Optical Distance Measurement Pulse Timing to Prevent Aliasing
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Solution Overview
Problem
Optical distance measurement technologies, particularly in driverless navigation, face limitations in measurement range due to aliasing effects caused by distributing energy over multiple pulses, leading to inaccurate object positioning and restricted maximum range.
Innovation Solution
A method that emits a sequence of measurement pulses with specific temporal pulse spacings, defined by a first set {T(delay)+i*T(Pulse)}, ensuring unambiguous transit time determination and minimizing aliasing effects, allowing for increased energy distribution and extended measurement range without waiting for twice the transit time between pulses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If multiple measurement pulses are emitted in rapid succession to distribute energy and extend measurement range, then the measurement range is improved, but aliasing effects occur causing ambiguous transit time determination
Solution Approach 1:
The patent applies periodic action by using a pulsed measurement signal with specific temporal spacing between pulses. The pulse train is emitted with a period that is shorter than the round-trip time to the farthest object, allowing multiple pulses to be sent while maintaining unambiguous distance measurement through correlation processing that identifies the correct pulse-echo pairing based on the known periodic pattern.
Solution Approach 2:
The patent changes the temporal parameter of pulse spacing to resolve the contradiction. By carefully selecting the pulse spacing within a specific set defined by T(delay)+i*T(Pulse) where the spacing is less than the round-trip time to the farthest object, the system enables higher pulse repetition rates while avoiding aliasing through mathematical processing that exploits the known pulse train structure.
2Use of energy by moving object
If pulse spacing is reduced to emit more pulses and maximize energy delivery, then the measurement range is extended, but the ability to unambiguously determine transit time is lost
Solution Approach 1:
The periodic emission of measurement pulses with a defined pattern allows the system to deliver maximum energy through multiple pulses while maintaining the ability to determine transit time. The receiver uses correlation processing to match the received signal against the known transmitted pulse train pattern, enabling unambiguous identification of which pulse corresponds to which echo even when pulses are closely spaced.
Solution Approach 2:
The system uses feedback through correlation processing where the received signal is compared against the known transmitted pulse train. This feedback mechanism allows the system to determine the correct transit time by identifying the time shift that maximizes the correlation between transmitted and received signals, thereby preventing information loss even with reduced pulse spacing.
3Measurement precision
If waiting time between pulses is extended to avoid aliasing, then measurement accuracy is maintained, but measurement speed and productivity decrease
Solution Approach 1:
The patent resolves this contradiction by using periodic pulse emission with spacing shorter than the round-trip time to the farthest object. The system maintains measurement accuracy through correlation processing that exploits the known periodic pattern, allowing faster pulse repetition rates without sacrificing accuracy. This enables high-speed scanning while maintaining unambiguous distance determination.
Solution Approach 2:
The system achieves continuous useful action by emitting pulses in a continuous train rather than waiting for full round-trip time between individual pulses. The correlation processing continuously analyzes the received signal to determine distances, enabling high-speed measurement and scanning applications without the productivity loss associated with extended waiting times between pulses.
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 unambiguous determination of transit time and maximizes measurement range while preventing aliasing effects, allowing for efficient scanning of both large and small distance ranges without prolonged waiting times, thus enhancing the accuracy and speed of distance measurements in driverless navigation systems.
Implementation Method 1
a scanning sensor, in particular a LIDAR (short for 'light detection and ranging') sensor is used for the measurement, which sensor emits periodic measurement pulses which are reflected at objects, wherein the reflected measurement pulses are detected
Implementation Method 2
They are based on the time-of-flight principle, wherein a scanning sensor, in particular a LIDAR (short for 'light detection and ranging') sensor is used for the measurement, which sensor emits periodic measurement pulses which are reflected at objects, wherein the reflected measurement pulses are detected. From the determination of the transit time of the measurement pulses from the sensor to the objects and back, the distance to these objects can be determined with the aid of the speed of light
Data Source
AI summary
A method for optical distance measurement is proposed which comprises the emission of a plurality of measurement pulses, the reflection of emitted measurement pulses at at least one object and the receipt of reflected measurement pulses. A sequence of measurement pulses is emitted, wherein the sequence comprises temporal pulse spacings between temporally successive measurement pulses, and wherein each measurement pulse of the sequence has a temporal pulse width of T(Pulse). The pulse spacings form a first set, wherein the first set is defined by {T(delay)+i*T(Pulse): i is an element of the natural numbers between 0 and j}, wherein for all values of i it holds that: T(delay)+i*T(Pulse)<(2T(delay)+2T(Pulse)), wherein the first set only comprises one element for all values of i between 0 and j, respectively, and wherein T(delay) defines a pulse spacing base unit.