Optical Encoder Angle Detection Displacement Compensation
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Solution Overview
Problem
Conventional optical encoders experience reduced detection accuracy of absolute angles due to displacement of the light irradiation position relative to the scale, caused by disc processing difficulties or age-related deterioration.
Innovation Solution
An optical encoder design featuring a rotating member with a semicircular light transmission or reflection portion, where photodetecting elements are arranged in a zigzag pattern, and a light absorption film is used to enhance signal-to-noise ratio, allowing for accurate absolute angle detection by setting a reference point at the center of the output signal's half-maximum and correcting for positional displacements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the absolute angle is directly detected from the position of each specified lattice window, then the detection structure is simple, but the detection accuracy is lowered when the irradiated position of light is displaced from reference
Solution Approach 1:
The patent implements feedback by measuring the actual angle range from the one-dimensional profile of the output signal and using this measurement to calculate a corrected amount. This corrected amount is then applied to adjust the detected absolute angle, creating a closed-loop system that compensates for displacement errors and maintains high detection accuracy despite positional variations.
Solution Approach 2:
The patent changes the parameter used for angle detection from direct lattice window position to the center at half maximum of the one-dimensional profile of the output signal. Additionally, it introduces a dynamic corrected amount based on the measured angle range, transforming the detection parameter from static to adaptive, which resolves the contradiction between simple structure and accurate detection under displacement conditions.
2Volume of moving object
If a slit is used to form the bright portion, then the optical system is compact, but dust clogging reduces detection accuracy
Solution Approach 1:
The patent segments the bright portion formation into two independent components: a light transmission portion (or reflection portion) that defines the geometric shape, and a light absorption film that controls light blocking. This segmentation allows the light transmission portion to be designed with larger dimensions to prevent dust clogging, while the absorption film maintains optical precision, thus resolving the contradiction between compactness and reliability.
3Reliability
If the light transmission portion is made larger to prevent dust clogging, then reliability improves, but the optical system volume increases
Solution Approach 1:
The light absorption film acts as an intermediary element that mediates between the light transmission portion and the photodetecting elements. It allows the light transmission portion to be enlarged for dust resistance while the absorption film precisely controls which light reaches the detectors, maintaining system compactness and optical precision without sacrificing reliability.
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
The encoder maintains high accuracy in detecting absolute angles even when the light irradiation position shifts, with reduced susceptibility to dust clogging and signal saturation, enabling miniaturization and improved resolution.
Implementation Method 1
a light source device for emitting light to be detected to the rotating member; and a photodetecting device including a scale having a plurality of photodetecting elements arranged thereon
Implementation Method 2
an area containing a part of the arrangement line is set as a bright portion to which the light to be detected is irradiated
Implementation Method 3
a semicircular light reflection portion whose diameter corresponds to the arrangement line is formed in the rotating member, and the bright portion is formed of the light to be detected reflected from the light reflection portion
Implementation Method 4
an output portion for outputting an output signal based on the light intensity of the light to be detected made incident to the photodetecting elements through the rotating member
Data Source
AI summary
There is provided an encoder in which the absolute angle can be detected with high accuracy even when the irradiated position of light to be detected with respect to a scale is displaced from a reference. In the encoder 1, a bright portion 19 in which the light to be detected is irradiated to an area containing half rounds of arrangement lines L1 and L2 of a scale plate 11 is formed and also a dark portion 20 to which no light to be detected is irradiated is formed in the area excluding the bright portion 19 by passing the light to be detected through a rotating plate 8 having a toothed gear with a semicircular opening portion 17 formed therein. Accordingly, in the encoder 1, even when the irradiated position of the light to be detected with respect to the scale plate 11 is displaced from the reference, the absolute angle of a measurement target can be detected with high accuracy by adding or subtracting the corrected amount based on the difference α° between the angle range corresponding to the width W at half maximum of the light intensity waveform P at the angle detection time and the reference angle range.