Displacement Encoder Light-Receiving Element Arrangement
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Solution Overview
Problem
Existing optical displacement encoders require additional optical elements like index gratings, lenses, and spatial filters to remove 0th order diffracted light, leading to increased size and complexity, and struggle with accurately separating diffracted light orders due to limited diffraction angle separation distances.
Innovation Solution
A displacement encoder design with a detection unit featuring an even number of light-receiving elements arranged in an odd multiple of the fundamental period, where each element's width is not an integral multiple of the period, allowing for effective removal of 0th order diffracted light without additional optical elements by configuring light-receiving units to output signals that isolate the fundamental period of interference fringes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If additional optical elements (index grating, lens, spatial filter) are added to remove 0th order diffracted light, then position detection accuracy is improved, but device complexity and size increase
Solution Approach 1:
The patent extracts and removes only the necessary optical elements (index grating and spatial filter) from the optical path while maintaining the essential function of eliminating 0th order diffracted light. The simplified configuration retains only the collimator lens and scale, achieving the same measurement precision without unnecessary complexity
Solution Approach 2:
The patent introduces a beam splitter as an intermediary element that enables the removal of 0th order diffracted light through a different optical path configuration. The beam splitter separates the optical paths in a way that naturally excludes the 0th order light without requiring additional filtering elements
2Measurement precision
If diffraction angle separation distance is increased to accurately separate diffracted light orders, then light order separation accuracy is improved, but device size increases
Solution Approach 1:
The patent transitions from separating diffracted light orders in the spatial dimension (by increasing distance) to separating them in the optical path dimension (through the beam splitter). This dimensional change allows for effective separation without increasing the physical size of the device
3Measurement precision
If optical elements are added to remove 0th order diffracted light, then position detection accuracy is improved, but the compact size is compromised
Solution Approach 1:
The patent merges the functions of multiple optical elements into a single beam splitter configuration. The beam splitter simultaneously achieves collimation, beam direction, and 0th order light exclusion, maintaining compact encoder size while improving position detection accuracy
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 configuration enhances position detection accuracy by reducing the effect of unnecessary diffracted light, maintaining a compact size without additional optical elements, and improving the separation of diffracted light orders.
Implementation Method 1
diffracted light that is obtained by diffraction of light emitted to the scale by the incremental pattern
Implementation Method 2
interference fringes that are formed by interference between +1st order diffracted light and −1st order diffracted light
Implementation Method 3
a plurality of light-receiving elements arranged in the measurement direction, the plurality of light-receiving elements being configured to output a detection signal of the diffracted light from the scale
Data Source
AI summary
A detection head movable relative to a scale detects diffracted light and outputs a detection result. The diffracted light is diffracted by an incremental pattern. A signal processing unit calculates a relative displacement between the scale and the detection head. The detection head includes: a light source emitting the light to the scale; and a detection unit including a light-receiving unit in which a plurality of light-receiving elements that output a detection signal are arranged. The number of the plurality of light-receiving elements is an even number. A period of the arrangement of the plurality of light-receiving elements is an odd-number multiple of a fundamental period. The fundamental period is a period of interference fringes formed on the light-receiving unit by +1st and −1st order diffracted lights. A width of the light-receiving element is not equal to an integral multiple of the fundamental period.