Haemin Jeon

A paired visual servoing system for 6-DOF displacement measurement of structures

In the previous study, a paired structured light system which incorporates lasers, cameras, and screens was proposed, and experimental tests validated the potential of a displacement measurement system for large structures. However, the estimation of relative translational and rotational displacements between two sides was based on an assumption that there is zero initial displacement and that three laser beams are always on the screens. In this paper, a calibration method is proposed to offset the initial displacement using the first captured image. The calibration matrix derived from the initial offset is used for subsequent displacement estimation. A newly designed 2-DOF manipulator for each side is visually controlled to prevent the laser beams from leaving the screen. As the manipulator actively controls the laser beams to target the center of the screen, it contains all three laser points within the bounds of the screen. To verify the feasibility of the proposed system, various simulations and experimental tests were performed. The results show that the proposed visually servoed paired structured light system solves the main problem with the former system and that it can be utilized to enlarge the estimation range of the displacement.

The displacement estimation error back-propagation (DEEP) method for a multiple structural displacement monitoring system

Visually servoed paired structured light system (ViSP) has been found to be useful in estimating 6-DOF relative displacement. The system is composed of two screens facing each other, each with one or two lasers, a 2-DOF manipulator and a camera. The displacement between two sides is estimated by observing positions of the projected laser beams and rotation angles of the manipulators. To apply the system to massive structures, the whole area should be partitioned and each ViSP module is placed in each partition in a cascaded manner. The estimated displacement between adjoining ViSPs is combined with the next partition so that the entire movement of the structure can be estimated. The multiple ViSPs, however, have a major problem that the error is propagated through the partitions. Therefore, a displacement estimation error back-propagation (DEEP) method which uses Newton–Raphson or gradient descent formulation inspired by the error back-propagation algorithm is proposed. In this method, the estimated displacement from the ViSP is updated using the error back-propagated from a fixed position. To validate the performance of the proposed method, various simulations and experiments have been performed. The results show that the proposed method significantly reduces the propagation error throughout the multiple modules.

Paired vision-based structural health monitoring system

In the previous study, a paired structured light-based deformation measurement system which incorporates lasers, cameras, and screens was proposed and experimental tests validated the potential of the proposed system. However, the experimental tests were limited to the relatively short distance and the estimation was based on an assumption that there is no initial deformation. In this study, a calibration of the initial offset is performed from the first vision scene, and then the deformation based on the initial position is estimated. The dynamic deformation estimation tests at a longer distance are performed to prove the scalability of the proposed system. These experimental results show that the proposed paired structured light system can successfully estimate the relative deformation and can be applied to the large civil infra-structures such as long-span bridges or high-rise buildings.

Robotic SHM and Model-Based Positioning System for Monitoring and Construction Automation

As civil infrastructures get larger and more complex, the development of robot technologies that help to construct, monitor, inspect, and manage civil infrastructures is in need. In this paper, we introduce two major robot technologies for construction and monitoring of civil infrastructures. The first one is the beacon-based localization technology for the robust localization of the robot and human. A novel beacon-based localization method is proposed where it utilizes the map information of the structure and the signal propagation model. The second one is the modular robot system for structural health monitoring (SHM) of large structures. To develop an SHM system that directly measures the deformation of the structure using low-cost sensor, a paired structured light (SL)-based modular robot system is proposed. The proposed module which uses one or two actuated lasers and a camera in pair is inexpensive to implement and it can directly measure the accurate relative deformation between any two locations on the structure. To demonstrate the feasibility and capability of the proposed methods, experimental results have been shown for each technology.

Virtual door algorithm for coverage path planning of mobile robot

This paper presents a novel coverage path planning algorithm for a mobile robot in indoor environment. Overall region is divided into several sub-regions based on the virtually extracted doors. The key idea of this method was obtained from the usual way of dividing an indoor environment into sub-regions, i.e., rooms based on the identification of doors. The proposed virtual door algorithm extracts the virtual doors by overlapping a Generalized Voronoi Diagram (GVD) and a configuration space eroded by the half of the door size. The region to region cleaning algorithm is also proposed based on the closing and opening of virtual doors. The performance of our algorithm has been tested on various real indoor environments using a commercially available cleaning robot.

Virtual Door-Based Coverage Path Planning for Mobile Robot

This paper presents a novel coverage path planning method in indoor environment for a mobile robot such as cleaning robot. Overall region is divided into several sub-regions based on the virtually extracted doors. The algorithm is inspired from the usual way of dividing an indoor environment into sub-regions, i.e., rooms based on the identification of doors. The virtual door algorithm extracts the virtual doors by combining a Generalized Voronoi Diagram (GVD) and a configuration space eroded by the half of the door size. The region to region cleaning algorithm is also proposed based on the closing and opening operations of virtual doors. The performance of the proposed algorithm has been tested on various real indoor environments using a commercially available cleaning robot.

High reflection tolerance of 1.25-Gb/s RSOA-based WDM PON employing spectrum-sliced ASE source

We investigate the impact of the reflection in an RSOA-based WDM PON utilizing the spectrum-sliced ASE source as the seed light. Since the spectrum-sliced ASE source has sufficiently large bandwidth to suppress the optical beat interference (OBI) noise, we can achieve the high reflection tolerance in comparison with that in a conventional WDM PON using the remodulation scheme. In the experiment, we systematically investigate the dependence of the reflection tolerance on the operating conditions such as the optical power and bandwidth of the spectrum-sliced ASE source injected into the RSOA. In the case when the injection power into the RSOA is low, the performance of the upstream signal becomes vulnerable due to the reflection-induced incoherent crosstalk and parasitic laser oscillation. However, we can improve the reflection tolerance significantly by increasing the optical power and the bandwidth of the spectrumsliced ASE source. By optimizing these operating conditions, we can achieve an excellent refection tolerance greater than -15 dB.

ViSP: visually servoed paired structured light system for measuring structural displacement

To inspect structural conditions, structural displacement is needed to be monitored at any time. Therefore, our previous study proposed a ViSP (Visually Servoed Paired structured light system) which is composed of two sides facing with each other, each with a camera, a screen, and one or two lasers controlled by a 2-DOF manipulator. In this system, the relative translational and rotational displacement between two sides can be estimated by calculating positions of the projected laser beams on the screens and the rotation angles of the manipulators. To validate the performance of the system, the various experimental tests with a two-story structural model were performed. The estimated results were compared with the results from a laser displacement sensor which can be considered as a reference. The results show that the presented system has potential of estimating the response of the structures with high accuracy in real time.

Reflection tolerance enhancement of RSOA-based WDM PON by using optical frequency dithering

We investigate the effectiveness of optical frequency dithering to enhance the reflection tolerance of RSOA-based WDM PONs. We show that the reflection-induced penalty can be substantially reduced in both directions by the same dithering frequency.

Vision-based 6-DOF displacement measurement of structures with a planar marker

The estimation of translational and rotational displacement of large structures is usually considered as major indicators for structural safety. Recently, several vision-based measurement methods have been developed. Most vision-based systems, however, estimate displacements in 1-D or 2-D space. There are six degree of freedom (6-DOF) measurement methods using combination of lasers and cameras. But, the system is complex to install and not easy to maintain. To mitigate this problem, this paper proposes a simple 6-DOF displacement measurement system using only one camera and a planar marker. Using the square shaped planar marker, whose world geometry is known a priori, the 6-DOF relation between the marker and the camera can be calculated. The camera with a built-in lens captures a marker image and detects corners of the marker. Using homography transformation, 6-DOF relative pose information to the structure is estimated. In order to verify the feasibility of the proposed system, experimental tests are performed. The system for experiments consists of a chargecoupled device (CCD) camera with a built-in 37× zoom lens for maker image processing. The square marker is installed about 20 meters distance away from the camera, and the displacement is estimated. The results show the applicability of the proposed 6-D measurement system to real structures.