New, low profile air bearing based rotary stage

3 min read

With its brushless direct-drive motor, integral precision encoder and an air bearing design combining high stiffness with exceptionally low axial, radial and tilt error motion. Aerotech’s new ABRS series rotary stage represents the ultimate in high pr

Aerotech’s ABRS series rotary air-bearing positioning stage has ultra-high precision, high speed and high torque · New, low profile air bearing based rotary stage aimed at the most demanding high-throughput applications

Aldermaston - UK, September 2006: With its brushless direct-drive motor, integral precision encoder and an air bearing design combining high stiffness with exceptionally low axial, radial and tilt error motion, Aerotech’s new ABRS series rotary stage represents the ultimate in high precision angular positioning with the added advantage of a very low vertical profile to combat stack-height related errors in multi axis positioning systems.

The new series is available in four sizes with nominal, square dimensions (width x depth) of 150 mm, 200 mm, 250 mm and 300 mm. Table tops have diameters of approximately 20 mm less than the width and each model includes a 360 degree reference scale. The maximum positioning resolution on the largest stage is 0.174 µrad (0.036 arc-sec) with speeds up to 500 rpm. Aimed at demanding high-throughput production and inspection applications, including semiconductor manufacture, optical metrology and nanotechnology device fabrication, the new range combines ultra-smooth and precise angular motion with extreme positioning stability and has further benefits of a very long life with virtually zero maintenance.

For such high precision applications, face error motion (the combination of axial and radial bearing errors resulting in a tilt angle of the rotating table top) is of fundamental importance. Aerotech’s specification for asynchronous tilt error is less than 0.4 µrad (<0.08 arc-sec) for the smallest model and below 0.2 µrad (<0.04 arc-sec) for the largest model. This is measured to ANSI/ASME standard B89.3.4m using the Donaldson ball reversal method for axes of rotation using both synchronous and asynchronous methods. Aerotech’s unique air bearing design with active preload brings together the precision and stiffness to ensure that its tilt error and planar performance is unrivalled for commercially available products with all other specifications being equally impressive.

However, the ABRS rotary stage precision does not compromise its load carrying or speed performance specifications - with maximum axial loads up to 950N (500 N radial load), the largest stage produces more than 30 Nm of peak torque and is capable of speeds in excess of 8 rev/sec thanks to Aerotech’s S series brushless and slotless direct-drive motors that produce high torque with minimal heating. The slotless S series motors are cog and torque-ripple free and with zero-backlash and exceptionally smooth velocity and torque control, the motor is ideal for scanning at low or high speeds or for highly stable positioning with very fast settling times. All these factors combine to ensure that production throughput is maximised and the completely non-contact design ensures a very long working long life with minimal maintenance.

As standard, a sine wave output encoder allows a fundamental angular resolution of 3600 lines/rev on the smallest stage and 18000 lines/rev on the largest 300 mm wide unit. A square-wave output encoder option is also available and the final resolution on the largest model is 0.174 µrad (0.036 arc-sec) with the A3200 Automation Platform controller with maximum multiplication and quadrature.

To ensure minimal stack-height related errors in multi axis positioning applications (caused by the effect of individual angular pitch, yaw and roll errors that culminate in a compound error at the point of measurement or reference), the ABRS has been designed with an extremely low height for an air bearing design. With overall height dimensions of only 80 mm, 90 mm, 100 mm and 110 mm, each model also includes a clear aperture for product feed-through, laser beam delivery or for general clearance. Construction material is aluminium, with a hard-coat (Rockwell 62) finish for maximum durability and each model is generously equipped with threaded and counter-bored mounting holes on tabletop and main body.

As with all Aerotech products, custom engineered modifications can include different mounting configurations or complete application specific re-design. Rate table and inertial guidance test-stand variants for the ABRS range are available on request from Aerotech.

Aerotech manufactures a wide range of servo amplifiers and advanced motion controllers to complement its high-performance mechanical positioning systems. The A3200 Digital Automation Platform is a software only, machine control system that runs on a standard PC. Combining motion control, HMI, PLC and vision control modules with an industry standard Firewire® high performance communication network, it will control up to 32 axes of high speed motion with Aerotech Ndrive digital servo amplifiers featuring 20 kHz position, velocity and current loops. An additional 10/100 Base T Ethernet interface may be used to add third party I/O and PLC’s. The A3200 is able to run the most complex, tightly synchronised motion and machine control functions with powerful .NET programming capability as well as native RS-274 G-code, the high level AeroBASIC™ or optional LabVIEW™ for complete flexibility.

The SoloistTM may also be used with the range as a standalone single axis digital servo controller with integral power supply and brushless servo amplifier. As an Ethernet based distributed drive solution with high level or .NET programming capability, the Soloist can perform coordinated point to point motion for up to 1000 axes.

For standalone systems ranging from laboratory research to advanced OEM equipment, Aerotech’s Ensemble™ Epaq is an integrated, 6-axis desktop or 19 inch rack mounted motion control and drive system. Based upon the A3200, with integral 10 A peak digital amplifiers, it is capable of driving and controlling linear and rotary brushless, brushed and micro-stepping motors. The Ensemble may be also be expanded to control a further three external drives, offering 9 axes of completely co-ordinated motion and machine control from a single competitively priced unit.

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