Optical Encoder Beam Shaping to Suppress Diffraction Interference
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Solution Overview
Problem
Conventional optical encoders suffer from measurement inaccuracies due to unwanted light interference patterns caused by diffraction at the beam-shaping element, leading to DC offsets and amplitude differences in differential signals, which degrade measurement accuracy.
Innovation Solution
The optical encoder employs a beam-shaping element that defines the beam shape such that the long-length contour portion has no correlation with the long-length side section, using a shielding plate with edges formed by circular arcs to randomize light distribution and suppress interference patterns, combined with an index grating to manage unwanted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a conventional aperture with rectangular or circular opening is used to limit beam size, then unwanted light is blocked, but diffraction interference patterns are generated causing measurement inaccuracies
Solution Approach 1:
The patent applies asymmetry by using a polygonal opening shape (such as hexagon, octagon, or dodecagon) instead of conventional symmetric rectangular or circular openings. This asymmetric polygonal shape disrupts the formation of regular diffraction interference patterns while maintaining effective blocking of unwanted light, thereby resolving the contradiction between blocking harmful light and maintaining measurement precision.
Solution Approach 2:
The patent employs curved edge designs in the polygonal opening, where at least some edges include curved portions rather than purely straight lines. This curvature modification further randomizes the diffraction pattern and reduces interference effects, addressing the contradiction between light blocking effectiveness and measurement accuracy.
2Measurement precision
If beam size is minimized to match light-receiving area, then measurement precision is improved, but assembly tolerance and processing accuracy requirements increase
Solution Approach 1:
The polygonal asymmetric opening shape creates a more robust beam profile that is less sensitive to minor positioning variations. The multiple edges and corners of the polygon distribute diffraction effects in a way that maintains beam quality even with small misalignments, thereby improving tolerance to assembly and processing errors while maintaining measurement precision.
3Ease of manufacture
If aperture opening is made larger to accommodate processing tolerances, then manufacturing is easier, but unwanted light interference increases
Solution Approach 1:
The polygonal opening shape allows for a larger effective aperture area while maintaining tight beam control. The asymmetric geometry with multiple edges creates diffraction patterns that are less coherent and more easily managed, enabling larger openings without proportionally increasing unwanted light interference, thus improving ease of manufacture.
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 reduces light interference effects, stabilizes signal detection, and maintains measurement accuracy even with misalignments or adhering substances, while allowing cost-effective manufacturing through simplified machining processes.
Implementation Method 1
unwanted light, such as stray light that has passed through an unintended optical path or high-order diffraction light
Implementation Method 2
The light beam that has entered into the scale 400 is branched off into two diffraction light beams
Implementation Method 3
interference fringes are formed in the space where the two beams overlap
Implementation Method 4
light-receiving means 600 provided with element rows 710 of light-receiving elements 700
Data Source
AI summary
An optical encoder includes: a scale having a scale grating; a light source that emits light; and a light-receiving device that receives light that has passed through the scale. The optical encoder also has a shielding plate that shapes the beam shape, which is the shape of the light emitted from the light source. The shielding plate is disposed between the light source and the scale and defines the beam shape such that the shape of a long-length contour portion and the shape of a long-length side section have no correlation with each other. The long-length contour portion is a portion extending in the measurement direction at the contour of the beam shape of the light emitted to the light-receiving device via the scale, and the long-length side section is a section extending in the measurement direction at the contour of the light-receiving device.