Design of an adaptive tracker for n-link rigid robotic manipulators based on super-twisting global nonlinear sliding mode control

This paper develops an adaptive super-twisting global nonlinear sliding mode control technique for n-link rigid robotic manipulators. A novel control law is designed to guarantee elimination of the reaching phase and existence of the sliding mode around the surface right from the initial time. Furthermore, the adaptive tuning law eliminates requirement of the knowledge about the upper bounds of external disturbances. By using the proposed method, a robust controller is designed so that the tracking error of rigid manipulator is convergent to the global nonlinear sliding surface in a finite time, and strong robustness with respect to large uncertainties and disturbances is guaranteed. Illustrative simulations on a two-link elbow robot manipulator and a three degree of freedom rigid manipulator are presented to show the robustness and effectiveness of the suggested design compared to other method. Moreover, a simulation as well as experimental study of a rotary inverted pendulum system demonstrates the applicability of the proposed method.     

Toward the heat convection enhancement of nanofluids flowing in a 3D microchannel affected by a nonuniform magnetic field

In the present investigation, the behavior of laminar convective flow and heat transfer in a three-dimensional horizontal square duct using different water-based nanofluids (Fe₃O₄/water, and carbon nanotubes/water) is numerically investigated. The channel is subjected to a periodic partial or full magnetic field. The outer surface is subjected to a constant heat flux density. The problem is numerically solved via the finite volume method with a second-order precision. The numerical simulations covered a range of the Reynolds number 50 ≤ Re ≤ 400, Hartmann number 0 ≤ Ha ≤ 50, and concentration of nanoparticles 0 ≤ ϕ ≤ 0.02 for different modes of the magnetic field application and direction. Examination of the hydrodynamic and thermal behavior shows significant heat transfer performances obtained when applying transversal and partial periodic magnetic fields simultaneously. More precisely, it is found that the favorable protocol improved the heat transfer rate by 85% in the duct flowing by the Ferrofluid at Ha = 50. Furthermore, findings illustrate that the overall heat transfer rate presented in terms of the mean Nusselt number and the highest compromise (heat transfer augmentation-pressure losses diminution) are obtained in the case of Fe₃O₄ nanoparticles for all taken values of Reynolds and Hartmann numbers, whatever the manner and direction of the applied magnetic field.     

From Trajectory Tracking Control to Leader–Follower Formation Control

Abstract

This work investigates the leader–follower formation control of multiple nonholonomic mobile robots. First, the formation control problem is converted into a trajectory tracking problem and a tracking controller based on the dynamic feedback linearization technique drives each follower robot toward its corresponding reference trajectory in order to achieve the formation. The desired orientation for each follower is selected such that the nonholonomic constraint of the robot is respected, and thus the tracking of the reference trajectory for each follower is feasible. An adaptive dynamic controller that considers the actuators dynamics in the design procedure is proposed. The dynamic model of the robots includes the actuators dynamics in order to obtain the velocities as control inputs instead of torques or voltages. Using Lyapunov control theory, the tracking errors are proven to be asymptotically stable and the formation is achieved despite the uncertainty of the dynamic model parameters. In order to assess the proposed control laws, a ROS-framework is developed to conduct real experiments using four ROS-enabled mobile robots TURTLEBOTs. Moreover, the leader fault problem, which is considered as the main drawback of the leader–follower approach, is solved under ROS. An experiment is conducted where in order to overcome this problem, the desired formation and the leader role are modified dynamically during the experiment.     

Preparation and luminescence properties of novel K2ZnP2O7: Mn2+ green phosphor

Novel green-emitting phosphors K₂Zn_1???xP₂O₇: x mol% Mn²⁺ have been successfully prepared using classical solid-state reaction method in air atmosphere, doped by different Mn²⁺ ion contents, namely x?=?0.5, 1, 1.25 and 1.5 mol%. The samples were characterized by the thermogravimetric (ATD/ATG/DSC), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), steady and time-resolved photoluminescence techniques. It was found that all K₂Zn_1???xP₂O₇: x mol% Mn²⁺ samples crystallize in the tetragonal phase with P4₂/mnm space group. Upon 425 nm excitation, K₂ZnP₂O₇: Mn²⁺ exhibits an intense broad green asymmetric emission band peaking at 520 nm, owing to the ⁴T₁→⁶A₁(⁶ S) transition of Mn²⁺ ion in K₂ZnP₂O₇. In addition, it is suggested that Mn²⁺ ions occupy more than one symmetry site in the host K₂ZnP₂O₇. The optimal Mn²⁺ ion concentration in K₂ZnP₂O₇:Mn²⁺ phosphor is 1 mol % and with the lifetime 9.81 ms.

     

Optimization of the Culture Medium Composition to Improve the Production of Hyoscyamine in Elicited Datura stramonium L. Hairy Roots Using the Response Surface Methodology (RSM)

Traditionally, optimization in biological analyses has been carried out by monitoring the influence of one factor at a time; this technique is called one-variable-at-a-time. The disadvantage of this technique is that it does not include any interactive effects among the variables studied and requires a large number of experiments. Therefore, in recent years, the Response Surface Methodology (RSM) has become the most popular optimization method. It is an effective mathematical and statistical technique which has been widely used in optimization studies with minimal experimental trials where interactive factors may be involved. This present study follows on from our previous work, where RSM was used to optimize the B5 medium composition in [NO(3-)], [Ca(2+)] and sucrose to attain the best production of hyoscyamine (HS) from the hairy roots (HRs) of Datura stramonium elicited by Jasmonic Acid (JA). The present paper focuses on the use of the RSM in biological studies, such as plant material, to establish a predictive model with the planning of experiments, analysis of the model, diagnostics and adjustment for the accuracy of the model. With the RSM, only 20 experiments were necessary to determine optimal concentrations. The model could be employed to carry out interpolations and predict the response to elicitation. Applying this model, the optimization of the HS level was 212.7% for the elicited HRs of Datura stramonium, cultured in B5-OP medium (optimized), in comparison with elicited HRs cultured in B5 medium (control). The optimal concentrations, under experimental conditions, were determined to be: 79.1 mM [NO(3-)], 11.4 mM [Ca(2+)] and 42.9 mg/L of sucrose.     

A new two-dimensional analytical subthreshold behavior model for submicron Triple Material Gate (TM) GaN MESFET

A new two-dimensional (2D) analytical model for a Triple Material Gate (TM) GaN MESFET has been proposed and modeled to suppress the short channel effects and improve the subthreshold behavior. The analytical model is based on a two-dimensional analysis of the channel potential, threshold voltage and subthreshold swing factor for TM GaN MESFET is developed. The aim of this work is to demonstrate the improved subthreshold electrical performances exhibited by TM GaN MESFET over dual material gate and conventional single material gate MESFET. The results so obtained are verified and validated by the good agreement found with the 2D numerical simulations using the ATLAS device simulation software. The models developed in this paper will be very helpful to understand the device behavior in subthreshold regime for future circuit applications.     

Characterisation and modelling of behaviour of a shape memory alloys

Shape memory alloys (SMAs) provide an attractive solid-state actuation alternative to engineers in various fields due to their ability to exhibit recoverable deformations while under substantial loads. This feature is of particular importance when utilising the smart composite materials reinforced by SMA. Many constitutive models describing this repeatable phenomenon have been proposed, where some models also capture the effects of rate-independent irrecoverable deformations in SMAs. This paper presents experimental investigations and numerical simulations on shape memory alloys. First, by consisting in determining the transformations of equiatomic Ti–Ni shape memory alloys by differential scanning calorimeter. Then, in order to validate a 3D numerical model of the pseudoelastic behaviour of SMA allowing a finite strain analysis, a set of experimental tests at various initial temperatures is proposed. Finally, the numerical simulations of uniaxial tests performed on shape memory alloys are presented and compared with experimental data, permitting the validation of the proposed modelling. Reasonably good correlation is obtained between the experimental and model predictions.     

Hard machining of hardened bearing steel using cubic boron nitride tool

In many cases, hard machining remains an economic alternative for bearing parts fabrication using hardened steels. The aim of this experimental investigation is to establish the behaviour of a CBN tool during hard turning of 100Cr6-tempered steel. Initially, a series of long-duration wear tests is planned to elucidate the cutting speed effects on the various tool wear forms. Then, a second set of experiments is devoted to the study of surface roughness, cutting forces and temperature changes in both the chip and the workpiece. The results show that CBN tool offers a good wear resistance despite the aggressiveness of the 100Cr6 at 60HRC. The major part of the heat generated during machining is mainly dissipated through the chip. Beyond 280 m/min, the machining system becomes unstable and produces significant sparks and vibrations after only a few minutes of work. The optimal productivity of machined chip was recorded at a speed of 120 m/min for an acceptable tool flank wear below 0.4 mm. Beyond this limiting speed, roughness (R_a) is stabilized because of a reduction in the cutting forces at high speeds leading to a stability of the machining system. The controlling parameter over roughness, in such hard turning cases, remains tool advance although ideal models do not describe this effect rationally. Surface quality obtained with CBN tool significantly compared with that of grinding despite an increase in the advance by a factor of 2.5. A relationship between flank wear (VB) and roughness (R_a) is deduced from parametric analysis based on extensive experimental data.