37 www.drivesncontrols.com March 2025 BEARINGS, BELTS AND CHAINS n bearing rumble would introduce errors. In such cases, air bearings provide the necessary continuous motion with minimum speed uctuations, and also last longer than mechanical bearings. nTravel ranges of 1m or more Unlike other frictionless technologies used in nanopositioning applications, air bearings are not limited to short travel ranges. For example, piezo exure guided mechanisms can provide sub-nanometre precision, high scanning speeds and share many of the advantages of air bearings, but their travel ranges are limited to micrometres or a few millimetres. With air bearings, motion ranges beyond 1m are achievable and the advantages of smaller air bearings carry over. nAccurate, frictionless motion In linear motion applications, precise positioning of a moving carriage within a few nanometres is achievable using non-contact, direct-drive motors and high-resolution optical encoders in combination with air bearings. For rotational applications, angular resolutions to tenths of arc-seconds are achievable using slotless torque motors as the driving force. Air bearings are often preferred in inspection, metrology and manufacturing applications due to their low hysteresis eect or reversal error, arising from a lack of mechanical contact and friction. Eliminating friction makes it possible to reduce hysteresis and improve repeatability and accuracy. Another technology to consider in precision positioning, with similar performance to air bearings, is magnetic levitation. Here, magnetic elds replace air as the supporting medium, but the control electronics are much more complex because all six degrees of freedom have to be monitored and controlled continuously. n Rotary motion with low eccentricity and wobble Rotary air bearings are highly eective in providing precise rotary motion due to their high stiness and the surfaceaveraging eect. In air bearing rotary stages, wobble or tilt errors are typically in the range of 0.1–1 arc-seconds – much smaller than with rotary stages based on mechanical bearings. nCost-e ciency Air bearings can use air pressure to provide actuation as well as guidance. This eliminates the need for extra electric motors, reducing complexity, size and cost. The absence of wear-and-tear and the need for maintenance cuts operating costs and improves ROIs. This may be the most important factor when designing highthroughput automation systems that need to operate 24/7 and have stringent uptime requirements. Air bearings oer multiple advantages over traditional bearings, including being more precise, accurate and durable. They are also quieter and produce less vibration. Air bearings are environmentally friendly and cost-eective. They can be designed to meet a variety of requirements in industries such as semiconductor manufacturing, precision machining, metrology, aerospace and scientic research. n A three-axis air bearing stage for laser processing, consisting of a rotary air bearing stage (1) and a compact planar XY stage (2). The surface averaging e ect of an air bearing (top) compared to a conventional mechanical bearing (bottom). Images: PI
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