Optoelectronic Sensor Combining Time-of-Flight and Triangulation
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Solution Overview
Problem
Current optoelectronic sensors face challenges in achieving high resolution and reliability for distance measurement, particularly with the time-of-flight method, due to interference from non-ideal boundary conditions such as reflective or shiny objects, and limitations in range and accuracy across different distances.
Innovation Solution
The use of a combination of time-of-flight and triangulation methods, where a line arrangement of avalanche photodiode elements measures light propagation time and the position of the received light spot, with a control and evaluation unit that accumulates multiple measurements in histograms to improve accuracy and robustness, and filters out noise and background events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If time-of-flight method is used for distance measurement, then long range measurement is achieved, but measurement precision deteriorates due to extremely short light transit times
Solution Approach 1:
The patent combines time-of-flight measurement with triangulation measurement into a single sensor system. The control unit performs both measurement methods simultaneously or alternately and selects or merges the results based on distance range and measurement quality, thereby achieving both long range capability and high precision measurement.
Solution Approach 2:
The patent introduces an additional measurement method (triangulation) as an intermediary solution to bridge the gap between time-of-flight method's long range capability and its precision limitations. The triangulation method serves as a mediator that provides accurate distance measurements for closer objects where time-of-flight precision is insufficient.
2Measurement precision
If triangulation method is used for distance measurement, then measurement precision is improved, but device complexity increases due to additional optical components
Solution Approach 1:
The patent designs the sensor system to perform multiple functions using the same basic components. The light source and light receiver serve both time-of-flight measurement and triangulation measurement functions. The control unit implements both measurement algorithms using the same hardware infrastructure, thereby reducing overall device complexity while maintaining high precision capabilities.
3Measurement precision
If avalanche photodiode elements operated in Geiger mode are used, then sensitivity is improved, but reliability deteriorates due to dead time and noise interference
Solution Approach 1:
The control unit implements feedback mechanisms to monitor and manage the operation of avalanche photodiode elements. By detecting dead time periods and noise events, the system can adjust measurement parameters, filter out unreliable data, and maintain consistent measurement quality. The feedback loop ensures that sensitive detections are validated and that unreliable measurements are identified and excluded.
Solution Approach 2:
The patent uses multiple avalanche photodiode elements arranged in a line, where only the elements currently receiving the light spot need to be actively evaluated. This partial action approach allows the system to maintain high sensitivity where needed while reducing the overall impact of dead time and noise from elements not currently in use. The system processes data from subsets of photodiode elements rather than requiring simultaneous reliable operation of all elements.
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 enhances the reliability and precision of distance measurement by combining the strengths of both methods, effectively handling interference and improving sensitivity and integrability while maintaining low costs.
Implementation Method 1
Each light-receiving element or pixel has one or more avalanche photodiode elements, each of which can be biased with a voltage above a breakdown voltage and thus operated in a Geiger mode
Implementation Method 2
A light transmitter emits a light pulse into a monitoring area, which is at least partially reflected back by the detected object and then, as a remitted light pulse, generates a receiving light spot on a light receiver
Implementation Method 3
In a SPAD, a bias voltage above the breakdown voltage is applied, and then a single charge carrier released by a single photon is sufficient to trigger an uncontrolled avalanche, which, due to the high field strength, recruits all available charge carriers
Data Source
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AI summary
An optoelectronic sensor (10) for detecting an object (20) in a monitoring area (18) is specified, comprising a light transmitter (12) for emitting a light pulse (16), a light receiver (26) for receiving the remitted light pulse (22) with a line arrangement of light receiving elements (26a), each comprising at least one avalanche photodiode element (26b) which can be biased with a voltage above a breakdown voltage and thus can be operated in a Geiger mode, and a control and evaluation unit (28) which is designed to determine the distance to the object (20) from the received signals of the avalanche photodiode elements (26b) in a first distance measurement from the light travel time between emission of the light pulse (16) and reception of the remitted light pulse (22).The control and evaluation unit (28) is further designed to determine the distance in a second distance measurement by means of triangulation from the point of impact of the remitted light pulse (22) on the line arrangement.