Distance Measurement Using Modulated Pulse Intervals
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Solution Overview
Problem
Modern pulse time-of-flight distance measuring apparatus face challenges in unambiguously mapping received pulses to transmitted pulses beyond the Multiple Time Around (MTA) zone, leading to incorrect distance measurements due to high pulse repetition rates and large measurement ranges.
Innovation Solution
The method involves varying the pulse interval according to a modulation signal, recording reflected pulses within different time windows, and analyzing the resulting distance measurement values to automatically determine the correct series least affected by the modulation, allowing for accurate distance measurement across multiple MTA zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high pulse repetition rate is used to quickly create large number of measurement points, then productivity is improved, but measurement precision deteriorates due to inability to unambiguously map received pulses to transmitted pulses beyond MTA zone
Solution Approach 1:
The pulse repetition rate is made dynamic by modulating it according to a known code sequence (e.g., pseudo-random code). Instead of using a constant high PRR that causes ambiguity, the PRR varies over time in a predictable pattern, allowing the receiver to correlate incoming pulses with the transmitted code and unambiguously identify which pulse each received pulse corresponds to, even beyond the traditional MTA zone.
Solution Approach 2:
The pulse repetition rate parameter is changed from a constant value to a time-varying parameter following a specific modulation code. This parameter change enables the system to encode temporal information into the pulse train, allowing receivers to distinguish between pulses from different MTA zones through code correlation, thereby maintaining measurement precision while operating at high productivity.
2Length of stationary object
If pulse repetition rate is increased to extend measurement range, then extent of measurable distance is improved, but reliability deteriorates due to pulse mapping ambiguity
Solution Approach 1:
The system employs code correlation as a form of feedback verification. The receiver correlates the incoming pulse sequence with the known transmitted code sequence to verify pulse origins. This feedback mechanism ensures that even when pulses from multiple MTA zones are present, the system can reliably identify and accept only those measurements that match the expected code pattern, thereby maintaining high reliability across extended measurement ranges.
Solution Approach 2:
The pulse transmission follows a periodic modulation pattern based on a code sequence (such as pseudo-random code with specific periodicity). This periodic structure allows the receiver to use correlation techniques to distinguish pulses from different periods/M TA zones, ensuring reliable measurement identification across extended ranges while maintaining the high pulse rates needed for long-distance measurement.
3Device complexity
If conventional pulse mapping methods are used beyond MTA zone, then device complexity is reduced, but measurement precision deteriorates due to incorrect pulse mapping
Solution Approach 1:
The patent replaces complex hardware-based pulse tagging or modulation schemes with a software-based code correlation approach. Instead of using separate channels or complex optical modulation to identify pulses from different zones, the system uses temporal coding with pseudo-random sequences and correlates the received signal with the known transmitted code in post-processing, achieving high precision measurement with relatively simple device architecture.
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 enables automatic and correct distance measurement in any MTA zone, overcoming the limitations of existing methods by evaluating multiple series of distance measurement values to select the one least influenced by pulse interval modulation, thereby extending the range of unambiguously measurable distances.
Implementation Method 1
measuring the time of flight of pulses reflected on those targets
Data Source
AI summary
A method for measuring distances of targets by measuring the time of flight of pulses, in particular laser pulses, reflected on those targets, including the steps of; transmitting pulses having a pulse interval which varies according to a modulation signal as transmitted pulses, and concomitantly recording of reflected pulses as received pulses; determining a first series of distance measurement values from times of flight between transmitted pulses and those received pulses which are respectively received within a first time window following each transmitted pulse; determining at least a second series of distance measurement values from times of flight between transmitted pulses and those received pulses which are respectively received within a second time window following each transmitted pulse; and determining that series of distance measurement values which is least affected by the modulation signal as result of the distance measurement.