Seungho Jung

VISUAL MEASUREMENT METHOD USING A CIRCULAR GROOVE IMAGE FOR MEASURING INTERNAL DEFECTS OF PIPES IN NUCLEAR POWER PLANT

During the overhaul period of nuclear power plants in Korea, an ROV(Remotely Operated Vehicle) enters the cold-leg pipes connected with the reactor to examine the state of the thermal sleeves and their positions in the safety injection nozzles. To measure the positions of the thermal sleeves or scratches with video images recorded during the examination, time- varying camera parameters should be known, such as the focal length and principal points used for the capturing each video image. In this paper, we propose a camera calibration and measurement scheme by using a single image containing two circular grooves of a cylindrical nozzle whose radius and distance are known.

Pipe Inspection Robot with an Automatic Tracking System Using a Machine Vision

This paper describes a mobile out-pipe inspection robot with an automatic pipe tracking system to apply it to the feeder pipe inspection for the PHWR. The inspection of the feeder pipe requires the robot to be able to travel the out bend of the pipe as close as possible. Since no detectable beacons or indications are attached on the pipe, two cameras are attached at the front and rear parts of the robot to measure the offset orientation angle between the pipe and the robot. The offset angle can be obtained by using the proposed image processing algorithm. The robot is composed of dual inch worm mechanisms which make it possible to move along the longitudinal direction and to rotate in a circumferential direction. These actuators are driven pneumatically. The robot is constructed and test in a mockup of the feeder pipes

Thermosonic Inspection of a Welded SUS Plate

The technique of bringing a sample to vibration in the near ultrasound regime (20 kHz and above) and to look at the thermal signal of the surface with an infrared camera has been used for several years as a nondestructive evaluation tool to detect defects such as cracks within materials. The basic idea of this technique is to excite the part with a short (~ 280 ms duration) pulse of ultrasonic power (~ 2 kW, ~ 20 kHz). The relative motion of defect faces causes the ultrasound energy to dissipate locally at the defect. In turn, this energy acts as a localized heat source (hot spot). The resulting surface temperature change in the vicinity of the defect is imaged by means of a thermal infrared camera. The sequence of images, taken before, during, and after the application of the ultrasonic pulse, reveals the presence of the defect. In this paper we show results of our investigations regarding the hot spot generation at defects in the welded thin SUS plate

Development of an underwater manipulator for maintaining nuclear power reactor

The safety and reliability of nuclear power plants has become more important recently. Inspection and maintenance of nuclear power plants should be continuously implemented. However, the limitation of a radiation exposure makes it difficult to work in nuclear power plants. So a robot is very useful to inspect and maintain the components of nuclear power plants because of reducing radiation exposure to human operators and improving reliability of the operation. Particularly, a nuclear reactor vessel is a restricted area because it has a high radiation level under water during an overhaul. An underwater manipulator is needed for detecting and removing a loose part in a nuclear reactor vessel. The loose part, that comes from any failed component or an item left during a construction, refueling or maintenance like metallic parts, bolts, nuts and washers, affects the safety of a nuclear power plant. An underwater manipulator is developed in this study for removing some particles at the bottom of a nuclear reactor vessel and a reactor coolant system. We developed a 5-DOF underwater manipulator. The developed underwater manipulator could work at 30 m under water with the radiation exposure.

DEFECT DETECTION WITHIN A PIPE USING ULTRASOUND EXCITED THERMOGRAPHY

An UET (ultrasound excited thermography) has been used for several years for a remote non-destructive testing in the automotive and aircraft industry. It provides a thermo sonic image for a defect detection. A thermograhy is based On a propagation and a reflection of a thermal wave, which is launched from the surface into the inspected sample by an absorption of a modulated radiation. For an energy deposition to a sample, the UET uses an ultrasound excited vibration energy as an internal heat source. In this paper the applicability of the UET for a realtime defect detection is described. Measurements were performed on two kinds of pipes made from a copper and a CFRP material. In the interior of the CFRP pipe (70mm diameter), a groove (width - 6mm, depth - 2.7mm, and length - 70mm) was engraved by a milling. In the case of the copper pipe, a defect was made with a groove (width - 2mm, depth - 1mm, and length - 110 mm) by the same method. An ultrasonic vibration energy of a pulsed type is injected into the exterior side of the pipe. A hot spot, which is a small area around the defect was considerably heated up when compared to the other intact areas, was observed. A test On a damaged copper pipe produced a thermo sonic image, which was an excellent image contrast when compared to a CFRP pipe. Test on a CFRP pipe with a subsurface defect revealed a thermo sonic image at the groove position which was a relatively weak contrast.

DEVELOPMENT OF A STEAM GENERATOR TUBE INSPECTION ROBOT WITH A SUPPORTING LEG

This paper presents details on a tube inspection robotic system and a positioning method of the robot for a steam generator (SG) in nuclear power plants (NPPs). The robotic system is separated into three parts for easy handling, which reduces the radiation exposure during installation. The system has a supporting leg to increase the rigidity of the robot base. Since there are several thousands of tubes to be inspected inside a SG, it is very important to position the tool of the robot at the right tubes even if the robot base is positioned inaccurately during the installation. In order to obtain absolute accuracy of a position, the robot kinematics was mathematically modeled with the modified DH(Denavit-Hartenberg) model and calibrated on site using tube holes as calibration points. To tune the PID gains of a commercial motor driver systematically, the time delay control (TDC) based gain tuning method was adopted. To verify the performance of the robotic system, experiments on a Framatome 51B Model type SG mockup were undertaken.

A remotely operated mobile robot with modular track mechanisms

This paper introduces a remotely operated robotic system being developed for urban search and rescue. The developed QuadTrack-I has four modular track arms which can be driven independently to get a traction force. The modular track arms can also be rotated with respect to their arm axes to lift the body or step over larger obstacles. The QuadTrack-I can carry a small articulated robot to collapsed areas where victims could be under rubble. QuadTrack-II is also under development to increase the traction power and mobility of QuadTrack-I. This paper describes the structures of the robots and shows some experimental results.

Development of a Robotic System for Searching Human Victims in Disasters

This paper introduces a mobile robotic system being developed for urban search and rescue. In order to search human victims in narrow spaces, we developed two types of serially linked mobile robots, named KAEROT-Centipede and KAEROT-SnakeTV1, that can climb over large vertical steps or travel inside narrow vertical pipes. To send such mobile robots to the disaster areas coping with large obstacles, we also developed a assistant mobile robot, named KAEROT-QuadTrack, that has 4 articulated track modules. This paper describes the mechanical structure and control architecture of the serially linked mobile robots and the supporting configuration for torque reduction of the assistant mobile robot during spinning motion that usually requires large driving torque. The experimental results show that such robotic systems have good mobility over the various terrains in disaster areas.

Development of a Tele-operated Underwater Robotic System for maintaining a light-water type power reactor

The safety and reliability of nuclear power plants is very important. An inspection and maintenance of nuclear power plants should be achieved simultaneously. However, the limitation of a radiation exposure makes it difficult to work in nuclear power plants. Therefore, a tele-operated robotic system is very useful for inspecting and maintaining the components of nuclear power plants because it reduces the level of a radiation exposure to the human operators and it improves the reliability of an operation. A tele-operated underwater robotic system is needed for detecting and removing a loose part in a nuclear reactor vessel. A loose part, which can come from any failed component or an item left during a construction, refueling or maintenance like metallic parts, bolts, nuts and washers, affects the safety of a nuclear power plant. In this paper, an underwater robotic system is developed for inspecting the bottom of a nuclear reactor vessel and a reactor coolant system and also for removing some particles in them. In order to evaluate the performance of the developed underwater robotic system, an experiment was performed in a small swimming tank. In the experiments, the developed robotic system could inspect the state of the tank and remove some particles successfully

Inch-Worm Robot with Automatic Pipe Tracking Capability for the Feeder Pipe Inspection of a PHWR

This paper describes a mobile inspection robot with an automatic pipe tracking system for a feeder pipe inspection in a PHWR. The robot is composed of two inch worm mechanisms. One is for a longitudinal motion along a pipe, and the other is for a rotational motion in a circumferential direction to access all of the outer surfaces of a pipe. The proposed mechanism has a stable gripping capability and is easy to install. An automatic pipe tracking system is proposed based on machine vision techniques to make the mobile robot follow an exact outer circumference of a curved feeder pipe as closely as possible, which is one of the requirements of a thickness measurement system for a feeder pipe. The proposed sensing technique is analyzed to attain its feasibility and to develop a calibration method for an accurate measurement. A mobile robot and control system are developed, and the automatic pipe tracking system is tested in a mockup of a feeder pipe.