Telecentric TOF Distance Sensing With Afocal Microlens Optics
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Solution Overview
Problem
Existing distance measuring apparatuses using time-of-flight methods suffer from reduced accuracy due to image blurring and light reception across multiple elements, which is not addressed by prior configurations that do not account for variations in object distance, leading to decreased precision.
Innovation Solution
The apparatus employs a light source unit with a microlens array and image-side telecentric lens forming an afocal system, along with a beam splitter, to maintain a consistent projected light width and one-to-one correspondence between light emitting and receiving elements, reducing image shift and size variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional light receiving optical system is used without adjusting imaging position according to object distance, then the device complexity is reduced, but the measurement precision deteriorates due to image blurring and light reception across multiple elements
Solution Approach 1:
The patent implements a movable light receiving element array that can dynamically adjust its imaging position along the optical axis according to object distance. The driving unit moves the light receiving element array to different positions based on detected object distance, enabling the system to maintain sharp focus and one-to-one correspondence between light emitting and receiving elements across varying distances, thereby resolving the contradiction between measurement precision and device complexity
Solution Approach 2:
The system uses a feedback mechanism where the object distance detection unit continuously monitors the distance to the target object and provides this information to the driving unit. The driving unit then adjusts the imaging position of the light receiving element array accordingly, creating a closed-loop control system that maintains optimal imaging conditions and ensures accurate distance measurement despite variations in object distance
2Measurement precision
If the imaging position is fixed, then the ease of operation is improved, but the measurement precision deteriorates due to image blurring at varying object distances
Solution Approach 1:
The light receiving element array is designed to be movable along the optical axis, transitioning from a fixed to a dynamic configuration. The driving unit automatically adjusts the imaging position based on object distance, eliminating the need for manual intervention while maintaining measurement precision across varying distances, thus resolving the contradiction between measurement precision and ease of operation
3Measurement precision
If the light receiving element array is positioned at a distance greater than the focal length of the telecentric lens, then the measurement precision is improved by reducing image shift, but the device complexity increases due to precise positioning requirements
Solution Approach 1:
The system employs feedback control where the object distance detection unit continuously monitors distance and the driving unit adjusts the light receiving element array position accordingly. This active compensation mechanism reduces sensitivity to manufacturing tolerances and assembly variations, allowing the system to achieve and maintain the required positioning precision through dynamic adjustment rather than relying solely on precise initial manufacturing
Solution Approach 2:
The patent changes the positioning parameter of the light receiving element array dynamically based on object distance. By adjusting the distance between the light receiving element array and the telecentric lens according to the object distance, the system optimizes the imaging conditions and reduces image shift, thereby improving measurement precision while managing manufacturing precision requirements through adaptive parameter adjustment
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 ensures high accuracy in distance measurement by maintaining a consistent projected light width and reducing image shift, thereby enhancing precision across varying object distances and manufacturing variations.
Implementation Method 1
a microlens array in which a plurality of microlenses are arranged... an optical system including an image-side telecentric lens, and configured to project light from the light source unit onto an object via the image-side telecentric lens
Implementation Method 2
A time-of-flight (TOF) distance measuring method is known, which measures a distance to an object (object distance) by measuring a time difference between irradiating light and detecting reflected light
Data Source
AI summary
An apparatus includes a light source unit including a light emitting element array in which a plurality of light emitting elements are arranged, and a microlens array in which a plurality of microlenses are arranged, a light receiving unit including a light receiving element array in which a plurality of light receiving elements are arranged, and an optical system including an image-side telecentric lens, and configured to project light from the light source unit onto an object via the image-side telecentric lens, and to cause the light receiving unit to receive reflected light from the object via the image-side telecentric lens. The microlens array and the image-side telecentric lens form an afocal system. A distance between the light receiving element array and an image-side principal point of the image-side telecentric lens is longer than a focal length of the image-side telecentric lens.