linear rod rail is to realize the linear reciprocating motion of mechanical components, the core principle is to replace the traditional sliding friction through the rolling body (ball or roller) rolling friction, in support of the load at the same time to achieve high-precision, low-resistance relative motion, the specific working mechanism can be disassembled into three key links.
First, the structural composition and force transmission path
core components
linear rod rail consists of a guide rail (fixed parts, long, surface machined with raceways), slider (moving parts, connected to the actuator), the rolling body (ball / roller, placed between the two raceways) and the return to the direction (to guide the rolling body cycle). The raceways usually have a Gothic (double arc) or V-shaped cross-section and form a point contact (ball) or line contact (roller) with the rolling elements.
Load transfer method
When the slide is subjected to an external load (radial, axial or tilting moment), the load is transferred via the slide raceways to the rolling elements, which in turn are transferred to the guideway raceways, which ultimately transmit the force to the machine frame. The number of rolling elements (usually 4-8 columns) and the contact angle (30°-45°) determine the distribution of the load: the radial load is borne by the perpendicularly oriented columns of rolling elements, the axial load is decomposed by the inclined columns of rolling elements, and the tilting moment is balanced by the difference in the forces of the rolling elements on both sides.
Second, the realization of rolling friction and cyclic movement
Rolling instead of sliding drag reduction mechanism
Rolling body and raceway contact for the point / line contact, the contact area is much smaller than the surface contact of sliding friction (such as sliding guideway contact area is 50-100 times of the ball guideway). When the slide along the rail movement, rolling body rolling in the raceway, the coefficient of friction is only 0.001-0.003 (sliding friction coefficient of 0.1-0.2), the required driving force to reduce more than 95%, while avoiding wear and tear generated by sliding friction and heat.
Rolling body cycle path
slider movement, the front end of the rolling body from the loading zone (bear the load of the raceway section) rolling to the return to the entrance, through the return to the internal curve channel (radius of curvature and the rolling body diameter match) into the non-loaded area (the slider inside the cycle of the groove), and then guided back to the back end of the return to the loading zone, the formation of a closed loop. This process makes the rolling body can be unlimited cycle use, support the long stroke movement of the slider.
Precision control and motion stability guarantee
The realization of straightness
The guideway raceway is processed through precision grinding, and the straightness error is controlled within 0.001-0.01mm/m. The rolling body is dimensionally consistent (diameter and length), and the rolling body has the same size (diameter and length). The size consistency of the rolling body (diameter tolerance ±0.001mm) ensures that the force at each contact point is uniform, and avoids the deviation of the slider trajectory due to the size deviation of individual rolling body. When the slider moves, the rigid constraints of the rolling elements along the raceway force the slider to strictly follow the linear trajectory of the guideway, realizing micron-level motion accuracy.
The role of preload
By adjusting the gap between the slider and the guideway (usually using double-nut preload or interference fit), the rolling body and the raceway produce a small amount of elastic deformation, eliminating the gap at the same time the formation of preload (10% -20% of the rated load). Preload can offset the gap caused by external load changes, to avoid shock vibration of the slider in the commutation movement, so that the reverse positioning error is controlled within 0.001mm.
Fourth, the friction characteristics and energy loss
Rolling friction energy dissipation
Rolling process, energy loss mainly comes from two parts: rolling body and raceway contact area of the elastic hysteresis (material compression and recovery of the energy difference, accounting for 70% of the total loss), rolling body and the collision friction of the return friction (accounting for 30%). Compared to sliding friction (coefficient of friction 0.1), rolling friction reduces energy loss by more than 97%, reducing motor drive power requirements to 1/10.
Influence of lubrication on friction
Grease forms an oil film (1-3 μm thick) between the rolling elements and the raceways, which reduces frictional wear caused by direct metal contact. The viscosity of the film should be matched with the running speed: use high viscosity grease for low speed and heavy load (to prevent the film from rupturing), and use low viscosity grease for high speed (to reduce the stirring resistance), to ensure that the coefficient of friction stabilizes within the range of 0.0015±0.0005.
Five, adaptive adjustment under special working conditions
Offset load compensation
When the slider is subjected to tilting moment, the rolling body in different positions is not uniformly loaded (one side of the load increases, the other side decreases), but the symmetrical design of the raceway makes the rolling body on the side of the force absorb the load through the elastic deformation, avoiding the localized overload. For example, 4 rows of ball guide can bear the overturning moment by the rolling elements in diagonal direction together, so that the maximum contact stress is controlled within the material fatigue limit.
Response to temperature changes
Working temperature changes (-20 ℃ to 80 ℃) will lead to thermal expansion and contraction of the guide and slider, through the selection of the same coefficient of linear expansion of the material (such as steel guide with steel slider) or reserved thermal deformation gap, can reduce the additional stress due to dimensional changes, to maintain the normal coordination of the rolling body and raceway.
In summary, the working principle of linear guide is through the cyclic movement of the rolling body, precision structure with reasonable force distribution, the sliding friction into low-loss rolling friction, and at the same time, with the help of rigid constraints and preloading design, to achieve "high-precision guiding + high load support + low-resistance movement" synergies for automation equipment, precision machine tools, etc. provide the core movement foundation. It provides the core motion foundation for automation equipment, precision machine tools, etc.
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