Laser-Camera Displacement Measurement via Retroreflector
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Solution Overview
Problem
Existing displacement measurement sensors face challenges in achieving millimetric-level precision, especially at distant measurement points, and are not suitable for structures like buildings, bridges, and historical structures due to accuracy degradation with distance.
Innovation Solution
A laser-camera interactive and image processing-based displacement measurement method that uses a laser to project a beam onto a black box at the measurement point, with a camera inside the box determining the coordinates of the laser beam's impact, allowing for precise calculation of displacement values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If non-contact sensors such as laser distance meters or fiber optics are used to measure displacement at distant points, then the measurement can be performed without physical contact, but measurement accuracy decreases as the distance between the sensor and the object increases
Solution Approach 1:
A retroreflector is introduced as an intermediary element at the measurement point. The retroreflector receives the laser beam and reflects it back to the sensor, creating a virtual image that can be captured by the camera. This intermediary allows the measurement system to maintain high precision even at large distances by providing a well-defined reference point for image analysis.
Solution Approach 2:
The system creates an optical copy (image) of the retroreflector's position on the camera sensor. By tracking the position of this optical copy in the image plane and converting it to real-world coordinates using calibration data, the system can measure displacement with millimetric precision at distances exceeding the direct line-of-sight capabilities of traditional laser distance meters.
2Measurement precision
If contact sensors such as LVDT or string potentiometers are used to achieve precise displacement measurements, then measurement accuracy is maintained, but the sensors must be attached to a reference point on the object which makes them unsuitable for structures like buildings, bridges, and historical structures
Solution Approach 1:
The mechanical contact-based measurement system is replaced with an optical non-contact system. Instead of physically attaching sensors to the structure, the system uses a laser to project a beam onto a retroreflector and a camera to capture the reflected light. This substitution eliminates the need for mechanical attachment while maintaining measurement precision, making the system suitable for diverse structures including historical buildings, bridges, and dams.
Solution Approach 2:
The retroreflector serves as a non-invasive intermediary that can be temporarily placed at the measurement point without permanent modification to the structure. It enables the optical measurement system to function without physical contact, thereby preserving the integrity of structures while allowing precise displacement measurements to be performed.
3Measurement precision
If high-precision non-contact measurement sensors are used to achieve millimetric-level precision at distant points, then measurement accuracy is improved, but the cost of the sensor increases significantly
Solution Approach 1:
The measurement function is segmented between a simple laser source, an inexpensive retroreflector, and a standard camera. Instead of using a single complex high-cost sensor, the system divides the measurement task across multiple simple, low-cost components. The laser provides illumination, the retroreflector provides a reference target, and the camera captures the optical image for analysis. This segmentation dramatically reduces overall system cost while maintaining measurement precision.
Solution Approach 2:
The system uses a standard camera to capture an optical copy of the retroreflector's position rather than requiring a specialized expensive sensor. By processing the image data and converting pixel coordinates to real-world displacement measurements through calibration, the system achieves millimetric precision using off-the-shelf camera technology, avoiding the need for costly specialized sensors.
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 method provides accurate displacement measurements unaffected by distance, is cost-efficient due to its simple structure and lack of need for high-specification components, and achieves results with millimeter-level precision.
Implementation Method 1
A laser mounted at a fixed point projects a beam onto a black box positioned at the measurement point
Implementation Method 2
Using a camera mounted on this box, the coordinates of the point where the laser beam strikes are determined
Data Source
AI summary
This invention relates to a system and method for measuring displacements occurring in all types of materials and structures under the influence of external loads. Through this invention, a laser-camera interactive and image processing-based displacement measurement method, as well as a measurement system for implementing this method, has been developed. A laser mounted at a fixed point projects a beam onto a black box placed at the measurement point, and the coordinates of the point where the laser beam strikes are determined using a camera mounted on this box, enabling the calculation of the displacement value.