Wancheol Myeong

Experimental Validation of Visually Servoed Paired Structured Light System (ViSP) for Structural Displacement Monitoring

Structural displacement is considered an important indicator to assess structural conditions. To directly measure the displacement in the time domain, a visually servoed paired structured light system was proposed. The system is composed of two sides facing each other, each with one or two lasers that are controlled by a visually servoed two-DOF manipulator, a camera, and a screen. The relative six-DOF displacement between the two sides can be estimated by calculating the positions of the projected laser beams on the screens and the rotation angles of manipulators. To verify the performance of the proposed system, two kinds of field tests were carried out. A prototype of the system was built and installed on a steel frame building structure and a railway bridge, respectively. The estimated displacements were compared with the reconstructed displacement from an accelerometer. The test results verify the performance of the system and its applicability to real structures.

Mechanism and system design of MAV(Micro Aerial Vehicle)-type wall-climbing robot for inspection of wind blades and non-flat surfaces

Wind turbines need annual inspections to investigate their states which may have damages, such as cracks, erosion, bonding defects, cavities and delamination. Wind blades inspection, however, is a difficult process which needs specialized equipment and well-trained technicians to perform it manually. In addition, most approaches to inspect require pre-installed infrastructures like ropes or other platforms, so they are not appropriate for a close investigation and has a low preference. To overcome these problems, the need for a wall-climbing robot has emerged. In this paper, we suggest a MAV (Micro Aerial Vehicle) type wall-climbing robot that has four rotors to make thrust force for flying and four wheels for wall-climbing so that it can fly, stick, and move on a vertical and non-flat surface. The overall inspection process has two parts; macro and micro inspections. The main concept was verified throughout simulations.

Multiple ViSPs (visually servoed paired structured light systems) for 6-DOF structural displacement estimation

Recently, structural health monitoring has gained great attention due to the deterioration of aging structures and rapid growth of massive structures. To monitor the structural conditions, a visually servoed paired structured light system (ViSP) for estimating 6-DOF relative displacement has been developed. The system is composed of two sides facing with each other, each with one or two lasers with a 2-DOF manipulator, two cameras, and a screen. By calculating the positions of the projected laser beams and rotation angles of the manipulators, the relative displacement can be estimated. To estimate the movement of the massive structure, entire structure is partitioned and the displacement at each partition is estimated by the each ViSP. In the multiple ViSPs, the movement of the entire structure can be estimated by multiplying the estimated displacements in a cascaded manner. However, it has a major problem that the error is propagated due to the multiplication. Therefore, a displacement error back-propagation (DEBP) method which uses the Newton-Raphson method inspired from the error-back propagation method is proposed. In this paper, the details of the ViSP and DEBP method are described.

Development of FAROS (fire-proof drone) using an aramid fiber armor and air buffer layer

In these days, high-rise buildings and large complex structures are rapidly increasing due to the advancement of construction technologies and other economic reasons. Since these urban spaces are densely populated, fire accident could be critical and accessing the situation at early stage is very important in order to suppress the fire and evacuate the residents. In that, aerial robot platform has advantages because of its ability to access to the place that is hard to reach. However, in most cases, their essential elements like electronic equipment are directly exposed to the air for decreasing its own weight and cooling effect. Therefore, it is not possible to operate the conventional drones near fire. In this paper, we developed the fireproof aerial robot platform that can endure the intermittent flame. The radial size of the robot is 600mm for indoor operation and safety.

A Vision-Based 6-DOF Displacement Measurement Method for Assembling PC Bridge Structures Using a Planar Marker

Precast concrete (PC) is used in many construction sites around the world, which is delivered after it is totally made on the plant. This is because it can reduce the rate of structural defection and building time. While in construction, many of PC materials are moved by a crane operator to specific positions just by looking. And the workers use hand gestures to fit a shear pin on the lower beam with an upper part. In this paper, a vision-guided method that is more efficient and faster than the conventional PC assembly methods is proposed. A vision-based 6-DOF displacement estimation method measures the relative displacement between the camera located in an upper slab and the marker located at the shear pin on the lower beam. Usually, PC slab has a quite long width, and it is not easy to estimate a precise 6-DOF information with just a pair of a camera and a marker. To mitigate this problem, multiple pairs of cameras and markers can be configured for large PC member and the beam. This paper deals with 6-DOF displacement estimation by using vision-based localization with a planar maker for PC construction sites. A camera detects the corner of the planar marker at first, and sub-pixel information is obtained for the corner and then the data are transferred to a main computer via Bluetooth communication. The main computer calculates 6-DOF displacement with corresponding points in the world coordinate frame. To show feasibility and robustness of the proposed method, some experiments are performed with varying distances.

Monte Carlo Localization and Multiple Vision Sensor Based 6-DOF Displacement Measurement System for the Rendezvous of PC Bridge Members

In construction site, many of building materials and structural members are moved and positioned by the crane operator. Due to the limitation of eyesight of a crane operator, it is not possible to place the precise position. Especially, nowadays, PC construction and prefabricated construction need a precise positioning system to reduce construction time and increase construction accuracy [1]. Vision-based 6-DOF estimation system can provide the relative position between two construction members in real time. Since the sizes of general construction members are normally more than 3m, displacement information about only one spot is not enough as the linear error is proportional to the distance from where the angular error occurs. Therefore, the multiple vision sensor approach will be effective to estimate an overall displacement of large construction member. One module consist of pair of camera and planar marker. We assume that this system will be applied for PC slab construction or replacement construction for repair. Two cameras are installed in the shear pockets on both ends of the PC slab whose width is about 10 m and the corresponding markers to cameras are installed the support beam where PC slab is supposed to be placed. Each datum from each sensor module will be transmitted to main computer using wireless technology and fused by Monte Carlo Localization (MCL) algorithm by which optimal pose information is estimated. doi: 10.12783/SHM2015/53

One-Way ViSP (Visually Servoed Paired structured light) for 6-DOF Structural Displacement Measurement

Structural health monitoring (SHM) of civil infrastructures has gained great attention since it is directly related to public safety. To estimate structural displacement, which is considered as one of important categories of SHM, a one-way type vision and laser-based 6-DOF displacement measurement system (one-way ViSP) is proposed. The system is composed of a transmitter with two laser pointers, a 1-D laser range finder (LRF), and a 2-DOF manipulator; and a receiver with a camera and a screen. The lasers and LRF project their parallel beams to the screen and the camera attached to the screen captures the image of the screen. The manipulator controls poses of the lasers and LRF for projected laser beams to be always inside the screen. By calculating positions of the laser beams and obtaining the distance from LRF, the relative displacement between two places can be estimated. The performance of the system has been verified from simulations.

Incremental Displacement Estimation Algorithm for Real-Time Structural Displacement Monitoring

The purpose of this paper is to suggest IDE (Incremental Displacement Estimation) algorithm for the previously proposed visually servoed paired structured light system. The system is composed of two sides facing with each other, each with one or two lasers with a 2-DOF manipulator, a camera, and a screen. The 6-DOF displacement between two sides can be estimated by calculating the positions of the projected laser beams and rotation angles of the manipulators. In the previous study, Newton-Raphson or EKF (Extended Kalman Filter) has been used as an estimation algorithm. Although the various experimental tests have validated the performance of the system and estimation algorithms, the computation time is relatively long since aforementioned algorithms are iterative methods. Therefore, in this paper, a non-iterative incremental displacement estimation algorithm which updates the previously estimated displacement with a difference of the previous and the current observed data is introduced. To verify the performance of the algorithm, experimental tests have been performed. The results show that the proposed non-iterative algorithm estimates the displacement with the same level of accuracy compared to the EKF with multiple iterations with significantly less computation time.