Loadpoint’s Direct Drive Rotary Tables Are The First For Precision Tasks With Angular Position Resolution Better Than 0.00002 Degrees


Precision Rotary TableSwindon, UK – Loadpoint Bearings has launched a revolutionary range of air bearing rotary tables employing a new design of direct drive system to achieve previously unattainable levels of resolution on angular position, better than 0.00002 degrees. This level of accuracy means that the rotary tables are ideally suited to demanding tasks such as dicing silicon wafers and high precision grinding and machining operations.

Developed originally for Loadpoint’s own use – and proven in trials on the company’s own dicing machines – the rotary tables are believed to be the first commercially available product of their type to integrate a direct drive motor. The motor itself – a brushless DC torque unit – is a very recent development. It is key to the air bearing table specification, enabling a design, which is low in height and free from cyclic errors and mechanical wear.

The new design resolves a host of issues associated with mechanically driven air bearing tables. Traditionally, the drive on these units has been provided by such devices as worm and wheel, pinch wheel, cable or harmonic drives. Each has associated disadvantages, the harmonic drive is physically large and has limited resolution on angular position whereas the others produce cyclic errors and are prone to wear, both of which impair operating accuracy.

The Loadpoint design overcomes all of these problems, achieving a resolution on angular position better than 0.00002 degrees (a parameter which is critically important on large diameter rotary tables) and axial and tilt motion errors of less than 0.25 um and 0.013 mrad respectively. The system resolution achieved is a function of the encoder type and the interpolation of its signal by the drive. A wide choice of encoder types offering different levels of resolution means that the user has considerable application flexibility in this respect.

Loadpoint is producing the new rotary tables in a range of sizes up to a maximum diameter of 0.5m. These can be with or without drives to suit different application requirements. A typical specification is illustrated in Fig 1 (see photo). The table, 320 mm in diameter, is currently used to support silicon wafers for dicing. It has an axial stiffness of 100 N/um, a load capacity of 1350 N and can generate 75 Nm peak, 6.5 Nm continuous torque.

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