Displacement Meter Band-Pass Filter Parameter Adaptation
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Solution Overview
Problem
Existing displacement meters face challenges in accurately measuring in-plane displacement of various measurement target objects due to limited applicability of measurement parameters, particularly the cut-off frequencies of filters, which are optimized for specific objects and conditions, leading to suboptimal performance with diverse surface properties and types.
Innovation Solution
A displacement meter equipped with an illumination assembly, photoelectric conversion element array, and calculation circuit that performs Fourier transforms and applies band-pass filters to images, with specific cut-off frequency settings for the band-pass filter (3M/(N×P)≤HPF≤10M/(N×P, 40M/(N×P)≤LPF≤60M/(N×P) based on magnification, pixel number, and pixel pitch, allowing for adaptable measurement across different objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed cut-off frequencies are used for filter calculation, then measurement is stable under certain conditions, but the parameters are applicable only to limited measurement target objects and measurement conditions
Solution Approach 1:
The patent applies dynamics by making the cut-off frequencies of the band-pass filter variable rather than fixed. The low cut-off frequency HPF and high cut-off frequency LPF are dynamically adjusted based on the magnification M of the optical system, the number of pixels N, and the pixel pitch P, allowing the filter parameters to adapt to different measurement conditions and target objects while maintaining measurement stability
Solution Approach 2:
The patent implements parameter changes by establishing specific mathematical relationships between the filter cut-off frequencies and the optical system parameters. The formulas 3M/(N×P)≤HPF≤10M/(N×P) and 40M/(N×P)≤LPF≤60M/(N×P) enable automatic adjustment of filter parameters according to the magnification, pixel count, and pixel pitch, thereby expanding applicability to diverse measurement targets
2Measurement precision
If cut-off frequency is determined according to paper type or preliminary measurement, then measurement accuracy is improved for that specific type, but the optimum cut-off frequency cannot be selected for other objects or combinations of surface properties
Solution Approach 1:
The patent achieves universality by creating a unified parameter setting method that works across different measurement target objects and surface properties. Instead of requiring separate calibration for each object type (paper, metal, etc.), the band-pass filter parameters are universally determined by the optical system's magnification M, pixel number N, and pixel pitch P, making the system applicable to diverse objects without preliminary measurements
Solution Approach 2:
The patent enables automatic parameter adaptation by establishing direct mathematical relationships between the filter cut-off frequencies and the optical system parameters. This eliminates the need for manual adjustment or preliminary measurements for different object types, as the parameters automatically change based on the system configuration
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 enables accurate and adaptable displacement measurement across a wide range of measurement target objects, including metals, low-reflectivity samples, and perfect-diffusion samples, by optimizing the removal of noise components and maintaining high measurement accuracy.
Implementation Method 1
an illumination assembly (3) configured to illuminate the measurement target object (2)
Implementation Method 2
a photoelectric conversion element array (6) configured to detect reflected light from the measurement target object (2)
Implementation Method 3
a light-receiving optical assembly (5) configured to condense light on the photoelectric conversion element array (6)
Data Source
AI summary
A displacement meter that measures displacement of an object includes a calculation circuit which calculates a displacement amount of the object using a cross-correlation function of plural images detected at different timings by a photoelectric conversion element array. The calculation circuit performs a Fourier transform on the images, applies a band-pass filter to the images having undergone the Fourier transform, and calculates the cross-correlation function using the images to which the band-pass filter has been applied. Assuming that a magnification of a light-receiving optical assembly is M, the number of pixels in the photoelectric conversion element array is N, and a pixel pitch is P (um), a low cut-off frequency HPF of the band-pass filter and a high cut-off frequency LPF of the band-pass filter satisfy: 3M/(N×P)≤HPF≤10M/(N×P), 40M/(N×P)≤LPF≤60M/(N×P).