Optical Encoder Sensing Assembly for Pollution-Resistant Absolute Positioning
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Solution Overview
Problem
Conventional optical encoders are sensitive to positional deviations and environmental pollution, requiring precise assembly and alignment, and have reduced sensing areas, which affects their accuracy and robustness.
Innovation Solution
An optical sensing assembly with a scale featuring two pattern areas and a sensor with three sensing areas, where the second patterns are gradually shifted, and sensing units are arranged in a phased array, utilizing incremental position signals and the Vernier effect for high-precision absolute position sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensing area of the light receiver is greatly reduced to achieve higher encoder accuracy, then measurement precision is improved, but the encoder becomes more sensitive to environmental pollution such as oil, dirt, and particulates
Solution Approach 1:
The code disk is divided into multiple code tracks (first code track, second code track, third code track) with different pattern densities. The light receiver is segmented into multiple sensing elements corresponding to each code track. This segmentation allows the system to use coarser patterns for absolute position detection (less sensitive to pollution) and finer patterns for precision measurement, resolving the contradiction between small sensing area and pollution sensitivity.
2Measurement precision
If conventional encoder architectures are used to achieve absolute position sensing, then measurement function is provided, but the system requires extremely precise assembly and alignment
Solution Approach 1:
The invention introduces a second spatial dimension by arranging multiple code tracks radially or concentrically on the code disk, rather than using a single linear code track. The light receiver similarly uses multiple sensing elements arranged in corresponding patterns. This dimensional expansion allows the system to encode absolute position information through the radial/concentric arrangement, reducing sensitivity to assembly errors in the traditional sensing direction.
3Measurement precision
If the sensing area is reduced to improve accuracy, then measurement precision is enhanced, but the robustness of the encoder against environmental factors deteriorates
Solution Approach 1:
Different regions of the code disk are assigned different pattern densities and functions. The outer code tracks with coarser patterns provide robust absolute position detection that is less sensitive to pollution, while inner code tracks with finer patterns provide high-precision measurements. Similarly, different sensing elements in the light receiver are optimized for different functions. This local differentiation allows the system to achieve high precision without sacrificing overall robustness.
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
Enhances encoder robustness against environmental pollution and improves assembly positioning, allowing for high-precision absolute position sensing with a smaller sensing area.
Implementation Method 1
The first sensing area is configured to sense a change of the first pattern area in the first direction. The second sensing area is configured to sense a change of the second pattern area in the first direction. The third sensing area is configured to sense a change of the second pattern area in the second direction. The light source is configured to emit light toward the scale.
Data Source
AI summary
An optical sensing assembly includes a scale, a sensor, and a light source. The scale includes a first pattern area and a second pattern area. The first pattern area includes first patterns periodically arranged in the first direction. The second pattern area includes second patterns periodically arranged in the first direction and a second direction. The sensor is configured to move relative to the scale in the first direction and includes a first sensing area, a second sensing area, and a third sensing area. The first sensing area is configured to sense a change of the first pattern area in the first direction. The second sensing area and the third sensing area are configured to sense changes of the second pattern area respectively in the first direction and the second direction. The light source is configured to emit light toward the scale.