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Air bearings provide vibration-free, accurate positioning in metrology
There are many applications within metrology – such as coordinate measuring machines (CMMs) – that require high precision positioning. This can be reliably achieved using motion stages, and bearings are a vital component of any motion stage set-up. There are many different variations of mechanical bearing available – including ball and roller models – but the more recent development of air bearings offers a number of advantages over mechanical options for these applications, enabling vibration-free motion and accurate velocity control.
Key highlights
- Air bearings as an alternative to ball- or roller-bearings, eliminate vibration
- Custom air bearings can be made by Physik Instrumente
- CMM as well as a range of other machine can benefit from air bearings
Precision and reliability
Motion stages are used across various applications that require precision positioning, including a wide range of metrology tools to measure the roundness, flatness, surface profiles and thickness of shafts, turbine blades, semiconductor wafers and other critical components. There are many types of motion stages, offering range motion profiles that vary in complexity, from a simple line to intricate three-dimensional patterns. However, the accuracy and smoothness of movements is always affected by the types of bearings used in the set-up, as vibrations or jitter can compromise the precision of positioning. Air bearing-based stages are an efficient way to minimise these disturbances, as this replaces direct contact with a thin film of air, which helps to avoid wear, friction, vibration and hysteresis effects. This makes it possible to satisfy performance criteria such as superior angular repeatability, geometric precision and minimal motion errors, as well as straightness and flatness for linear bearings, and axial and radial runout for rotary bearings. One example is Physik Instrumente (PI), which supplies high precision positioning technology and piezo applications in the semiconductor industry, life sciences, photonics and in industrial automation. PI rotary air bearings aim to ensure axial motion error of less than +/-25 nanometres, which allows measurement systems to detect roundness errors well under 0.1µm.
Tailored motion systems
PI designs and manufactures bearings to support metrology applications – including CMMs – making it possible to create metrology equipment with sub-micron precision. The company works with leading manufacturers around the world and offers custom-made air bearing motion systems for instances where the standard product range does not satisfy application requirements, such as for measuring complex geometries with extreme precision. Even though PI does not offer complete CMMs, the company can design and build a custom multi-axis air bearing motion system, supplied with all necessary parts for reliable installation and operation. This includes a granite structure, together with drive and feedback technology, cabling, controller, and a machine base with vibration isolation. These systems often combine linear and rotary motion, with up to eight synchronized axes of motion.