Optical Distance Measurement Using Segmented Pulse Histograms
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Solution Overview
Problem
Current optical distance measurement technologies using the time-of-flight principle are limited by the need for a minimum time gap between measurement pulses to avoid aliasing, which restricts the maximum detection range and increases peak power requirements, while also desiring low peak power and rapid measurement results for applications like driver assistance.
Innovation Solution
The method involves transmitting multiple measurement pulses during two consecutive measurement intervals with different transmission times, determining propagation times by subtracting transmission times from reception times, and creating histograms to accurately determine the correct propagation times and distances, thereby increasing detection range and reducing peak power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement pulses are transmitted at longer intervals to avoid aliasing effects, then measurement ambiguity is avoided, but the maximum detection range is reduced and detection probability decreases
Solution Approach 1:
The measurement process is divided into multiple measurement intervals, each containing multiple measurement pulses. This segmentation allows the system to process pulses in organized groups, enabling accurate assignment of reflected pulses to their source transmission events even when multiple pulses are present, thereby maintaining detection probability while avoiding aliasing effects.
Solution Approach 2:
Transmission times of measurement pulses are stored in advance in a storage element before the pulses are transmitted and before reflections are received. This preliminary storage of transmission time information enables the receiving element to accurately determine which transmitted pulse corresponds to each received reflection, eliminating measurement ambiguity without requiring extended time intervals between pulses.
2Reliability
If the time budget is increased to improve detection probability, then more measurement pulses can be transmitted, but measurement results are not available promptly for time-critical applications
Solution Approach 1:
Multiple measurement pulses are transmitted within each measurement interval without waiting for previous pulses to complete their round trip. The system continuously transmits and processes pulses in overlapping intervals, maintaining continuous useful action. This allows detection probability to improve with more pulses while measurement results remain available promptly through parallel processing of multiple intervals.
3Length of stationary object
If peak power of measurement pulses is increased to improve detection range, then reflections from distant objects can be detected, but eye safety requirements are violated
Solution Approach 1:
The detection process is segmented into multiple measurement intervals with multiple pulses each, allowing the system to accumulate detection opportunities over time. This enables the use of lower peak power pulses while maintaining detection capability through statistical accumulation of multiple measurements, thus extending effective detection range without violating eye safety limits on peak power.
Solution Approach 2:
Measurement pulses are transmitted in periodic sequences organized into measurement intervals. This periodic structure with multiple pulses per interval allows the system to achieve reliable detection through repeated measurements at safe power levels, effectively extending detection range while maintaining compliance with eye safety requirements that limit peak power exposure.
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 allows for an increased maximum detection range without extending the time budget or increasing peak power, while maintaining high detection probability and providing rapid measurement results suitable for time-critical applications.
Implementation Method 1
They are based on the time-of-flight (ToF) principle. A scanning sensor, particularly a LIDAR (short for 'light detection and ranging') sensor, is used for the measurement. It periodically emits measurement pulses that are reflected by objects. The reflected measurement pulses are then detected. By determining the travel time of the measurement pulses from the sensor to the objects and back, the distance to these objects can be determined using the speed of light.
Implementation Method 2
A scanning sensor, particularly a LIDAR (short for 'light detection and ranging') sensor, is used for the measurement. It periodically emits measurement pulses that are reflected by objects. The reflected measurement pulses are then detected.
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
A method (100) for optical distance measurement is proposed, wherein within a first measurement interval (10) a first plurality of measurement pulses (13) is emitted by means of a transmitting element of a transmitting unit at first emission times (101), and wherein within a second measurement interval (11) a second plurality of measurement pulses (13) is emitted by means of the transmitting element of the transmitting unit at second emission times (102). The method (100) comprises the reception (103) of reflected measurement pulses by means of a receiving element of a receiving unit associated with the transmitting element at reception times. The method further comprises determining (106) a first set of transit times for each received measurement pulse, wherein the first set of transit times is determined using the first emission times.Furthermore, the method (100) comprises determining (107) a second set of transit times for each received measurement pulse, wherein the second set of transit times is determined using the second transmission times. The method (100) comprises creating (108) at least one histogram (15) for the receiving element and entering the first and/or second set of transit times into the histogram.