Wavelet network solution for the inverse kinematics problem in robotic manipulator

Wavelet network, a class of neural network consisting of wavelets, is proposed to solve the inverse kinematics problem in robotic manipulator. A wavelet network suitable for dealing with multi-input and multi-output system is constructed. The network is optimized by reducing the number of wavelets handling large dimension problem according to the sample data. The algorithms for sparseness analysis of input data and fitting wavelets to the output data with orthogonal method are introduced. Then Levenberg-Marquardt algorithm is used to train the network. Simulation results showed that this method is capable of solving the inverse kinematics problem for PUMA560.

Lie Symmetry and Conserved Quantity of Three-Order Lagrangian Equations for Non-conserved Mechanical System

Based on the infinitesimal and one parameter transformation, the problem of Lie symmetry of three-order Lagrangian equations has been studied. Under Lie transformation, the sufficient and necessary condition which keeps three-order Lagrangian equations to be unchanged and the invariant are obtained in this paper.

Creep behavior of SnAgCu solders with rare earth Ce doping

Extensive testing was carried out to study the effects of rare earth Ce doping on the properties of SnAgCu solder alloys.The addition of 0.03%(mass fraction) rare earth Ce into SnAgCu solder may improve its mechanical properties,but slightly lower its melting temperature.The tensile creep behavior of bulk SnAgCuCe solders was reported and compared with SnAgCu solders.It is found that SnAgCuCe solders show higher creep resistance than SnAgCu alloys.Moreover,Dorn model and Garofalo model are successfully used to describe the creep behavior of SnAgCu and SnAgCuCe alloys.The parameters of the two creep constitutive equations for SnAgCu and SnAgCuCe solders are determined from separated constitutive relations and experimental results.Nonlinear least-squares fitting is selected to determine the model constants.The experimental data of the stress-creep strain rate curves are in good agreement with the theoretical ones.

Influence of Mechanical Grinding on the Interface Characteristics of Rice/Wheat Straws

The mechanical grinding method was used to make rice and wheat straw flakes and the properties of the interface of straws before and after grinding were evaluated. The particle boards were prepared using two kinds of straw flakes, respectively and their physical and mechanical properties were investigated. The results showed that the rice straw was easier to be broken when compared with wheat straw and the inner surface of cells in grinded straws was exposed remarkably. The characteristic peaks of lignin and cellulose on the surface of wheat straw were more significant than rice straw. The free-radical concentrations of straws were increased dramatically after being grinded with heating in the range from I00 ~C to 200 ~C. The surface free energy of straws was also improved after being grinded and the value in wheat straw was higher than that of rice straw, which implies that wheat straw was easier to be bonded than rice straw. The physical and mechanical properties of two kinds of straw particle boards could achieve the requirements of Chinese National Standards of GB 4897.3-2003, while wheat straw particle boards had better properties than those made from rice straws.

Study on the Agricultural Fuel Consumption Subsidy Policy for Wheat Straw Low Stubble——Taking the Investigation of Wheat Combine Harvester as an Example in Xushui District of Hebei Province

With the improvement of agricultural mechanization equipment levels, the mechanized wheat harvesting level has been above 80% and the rate of wheat straw returned has increased significantly in the main wheat production of wheat of northern countryside in China. Chinese government popularized the beneficial agronomic measures in the process of wheat straw returned field by mechanization. The agronomic measure was reducing the wheat straw stubble height(WSSH) not more than 20 cm.However, local government didn't apply and disseminate the measure, because in practice the cost of fuel consumption was high, and the operation time of harvesting was longer than ever. The machinery operators and farmers needed to support extra fuel cost and time if they took government's advice. In fact, the objective subsidy policy of fuel cost on reducing WSSH was not been formulated by all levels of government. Therefore, the set of agronomic measure couldn't be popularized in main wheat production area of North China. Our research addressed to master the changing feature of fuel cost and mechanical efficiency,seeking suitable subsidy standard, providing some useful and constructive suggestions to improve subsidy policy of fuel consumption cost for national government department. The study carried out the tracking experiments of the operation efficiency and fuel costs of farm harvester in the situation of different WSSH in 2010 in Xushui District of Hebei Province. In conclusion, the operation time of harvesting decline and machinery fuel consumption cost increased along with the decreasing of WSSH. First for the older harvester, the operation efficiency would decline by 18.7% when the WSSH changed from 20 cm to 10 cm, the cost would increase 4.7%, exact cost was 152.2CNY per hectare. For the new harvester, the operation efficiency would decline by 39.9% when the WSSH changed from 20 cm to 15 cm, the cost would increase 4.6%, exact cost was 368.4CNY per hectare. We provided about 375 CNY per hectare to the mechanical operators and farmer who attended this project, and they were willing to accept the subsidies. We also put forwards some policy suggestions on promoting agronomic measures of reducing WSSH including strengthen the construction of agricultural machinery service system, practise a special fuel consumption subsidies of agricultural machinery and open up new paths for combine sales and circulation.

Dodging the Potholes： The Spatio-Distribution and Socio-Economic Impacts of Potholes in the Residential Areas of Gweru, Zimbabwe

Since the year 2000, the city of Gweru has had an unprecedented proliferation of unattended potholes on most of its roads. These potholes have caused discomfort to the motoring public, caused death to others and damaged vehicles. This paper presents the results of a study that sought to establish the spatial distribution of potholes and determine their socio-economic impacts in Gweru＇s residential areas. Pothole location and dimensions were measured in the field whilst interviews and questionnaires were administered to vehicle owners, motor mechanic experts, drivers and the travelling public to determine their socio-economic and mechanical impacts. Stratified, convenience and purposive sampling methods were used in the selection of study streets and respondents to questionnaires and interviews. Results revealed that potholes are more concentrated in high density residential areas compared to low density areas. This is primarily due to the substandard construction of roads done in high density residential areas. Other causes of pothole formation identified during this study are poor drainage on the roads, rainfall impact, advanced age of roads, poor or lack of maintenance, type and volume of traffic as well as the effect of tree-root prying on paved surfaces. It is recommended that Gweru City Council enters into partnerships in road construction. The city should also establish fundraising projects to augment its budget. This would help ease problems of service delivery including road maintenance. Signposts can be erected to warn drivers about these hazards in the most affected streets and suburbs. It is also important that council set aside a toll-free telephone line link with road users so that areas where new potholes have been detected are quickly reported and attended to. This will not only save lives but also reduce road maintenance costs and vehicle damage.

MQL:A New Way to Clean Production

Cost, the effect on the environment, and health issues are relevant when considering the choice of a lubricant and application system in a modern metal cutting process. This paper provided a general introduction to metalworking fluids, reviewed the benefits and negative effects attributed to the production of mist during cutting processes. Due to the increasing concern over workers exposed to cutting fluid mist, and to achieve the recommended exposure limit, much attention was focused on how to minimize or prevent the mist formation. Different proposed techniques were analyzed, each of them has its advantages and limitations. Finally, the benefits of minimum quantity of lubrication (MQL) technique over all other techniques were studied.

A NOVEL INDOOR GEO-LOCATION METHOD USING MIMO ARRAY

In a Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) based Wireless Local Area Network (WLAN) system, both Access Points (APs) and Mobile Termi-nals (MTs) are configured with multiple antennas, to make novel indoor geo-location method possible. In this paper, we presented a novel Least Square Support Vector Machine (LS-SVM) based data fusion algorithm to fuse signal strength measurements for indoor geo-location using only a single AP with MIMO arrays. We evaluate our proposed algorithms under indoor environments by MATLAB simulations. Simulation results show that our MIMO-based algorithm is superior to conventional least square algorithm.

Image Analysis of Fabric Pilling Based on Light Projection

The objective assessment of fabric pilling based on light projection and image analysis has been exploited recently.The device for capturing the cross-sectional images of the pilled fabrics with light projection is elaborated.The detection of the profile line and integration of the sequential cross-sectional pilled image are discussed.The threshold based on Gaussian model is recommended for pill segmentation.The results show that the installed system is capable of eliminating the interference with pill information from the fabric color and pattern.

Development of a Small-Scale Universal Apparatus for Evaluating Soil-Structure Interaction

This paper describes design and calibration procedures of a new small-scale testing apparatus for evaluating soil-structure interaction. Two distinct modes of loadings, such as, direct shear and pullout loadings on flexible and rigid reinforcements are implemented by the multiple functionalities of the apparatus through the use of single loading frame, dividing mechanism, instrumentation and data acquisition systems. The design is similar to the conventional apparatus; however, it includes some key modifications to adapt additional features of reinforcements. For the pullout test, the top half of the pullout box is fixed with the bottom half of the pullout box, while for the direct shear test, the top half is allowed to slide horizontally on low friction roller bearings connected to the driving mechanism. Mechanical loadings through a steel plate are used to apply the normal load in the pullout and direct shear apparatus. A series of shear and pullout tests are performed to validate the functionality of the apparatus and to examine relationships between the reinforcements and its shear and pullout resistances.

A method to compress vibration signals using wavelet packet transformation combined with sub-band vector quantization

A novel compression method for mechanical vibrating signals,binding with sub-band vector quantization(SVQ) by wavelet packet transformation(WPT) and discrete cosine transformation(DCT) is proposed.Firstly,the vibrating signal is decomposed into sub-bands by WPT.Then DCT and adaptive bit allocation are done per sub-band and SVQ is performed in each sub-band.It is noted that,after DCT,we only need to code the first components whose numbers are determined by the bits allocated to that sub-band.Through an actual signal,our algorithm is proven to improve the signal-to-noise ratio(SNR) of the reconstructed signal effectively,especially in the situation of lowrate transmission.

巧解难题

▲①在高科技领域里,科技人员的作用当然是关键的,但普通劳动者的聪明才智同样重要。

Multivariable wavelet finite element for flexible skew thin plate analysis

Flexible skew thin plate is widely used in mechanical engineering,architectural engineering and structural engineering.High-precision analysis is very important for structural design and improvement.In this paper,the multivariable wavelet finite element(MWFE)based on B-spline wavelet on the interval(BSWI)is constructed for flexible skew thin plate analysis.First,the finite element formulation is derived from multivariable generalized potential energy function.Then the generalized field variables are interpolated and calculated by BSWI.Different from the traditional wavelet finite element,the analysis precision can be improved because the generalized displacement and stress field variables are interpolated and calculated independently,the secondary calculation and the computational error are avoided.In order to verify the effectiveness of the constructed MWFE,several numerical examples are given in the end.

Construction of adaptive redundant multiwavelet packet and its application to compound faults detection of rotating machinery

It is significant to detect the fault type and assess the fault level as early as possible for avoiding catastrophic accidents.Due to diversity and complexity,the compound faults detection of rotating machinery under non-stationary operation turns to be a challenging task.Multiwavelet with two or more base functions may match two or more features of compound faults,which may supply a possible solution to compound faults detection.However,the fixed basis functions of multiwavelet transform,which are not related with the vibration signal,may reduce the accuracy of compound faults detection.Moreover,the decomposition results of multiwavelet transform not being own time-invariant is harmful to extract the features of periodical impulses.Furthermore,multiwavelet transform only focuses on the multi-resolution analysis in the low frequency band,and may leave out the useful features of compound faults.To overcome these shortcomings,a novel method called adaptive redundant multiwavelet packet(ARMP) is proposed based on the two-scale similarity transforms.Besides,the relative energy ratio at the characteristic frequency of the concerned component is computed to select the sensitive frequency bands of multiwavelet packet coefficients.The proposed method was used to analyze the compound faults of rolling element bearing.The results showed that the proposed method could enhance the ability of compound faults detection of rotating machinery.

Research on Damage in Trabecular Bone of the Healthy Human Acetabulum at Small Strains Using Nonlinear Micro-finite Element Analysis

The mechanical properties of the pelvic trabecular bone have been studied at the continuum level. However, nothing is known about the tissue-level damage in the trabecular bone of the healthy human acetabulum at apparent small strains characteristic of habitual. By a DAWING 4000 A supercomputer, nonlinear micro-finite element (μFE) analysis was performed to quantify tissue-level damage accumulation in trabecular bone at small strains. The data indicate that damage in trabecular bone commence at 0.2% apparent strain. The findings imply that tissue yielding can initiate at very low strains in the trabecular bone of the healthy acetabulum and that this local failure has negative consequences on the apparent mechanical properties of trabecular bone.

An index for deformation controllability of small-volume materials

Mechanical tests on small-volume materials show that in addition to the usual attributes of strength and ductility, the controlla- bility of deformation would be crucial for the purpose of precise plastic shaping. In our present work, a ＂mechanical controlla- bility index＂ （MCI） has been proposed to assess the controllability of mechanical deformation quantitatively. The index allows quantitative evaluation of the relative fraction of the controllable plastic strain out of the total strain. MCI=0 means completely uncontrollable plastic deformation, MCI=∞ means perfectly controllable plastic shaping. The application of the index is demonstrated here by comparing two example cases： 0.273 to 0.429 for single crystal A1 nanopillars that exhibit obvious strain bursts, versus 3.17 to 4.2 for polycrystalline A1 nanopillars of similar size for which the stress-strain curve is smoother.

A data-driven threshold for wavelet sliding window denoising in mechanical fault detection

Wavelet denoising is an effective approach to extract fault features from strong background noise.It has been widely used in mechanical fault detection and shown excellent performance.However,traditional thresholds are not suitable for nonstationary signal denoising because they set universal thresholds for different wavelet coefficients.Therefore,a data-driven threshold strategy is proposed in this paper.First,the signal is decomposed into different subbands by wavelet transformation.Then a data-driven threshold is derived by estimating the noise power spectral density in different subbands.Since the data-driven threshold is dependent on the noise estimation and adapted to data,it is more robust and accurate for denoising than traditional thresholds.Meanwhile,sliding window method is adopted to set a flexible local threshold.When this method was applied to simulation signal and an inner race fault diagnostic case of dedusting fan bearing,the proposed method has good result and provides valuable advantages over traditional methods in the fault detection of rotating machines.

A pseudo wavelet system-based vibration signature extracting method for rotating machinery fault detection

The rotating machinery,as a typical example of large and complex mechanical systems,is prone to diversified sorts of mechanical faults,especially on their rotating components.Although they can be collected via vibration measurements,the critical fault signatures are always masked by overwhelming interfering contents,therefore difficult to be identified.Moreover,owing to the distinguished time-frequency characteristics of the machinery fault signatures,classical dyadic wavelet transforms(DWTs) are not perfect for detecting them in noisy environments.In order to address the deficiencies of DWTs,a pseudo wavelet system(PWS) is proposed based on the filter constructing strategies of wavelet tight frames.The presented PWS is implemented via a specially devised shift-invariant filterbank structure,which generates non-dyadic wavelet subbands as well as dyadic ones.The PWS offers a finer partition of the vibration signal into the frequency-scale plane.In addition,in order to correctly identify the essential transient signatures produced by the faulty mechanical components,a new signal impulsiveness measure,named spatial spectral ensemble kurtosis(SSEK),is put forward.SSEK is used for selecting the optimal analyzing parameters among the decomposed wavelet subbands so that the masked critical fault signatures can be explicitly recognized.The proposed method has been applied to engineering fault diagnosis cases,in which the processing results showed its effectiveness and superiority to some existing methods.

Maximal-overlap adaptive multiwavelet for detecting transient vibration responses from dynastic signal of rotating machineries

Vibration signal is an important prerequisite for mechanical fault detection. However, early stage defect of rotating machiner- ies is difficult to identify because their incipient energy is interfered with background noises. Multiwavelet is a powerful tool used to conduct non-stationary fault feature extraction. However, the existing predetermined multiwavelet bases are independ- ent of the dynamic response signals. In this paper, a constructing technique of vibration data-driven maximal-overlap adaptive multiwavelet （MOAMW） is proposed for enhancing the extracting performance of fault symptom. It is able to derive an opti- mal multiwavelet basis that best matches the critical non-stationary and transient fault signatures via genetic algorithm. In this technique, two-scale similarity transform （TST） and symmetric lifting （SymLift） scheme are combined to gain high designing freedom for matching the critical faulty vibration contents in vibration signals based on the maximal fitness objective. TST and SymLift can add modifications to the initial multiwavelet by changing the approximation order and vanishing moment of mul- tiwavelet, respectively. Moreover, the beneficial feature of the MOAWM lies in that the maximal-overlap filterbank structure can enhance the periodic and transient characteristics of the sensor signals and preserve the time and frequency analyzing res- olution during the decomposition process. The effectiveness of the proposed technique is validated via a numerical simulation as well as a rolling element beating with an outer race scrape and a gearbox with rub fault.