Fresnel Lens Optoelectronic Sensor Transit Time Error Correction
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Solution Overview
Problem
Conventional optoelectronic sensors using classic lenses face limitations in measuring range due to the maximum effective lens diameter, leading to larger designs and increased costs, while Fresnel lenses, which could offer a more compact design, introduce systematic transit time errors that affect measurement accuracy.
Innovation Solution
Employing a Fresnel lens or belt lens in the receiving optics with a correction mechanism to store and adjust for the systematic transit time errors, allowing for a more compact and cost-effective design without compromising measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a Fresnel lens is used in the receiving optics, then the design becomes more compact and cost-effective, but systematic transit time errors are introduced that affect measurement accuracy
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing correction values for the systematic transit time errors in a lookup table or memory. The correction data is prepared in advance based on the known optical path differences in different zones of the Fresnel lens, allowing real-time compensation without complex calculations during measurement.
Solution Approach 2:
The patent implements feedback by using the measured transit time to determine which correction value to apply. The system measures the raw transit time, uses it to index into correction data (either from a lookup table or through a correction function), and applies the appropriate correction to obtain the accurate distance, creating a closed-loop correction mechanism.
2Reliability
If a classic lens with maximum effective diameter is used, then measurement range is improved, but the design size and manufacturing cost increase
Solution Approach 1:
The patent applies segmentation by dividing the lens into multiple zones with different optical paths. The Fresnel lens consists of concentric annular zones, each contributing to the overall light gathering capability. This segmentation allows the lens to achieve large effective diameter equivalent performance in a compact form factor, maintaining measuring range while reducing physical size.
Solution Approach 2:
The patent changes the optical parameters by introducing controlled transit time variations through the Fresnel lens zone structure. By carefully designing the zone widths and depths, the lens maintains its light-gathering ability (effective diameter) while compressing the physical thickness. The parameter change from a simple curved surface to a stepped Fresnel profile enables compactness without sacrificing optical performance.
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
Enables a reduced f-number, increased range, or smaller design with minimal impact on measurement accuracy by correcting for the transit time errors introduced by Fresnel or belt lenses, resulting in a more efficient and cost-effective optoelectronic sensor.
Implementation Method 1
A classic lens works exclusively with the effect of light refraction
Implementation Method 2
an outer area with total internal reflection (TIR) is provided in order to deflect the light from there into the focal point
Implementation Method 3
The time of flight of light is often measured using a known phase or pulse method in order to determine the distance from a touched object
Data Source
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AI summary
A distance-measuring optoelectronic sensor (10) for detecting an object (20) in a monitoring area (18) is specified, comprising a light transmitter (12) for emitting a light beam (16), a light receiver (26) for generating received signals from the light beam (22) reflected from the object (20), a receiving optic (24) arranged upstream of the light receiver (26) for focusing the reflected light beam (22) onto the light receiver (26), and an evaluation unit (28) designed to determine the distance of the object (20) from the time of flight of light between the emission of the light beam (16) and the reception of the reflected light beam (22). The receiving optics include a Fresnel lens (24) or a belt lens, and the evaluation unit (28) is designed to correct the distance from a relationship between the measured distance and a time-of-flight deviation introduced by the Fresnel lens (24).