An inertial measurement system for estimating gait parameters indicating cognitive impairment is developed for use during large-scale health checkups. Current health checkups conduct a 10 m fastest gait examination to assess signs of cognitive impairment and physical performance. Earlier methods require examiners to follow a subject and measure the gait time using a stopwatch. The method proposed herein reduces burdens on examiners. Several gait parameters in addition to the gait time of many subjects can be measured simultaneously and quantitatively from three-dimensional foot movements estimated using inertial sensors comprising two accelerometers and two gyroscopes with different measurement range attached to both feet. Gait parameters derived from the inertial sensor are gait time, stride length, gait cycle, gait velocity, toe angle, toe height, and the percentage of swing phase. The gait condition, such as walking or running, is distinguished from the moment of toe off and heel contact of both feet. In all, 1406 subjects with ages of 19-93 years old were given instructions to walk at their highest velocity on a straight 16-m-long walking course. Mini-Mental State Examination (MMSE) is conducted on subjects. The score is used as a reference valuation of the cognitive impairment level. Experimental results show that the proposed measurement system provides equal performance to that obtained using a stopwatch and improves correlation between the MMSE score and the fastest 10 m gait time of subjects who did not run. Furthermore, it is confirmed that the proposed measurement system using inertial sensors can quantitatively provide spatiotemporal gait parameters to evaluate the physical performance in a short time during the large-scale health checkups.
This paper describes the designing and manufacturing process of a complex special utility vehicle (SUV) using the methodical design approach for which the basics were explained decades ago in Germany. The application steps of the design methodology with comprehensive data are clearly outlined and the experiences gained during the project along with the authors’ experiences in design research and design practice over 25 years are generously shared. This paper contributes to the methodical approach laid by Pahl & Beitz with an industrial example proving its applicability in real engineering design applications. The proposed solutions for difficulties encountered in the process are especially valuable and applicable for SMEs (small and medium-sized enterprises) in the field. Such details are reported with comprehensive discussions in this paper.
This paper proposes an advanced mesh generation technique that reuses the proven analysis models by searching for similar sub-parts. The purpose of this development is to reduce interactive mesh improvement work time and to comply with the mesh specifications. In particular shell mesh generation, working time of complex thin parts such as resin parts is long, which causes issues for front-loading. Furthermore, quality improvement and standardization of analysis models are required because the general designers have to manage V&V (Verification & Validation). This technique consists of two distinctive techniques. First, it is the technique to search the subparts from newly designed CAD which have similar shape with the archived feature sub-parts contained in the proven CAD models. In this technique, the similar sub-parts are retrieved from a CAD model described by boundary representation and made correspondence relation surface pairs of a retrieval model (proven model) and a target model (CAD of new design). A similarity score is calculated based on geometrical similarity and topological similarity. Geometric similarity is based on geometric information such as areas and perimeters. Topological similarity is based on the surface connection differences. Second, mesh can be generated automatically by arranging and merging the know-how meshes based on the relationship of the surfaces by similar sub-parts search technique. Experimental results show that this technique can efficiently generate a mesh without interactive mesh improvement operation which was conventionally taken several hours.
In recent decades, new optimization algorithms have attracted much attention from researchers in both gradientand evolution-based optimal methods. Many strategy techniques are employed to enhance the effectiveness of optimal methods. One of the newest techniques is opposition-based learning (OBL), which shows more power in enhancing various optimization methods. This research presents a new edition of the Differential Evolution (DE) algorithm in which the OBL technique is applied to investigate the opposite point of each candidate of self-adaptive control parameters. In comparison with conventional optimal methods, the proposed method is used to solve benchmark-test optimal problems and applied to real optimizations. Simulation results show the effectiveness and improvement compared with some reference methodologies in terms of the convergence speed and stability of optimal results.
For cutting a SiC substrate coated with a metal film stably, a novel ductile-mode dicing process was developed using a blade made of a single body of poly-crystalline diamond (PCD) with only 50 μm in thickness. It is difficult for a conventional diamond blade with metal binder to cut the SiC substrate in a straight line accurately due to insufficient buckling strength. In addition, self-sharpening effect of the cutting edge is suppressed by adhesion of metal film to blade surface. In this study, a rake face and a flank face of the cutting edge were formed by irradiating pulsed laser light tangentially to the cutting edge. Under the high speed rotation condition of 30,000 rpm (500 s-1), the developed PCD blade acts on the workpiece with the continuous cutting edge in a stable posture due to the inertial force of the rotation, and the depth of cut per a cutting edge is about 5 nm. Under these conditions, the ultrafine cutting tip of the metal film also becomes on the order of nanometers. 4H-SiC substrate 350 μm in thickness with Au / Ni / Ti film was cut using the developed PCD blade. Under the half cut condition, there was no chipping or crack on the surface, and the bottom of the groove was finished in a mirror state. Under the full cut condition with a width of 50 μm, the SiC substrate and the metal film were cut at once, and any crack did not occur at the interface between SiC and the metal film. As the result, it was demonstrated that ductile mode machining was realized and the metal film did not adhere to the cutting edge.
PDD2 (proportional + derivative + second derivative) compensator has been standardly used for position control of the pneumatic stage. This compensator is based on the integral characteristics of a pneumatic system composed of pipes, servo valves, and pneumatic cylinders. At this time, since the output of this compensator is integrated through the pneumatic system, PID control of the position is possible. However, the positioning of the pneumatic stage is slower than that of the electromagnetic actuators such as a linear and a ball screw stages. Generally, when either the controlled object or the compensator has a slow response, the response of the control system becomes slow. In the previous studies, the pneumatic stage itself, which is the controlled object, was focused on. Local feedback applied to the pneumatic and mechanical systems realized high-speed positioning. However, the influence on the positioning response using PDD2 compensator, which forms the framework of the position control, has not been considered. Therefore, this note focuses on the structure of PDD2 compensator. Here, the characteristics of this compensator are reinterpreted. Specifically, it is shown that a slow response cannot be avoided intrinsically due to the structure of this compensator. Furthermore, modified PDD2 compensator with improved slow response is proposed.
Emotion is an internal and subjective experience that plays a significant role in human life. There are several methods of recognizing emotions in people, the most authentic of which is using physiological signals, as they are beyond one’s control and strongly correlated with human emotions. This study aims to develop an emotion recognition system based on three physiological signals, namely, brainwave, heartbeat, and facial muscular activity. It utilizes deep neural network (DNN) and the T method of Mahalanobis-Taguchi system (MTS) to process the multiple physiological signals and further recognize the states of human emotion. As such, nine emotions are effectively recognized on a two-dimensional model through the DNN, then compared against several other algorithms, such as MTS, SVM, Naive Bayes, and K-means, where its superior accuracy is validated. Moreover, although the T method only improves the classification accuracy on the valence state, it rather obtains the intensity of emotion in different states. Furthermore, in this study, the proposed DNN is implemented into a wide range of applications for an accurate understanding of the human emotional states, whereas the T method is utilized to respond to the emotional intensity in different states. Finally, a real-time emotion recognition system is developed with DNN as the classifier; this system can directly monitor the variation of the human emotion through reliable and objective emotion analysis results from the physiological signals. Thus, the method can provide useful treatment effect information for robots or assistive apparatus serving activities of daily living.
Singular configurations must be avoided in the practical manipulation of parallel mechanism. This paper presents an approach of singularities analysis of six degrees of freedom (DOF) parallel mechanism applying geometric algebra. Twists of all passive joints in each limb are described in geometric algebra while all the active joints are locked. And wrenches produced from each limb and acting on the moving platform are derived from the calculations of the outer product and its dual of the corresponding twists. The singular condition of parallel mechanism depends on whether the wrenches acting on the moving platform failed to constrain all the motions, which can be accomplished by the outer product with its duality followed. Two six-DOF parallel mechanisms 6-UPS and 6-PUS are introduced to verify the approach proposed in this paper. The results indicate that geometric algebra can also be used for singularity analysis of six-DOF parallel mechanism.
For the damaged jib structure of mobile cranes in service, it is difficult for users to make a decision for using, repairing or scrapping and to achieve the balance of economy and security. The decision-making method of jib structure remanufacturing scheme is proposed based on characteristic life and strength redundancy and the decision-making system is developed. The damage location is divided into two regions according to failure modes. For the tensile stress region, test points with fatigue residual life are screened out. Then, with reliability theories consist of probability distribution fitting and goodness of fit test and adaptable double fruit fly algorithm being as the basis, the theoretical model of characteristic life reliability analysis of damaged jib section is built, and the fatigue life reliability of each detection point is obtained. Next, combined with the reliability threshold given in the original design, the remanufacturing scheme of each detection point is determined. For the compressive stress region, detection points entered into the repair admittance period is selected. On the basis of failure mode database, parameterized finite element model simulation computing platform and repair experimental data, the strength hierarchical analysis model of damaged jib section is established according to the generalized strength degradation process of jib structure. And the remanufacturing scheme of corresponding detection point is confirmed in combination with the minimum intensity redundancy factor. The remanufacturing scheme of damaged jib section is determined in the light of the remanufacturing scheme result set of various detection points. Taking the damaged jib structure of QY130t truck crane in service as an example, the feasibility and applicability of the method and system are verified.
To increase recording density, a head positioning control system of a hard disk drive (HDD) has to compensate for vibration due to mechanical resonances of the system. In this study, a novel scheme of an adaptive feedforward cancellation (AFC) is proposed to compensate for the vibration due to the mechanical resonances. Compared to a notch filter, which is commonly used to compensate for the vibration, the proposed AFC has the advantage of estimating the amplitude of the vibration from the output signal. In addition, although the proposed AFC can be implemented as a discrete system, the design parameters: frequency, damping ratio, and gain can be set directly in a digital signal processor. The proposed control system was applied to a dual-stage actuator system, which is the mainstream head positioning control system of the current HDDs. The results indicate that the proposed system could compensate for the vibration due to the mechanical resonance.
During the operation of vehicles, it is found that dramatic vibration occurs when the engine rotation speed reaches a certain value. In order to study this phenomenon, a theoretical model of automobile transmission system is developed in this paper. This model includes four sub-models of gearbox, drive shafts, main reducer and rear axle, which take into account the inhomogeneous transmission speed of universal joint of drive shafts as well as the effect of time-varying and nonlinear factors of main reducer gears. In this model, the transmission system is an elastic system characterized by mass, stiffness and damping. The torsional vibration responses of transmission system are simulated, and the natural frequencies of transmission system and corresponding mode shapes are calculated using this model. Simulation results indicate that the maximum amplitude of torsional vibration response appears at a certain speed. On the other hand, experimental investigation on the effect of rotation speed on torsional vibration is conducted to verify the theoretical model. Experimental results also show there is the maximum amplitude of torsional vibration response appearing at a certain speed. The results of FEA indicate that the excitation frequencies of drive shaft are quite close to the first order natural frequency of drive shaft, and the resonant vibration of drive shaft would induce the resonant vibration of transmission system, given that the first order natural frequency of drive shaft is quite close to the third order natural frequency of transmission system. In particular, it is discovered that deviations between the rotation speeds corresponding to the maximum amplitude of angular displacement and the rotation speeds corresponding to the maximum amplitude of angular acceleration exist for both theoretical simulation and experimental measurements.
In this study, we consider the scheduling problem for two-machine flowshops with jobs of the different release times. In many real situations, jobs can be arrived at different times due to progress of jobs in the preceding stage or the status of supply of raw materials. We set the objective function of this problem to minimize the total tardiness of jobs. This job arrival constraint tends to reduce the scheduling efficiency of the production system especially in the sense of total tardiness. We developed dominance properties, lower bound and heuristics for upper bound, and adopted them to a branch-and-bound algorithm to obtain the optimal schedule for the objective of minimizing total tardiness. To test the performance of the proposed algorithm and evaluate the efficiency of the dominance properties and the lower bound, we randomly generate the problem instances and test the problem instances with the proposed algorithms. The experiment results show that CPU times are reduced by our lower bound and dominance properties.
Sine movable tooth drive has the smallest radial size. Working efficiency is one of the important factors of the performance evaluation of the drive. Here, based on analyzing entrainment speed and forces of sine movable tooth drive, the equations of the minimum oil film thickness and meshing efficiency for the drive is proposed. The minimum oil film thickness and meshing efficiency of the drive is studied, and the changes of the meshing efficiency along with main parameters are analyzed. Results show that the minimum oil film thickness between the movable teeth and central input shaft is higher than that between the movable teeth and shell, and the meshing efficiency of the drive is between 79.74% and 84.67%, and the average efficiency is 82.48% which is near the experimental result of 82.25%.
Increasing attention has been paid to the effective management and reuse of CAD model resources. Aiming at the problems of low efficiency of model reuse and poor accuracy in the function labeling process of assembly models, this paper presents an effective probability-based model labeling strategy for complex assemblies. It is a proper method to realize automatic labeling of assembly functional semantics through active learning. Different from part model retrieval, an assembly model is described through graph theory and a bag-of-relationships model. The assembly relationships of assembly model and the information of key functional parts are considered synthetically. Then a two-tiered model retrieval mechanism is constructed to reduce the computation time cost and improve retrieval efficiency. Further, the concept of functional ontology is introduced to establish the normalized expression of the key functional semantics of the assembly model. The functional semantic annotation of the key parts of the CAD assembly model is carried out through a probability-based labeling framework to map the model shape structure to functional semantics, thus mitigating the “semantic gap” problem. Experimental results demonstrated that this method could improve the accuracy of functional semantic annotation of the assembly model, reduce the difficulty of labeling, and improve the reusability of 3D CAD models as a design resource.
In this study, we present a material-orientation optimization method for tailoring the thermal displacements of laminated composite shell structures to required target values. The square displacement error norm between the displacements and the target values is minimized by varying the distributed anisotropic material orientation of each layer. The optimum design problem is formulated as a distributed-parameter, or a design parameterization-free optimization problem, and the sensitivity function with respect to the material orientation variation is theoretically derived based on the variational method. The optimal material orientation variation is determined by the H1 gradient method with Poisson’s equation, where the sensitivity function is applied as the Robin condition to vary and optimize the material orientation distribution. Then, the optimal material orientation variation is determined as the temperature distribution by the Poisson’s equation, which ensures the continuous material distribution. The optimal design examples show that the proposed optimization method can effectively produce the optimum material orientation with a smooth curvilinear distribution for tailoring thermal or static deformation of a laminated composite shell structure.
Idlers, one of the important parts of belt conveyors, are substantial and constitute approximately one-third of the equipment cost. Therefore, idlers in conveyor systems must be optimized. This study designs a new kind of idler on the basis of theoretical calculation and coupling simulation, with the shaft, shell, and labyrinth gland of the idler as optimization variables and overall cost and life span of the idler as objective functions. According to each independent variable of the idler, this idler adopts the equal strength beam concept and maximizes the overall carrying capacity of the shaft and the bearing by using a hollow step-shaft. The idler effectively adopts the one-piece casting labyrinth gland, thereby automatically enhancing the sealing effect with a screw structure in different rotation directions. The simulation analysis shows that under certain working conditions, the stress of the new idler shaft is one-third of the stress of the traditional idler shaft, and the strain is one-half of the traditional idler shaft, and the effect is obvious. A reliability analysis of the idler system is described in this work through the establishment of a fault tree, determination of the logical relationship of each component and provides methods for further research. Finally, the idler is verified to be practical in engineering applications, with a 10% cost reduction and considerable economic benefits.
Under the cloud manufacturing (CMfg) environment, a multilayer semantic matching model of design requirement and cloud service resource based on ontology was proposed to guarantee the rapid and accurate matching of resource services to meet the cloud user design requirement. First, the CMfg classification of demand and service was analyzed, and the ontology description was derived according to the service resource classification. From the aforementioned service resource classification, the multilayer matching model was established. The model included six matching stages, namely, base information matching, function information matching, state information matching, quality of service information matching, manufacturing capability information, and comprehensive matching. Then, the matching algorithm of each layer was quantitatively established and described to achieve intelligent matching of the service resource. Meanwhile, an improved analytic hierarchy process was presented to express the influence of each layer on its matching goal scientifically, ensuring that each affecting factor is reasonable. Finally, a case was used to prove the correctness and practicality of the proposed method.
This thesis report on a novel bellows-driven, two-dimensional, pneumatic ultra-precise positioning system. A dynamic surface control (DSC) method based on nonlinear extended state observer (NESO) is proposed to solve the control problem of nonlinear pneumatic servo positioning system. The bellows are used as actuators and the mathematical model is established according to the dynamic characteristic equation of the system. Considering the unknown state signal of two-dimensional pneumatic servo system, a fourth-order NESO is developed to conquer these problems. Dynamic surface control is adopted to eliminate the problem of differential expansion and simplify the design of controller and parameters. Afterwards, the selection of suitable Lyapunov's function proves that all signals of the system are bounded Furthermore, through practical application, the control method proposed in this paper guarantees the asymptotic stability of the pneumatic two-dimensional ultra-precision servo positioning system and the requirement of ultra-precision with large stroke and ultra-precise is realized.
This study demonstrates a novel method for vibration damping using a piezoelectric element. A piezoelectric transducer excited by ultrasonic vibrations is placed in contact with a vibrating object in a direction perpendicular to the vibration. In conventional methods, piezoelectric elements attached to vibrating objects are excited in the same direction as the vibration direction of the object. Such methods require complicated control and measurements for maintaining the vibration of the transducer in the phase opposite to the object’s vibration, to exert the damping effect. In contrast, the proposed method does not require adjustment of the transducer’s vibration phase according to the object because this method manipulates a friction loss between the transducer and a vibrating object for damping. This study confirmed a damping effect with the proposed method by conducting hammering tests on a cantilever. Furthermore, the parameters influencing the damping effect and the damping principle were considered. The damping ratio obtained from these tests was approximately 10 times the value when a non-excited transducer was statically pressed to the cantilever. Moreover, the test results suggested that the magnitude of the damping effect could be estimated by measuring the current flowing in the transducer, and that an optimal current to achieve the highest damping effect exists. The damping effect by the proposed method is considered to be triggered with a slip between the transducer and a vibrating object by suppressing the transverse oscillation of the transducer using the inertia effect caused by the transducer’s excitation. Furthermore, the increase of the impact force applied to the object by the excitation improves the damping effect. By measuring the stress waves in a long bar based on the one-dimensional elastic wave propagation theory, the impact force caused by the excited transducer was measured. The impact force had a peak at a specific current and changed with the same tendency as the damping ratio. The results suggested that both suppressing the transducer’s transverse oscillation and increasing the impact force cause the high damping effect by using the proposed method.
Mud-caking of the cutterhead in a tunnel boring machine (TBM) has been commonly encountered when a TBM is excavating through strongly weathered rock or clay. Not only the opening of cutterhead could be blocked to cause problem for muck flowing through, mud-caking of a cutterhead will also lead to the increase of thrust and torque, as well as compromise of tunneling efficiency. To predict the mud-caking status in real time, a prediction model was established based on cutter temperature characteristics, and a bus-based detection system was designed to monitor cutter wear and temperature in tunneling. Such prediction model and detection system were verified on an earth pressure balance (EPB) TBM at a Shenzhen metro project. The research demonstrated that the detection system performed its function of monitoring cutter wear and temperature changes in real time. A dynamic prediction of cutterhead mud-caking status was also proved using the prediction model.
The loading system of the existing hydraulic motor performance test platform is complicated, the interference is too much, and it is not suitable to measure the hydraulic motor noise level. In this paper, a new platform for measuring the sound pressure level of the hydraulic motor noise is designed. It satisfies the requirement of simplification and less interference in other parts of the noise test except for the test object and ensures the accuracy of test results. This paper firstly introduces the hydraulic system and its principle, calculates the relations of the flow, pressure and power theoretically and verifies them with AMEsim. Then the control part, mechanical structure and semi-anechoic room of the hydraulic system are introduced and the method in the noise experiment is also explained. Finally, the noise level of a bent-axis type hydraulic piston motor is measured in the semi-anechoic room. The background noise and hydraulic motor noise under different conditions are tested by the Danish BK acoustic test system to verify the functionality and stability of the test platform and the noise spectrum, the efficiency of hydraulic system and the effect of the power recovery are analyzed.