- Open Access
Intensity-based laser distance measurement system using 2D electromagnetic scanning micromirror
© The Author(s) 2018
- Received: 6 September 2018
- Accepted: 26 November 2018
- Published: 30 November 2018
In this research, we present the feasibility testing results of a simple distance measurement system using microfabricated scanning micromirrors. Two different configurations have been tested with different types of micromirrors. In the first configuration, Lissajous scan pattern has been generated with horizontal scan frequency of 715 Hz, and the intensity of the laser beam reflected from the object has been measured with avalanche photodiode to estimate the distance. The position of the beam has been tracked using a separate position sensitive detector. Signals from both sensors are synchronized by eliminating the signal delay, which enables the detection of the distance of a specific point in the 2-dimensional scan pattern. In the simplified configuration, faster scanning micromirror with horizontal scan frequency of 28.8 kHz has been used to increase the resolution and position sensitive detector has been removed from the system by synchronizing the driving current waveform with the avalanche photodiode signals. Distance measurement from 20 to 50 cm has been demonstrated with the developed system.
Recently, technologies related to the optical measurement of 3-dimensional (3D) profile or distance is gaining significant research momentum due to growing needs in various fields of application. LIDAR (light detection and ranging) sensor has become a crucial component for data collection and reconstruction of the 3D space surrounding the autonomous vehicle, and facial or gesture recognition sensors are being actively deployed in hand-held smart devices and automotive vehicles. In general, three different approaches are used for optical distance measurement using the laser beam as a light source, which are TOF (time-of-flight) measurement, triangulation, and intensity measurement methods. The TOF measurement utilizes the time difference between outgoing and incoming laser pulses . Although the long-distance measurement capability with high accuracy makes the technique an attractive choice for applications such as LIDAR systems for autonomous vehicles, complex and costly architecture for photon-counting and autocorrelation algorithms are required. Despite the low system complexity and fast response, utilization of triangulation is limited as the measurable distance is proportional to the reflected laser beam displacement . Intensity measurement method requires a very simple system architecture, which makes it a reasonable choice for short range distance measurement and motion tracking. Laser sensing display and gesture recognition system from the University of Tokyo are good examples of the intensity-based distance measurement systems [3–5]. As the 3D measurement of distance inherently requires the scanning of laser beam in 2D (2-dimensional) space, motorized scanners are widely used in conventional systems. Recently, various approaches have been proposed to utilize MEMS (microelectromechanical systems) scanners in these applications, which can potentially provide a significant reduction of overall volume and cost of the system [1, 6].
Although the proposed intensity-based distance measurement system cannot provide an accurate estimation of the absolute distance, relative differences in intensity or rough estimate of the distance and position of an object in 2D space can be obtained. Therefore, the location and approximate profile of the object can be found. Also, the distance of the object at the center of the scan pattern matches relatively well with the equation derived with distance measurement experiment. When the intensity versus distance equations are established for objects located at various positions and angles, it is possible to detect the distances with more accuracy. Therefore, through more experiments and optimization of the optics, more advanced intensity-based distance sensor using a 2D MEMS scanner can be developed for motion tracking and gesture recognition.
Feasibility testing result of an intensity-based distance measurement system using 2D MEMS scanning micromirror has been presented. Two types of electromagnetic MEMS scanners with different scan frequency have been utilized to create 2D scan patterns. The optical setup for receiving the reflected laser beam from the target object has been constructed. An APD sensor has been utilized in measuring the intensity of the reflected beam, and a PSD sensor has been utilized for detecting the reflected beam position and scan pattern. By synchronizing the APD and PSD outputs, the position and distance of the object in the 2D space can be detected. Also, the PSD sensor can be removed from the optical setup by synchronizing the input waveform applied to the scanner and the APD sensor signal. Although dependence on object surface roughness and reflectivity could not be removed, detection of approximate distance and the position of the target object with simple architecture using a single APD sensor has been demonstrated. For the object with known reflectivity and position, the distance can be determined with more accuracy. Although further experimentation would be required to improve the accuracy of measurement, the feasibility of utilizing 2D MEMS scanner in an intensity-based distance measurement application has been verified successfully.
KK carried out the experiments, and KK, JH, and C-HJ analyzed the experimental results, and drafted the manuscript. All the authors discussed the proposed architecture and experimental results. All the authors read and approved the final manuscript.
The authors declare that they have no competing interests.
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2017R1A2B4007830), Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2014R1A1A2057721), and by the Center for Integrated Smart Sensors as GFP (CISS-2012M3A6A6054204).
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