Tribochemical reaction of hydrogenated diamond-like carbon films: a clue to understand the environmental dependence

Tribological behavior of hydrogenated diamond-like carbon (DLC) films and Si incorporated DLC (Si-DLC) films deposited on Si (100) wafer by r.f.-plasma assisted chemical vapor deposition were investigated by ball-on-disk type tribometry in various environments. The friction tests were performed in ambient air of relative humidity ranging from 0% to 90% or dry oxygen environment. We focused on the tribochemical reactions by analyzing chemical composition, chemical bond structure and agglomerated shape of the debris. High and unstable friction behavior was observed in both humid air and dry oxygen environments. In these environments, Auger spectrum analysis showed that the debris contained large amounts of Fe. Significant incorporation of Fe in the debris resulted from the wear of the steel ball, which might be enhanced by the surface oxidation of the ball. These results show that the humidity dependence of friction coefficient is not an inherent tribological property of DLC films but results from the surface reaction of the steel ball in humid environments. Two possible reasons for the Fe rich debris affecting the friction behavior are presented. Reduced dependence of the friction coefficient on the relative humidity observed for Si-DLC films is discussed in terms of the two possible reasons.     

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.     

Internet-based Real-time obstacle avoidance of a mobile robot

In this research, a remote control system has been developed and implemented, which combines autonomous obstacle avoidance in real-time with force-reflective tele-operation. A teleoperated mobile robot is controlled by a local two-degrees-of-freedom force-reflective joystick that a human operator holds while he is monitoring the screen. In the system, the force-reflective joystick transforms the relation between a mobile robot and the environment to the operator as a virtual force which is generated in the form of a new collision vector and reflected to the operator. This reflected force makes the tele-operation of a mobile robot safe from collision in an uncertain and obstacle-cluttered remote environment. A mobile robot controlled by a local operator usually takes pictures of remote environments and sends the images back to the operator over the Internet. Because of limitations of communication bandwidth and the narrow viewangles of the camera, the operator cannot observe shadow regions and curved spaces frequently. To overcome this problem, a new form of virtual force is generated along the collision vector according to both distance and approaching velocity between an obstacle and the mobile robot, which is obtained from ultrasonic sensors. This virtual force is transferred back to the two-degrees-of-freedom master joystick over the Internet to enable a human operator to feel the geometrical relation between the mobile robot and the obstacle. It is demonstrated by experiments that this haptic reflection improves the performance of a tele-operated mobile robot significantly.     

Nitride-based high power flip-chip near-UV leds with reflective submount

Nitride-based high power flip-chip near-ultraviolet (UV) light emitting diodes (LEDs) with a reflective mirror are fabricated by depositing Al onto a Si submount. It is demonstrated that the Al layer coated onto a Si submount can effectively reflect downward emitting photons for flip-chip LEDs. Although the operation voltage of the proposed LEDs is slightly increased, it is found that the output power is at least 30% higher than that of conventional LEDs. It is also found that flip-chip near-UV LEDs are more reliable than conventional non-flip-chip LEDs     

Effect of overload on fatigue crack retardation of aerospace Al-alloy laser welds using crack-tip plasticity analysis

Investigations on fatigue crack growth retardation due to single tensile and periodic multiple over load in strength undermatched laser beam welded 3.2 mm thick aerospace grade aluminium alloy 2139-T8 sheets are conducted. The effect of overload on the fatigue crack propagation behaviours of the homogenous base metal and welded panels (200 mm wide, centre cracked) was compared using experimental and FE analysis methods. The effective crack tip plasticity has been determined in homogeneous M(T) specimens using Irwin’s method and in both homogeneous and laser welded specimen by calculating crack tip plastic strain using FE analysis for single tensile overload. The crack retardation due to the overload in welded specimens is described by the Wheeler Model. The crack tip plastic zone size in the welded specimen was determined by FE analysis using maximum plastic zone extension at the mid sheet thickness. The results show that the Wheeler Model can be implemented to the highly heterogeneous undermatched weld to describe the crack retardation in fatigue following single tensile overload. Fatigue crack growth retardation due to single overload is found to be larger than the base metal. However, after periodic multiple overload, shorter crack retardation has occurred for undermatched welds than the base metal.     

Advanced compensation technologies for large‐sized UHD OLED TVs

In this paper, we present novel organic light‐emitting diode (OLED) display panel compensation technologies for large‐sized ultra‐high‐definition OLED TVs considering variations of threshold voltage, mobility, channel size, OLED efficiency, and OLED uniformity. Using these technologies, we have successfully launched 55‐, 65‐ and 77‐in. ultra‐high‐definition OLED TVs.     

Efficient location and allocation strategies for undesirable facilities considering their fundamental properties

The phrase “not in my backyard” (NIMBY) refers to the well-known social phenomena in which residents oppose the construction or location of undesirable facilities near their homes. Examples of such facilities include electric transmission lines, recycling centers and crematoria. Due to the opposition typically encountered in constructing an undesirable facility, the facility planner should understand the nature of the NIMBY phenomena and consider it as a key factor in determining facility location. We examine the characteristics of NIMBY phenomena and suggest two alternative mathematical optimization models with the objective of minimizing the total degree of NIMBY sentiments. Genetic algorithms are proposed to solve our linear and nonlinear integer programs. The results obtained via genetic algorithms for our linear integer programs are compared with those of CPLEX to evaluate their performance. The nonlinear programs are tested with various allocation policies. Sensitivity analysis is conducted about several system parameters.     

Spatiotemporal bag-of-features for early wildfire smoke detection

Wildfire smoke detection is particularly important for early warning systems, because smoke usually rises before flames arise. Therefore, this paper presents an automatic wildfire smoke detection method using computer vision and pattern recognition techniques. First, candidate blocks are identified using key-frame differences and nonparametric smoke color models to detect smoke-colored moving objects. Subsequently, three-dimensional spatiotemporal volumes are built by combining the candidate blocks in the current key-frame with the corresponding blocks in previous frames. A histogram of oriented gradient (HOG) is extracted, and a histogram of oriented optical flow (HOOF) is extracted as a temporal feature based on the fact that the direction of smoke diffusion is upward owing to thermal convection. From spatiotemporal features of training data, a visual codebook and a bag-of-features (BoF) histogram are generated using our proposed weighting scheme. For smoke verification, a random forest classifier is built during the training phase using the BoF histogram. The random forest with the BoF histogram can increase the detection accuracy performance when compared with related methods and allow smoke detection to be carried out in near real time.     

Failure analysis of R-regions of CFRP hat-shaped structure under pull-off load

Journal of Mechanical Science and Technology - As a kind of typical structure, the hat-shaped structure (HSS) is widely used in carbon fiber reinforced plastics (CFRP) aircraft parts. In this work,...