Lensless Photoelectric Encoder Using Pseudo-Random Interference
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Solution Overview
Problem
Existing photoelectric encoders with lenses or lens arrays face issues of large size and high costs, while lens-less encoders struggle with light divergence and interference patterns at larger distances, leading to measurement inaccuracies and susceptibility to foreign matter.
Innovation Solution
A photoelectric encoder design that uses an absolute scale with a grating and dark pattern, an incoherent light source, and an auxiliary grating to generate an interference pattern, allowing for a large gap between the scale and detection head without a lens, using the conditional expression θL ≤ tan^-1(P_DATA^2 / (u + v) to prevent light crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a lens is used to guide light from the scale to the detector, then the device can detect pseudo-random patterns accurately, but the device size becomes large and costs increase
Solution Approach 1:
The patent extracts and removes the lens component from the optical system, replacing it with a lens-less configuration that uses a pseudo-random code pattern on the scale and a corresponding detection algorithm to achieve accurate position detection without requiring traditional optical focusing elements
Solution Approach 2:
The patent replaces the mechanical/optical lens-based light guidance system with a computational approach using pseudo-random coding and correlation detection, substituting physical optical components with signal processing methods to achieve the same measurement function
2Volume of moving object
If a lens array is used instead of a lens, then the device size is reduced, but the costs remain high
Solution Approach 1:
The patent removes the lens array component entirely, using instead a planar pseudo-random code pattern that can be manufactured using standard photolithography techniques, eliminating the need for expensive precision lens arrays while maintaining detection accuracy
3Length of stationary object
If the distance between the scale and the photo detector is increased, then the device can accommodate larger gaps, but light divergence causes the photo detector to fail to detect the pseudo-random pattern
Solution Approach 1:
The patent changes the optical parameters by using incoherent light with a broad spectrum instead of coherent laser light, and combines this with a pseudo-random code pattern and correlation detection algorithm to maintain detection accuracy over larger distances without requiring parallel light beams
4Stability of the object's composition
If a coherent light source such as a laser is used to emit parallel light, then light divergence is prevented, but light diffraction occurs due to interaction with the pseudo-random pattern, causing interference
Solution Approach 1:
The patent changes the light source parameters from coherent laser light to incoherent broadband light, which eliminates the diffraction and interference problems associated with coherent light while maintaining sufficient parallelism through the optical design and correlation detection method
Solution Approach 2:
The patent converts the potential harm of using incoherent light (which naturally diverges) into a benefit by combining it with pseudo-random coding and correlation detection, where the divergence is compensated for through the mathematical properties of the pseudo-random sequence rather than requiring perfectly parallel light
5Measurement precision
If the gap between the scale and the detection head is narrowed significantly, then light divergence and interference are reduced, but the encoder cannot be measured when the gap varies due to scale flexure or foreign matter entry
Solution Approach 1:
The patent changes the detection methodology from direct optical imaging to pseudo-random code correlation detection, which is inherently more tolerant of gap variations and foreign matter, allowing reliable measurement even when the gap changes due to flexure or contamination
Solution Approach 2:
The patent incorporates a tolerance buffer by using the statistical properties of pseudo-random sequences, which provide robust correlation peaks even with significant signal degradation, thereby cushioning against the effects of gap variations and foreign matter before they cause measurement failure
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
Enables accurate detection of pseudo-random data with a larger gap between the scale and detection head, reducing costs and improving robustness against foreign matter and flexure, while maintaining measurement precision.
Implementation Method 1
an auxiliary grating that is placed on a light path where a light ray emitted from the light source passes through the absolute pattern and enters the light receiving unit
Implementation Method 2
an interference pattern generation means that generates an interference pattern in combination with the grating part
Data Source
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AI summary
A photoelectric encoder (100) includes an absolute scale (110) provided with an absolute pattern based on pseudo-random data, and a detection head (120) including a light source (121) that emits light to the absolute pattern of the absolute scale, and a light receiving unit (122) that receives light from the absolute pattern, and it detects an absolute position (200) of the detection head with respect to the absolute scale. In the photoelectric encoder, the absolute pattern (200) is composed of a grating part (210) and a dark part (220) arranged in a repetitive manner. The photoelectric encoder further includes an interference pattern generation means that generates an interference pattern in combination with the grating part, and an interference pattern signal processing unit that detects the pseudo-random data of the absolute pattern based on the interference pattern received by the light receiving unit.