![]() ![]() High-precision runner blocks are designed to provide extremely smooth motion as the balls circulate in the bearing raceways.Positioning accuracy Bearing circulation can cause precision-reducing vibration during the transition from load-bearing to nonload bearing zones in the runner block. The result is consistent, extremely smooth motion as balls circulate in the bearing raceways. For example, Bosch Rexroth’s High-Precision ball rail uses a steel insert with relief zones that dampen ball-entry forces at the ends of the raceway. Some manufacturers optimize the bearings’ transition-point geometry with specialized high-precision runner blocks to minimize vibrations. Spending more on components and not addressing the structural elements’ flatness and straightness wastes money and diminishes travel accuracy for the axis and machine.Īlso, bearings circulating inside a linear guide can cause precision-reducing vibration as the bearings transition from “load-bearing” to “nonload-bearing” conditions. Keep in mind that as the tolerance band decreases, component costs increase. For example, Bosch Rexroth, Charlotte, N.â⁜., offers products covering a range of six accuracies, from N (Normal Precision) height/width tolerances of ☑00 μm/±40 μm to UP (Ultra Precision) height/width tolerances of ±5 μm. High-quality travel-guidance systems follow industry standard tolerances for height, width, and parallelism. Minimizing these motions depends on the quality of the linear guide and the surface on which it mounts. ![]() Travel accuracy measures pitching, yawing, and rolling. Linear-motion systems typically conform to their mounting surfaces, so travel accuracy varies with machine surface alignment, preparation, and tolerances. Minimizing these motions depends on the quality of the travel guidance system and the surface it mounts on. Travel accuracy measures pitching (up and down), yawing (side to side), and rolling (around the axis). Engineers can improve these parameters by focusing on the following six areas. Repeatability relates to how precisely a linear-motion system positions itself when repeatedly approaching a position from the same direction, taking into account deviations in actual position from the target position. So positioning accuracy is the maximum deviation between the actual and target positions during each motion. Accuracy, the discrepancy between a movement’s target position and the actual position, reflects motion targets being approached from different directions (multidirectional). Precision is a combination of accuracy and repeatability. Let’s start by considering how to define precision. Even machines equipped with the most-sophisticated motion controllers wonât run with exact precision unless their mechanical components are appropriately specified for the application. It’s also important to know the operating environment, because some environments make it more challenging to hit the required target. So the industry and application usually determine the needed level of precision. standards seen in packaging or newspaper printing. Granted, different markets have varying definitions of precision, from nanoscale levels in the semiconductor industry to the relatively generous 0.01-in. Armed with even with the most-sophisticated motion controller, engineers can still find it difficult to attain precise linear motion unless the mechanical components are appropriately designed for the application. ![]()
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