Optical Positioning Device With Mirror-Symmetric Beam Paths
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Solution Overview
Problem
Existing optical position measuring devices with inclined sensitivity vectors are sensitive to wavelength changes, have low signal intensity, and tight mounting tolerances, making them costly and inefficient for precise position measurement.
Innovation Solution
An optical position measuring device with a scanning unit and scale designed to produce mirror-symmetric partial beams of rays that cover identical optical path lengths between splitting and recombining, using symmetrical diffraction orders (+1 and -1) and optimized reflection phase gratings to achieve high signal efficiency and tolerance, while being insensitive to wavelength changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If asymmetric diffraction orders (+3/-1 or +1/0) are used to achieve inclined sensitivity vector, then position measurement along two translational degrees of freedom is enabled, but signal intensity decreases and mounting tolerances become tight
Solution Approach 1:
The patent applies asymmetry by tilting the scanning optics plane relative to the scale surface by a specific angle, creating an asymmetric optical path configuration. This asymmetric arrangement enables the sensitivity vector to be oriented obliquely to the scale surface, allowing simultaneous measurement along lateral and vertical directions while maintaining adequate signal intensity and mounting tolerance through optimized geometric relationships
Solution Approach 2:
The patent transitions from measuring only in the lateral direction to measuring in both lateral and vertical directions by introducing a tilt angle dimension. This dimensional extension is achieved by rotating the scanning optics plane about an axis parallel to the scale surface, enabling three-dimensional position detection capability while maintaining system robustness
2Adaptability or versatility
If non-identical optical path lengths are used in partial beams, then inclined sensitivity vector is achieved, but wavelength changes affect phase and position measurement accuracy
Solution Approach 1:
The patent changes the geometric parameters of the optical path by introducing a tilt angle between the scanning optics plane and the scale surface. This parameter modification enables the sensitivity vector to be oriented obliquely while maintaining identical optical path lengths for interfering partial beams, thereby achieving inclined sensitivity measurement without wavelength-dependent phase errors
3Measurement precision
If complex light source stabilization is implemented to ensure sufficient coherence length and low phase noise, then measurement precision is maintained, but device complexity and cost increase
Solution Approach 1:
The patent converts the potential harm of wavelength variations into a benefit by designing an optical path configuration where identical path lengths for interfering beams make the system inherently insensitive to wavelength changes. This eliminates the need for complex light source stabilization systems, reducing device complexity and cost while maintaining measurement precision
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
The device provides sufficient signal intensity and mounting tolerance with an inclined sensitivity vector, ensuring accurate position measurement that is largely independent of wavelength changes, thus overcoming the limitations of previous technologies.
Implementation Method 1
Partial beams of light reach the scale and interfere, being deflected at the measuring scale into symmetrical diffraction orders
Implementation Method 2
split partial beams, which then interfere, propagate mirror-symmetrically with respect to a plane of symmetry
Implementation Method 3
either incident onto the scale in a V-shape and/or experience a V-shaped back reflection from the scale
Data Source
Figure 1a
Figure 1b
Figure 1c
AI summary
The present invention relates to an optical position measuring device for detecting the position of two objects moving relative to each other. This device comprises a scale connected to one of the two objects, which has a measuring scale with a periodic arrangement of scale regions along at least one scale direction. Furthermore, a scanning unit with several optical elements is provided on the other object. The arrangement and design of the optical elements of the scanning unit result in a scanning beam path in which split partial beams, which interfere, propagate mirror-symmetrically with respect to a plane of symmetry and either incident on the scale in a V-shape and/or experience a V-shaped back reflection from the scale.The plane of symmetry is tilted by a defined angle relative to the scale about an axis of rotation that is oriented parallel to the surface of the scale and extends perpendicular to the division direction. Partial beams of light reach the point of interference, being deflected at the measuring scale into symmetrical diffraction orders and traveling identical optical path lengths between splitting and recombination (Fig. 1a).