Showing papers in "International Journal of Precision Engineering and Manufacturing in 2010"

A survey of climbing robots: Locomotion and adhesion

Abstract: Climbing robots are robotic systems to move over 2D or complex 3D environments such as walls, ceilings, roofs, and geometric structures and to conduct various tasks. They will not only replace human workers for carrying out risky tasks in hazardous environments, but also increase operational efficiency by eliminating the costly erection of scaffolding and staffing costs. Climbing robots have special characteristics and the ability to adhere to different types of 2D or 3D surfaces, move around, and carry appropriate tools and sensors to work, while self-sustaining their bodies. Therefore, the most significant criterion for designing a climbing robot is to equip it with an appropriate locomotive and adhesion mechanism for adapting to the given environmental requirements. In this paper, a classification of climbing robots and proper examples with a brief outline are presented with considerations of the locomotive and adhesion mechanisms. Also, a list of climbing robots is provided with respect to fields of application that range from cleaning tasks in the construction industry to human care systems in the biomedical service industry.

Tool wear, chip formation and workpiece surface issues in CBN hard turning: A review

Abstract: Steel parts that carry critical loads in everything from automotive drive trains and jet engines to industrial bearings and metal-forming machinery are normally produced by a series of processes, including time-consuming and costly grinding and polishing operations. Due to the advent of super-hard materials such as polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning has become an attractive alternative to grinding for steel parts. The potential of hard turning to eliminate the costs associated with additional finishing processes in conventional machining is appealing to industry. The objective of this paper, is to survey the recent research progress in hard turning with CBN tools in regard of tool wear, surface issues and chip formation. A significant pool of CBN turning studies has been surveyed in an attempt to achieve better understanding of tool wear, chip formation, surface finish, white layer formation, micro-hardness variation and residual stress on the basis of varying CBN content, binder, tool edge geometry, cooling methods and cutting parameters. Further important modeling techniques based on finite element, soft computing and other mathematical approaches used in CBN turning are reviewed. In conclusion, a summary of the CBN turning and modeling techniques is outlined and the scope of future work is presented.

Surface texturing by micro ECM for friction reduction

Abstract: Surface texturing with micro-dimples is a known method for friction reduction under lubricated sliding contact, and various machining techniques have been researched and developed in order to fabricate micro-dimple patterns. However, previous fabrication methods possess several problems, such as causing thermal damage on the workpiece or limiting the available workpiece geometry. In micro ECM, micro features can be machined without any resulting thermal or mechanical damage. From this perspective, micro ECM has certain advantages over surface texturing. Also, micro ECM is applicable to non-planar workpieces. In this research study, micro ECM with microsecond pulses was applied in order to fabricate a micro-dimple pattern. The machining characteristics were investigated in fabricating micro dimples on AISI 440C specimen. On the basis of the experimental results, a O 300 μm dimple pattern was successively produced on the AISI 440C specimen. A friction test on the textured specimen was performed and compared with a non-textured specimen. The enhancement of frictional performance was successfully demonstrated experimentally.

Tribological effects of fullerene (C60) nanoparticles added in mineral lubricants according to its viscosity

Abstract: In this study, the tribological behaviors of fullerene nanoparticles-added mineral oil were investigated as a function of viscosities (e.g., 12, 30, 55, 96 and 145 mm2/s). Extreme pressure and anti-wear properties were evaluated using a four-ball tester, respectively. The lubrication tests were performed with a disk-on-disk tester for different normal loads. Tribological properties were evaluated by measuring friction surface temperature and the friction coefficient, and interpreted in terms of the Stribeck curve. We note that the weld points of the raw- and nano-oil increased as the oil viscosity increased and weld points for all nano-oil were higher than those of raw oil. Also the wear scar diameters of the raw- and nano-oil decreased as the oil viscosity increased and wear scar diameters for all nano-oil were less than those of raw oil. Also, we have found that the difference of friction coefficient between raw oil and nano-oil was outstanding when the viscosity of raw oil was low and the normal load is high. Our results indicate that the addition of fullerene additives in lubricant was more effective when the viscosity of raw oil was low under the higher normal load conditions.

Optimization of conformal cooling channels with array of baffles for plastic injection mold

Abstract: Cooling system has an important role in the injection molding process in terms of not only productivity and quality, but also mold-making cost. In this paper, a conformal cooling channel with an array of baffles is proposed for obtaining uniform cooling over the entire free-form surface of molded parts. A new algorithm for calculating temperature distribution through molding thickness, mold surface temperature and cooling time was presented. The relation among cooling channels’ configuration, process parameters, mold material, molding thickness and temperature distribution in the mold for a given polymer is expressed by a system of approximate equations. This relation was established by the design of experiment and response surface methodology based on an adequate physical-mathematical model, finite difference method and numerical simulation. By applying this approximate mathematical relation, the optimization process for obtaining target mold temperature, uniform temperature distribution and minimizing the cooling time becomes more effective. Two case studies were carried out to test and validate the proposed method. The results show that present approach improves the cooling performance and facilitates the mold design process in comparison to the trial-and-error simulation-based method.

A review of focused ion beam sputtering

Abstract: This paper reviews the applications of focused ion beam (FIB) sputtering for micro/nano fabrication. Basic principles of FIB were briefly discussed, and then empirical and fundamental models for sputtering yield, material removal rate, and surface roughness were presented and compared. The empirical models were more useful for application compared to fundamental models. Fabrication of various micro and nano structures was discussed. Trimmed atomic force microscope (AFM) tips were tested in measurement and imaging of high aspect ratio nanopillars where higher accuracy and clarity were observed. Micromilling tool fabricated using FIB sputtering was used to machine microchannels. Slicing and dwell time control approaches on FIB sputtering were presented for the fabrication of three dimensional microcavities. The first approach is preferred for practical applications. The maximum aspect ratio of 13:1 of the microstructures was achieved. The minimum size of the nanopore was in the range of 2–10 μm. Cavities of microgear of 70 μm outside diameter were sputtered with submicrometer accuracy and 2–5 nm average surface roughness. The microcavities were then filled with polymer in a subsequent micromodling process. The replicated microcomponents were inspected with scanning electron microscope where faithful duplication of accuracy and surface texture of the cavity was observed.

Bubble actuation by electrowetting-on-dielectric (EWOD) and its applications: A review

Abstract: This paper reviews the principles, operations, and applications of bubble-based electrowetting-on-dielectric (EWOD). EWOD has proved to be an efficient tool in digital microfluidics that employs discrete droplets, and various applications that use the principles of EWOD have been developed from lab-on-a-chip to optical systems. Similar to its use with droplets, EWOD can also be applied to gaseous bubbles. This review begins with a discussion of the principles of EWOD for a bubble on an electrode covered with a hydrophobic dielectric layer. It then addresses EWOD actuation and the transportation of a bubble in an aqueous medium, along with a physical explanation of bubble motion. The operation of EWOD is then extended to the on-chip creation/elimination and splitting of bubbles. In particular, micro-mixers and pumps are discussed as potential applications of these operations. Unlike droplets, bubbles can be easily oscillated by external excitation, which provides additional functionalities. By integrating EWOD with external excitation, a number of new advanced applications are introduced, including the capture/separation of particles and the propulsion of objects. In these advanced operations, cavitational microstreaming flows and acoustic radiation forces are mainly responsible for the physical mechanisms. This paper also discusses these advanced operations along with their underlying physics. It is expected that in addition to bubble oscillation, other bubble actuation modes will create new functionalities and new potential applications.

Diamond face grinding of WC-Co composite with spark assistance: Experimental study and parameter optimization

Abstract: Electro-discharge machining (EDM) characteristics of tungsten carbide-cobalt composite are accompanied by a number of problems such as the presence of resolidified layer, large tool wear rate and thermal cracks. Use of combination of conventional grinding and EDM (a new hybrid feature) has potential to overcome these problems. This article presents the face grinding of tungsten carbide-cobalt composite (WC-Co) with electrical spark discharge incorporated within face of wheel and flat surface of cylindrical workpiece. A face grinding setup for electro- discharge diamond grinding (EDDG) process is developed. The effect of input parameters such as wheel speed, current, pulse on-time and duty factor on output parameters such as material removal rate (MRR), wheel wear rate (WWR) and average surface roughness (ASR), are investigated. The present study shows that MRR increases with increase in current and wheel speed while it decreases with increase in pulse on-time for higher pulse on-time (above 100 µs). The most significant factor has been found as wheel speed affecting the robustness of electro- discharge diamond face grinding (EDDFG) process.

A review of adhesion and friction models for gecko feet

Abstract: The attachment pads of geckos exhibit the most versatile and effective adhesive known in nature. Their fibrillar structure is the primary source of high adhesion and their hierarchical structure produces the adhesion enhancement by giving the gecko the adaptability to create a large real area of contact with surfaces. Although geckos are capable of producing large adhesive forces, they retain the ability to remove their feet from an attachment surface at will. Detachment is achieved by a peeling motion of the gecko’s feet from a surface. During the last few years, many researches have been conducted to develop the theoretical models that explain the gecko to adhere and detach from surfaces at will, including micro/macroscopic gecko adhesion, friction and peeling models for gecko hierarchical fibrillar structure contacting to rough surface. This review describes the progress in the modeling filed for gecko adhesion, friction and peeling, and discussed the future issues for gecko modeling.

A review on the preload technology of the rolling bearing for the spindle of machine tools

Abstract: The performance of the spindle system and bearings in a machine tool is largely influenced by the preload applied to bearings. Therefore, it is a very important issue to determine a proper preload in bearings and apply it to bearings for satisfying the performance required in bearings according to its operation conditions. This study performed a review on the preload technologies through classifying these technologies into three categories; a preload configuration technology that properly determines the preload for optimizing the performance of bearings, a preload application technology that applies the determined preload to bearings during the operation of a spindle system as a reliable way, and a preload measurement technology that verifies the preload applied to an actual spindle system.

Dynamic Modeling and Analysis of Drum-type Washing Machine

Abstract: In this study, dynamic analysis of a drum-type washing machine has been conducted using a simplified dynamic model considering gyroscopic effects. Its mathematical model has 6-degree of freedom in the complex coordinate space into which is transformed real coordinate space to understand the whirling motion easily. Dynamic analysis is performed using MATLAB. For the purpose of numerical verification, the results for unbalance response are presented and compared with the experimental vibration test. The mathematical model proves quite good accuracy in predicting dynamic characteristics which could be changed by the parameters of design variable and can reduce design cycle shortly. Dynamic characteristics of a washing machine are shown through shape and directivity index (SDI), whirling orbits, rigid and flexible mode of a drum type washing machine during drum run-up. In designing drum type of washing machine, it is efficient than finite element method to analyze behaviors of drum and tub.

Assessment of running safety of railway vehicles using multibody dynamics

Abstract: An analysis model for multibody systems was developed to assess the running safety of the Saemaeul train passing through curves. Sensitivity analyses based on the variation of parameters related to derailments were conducted using this model and the ADAMS/Rail software package. These analyses showed that the derailment coefficient and the unload ratio of the right wheel were higher than that of the left wheel at low speed, but lower at high speed. The derailment coefficient and the unload ratio increased as the curve radius decreased. The derailment coefficient increased but there was no change in the unload ratio as the length of transition curves increased. The derailment coefficient and the unload rate increased in proportion to the increase in track cant.

Evaluation of cellulose electro-active paper made by tape casting and zone stretching methods

Abstract: Cellulose has been discovered as a smart material that can be used as sensor and actuator material. In this paper, cellulose smart material termed as electro-active paper (EAPap) is prepared by an automated process that includes tape casting and zone stretching. To evaluate characteristics of the EAPap, its Young’s modulus and piezoelectric charge constant are measured depending on the orientation angle, in comparison with the manually fabricated EAPap results. The zone stretching method can effectively align the cellulose fibers in the EAPap so as to improve its Young’s modulus as well as piezoelectric charge constant. The 0 degree oriented sample shows its maximum Young’s modulus and the 45 degree oriented sample exhibits the maximum piezoelectric charge constant. This 45 degree is associated with its shear piezoelectricity. The actuator performance of EAPap is evaluated by measuring its bending displacement depending on the orientation angle and the excitation voltage. The 45 degree oriented sample exhibits the maximum bending displacement. Details of the material preparation, the automation process, characterization and the actuator performance are addressed. This automated process that includes tape casting and zone stretching is suitable for mass production of the EAPap.

Position and orientation detection of capsule endoscopes in spiral motion

Abstract: In this paper, a position and orientation detection method for the capsule endoscopes devised to move through the human digestive organs in spiral motion, is introduced. The capsule is equipped with internal magnets and flexible threads on their outer shell. It is forced to rotate by an external rotating magnetic field that produces a spiral motion. As the external magnetic field is generated by rotating a permanent magnet, the 3-axes Cartesian coordinate position and 3-axes orientation of the capsule endoscopes can be measured by using only 3 hall-effect sensors orthogonally installed inside the capsule. However, in this study, an additional hall-effect sensor is employed along the rotating axis at a symmetrical position inside the capsule body to enhance measurement accuracy. In this way, the largest position detection error appearing along the rotating axis of the permanent magnet could be reduced to less than 15mm, when the relative position of the capsule endoscope to the permanent magnet is changed from 0mm to 50mm in the X-direction, from −50mm to +50mm in the Y-direction and from 200mm to 300mm in the Z-direction. The maximum error of the orientation detection appearing in the pitching direction ranged between −4° and +15°.

Comparative study of conventional and micro WEDM based on machining of meso/micro Sized Spur Gear

Abstract: This paper discusses the comparison of micro machining process using conventional and micro wire electrical discharge machining (WEDM) for fabrication of miniaturized components. Seventeen toothed miniaturized spur gear of 3.5 and 1.2 mm outside diameter were fabricated by conventional and micro WEDM respectively. The process parameters for both conventional and micro WEDM were optimized by preliminary experiments and analysis. The gears were investigated for the quality of surface finish and dimensional accuracy which were used as the criteria for the process evaluation. An average surface roughness (Ra) of 50 nm and dimensional accuracy of 0.1–1 µm were achieved in micro WEDM. Whenever applied conventional WEDM for meso/micro fabrication, a Ra surface roughness of 1.8 µm and dimensional accuracy of 2–3 µm were achieved. However, this level of surface roughness and dimensional accuracy are acceptable in many applications of micro engineering. A window of conventional WEDM consisting of low energy discharge parameters is identified for micromachining.

Sensitivity control of a MR-damper semi-active suspension

Abstract: In this paper, numerical aspects of a sensitivity control for the semi-active suspension system with a magnetorheological (MR) damper are investigated. A 2-dof quarter-car model together with a 6th order polynomial model for the MR damper are considered. For the purpose of suppressing the vertical acceleration of the sprung-mass, the square of the vertical acceleration is defined as a cost function and the current input to the MR damper is adjusted in the fashion that the current is updated in the negative gradient of the cost function. Also, for improving the ride comfort, a weighted absolute velocity of the sprung-mass is added to the control law. The implementation of the proposed algorithm requires only the measurement of the relative displacement of the suspension deflection. The local stability of the equilibrium point of the closed loop nonlinear system is proved by investigating the eigenvalues of the linearized one. Through simulations, the passive suspension, the skyhook control, and the proposed sensitivity control are compared.

Investigation of Short Pulse Electrochemical Machining for Groove Process on Ni-Ti Shape Memory Alloy

Abstract: Ni-Ti, a shape memory alloy (SMA), can recover from deformation to its initial shape when heated. With using this effect, Ni-Ti SMA is applied for several industries such as a medical industry, an aerospace, electrical application on a part of micro structure. The Ni-Ti alloy used for SMA is composed of approximately 56% nickel and 44% titanium. With this composition, Ni-Ti alloy cannot be machined efficiently using traditional machining tools and methods such as the lathe, milling, and drilling because it shares the poor heat dispersion characteristics of titanium. Thus, Ti-Ni SMA should be machined using non-traditional machining methods. Electrochemical micro machining (EMM) is one form of non-traditional machining that can be applied to Ni-Ti SMA. As an anodic dissolution process, EMM allows the machining of complex shapes in Ti-Ni SMA without the generation of heat and without causing tool wear during the machining process. In this study, through the experiment that making the micro-groove, the characteristic of short pulse electrochemical machining (SPECM) process is accomplished to Ni-Ti SMA. And an evaluation of various machining factors for Ni-Ti SMA is also performed, through the substitution of different types of power source and machining time, and through simulation of the material removal rate (MRR). The experimental and simulation results are analyzed and compared.

Development of a 3-axis desktop milling machine and a CNC system using advanced modern control algorithms

Abstract: In this paper, we introduce a desktop-size 3-axis milling machine and a CNC system which was developed to operate the 3-axis milling machine. The 3-axis milling machine has a mini-desktop size of 200×300×200 mm3 and its cutting volume is 20×20×20 mm3. The vertically installed XY stage is driven by voice-coil motors, and for the zaxis, a magnetically preloaded air bearing and a linear motor are used. The air spindle runs at up to 160,000 rpm. The gravity force is acting on the y-direction, so a weight balancer using an air bearing cylinder is installed to cancel out the gravity force acting on the XY stage in the y-direction. The CNC system designed for the 3-axis milling machine consists of two parts. The one is a graphical user interface program which runs under Microsoft Windows and the other is a DSP program which is implemented on a DSP board with TI TMS320C6701 chips. A G-code interpreter is included in the CNC system which can interpret and interpolate a basic set of G-codes and M-codes in real-time. To improve the performance of servo control loop in the CNC system beyond the traditional PID-type control, several modern control algorithms have been tested including H∞ control, input shaping control, disturbance observer and cross-coupled control on the 3-axis milling machine. Experimental results show the effectiveness and drawbacks of each control scheme when they are applied to the 3-axis desktop milling machine.

Fracture behaviour of adhesively-bonded composite materials under impact loading

Abstract: In this paper, a polymeric unidirectional carbon-fibre epoxy-resin composite is both experimentally and numerically investigated to study the nonlinear material behavior of impacted DCB (Double Cantilever Beam) specimens. For the impact analysis, the load and the displacement applied from pin onto end block as well as the crack energy release rate are measured and compared with the finite element analysis results. The energy release rate is a critical measure of the resistance to crack propagation, which can be estimated by the force and displacement at the crack tip. It is found that the energy release rate measured from impact tests on the specimens is well predicted by the suggested finite element model in this study.

Enhanced SLAM for a mobile robot using extended Kalman Filter and neural networks

Abstract: This paper presents a Hybrid filter based Simultaneous Localization and Mapping (SLAM) scheme for a mobile robot to compensate for the Extended Kalman Filter (EKF) based SLAM errors inherently caused by its linearization process. The proposed Hybrid filter consists of a Radial Basis Function (RBF) and EKF which is a milestone for SLAM applications. A mobile robot autonomously explores the environment by interpreting the scene, building an appropriate map, and localizing itself relative to this map. A probabilistic approach has dominated the solution to the SLAM problem, which is a fundamental requirement for mobile robot navigation. The proposed approach, based on a Hybrid filter, has some advantages in handling a robotic system with nonlinear dynamics because of the learning property of the neural networks. The simulation and experimental results show the effectiveness of the proposed algorithm comparing with an EKF based SLAM and Multi Layer Perceptron (MLP) method.

Manufacture of an injection mould with rapid and uniform cooling characteristics for the fan parts using a DMT process

Abstract: The aims of the present study is to manufacture an injection mould with a pair of conformal cooling channels in each blade of the mould for a plastic fan part via laser-aided direct metal tooling (DMT) process to achieve both rapid and uniform cooling characteristics. The features of the design and the manufacturing process for the injection mould as well as the characteristics of the manufactured mould were discussed. Three-dimensional injection moulding analyses were performed to obtain a proper design of the conformal cooling channels. Injection moulding experiments were carried out to investigate the practical applicability of the fabricated mould and the influence of the cooling time on the qualities of the moulded product. The results of the experiments showed that a plastic fan part with superior qualities can be fabricated from the designed mould when the cooling time is 13 s. The efficiency of the designed mould was examined through a comparison of the product from the newly designed mould and that from a previously designed mould with linear cooling channels in terms of product qualities as well as the cooling and cycle times. The results of the comparison showed that the newly designed mould can remarkably reduce the positional error distributions and the eccentricity of the moulded product. In addition, it was shown that the cooling and cycle times of the designed mould can be shortened to 35.0 % and 25.7 % of those of the previously designed mould, respectively.

Study on precision grinding of screw rotors using CBN wheel

Abstract: With increasing demands for high-speed and high-precision machining technology, CBN shape grinding is an effective means in the field of precision machining for screw rotors. Aiming at the high precision machining of screw rotors, a mathematical model for the axial profiles of the CBN wheel for machining screw rotors is developed based on theory of gear engagement. Small electroplated CBN wheel is firstly used to grinding screw rotors. Taking the backlash of screw rotors and the coating thickness of CBN layer into consideration, the modification of the base body of the wheel shape is introduced into the design of CBN wheel. For reducing the tooth profile errors of screw rotors induced by mounting errors and wears of CBN wheel, a mathematical model of the error analyses is established and the influence curves of the profile errors affected by mounting errors and radius error of grinding wheel are proposed. The electroplated CBN wheels for the screw rotors are made to verify the validity and effectiveness of the presented method and the machining experiments were performed. Results of this study reveals that the method proposed in this paper can be used as the precision grinding of screw rotors.

A study on copper micromachining using microorganisms

Abstract: Biomachining using microorganisms to remove metal from a workpiece is an alternative technology for machining processes that may have environmental advantages. Studies of the characteristics of micromachining using microorganisms such as Acidithiobacillus ferrooxidans will explore and improve the capabilities of this alternative machining process. The objective of this study is to investigate the surface roughness and the material removal rate characteristics in biomachining of copper for various machining times. We present the biomachining of copper using A. ferrooxidans, including bacterial culturing and workpiece preparation, and a comparison of the surface roughness, visible surface appearance of the workpiece, and material removal rate before and after biomachining process.

Beam vibration control using cellulose-based Electro-Active Paper sensor

Abstract: Cellulose based Electro-Active Paper (EAPap) has recently shown a great potential as an environment-friendly smart material due to its biodegradability, biocompatibility and flexibility. Lots of studies have been conducted to investigate the basic smart characteristics of EAPap, but its application has not yet developed well. In this paper, the possibility of cellulose-based Electro-Active Paper (EAPap) as a piezoelectric sensor was investigated by the vibration control of the cantilevered beam. The EAPap sample was attached at the root of the cantilevered beam and used as a vibration sensor. The piezoceramic patch was also attached at the root of the beam and played as an actuator. The voltage output of EAPap showed exact dynamic characteristics of the cantilevered beam. The frequency bandwidth and quality factor of EAPap were similar to those of piezoceramic patch, which results EAPap has similar sensing capability of piezoceramic patch. To find the application of EAPap sensor, beam vibration control was performed. EAPap sensor output was considered as a position error of the cantilevered beam and a simple PID controller was designed to suppress the vibration of the beam. The EAPap sensor output provided clear time response of the beam. The controlled system showed good vibration control performance of the beam. The results provided that the piezoelectric characteristic of EAPap has a great potential as a sensor and also as a new smart material.

A study on deburring of magnesium alloy plate by magnetic abrasive polishing

Abstract: Drilling is one of the most important machining operations in manufacture process. When drilling process is applied, unexpected burrs will be formed on the surface of workpiece. Even a small burr can cause unwanted problems, resulting in low quality products. In order to get better drilled parts, it is very important to know characteristics of burr formation and to remove the burr from the drilled surface with machining process. In this study, magnetic abrasive polishing (MAP) was used to research the deburring factors of magnesium alloy. Moreover, design of experiments was performed to evaluate parameters’ effect on the MAP process. As a result, it was seen that the MAP was useful to remove the burrs on the workpiece without damage from its original surface.

Development and evaluation of tool dynamometer for measuring high frequency cutting forces in micro milling

Abstract: A tool dynamometer is developed for measuring the high frequency cutting forces, and evaluated in micro milling of aluminum 6061-T6 using a tungsten carbide (WC) micro end mill. To improve the accuracy and productivity of the machining process, it is essential to monitor and control the machining process by measuring cutting forces. In order to improve the precision and quality of machined parts, high-speed machining with smaller micro tools is required, causing higher frequency cutting forces. The first natural frequency of tool dynamometers is high enough to precisely measure the high cutting forces. We investigate dynamic characteristics of the tool dynamometer theoretically and experimentally. The measurable frequency range of the developed tool dynamometer was higher than the commercial tool dynamometer, and the measured cutting force signals were not distorted at high-speed of above 60,000 rpm. The results showed that the developed dynamometer is able to measure the static and dynamic force components in high-speed micro milling.

Rapid surface reconstruction from a point cloud using the least-squares projection

Abstract: A new approach for the rapid and robust surface reconstruction from a point cloud is presented based on the distance field and the least-squares projection (LSP) algorithm. This novel approach works directly on the point cloud without any explicit or implicit surface reconstruction procedure. First, a coarse base polygonal model was created directly from the distance field for the given point cloud through the iso-surface extraction. After acquiring a rough base polygonal model, we obtain a quality polygonal model through the iterative refinement and least-squares projection which projects current working polygonal model onto the point cloud in a least-squares sense. The main contribution of this work is the robust and fast surface reconstruction from randomly scattered 3D points only without any further information. We demonstrate the validity and efficiency of this new approach through a number of application examples.

A Robust Control of Electro Hydrostatic Actuator Using the Adaptive Back-Stepping Scheme and Fuzzy Neural Networks

Abstract: In general, the position control of electro hydrostatic actuator(EHA) systems is difficult because of the large variation of the effective bulk modulus of the working fluid, which is due to the absence of a heat exchanger like a reservoir tank, the friction between the cylinder and piston, and the external disturbance force. Moreover, it is difficult to identify the values of the effective bulk modulus and friction. In this paper, the variation of the effective bulk modulus, friction, and external disturbance are considered as uncertainties of EHA systems. To solve the problems due to these system uncertainties, an adaptive back-stepping control scheme with fuzzy neural networks(FNNs) is proposed. The effectiveness of the adaptive back-stepping control(ABSC) system with FNNs was compared with those of the standard back-stepping control(BSC) system and the ABSC system through computer simulation.

Motor current prediction of a machine tool feed drive using a component-based simulation model

Abstract: In recent times, simulation techniques have been rapidly accepted by the machine tool industry. However, most existing simulation studies have focused on a particular machine tool and described an entire machine tool feed drive as a single combined system. This paper presents a method to accurately predict motor current (torque) behavior and acquire a more generalized and accurate dynamic simulation model for a machine tool feed drive. To improve the generality, a component-based approach is introduced. In this approach, the feed drive model is composed of subcomponent models, and each component mechanism is then independently modeled. In the developed model structure, the parameters of the subcomponent model can easily be determined by using product datasheets or simple parameter identification based on motor current measurements. To enhance the model accuracy in predicting the motor current, an improved friction model including time-dependent frictional characteristics and rolling contact conditions was introduced to the simulation. The performance of the developed dynamic simulation model is demonstrated through a comparison with real machine tool behavior.

Analysis of Silicon via Hole Drilling for Wafer Level Chip Stacking by UV Laser

Abstract: For stacking wafers/dies, through-silicon-vias (TSVs) need to be created for electrical connection of each wafer/die, which enables better electrical characteristics and less footprints. And for via hole processing, chemical methods such as DRIE (Deep Reactive Ion Etching) are mostly used. These methods suffer the problems of slow processing speed, being environment-unfriendly and damage on the existing electric circuits due to high process temperature. Furthermore, masks are also needed. To find an alternative to the methods, researches on the laser drilling of via holes on silicon wafer are being conducted. This paper investigates the silicon via hole drilling process using laser beam. The percussion drilling method is used for this investigation. It is also examined how the laser parameters- laser power, pulse frequency, the number of laser pulses and the diameter of laser beam- have an influence on the drilling depth, the hole diameter and the quality of via holes. From these results, laser drilling process is optimized. The via hole made by UV laser on the crystal silicon wafer is 100µm deep, has the diameter of 27.2µm on the top, 12.9µm at the bottom. These diameters deviate from the target values by 2.8µm and 0.4µm respectively. These values correspond to the deviation from the target taper angle of the via hole by less than 1°. The processing speed of the laser via hole drilling is 114mm/sec, therefore, etching process can be replaced by this method, if the number of via holes on a wafer is smaller than 470,588. The ablation threshold fluence of silicon is also determined by a FEM model and is verified by experiment.