Finite-Time Dynamic Tracking Control of Parallel Robots with Uncertainties and Input Saturation.

This paper considers the finite-time dynamic tracking control for parallel robots with uncertainties and input saturation via a finite-time nonsingular terminal sliding mode control scheme. A disturbance observer is designed to estimate the lumped disturbance in the dynamic model of the parallel robot, including modeling errors, friction and external disturbance. By introducing the fractional exponential powers into the existing asymptotic convergent auxiliary system, a novel finite-time convergent auxiliary system is constructed to compensate for input saturation. The finite-time nonsingular terminal sliding mode control is proposed based on the disturbance estimation and the state of the novel auxiliary system, so that the convergence performance, control accuracy and robustness are improved. Due to the estimation and compensation for the lumped disturbance, the inherent chattering characteristic of sliding mode control can be alleviated by reducing the control gain. The finite-time stability of the closed-loop system is proved with Lyapunov theory. Finally, simulation and experimental research on the dynamic control of a conveying parallel robot are carried out to verify the effectiveness of the proposed method.

On multi-axis motion synchronization: The cascade control structure and integrated SMC-ADRC design.

In this paper, the cascade control (CC), a structure popular among practitioners in many industry sectors, is used to bridge the two prominent research methodologies in SMC and ADRC for the purpose of multi-axis motion synchronization. In particular, the cascade sliding mode control(C-SMC) is first proposed, from which the cascade active disturbance rejection control (C-ADRC) is derived. This allows the linear and fal-function based nonlinear control actions to be naturally integrated and the controller parameters can be tuned easily with the proposed space-time scaling method. The control law is constructed and validated in multi-axis motion synchronization of parallel mechanisms. The results show that the proposed scheme is effective and practical, with the robustness associated with the bandwidth constraints.

Active disturbance rejection synchronization control for parallel electro-coating conveyor.

A bandwidth-parameterized active disturbance rejection synchronization control (ADRSC) is proposed for the parallel electro-coating conveyor. The Laplacian matrix is extracted from the newly defined adjacent-cross-coupling errors and embedded in the controller. It is shown that the proposed ADRSC possesses the capability to achieve synchronization by reformulating cross-coupling as average disturbance to be rejected, thus reducing the dynamics to the canonical form of chained integrators. Furthermore, the upper bound of the bandwidth is established as the trade-off between the accuracy of synchronization and stability. The main contribution of this paper is to extend the active disturbance rejection principle to the accommodation of cross-coupling in synchronization. Simulations and experiments show that this proposed method is effective and practical.

Charge-assisted non-volatile magnetoelectric effects in NiFe2O4/PMN-PT heterostructures.

Electric field tuning of magnetization is a viable path to realize magnetoelectric (ME) coupling effect while developing novel multifunctional devices. The combined charge and strain effects can produce multilevel manipulation in multiferroic heterostructures. Both charge and strain co-mediated ME effects were investigated in NiFe2O4/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (NFO/PMN-PT) and NFO/Pt/PMN-PT heterostructures. The charge effect was detected by the existence of magnetization imparities between the positive and negative fields. The imparities could be enlarged by inserting a Pt buffer layer between the NFO film and PMN-PT substrate. The suppressed depolarization field effect enhanced ferroelectric polarization of PMN-PT, which strengthened the polarization-dependent charge effect in the NFO/Pt/PMN-PT heterostructures. The enhancement of the charge effect helped achieve a stronger ferromagnetic-ferroelectric coupling effect.

Waist-to-height ratio as a screening measure for identifying adolescents with hypertriglyceridemic waist phenotype.

OBJECTIVE: The purpose of the present study was to investigate the relationship between waist-to-height ratio (WHtR) and the hypertriglyceridemic waist (HTGW) phenotype to test the hypothesis that WHtR can identify adolescents at high risk of the HTGW phenotype. METHODS: In 2006, anthropometric measurements were assessed in a cross-sectional population-based study of 3136 Han adolescents aged 13-17 years. Blood samples were collected to measure triacylglycerol concentrations. WHtR was calculated by waist circumference/height. The HTGW phenotype was represented by the simultaneous presence of elevated serum triglycerides and increased waist circumference. The ability of WHtR to accurately define the HTGW phenotype was assessed by area under the curve (AUC). RESULTS: The prevalence of the HTGW phenotype was 3.3% (boys 3.6% vs. girls 2.9%, χ2=1.424, p=0.233). The prevalence of the HTGW phenotype increased with WHtR (p<0.001). The accuracy of WHtR in the identification of the HTGW phenotype (as assessed by AUC) was over 0.85, both in boys and girls (AUC: 0.956 in boys and 0.961 in girls). WHtR cutoff values, chosen to maximize sensitivity plus specificity, for the HTGW phenotype were calculated to be 0.48 in boys and 0.46 in girls. The sensitivities were 98.3% in boys and 97.7% in girls. The specificities were 88.0% in boys and 86.8% in girls. CONCLUSIONS: WHtR is simpler than the HTGW phenotype and does not require blood tests. The prevalence of the HTGW phenotype increased with WHtR. Higher WHtR can identify adolescents with high risk of the HTGW phenotype.

Mid-upper arm circumference as a screening measure for identifying children with hypertension.

BACKGROUND: Overweight and obesity, defined by BMI and waist circumference cut-off points, have long been recognized as risk factors for hypertension. Another proposed indicator of obesity in children is mid-upper arm circumference (MUAC). OBJECTIVE: The aims of this study were to determine whether MUAC could be used to identify hypertension in Han children aged 7-12 years. PARTICIPANTS AND METHODS: In 2011, anthropometric measurements were assessed in a cross-sectional population-based study of 1352 Han children aged 7-12 years. Hypertension was defined according to the 2004 National High Blood Pressure Education Program Working Group definition. Receiver operating characteristic curve analyses were carried out to assess the accuracy of MUAC as diagnostic tests for hypertension. RESULTS: The accuracy levels of MUAC for identifying hypertension [as assessed by area under the curve (AUC)] were over 0.85 in boys (AUC: 0.894), but not in girls (AUC: 0.831), and the cut-off values were the 75th percentile for boys and girls. The sensitivities were 87.5% in boys and 70.0% in girls. The AUC of MUAC was not significantly different from the AUC of BMI and waist circumference for both boys and girls (P>0.05). CONCLUSION: The present study shows that MUAC is a simple, inexpensive, and accurate measurement for identifying hypertension in Han children. MUAC is equivalent to BMI and waist circumference as a screening test for hypertension.

Hypertriglyceridemic waist-to-height ratio phenotype: association with atherogenic lipid profile in Han adolescents.

Hypertriglyceridemic waist (HW) phenotype was associated with an atherogenic lipid profile in adolescents. But unlike adults, the cutoffs of waist circumference are age- and gender-specific standards and are less feasible for non-professional use. The present study tested the hypothesis that simple variables, such as waist-to-height ratio (WHtR) and serum triacylglycerol (TG) concentrations, could be used as screening tools for the identification of adolescents characterized by atherogenic lipid profile. In 2006, anthropometric and biochemical measurements were assessed in a cross-sectional population-based study of 3136 Han adolescents, aged 13-17 years. The hypertriglyceridemic waist-to-height ratio (HWHtR) phenotype was defined as serum TG concentrations ≥1.47 mmol/L and WHtR ≥0.48 for boys and ≥0.46 for girls. Hypercholesterolemia (total cholesterol ≥5.18 mmol/L), high low-density lipoprotein cholesterol (LDL-C ≥3.37 mmol/L), low high-density lipoprotein cholesterol (HDL-C <1.03 mmol/L), and high non-HDL-C (≥3.76 mmol/L) were considered as atherogenic lipid profiles. After control for age and sex, adolescents with the HWHtR phenotype were more likely to have hypercholesterolemia (odds ratio (OR) = 7.8, 95 % confidence interval (CI) = 3.5-17.3, P < 0.001), high LDL-C (OR = 9.4, 95 % CI = 2.8-31.2, P < 0.001), low HDL-C (OR = 10.8, 95 % CI = 6.9-17.0, P < 0.001), and high non-HDL-C (OR = 22.9, 95 % CI = 10.0-52.2, P < 0.001) than those adolescents with normal WHtR and normal serum TG concentrations. CONCLUSION: The present study demonstrates that HWHtR phenotype is a simple marker for identifying adolescents with atherogenic lipid profile. Compared with HW phenotype, HWHtR phenotype is a non-age-dependent index with higher applicability to screen for cardiovascular risk factors in adolescents. WHAT IS KNOWN: • The hypertriglyceridemic waist phenotype is represented by the simultaneous presence of elevated serum triacylglycerol and increased waist circumference. Hypertriglyceridemic waist phenotype can identify adolescents with metabolic syndrome. But the cutoffs of waist circumference are age- and gender-specific standards and are less feasible for non-professional use. WHAT IS NEW: • The present study demonstrates that hypertriglyceridemic waist-to-height ratio phenotype is a simple marker for identifying adolescents with atherogenic lipid profile. Compared with hypertriglyceridemic waist phenotype, hypertriglyceridemic waist-to-height ratio phenotype is a non-age-dependent index with higher applicability to screen for cardiovascular risk factors in adolescents.