Optical Encoder Slit Phase Configuration for Signal Distortion Reduction
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Solution Overview
Problem
Optical encoder devices face significant distortion issues due to high-order harmonic waves in their output signals, which are not adequately addressed by existing methods that attempt to cancel specific harmonic waves by adjusting slit intervals or phase differences, resulting in residual distortion rates above 1.55%.
Innovation Solution
The optical encoder device employs a configuration where the number of second light transmissive slits in the stationary slit plate is defined as S = nxn' with specific phase differences, allowing for the cancellation of third and fifth harmonic waves, thereby reducing distortion by shifting the positions of these slits relative to the movable slit plate's first light transmissive slits, allowing for a more flexible design with lower distortion rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the slits in the stationary member or light receiving elements are disposed at intervals equal to the pitch P of the slits in the movable member, then the device structure is simple, but the output signal has significant distortion with a distortion rate of 12.11%
Solution Approach 1:
The patent divides the stationary member's slits into multiple groups (first group, second group, third group, fourth group) with different phase differences relative to the movable member's slits. Each group contributes to canceling specific harmonic components, thereby segmenting the distortion cancellation function across multiple slit groups rather than using a single uniform configuration.
Solution Approach 2:
Different slit groups are assigned different phase differences (0, P/6, P/10, P/12) to address different harmonic components locally. This local differentiation in phase configuration allows targeted cancellation of specific distortion components while maintaining overall system simplicity.
2Measurement precision
If phase difference of 1/6 is provided between two slits to cancel third harmonic wave, then the distortion rate is reduced to 4.63%, but the device still has residual distortion and requires specific slit configurations
Solution Approach 1:
The patent segments the distortion cancellation into multiple stages by creating four distinct slit groups, each targeting specific harmonic components. This segmentation allows progressive reduction of distortion from 4.63% to 0.009% by systematically addressing different harmonic orders.
Solution Approach 2:
The patent changes the phase difference parameter across different slit groups (0, P/6, P/10, P/12) to optimize cancellation of different harmonic components. This parameter variation enables systematic distortion reduction without requiring complex structural modifications.
3Measurement precision
If phase difference of 1/12 is provided between four slits to cancel third harmonic wave, then the distortion rate is reduced to 1.60%, but the number of slits increases and design flexibility is reduced
Solution Approach 1:
The patent segments the slit configuration into four functional groups with different phase characteristics, allowing flexible combination to achieve distortion cancellation. This segmentation provides design flexibility by enabling selective activation or configuration of different slit groups based on specific application requirements.
Solution Approach 2:
The stationary member's slit groups serve multiple functions: they generate the primary measurement signal, cancel third harmonic distortion, cancel fifth harmonic distortion, and provide design flexibility. This multi-functionality reduces the need for separate components and maintains adaptability.
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 effectively reduces the distortion rate to equal or less than 1%, using a smaller number of slits compared to previous methods, and allows for the flexible determination of the number of slits in the stationary member or light receiving elements, maximizing the utilization of the light receiving element's length and width.
Implementation Method 1
a light emitting element 1, a light receiving element 2 disposed to face the light emitting element 1, a movable slit plate 3 disposed between the light emitting element 1 and the light receiving element 2
Implementation Method 2
the light receiving element 2 disposed to face the light emitting element 1... generates an output signal in accordance with the amount of transmitted light
Data Source
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AI summary
An optical encoder device is provided, in which first light transmissive slits are formed in a movable slit plate and second light transmissive slits are formed in a stationary slit plate. The number of the second light transmissive slits is defined as S. The second light transmissive slits are formed in the stationary slit plate such that when one of the second light transmissive slits is optically coincident with one of the first light transmissive slits, the remaining S-1 second light transmissive slits are shifted in position from other first light transmissive slits corresponding to the remaining second light transmissive slits by S-1 phase differences.