Development of a motion simulator for testing a mobile surveillance robot

A 6-axis motion simulator has been developed, in order to regenerate UGV (unmanned ground vehicle) motion and to test the stabilization system of the mobile surveillance robot that is mounted on the UGV. For developing the 6-axis motion simulator, a simulation-based design procedure was introduced. The 3D geometric model of the motion simulator was created by using 3D CAD modeler ProE. The multibody dynamics model of the motion simulator has also been created by using the general purpose dynamic analysis program ADAMS to validate the design of the motion simulator. Dynamics and control co-simulation model for the motion simulator has been also established for control performance analyses. Actual hardware of the motion simulator has been fabricated based on the proposed simulation based design. Hardware test of the motion simulator has been tried to validate the design. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Oskar Wallrapp was awarded a Ph.D. degree in Mechanical Engineering at the Technical University of Berlin, Germany in 1989. Dr. Wallrapp is currently a Professor in the Department of Precision and Micro Engineering, Muenchen University of Applied Science, Munich, Germany. His research interests are mechanism analysis and design, robotics, and bio-mechanics. Sung-Soo Kim received a Ph.D. degree in Mechanical Engineering from the University of Iowa in 1988. Dr. Kim is currently a Professor in the Department of Mechatronics Engineering at Chungnam National University in Daejeon, Korea. His research interests are real-time multibody formulation and its application to the automotive systems and military robot systems.     

Wetting characteristics of a water droplet on solid surfaces with various pillar surface fractions under different conditions

A numerical study was carried out using a molecular dynamics program to examine the wetting characteristics of nano-sized water droplets on surfaces with various pillar surface fractions under different conditions. Square-shaped pillars had surface fractions that increased from 11.1 % to 69.4 %. The pillars had 4 different heights and 3 different surface energies. When the pillar surface fraction changed, the contact angle of a water droplet also changed due to the attraction between the droplet and the pillar surface or the inner attraction of the water molecules. The pillar height also has different effects on the water droplet depending on the magnitude of surface energy.     

Ultra-sensitive thermal conductance measurement of one-dimensional nanostructures enhanced by differential bridge

Thermal conductivity of one-dimensional nanostructures, such as nanowires, nanotubes, and polymer chains, is of significant interest for understanding nanoscale thermal transport phenomena as well as for practical applications in nanoelectronics, energy conversion, and thermal management. Various techniques have been developed during the past decade for measuring this fundamental quantity at the individual nanostructure level. However, the sensitivity of these techniques is generally limited to 1 × 10(-9) W∕K, which is inadequate for small diameter nanostructures that potentially possess thermal conductance ranging between 10(-11) and 10(-10) W∕K. In this paper, we demonstrate an experimental technique which is capable of measuring thermal conductance of ～10(-11) W∕K. The improved sensitivity is achieved by using an on-chip Wheatstone bridge circuit that overcomes several instrumentation issues. It provides a more effective method of characterizing the thermal properties of smaller and less conductive one-dimensional nanostructures. The best sensitivity experimentally achieved experienced a noise equivalent temperature below 0.5 mK and a minimum conductance measurement of 1 × 10(-11) W∕K. Measuring the temperature fluctuation of both the four-point and bridge measurements over a 4 h time period shows a reduction in measured temperature fluctuation from 100 mK to 0.6 mK. Measurement of a 15 nm Ge nanowire and background conductance signal with no wire present demonstrates the increased sensitivity of the bridge method over the traditional four-point I-V measurement. This ultra-sensitive measurement platform allows for thermal measurements of materials at new size scales and will improve our understanding of thermal transport in nanoscale structures.     

Adaptive control and stability analysis of nonlinear crane systems with perturbation

This paper presents an adaptive control approach using a model matching technique for 3-DOF nonlinear crane systems. The proposed control is linearly composed of two control frameworks: nominal PD control and corrective control. A nonlinear crane model is approximated by means of feedback linearization to design nominal PD control avoiding perturbation. We propose corrective control to compensate system error feasibly occurring due to perturbation, which is derived by using Lyapunov stability theory with bound of perturbation. Additionally, we achieve stability analysis for the proposed crane control system and analytically derive sufficient stability condition with respect to its perturbation. Numerical simulation is accomplished to evaluate our proposed control and demonstrate its reliability and superiority compared to traditional control method.     

Evaluation of structural reliability of mems device in digital video disk systems

In this paper, we describe the reliability evaluation for MEMS devices, especially designed tbr DVD(Digital Video Disk) application. These MEMS devices are fabricated as a mirror plane (shutter plane) used in DVD data picking up. This micromachined annular shutter mirror (ASM) acts as an adjusting means of the numerical aperture. The electrostatic force can drive the upper plane up and down for focusing or defocusing of incident laser beam to the selected recording plane. So we need to evaluate the micromechanical properties of thin film structural materials to ensure the reliability of those MEMS devices. For those, we perfl)rm the fatigue tests onto the devices in the conditions of much accelerated than those of normal driving. The applied electrostatic force can induce the change of the thin film properties, and those are observed by direct and indirect methods (XRD and electrical system). And then, we compare the fatigue effects with electrical, optical data from the intentionally-fatigue-applied specimen and as-fabricated one under accelerated conditions. Consequently, we can estimate the structural reliability and will provide the effective suggestion data for the fabrication of stable mirror material before commercialization.     

A study of creep-fatigue life prediction using an artificial neural network

In this study, using AISI 316 stainless steel, creep-fatigue tests were carried out under various test conditions (different total strain ranges and hold times) to verify the applicability of the artificial neural network method to creep-fatigue life prediction. Life prediction was also made by the modified Coffin-Manson method and the modified Ostegren method using 21 data points out of a total 27 experimental data points. The six verification data points were carefully chosen for the purpose of evaluating the predictability of each method. The predicted lives were compared with the experimental results and the following conclusions were obtained within the scope of this study. While the creep-fatigue life prediction by the modified Coffin-Manson method and the modified Ostegren method had average errors of 35.8% and 47.7% respectively, the artificial neural network method had only 15.6%. As a result, the artificial neural network method with the adaptive learning rate was found to be far more accurate and effective than any of the others. The validity of the artificial neural network method for life prediction checked with the six verification data points also proved to be very satisfactory.     

Experimental study on the energy flow analysis of underwater vibration for the reinforced cylindrical structure

Energy flow analysis (EFA) can be used effectively to predict structural vibration in the medium-to-high frequency ranges. In this study, the energy flow finite element method (EFFEM), based on EFA, was used to predict the vibrations of a reinforced cylindrical structure in water. The predicted results of the vibrational energy density for the structure were compared with corresponding experimental results. The structure was divided into several subsystems in the experiment, with several accelerometers attached to each subsystem. The input power excited into the experimental structure was measured using an impedance-head adhered to an exciter. Measured input power was used to predict vibration of the reinforced cylindrical structure by EFFEM in water for comparing experimental and numerical results. A comparison between the experimental and predicted results for the vibrational energy density showed that EFFEM was an effective tool for predicting structural vibration.     

Real-time quality monitoring and control system using an integrated cost effective support vector machine

The quality monitoring and control (QMC) has been an essential process in the manufacturing industries. With the advancements in data analytics, machine-learning based QMC has become popular in various manufacturing industries. At the same time, the cost effectiveness (CE) of the QMC is perceived as a main decision criterion that explicitly accounts for inspection efforts and has a direct relationship with the QMC capability. In this paper, the cost-effective support vector machine (CESVM)-based automated QMC system (QMCS) is proposed. Unlike existing models, the proposed CESVM explicitly incorporates inspection-related expenses and error types in the SVM algorithm. The proposed automated QMCS is verified and validated using an automotive door-trim manufacturing process. Next, we perform a design of experiment to assess the sensitivity analysis of the proposed framework. The proposed model is found to be effective and could be viewed as an alternative or complementary tool for the traditional quality inspection system.

     

A study on 65 % potential efficiency of the gas turbine combined cycle

Journal of Mechanical Science and Technology - This study investigates the possibility of achieving 65 % efficiency in a gas turbine combined cycle. Several options to realize it were compared. A...     

Fabrication of nanoporous silicon carbide fibres by thermal treatment

Abstract

Nanoporous silicon carbide fibres were prepared by curing and heat treatment of melt spun polycarbosilane (PCS) fibres. During the curing process, green PCS fibres were thermally oxidised at the temperature between 180 and 220°C and time between 2 and 10 h for cross-linking among the molecule chains in the PCS and controlling the oxygen concentration and distribution. After thermal oxidation, fibres were heat-treated between 1200 and 1600°C for the conversion to SiC phase. About 15–20 wt-% of oxygen was analysed after heat treatment at 1200°C and it can be possible to pyrolyse without melting or deformation of fibre. At a temperature above 1400°C, the uniform distribution of nanopores was observed on the fibre surface, and the size of pores was increased with curing and heating condition. This type of nanoporous SiC fibre is expected to be a good candidate for high temperature catalyst or catalytic supports.