Hyun-Jun Park

Pneumatic robot based on inchworm motion for small diameter pipe inspection

By using only one pneumatic line, an inchworm like micro robot for pipe inspection is invented. This paper is based on drilling different-sized micro holes in two plates among three chambers. The rear clamp, the elongation module, and the front clamp work sequentially as the air flows to each chamber. It enables the robot not only to generate inchworm like locomotion, but also to allow significant reduction of the stiffness of pneumatic lines and the drag force due to one pneumatic line. In addition, a micro robot with diameter of 10 mm could be accomplished owing to its simple structure of chambers. In order to operate the robot efficiently, the stroke according to the supplied pneumatic pressure is investigated. Based on the result, maximum theoretical velocity is obtained by tuning the air insufflation time under in-pipe condition. Finally, the adoptability of the robot is tested under variation of pipe diameter.

Wireless guided wave and impedance measurement using laser and piezoelectric transducers

Guided-wave-?and impedance-based structural health monitoring (SHM) techniques have gained much attention due to their high sensitivity to small defects. One of the popular devices commonly used for guided wave and impedance measurements is a lead zirconate titanate (PZT) transducer. This study proposes a new wireless scheme where the power and data required for PZT excitation and sensing are transmitted via laser. First, a modulated laser beam is wirelessly transmitted to the photodiode connected to a PZT on a structure. Then, the photodiode converts the laser light into an electric signal, and it is applied to the PZT for excitation. The corresponding responses, impedance at the same PZT or guided waves at another PZT, are measured, re-converted into laser light, and wirelessly transmitted back to the other photodiode located in the data interrogator for signal processing. The feasibility of the proposed wireless guided wave and impedance measurement schemes has been examined through circuit analyses and experimentally investigated in a laboratory setup.

The development of a PZT-based microdrive for neural signal recording

A hand-controlled microdrive has been used to obtain neural signals from rodents such as rats and mice. However, it places severe physical stress on the rodents during its manipulation, and this stress leads to alertness in the mice and low efficiency in obtaining neural signals from the mice. To overcome this issue, we developed a novel microdrive, which allows one to adjust the electrodes by a piezoelectric device (PZT) with high precision. Its mass is light enough to install on the mouse’s head. The proposed microdrive has three H-type PZT actuators and their guiding structure. The operation principle of the microdrive is based on the well known inchworm mechanism. When the three PZT actuators are synchronized, linear motion of the electrode is produced along the guiding structure. The electrodes used for the recording of the neural signals from neuron cells were fixed at one of the PZT actuators. Our proposed microdrive has an accuracy of about 400 nm and a long stroke of about 5 mm. In response to formalin-induced pain, single unit activities are robustly measured at the thalamus with electrodes whose vertical depth is adjusted by the microdrive under urethane anesthesia. In addition, the microdrive was efficient in detecting neural signals from mice that were moving freely. Thus, the present study suggests that the PZT-based microdrive could be an alternative for the efficient detection of neural signals from mice during behavioral states without any stress to the mice. (Some figures in this article are in colour only in the electronic version)

Capsular locomotive microrobot for gastrointestinal tract.

Diagnosis using a flexible endoscope in gastro-intestinal tract becomes very important. In addition, the endoscope is a basic tool of diagnosis and treatment for digestive organ. However, the operation of endoscope is very labor intensive work and gives patients some pains. Therefore, the capsule-type endoscope is developed for the diagnosis of digestive organs. For its conveniences for diagnosis, the capsule endoscope comes into the spotlight. However, it is passively moved by the peristaltic waves of gastro-intestinal tract and thus has some limitations for doctor to get the image of the organ and to diagnose more thoroughly. In order to solve these problems, therefore, a locomotive mechanism of capsule endoscopes has being developed. For the locomotion in the gastro-intestinal tract, our proposed capsule-type microrobot has synchronized multiple legs that are actuated by a linear actuator and two mobile cylinders inside of the capsule. For the feasibility test of the proposed locomotive mechanism, a series of in-vitro experiments using small intestine without incision were carried out. In addition, in-vivo animal tests under a general anesthesia are also executed. From the experimental results, we conclude that the proposed locomotive mechanism is not only applicable to micro capsule endoscopes but also effective to advance inside of intestinal tract

Integrated guided wave generation and sensing using a single laser source and optical fibers

This study proposes an integrated lead zirconate titanate/fiber Bragg grating (PZT/FBG) system that can generate and measure guided waves for structural health monitoring (SHM) using a common laser source and optical cables. Among various SHM devices used for guided wave generation and sensing, PZT transducers and FBG sensors have been widely used because of their light weight, non-intrusive nature and compactness. To take the best advantage of the merits of these SHM devices, a combination of PZT-based guided wave generation and FBG-based sensing has been attempted by some researchers. However, the existing hybrid approaches have two independent systems: a wave generation system using electrical devices and a sensing system with optical devices. We have developed a fully integrated PZT/FBG system that uses a single laser source and optical cables. This system can alleviate problems associated with conventional electrical cables, such as electromagnetic interference, signal attenuation and vulnerability to noise. A tunable laser, the common power source for guided wave generation and sensing, is modulated and amplified to excite PZT. This laser is also used with FBG sensors for measuring high-speed strain changes induced by guided waves. The feasibility of this system has been experimentally demonstrated using an aluminum plate.

Development of an optic-based guided wave excitation technique

In recent years, nondestructive testing (NDT) has gained popularity for structural health monitoring and damage detection applications. Among the NDT methods, guided wave based NDT techniques have attracted the attention of many researchers due to their relatively long sensing range. These guided waves can be generated in a structure and sensed by a variety of techniques. The present study proposes a new scheme for PZT excitation and sensing based on laser and optoelectronic technologies, where power as well as data can be transmitted via laser. This paper mainly focuses on the excitation aspect. An arbitrary waveform is generated using a light source and transmitted to the PZT. A photodiode connected to the PZT then converts the light into an electrical signal and excites the PZT. The technique can be configured either for wired or wireless PZT excitations. Finally, the feasibility of the proposed power transmission scheme has been experimentally demonstrated in a laboratory setup.

Development of structural health monitoring systems for railroad bridge testbeds

Recently a challenging project has been carried out for construction of a national network for safety management and monitoring of civil infrastructures in Korea. As a part of the project, structural health monitoring (SHM) systems have been established on railroad bridges employing various types of sensors such as accelerometers, optical fiber sensors, and piezoelectric sensors. This paper presents the current status of railroad bridge health monitoring testbeds. Emerging sensors and monitoring technologies are under investigation. They are local damage detection using PZT-based electro-mechanical impedances; vibration-based global monitoring using accelerations, FBG-based dynamic strains; and wireless sensor data acquisition systems. The monitoring systems provide real-time measurements under train-transit and environmental loadings, and can be remotely accessible and controllable via the web. Long-term behaviors of the railroad bridge testbeds are investigated, and guidelines for safety management are to be established by combining numerical analysis and signal processing of the measured data.

Development of a non-contact PZT excitation and sensing technology via laser

In recent years, guided wave based structural health monitoring (SHM) techniques have attracted much attention, because they are not only sensitive to small defects but also capable to cover a wide range in plate and pipe like structures. The guided waves in a structure can be generated and sensed by a variety of techniques. This study proposes a new wireless scheme for PZT excitation and sensing where power as well as data can be transmitted via laser. A generated waveform by modulation of a laser is wirelessly transmitted to a photodiode connected to a PZT on the structures. Then, the photodiode converts the light into an electrical signal and excite the PZT and the structure. Then, the reflected response signal received at the sensing PZT is re-converted into a laser, which is wirelessly transmitted back to another photodiode located in the data acquisition unit for damage diagnosis. The feasibility of the proposed power and data transmission scheme has been experimentally investigated in a laboratory setup. Using the proposed technology, a PZT transducer can be attached to a structure without complex electronic components and a power supply.

Inchworm-Like Robotic Colonoscope UsingLegs for Clamping

For the reliable clamping of a robotic colonoscope inside the colon, we propose a clamping module consisting of six legs at the front and a trigger at the rear. In addition, a pneumatic-line based locomotive mechanism, which was developed previously for in-pipe inspection, is adopted to reduce the friction force between the pneumatic lines and the locomotion environment. In order to evaluate locomotion performance, a robot with a diameter of 15 mm and a length of 110.250 mm is used. Based on control signal from LabVIEW, it is tested in acrylic pipe and pigs colon. The proposed robot is able to move in the curved path which has a radius of over 25 mm. The speed of the robot is 33 mm/s in a straight path and 12.1 mm/s on a vertical path. The proposed robot, which has one pneumatic line and two clamping modules, conclusively shows reliable locomotion performance under in vitro condition.

Non-explosive Low-shock Separation Device for small satellite

This paper describes the development of non-explosive separation(NES) device which can be equipped on a small satellite. It comprises mechanism itself and spring-type shape memory alloy(SMA) actuator. In order to design SMA actuator properly, the necessary actuation force is measured. Based on that result, SMA actuator is designed and fabricated. Finally, SMA actuator and the proposed mechanism are integrated. In order to evaluate performance of the developed NES, we carried out a response time test, preload test and shock level test. In near future, we expect to replace the imported NES device with the developed device.