Optical Readhead Grating Configuration for Shadow-Free Positioning
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Solution Overview
Problem
Existing readheads for measuring devices face challenges in positioning the analyser close to the graduated scale due to the need for optimal light projection and modulation, which is hindered by the physical presence of the analyser and results in unwanted shadows, making it difficult to maintain accuracy.
Innovation Solution
The readhead employs a system with multiple graduated gratings of different periods and distances to generate a light distribution that allows the analyser to be positioned further away from the graduated scale without obstructing lighting, using a first interaction between the first grating and the scale to produce a modulation distribution, a second interaction between a second grating and the scale's image to create a period of image, and a third interaction between the emitter and the image to produce a reading distribution, enabling the analyser to receive light representative of the readhead's movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the analyser is disposed close to the graduated scale to optimize light projection and modulation, then the measurement precision is improved, but the analyser causes unwanted shadows and obstructs the lighting of the graduated scale
Solution Approach 1:
The patent introduces a second graduated grating disposed at a second distance from the graduated scale, creating a multi-dimensional optical path. The analyser receives light that has interacted with both the first grating (close to the scale) and the second grating (further away), effectively separating the measurement function from the shadow-casting position. This dimensional arrangement allows optimal light modulation to be achieved without the analyser directly obstructing the lighting path.
Solution Approach 2:
The second graduated grating acts as an intermediary element between the light source and the analyser. It receives the modulated light from the first grating and re-modulates it, allowing the analyser to be positioned further from the graduated scale while still receiving sufficiently modulated light for accurate measurement, thereby eliminating the shadow problem.
2Object-generated harmful factors
If the analyser is disposed further away from the graduated scale to avoid causing shadows, then the harmful factors are reduced, but the light projection contrast and modulation deteriorate
Solution Approach 1:
By disposing the second graduated grating at a second distance from the graduated scale and having the analyser receive light after interaction with both gratings, the system creates an extended optical path that maintains light modulation quality even when the analyser is positioned further from the scale, thus preserving measurement precision while avoiding shadows.
Solution Approach 2:
The patent combines the functions of two graduated gratings - the first grating for initial light modulation close to the scale, and the second grating for re-modulation at a distance. This merging of functions ensures that the analyser receives strongly modulated light even when positioned away from the graduated scale, maintaining contrast and 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 configuration allows for accurate determination of the readhead's movement relative to the graduated scale while preventing the analyser from causing shadows or obstructing the lighting, thus maintaining the required accuracy and flexibility in positioning.
Implementation Method 1
a light emitter that emits a light beam to light the graduated scale... the interaction between the graduated grating and the graduated scale thereby generating a distribution of light with a period of modulation
Implementation Method 2
the interaction between the graduated grating and the graduated scale thereby generating a distribution of light with a period of modulation
Implementation Method 3
an analyser that receives at least part of the light transmitted or reflected on said graduated scale, from which it is capable of generating electrical signals
Data Source
Figure 1~2
Figure 3~4
AI summary
Readhead for a measuring device, comprising a graduated grating (11), and a light emitter (10) for lighting a graduated scale (2) through said grating (11). The readhead (1) is movable with respect to the scale (2), a distribution of light with a period of modulation in a plane which is at a determined distance with respect of said scale(2) being obtained, after a first interaction between the scale (2) and the grating (11). In said plane, a grating (12) with a period different to but close to the period of modulation is disposed, a new distribution of light with a period of image which corresponds with a image of the scale (2) being obtained as a result of the superposition between said grating (12) and the period of modulation. The readhead (1) comprises also another grating (13) which interacts with said image.