Principle and application of ball screw

I introduction

Ball screwis an ideal product that converts rotary motion into linear motion or linear motion into rotary motion.

Ball screw is composed of screw, nut, steel ball, prepressing sheet, reverser and dustproof device. Its function is to convert rotary motion into linear motion, which is the further extension and development of the Ekum screw. The important significance of this development is to change the bearing from sliding motion to rolling motion. Because of its small friction resistance, ball screws are widely used in various industrial equipment and precision instruments.

Ball screw is the most commonly used transmission element in machine tools and precision machinery. Its main function is to convert rotary motion into linear motion, or to convert torque into axial repeated force. At the same time, it has the characteristics of high precision, reversibility and high efficiency.

Main parameters of ball screw are: nominal diameter and lead.
In addition ball screw, we also have other products, such asservo motorandstepper motor.

Second, the principle

1. Ball screw (which has basically replaced trapezoidal screw, commonly known as screw) is used to convert rotary motion into linear motion; Or an actuator that converts linear motion into rotary motion, and has high transmission efficiency, accurate positioning and the like.
2. When the ball screw is used as the active body, the nut will be converted into linear motion with the rotation angle of the screw according to the lead of the corresponding specification, and the passive workpiece can be connected with the nut through the nut seat, thus realizing the corresponding linear motion.

Ball screw bearings provide a wide range of standardized products for various applications. Widely used in machine tools, the circulation modes of balls are circulating conduit type, circulator type and end cap type. Pre-pressing methods include positioning pre-pressing (double-nut method, position pre-pressing method) and constant pressure pre-pressing. Choose the appropriate type according to the application. There are precision ball screws with high precision grinding processing (the precision is divided into 6 grades from CO-C7) and cold-rolled ball screw bearings with high precision cold-rolling processing (the precision is divided into 3 grades from C7-C10).

III. Uses

Super DN ball screw: high-speed machine tool, high-speed integrated machining center.
End cap ball screw: quick handling system, general industrial machinery, automatic machinery.
High-speed ball screw: CNC machinery, precision machine tools, industrial machinery, electronic machinery and high-speed machinery.
Precision grinding ball screw: CNC machinery, precision machine tools, industrial machinery, electronic machinery, conveying machinery, aerospace industry, actuators and valve switching devices used by other antennas, etc.
Rotary nut (R1) series ball screws: semiconductor machinery, industrial robots, woodworking machines, laser processing machines, conveying devices, etc.
Rolling ball screw: low friction, smooth operation, fast supply and low price.
Heavy-duty ball screw: all-electric injection molding machine, punching machine, semiconductor manufacturing device, heavy-duty brake, industrial machinery, forging machinery.

IV. TYPE

There are two common circulation modes: external circulation and internal circulation. In the process of ball circulation, sometimes it is out of contact with the lead screw, which is called external circulation;

 Always keep in contact with the screw is called internal

circulation.
1) External circulation: The external circulation means that the balls return to the screw nut through the spiral groove or cannula on the outer surface of the nut and re-enter the circulation. The return modes of the outer circulating ball screw nut pair according to the ball circulation mainly include end cap type, cannula type and spiral groove type. Common external circulation mode: end cap type; Intubation type; Spiral groove type. End cap, a longitudinal hole is machined in the nut to serve as the return passage of the ball, and the cover plates at both ends of the nut are provided with return ports of the ball, from which the ball enters the return pipe to form a cycle. Intubation type, which uses bent pipe as return pipe. This structure has good manufacturability, but because the pipe protrudes out of the nut body, its radial size is larger. Spiral groove type, in which a spiral groove is milled on the outer circle of the nut, through holes are drilled at both ends of the groove and tangent to the thread raceway to form a return channel. This structure is smaller in radial dimension than the cannulated structure, but it is more complicated to manufacture. The external circulation structure and manufacturing process of the external circulation ball screw are simple and widely used. Its disadvantage is that the seam of the raceway is difficult to be smooth, which affects the stability of the ball raceway.

Internal circulation: The internal circulation adopts reversers to realize ball circulation. There are two types of reversers. The cylindrical key reverser, the cylindrical part of which is embedded in the nut, has a reverse groove at its end. The reverse groove is positioned by the circular key on the cylindrical outer surface and its upper end to ensure alignment with the direction of the thread raceway. Round insert reverser, which is a general round head Ping Jian insert. The insert is embedded in the groove of the nut, and its end is provided with a reverse groove, which is positioned by the outer contour of the insert. Compared with the two kinds of reversers, the latter is smaller in size, thus reducing the radial size and axial size of the nut. However, the outer contour of the reverser and the dimensional accuracy of the notch on the nut are required to be high.

V. Characteristics

1. Low friction loss and high transmission efficiency.
Because there are many balls rolling between the screw shaft and the screw nut of the ball screw pair, it can get higher movement efficiency. Compared with the past sliding screw pair, the driving torque is less than 1/3, that is, the power required to achieve the same motion result is 1/3 of that of using sliding screw pair. It is very helpful in saving electricity.
2, high precision
Ball screw pair is generally produced by the highest level mechanical equipment in the world, especially in the factory environment of grinding, assembly and inspection. The temperature and humidity are strictly controlled, and the precision is fully guaranteed due to the perfect quality management system.
High-speed feed and micro-feed are possible.
Because the ball screw pair uses the ball motion, the starting torque is extremely small, and the creeping phenomenon like sliding motion will not occur, which can ensure the accurate micro-feed.
4, high axial rigidity
The ball screw pair can be pre-pressed, and the axial clearance can reach a negative value due to the pre-pressing, thus obtaining higher rigidity (when the ball screw is actually used in mechanical devices, etc., the rigidity of the nut can be enhanced due to the repulsive force of the ball).
5, can’t self-lock, with the reversibility of transmission.