Yoha Hwang

Dental Training System using Multi-modal Interface

AbstractWe present a dental training system through multi-modal interface such as visual, auditory and haptic sensations. The system allows dental students to learn dental procedures and handling dental instruments with realistic feelings and evaluate their performance. To implement this system, it requires stable and fast haptic rendering algorithm, visual model deformation techniques on the virtual tooth being deformed, and sound rendering to simulate contact sound between the virtualtool and tooth. We enhance previous volume-based haptic modeling systems for haptic dental simulation. Collision detection and force computation are implemented on an offset surface rather than the implicit surface to simulate physical interactions between the virtual dental tool and tooth model. To bridge the gap between fast haptic process (1 KHz) and much slower visual update frequency (~30Hz), the system generates intermediate implicit surfaces between two consecutive physical models being deformed resulting in smooth f...

A novel online rotor condition monitoring system using fiber Bragg grating (FBG) sensors and a rotary optical coupler

Online strain measurement of rotating blades has been achieved with fiber Bragg grating (FBG) sensors and a rotary optical coupler constituted by two lenses and an air gap between them. In addition to the FBG sensors installed in blades, a FBG sensor having a minimal effect on the deformation of a blade was introduced and utilized to compensate the inevitable light intensity loss change due to shaft rotation. The rotary optical coupler enables continuous transmission of optical information about local deformation on a blade to a signal processing unit at the stationary side. Strains at five different locations along the blade were successfully measured online, while the rotating speed is changed rapidly.

Pattern Recognition of Rotor Fault Signal Using Bidden Markov Model

Hidden Markov Model(HMM) has been widely used in speech recognition, however, its use in machine condition monitoring has been very limited despite its good potential. In this paper, HMM is used to recognize rotor fault pattern. First, we set up rotor kit under unbalance and oil whirl conditions. Time signals of two failure conditions were sampled and translated to auto power spectrums. Using filter bank, feature vectors were calculated from these auto power spectrums. Next, continuous HMM and discrete HMM were trained with scaled forward/backward variables and diagonal covariance matrix. Finally, each HMM was applied to all sampled data to prove fault recognition ability. It was found that HMM has good recognition ability despite of small number of training data set in rotor fault pattern recognition.

Determination of local thrust coefficients of an aerospace component with the fibre Bragg grating array

Abstract This paper describes a novel thrust measurement on a rotating wooden blade using the fibre Bragg grating (FBG) array. Five FBG sensors created in a single fibre were installed on the surface of a blade along the radial direction and one FBG sensor was placed in the middle of a rotor shaft. Measurements were performed with two wooden blades under loading in hover and with a dynamic FBG interrogator maintaining six channels for analysing optic signals. Distributed forces normal to the surface of a blade were determined with the assumptions of the Euler—Bernoulli beam theory, and local thrust coefficients were calculated with blade element momentum theory (BEMT). Direct comparison between measured local thrust coefficient values and calculated ones was performed and good agreement was obtained on the local thrust coefficient versus the dimensionless radial distance chart. Additionally, the deflection shape of the blade in the flapwise direction was determined at various rotational speeds. Theoretical and experimental procedures described in this article offer an effective and improved method for the measurement and analysis of thrust coefficients for blade design as well as maintenance.

Dynamic analysis of constrained multibody systems using Kane's method

A new formulation for the dynamic analysis of constrained multibody systems is presented in this paper. The formulation employs Kanes method along with the null space method. Kanes method reduces the dimension of equations of motion by using partial velocity matrix introduced in this study : it can improve the efficiency of the formulation. Three numerical examples are given to demonstrate the accuracy and efficiency of the formulation.

New Active Muffler System Utilizing Destructive Interference by Difference of Transmission Paths

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.

On-line Strain Measurement of Rotating Blade Using Fiber Bragg Grating Sensors and Beam Coupler

Measurement of blade strain with sensors directly installed on the blade has one critical issue, how to send the sensor signal to the ground. Strain-gauges have been dominantly used to directly measure stress of a blade and either a slip ring or a telemetry system has to be used to send measured signal to the ground. However, both systems have many inherent problems and sometimes very severe limitations to be practically used. In this paper, new on-line strain monitoring method using. FBG(Fiber Bragg Grating) sensors and a beam coupler is introduced. Measurement of rotor stress using FBG sensors is nothing new, but unlike other system which installs all necessary instruments on the rotor and use telemetry system to send data to the ground, this system makes use of light`s unique characteristic - light travels through space. In this new approach, single optical fiber with many FBG sensors is installed on the blade and all other necessary instruments can be installed at ground thereby giving tremendous advantages over slip ring or telemetry system. A reference sensor is also introduced to compensate the beam coupler`s transmission loss change due to rotation. The suggested system`s good performance is demonstrated with experiments.

A Study on Discrete Hidden Markov Model for Vibration Monitoring and Diagnosis of Turbo Machinery

Condition monitoring is very important in turbo machinery because single failure could cause critical damages to its plant. So, automatic fault recognition has been one of the main research topics in condition monitoring area. We have used a relatively new fault recognition method, Hidden Markov Model(HMM), for mechanical system. It has been widely used in speech recognition, however, its application to fault recognition of mechanical signal has been very limited despite its good potential. In this paper, discrete HMM(DHMM) was used to recognize the faults of rotor system to study its fault recognition ability. We set up a rotor kit under unbalance and oil whirl conditions and sampled vibration signals of two failure conditions. DHMMS of each failure condition were trained using sampled signals. Next, we changed the setup and the rotating speed of the rotor kit. We sampled vibration signals and each DHMM was applied to these sampled data. It was found that DHMMs trained by data of one rotating speed have shown good fault recognition ability in spite of lack of training data, but DHMMs trained by data of four different rotating speeds have shown better robustness.

Multibody Dynamics Analysis for Contacting Rigid Bodies

This paper presents a new method for calculating contact position and contact force. The proposed method calculates accurate contact position by introducing intermediate parameters. Accurate contac t force can be obtained by solving reduced equations of motion iteratively. This method can be applied to calculate not only contact force on contact points but also contact force on kinematic joints such as a rotational joint and a translational joint. Four numerical examples are given to demonstrate the effectiveness of the proposed algorithm.

Dynamic Analysis of Constrained Multibody Systems Undergoing Collision

This paper presents a method for the dynamic analysis of constrained multibody systems undergoing abrupt collision. The proposed method uses a longer time interval to check collision than that of c onventional method. This reduces the computational effort significantly. To calculate collision points on two colliding rigid bodies, one may introduce constraints of contact. However, this causes reduction of degree of freedom and difficulty of numerical analysis. The proposed method can calculate collision points without above mentioned problems. Three numerical examples are given to demonstrate the computational efficiency and the usefulness of the proposed method