Shutterless Electro-Optical Distance Meter for Phase Drift Reduction
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Solution Overview
Problem
Existing phase-difference-type electro-optical distance meters suffer from complex structures due to the use of shutters and temperature phase drifts, leading to measurement errors and prolonged observation times.
Innovation Solution
An electro-optical distance meter design that eliminates the need for a shutter by using two light emitting elements and a frequency converter group to convert light signals into intermediate frequencies, allowing simultaneous measurement of distance and reference paths, and employing modulation frequencies below 10 MHz to reduce temperature phase drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shutter is used to switch between distance measurement path and reference optical path, then the measurement can be performed sequentially, but the observation time is prolonged and temperature phase drift errors occur
Solution Approach 1:
The patent applies periodic modulation to the light sources, where the first light emitting element is modulated at a main frequency and the second light emitting element is modulated at an adjacent frequency. This periodic modulation enables temporal separation of the two light paths without requiring a mechanical shutter, thus reducing observation time while maintaining measurement precision through frequency-based path differentiation.
2Measurement precision
If a shutter is used to switch between distance measurement path and reference optical path, then sequential measurement is possible, but temperature phase drift difference between light receiving elements and electric parts generates errors
Solution Approach 1:
The patent uses feedback through frequency comparison, where the phase difference between the main frequency signal and adjacent frequency signal is measured and used to calculate distance. This feedback mechanism continuously compensates for temperature phase drift by comparing the two paths, eliminating errors caused by temperature variations in light receiving elements and electric parts.
Solution Approach 2:
The patent changes the frequency parameter of the light modulation, using a main frequency for the distance measurement path and an adjacent frequency for the reference path. This parameter change enables simultaneous measurement of both paths without a shutter, and the frequency difference allows for compensation of temperature phase drift through arithmetic operations on the phase differences.
3Productivity
If two light emitting elements and two light receiving elements are used, then simultaneous measurement of distance and reference paths is possible, but the device structure becomes complicated
Solution Approach 1:
The patent makes the single light receiving element universal by enabling it to receive and differentiate both the distance measurement light (modulated at main frequency) and the reference light (modulated at adjacent frequency). This multi-functionality allows one light receiving element to perform the work of two, and the beam splitter serves dual purposes, thereby reducing device complexity while maintaining simultaneous measurement capability.
Solution Approach 2:
The patent merges the functions of two light receiving elements into one by using frequency discrimination. The single light receiving element detects both frequencies simultaneously, and the frequency converter group separates the signals based on their different frequencies. This combining of functions reduces the number of components and simplifies the overall device structure.
4Measurement precision
If high modulation frequencies are used, then measurement resolution is improved, but temperature phase drift increases
Solution Approach 1:
The patent changes the modulation frequency parameter to be low (10 MHz or less), which reduces temperature phase drift in the light emitting and receiving elements. Although lower frequencies reduce measurement resolution, the patent compensates by using frequency comparison between the main frequency and adjacent frequency signals, allowing accurate distance measurement despite the lower absolute frequency.
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 simplified configuration reduces temperature phase drifts, enables faster measurements, and lowers manufacturing costs while maintaining measurement accuracy and power efficiency.
Implementation Method 1
a frequency converter group that is connected to the light receiving element and is configured to convert received light signals based on the distance measurement light and the reference light into intermediate frequency signals
Implementation Method 2
a phase difference changes corresponding to a distance
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
Provided is a phase-difference-type electro-optical distance meter that does not use a shutter for switching a reference optical path and a distance measurement path, and has a simpler configuration than the prior art while reducing a temperature phase drift. An electro-optical distance meter 100 includes: a first light emitting element 20 that transmits a distance measurement light modulated based on main modulation frequencies F2, F3 to a distance measurement optical path 21; a second light emitting element 30 that transmits a reference light modulated with adjacent modulation frequencies F2+b·F2, F3+b·F3 close to the main modulation frequencies F2, F3 to a reference optical path 31; a light receiving element 40 that receives a distance measurement light and a reference light; and frequency converters 44, 49 that receive inputting of a light reception signal based on the distance measurement light and the reference light and signals of local frequencies 2+a·F2, F3+a·F3, and generate a distance measurement intermediate frequency signal based on the distance measurement light and a reference intermediate frequency signal based on the reference light, wherein a distance to a target reflection object 22 is calculated by subtracting the reference intermediate frequency signal from the distance measurement intermediate frequency signal, and the main modulation frequencies F2, F3 are 10 MHz or less.