Linear motion is almost ubiquitous in our daily and working environments. From an industrial technology perspective, linear motion has several key performance indicators: rigidity, precision, and speed. Different applications have different requirements for linear motion. For example, in the machine tool industry, the main requirements for linear motion are rigidity and precision, used to achieve precise motion trajectory control. In automatic loading and unloading systems, the main requirements for linear motion are speed and rigidity, used to achieve rapid point-to-point control, which necessitates the use of high-speed linear guides.
Currently, the linear guides used worldwide to achieve linear motion are mainly ball linear guides and roller linear guides. Ball linear guides are primarily used in applications requiring high rigidity and high precision, such as the machine tool industry; while roller linear guides are mainly used in factory automation projects requiring high speed, with a maximum linear speed exceeding 10m/s, making them a typical representative of high-speed linear guides.
1. High-speed characteristics of roller linear guides:
Many factory automation projects do not require the high rigidity and precision demanded by the machine tool industry; instead, they require high speeds under appropriate precision and rigidity conditions. Roller linear guides are ideal for this application. HEPCO roller linear guides achieve high-speed linear motion through V-bearings rolling on V-shaped guide surfaces or spherical roller bearings rolling on square guide surfaces. Roller linear guides are widely used in factory automation projects such as automated loading and unloading, and gantry robots.
The following characteristics of HEPCO high-speed linear guides make them suitable for high-speed applications with linear speeds exceeding 10 meters per second:
A: The roller bearing has a precision grade of P4, and some precision indicators reach P2. The clearance is precisely controlled to ensure the smoothness of the slider when running at high speed.
B: The V-groove surface or arc raceway surface of the outer ring of the roller bearing is surface hardened to a hardness of HRC60; the surface of the guide rail is also surface hardened to a hardness of HRC60; this ensures a long service life of the guide rail under high-speed operation.
C: The guide rail uses a surface hardening process, while the core remains soft; therefore, the rigidity and toughness of the guide rail are well balanced. It is suitable for high-speed applications with frequent acceleration and deceleration.
D: The roller bearing uses a precision sealing process and high-quality grease. Even when running at high speed, the lubrication between the rolling elements and the raceway is still sufficient, and good heat dissipation is achieved; this ensures that the roller bearing is maintenance-free for its entire life.
E: The rolling between the roller bearing and the guide rail takes place in an open space, rather than in a small, enclosed space, which effectively solves the heat dissipation problem during high-speed operation.
Based on roller guides and combined with synchronous belt drive/gear and rack drive, it is a modular linear module, which greatly facilitates design and assembly;
Based on the same principle, the roller arc guide also has excellent high-speed running performance, with a maximum circumferential running linear speed exceeding 5 meters per second:
2. Adaptability of ball linear guides to high-speed applications:
Ball linear guides are not very suitable for high-speed applications. The following is an analysis from a product design perspective:
Ball linear guides are widely used in various industries due to their high transmission efficiency, high load-bearing capacity, and high dynamic and static stiffness. The arc raceways of both the guide rail and the slider are hardened and precision ground. After passing through the load-bearing raceways of the guide rail and slider, the steel balls enter the unloading raceway of the reversing mechanism, thus achieving the infinite cyclic motion of the steel balls and the reciprocating linear motion of the slider, as shown in the figure below:
As the slider moves rapidly, the steel ball enters the directional mechanism from the bearing raceway and then enters the slider's reversing hole. The steel ball moves along a 180-degree semi-circular arc within the reversing mechanism, constantly changing its direction until it finally achieves complete reversal. The wall of the reversing hole continuously applies resistance to the steel ball, causing it to change direction. Regardless of speed, the steel ball constantly impacts the reversing mechanism. If the speed is very high, the impact on the directional mechanism will be too great, not only accelerating wear and tear on the reversing mechanism but also generating significant noise.
The contact angle between the steel ball and the guide rail is 45 degrees. Therefore, the spatial direction of the steel ball's rotation axis changes continuously during its rotation, with no discernible direction. According to theoretical mechanics principles, this motion generates a gyroscopic torque, which causes the steel ball to slide along the raceway. At high speeds, this sliding effect is very significant, generating substantial sliding friction, resulting in tremendous noise and accelerated wear of the raceway.
In high-speed applications, heat dissipation is crucial. The numerous balls in a ball linear guide roll on the raceway within a sealed cavity, making heat dissipation difficult. Poor heat dissipation can lead to increased preload on the slider, resulting in increased running resistance or even jamming.
The aforementioned characteristics make ball linear guides unsuitable for high-speed applications, as they not only wear out quickly but also generate significant noise.
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