Time-of-Flight Sensor Correction for Distance-Dependent Walk Error
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Solution Overview
Problem
Existing LiDAR sensors suffer from distance-dependent walk errors due to parallax and varying optical power on photodiodes forming a pixel, which cannot be satisfactorily corrected using distance-independent lookup tables, leading to residual measurement errors up to 15 cm.
Innovation Solution
A method that determines individual peak heights and widths for each detector element, using calibration tables to calculate distance-dependent correction values, compensating for the sensor's architecture and parallax effects, thereby improving distance accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If distance-independent lookup tables are used to correct walk error, then correction simplicity is improved, but measurement precision deteriorates due to residual errors up to 15 cm
Solution Approach 1:
The patent changes the correction parameters from distance-independent to distance-dependent by determining individual peak heights and widths for each detector element based on the total peak height and distance value. This allows the correction values to adapt to varying distances, resolving the contradiction between correction simplicity and measurement precision.
Solution Approach 2:
The patent segments the correction process by determining individual peak heights and widths for each detector element separately rather than using a single correction table for all elements. This segmentation enables distance-dependent correction while maintaining operational simplicity through automated calculation.
2Reliability
If multiple photodiodes are connected to form a pixel, then signal detection capability is improved, but measurement precision deteriorates due to parallax effects and varying optical power
Solution Approach 1:
The patent applies local quality by determining individual peak heights and widths for each detector element based on its specific characteristics and the total peak height. This allows each photodiode to be corrected according to its local conditions, compensating for parallax effects and varying optical power while maintaining the benefits of multiple photodiodes.
Solution Approach 2:
The patent uses feedback by determining individual peak heights and widths as a function of the total peak height and distance value. This feedback mechanism allows the correction values to adapt to the actual measurement conditions, resolving the contradiction between signal detection capability and measurement precision.
3Area of stationary object
If the laser spot position shifts across photodiodes with distance, then coverage area is improved, but measurement precision deteriorates due to changing optical power ratios
Solution Approach 1:
The patent applies dynamics by making the correction values distance-dependent rather than static. The individual peak heights and widths are determined as a function of the distance value, allowing the correction to adapt dynamically to the laser spot position shifts and changing optical power ratios across different distances.
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
The method enhances LiDAR sensor accuracy by compensating for distance-dependent walk errors, reducing residual measurement errors and improving overall distance precision.
Implementation Method 1
The distance of an object in the vicinity of the sensor is determined by measuring its time of flight. In this measurement, a LiDAR sensor emits a signal, such as a pulsed laser signal, which is reflected by the object. The reflected pulses are detected by the sensor as an echo signal. Based on this echo signal, the sensor determines the time of flight of the pulses from the sensor to the object and back
Implementation Method 2
Photodiodes, preferably avalanche photodiodes (APDs), and especially single-photon avalanche photodiodes (SPADs), are typically used to detect the echo signal. These enable the counting of photons arriving at their surface, particularly single-photon counting
Implementation Method 3
Photodiodes, preferably avalanche photodiodes (APDs), and especially single-photon avalanche photodiodes (SPADs), are typically used to detect the echo signal. These enable the counting of photons arriving at their surface, particularly single-photon counting. However, the use of SPADs, where an avalanche is triggered by the impact of a single photon
Data Source
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AI summary
In one embodiment, a method for providing at least one correction value for an output distance image of a time-of-flight sensor (10) comprises the following steps: feeding in a single image, wherein one, preferably each, data point (14) of the single image includes a distance value, a total peak height and a total peak width, each determined from an echo signal (S') received by the time-of-flight sensor (10) by at least two detector elements (14a, 14b); for several data points, preferably for each data point (14), of the single image, determining at least two individual peak heights as a function of the total peak height and the distance value of the respective data point and determining at least two individual peak widths as a function of the total peak width and the distance value of the respective data point;for several data points, preferably for each data point (14) of the single image, determining a distance-dependent individual distance correction value for one, preferably for each, detector element (14a, 14b) based on the individual peak height or on the basis of the individual peak height and the individual peak width, and providing a total distance correction value of the respective data point as a function of the individual distance correction values.