Laser Scanner Intensity Correction for Edge Detection
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Solution Overview
Problem
Existing laser scanners for automatic doors and windows struggle to accurately detect small objects near the frame that delimits the monitoring area due to inaccuracies in time-of-flight measurements, particularly in the 'gray zone' where the object's reflectivity differs significantly from the frame's, leading to unreliable detection.
Innovation Solution
The laser scanner employs an intensity comparison with a predefined threshold to correct time-of-flight measurements by using an avalanche photodiode for intensity evaluation, averaging over multiple pulses, and storing reference intensities to adapt to environmental changes, ensuring accurate detection even in edge areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If time-of-flight measurement is used to detect objects in the monitoring area, then the detection range and coverage are improved, but the measurement precision deteriorates in the edge area near the frame due to the gray zone effect
Solution Approach 1:
The patent combines two different measurement methods - time-of-flight measurement and intensity measurement - into a unified detection system. The evaluation unit integrates results from both methods to determine object presence, allowing the system to leverage the strengths of each method while compensating for their individual weaknesses in the edge area
Solution Approach 2:
The patent introduces intensity measurement as an intermediary parameter to resolve the ambiguity in the gray zone. By measuring the intensity of reflected laser pulses and comparing it with reference values, the system can detect objects even when time-of-flight measurements are unreliable near the frame edge
2Area of stationary object
If the monitoring area is extended close to the frame, then the detection coverage is improved, but the detection reliability deteriorates for small objects in the edge area
Solution Approach 1:
The system uses feedback from intensity measurements to correct and verify time-of-flight measurement results. The evaluation unit continuously compares measured intensity values with stored reference values and uses this feedback to confirm or reject object detections, significantly improving reliability in the edge area
Solution Approach 2:
The patent performs preliminary intensity measurements during a learning phase to establish reference values for different areas of the monitoring region. These pre-stored reference values are then used during normal operation to quickly and reliably detect objects without requiring real-time complex analysis
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 detection reliability for small objects by correcting time-of-flight inaccuracies, allowing for robust and precise identification of objects near the frame, even in challenging conditions.
Implementation Method 1
determine the position of an object in the surveillance area via a time-of-flight measurement of a transmitted and received laser pulse
Implementation Method 2
The intensity is measured by evaluating the received pulse width. An avalanche photodiode is used as the detector
Data Source
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AI summary
The invention relates to a laser scanner (10, 32) for monitoring a monitoring region (36) in front of an opening that can be closed by a closing means, by the design of which closing means a hazard region (40) in the monitoring region (36) is defined, the monitoring region (36) being delimited at least on one side by a frame (34), in front of which an edge region (38) is located, comprising a laser transmitting/receiving unit (12), furthermore a propagation time sensing means (14) being provided, which determines the position of an object (22, 44, 46) in the monitoring region (36) by means of a propagation time measurement of a transmitted and received laser pulse, an evaluation unit (18) being provided, by means of which first object information is produced, namely whether an object was sensed by means of the propagation time measurement, furthermore an intensity sensing means (16) being provided, by means of which the received laser pulse is evaluated with respect to the intensity thereof and the sensed intensity is compared with a reference intensity stored in a memory unit (24), second object information being provided in the event of deviation beyond a certain threshold value, namely whether an object is located in the hazard edge region on the basis of the intensity deviation, and a "safety signal" being generated by the evaluation unit (18) if either the first or the second object information is positive.