MOTION SYSTEMS HANDBOOK
Common linear guide permutations Linear rails are linear assemblies that have tandem tracks (usually on one monolithic run) containing load-supporting balls or rollers. The backbone of many industrial applications, they provide low-friction guidance and high stiffness for loads that can range from just a few grams to thousands of kilograms. Their variety of sizes, accuracy classes, and preloads make linear rails suitable for virtually any performance requirement. The reasons for using linear rails are numerous, but their most obvious benefits over other types of guides are load capacity, travel accuracy, and rigidity. For example, round shaft guides
can withstand only downward or liftoff loads, whereas linear rail guides can withstand downward loads and liftoff loads … as well as moment loads. Unlike crossed-roller guides for which travel is often limited to 1 meter or less, linear rails can provide very long travel lengths. When compared to plain bearing guides, linear rails also have higher stiffness and rigidity, and often have better load and life characteristics. Linear guides also provide a high level of travel accuracy, thanks to precise machining of one or both edges of the rail, which act as reference surfaces. With two, four, or six rows of rolling elements — either spherical balls or cylindrical rollers — stiffness is also high … and deflection of the bearing block is minimal. All of these attributes combine to provide a linear guide system that is perfectly suited for applications that require high precision, high rigidity, and long life. So here we outline common applications for these linear components in typical sizes. Single-rail applications: Because linear rails have load-supporting balls (or rollers) on each side of the rail assembly, they can withstand overhung loads, even when just a single rail is used. In contrast, round shaft linear guides must be used in pairs when overhung loads are present. Because of this feature, numerous applications use a single linear rail, to save space or to prevent issues with misalignment among other components in the system. Here are a few examples of applications that use a single linear rail.
Linear actuators are typically characterized by their drive mechanism — belt drive, ball or leadscrew drive, pneumatic drive, and so forth. But it’s not unusual for rod-style electric actuators to be classified by the input voltage — commonly 12 or 24 volts — of their integrated motors. 12-V linear actuator illustration courtesy Firgelli Automations
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DESIGN WORLD — MOTION
8 • 2020
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