Manufacturing becomes increasingly complex as more variations and uncertainties are introduced to the system. Human competencies are valuable to the operation and are considered to be the most flexible manufacturing component. However, there is still lack of study on the impact of human aspects to the cellular manufacturing system performance. This article reports a case study application to evaluate the human impact in the complex cellular manufacturing system. Specifically, this work shows a systematic approach to depict and evaluate the human dynamics and attributes in measuring the labor utilization and determining the ideal man-machine configuration. The literature on modelling technologies relevant to cellular manufacturing design and change is presented to provide the rationale for the use of heuristic and enterprise modelling for this study. Evaluations on the existing human system model, CIMOSA and the heuristic mathematical model resulted in the development of an enhanced human system model framework. The newly developed model focuses on the aspects of human dynamics and attributes. To improve human work measurement data accuracy, the model also uses Maynard Operational Sequence Technique (MOST). An expert system was also developed which greatly reduced the time and effort spent on data entry and data analysis. An example using a multi-national semiconductor assembly and test company is presented where 20% improvement in resource efficiency and additional machine to a labor reconfiguration was achieved without any human fallout.
In this paper, a numerical method for forward kinematics of general Stewart manipulator using natural coordinates is presented. The kinematic equations are in quadratic forms and the corresponding Jacobian matrix is a linear function of coordinates because of using natural coordinates. According to the characteristics of the kinematic equations, the Newton-Raphson algorithm is simplified to decrease the renewal time of iterations between equations and Jacobian matrix, and used to solve the kinematic equations. The singularity and convergence problems of the algorithm are discussed. Furthermore, the method using natural coordinates is compared with the traditional method using rotation matrix through numerical examples. Comparison results show that the method using natural coordinates is very accurate, more efficient, and has a greater convergence domain.
To solve the problems of small flow and low efficiency for a reciprocating piston pump, a new type of rotary piston pump, triangular rotor pump (TRP), is proposed. Its mechanical structure and working principles are introduced and a mathematical model of the key pump structure and the design requirements for the key sealed components are presented. Experiments involving different outlet sizes and shaft speeds are performed on the AB-1.25D-type TRP. Through Fluent numerical calculation, the fluid flow line, velocity vector, and pressure distribution inside the TRP are analyzed. The results show that, for outlet size a (b) and 190(160)-r/min speed, the pump flow rate reaches a maximum of 8.83 (7.34) m3/h, the shaft power is 5.2 (5.1) kW, and the total efficiency exceeds 72%(65.7%). The numerical calculation results show that four vortices appear in the working-chamber (W-C) for different working processes and areas. The W-C pressure first increases and then decreases, and the maximum pressure occurs at the beginning of the stable full-pressure state. The experimental results for the pressure coefficient, flow coefficient, and total efficiency agree well with the numerical results. The TRP exhibits good performance and can be used in deep mine drainage, long-distance pipeline transportation, and grouting.
In this work, a folding experiment was performed to investigate the time-dependent creasing characteristics of white-coated paperboard of 0.3mm thickness. After folding up to the tracking angle of 90° under a specified rotational velocity, the creased part was hold for a chosen short time (0~20s) and the time-dependent release behavior of folding angle was experimentally investigated for the elapsed release time of 10s. When using the paperboard scored with a specified indentation depth, both the hold time of folded posture of creased part and the rotational velocity of fixture were varied. The folding angle of the paperboard was measured by a CCD camera of digital microscope and the bending moment resistance was measured by a load cell of bending test apparatus in the folding experiment. Through the experiment, it was found that the time-dependent release angle consisted of the hold time based intercept part and the creep-recovery based gradient part as a logarithmic function of the elapsed release time. When varying the folding velocity against a fixed unfolding velocity, the unfolded released behavior was isolated by the hold time from the first half folding velocity. Seeing the drop rate of bending moment at the tracking position and the dependency of initial release angle on the rotational velocity, a transient state and quasi-stationary state of bending moment relaxation were revealed.
Planar enveloping hourglass worm (TP worm) with better load capacity and transmission efficiency is a type of transmission superior to traditional cylindrical worm. It could be used to lightweight design. As the flank of the worm is a complex toroidal surface, higher demands are needed for the manufacture and the assembly. This paper proposes a new principle to adjust the processing precision of the worm. The principle is based on the research on the influence of the parameter errors on the deviations of the feature lines on the flank. With different types of parameter errors, the shape and the value of the deviation curves of the feature lines are different. At last, two cases are introduced to verify that the principle could be used to improve the precision of the TP worm.
To solve problems of conventional mobile robots, such as constrained mobility due to nonholonomic wheels or complicated structure due to specialized wheels, we propose a novel omnidirectional mobile robot named slidable-wheeled omnidirectional mobile robot (SWOM). SWOM has three conventional wheels connected to the main body by passive sliding joints, which enable the main body to make omnidirectional movement in spite of the nonholonomic constraints on the wheels. Thus, SWOM achieves both superb mobility and simple structure. However, its behavior is described as a nonlinear system with nonholonomic constraints, which has difficulty with control because this type of system does not have a general design method for a stabilizing controller. This study aims to develop a controller for SWOM using state feedback linearization. This paper presents the following achievements: An exactly linearized state equation is derived using feedback and coordinate transformation based on the kinematics of SWOM. The unwanted singular configurations of the system are discussed and a control strategy to avoid them is proposed. Then, a stabilizing controller that enables SWOM to reach a designated position and orientation is designed. Through a numerical simulation and an experiment using a SWOM prototype, the effectiveness of the developed control system was verified.
The optimum design of an involute K-H-V PDSTND is restudied and remains a difficult task even using a profile shift for the design case discussed in the literature. In fact, the difficulty arises from the design with a very high efficiency and the peculiar tip interference. Because of the failure to obtain feasible designs using profile-shifted full-depth and stub teeth, another feasible design scheme is used by altering the addendums of involute profile-shifted full-depth teeth. In this study, the objective function of the optimum design is a weighted combination of two main performance factors, i.e., the reciprocal of the contact ratio and the working pressure angle. The optimization problem is solved using a combined-mutation differential evolution algorithm. The performance can be improved using the afore-mentioned design scheme; however, there is still room for improvements. Therefore, the use of different modules in mesh for involute profile-shifted full-depth teeth with variation in addendum is proposed and the corresponding meshing equation is derived. The findings show that further improvements on the performance can be achieved.
An inventory management problem is theoretically discussed for a factory having effects of lead times in replenishing the inventory, where it stocks materials used for its products. It is assumed that the factory can dynamically control the size of ordering materials. By applying the stochastic control theory, the optimal control of the ordering size is derived, in which the expected total cost up to an expiration time is minimized. First, a new stochastic model is constructed for describing an inventory fluctuation of the factory by the use of a non-diffusive stochastic differential equation, where an analytic time is introduced so that the inventory process can be a Markov process even though it is affected by lead times. Next, an optimal control is formulated by introducing an evaluation function quantifying total costs. Based upon them, the Hamilton-Jacobi-Bellman (HJB) equation is derived, whose solution gives the optimal control. Finally, the optimal control is quantitatively examined through numerical solutions of the HJB equation. Numerical results indicate that if time up to an expiration time is short then the optimal control is affected by it, otherwise, the optimal control does not depend on it.
The virtual machining is one of the most important techniques to estimate the complex various machining parameters of machined parts before operating the real machining, in order to obtain the accuracy, precision and reliability. The objective of this present research was to propose a comparison between simulation model of the shape generation processes in the turning operations of the generated faces and real turning process experiments, based on the machining parameters, kinematic motion deviations, the inserted cutter geometries, tool wear and deflection of workpieces. The simulation of virtual machining in this turning process was applied to the verifications of the turned faces. The proposed model presented in this research was based on both the shape generation motions and the cutting tool geometries of turning processes. The individual motions were mathematically described by combining 4 by 4 transformation matrices including the kinematic motion deviations. A systematic method was also proposed to verify the 3D tolerances of cylindricity for the turned faces based on the simulation results. The real turning process was machined on a CNC turning center based on the design of experiments by using Taguchi approach, orthogonal array L9 (33), after that, the inspection of the cylindricity on a Coordinate Measuring Machine (CMM) was performed. The results of the comparison confirmed that the simulation of virtual turning processes was similar to the actual turning processes, which was approximately different at 4.055 %.
Heavy duty tractor plays a vital role in traffic transport industry, in roads and building construction. In all of these applications, the structural failure of vehicle is the key issue in the process of safe running. This paper is devoted to the investigation of dynamic characteristics and fatigue reliability for the heavy duty tractor. Appling the non-similar substructure modeling technology, the novel integrated simulation model of heavy duty tractor is established. The total number of elements of the simulation model are reduced obviously from 4,380,449 to 117,065. A complete experimental process, which contains selecting digital acquisition module, the layout of sensors, the data processing, etc., is presented. The validity of the analysis method and the simulation model is verified by comparing with experimental results. The analysis methods of the random frequency domain and the multiaxial fatigue are employed to obtain the fatigue damage samples of heavy duty tractor. Meanwhile, the influences of confidence, pre-stress field and channel correlation on reliability are discussed. Moreover, on the basis of the system reliability distribution, the reliability of determined life and the index of B10 life are assessed. This study gives a reference for avoiding the structural failure and enhancing the system safety.
The classical C2 quintic Hermite interpolation curve not only needs the positions and derivatives but also needs the second-order derivatives as input. For most applications, one has to estimate the second-order derivatives in advance. In addition, the classical C2 quintic Hermite interpolation curve is unique once the input data are fixed, the shape of the curve will not be modified when the interpolation is poor. In this paper, a class of C2 quintic Hermite interpolation curve with free parameters that only needs the points and tangent vectors as input is presented. Due to the self-contained free parameters, the shapes of the proposed interpolation curve can be controlled. Moreover, the free parameters can be chosen reasonably so that the interpolation curve can meet some certain geometric requirements. Some numerical experiments show the feasibility of the proposed methods.
The discrete wavelet transform is a well-known mathematical tool for shape recognition. In this study, a wavelet descriptor with two shape signatures, i.e., centroid distance and triangular centroid area, is developed for shape synthesis for path generation of planar mechanisms. This study is the first to apply the discrete wavelet transform for direct shape synthesis with the two-phase synthesis method for path generation problems. The problem of invariance in the similarity transform for the proposed wavelet descriptor is introduced. The proposed wavelet descriptor contains not only the approximation coefficients but also all the detail coefficients up to a prescribed decomposition level. A geometric-based approach which has been discussed in the literature is used for the scale-rotation-translation synthesis. The differential evolutionary algorithm with a combined mutation strategy is used to solve the optimization problems for shape synthesis. The proposed wavelet-based shape synthesis method is applied to solve five difficult path generation problems for the special paths generated by geared five-bar mechanisms discussed in the literature. The effects of the Haar, Daubechies-1, Daubechies-2 and Daubechies-3 wavelets as well as the number of levels from 1 to 3 on the synthesis results are investigated. Finally, the proposed wavelet-based shape synthesis method successfully solves the path generation problems. The generating coupler curves approximate the desired paths quite well except for one of the five paths. If only the approximation coefficients or only the detail coefficients are employed, the obtained optimum shape may appear similar but does not match the prescribed pattern, e.g. has an incorrect aspect ratio. The most suitable decomposition level depends on the nature of discrete shape signatures and the type of wavelet. The present synthesis results are compared to those obtained with other methods described in the literature.
The study proposes a methodology for extracting and applying expectation effect in multisensory user-product interaction to balance the design attributes that satisfy must-be and attractive qualities in the Kano model. Satisfying both qualities is assumed to be an objective of product design. This study modeled users' cognitive process of cyclic user-product interactions. Using the model, the proposed method extracts users' cognitive structure and state transitions while interacting with a product. The cognitive structure reveals the design attributes affecting must-be and attractive qualities as well as prior cue of the expectations of these qualities. Tolerance for design attributes to satisfy both qualities and the expectation effect of prior factors are discussed. The methodology is validated using a hair dryer as a case product. Another case product (camera) demonstrates how cognitive cues work as well as sensory cues as expectation effect. The proposed methodology supports designers and researchers in structuring multisensory user-product interactions as a series of state transitions of users' cognitive model. The structure helps to extract product attributes that affect both attractive and must-be perceived qualities and attributes involving expectation effect on product qualities. The method of experiment 1 can be applied to assess tolerance for product attributes to satisfy perceived qualities. The method of experiment 2 can be applied to assess the effect of prior expectation induced by both sensory and cognitive attributes, such as a product class, on perceived quality.
In order to realize autonomous machining, it is necessary not only to automate the preparation tasks for machining but also to verify the machining results during the process. Therefore, this study realized the automation of planning for on-machine measurement, where measurement is conducted at the necessary time during the machining process based on process planning. Furthermore, when a machining abnormality is detected based on the measurement results, the proposed system automatically judges whether to stop machining or to re-machine the affected region. In the proposed system, measurement is conducted after the machining of a region that has an influence on the next machining process according to the association chart, which shows the subordination relationships of the geometrical constraints among removal volumes. If measurements indicate excess cutting, the system immediately stops machining because it is impossible for the workpiece to be modified. If measurements indicate incomplete cutting, the system re-machines the affected region and continues the machining process by recursively applying the NC program for the target removal volume. A case study was conducted in order to validate the proposed method of automated planning of on-machine measurement and re-machining. The result showed that the proposed system can automatically determine whether to stop or continue machining according to the measurement results.
The deformation mechanisms in powder compaction can be described by a constitutive model, which is the cornerstone for modeling the powder compaction process by finite element simulation. Therefore, establishing a proper constitutive model is of great importance to investigate the forming rule of powder compaction as well as optimize the mold design and process parameters. The compaction behavior of 6061 aluminum alloy powder was described by the Drucker-Prager Cap (DPC) model. The model parameters and the powder densification behavior were determined and investigated by various powder compaction experiments. The modified DPC model with the determined material parameters was validated using finite element simulation method in ABAQUS with USDFLD user subroutine. The simulation results are consistent with the experiment measurements indicating that the established constitutive model can accurately describe the compaction behavior of 6061 aluminum alloy powder. Especially for the relative density exceeds 0.75, the simulation accuracy is quite high, which means that the determined model can well describe the powder behaviors at later stage of compaction process. In addition, eight representative compaction equations were employed to fit the powder die compaction experimental data and the results showed that Kawakita equation is most suitable to describe the relationship between the pressure and density for the cold die compaction process of 6061 aluminum alloy powder. Taking friction coefficient and temperature into account, a warm compaction equation of 6061 aluminum alloy powder was established. High fitting precisions of the warm compaction equation were obtained with the temperature T1 of 100°C~150°C and the friction coefficient μ of 0~0.1.
The combination of the carbon fiber composite and 3D printing technology can be a powerful approach to produce the high-strength light-weight and complex construction mechanical parts. Compared with the short carbon fiber which has been widely used, application of continuous carbon fiber in 3D printing can undoubtedly better play its good mechanical properties. Usually, complex parts include multiple independent contours, which lead to discontinuous paths in the 3D printing process.For the continuity characters of the continuous carbon fiber composite, it needs to be sheared off due to the discontinuous molding printing path, so as to ensure the quality of the forming process. To solve this problem, a shearing method is put forward and the shearing device is realized. Based on the 3D printing planning path by the slicing process, the actual shearing position is calculated by shearing position recognition and distance compensation between the jump and the shearing point. On the basis of this method, the corresponding shearing device is designed to build a shearing system. The accuracy and feasibility of the continuous carbon fiber shearing system is verified by simulation analysis of path jump and single-layer and multi-layer model 3D printing experiment. The method provides basis for the realization of continuous carbon fiber composites 3D printing.
The objective of this research is to efficiently solve discontinuous optimization problems as well as optimization problems with large infeasible regions in the design variables space. Recently, major optimization targets have been changed to more complicated ones such as topology optimization problem, discontinuous optimization problem, robust optimization problem and high dimensional optimization problem. The aim of this research is to efficiently solve the complicated optimization problems by using machine learning technologies. In aerodynamic optimization problems at supersonic flow conditions, it is confirmed that aerodynamic objective functions have discontinuity due to shock waves and it needs to treat the discontinuous functions and large infeasible regions via strong shock waves. In this research, therefore, we develop an efficient global optimization method for discontinuous optimization problems with infeasible regions using classification method (EGODISC). The developed method is compared with a Bayesian optimization method using the Matern 5/2 kernel Gaussian process regression and a genetic algorithm to verify the usefulness of the developed method. The Bayesian optimization falls into an infinite loop in its optimization process by selecting an additional sample point in the infeasible regions. On the other hand, the developed method can work well with the infeasible regions in the design variables space. It is confirmed that EGODISC can be effectively used with discontinuous aerodynamic objective functions. It is also confirmed that EGODISC can be effectively used for a shape optimization problem with large infeasible regions by the negative thickness of airfoil.
This paper proposes a vibration control method of an automotive drive system with backlash to maintain stability and control performance under the control period constraint due to an engine's characteristics. Reducing the vibrations of the automotive drive system remains a challenge when improving the riding comfort and driving performance of automobiles. In particular, a vibration control method must be developed to compensate for the backlash of differential gears because this element degrades the vibration control performance. Furthermore, engines used as actuators have a constraint in which control cycles are made longer due to restrictions of the input update. The roughly updated cycles adversely affect not only the high vibration control performance but also the stability. In this study, we validate the control system for an automotive drive system with backlash by considering the input update limitation. First, a basic experimental device, which abstracts actual vehicles to focus on the influence due to backlash while reflecting only the basic structure of an automotive drive system, is created. Then to cope with the control cycle constraint, sampled-data H2 control is applied. The servo system is constructed by applying an approximate integrator and frequency shaping. As an approach to compensate for backlash, we propose a simple and practical control mode switching technique. Finally, the effectiveness of the control system is verified experimentally. The results are compared to the control results with those obtained by the traditional discrete approximation.
This paper aims to estimate the indentation resistance and deformation shape of a 0.5mm thickness acrylic Pressure Sensitive Adhesive (PSA) sheet subjected to a wedge indentation. As for the effect of apex angle of a wedge blade on the cutting characteristics of the PSA sheet, a 60° wedge blade was mainly investigated through experiments and numerical simulations, while the wedge angles of 42, 16° were discussed with respect to the subduction profile of wedged surface. For the sake of development of PSA deformation model, the Prony series based viscoelastic properties were determined by the shear stress relaxation test. Also, the equivalent Young's modulus was estimated by comparing with an out-of-plane compressive experiment and a Finite Element Method (FEM) based compressive simulation. Through the experimental wedge indentation using the 60° wedge blade, three stages of cutting load response were detected: (1) an exponential response, (2) an extremely increasing response based on the saturated inclined angle of subduction zone, and (3) a saturated gradient for the final stage. Furthermore, it was clarified that the proposed FEM model of viscoelastic-deformable sheet subjected to the 60° wedge indentation was applicable for simulating the cutting deformation for the early stage less than 60% of the thickness. The simulated inclined angle of subduction zone tended to be linearly increased with the indentation depth up to a certain extent, whereas the experimental inclined angle saturated to a constant for the indentation depth larger than 70% of the thickness. One of the reasons why the experimental cutting force was higher than the simulated result was explained as the wetting spreading effect due to the yield flow of PSA sheet. In the latter stage of indentation, the correlation between the mismatching of cutting line force and the mismatching of inclined angle of subduction zone was revealed.
A workpiece attitude during polishing process is known to affect material removal rate distribution, which is one of the most significant properties in polishing process. Though, the effect of the attitude in double-sided polishing process has not been discussed in the past literatures. Hence, a method for estimating the distribution in double-sided polishing of a thick square workpiece considering the attitude is developed, and the effect of the attitude to the material removal rate distribution is investigated utilizing the method in the present study. In the developed method, the attitude is identified based on the equilibrium of force and moment applied to the workpiece by the contact against upper and lower pads. And distribution of contact pressure between the workpiece and pads is calculated under the identified workpiece attitude. Then, the material removal rate distribution is estimated from the contact pressure distribution and relative velocity distribution, which is calculated from the conditions of geometry and rotational speed, based on Preston’s law. It is confirmed that the material removal rate increases as the position is closer to the leading edge of the workpiece because of the workpiece tilt. And this variation increases as the workpiece becomes thicker and smaller. Therefore, it is confirmed that the effect of the workpiece attitude to the material removal rate distribution is significant, and considering the workpiece attitude is significant for investigating the material removal rate distribution in double-sided polishing of a thick or small workpiece.
Cell-load variation is considered as a major shortcoming in cellular manufacturing systems. It can cause long queues in front of machines and impose extra costs to the cellular layouts. In this paper the impact of inflation on cell-load variation in cellular manufacturing systems is examined. For this purpose, a new method is proposed for scheduling dynamic cellular manufacturing systems in the presence of bottleneck and parallel machines. The aim is finding the trade-off values between in-house manufacturing and using outsource services while system costs are not deterministic and may be varied from period to period by inflation. To solve the model, a hybrid Multi-layer perceptron is developed because of the high potential of outcomes to be trapped in the local optima. Our findings show that the condition of dynamic costs affects the routing of materials in process and may induce machine-load variation that yield to cell-load diversity. An increase in changing costs causes the loading level of each cell to vary, which in turn results in the development of “complex dummy sub-cells.” The results indicate that the proposed method can significantly reduce the level of cell-load variation in CMS.
In this research, we propose a method to evaluate both speed and accuracy performance of CNC machine tools at the same time. An important facet of the contouring performance of machine tools with computer numerical control (CNC) is the machining of workpieces within the desired accuracy and within as short a time as possible. For this reason, a method for evaluating speed and accuracy in the two dimensions of speed and error based on the actual trajectory, which is the actual movement trajectory with respect to the linear axes of CNC machine tools, has been proposed. In this research, we explain the method proposed for linear axes and propose a method to evaluate the speed and accuracy of a rotary axis and a linear axis in the two dimensions of speed and error by introducing a cylindrical surface to the combined movement of the rotary and linear axes. With experiments, we quantitatively evaluated the speed and accuracy of multiple CNC machine tools using two-dimensional representation with graphs of the actual speed and maximum error for the combined movement of a rotary axis and a linear axis.
Coupling and shaft assemblies in paper and pulp industries make use of dissimilar joints of austenitic/ferritic stainless steels AISI 316L and AISI 430. The joining of these 4mm thick Ni-Cr based AISI 316L and Cr based AISI 430 alloys were carried out by adopting current continuous (CCGTAW) and pulsing current (PCGTAW) in Gas Tungsten Arc Welding has been addressed. Ni-Cr based ERNiCr-3 and Ni-Cu based Nb-free ERNiCu-7 filler rods were employed to join these types of dissimilar combinations. The weldments were systematically characterized using optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). It is recommended from the studies that the welds obtained from ERNiCu-7 fillers were free from deleterious Laves phase formation. Irrespective of fillers, the tensile failures were experienced at the base metal side of AISI 430. In ambient temperature condition Charpy V-notch impact trials highlighted that the weld joints employing ERNiCu-7 observed better tensile and impact toughness than current continuous GTAW weldments. This study is highly demanded in paper and pulp industries and effectively addressed the choice of fillers in conquering the Laves phase.