Catadioptric Optics for Laser Scanner Stray Light Reduction
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Solution Overview
Problem
Laser scanners face challenges in optics design due to the need for precise alignment and large size, as well as issues with stray light effects from contamination and windscreen reflections, particularly when using rotating mirrors or rotatable measuring heads.
Innovation Solution
A catadioptric receiving optics system with a moving optical unit that includes a refractive lens and reflective mirror elements, integrated with a common electronics card, which allows for compact size and reduced sensitivity to stray light, enabling a 360° surveillance area coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a rotating mirror is used for beam deflection, then the scanning function is achieved, but the alignment precision requirements increase and the device size increases
Solution Approach 1:
Instead of using a rotating mirror to deflect the beam, the patent inverts the approach by using a stationary mirror in combination with a rotating laser source. The laser beam is emitted from a rotating source and reflected by a stationary mirror, achieving the same scanning effect while eliminating the complex alignment requirements of a rotating mirror system
Solution Approach 2:
The patent divides the scanning function into two separate components: a rotating laser source that provides angular positioning and a stationary mirror that provides beam direction. This segmentation allows each component to be optimized independently, reducing the overall alignment precision requirements
2Ease of operation
If a rotating mirror is used for beam deflection, then the scanning function is achieved, but the device size increases
Solution Approach 1:
The patent inverts the conventional scanning architecture by making the laser source rotate instead of the mirror. This allows the use of a small, lightweight rotating assembly with a stationary mirror, significantly reducing the overall device volume while maintaining the scanning function
Solution Approach 2:
The patent uses a stationary mirror to replicate the beam deflection function that would otherwise require a large rotating mirror. The stationary mirror acts as a fixed reference that redirects the rotating laser beam, achieving the same optical path with minimal space requirements
3Reliability
If the windscreen is present, then the sensor is protected, but stray light effects increase due to contamination and reflections
Solution Approach 1:
The patent extracts the beam shaping function from the windscreen area by using dedicated beam shaping optics positioned in the rotating laser assembly. This separates the protective function (windscreen) from the optical function (beam shaping), allowing the windscreen to focus on protection while the dedicated optics handle beam formation, reducing stray light paths
Solution Approach 2:
The patent introduces beam shaping optics as an intermediary element between the laser source and the windscreen. These optics are positioned to shape the beam before it reaches the windscreen, minimizing the generation of stray light reflections and contamination effects on the protective surface
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 solution achieves a high ratio of effective optical surface to size, minimizing the sensor's overall dimensions and enhancing its robustness against stray light, while maintaining high accuracy and reliability for three-dimensional contour measurement.
Implementation Method 1
a receiving lens refractoryly concentrating the received light
Implementation Method 2
a reflectively concentrating mirror element
Implementation Method 3
The light is remitted to objects in the surveillance area and evaluated in the scanner
Data Source
Figure 1
AI summary
PROBLEM TO BE SOLVED: To provide a laser scanner of a photoelectronic sensor improved in a structure using scanning light which is moved periodically.SOLUTION: A photoelectronic sensor 10 for detecting an object in a monitoring area 18 includes: a light emitter 12 for emitting an outgoing beam 16; a light receiver 26 for generating a light-receiving signal from diffusely reflected light 20 by the object in the monitoring area 18; light-receiving optical systems 22 and 24 having at least a light-receiving lens 22 for converging the diffusely reflected light 20 on the light receiver 26; an optical unit 32 which can be driven around a rotary shaft 34, and in which the light emitter 12 and the light receiver 26 are stored with the light-receiving optical systems 22 and 24 for periodically scanning the monitoring area 18; and evaluation units 28 and 42 for acquiring information about the object in the monitoring area 18 on the basis of the light-receiving signal. In the sensor 10, the light-receiving optical systems 22 and 24 include a reflective element 24 for forming a beam.