Distance Measuring Device Using Frequency-Differentiated Bandpass Filters
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Solution Overview
Problem
Current distance measurement techniques using pulsed light face challenges with high precision due to the need for expensive and power-consuming A/D converters with high sampling frequencies, and methods to avoid these issues, such as processing signals at different timings, result in decreased precision and increased costs.
Innovation Solution
A distance measuring device employing first and second band pass filters with different center frequencies, a mixing circuit, and a distance calculating unit that processes signals using FFT analysis and phase conversion to enable accurate distance calculation without requiring high sampling rate A/D converters, allowing for simultaneous processing of reference and measuring signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the pulse width of pulsed light is decreased to improve distance measurement precision, then measurement precision is improved, but the sampling frequency requirement of the A/D converter must be increased correspondingly
Solution Approach 1:
The patent changes the frequency parameter of the detection signal by passing it through a band-pass filter, converting the high-frequency pulsed light signal into a lower frequency damped oscillation signal. This allows the A/D converter to operate at a lower sampling frequency while still achieving high distance measurement precision through subsequent phase difference calculation.
2Speed
If the detection signal is converted to low frequency through a band-pass filter to reduce sampling frequency requirements, then sampling frequency requirement is reduced, but the damped oscillation waveforms of reference and measuring signals may overlap and cannot be detected correctly
Solution Approach 1:
The patent applies preliminary action by processing the measuring signal and reference signal through different band-pass filters with different center frequencies before they reach the A/D converter. This preliminary frequency differentiation prevents waveform overlap and enables correct detection, while still allowing the use of lower sampling frequencies.
3Device complexity
If external and internal optical paths are made switchable to sample measuring and reference light at different timings, then signal processing is simplified, but measurement time is doubled and calculation errors occur due to time differences
Solution Approach 1:
The patent merges the processing of measuring light and reference light by allowing both signals to be input simultaneously to the same A/D converter through different band-pass filters. This eliminates the need for separate sampling at different timings, reducing measurement time to one-half while maintaining processing simplicity through unified digital signal processing.
4Productivity
If two A/D converters are prepared to sample reference and measuring signals respectively, then simultaneous processing is achieved, but the characteristics of two A/D converters cannot be made uniform leading to decreased measurement precision
Solution Approach 1:
The patent makes a single A/D converter universal by designing it to handle both reference signals and measuring signals through different band-pass filters. This eliminates the need for two separate A/D converters, ensuring uniform characteristics while still achieving simultaneous processing of both signals through the same converter.
5Measurement precision
If measurement is performed multiple times and results are averaged to reduce calculation error variation, then measurement precision is improved, but overall measurement time and power consumption are increased
Solution Approach 1:
The patent applies preliminary action by differentiating the frequencies of reference and measuring signals before they reach the A/D converter using different band-pass filters. This preliminary frequency separation enables accurate phase difference calculation from a single measurement, eliminating the need for multiple repeated measurements and averaging, thus reducing overall measurement time while maintaining high precision.
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 approach reduces calculation errors and maintains high precision in distance measurement while avoiding the need for costly and power-intensive high-frequency A/D converters, enabling efficient and accurate distance measurement without increasing overall processing time or cost.
Implementation Method 1
a first band pass filter (203) that receives a detection signal of reference pulsed light (107) that has propagated through a predetermined optical path, thereby generating a first signal, and a second band pass filter (204) that receives a detection signal of distance measuring pulsed light (106)
Implementation Method 2
a mixing circuit (207) that mixes the first signal and the second signal and generates a mixed signal
Implementation Method 3
an A/D converter (209) that receives the mixed signal
Implementation Method 4
a separated-signal calculating unit (211) that processes output from the A/D converter (209) by FFT analysis after the A/D converter (209) receives the mixed signal, thereby generating a first separated signal corresponding to the first signal and a second separated signal corresponding to the second signal
Implementation Method 5
a converting unit (212) that converts a phase of at least one of the first separated signal and the second separated signal into a phase of a predetermined frequency so that the first separated signal and the second separated signal have the same frequency
Data Source
AI summary
A distance calculating unit includes a first filter that receives a detection signal of reference pulsed light, a second filter that receives a detection signal of measuring pulsed light, an adder circuit that adds the outputs from the two filters together, an A/D converter that receives the output signal from the adder circuit, and a separated-signal calculating unit that analyzes the output from the A/D converter and that generates a first separated signal corresponding to a reference detection signal and a second separated signal corresponding to a measurement detection signal. The distance calculating unit further includes a conversion processing unit that converts the phase of at least one of the two separated signals into a phase of a predetermined frequency, and a distance calculating unit that calculates a distance to an object by using a phase difference between the two separated signals in the predetermined frequency.