XY Table Encoder Arrangement for Abbe Condition Compliance
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Solution Overview
Problem
High-precision XY tables face challenges in achieving accurate position measurement due to the limitations of existing measurement systems, including expensive and inaccurate laser interferometers, complex cross grating production, and failure to comply with the Abbe condition, leading to inaccuracies from tilting movements and environmental variations.
Innovation Solution
The use of 1Dplus encoders with longitudinal and transverse tracks, along with additional scanning heads, ensures compliance with the Abbe condition by accurately measuring in-plane degrees of freedom, minimizing tilting errors, and incorporating thermal correction to maintain precision, while decoupling measurement and force frames prevents deformation and measurement errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If plane mirror laser interferometers are used for position measurement, then measurement range is sufficient, but measurement precision deteriorates due to air refractive index fluctuations causing typical deviations of 50 nm
Solution Approach 1:
The patent replaces optical laser interferometers with a mechanical encoder system consisting of a scale and scanning head. This mechanical substitution eliminates the air column refractive index problem that limits laser interferometer precision, while maintaining the ability to measure large positions through the mechanical scanning mechanism.
Solution Approach 2:
The patent extracts the measurement function from the air-dependent optical system and implements it through a mechanical encoder system that operates independently of atmospheric conditions. The scale and scanning head configuration removes the harmful dependency on air refractive index while preserving measurement capability.
2Measurement precision
If cross grating encoders are used for position measurement, then measurement precision improves, but device complexity increases due to complex production of large and highly precise cross gratings
Solution Approach 1:
The patent segments the two-dimensional measurement function into two separate one-dimensional linear scales arranged perpendicular to each other. Each scale is scanned by dedicated scanning heads, dividing the complex cross grating production into simpler linear scale productions while maintaining the ability to measure both X and Y positions simultaneously.
Solution Approach 2:
The patent resolves the complexity of two-dimensional measurement by using two one-dimensional scales in perpendicular dimensions. The first scale measures position in one direction while the second scale, oriented perpendicularly, measures position in the orthogonal direction, eliminating the need for complex cross grating patterns.
3Device complexity
If 1Dplus encoders are used on transverse arm above working plane, then device complexity is reduced, but measurement precision deteriorates because Abbe condition cannot be complied with leading to inaccuracies from tilting movements
Solution Approach 1:
Instead of placing the encoder above the working plane (as in conventional gantry arrangements), the patent inverts the arrangement by placing the scale on the movable table and the scanning heads on the stationary reference frame. This inversion enables compliance with the Abbe condition while maintaining the simplicity of 1Dplus encoder technology.
Solution Approach 2:
The patent makes the movable table serve a dual function: as the workpiece carrier and as the carrier for the encoder scale. This multi-functionality eliminates the need for separate encoder mounting structures above the working plane, enabling Abbe condition compliance without increasing device complexity.
Data Source
AI summary
An XY table with a measuring arrangement for position determination is described, comprising a fixed reference part (B) and an intermediate part (F) that moves relative to the reference part (B) in a first direction (Y), with an object (O) that moves relative to the intermediate part (F) in a second direction (X), wherein a part to be processed (W) is disposed on the object (O) or on the reference part (B), and for the first direction (X) with at least one 1Dplus encoder (M1, M2) for measuring in-plane degrees of freedom (X, Y, Rz) between the reference part (B) and the intermediate part (F), and for the second direction (X) with at least one 1Dplus encoder (M3, M4) for measuring the in-plane degrees of freedom (X, Y, Rz) between the object (O) and the intermediate part (F), so that the position (Xo, Yo) of a tool center point (TCP) at the object (O) or part (W) can be detected. In the process, the 1Dplus encoder (M1, M2, M3, M4) is disposed constructively such that the projection thereof in the plane spanned by the first and second direction (X, Y), said plane containing the tool center point (TCP), lies within the entire range of motion of the XY table outside of part (W). This allows the maintenance of the Abbe condition and thereby the precise detection of the tool center point (TCP) at the object (O) using simple 1Dplus encoders.