PMD Sensor Distance Determination Using Runtime Validation
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Solution Overview
Problem
High-frequency PMD sensors face challenges in unambiguously determining distances due to shorter detection ranges and potential erroneous signals from highly reflective objects, while using multiple frequencies prolongs measurement cycles and limits optimal light and frequency combinations.
Innovation Solution
A method that includes a runtime measurement to verify if the reflected signal lies within a detection range, allowing for unambiguous distance determination using high modulation frequencies without extending the measurement cycle, by emitting an additional light pulse and checking for its reflection within a specific time interval, thereby discarding phase shifts from outside the range and optimizing the detection process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high modulation frequencies are used, then measurement efficiency and local resolution are improved, but detection range is shortened and unambiguous distance determination becomes difficult
Solution Approach 1:
The patent segments the detection process into two independent parts: phase shift measurement for distance calculation and run-time measurement for range validation. This segmentation allows high-frequency modulation to be used for efficient phase measurement while a separate run-time check ensures unambiguous distance determination by verifying signals fall within the valid detection range.
Solution Approach 2:
The patent introduces an intermediary run-time measurement mechanism that acts as a validator between the phase shift measurement and final distance determination. This intermediary step checks whether reflected signals originate from within the detection range, thereby resolving the ambiguity issue without compromising measurement efficiency.
2Length of stationary object
If multiple modulation frequencies are combined, then detection range is expanded, but measurement cycle duration is significantly prolonged
Solution Approach 1:
The patent extracts the detection range validation function from the multi-frequency phase measurement process. Instead of using multiple frequencies to expand detection range, the invention uses a single high-frequency phase measurement combined with an extracted run-time validation step, thereby maintaining fast measurement cycles while ensuring accurate distance determination.
3Productivity
If high modulation frequencies are used, then measurement efficiency increases, but erroneous signals from highly reflective objects become more problematic
Solution Approach 1:
The patent implements a feedback mechanism where the run-time measurement result feeds back into the distance determination process. If the run-time measurement indicates a signal originates from outside the detection range (as would happen with highly reflective objects), the corresponding phase shift measurement is discarded, thereby preventing erroneous distance calculations while maintaining high measurement efficiency.
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 increases flexibility in configuring the measurement process, reduces the number of modulation frequencies needed, and enhances detection range and efficiency, while minimizing exposure time and measurement errors, allowing for higher modulation frequencies and improved local resolution.
Implementation Method 1
PMD sensors (Photonic Mixing Device-Sensor) are well-known in the art as optical sensors, whose functional principle is based on the time-of-flight-principle (time of flight). A measuring signal emitted from a signal source is reflected at an object and is received again by a signal detector.
Implementation Method 2
Hereby, light-measuring signals, modulated by a modulation frequency, are usually used, wherein a phase shift is determined by comparing the emitted and the received measuring signal. From this phase shift, distances to the object can be calculated
Implementation Method 3
performing a runt-time measurement for an individual signal reflected on the object during a time interval beginning with the transmission of the individual signal and ending at a time point that corresponds to traversing the detection range twice
Data Source
AI summary
A method to determine a distance of an object to a motor vehicle using a PMD sensor, includes measuring a phase shift of a measurement signal reflected on the object for at least one modulation frequency, the modulation frequency is selected so that in a detection range beginning at the motor vehicle a distance is unambiguously determinable from the phase shift; performing a runtime measurement for an individual signal reflected on the object during a time interval beginning at a first time point where the individual signal is emitted and ending at a second time point corresponding to a time required by the individual signal to travel twice the detection range when the reflected individual signal is measured during the time interval, determining a distance from the phase shift; and when the reflected individual signal is not measured during the time interval, discarding the phase shift without determining a distance.