Deflecting Mirror Shielding to Prevent LiDAR Ghosting
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Solution Overview
Problem
Existing distance measurement devices suffer from ghosting due to return light entering the device through the side surfaces of the deflecting mirrors, leading to the detection of non-existent objects.
Innovation Solution
The device incorporates shielding portions and low reflecting portions on the side surfaces of the deflecting mirrors to prevent return light from entering or being reflected inside the device, using black ink to form these areas on the deflecting mirrors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the deflecting mirrors are used without shielding portions, then the device structure is simple, but return light enters through side surfaces causing ghosting and reducing measurement accuracy
Solution Approach 1:
The deflecting mirror is divided into multiple surfaces: a reflecting surface for the main function and shielding portions on side surfaces. This segmentation allows the mirror to simultaneously perform reflection and block return light paths, resolving the contradiction between maintaining simple structure and preventing ghosting.
Solution Approach 2:
Different portions of the mirror are given different properties: the reflecting surface maintains high reflectivity for the transmission wave, while the side surfaces are treated with shielding portions (black ink or dark material) to absorb or block return light. This local differentiation eliminates ghosting while preserving the mirror's primary function.
2Reliability
If shielding portions are added to the deflecting mirrors, then ghosting is reduced, but the manufacturing process becomes more complex
Solution Approach 1:
The shielding portions are implemented by changing the optical parameter (reflectivity/absorptivity) of specific areas on the mirror surface. This can be achieved through simple surface treatments like applying black ink, spray paint, or dark coatings, which are inexpensive and easy to apply compared to manufacturing entirely new mirror components.
3Measurement precision
If the side surfaces of deflecting mirrors are left untreated, then manufacturing is easier, but return light is reflected inside the device causing detection errors
Solution Approach 1:
The side surfaces of the mirror, which could potentially cause harmful reflections, are treated with shielding portions that convert these surfaces into light-absorbing elements. The same mirror structure that provides reflection functionality also incorporates the shielding capability through surface treatment, turning a potential harm source into a beneficial feature.
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 configuration significantly reduces the occurrence of ghosting by minimizing the amount of return light detected at the receiving portion, enhancing the accuracy of distance measurements.
Implementation Method 1
a deflecting mirror which is rotationally driven is used at the distance measurement device to perform deflection scanning for a transmission wave, and a transmission wave output from a transmitting portion is reflected at the deflecting mirror
Implementation Method 2
Each of the pair of deflecting mirrors includes shielding portions through which passage of the transmission waves is suppressed
Data Source
AI summary
A mirror module includes a pair of deflecting mirrors which deflect a transmission wave and a reflected wave in a direction in accordance with a rotation angle of a reflecting surface and rotates in accordance with drive of a motor. A dividing plate divides the pair of deflecting mirrors into two portions of a transmission deflecting portion and a reception deflecting portion. Each of the pair of deflecting mirrors includes shielding portions through which passage of the transmission waves is suppressed on at least one of a side surface closer to a transmissive window in a state where the reflecting surface faces the transmitting portion out of both side surfaces located across a rotational axis at the transmission reflecting portion or a side surface farther from the transmissive window in a state where the reflecting surface faces the receiving portion out of both side surfaces located across the rotational axis at the reception deflecting portion.