Linear guide rail is often referred to as a guide rail for short. Its role is to support and guide the moving parts to reciprocate in a straight line along a given trajectory and stroke.The guide rail is composed of two relatively moving parts. One part is fixed to the rack and is called the fixed rail, and the other moves on the fixed rail and is called the moving rail.

The guide rail is mostly used for actuators that need to make linear reciprocating motion.The motion performance of the guide rail requires stability, no crawling, and accurate positioning at low speeds, and small inertia, no overshoot or oscillation at high speeds.The accuracy, carrying capacity and life of the guide rail have a direct impact on the accuracy, carrying capacity and life of the system.

According to the friction properties of the rail surface, the guide rail can be divided into sliding guide rail, rolling guide rail, hydrostatic guide rail, air flotation guide rail, and magnetic levitation guide rail.The sliding guide rail has a simple structure, good rigidity, high frictional resistance, fast wear during continuous operation, and high requirements for the scraping and grinding process of the rail surface in manufacturing.The static friction factor of the sliding rail is very different from the dynamic friction factor, so crawling may occur during low-speed movement.

Sliding guide rails are commonly used in the workbench or bed guide rails of various machine tools. Most of the moving rails are assembled on the workbench, slide table, skateboard, guide shoe, headstock, etc.The cross-section of the guide rail is rectangular, dovetail, V-shaped, round, etc.Several cross-sectional shapes are often used in combination in heavy machinery to jointly assume the role of guiding and supporting.

A rolling rail is a rolling element, such as a ball, roller, needle roller or rolling bearing, placed between a moving part and a supporting part.The advantages of rolling guide rails are: the coefficient of friction is not greater than 1/10 of the coefficient of friction of the sliding guide rail, the static friction factor is small compared with the dynamic friction factor, and it is not easy to crawl. It can be dragged by a low-power motor, with high positioning accuracy and long life.

Characteristics of sliding rail

The characteristic of the sliding guide rail is the use of media between the guide rail and the sliding member. The types of media include solid anti-friction materials, oil, and air. Therefore, the sliding guide rail is divided into different types.

The most common anti-friction guide rail is a solid anti-friction material, such as polyvinyl chloride or bronze mixed material, installed on the mobile assembly to reduce the friction of the guide rail.The anti-friction material should be designed with an oil tank to meet the needs of oil lubrication or other forms of lubrication between the moving assembly and the surface of the guide rail.

The most widely used is hydraulic media, a typical representative of which is the hydrostatic guide rail.Under the action of pressure, the hydraulic oil enters the groove of the sliding assembly, forming an oil film between the guide rail and the sliding assembly, isolating the guide rail from the moving assembly, which can greatly reduce the friction of the moving assembly, thereby playing a lubricating role.

The hydrostatic guide rail has a good effect on the lubrication of large-load movement, and it also has a certain compensation effect on eccentric loads.For example, when a processing machine tool is processing a large sand box, the sand box just moves to the end of the stroke of the machine tool. At this time, the hydrostatic guide rail can increase the oil pressure, so that the guide rail still accurately maintains the state of horizontal load.Some horizontal boring and milling machines also use this technique to compensate for the decrease in spindle speed during deep hole machining.Another kind of guide rail that uses oil as a medium is the dynamic pressure guide rail. The difference between it and the static pressure guide rail is that it does not use pressure, but uses the viscosity of the oil to avoid direct contact between the moving assembly and the guide rail.The advantage of this is that the hydraulic oil pump can be saved.

Air is also a common medium between the sliding guide rail and the sliding assembly. It is also divided into two forms, pneumatic hydrostatic guide rail and pneumatic dynamic pressure guide rail. Its working principle is similar to that of the hydrostatic guide rail and the dynamic pressure guide rail in the hydraulic guide rail.

Adjustability is a unique advantage of linear sliding rails.According to the use of the guide rail, the linear sliding guide rail system will be equipped with adjustable edges, the number of which is one or more.Since the moving assembly must move along the side of the linear guide rail, it is necessary to ensure that the moving assembly is in close contact with the side of the guide rail, so the guide rail must have an adjustable function.

The most commonly used adjustment method is to place the oblique iron between the moving assembly and the opposite side of the rail contact surface.The shape of the oblique iron adopts tapered strips of angle iron.If the sliding part or guide rail wears out and the gap between the contact surfaces is generated, the guide rail can be accurately compensated by adjusting the oblique iron to eliminate the gap between the moving part and the guide rail.

Machine tool manufacturers have developed a patented technology for automatic adjustment of oblique iron and widely adopted it.The basic principle of this technology is to keep the oblique iron at a fixed spring pressure. Once the moving parts or the guide rail system wear out, the oblique iron can automatically eliminate the gap between the two.

Rolling rail

Rolling guide rail is a kind of linear guide rail.Rolling linear slide rail is a kind of rolling guide. It consists of steel balls that make an infinite rolling cycle between the slider and the slide rail, so that the load platform can easily move linearly with high precision along the slide rail, and its coefficient of friction can be reduced to 1/50 of the traditional sliding guide, so that it can easily achieve μm-level positioning accuracy.

Advantages of rolling rails

1. The sensitivity is high, and the coefficient of dynamic friction and static friction is very different, so the movement is stable, and crawling is not easy to occur when moving at low speeds.

2. The positioning accuracy is high, and the repeated positioning accuracy can reach 0.2μm.

3. Low frictional resistance, light movement, low wear, and good accuracy retention.

The rolling guide rail is particularly suitable for occasions where the working parts of the machine tool require uniform movement, sensitive movement and high positioning accuracy.

Classification of rolling rails

1. Ball guide rail

The guide rail uses a ball ball as the rolling element, with good motion sensitivity and high positioning; however, its carrying capacity and stiffness are small, and it is generally necessary to improve the carrying capacity and stiffness through preload.In order to avoid the loss of accuracy by pressing pits on the guide rail, the guide rail surface is generally made of quenched steel.The ball guide rail is suitable for CNC machine tools with small moving parts and small cutting force.

2. Roller guide rail

The bearing capacity and stiffness of the guide rail are greater than that of the ball guide rail, but the installation requirements are also high.Poor installation will cause offset and lateral sliding, which will speed up the wear of the guide rail and reduce the accuracy.At present, CNC machine tools, especially those with large loads, usually use roller rails.

3. Needle roller guide rail

The needle roller of the needle roller guide rail is longer than the length of the roller of the same diameter.The needle roller guide rail is characterized by its small size and compact structure.In order to improve the movement accuracy of the workbench, the size of the needle roller should be grouped by diameter.The needle roller guide rail is suitable for machine tools where the size of the guide rail is limited.

According to whether the rolling rail is preloaded or not, the rolling rail can be divided into two categories: preloaded and non-preloaded.The advantage of preloading is that the stiffness of the guide rail is improved. It is suitable for the guide rail with large subversion torque and vertical direction. The coordinate axis of CNC machine tools usually adopts this kind of guide rail.Rolling rails without preload are commonly used in transfer mechanisms such as manipulators and tool banks of CNC machine tools.

Disadvantages of rolling rails

The damping of the rolling guide rail is small and it is easy to cause overshoot or oscillation, the stiffness is low, the manufacturing is difficult, and it is more sensitive to dirt and rail surface errors.Rolling rails are mostly used in optical machinery, precision instruments, CNC machine tools, textile machinery, etc.There is fluid between the moving rail and the fixed rail of the hydrostatic guide rail, the air flotation guide rail and the magnetic levitation guide rail. The friction is smaller, there is almost no wear, and there is no crawling phenomenon, but the stiffness is low, the damping is small, and the design, manufacturing and operation control are more complicated.

According to the structure of the rolling guide rail, the guide rail can be divided into open guide rail and closed guide rail.The open guide rail must rely on external forces, such as its own gravity, in order to ensure the correct contact between the moving rail and the rail surface of the fixed rail. This kind of guide rail has a large ability to withstand the positive pressure of the rail surface, and the ability to withstand partial loads and overturning moments is poor.The closed guide rail relies on its own cross-sectional shape to ensure the correct contact of the rail surface, and has a strong ability to withstand partial loads and overturning moments, such as dovetail-shaped guide rails.The main factors that affect the accuracy of the guide rail are: straightness, parallelism of the two rail surfaces, roughness of the rail surface, wear resistance, stiffness, lubrication measures, etc.