Optical Positioning Device with Direction-Selective Deflection Elements
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Solution Overview
Problem
Optical position measuring devices using vernier scanning are susceptible to contamination of the measuring graduation, leading to uneven influences on scanning signals and errors in position determination.
Innovation Solution
An optical position measuring device with a scale and a scanning unit, featuring two detector arrangements and direction-selective deflection elements that create a periodic Vernier fringe pattern, ensuring all scanning signals are equally influenced by contamination, thus minimizing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Vernier scanning with different periodicities is used to achieve high measurement precision, then measurement precision is improved, but the system becomes susceptible to contamination effects causing signal errors
Solution Approach 1:
The patent applies local quality by making the two scanning beams scan different spatial regions (first beam scans first region, second beam scans second region) while both regions are subject to the same contamination conditions. This allows the system to maintain high measurement precision through Vernier scanning while ensuring that contamination affects both beams uniformly, thereby maintaining signal reliability.
Solution Approach 2:
The patent segments the scanning function into two separate scanning beams with different periodicities that scan different regions. This segmentation enables the system to generate multiple scanning signals that can be processed to determine position while being equally affected by contamination, thus resolving the contradiction between precision and reliability.
2Measurement precision
If multiple scanning divisions with different periodicities are used to generate phase-shifted signals, then position determination accuracy is improved, but uneven contamination effects on individual signals cause errors
Solution Approach 1:
The patent implements local quality by directing different scanning beams to different spatial regions (first region and second region) on the scale. Both regions are locally affected by contamination in the same manner, ensuring uniform contamination impact. This resolves the issue of uneven contamination effects while maintaining the ability to generate phase-shifted signals for accurate position determination.
3Reliability
If single-field scanning is used to minimize contamination effects, then reliability under contamination is improved, but the complexity of the optical system increases
Solution Approach 1:
The patent applies segmentation by dividing the scanning function into two separate scanning beams that scan different regions of the scale. This segmented approach achieves single-field scanning conditions (where contamination affects all signals uniformly) while maintaining a relatively simple optical system compared to more complex contamination mitigation approaches.
4Reliability
If scanning beams scan different measurement division ranges to achieve single-field scanning, then contamination resistance is improved, but the device complexity increases
Solution Approach 1:
The patent implements local quality by having different scanning beams scan different spatial regions (local areas) of the scale. Both regions are subject to the same contamination conditions, achieving contamination resistance. The optical system remains relatively simple as it uses standard Vernier scanning components arranged to scan different local regions rather than requiring complex additional mechanisms.
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 generates stable scanning signals even with local contamination or defects, maintaining accurate position determination without amplitude ratio and pulse duty factor fluctuations.
Implementation Method 1
the beams emitted by a light source strike the scale and the at least one scanning division one or more times along the scanning beam path before they reach the detector assembly. In the event of relative movement of the scale and scanning unit along the measuring direction, the detector assembly generates several displacement-dependent, phase-shifted scanning signals
Implementation Method 2
at least two direction-selective deflection elements are provided, which are assigned to the at least two scanning divisions and cause a deflection of the beams passing through the different scanning divisions towards a jointly illuminated sub-area on the measuring division
Data Source
Figure 1
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AI summary
The present invention relates to an optical position measuring device for detecting the position of two objects moving relative to each other, which are connected to a scale and a scanning unit. The scale has a measuring scale extending along the measuring direction with a specific scale periodicity. The scanning unit comprises at least one light source, at least one scanning plate, and at least two detector assemblies. At least two scanning scales with a specific scale periodicity are arranged perpendicular to the measuring direction, adjacent to each other, on one side of the scanning plate, wherein the scale periodicity differs from the measuring scale periodicity.The at least two scanning divisions are each assigned at least two direction-selective deflection elements on the opposite side of the scanning plate. These deflection elements deflect the beams passing through the scanning divisions towards a jointly actuated measurement division sub-area. The beams incident from the actuated measurement division sub-area each strike the at least two detector assemblies as periodic Vernier fringe patterns with a fringe pattern periodicity SP. These detector assemblies comprise a plurality of light-sensitive detector elements arranged periodically along the measurement direction (Fig. 1).