Optoelectronic Sensor Axicon Filter Design
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Solution Overview
Problem
Existing optoelectronic sensors face challenges in effectively suppressing extraneous light, particularly in bright environments or when measuring distances with poorly reflecting objects, which affects the signal-to-noise ratio and accuracy of distance measurement.
Innovation Solution
The use of a non-imaging optical element with a negative axicon-like shape in the reception path of the sensor, which reduces the angle of incidence and allows for a more precise optical filter design, effectively blocking extraneous light while maintaining a narrow bandwidth, thereby improving the signal-to-noise ratio and sensor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a bandpass filter is positioned near the receiving lens in the parallel beam path to achieve narrow filter edges, then the filter edges can be made very narrow, but the bandpass filter has to have large mechanical dimensions and is therefore very expensive
Solution Approach 1:
Instead of placing the filter in the parallel beam path near the receiving lens where narrow filter edges require large dimensions, the patent inverts the approach by placing the filter in the focal plane of the receiving lens where the beam is already converged. This allows the use of a much smaller filter with the same spectral selectivity, reducing cost and complexity while maintaining measurement precision.
2Device complexity
If the bandpass filter is placed in the vicinity of the light receiver to use a small and inexpensive filter, then the filter can be small and inexpensive, but the angles of incidence on the filter become large causing filter edge shifts
Solution Approach 1:
The patent introduces a beam homogenizing element (such as a diffuser or integrating rod) as an intermediary between the receiving lens and the filter. This element transforms the divergent beam with large angles of incidence into a beam with more uniform, smaller angles of incidence on the filter surface. This allows the use of a small, inexpensive filter while maintaining stable filter edges and accurate wavelength selection.
3Object-affected harmful factors
If a mechanical shutter is used to suppress extraneous light, then spatial extraneous light suppression is achieved, but the device complexity increases
Solution Approach 1:
The patent replaces the mechanical shutter system with an optical filter-based solution. By using a bandpass filter positioned in the focal plane with appropriate beam conditioning, the system achieves extraneous light suppression through spectral filtering rather than mechanical beam blocking. This eliminates moving parts, reduces device complexity, and improves reliability while maintaining effective suppression of extraneous light.
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 solution enhances the suppression of extraneous light, leading to improved signal-to-noise ratio and increased accuracy in distance measurements, even in challenging environments, by allowing a narrower optical filter design that is less dependent on angle of incidence, thus increasing the sensor's range and precision.
Implementation Method 1
An optical filter is matched to the wavelength range of the light emitter in order to only let the emitted light that is reflected through and block out extraneous light outside of its spectrum
Implementation Method 2
The use of a non-imaging optical element with a negative axicon-like shape in the reception path of the sensor, which reduces the angle of incidence
Implementation Method 3
avalanche photodiodes (APD, Avalanche Photo Diode) are conventionally used in some optoelectronic sensors. The incident light triggers a controlled avalanche (avalanche effect). As a result, the charge carriers generated by incident photons are multiplied, and a photocurrent is produced
Implementation Method 4
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. This type of distance measurement is also known as ToF (Time of Flight) or LIDAR (Light Detection and Ranging)
Data Source
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AI summary
An optoelectronic sensor (10) for detecting an object (20) in a monitoring area (18) is described, comprising a light transmitter (12) for emitting transmitted light (16) of a wavelength range, a light receiver (32) for generating a received signal from the transmitted light (22) reflected by the object (20), a receiving optic (24) arranged upstream of the light receiver (32) which includes at least a first optical element (26) for focusing the reflected transmitted light (22), a second optical element (28) for reducing the angle of incidence, and an optical filter (30) tuned to the wavelength range for suppressing ambient light, as well as an evaluation unit (34) configured to generate object information from the received signal. The second optical element (28) has light-scattering properties.