Displacement Sensor Thermal Aberration Management
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Solution Overview
Problem
Existing displacement sensors for image forming devices face challenges in maintaining accuracy due to thermal aberrations, particularly when the illumination optical system's image of the light source shifts between the front and rear principal points of the imaging optical system, leading to increased errors in displacement measurement.
Innovation Solution
A displacement sensor with both illumination and imaging optical systems constructed as converging types, where the imaging optical system's optical axis is configured to ensure the image of the emission unit remains anterior or posterior to the principal points of the imaging optical system, minimizing the impact of temperature-induced shifts and maintaining accurate displacement detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the illumination optical system and imaging optical system are both constructed as converging types, then the device complexity is reduced, but the measurement precision deteriorates due to thermal aberrations causing the image of the emission unit to shift between principal points
Solution Approach 1:
The patent applies parameter changes by adjusting the optical configuration parameters - specifically setting the illumination optical system and imaging optical system both as converging types with specific focal lengths and arrangement distances. This changes the system from a mix of collimating and telecentric systems to a simplified converging-converging configuration, accepting certain thermal aberration trade-offs for reduced complexity
Solution Approach 2:
The patent inverts the conventional approach by making both optical systems converging rather than using the traditional collimating-telecentric combination. This inversion simplifies the overall optical design and reduces the number of optical elements, even though it introduces thermal aberration sensitivity that must be managed through careful parameter selection
2Reliability
If the image of the emission unit shifts between the front and rear principal points of the imaging optical system due to temperature changes, then the reliability deteriorates, but maintaining a fixed position would require more complex thermal compensation mechanisms
Solution Approach 1:
The patent converts the harmful effect of thermal expansion into a beneficial one by designing the optical system so that the image of the emission unit naturally shifts between the front and rear principal points of the imaging optical system as temperature changes. This controlled shifting, rather than being prevented, becomes the mechanism for maintaining measurement reliability without requiring active thermal compensation
Solution Approach 2:
The patent applies beforehand cushioning by pre-designing the optical parameters (focal lengths, arrangement distances) to anticipate and accommodate temperature-induced shifts. The system is configured in advance to tolerate and even utilize the expected thermal movement, cushioning against reliability issues without needing reactive compensation mechanisms
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 the error in displacement measurement caused by thermal aberrations, ensuring precise detection of target displacement regardless of temperature fluctuations, thereby enhancing the accuracy and reliability of the sensor.
Implementation Method 1
an illumination optical system configured to convert the first laser light into first converging light
Implementation Method 2
an imaging optical system configured to convert light reflected from the target into second converging light
Implementation Method 3
A semiconductor laser irradiates a target with laser light
Implementation Method 4
speckle pattern appears in each image of the target... This interference of light provides the distribution of amounts of the reflected light with 'speckle pattern'
Implementation Method 5
an image sensor element such as a charge coupled device (CCD) captures light reflected by the target
Data Source
AI summary
In a displacement sensor, an illumination optical system, which converts laser light emitted from an emission unit into first converging light, and irradiates with the first converging light a detection space through which a target moves. An imaging optical system converts laser light reflected from the target into second converging light, and irradiates with the second converging light a light-receiving surface of a detection unit. The image of the emission unit into which the illumination optical system focuses the first converging light is displaced along the optical axis of the imaging optical system by a temperature change of the illumination optical system. The range in which the image is displaced is limited to be located either anterior to the front principal point of the imaging optical system, or posterior to the rear principal point of the imaging optical system.