Planar XYZθ Positioning System with Aerostatic Bearings
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Solution Overview
Problem
Conventional XYZθ positioning systems suffer from positional accuracy issues due to coupled errors in stacked axes, require large footprints, and are inefficient in spatial design, making them unsuitable for applications with spatial constraints.
Innovation Solution
A decoupled XYZθ positioning apparatus with a rigid flat base, featuring Y-axis linear actuators in a H-configuration, Z-axis with aerostatic bearings, and elastic linkage elements to uncouple errors, along with optical sensing for closed-loop feedback control, achieving high precision and low profile with moderate footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional stacked XYZθ positioning system is used, then the system can achieve positioning function, but the positional accuracy deteriorates due to coupled errors from each axis
Solution Approach 1:
The positioning system is segmented into independent planar stages (X-stage and Y-stage) that operate on separate rigid reference surfaces. Each stage has its own air bearing elements and linear motor, allowing independent motion control without error propagation between axes. The Z-axis lift stage is also decoupled from the X-Y plane motion.
Solution Approach 2:
Air bearing elements are introduced as intermediaries between the moving stages and the rigid reference surfaces. These air bearings provide frictionless support and precise positioning without mechanical contact, eliminating mechanical error transmission between axes while maintaining stable reference surface relationships.
2Adaptability or versatility
If a conventional stacked XYZθ positioning system is used, then the system can provide multi-axis motion, but the footprint becomes large and spatial efficiency deteriorates
Solution Approach 1:
The system uses a H-configuration for the Y-axis actuators, where two Y-axis linear actuators are arranged vertically one above the other instead of stacking them horizontally. This vertical arrangement reduces the horizontal footprint while maintaining full Y-axis motion capability. The Z-axis lift stage operates vertically, further utilizing the vertical dimension to minimize horizontal space requirements.
Solution Approach 2:
The Z-axis lift stage is nested within the X-Y planar stage structure, allowing the lifting motion to occur within the existing horizontal footprint rather than requiring additional horizontal space. The aerostatic bearing mechanism supports the lifted position without requiring external spatial expansion.
3Manufacturing precision
If adjustment is made to any axis in a conventional stacked system, then the positioning of that axis is improved, but the positioning of other axes deteriorates due to alignment dependency
Solution Approach 1:
Each axis is equipped with independent closed-loop feedback control using linear optical encoders that measure position relative to the rigid reference surfaces. This segmentation of measurement and control functions allows each axis to be adjusted and calibrated independently without affecting the alignment or positioning accuracy of other axes, as each axis has its own dedicated feedback system.
4Measurement precision
If a decoupled design with multiple air bearings is used, then the positioning accuracy is improved, but the air consumption and cost increase
Solution Approach 1:
Multiple air bearing elements are merged into integrated air bearing assemblies that support entire stages rather than individual components. The X-stage and Y-stage each have their own aerostatic bearing mechanisms that provide multi-point support simultaneously, reducing the total number of separate air bearing units required while maintaining positioning accuracy and reducing overall air consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances positional accuracy, reduces errors, and minimizes footprint, enabling high-speed and precise positioning while maintaining a compact design, independent of Z-axis weight and dynamics, thus improving overall system performance.
Implementation Method 1
The Z-axis is provided with an aerostatic bearing mechanism that floats on thin film of externally pressurized air on top of the rigid flat base
Data Source
AI summary
A positioning system having a flat base comprising (i) a X-axis assembly having a X-axis linear actuator means arranged orthogonal to the Y-axis; (ii) a Y-axis assembly having a pair of Y-axis linear actuator means mounted onto the flat base forming a H-configuration; (iii) a Z-axis assembly having an aerostatic bearing mechanism that floats on thin film of externally pressurized air on top of the flat base; and a θ-axis actuator anchored from the X-axis to drive the Z-axis assembly which carries a workpiece, wherein the Z-axis assembly is rotated with the rotary axis for the θ-axis perpendicular to the flat base.