Search results

Branched articulated robots (BARs) are highly non-linear systems; accurate dynamic identification is critical for model-based control in high-speed and heavy-load applications. However, due to some dynamic parameters being redundant, dynamic models are singular, which increases the calculation amount and reduces the robustness of identification. This paper aims to propose a novel methodology for the dynamic analysis and redundant parameters elimination of BARs.

At first, the motion of a rigid body is divided into constraint-dependent and constraint-independent. The redundancy of inertial parameters is analyzed from physical constraints. Then, the redundant parameters are eliminated by mapping posterior links to their antecedents, which can be applied for re-deriving the Newton–Euler formulas. Finally, through parameter transformation, the presented dynamic model is non-singular and available for identification directly.

New formulas for redundant parameters elimination are explicit and computationally efficient. This unifies the redundant parameters elimination of prismatic and revolute joints for BARs, and it is also applicable to other types of joints containing constraints. The proposed approach is conducive to facilitating the modelling phase during the robot identification. Simulation studies are conducted to illustrate the effectiveness of the proposed redundant parameters elimination and non-singular dynamic model determination. Experimental studies are carried out to verify the result of the identification algorithm.

This work proposes to determine and directly identify the non-redundant dynamic model of robots, which can help to reduce the procedure of obtaining the reversible regression matrix for identification.

The purpose of this paper is to present a numerical model to investigate the dynamic behavior and force coefficients of a compact squeeze film damper with dual film clearances adjusted by an elastic ring, known as elastic ring squeeze film damper (ERSFD).

The governing equations of ERSFD as well as the boundary conditions are obtained based on Reynolds equation. A simplified Greenwood–Williamson model is implemented to investigate the contact behavior between the elastic ring and the journal. The interactions between the films and the elastic ring are achieved by block iterative method.

The radial deformation as well as velocity of the elastic ring are captured to illustrate the pressure profiles of the inner and outer films. High-order frequency components related to the number of the boss N are observed on the frequency spectrum of the film force. The force coefficients of the ERSFD are constant for a wider range of non-dimensional whirling radius ε compared with conventional squeeze film damper.

The force coefficients of the ERSFD are obtained by assuming that the journal center moves in a circular centered orbit. High-order frequency components related to the number of bosses N are observed. These findings may provide helpful materials for the application of the ERSFD.

Since robot’s structural stiffness is usually less than 1 N/µm, mode coupling chatter occurs frequently during robotic milling process, and chatter frequency is close to the natural frequency of the robot itself. Chatter not only affects the surface quality but also damages the robot and reduces the positioning accuracy. Therefore, it is necessary to predict chatter in robotic machining process.

A three-dimensional dynamic model for robot’s spatial milling plane is established, and a corresponding stability criterion is obtained. First, the cutting force in milling plane is transformed into the coordinate system of the robot principal stiffness direction based on homogeneous transformation matrix. Then the three-dimensional stability criterion under milling process can be obtained by using system stability analysis. Furthermore, the circle diagram of mode coupling chatter stability is drawn. Each feeding direction’s stability under the two processing forms, referred as spindle vertical milling and spindle horizontal milling, is analyzed.

The experimental results verify that the three-dimensional stability criterion can avoid chatter by selecting machining feed direction in stable area.

This paper established a three-dimensional dynamic model in robot’s spatial milling plane and proposed a three-dimensional stability criterion according to the Routh criterion. The work is also expected to be an efficient tool in the development of robotic milling technology.

The purpose of the paper is to examine observed differences in China's ethnic majority and minority patterns of labor force participation and to decompose these differences into treatment and endowment effects.

Data from the three most recent population censuses of China are employed to explore differences in the labor force participation rates of a number of China's important ethnic groups. Gender‐separated urban labor force participation rates are estimated using logit regressions, controlling for educational attainment, marital status, pre‐school and school‐age children, household size, age, and measures of local economic conditions. The focus is on the experience of six minority groups (Hui, Koreans, Manchu, Mongolians, Uygurs, and Zhuang) in comparison to the majority Han. The technique developed by Borooah and Iyer is adopted to decompose the differences in labor force participation rates between pairs of ethnic groups into treatment and endowment effects.

Sizeable differences are found between the labor force participation rates of prime‐age urban women of particular ethnic groups and the majority Han. Men's participation rates are very high (above 95 percent) and exhibit little difference between Han and ethnic minorities. For almost all pairwise comparisons between Han and ethnic women, it is found that differences in coefficients account for more than 100 percent of the Han‐ethnic difference in labor force participation. Differences in endowments often have substantial effects in reducing this positive Han margin in labor force participation. Roughly speaking, treatment of women's characteristics, whether in the market or socially, tend to increase the Han advantage in labor force participation. The levels of these characteristics on average tend to reduce this Han advantage.

The paper analyses only one aspect of the economic status of China's ethnic minorities – labor force participation. It would be useful also to examine income, educational attainment, occupational attainment, and unemployment.

This paper contributes to and expands the scant literature on ethnicity in China's economic transition.

The purpose of this paper is to extend current knowledge by focusing on three geographic factors (minority-Han residential segregation, rural-urban disparities and regional differences) and their effects on educational and occupational outcomes of Chinese ethnic minorities from 2000 to 2010.

Data from the 2000 and 2010 Chinese decennial censuses were used, and both descriptive and multivariate analyses were conducted.

Results revel that there were regional differences in terms of educational segregation between minorities and the Han. It was also difficult for minority groups that were residentially segregated from the Han and mainly located in rural areas or western/southeastern regions to obtain high-level education. When minority groups were residentially segregated from the Han, they tended to have higher levels of occupational segregation from the Han; while minority groups with larger percentages of rural residents tended to have smaller percentages of people obtained high-status occupations. Despite China’s rapid social and economic development, ethnic disparities in education did not significantly change, and ethnic gaps in occupational attainment were widened from 2000 to 2010.

Geographic sources of ethnic conflicts in China should not be overlooked, and future researchers should also conduct studies on Chinese ethnic minorities at individual or household level.

This study contributes to the literature in two major ways: first, all Chinese minority groups were included in the analyses to clarify intra-ethnic differences; second, data from two Chinese decennial censuses and longitudinal statistical modeling were used to investigate the effect of time on ethnic stratification.

The purpose of this paper is to study the identification methods for multivariable nonlinear Box‐Jenkins systems with autoregressive moving average (ARMA) noises, based on the auxiliary model and the multi‐innovation identification theory.

A multi‐innovation generalized extended least squares (MI‐GELS) and a multi‐innovation generalized ex‐tended stochastic gradient (MI‐GESG) algorithms are developed for multivariable nonlinear Box‐Jenkins systems based on the auxiliary model. The basic idea is to construct an auxiliary model from the measured data and to replace the unknown terms in the information vector with their estimates (i.e. the outputs of the auxiliary model).

It is found that the proposed algorithms can give high accurate parameter estimation compared with existing stochastic gradient algorithm and recursive extended least squares algorithm.

In this paper, the AM‐MI‐GESG and AM‐MI‐GELS algorithms for MIMO Box‐Jenkins systems with nonlinear input are presented using the multi‐innovation identification theory and the proposed algorithms can improve the parameter estimation accuracy. The paper provides a simulation example.

This paper aims to establish a method to optimize reflow profiles and achieve high reliability of solder joints on the basis of the heating factor, Q_η, a measure of the reflow profile related to reliability of reflow processed products.

The focus of the paper is on how to realize the optimal range of Q_η, since there is no need to pay particular attention to the shape of a reflow profile when performing a heating factor‐based optimization. The coldest point on the printed circuit board assembly (PCA), which experiences the minimum heating factor (Q_η^min) during the reflow process, was used to set the lower limit of the optimal range (Q_η^L). If Q_η^min approaches Q_η^L and the temperature difference across the PCA is minimized, then the solder joints on the PCA will all experience heating factors within the optimal range, ensuring high quality reflow soldering. Establishing an initial reflow profile may be performed using profiling software. The resultant oven recipe may then be used as the reference recipe by which to apply the heating factor‐based optimization. A combinatorial parameter, H_t, is defined to represent the temperature settings of all the top heating zones within the heating section of the reflow oven. The relative difference between H_t and each top heating zone temperature setting is derived from the reference recipe, and H_t is then adjusted to achieve Q_η^L for Q_η^min. This is achieved by using a least squares estimation method to build a regression model for Q_η^min versus H_t.

Experiments and regression analysis have demonstrated that Q_η^min varied linearly with H_t, with α denoting its slope. With a measured Q_η^min in response to the reference setup after the first run of a PCA, H_t should be increased by ((Q_η^L−Q_η^min)/α) to attain Q_η^L in the second run. Thereby, a suitable reflow process recipe can be obtained with only two reflow runs where Q_η^min is close to Q_η^L.

The optimal range of heating factor for lead‐free solder pastes is currently unknown, and the method to establish the required oven recipe for achieving a required reflow profile requires further exploration.

Provides a methodology for reducing the risk of process‐related reliability issues in lead‐free soldering.

Q_η^L can be fairly quickly achieved for Q_η^min with the approach established in this paper, facilitating the formation of solder joints with high reliability during the reflow soldering process.

This paper aims to offer a convenient method to develop an oven recipe for a specific soldering profile in a reflow process. The method is devised to quickly achieve proper profile shape and heating factor Q_η, a measure of success for high reliability of the solder joints reflowed.

An in‐depth analysis of the heating mechanism and some experiments of the reflow soldering process are performed to research on how to realize a specific shape reflow profile were conducted.

Heating mechanism analysis and experiments demonstrate that the combinatorial parameters based method is feasible to do thermal profiling.

The mapping function among a particular configured PCBA, an oven used, a target reflow profile and an optimal range of the heating factor should be further established for fast and reliable production of reflow soldering.

Provides a methodology for designing an oven recipe for reflow soldering production.

An oven recipe can be quickly attained with the approach established in this paper, facilitating the formation of solder joints with high reliability during the reflow soldering process.

Based on the inverse kinematics and task space dynamic model, this paper aims to design a high-precision trajectory tracking controller for a 2-DoF translational parallel manipulator (TPM) driven by linear motors.

The task space dynamic model of a 2-DoF TPM is derived using Lagrangian equation of the first type. A task space dynamic model-based feedforward controller (MFC) is designed, which is combined with a cascade PID/PI controller and velocity feedforward controller (VFC) to construct a hybrid PID/PI+VFC/MFC controller. The hybrid controller is implemented in MATLAB/dSPACE real-time control platform. Experiment results are given to validate the effectiveness and industrial applicability of the hybrid controller.

The MFC can compensate for the nonlinear dynamic characteristics of a 2-DoF TPM and achieve better tracking performance than the conventional acceleration feedforward controller (AFC).

The task space dynamic model-based hybrid PID/PI+VFC/MFC controller is proposed for a 2-DoF linear-motor-driven TPM, which reduces the tracking error by at least 15 percent compared with conventional hybrid PID/PI+VFC/AFC controller. This control scheme can be extended to high-speed and high-precision trajectory tracking control of other parallel manipulators by reprogramming the feedforward signals of traditional cascade PID/PI controller.

The purpose of this paper is to propose a novel managerial approach for improving traditional intellectual capital (IC) management, and its other latter improved approaches, by integrating the comprehensive IC model with more reliable decision science methods, including the Delphi technique and the analytic network process. This proposed integration endeavors to resolve the issues of IC management related to intuitive decisions by executives and the lack of information regarding the relationships among the considered elements.

The proposed method was applied to a real case study of a logistics organization. This application is expected to increase the IC study in this field since logistics is identified as an underdeveloped business in the field of IC management. In this study, the proposed method was used to identify the priorities of IC management of the firm.

The obtained results showed that the method provides a new managerial approach to IC management by conveying the important weights and priorities of the major and minor IC elements of a logistics business. The obtained outcome also confirmed the results of past studies.

This study provides a systematic and scientific decision framework that improves previous IC management approaches. This proposed method conveys a new management approach by including proper decision science methods with the comprehensive IC framework. This hybrid concept has not been explored by previous IC management approaches.