Why do some screw drives have obvious friction feelings, and some are very smooth

In fact, the first floor is basically right, the ball screw has a very low friction coefficient under good lubrication, after all, it is a point contact, and the amount of wear and tear is also less for long-term use, which is necessary for CNC machine tools that require high machining accuracy and long-term stable machining accuracy, and the lower transmission resistance also lays the foundation for higher speed transmission. The use of ball screws is also one of the reasons for the high processing efficiency of CNC machine tools, of course, this is only an auxiliary reason. CNC machine tools, especially machining centers, have a very standard tool magazine, the speed of tool change is very fast, coupled with very fast spindle speed, a very mature control system plus stepper motors, servo motors and other precise power sources, and even many machining centers mature multi-axis linkage processing without changing clamps, so that the processing efficiency and machining accuracy can be doubled.

Of course, not only the circulating ball raceway, in fact, there are also awl rollers, you can check the relevant information for details. CNC especially machining center such equipment, is the future of the development of the processing industry of the general trend, I believe you have now seen this prospect, if you want to learn more related knowledge, of course, if you have a big ambition, do not need to learn this, understand and understand it

The design principle of screw drive is: the ball screw is used as the active body, and the nut will be converted into linear motion according to the lead of the corresponding specification with the rotation angle of the screw rod, and the passive workpiece can be connected by the nut seat and the nut, so as to achieve the corresponding linear motion.

Ball screw is the most commonly used transmission element in tool machinery and precision machinery, its main function is to convert rotary motion into linear motion, or torque into axial repeated force, and at the same time has the characteristics of high precision, reversibility and high efficiency. Due to their low frictional resistance, ball screws are widely used in a variety of industrial equipment and precision instruments.

The ball screw is composed of a screw, a nut, a steel ball, a pre-compression sheet, a reverser, and a dust preventer. Its function is to convert the rotational motion into linear motion, which is a further extension and development of the Eckham screw, and the significance of this development is to change the bearing from a sliding action to a rolling action.

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Changing the direction of transmission, there is a rotational motion that transforms into a linear motion.

The screw rod conveys similar to the bolt nut, you control the nut not to move, rotate the bolt, the bolt can move axially, on the contrary, control the bolt not to move, rotate the nut, the nut can move axially. If you change to a screw rod, the screw nut corresponds to the nut, and the screw rod corresponds to the bolt. Conventionally, the two ends of the screw rod are fixed by bearing housings and rotated by motors.

It should be noted here that in the screw rod transmission, the screw mother has two degrees of freedom of rotation and movement, and the conventional only needs to move this degree of freedom, so it is generally necessary to restrain the rotation of the screw mother through the guide rail, that is, the screw mother carries out linear motion along the axial direction on the guide rail.

It is possible to study the rotational transmission of the x-axis and y-axis of the lower test bench.

The transmission efficiency of the ball screw nut pair is as high as 85 98, which is 2 4 times that of the ordinary sliding screw, and its static and dynamic friction coefficient is actually no different, and it is one of the effective measures to improve the sensitivity of the feed system, positioning accuracy and prevent creeping, so it is widely used by CNC machine tools and the technical transformation of old equipment. The transmission efficiency of the ball screw pair is very high, and it can not be white-locked, and when it is used to drive vertically moving parts, it is necessary to prevent the reverse transmission due to the self-weight of the parts when the transmission is interrupted. 1) Adopt a servo motor or stepper motor that cannot be reversed by itself, but the reverse torque of the motor needs to be greater than the inertia torque of the transmission parts.

2) Use electromagnetic or mechanical brakes, or overtake clutches in one direction. 3) Adopt a worm reducer that cannot be reversed. In order to improve the sensitivity, positioning accuracy and prevent creeping of the feed system, it is necessary to reduce the friction of the feed system of the CNC machine tool and reduce the difference between the static and dynamic friction coefficients.

Therefore, the linear motion mechanism with a short stroke is often used as a ball screw nut pair. It is a new type of transmission device that converts linear motion and rotary motion into each other. It eliminates backlash and applies preload, which helps improve positioning accuracy and stiffness.

The two ends of the stroke of the ball screw pair should be provided with stroke protection devices to prevent the use of excess stroke. If the ball screw pair is used beyond the stroke, the ball screw pair may be hit by the ball falling off, the circulating parts are damaged, the groove track is indented and other faults, resulting in poor operation, reduced accuracy, shortened life and even damage, so it is forbidden to use beyond the stroke. In the unlikely event that the itinerary is overused, the best way to do so is to ask the manufacturer for assistance.

Because the friction between the lead screw and the ball nut is very small, if the ball screw without preload (or slight preload) is placed vertically, the ball nut will fall off from the lead screw due to its own weight, so it is necessary to pay attention to avoid putting the ball screw mechanism without preload in an upright state to prevent the ball nut from falling off due to its own weight, especially when using it vertically. Accidental drops may damage components. In this case, it is recommended that the manufacturer carry out an inspection.

When using ball screws vertically, it is recommended to prevent the table from falling off by installing a protective structure such as a safety nut. Handle gently, and it is forbidden to knock on the lead screw and ball nut, such as when the circulating ball, return pipe, lead screw outer diameter, groove, etc. This can cause poor circulation, which can lead to loss of function of the product.

In particular, the external circulation type return pipe protrudes on the outside of the nut, which is easily subject to collision or damage, and special care is required to prevent collision or damage, and it is strictly forbidden to knock and disassemble the co-flow pipe, so as not to cause the steel ball to be blocked. Movement is not smooth. After the lead screw and nut are assembled, the semicircular spiral groove on the lead screw and nut forms a spiral raceway with a circular cross-section.

When the lead screw rotates, the ball rolls forward in the spiral raceway, and the driving screw does not move in a straight line. In order to prevent the balls from escaping the other end of the nut and to recycle the balls, the balls are rolled several times on the lead screw and then returned one by one to the raceway between the lead screw and the nut by means of a return guide (e.g. a return tube). Forming a closed loop, and so on.

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1. Not of the same nature.

1. Ball screw: It is the most commonly used DAO transmission element in machine tools and precision machinery.

2. Trapezoidal screw: trapezoidal screw products are easy to knot.

Tailor specific applications to achieve the desired performance while keeping costs to a minimum.

2. Different characteristics.

1. Ball screw pair: it has the characteristics of high precision, good reversibility and high efficiency. Ball screws are widely used in various industrial equipment and precision instruments because of their low frictional resistance.

2. Trapezoidal screw: In the process of cyclone milling screw, threading and knurling are completed at one time, with high efficiency, low cost and low machining accuracy. Its structural design ideas and schemes have good application value.

3. Different uses.

1. Ball screw pair: its main function is to convert rotary motion into linear motion, or torque into axial repetitive force, and rotary motion into linear motion. This is a further promotion and development of exem screws.

The significance of this development is to change the bearing from a sliding motion to a rolling motion.

2. Trapezoidal lead screw: suitable for rough machining of large threads.

Ball screws.

Trapezoidal zhi screw.

The main differences between ball screws and trapezoidal screws are as follows:

1. Exercise efficiency.

Because there is a ball between the lead screw and the nut of the ball screw pair to do rolling motion, so it can get a higher motion efficiency, and the trapezoidal screw, the driving torque is less than 1 3, therefore, not only can the rotary motion be converted into linear motion, but also can easily change the linear motion into rotary motion.

2. Lead accuracy.

Ball screws are often used in high-precision equipment. There is a linear travel difference in the process of forward and reverse movement of trapezoidal lead screws. There is inevitably a gap between the trapezoidal nut and the lead screw, and reducing or eliminating this gap through a specially designed nut mechanic increases the frictional load and increases the manufacturing cost.

Long-term wear and tear can also increase clearance. The ball screw pair can be preloaded or cleared according to customer requirements. By adjusting the ball screw drive clearance (increasing preload), the reverse transmission accuracy and axial stiffness are guaranteed.

3. Production cost.

The production cost of ball screws is higher, the process is more complex, and the required production and supporting equipment are more expensive. With the increase of production capacity and the increase of scale, the cost of ball screws is gradually decreasing, and the rolling screws are cold-rolled, with high efficiency and relatively short delivery time.

4. Service life.

The ball screw has low rolling wear, good accuracy retention and long service life.

5. Rotation speed.

Ball screws can achieve high-speed round-trip transmission.

The main difference between a ball screw and a trapezoidal screw is the way in which the load is carried between the moving surfaces. Ball version screws use recirculating ball bearing weights to minimize friction and increase efficiency, while trapezoidal lead screws take advantage of the low coefficient of friction between sliding surfaces. Therefore, trapezoidal lead screws are usually not as efficient as ball screws.

Analysis of the tribological mechanism shows that the sliding friction is certainly less feasible than that of the transmission using recirculating ball technology. Fatigue life equations (e.g. L10 life) are reliable in their range of application.

Based on the above, it can be known that ball screws and trapezoidal screws are also very different in the application field because of the difference in performance and life capacity.

Although ball screws have many advantages (load, stiffness, efficiency, load cycle, and availability), the cost is relatively high. Although they are cost-effective compared to other translational linear motion solutions, the design of ball screws is more complex, requiring hardened precision bearing surfaces and a ball circulation device. The trapezoidal lead screw, on the other hand, is small in size, flexible in design, has low noise and corrosion resistance under normal use, and can be configured with a self-locking function to meet the needs of vertical applications.

They play an important role in many areas of application, but of course they have some limitations.

The working principle of trapezoidal screw is as follows: trapezoidal screw relies on the oil film between the screw mother and the screw to produce relative sliding work, and the internal sliding friction calmly completes the linear movement.

The working principle of the ball screw is as follows: when the lead screw is used as the active body, the nut will be converted into linear motion according to the lead of the corresponding specification with the rotation angle of the lead screw, and the passive workpiece can be connected by the nut seat and the nut, so as to achieve the corresponding linear motion.

Ball screws are also called precision screws; Trapezoidal lead screws include precision lead screws and ordinary lead screws, and it is recommended to refer to Yugong machine tools to produce lead screw equipment. ‍

The trapezoidal screw movement is a low-pay mechanism with surface contact, large friction and easy wear, and there is a gap in the transmission pair, and there is a vacancy when rotating in the opposite direction, and the capacity accuracy is low. The ball screw is a high auxiliary mechanism, the moving parts are quenched to extremely high hardness, the transmission accuracy is high, the friction is small, not easy to wear, the life is long, the matching parts have no gap, and are widely used in precision machinery, such as CNC machine tools, coordinate boring machines and other occasions. The answer is relatively simple and can summarize the content.

The differences are: 62616964757a686964616fe59b9ee7ad9431333431353262

1) When the ball screw moves, it is rolling friction, and the trapezoidal screw is sliding friction.

2) The friction of the ball screw is less than that of the trapezoidal screw, only 1 3 of the trapezoidal screw

3) There is a ball as a rolling element between the nut and the screw of the ball screw, and the trapezoidal screw nut and the screw are in direct contact.

4) The diameter of the ball screw nut is larger than the large diameter of the screw, and the diameter of the trapezoidal lead screw nut is smaller than the large diameter of the screw.

5) When the output torque is the same, the motor driving force required by the ball screw is less than that of the trapezoidal screw.

6) Because the ball screw is rolling friction, it will not produce the crawling phenomenon that trapezoidal screw is prone to.

7) The ball screw can be operated fretting because of the small starting torque and flexibility.

How trapezoidal lead screws work:

1. According to the national standard GB and application examples, the ball screw (which has basically replaced the trapezoidal screw and has been commonly known as the lead screw) is used to convert the rotary motion into linear motion;

Or convert the linear motion into an actuator for rotary motion, and have the characteristics of high transmission efficiency and accurate positioning;

The whirlwind milling screw processing thread and knurling are completed at one time, and the process efficiency is high, the cost is low, and the processing accuracy requirements are not too high.

Cyclone milling method is a high-efficiency threading method, suitable for large batch of thread roughing, the process is to use carbide cutter to carry out high-speed milling of threads, it has the advantages of good tool cooling and high production efficiency.

Threads that do not require high precision can be cut in one go using this method. The rotary axis of the whirling cutter is related to the axis of the workpiece, and the crossing angle is an angle (equal to the spiral rising angle). The machining process includes the rotational motion of the workpiece, the spiral axial feed movement (or tool feed) of the workpiece, and the rotational motion of the cutting edge on the milling cutter.