ball screw pair is called micro large lead ball screw pair

large lead ball screw pair refers to the nominal diameter d0 ≥ 16mm, screw rise angle 17 °≥ φ> For ball screw pairs with a lead of 9 ° or d0 ≤ pH ≤ d0, for the spiral rise angle φ> 17 ° is called super large lead ball screw pair

heavy ball screw pair refers to the ball screw pair with nominal diameter d0 ≥ 125mm

2 structure of ball screw pair

the structure of ball screw pair is traditionally divided into internal circulation structure (represented by circular reverser and elliptical reverser) and external circulation structure (represented by intubation). These two structures are also the most commonly used structures. There is no essential difference between the two structures, but the installation and connection size of the internal circulation structure is small; The installation and connection size of the external circulation structure is large. At present, there are more than 10 kinds of structures of ball screw pairs, but the commonly used ones mainly include (Figure 2, attached table): internal circulation structure; External circulation structure; End cover structure; Cover plate structure

Figure 2 main structure of ball screw pair

internal circulation structure reverser has a variety of shapes, but the commonly used shapes are round and oval. Due to the short reverse channel of the round ball, it is not as smooth as the oval structure. Now, the best reverser structure is the elliptical inner channel structure. Because the ball reverses without passing through the top of the lead screw, which is similar to the external circulation structure, the influence of the chamfer error of the top of the lead screw on the ball reverse is eliminated. However, the complex manufacturing process has affected the promotion of this structure. Attached table comparison of structural characteristics of ball screw pair

type characteristics number of cycles nut size number of cycles internal circulation structure through the reverser to form a ball circulation circuit, each reverser to form a ball chain. Therefore, the bearing capacity is small. It is suitable for micro ball screw pairs and ordinary ball screw pairs. More than 12 rows of small external circulation structures form a ball circulation circuit through cannula, and each cannula has at least 1.5 turns of ball chain, so the bearing capacity is large. Suitable for small lead, general lead, large lead and heavy ball screw pairs. 1.5 the structure of more than one row of large end caps above forms a ball circulation circuit through the end caps at both ends of the nut, and each circuit has at least one circle of ball chain with large bearing capacity. It is suitable for multi head ball screw pairs with large lead and super large lead. 1. The above two rows of small cover plates form a ball circulation circuit through the cover plates. Each nut has a cover plate, and each cover plate forms a ball chain of at least 1.5 turns. Suitable for micro ball screw pairs. 1.5 the accuracy of ball screw pair in the above 1

3

in the past, in order to obtain high positioning accuracy, it was mainly achieved by improving the accuracy of the ball screw pair itself. Therefore, the requirement for the lead cumulative error of the ball screw is very high, which brings difficulties to the manufacturing of the ball screw pair and increases the production cost of the ball screw pair. In particular, high-precision ball screw pairs can only be processed by CNC thread grinding machines or laser feedback thread grinding machines. With the continuous development of science and technology, people have mastered the CNC compensation technology. Therefore, high positioning accuracy can be obtained without high-precision ball screw pairs. In order to meet the requirements of numerical control compensation technology, the international standard ISO and the ministerial standard jb3162, in which the single chip microcomputer control system circuit is shown in All require the stroke variation of the ball screw pair, such as the stroke variation within the effective stroke, the stroke variation within any 300mm stroke, and the stroke variation within 2 π radians. Its purpose is to control the straightness of the travel error of the ball screw pair, that is, the linearization of the travel error of the ball screw pair. Create conditions for NC error compensation

4 performance of ball screw pair

with the continuous development of science and technology, people have higher and higher requirements for ball screw pair. In order to achieve high positioning accuracy and smooth operation of mechanical products, it is required that ball screw pair not only has high accuracy, but also operates smoothly without blockage. The smooth operation of the ball screw pair mainly depends on the variation of the pre tightening torque of the ball screw pair. The smoothness of the ball chain movement of the ball screw pair is different at different speeds. Therefore, the pre tightening torque of the ball screw pair is also different. The international standard iso3408-3-1992 and the ministerial standard jb3162.2-92 specify the tolerance of the pre tightening torque of the ball screw pair when the speed is 100r/min

due to machining errors, such as the inconsistency of the pitch diameter and total length of the ball screw, the lead error of the screw and nut, the tooth shape error of the raceway between the screw and nut, and the roughness of the thread raceway, the dynamic pre tightening torque of the ball screw pair is not constant on the full length of the screw thread, which directly affects the stability of the drive system, and thus affects the positioning accuracy of the ball screw pair. Therefore, the magnitude of the pre tightening torque variation of the ball screw pair is an important indicator to reflect the performance of the ball screw pair

in recent years, people have begun to pay attention to the magnitude of the preload torque variation of the ball screw pair. Previously, people only paid attention to the comprehensive stroke error curve of the ball screw pair, and now they also begin to pay attention to the preload torque curve of the ball screw pair. Because of these two curves, ball screws are widely used in many industries, and the performance of screw pairs can be well reflected

in order to meet the above requirements, Beijing Machine Tool Research Institute has successively developed a comprehensive stroke error measuring instrument for ball screw pairs and a preload torque measuring instrument. With modern measurement means and high-precision sensors, the travel error curve and pre tightening torque curve can be displayed in real time during the measurement process, and a complete measurement report can be printed, which provides a reliable detection means for measuring the assembly quality of ball screw pair

with the development of CNC machine tools, "high speed and high efficiency" has become the goal pursued by manufacturers. For high-speed drive and positioning components, linear motors have been introduced abroad and have been used in machining centers. The rapid feed speed has reached more than 160m/min and the acceleration has reached more than 4G, posing a severe challenge to the ball screw pair. However, due to the disadvantages of high price, complex control system, and the fact that the Yulian Group employs an international first-rate expert team, measures need to be taken to solve the problems of magnets attracting metal chips, the harm of strong magnetism to human body, and heating, etc., it is difficult to popularize in recent years. Ball screw pairs are still the most preferred choice for high-speed drive, and most foreign high-speed machining centers still use ball screw pairs. In order to achieve the purpose of high-speed drive, the design uses a large lead ball screw pair with a lead of 32mm while increasing the motor speed (the maximum speed of the motor can reach 4000R/min). For example, Mazak company of Japan uses ball screw pair on ff660 machine tool, which has a fast moving speed of 90m/min and an acceleration of 1.5g

in the past, worried about the impact of the large lead ball screw pair drive on the accuracy of the machining center, the lead pH ≤ 10mm was taken in the design. With the progress of science and technology, it can be seen from the 1999 Japan International Machine Tool Exhibition that the design and research of most high-speed machining centers now use large lead ball screw pairs

the main problems of ball screw pair in high-speed drive are noise, temperature rise and accuracy. The main reasons for the noise of the ball screw pair are: the smoothness of the ball in the circulating circuit, the collision between the balls, the roughness of the raceway, the bending of the screw, etc. The temperature rise of ball screw pair is mainly caused by the friction between ball and screw, nut, reverser and the friction between balls. To solve the above problems, we should first start with the structural design of the ball screw pair and take measures to solve the existing problems; On the other hand, we should improve the internal quality of products through reasonable technological process; Select the appropriate pre tightening torque of ball screw pair; Reduce the variation of the pre tightening torque of the ball screw pair, so that the ball screw pair can meet the requirements of high-speed drive

in a word, with the continuous development of society, users' requirements for ball screw pairs are becoming more and more strict and diverse, prompting ball screw manufacturers to continuously improve product quality and develop new varieties to meet users' needs. (end)

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