# Ball Screw

In mechanics, a ball screw device is a mechanical linear actuator that translates rotational motion to linear motion with some friction forces. A threaded shaft can offer a helical raceway for ball bearings which move as a precision screw. Like it is able to apply or withstand high thrust loads, they can do so with minimal internal frictions inside the device, making the operation much smoother.

The mechanism above mentioned are made to close tolerances and are therefore suitable for use in situations in which high precision is a must be. Accordingly, the ball assembly acts as the nut in the design while the threaded shaft here is the screw. Contrary to the conventional lead screws, ball screws tend to be rather bulky, because of the fact that they need to have a mechanism to re-circulate the balls. In the meantime, another form of linear actuator based on a rotating rod is the thread-less ball screw, that is, the well known "rolling ring drive".

In this design, three or even more rolling-ring bearings are arranged symmetrically in a housing surrounding a smooth (thread-less) actuator rod. And, the bearings are set at an angle to the rod, and this angle determines the direction and rate of linear motion per revolution of the rod.

## Types of Ball Screw

### What is a ball screw

In mechanics, a ball screw device is a mechanical linear actuator that translates rotational motion to linear motion with some friction forces. A threaded shaft can offer a helical raceway for ball bearings which move as a precision screw. Like it is able to apply or withstand high thrust loads, they can do so with minimal internal frictions inside the device, making the operation much smoother.

### Tolerance

The mechanism above mentioned are made to close tolerances and are therefore suitable for use in situations in which high precision is a must be. Accordingly, the ball assembly acts as the nut in the design while the threaded shaft here is the screw. Contrary to the conventional lead screws, ball screws tend to be rather bulky, because of the fact that they need to have a mechanism to re-circulate the balls.

In the meantime, another form of linear actuator based on a rotating rod is the thread-less ball screw, that is, the well known "rolling ring drive". In this design, three or even more rolling-ring bearings are arranged symmetrically in a housing surrounding a smooth (thread-less) actuator rod. And, the bearings are set at an angle to the rod, and this angle determines the direction and rate of linear motion per revolution of the rod. The most famous advantageous of this design over the conventional ball screw and leads crew is the practical elimination of backlash and loading caused by preload nuts, which grants much benefits to the mechanical mechanism as well as the operational process.

### Application

Today, ball screws are widely used in machine tools, aircraft and missiles to move control surfaces, especially for electric fly by wire, and in automotive power steering to translate rotary motion force from an electric motor to the axial motion of the steering racks. Furthermore, ball screws are also adopted in robots and precision assembly equipment. Some of the high precision ball screws are used in steppers for semiconductor manufacturing, granting better accuracy.

Like linear motor, in the sector of machinery, a linear motor is a machine designed to convert one form of energy source into the linear mechanical energy. One of the most commonly known example is the heat engines, such as the internal combustion engine, burn a fuel (such as gas) to create heat which is then used to do work afterwards. Meanwhile, electric motors convert electrical energy into mechanical motion, and pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. To sum up, linear motor generates linear force from a power source, granting stable movement.

### Development and history

Speaking of the development, the ball screw was invented independently by H.M. Stevenson and D. Glenn. They were issued in 1898 patents 601,451 and 610,044 respectively, so the inventions were conducted independently. As the industrial development goes by with the industry revolution, the demands for a smooth soar, making this demand more and more recognizable.

In the early era, some precise screw shafts were manufactured by starting with a low precision screw shaft, later, lapping the shaft with several spring-loaded nut laps as the standard procedure. After that, there are also many processes which are not mentioned here. Then, the very repeatable shaft's pitch was measured and inspected against a distance standard.

Currently, a similar procedure is sometimes adopted today to produce reference standard screw shafts, or master manufacturing screw shafts. A ball screw is used to expand the Deployable Tower Assembly structure on the James Webb Space Telescope. In grinding machinery, bearing is very crucial. Usually, rolls are commonly used in many industrial sectors for processing products, for paper, paint, steel, textiles, and rubber material processing. The length of the rolls varies from a few centimeters up to six meters or more, and throughout the length, a highly finished surface is required.

In practical usages, these rolls give sheet metal work pieces the high finish, which is required without polishing or further buffing. If the rolls are designed to be used for cold-forming metal, then the great pressure between the work and the rolls would cause the rolls to spring apart at the center. Once if such situation occurred, the rolled metal would be thicker at the center while thinner at the edges if the perfectly uniform diameter rolls were used for this purpose. Therefore, the desirable correct curve of the face of the roll needs to be carefully calculated.

In addition, when it comes to roll grinding, machines should occur with a crown or convex surface for precision. Usually roll grinders would have provisions for rotating the rolls on their own bearings. And, they may also rotate on the tailstock and headstock centers.

### The trend in machinery

Ever since the machine tools are the most fundamental capital goods for manufacturers and play the critical role that determines the final output of the end products, the quality of the machine tool becomes the key point of the quality of the manufacturers’ final end products. The inventory of machine tools varies from time to time. Now after the invention of the machining centers and the programmed controlling system (CNC, computer numerical control), the standards of machining become more and more rigid compared with the standards before. Besides the CNC machining centers, there are also CNC turning centers, CNC milling machines, CNC tapping and milling centers, CNC drilling and milling centers, and many other models.

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