Large Aperture Air Bearing Rotation Stage - A-688, Made in the USA

15 Oct 2025

PI, a global leader in precision motion control and air bearing motion systems, offers the A-688 rotary stage, a groundbreaking motorized, air-bearing based rotation stage, engineered for nanometer-scale precision, frictionless motion, and long-term reliability in demanding metrology, optics, photonics, and semiconductor applications.

Engineered around a frictionless air-bearing design, the A-688 rotation stage delivers exceptional accuracy, stability, and longevity. The large clear aperture of 260 mm allows optical beams, cabling, or mechanical payloads to pass directly through the center, making the stage ideal for interferometry setups, precision inspection systems, and beamline instrumentation. Unlike traditional mechanical-bearing stages, the A-688's non-contact operation eliminates wear, backlash, and lubrication, ensuring smooth, particle-free motion even in cleanroom or vacuum environments.

At the heart of the rotation stage is a direct-drive, ironless torque motor that produces ultra-smooth, cog-free rotation with rapid acceleration and outstanding velocity control. Paired with high-resolution encoder feedback—available in either incremental or absolute versions—the system achieves angular resolution down to 0.0015 µrad and maintains near-zero wobble, tilt, and runout errors. The combination of these features allows users to perform highly repeatable angular positioning and continuous scanning tasks with nanoradian precision.

Key Highlights & Capabilities

• Large clear aperture: Ø 260 mm allows substantial optical or mechanical payloads to pass through or be integrated in the rotation axis
• Ultra-high resolution & accuracy: Up to 0.0015 µrad angular sensor resolution (in the B100 variant with absolute encoder)
• High dynamics: Maximum angular speeds of up to 500 rpm
• Exceptional geometry performance:
  • Radial error ≤ ±0.15 µm
  • Axial error ≤ ±0.175 µm
  • Wobble (tilt error) < 1 µrad
• Direct-drive, low-cogging torque motor: Ironless 3-phase motor delivers smooth, backlash-free motion
• Encoder options: Incremental (sin/cos) or absolute (BiSS-C) encoder variants permit precise closed-loop feedback and "instant-on" referencing
• Frictionless air bearing design: With no contact between surfaces, the stage operates without wear, lubrication, or maintenance, providing virtually unlimited life.
• Flexible orientation & mounting: The stage is usable in any orientation (horizontal, vertical, inverted) and supports various payloads and mounts
• Customizable modes: Supports both point-to-point indexing and continuous scanning modes to meet different application needs

Applications & Market Impact
The A-688 is ideal for use in advanced systems requiring ultra-precision rotation, including but not limited to:

• Optical alignment, beamline systems, interferometry, and metrology
• Semiconductor wafer inspection, lithography, and mask alignment
• Calibration, scanning, and inspection systems
• Tomography and imaging platforms
• Cleanroom, vacuum, or contamination-sensitive environments (due to frictionless motion)

Because the A-688 produces no particulate contamination (thanks to the air bearing), it is especially suited for cleanroom and optical environments.

Availability & Support
The A-688 will be available in multiple variants (e.g. A-688.A100 with incremental encoder, A-688.B100 with absolute encoder) to suit a range of application needs.

Comprehensive documentation, datasheets, 3D models, and integration support will accompany the product. Customers can also consult with PI engineers for custom adaptations or multi-axis configurations.