Optical Position Measuring Device Moiré Twisting Error Compensation
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Solution Overview
Problem
Existing optical position measuring devices face challenges with moiré twisting errors that lead to signal intensity drops and measurement inaccuracies, particularly in high-resolution applications.
Innovation Solution
The design incorporates a scale with integrated reflector elements and a measuring graduation that splits light beams into partial beams, which are deflected and reflected to compensate for moiré twisting, eliminating erroneous effects and allowing for increased adjustment tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional scale and scanning unit design is used, then the device structure is simple, but moiré twisting errors occur leading to signal intensity drops and measurement inaccuracies
Solution Approach 1:
The patent combines the scale and scanning unit into a integrated assembly where the scale is directly coupled to the scanning unit. This merging eliminates relative movement and misalignment between the two components, thereby preventing moiré twisting errors while maintaining measurement precision. The combined structure ensures that the scale and scanning unit move together as a single unit, avoiding the harmful effects of differential motion.
2Measurement precision
If small graduation periods are used for high resolution, then measurement precision increases, but the device becomes more sensitive to moiré twisting errors
Solution Approach 1:
The patent applies preliminary anti-action by pre-aligning the scale and scanning unit in a fixed relative position through the combined structure. This pre-established alignment prevents moiré twisting from occurring in the first place, thereby maintaining measurement reliability even when using small graduation periods for high resolution. The design proactively counteracts potential misalignment issues before they can affect measurement accuracy.
3Ease of operation
If oblique illumination is used to separate partial beams of rays, then beam separation is achieved, but scanning optics symmetry is reduced and adjustment tolerances are minimized
Solution Approach 1:
The patent introduces asymmetry through the combined structure of the scale and scanning unit, which breaks the symmetry requirements of the optical path. This asymmetric design allows partial beams of rays to be separated without requiring oblique illumination, thereby maintaining optical symmetry and large adjustment tolerances while achieving the necessary beam separation for detection.
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 solution effectively corrects moiré twisting errors, maintaining signal intensity and enabling larger adjustment tolerances, especially in high-resolution devices, by using a combined structural unit with reflector elements and a diffractive/cylindrical lens structure.
Implementation Method 1
the beam of rays coming from a light source is split into at least two partial beams of rays, which in the scale each impinge on the measuring graduation twice and once on the reflector element
Implementation Method 2
at least one optical reflector element in the form of a retroreflector... The partial beams of rays reflected by the scale for the first time are reflected back in the direction of the scale via the retroreflector
Implementation Method 3
one usually speaks of a so-called moiré rotation. Such moiré distortions result in a drop in the scanning signal intensity and undesirable errors in the position measurement
Implementation Method 4
the measuring graduation is designed such that the at least two partial beams of rays incident from oppositely symmetrical directions experience an opposite deflection effect
Implementation Method 5
the measuring graduation is designed as an alternating linear cylindrical lens structure
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3
AI summary
The invention relates to an optical position measuring device for detecting the relative position of a scanning unit and a scale that can be moved in relation to the scanning unit in at least one measuring direction. The scale is a combined structural unit comprising at least one reflector element and a measurement graduation. A light source and at least one detector element are associated with the scanning unit. The scanning unit comprises splitting means which split the beam of rays emitted by the light source into at least two partial beams of rays in the measuring direction, said partial beams of rays then propagating towards the scale.