LIDAR system with electromagnetic two-axis scanning micromirror based on indirect time-of-flight method
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This paper presents a light detection and ranging (LIDAR) system using electromagnetically actuated two-axis scanning micromirror. The distance measurement with the LIDAR is based on the indirect time-of-flight method using the relative ratio of the accumulated charges in capacitors connected to photodiode pixels, which is determined by the time difference between the transmitted and reflected light pulse. The micromirror has double gimbaled structure for two-axis actuation and circular reflection plate with the diameter of 3 mm. The horizontal scan angle of 49.13° was obtained by the resonant actuation at 28 kHz, and the vertical scan of 29.23° was achieved by the sinusoidal forced actuation at 60 Hz. The distance to multiple targets could be measured at once by laser scanning using the micromirror, and the distance profile LIDAR image was constructed by the measurement results.
KeywordsLIDAR system Micromirror Indirect time-of-flight method Distance measurement
The LIDAR system has been one of the important research topics in the remote sensing technologies for three-dimensional imaging based on the distance measurement and diverse environmental monitoring. LIDAR has been studied intensively to be applied to the various applications such as autonomous vehicles, obstacle detection and security [1, 2, 3, 4, 5]. In the conventional LIDAR system, a motorized laser scanning unit such as galvanometer scanner is widely used for the detection of large area. In addition, LIDAR system has the disadvantages of having a large and heavy units with high cost. Recently, many research activities have been directed toward the development of LIDAR system using the micromirror, which has small size, light weight and low power consumption [6, 7].
In the LIDAR systems, the phase shift and time-of-flight method have been applied for the distance measurement. Laser beam is emitted to the target and reflected through receiving lens. In the phase shift method, the intensity modulated beam at a particular frequency is emitted to the target, and phase shift is produced in the reflected light depending on the distance to target [2, 8]. Even with the precise measurement of distance, however, the phase shift method requires a complicated system including laser beam modulation and data processing system. In addition, the phase shift method has disadvantage to be applied to real-time measurement because long processing time is required for precise distance ranging [1, 9]. Time-of-flight method calculates the distance using time difference between transmitted and reflected light beam . Time-of-flight method enables a simple system setup and distance calculation, but can make relatively large measurement error compared with the phase shift method . The indirect time-of-flight calculates the distance to a target by measuring the phase difference between the emitted and the reflected pulse. Since the relative ratio of the phase difference determined by two pulse signals is used for the measurement of distance, the high-precision time measurement sensor is not required for the indirect time-of-flight method [11, 12, 13, 14].
In this paper, we present the LIDAR system using electromagnetically actuated two-axis scanning micromirror based on the indirect time-of-flight method. The indirect time-of-flight method uses the relative ratio of the accumulated charges in capacitors connected to image sensor pixels, which is determined by the time difference between transmitted and reflected light beam. The distance measurement and imaging was demonstrated using the two-dimensional laser scanning with micromirror. Since the micromirror has a high scanning speed with small volume, it can make the system more compact and simple with high measurement rate compared to the system using conventional motor-based laser scanning units [6, 15, 16].
Design and experimental setup
Electromagnetic two-axis scanning micromirror
LIDAR image and distance measurements
In this paper, the feasibility of the LIDAR system using electromagnetic two-axis scanning micromirror has been successfully demonstrated based on indirect time-of-flight method. By using the transmitted laser scan with the micromirror and the ratio of the accumulated charges in capacitors determined by the reflected light, the distance to multiple targets could be measured at the same time, and the distance profile LIDAR image could be obtained. The distance measurement results show that the scanning micromirror can be readily applied to the indirect time-of-flight LIDAR system. The proposed LIDAR system is expected to be used in various application areas with further improvement of the LIDAR optics combined with the scanning micromirror.
JHP devised the idea and supervised the project. JHP, SHC, SWL, and SKL discussed the design and experimental setup. SHC performed the LIDAR experiment using the scanning micromirror. JHP and SHC drafted the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Availability of data and materials
This research was supported by the Space Core Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2013M1A3A3A02042410).
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