Linear guide rail, also known as linear rail, linear rail, linear rail for linear reciprocating motion, has a higher rated load than linear bearing, and can bear a certain amount of torque. high-precision linear motion can be realized under high load.
It acts on supporting and guiding moving parts, reciprocating in a straight line in a given direction.
According to the friction properties, the linear motion guideway can be divided into sliding friction guideway, rolling friction guideway, elastic friction guideway, fluid friction guideway and so on.
Linear bearings are mainly used in automatic machinery, such as German imported machine tools, paper bowl machines, laser welding machines, etc., of course, linear bearings and linear shafts are used together.
Like the linear guideway is mainly used in the mechanical structure with high precision, the slider-changes the motion from a curve to a straight line.
The new guideway system enables the machine tool to obtain fast feed speed, which is the characteristic of linear guideway when the spindle speed is the same.
Like the plane guideway, the linear guideway has two basic elements; one is the fixed element as the guide, and the other is the moving element.
Because the linear guideway is a standard part, for the machine tool manufacturer.
The only thing to do is to process a plane to install the guideway and adjust the parallelism of the guideway.
Of course, in order to ensure the accuracy of the machine tool, a small amount of scraping of the bed or column is essential, and in most cases, the installation is simple.
Guide rails and balls
The guide rail is hardened steel, which is finely ground and placed on the installation plane.
Compared with the plane guide, the geometric shape of the cross section of the linear guide is more complex than that of the plane guide. the reason for the complexity is that grooves need to be machined on the guides to facilitate the movement of sliding elements, and the shape and number of grooves depend on the function of the machine tool.
For example, a guideway system which bears both linear force and subversive moment is compared with the guideway which only bears linear force.
There is a big difference in design.
There is no intermediate medium between the moving element and the fixed element of the linear guide, but a rolling steel ball is used.
Because the rolling steel ball is suitable for high-speed movement, low friction coefficient and high sensitivity, it meets the working requirements of moving parts, such as tool holder, drag plate and so on.
The basic function of the fixed element (guide rail) of the linear guideway system is like the bearing ring, the bracket for installing the steel ball, in the shape of “v”.
The bracket covers the top and sides of the guide rail.
In order to support the working parts of the machine tool, a set of linear guides has at least four brackets.
Used to support large working parts, the number of brackets can be more than four.
When the working parts of the machine tool move, the steel ball circulates in the bracket groove, allocating the wear amount of the support to each steel ball, thus prolonging the service life of the linear guideway.
In order to eliminate the gap between the support and the guideway, preloading can improve the stability of the guideway system and obtain the preloading.
An oversized steel ball is installed between the guide rail and the bracket.
The diameter tolerance of the steel ball is ±20 microns, and the steel balls are screened and classified in increments of 0.5 microns, which are respectively installed on the guide rails. The size of the preload depends on the force acting on the steel balls.
If the force acting on the steel ball is too large, the preloading time of the steel ball is too long, which leads to the increase of the motion resistance of the support.
There is a balance problem here; in order to improve the sensitivity of the system and reduce the motion resistance, it is necessary to reduce the preload accordingly, and in order to improve the motion accuracy and accuracy maintenance, it is required to have enough pre-negative numbers, which are two contradictory aspects.
When the working time is too long, the steel ball begins to wear, and the preload acting on the steel ball begins to weaken, which leads to the decrease of the motion accuracy of the working parts of the machine tool.
If the initial accuracy is to be maintained, the guide bracket must be replaced, or even the guide rail must be replaced.
If the guideway system already has the function of preloading.
The accuracy of the system has been lost and the only way is to replace the rolling element.
The design of the guideway system strives to have the maximum contact area between the fixed element and the moving element, which can not only improve the bearing capacity of the system, but also withstand the impact force caused by intermittent cutting or gravity cutting, and spread the force widely. expand the area of bearing capacity.
In order to achieve this, there are a variety of groove shapes in the guideway system, and there are two representative ones, one is called the Gothic (pointed arch), the shape is the extension of the semicircle, the contact point is the vertex, and the other is a circular arc, which can also play the same role.
No matter which kind of structure, there is only one purpose, and strive for more rolling steel ball radius to contact with the guideway (fixed element).
The factor that determines the performance characteristics of the system is how the rolling element touches the guideway, which is the crux of the problem.
Advantages and Features of Linear Guide Rail
- When linear guide is used as linear guide with high positioning accuracy, because the friction mode of linear guide is rolling friction, not only the friction coefficient is reduced to 1 to 50 of sliding guidance, but also the difference between dynamic friction and static friction becomes very small, so when the bed moves, there will be no skidding, which can reach [very high accuracy] um level and set the accuracy.
- The traditional sliding guide with less wear can maintain the accuracy for a long time, which will inevitably lead to poor motion accuracy of the platform due to the countercurrent action of oil film, and insufficient lubrication during motion, resulting in the wear of the contact surface of the running track, which seriously affects the precision. The wear of rolling guidance is very small, so the machine can maintain accuracy for a long time.
- The use of high-speed movement greatly reduces the driving horsepower needed by the machine because the friction force of the linear guide rail is very small, it only needs less power to make the bed run, especially when the working mode of the bed is regular round-trip movement. It can obviously reduce the force loss of the machine, and the heat caused by friction is small, so it can be used for high-speed operation.
- It can bear the load of the upper and lower left and right at the same time because of the special beam structure design of the linear guide rail, it can bear the load of the upper and lower left and right directions at the same time, and the lateral load that can be borne by the sliding guidance in the direction of parallel contact surface is lighter, which is easy to cause poor accuracy of machine operation.
- When assembling easily and interchangeably, as long as the assembly surface of the guide rail on the machine table is milled or ground, and the guide rail and slider are fixed on the machine according to the recommended steps, the high accuracy of machining and the traditional sliding guidance can be paid attention to. The running track must be shoveled, which is both time-consuming and time-consuming, and once the machine accuracy is poor, the linear guide rail has interchangeability.
The slider cargo guideway can be replaced separately to the linear guideway group and the machine can be guided with high accuracy again.
- If the lubrication structure is simple, if the sliding guide is insufficient, it will become the contact surface metal direct friction loss bed, while the sliding guide is not easy to lubricate, it is necessary to drill a hole to supply oil in the appropriate position of the bed, and the linear guide rail is already installed with an oil nozzle. oil can be injected directly with an oil injection gun, or it can be replaced with a special oil pipe joint to connect the oil supply pipe to automatically supply the oil.
Linear Guide Rail And Linear Motor
Linear motors are increasingly replacing the driving devices with wear-prone mechanical transmission parts in industrial applications.
They can provide high speed and acceleration, good adjustment accuracy and accurate positioning.
The advantage of a linear motor is that the electric energy supplied can be directly converted into linear motion, and there is no need for any intermediate components for torque conversion machinery.
The mechanical efficiency of the linear system driven directly is much higher than that of the rotary system.
In the linear motor system, the only necessary mechanical component is the linear guideway.
Therefore, the mass of the moving part of the guide device should be kept as small as possible, and the reason why the quality of the linear guide rail should be small is that the moving mass will have a direct impact on the adjustment of the linear motor.