Optical Positioning Device Detector Segmentation
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Solution Overview
Problem
Conventional high-resolution optical position-measuring devices face challenges in maintaining signal quality under non-ideal operating conditions, such as contamination and misalignment of components, due to technological limitations in detector element size and edge capacitances, which restrict the scanning of stripe patterns to periods above 40 μm.
Innovation Solution
The optical position-measuring device incorporates periodic diaphragm structures with transparent and opaque areas, arranged in front of detector elements, ensuring identical area sums and centroid positions across groups, and optimized for equal surface sensitivity moments, to maintain signal quality even under non-ideal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resolution of the position-measuring device is increased, then the measurement precision is improved, but the minimum stripe pattern period that can be scanned is restricted to above 40 μm due to detector element size limitations
Solution Approach 1:
The detector element is divided into multiple sub-detector elements (e.g., 2x2 or 3x3 grid), allowing the effective detection area to be segmented into smaller functional units. This segmentation enables the scanning of finer stripe pattern periods while maintaining adequate signal generation capability, thus resolving the contradiction between high resolution and minimum scanable period.
Solution Approach 2:
The invention transitions from considering only the one-dimensional width of detector elements to utilizing the two-dimensional area of detector elements. By dividing the detector area into multiple sub-elements in both width and height dimensions, the effective sampling density increases without requiring proportionally smaller detector widths, thereby enabling scanning of smaller stripe periods while maintaining signal quality.
2Measurement precision
If smaller detector element structures are used to achieve higher resolution, then the measurement precision is improved, but the proportion of edge capacitances in the total capacitance increases, degrading signal quality
Solution Approach 1:
By segmenting each detector element into multiple sub-detector elements, the total capacitance is distributed across more individual units. This segmentation reduces the relative impact of edge capacitances on the total capacitance, as the bulk capacitance from multiple sub-elements dominates over the edge effects, thereby maintaining signal quality at higher resolutions.
Solution Approach 2:
The signals from multiple sub-detector elements within each detector element are combined (summed) to generate the final scanning signal. This merging process increases the total signal amplitude and improves the signal-to-noise ratio, compensating for the increased edge capacitance effects and maintaining reliable signal quality even with smaller detector structures.
3Measurement precision
If diaphragm structures are placed in front of the detector arrangement to improve signal quality, then the measurement precision is improved, but the alignment precision requirements increase significantly for small detector elements
Solution Approach 1:
The invention extracts and removes the diaphragm structure from the optical path, relying instead on the inherent properties of the divided detector elements and their connection patterns to achieve signal quality improvement. This eliminates the alignment precision requirements associated with diaphragms while maintaining the benefit of reduced edge capacitance effects through detector segmentation.
Solution Approach 2:
The patent introduces the sub-detector element structure and its specific connection pattern as an intermediary mechanism between the incident light and the final scanning signal. This intermediary structure provides the necessary signal conditioning and edge capacitance management without requiring additional optical components like diaphragms, thereby avoiding increased alignment precision requirements.
4Ease of operation
If larger detector elements are used to reduce alignment sensitivity, then the ease of operation is improved, but the measurement precision deteriorates due to inability to scan fine stripe patterns
Solution Approach 1:
Each large detector element is segmented into multiple sub-detector elements, allowing the physical detector element to remain large (maintaining low alignment sensitivity) while the functional detection units are small enough to resolve fine stripe patterns. This segmentation enables the system to enjoy both the alignment robustness of large detectors and the resolution capability of small detectors.
Solution Approach 2:
The invention applies different functional qualities to different parts of the detector element structure. The overall detector element maintains large dimensions for alignment robustness, while the internal sub-elements provide fine spatial resolution. This local differentiation of quality allows simultaneous achievement of ease of operation and high 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
This design ensures high-quality scanning signals with reduced edge capacitances, increased bandwidth, and lower noise, making the system insensitive to contamination and misalignment, and applicable for both linear and rotary position measurements.
Implementation Method 1
the scanning unit has a light source, one or more gratings and a detector arrangement. A plurality of groups of detector elements arranged in a detection plane are provided on the side of the detector arrangement
Data Source
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AI summary
The measuring device comprises a measuring standard (10) connected to an object and including an incremental graduation (12) extending in measuring direction (X), scanning unit (20) connected to other object and including a light source (23), grating (26), and detector system (27). The detector system has several groups of detector elements. The centroid of detector elements of a group is identical to the centroid of detector elements of each other group. The periodic diaphragm structures (29) are arranged in front of a light-sensitive region of detector elements. The optical position-measuring device comprises a measuring standard connected to one of the two objects and including an incremental graduation extending in the measuring direction, and a scanning unit connected to the other object and including a light source, a grating, and a detector system. The detector system includes several groups of detector elements arranged in a detection plane and adapted to generate several position-dependent, phase-shifted scanning signals, in response to relative movement of the two objects, by scanning a periodic fringe pattern resulting in the detection plane. Each group of detector elements has in-phase scanning signals. The sum of areas of the detector elements of a group is identical to the sum of areas of the detector elements of each other group. The centroid of the detector elements of a group is identical to the centroid of the detector elements of each other group. The periodic diaphragm structures are arranged in front of a light-sensitive region of the detector elements.