A guide rail that puts some rotating bodies (balls, rollers or needle rollers) between the bearing guide and the moving parts so that the matching two guide rail surfaces do not directly contact is called a rotating guide rail.

The rotating guide rail is characterized by low friction resistance, light and flexible movement; small wear and tear, can maintain long-term accuracy; dynamic and static friction coefficient difference is small, low speed is not easy to appear "crawling" phenomenon, so the movement is uniform and stable. Therefore, the rotating guide rail is increasingly widely used in the equipment requiring micro-movement and precise positioning. The disadvantages of the rotating guide rail are: the guide rail surface and the rotating body are in point contact or line contact, poor vibration resistance and large contact stress, so the surface hardness of the guide rail is required to be high: the shape accuracy of the guide rail and the dimensional accuracy of the rotating body are required to be high.

1. structure form

Ball guides-V-flat cross-section ball guides, double V-section ball guides and round cross-section ball guides. Since the ball and the guide surface are in point contact, the movement is light, but the rigidity is low and the carrying capacity is small. Commonly used in the weight of moving parts, the load is not large occasions.

Roller guide-the roller in the roller guide is in line contact with the guide surface, so its carrying capacity and rigidity are larger than the ball guide, the wear resistance is better, and the flexibility is slightly worse. The roller is more sensitive to the flatness of the guide rail, and it is easy to produce lateral deviation and sliding, so that the resistance of the guide rail increases, the wear is accelerated, and the accuracy is reduced. The larger the diameter of the roller, the more sensitive it is to the unflatness of the guide rail.

When the structure size is limited, a roller with a smaller diameter can be used, which is called a needle guide. Roller guide rail support is a standard component, which has the advantages of simple installation and lubrication, easy adjustment and protection. Because the roller rotates in the closed raceway, it can be used on the guide rail with a large stroke.

General topics for the design of 2. rotating guides

1, the choice of structural form: rotating guide rail according to its structural characteristics, divided into open and closed two. The open rotating guide rail is used for occasions where the external load acts on the middle of the two guide rails and the weight of the moving parts can be maintained in good contact with the guide rails. The opposite is true for closed rails. The ball guide has good flexibility, simple structure and easy manufacture, but its carrying capacity is small and its rigidity is low. It is often used in occasions with high precision, flexible movement and light load. The roller (needle) guide rail has high rigidity and strong carrying capacity, but it requires high position accuracy. The rotating guide rail adopts standard rotating bearing, which has simple structure, easy manufacture and convenient lubrication. Appropriate for medium precision occasions. In order to increase the bearing capacity of the rotating rail, a preload can be applied. At this time, the rigidity is large, and there is no gap, and the accuracy is improved accordingly, but the damping is larger than that without preload, the manufacturing is complicated, and the cost is high. Therefore, it is mostly used for precision guide rails.

2. Select the length: Generally, the length of the guide rail should be as short as possible under the condition of meeting the movement stroke of the guide rail.

When the circulating rotating guide rail is adopted, the stroke length of the moving part is not limited. Rotating body size and number: rotating body diameter, carrying capacity, friction resistance is small. For ball guides, the ball diameter increases and the stiffness increases (the stiffness of the roller guide is independent of the roller diameter). Therefore, if not limited by the structure, should be limited to the size of the larger rotating body. The friction resistance of the needle roller guide is large, and the needle roller may slide. Therefore, as far as possible do not use the needle roller guide (especially when the diameter of the needle roller is less than 4mm), when the number of rotating bodies increases, the bearing capacity and rigidity of the guide rail also increase. However, the number of rotating bodies should not be too much, too much will increase the uneven distribution of load on the rotating body, but the stiffness decreased. If the number of rotating bodies is too small, manufacturing errors will significantly affect the guiding accuracy of the moving parts. Generally, the number of rotating bodies is as small as 12 on one rotating belt.

Stiffness and pre-tightening method of 3. rotating guide rail:

1. When the worktable moves back and forth, the pressure of the worktable on the rotating bodies at both ends will change. The rotating body with large force will deform greatly, and the rotating body with small force will deform little. When the guide rail is in position 1, the rotating bodies at both ends receive equal force and the worktable remains horizontal: when the guide rail moves to position 1 or I, the rotating bodies at both ends receive unequal force and deform inconsistently, causing the worktable to tilt at an angle a, thus causing errors.

2, in order to reduce the deformation of the guide rail, the progress of stiffness, in addition to the reasonable choice of rotating body shape, size, number and appropriate increase the thickness of the table, commonly used preloading method to improve the stiffness of the guide rail. The dovetail turns the track, and the preload is obtained and controlled by moving the track plate. The test confirmed that: with the increase of the amount of interference, the stiffness of the guide rail began to increase sharply, to a certain extent, and then increase the amount of interference, the stiffness will not significantly improve the traction with the increase of the amount of interference increases, but in a certain limit change is not big, the amount of interference exceeds a certain value, the sharp increase. Therefore, a reasonable amount of interference should make the guide rail stiffness better and traction is not.

4. Technical Requirements

The quality of the guide rail depends on its manufacturing accuracy and installation accuracy. The design should be based on the requirements of use, and a number of technical conditions for rotating the guide rail should be formulated. The following items and data can be used for reference: the roughness between the two guide rail surfaces is generally 3 microns;

Guide not straight is generally 10-15 microns, precision less than 10 microns. The diameter difference of rotating bodies, for general guide rails, the diameter difference of all rotating bodies is not more than 2 microns, and the diameter difference of each group of rotating bodies is not more than 1 micron. For precision guide rails, the diameter difference of all rotating bodies is not more than 1 micron, and the diameter difference of each group of rotating bodies is not more than 0.5 microns: the taper of rollers is within the range of roller length, and the diameter difference of large and small ends is less than 0.5-1 micron: surface finish should usually be scraped: within 25x 25cm 2, the contact spots are 20-25 points, the upper limit of precision is taken, and the lower limit is generally taken.