Position-measuring device with shared Moiré axis
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Solution Overview
Problem
Conventional position-measuring devices face errors due to Moiré tilting between the scanning unit and measuring graduation, particularly in high-resolution measurements, and are prone to contamination and high costs due to separate scanning of incremental scale-division tracks.
Innovation Solution
A position-measuring device with two parallel incremental scale-graduation tracks and a reference-marking track, where the incremental and reference-pulse signals share a neutral Moiré axis, minimizing errors from tilting and using a scanning unit with distinct scanning devices for each signal type, ensuring stable incremental-signal amplitudes even under strong Moiré tilting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If reference markings are placed laterally adjacent to the scanned incremental graduation track, then reference-pulse signals can be generated, but Moiré tilting causes position shifts between reference-pulse and incremental signals leading to faulty position determination
Solution Approach 1:
The patent merges the reference-marking track with the incremental scale-graduation tracks by positioning them in the same scanned field. The reference markings are integrated into the measurement scale structure itself, allowing both reference-pulse and incremental signals to be generated from a single scanned field, eliminating the lateral offset that causes Moiré tilting errors.
Solution Approach 2:
The patent introduces a beam splitter as an intermediary optical element that divides the scanned field into separate detection paths. This allows the scanning beam to simultaneously illuminate both the reference markings and incremental graduations in the same field, while the beam splitter directs the reflected light to separate detectors, enabling independent signal processing without physical separation of the markings.
2Reliability
If two incremental scale-division tracks are scanned separately to generate 90° phase-shifted signals, then Moiré tilting faults are minimized, but the arrangement becomes relatively expensive and prone to contamination
Solution Approach 1:
The patent combines the scanning of both incremental scale-division tracks into a single scanned field. Both tracks are positioned within the same measurement scale such that one scanning beam pass illuminates and reads both tracks simultaneously, eliminating the need for separate scanning mechanisms while maintaining the ability to generate phase-shifted incremental signals.
Solution Approach 2:
The single scanning beam and optical path serve multiple functions: it simultaneously reads both incremental scale-division tracks to generate phase-shifted signals, and also detects reference markings within the same field. This multi-functional approach eliminates redundant scanning hardware while maintaining measurement capabilities.
3Measurement precision
If incremental scale-graduation tracks are scanned separately with separate scanning devices, then high-resolution position measurements can be achieved, but contamination of one track leads to faulty measurements
Solution Approach 1:
The patent positions both incremental scale-graduation tracks within a single scanned field so that one scanning beam simultaneously illuminates both tracks. This allows the system to read both tracks in a single pass, maintaining high-resolution measurement capability while ensuring that both tracks are equally exposed to the same environmental conditions, reducing the risk of differential contamination.
Solution Approach 2:
The patent ensures that both incremental scale-graduation tracks are subjected to identical scanning conditions, illumination, and environmental exposure by positioning them in the same scanned field. This homogeneous treatment reduces the likelihood of differential contamination or degradation between tracks, improving measurement reliability.
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 solution provides reliable position determination with minimal error and increased stability, especially for high-resolution measurements, by ensuring the incremental and reference-pulse signals are correctly aligned and less affected by tilting, and reduces the risk of contamination and costs associated with separate scanning.
Implementation Method 1
The scanning unit includes a first scanning device for generating the reference-pulse signal and a second scanning device for generating the incremental signals. To generate the incremental signals, a scanning beam acts at least once on each incremental graduation in an incremental-signal scanning field.
Implementation Method 2
a problem with such an arrangement is that, if undesired tilting about an axis perpendicular to the measuring-graduation plane (a so-called Moiré tilt) occurs between scanning unit and measuring graduation, this will cause a shift in the position of the generated reference-pulse signal relative to the incremental signal
Data Source
AI summary
A position-measuring device includes a scanning unit and a measuring graduation that is displaceable thereto in at least one measuring direction. The measuring graduation includes two incremental-graduation tracks extending in parallel in the measuring direction, between which a reference-marking track having at least one reference marking at a reference position extends. The scanning unit includes a first scanning device for generating the reference-pulse signal and a second scanning device for generating the incremental signals. To generate the incremental signals, a scanning beam acts at least once upon each incremental graduation in an incremental-signal scanning field.