Crossed Scale Optical Position Measuring Device
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Solution Overview
Problem
Existing optical position-measuring devices using crossed diffraction gratings cannot accurately measure movements perpendicular to the table plane, and additional sensors like capacitive styluses do not meet the stringent accuracy requirements of the semiconductor industry, while extended crossed gratings are difficult to produce accurately.
Innovation Solution
An optical position-measuring device with two crossed scales and a scanning bar, where the scale is offset in a third direction, allowing light to pass through and be split by diffraction structures on both the scanning bar and scale, generating periodic signals due to interference, enabling measurement of the scanning distance between the scales.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If two crossed scales are used to measure position in two directions, then measurement capability in both directions is improved, but the ability to measure scanning distance perpendicular to the table plane deteriorates
Solution Approach 1:
The patent introduces a third measurement dimension by offsetting the second scale perpendicular to the table plane. The light path is configured to travel between the first and second scales, enabling measurement of scanning distance in the third direction while maintaining position measurement capability in the first two directions through the crossed grating configuration.
2Adaptability or versatility
If additional distance sensors are added to measure scanning distance, then measurement versatility is improved, but measurement precision deteriorates due to insufficient accuracy of sensors like capacitive styluses
Solution Approach 1:
The patent replaces mechanical distance sensors (capacitive styluses, tangent sensors) with an optical measurement system using diffraction gratings and light interference. This substitution provides nanometer-level measurement precision for scanning distance while maintaining the ability to measure all six degrees of freedom of the table.
3Adaptability or versatility
If extended crossed gratings are produced to increase measurement range, then measurement capability is improved, but manufacturing precision deteriorates due to difficulty of accurate production
Solution Approach 1:
The patent divides the measurement system into two separate crossed scale assemblies instead of using one extended grating. Each scale has a manageable size that is easier to manufacture with high precision. The scales work together through the optical path to provide extended measurement capability without requiring a single large, difficult-to-manufacture grating structure.
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 configuration allows for accurate measurement of shifts in both directions within the table plane and the scanning distance, meeting the high accuracy needs of the semiconductor industry without the limitations of existing technologies.
Implementation Method 1
measuring standards having optical diffraction gratings which split incident light into different partial beams by diffraction
Implementation Method 2
By combining suitable partial beams, periodic signals are obtained in a photodetector in response to a shift of the one measuring standard relative to the other, due to the interference of the two partial beams
Data Source
AI summary
An optical position-measuring device includes a scanning bar extending in a first or second direction, and a scale extending in the other direction. The scale is offset by a scanning distance from the scanning bar in a third direction perpendicular to the first and second directions. The device has a light source whose light penetrates the scanning bar at an intersection point of the scanning bar and scale to fall on the scale and arrive back at the scanning bar. At a detector, the light is split by diffraction into different partial beams at optically effective structures of the scanning bar and scale and combined again. A periodic signal is obtained in the detector in response to: a shift between the scanning bar and scale in the first direction due to interference of combined partial beams, and a change in the scanning distance between the scanning bar and scale.