Mobile robot characterized by dynamic and kinematic equations and actuator dynamics: Trajectory tracking and related application

This paper establishes control strategies for wheeled mobile robots which are subjected to nonholonomic constraints. The mobile robot model includes the kinematic and dynamic equations of motion and the actuator dynamics. Using the notion of virtual vehicle and the concept of flatness, and applying the backstepping methodology the paper proposes control schemes for trajectory tracking for the considered augmented model of the mobile robot. The resulting controller ensures exponential convergence to a desired trajectory. Applications of the tracking controller for convoy-like vehicles governed by the augmented models are considered as well. Simulation results and lab experiments are demonstrated.     

DESIGN AND ANALYSIS OF NOVEL ACTIVE ACTUATOR TO CONTROL LOW FREQUENCY VIBRATIONS OF SHAFT SYSTEM

Aiming at providing with high-load capability in active vibration control of large-scale rotor system, a new type of active actuator to simultaneously reduce the dangers of low frequency flexural and torsional vibrations is designed. The actuator employs electro-hydraulic system and can provide a high and circumferential load. To initialize new research, the characteristics of various kinds of active actuators to control rotor shaft vibration are briefly introduced. The purpose of this paper is to introduce the preliminary results via presenting the structure, functions and operating principles, in particular, the working process of the electro-hydraulic system of the new actuator which includes a set of high speed electromagnetic valves and a series of sloping cone-shaped openings, and presenting the transmission relationships among the control parameters from control signals into the valves to active load onto shaft. The course of the work is dynamic, and a series of spatial forces and moments are put on the shaft to get an external resultant force to reduce excitations that induce vibration of shafts. By checking states of vibration, the actuator can control the impulse width and the interval of injection time for applying different control force to a vibration shaft in two circumference directions through the regulating action of a set of combination directional control valves. The results from simulating analysis and experiment show evidence of that this design can satisfy the case of active process of decreasing of flexural and torsional vibrations.     

Microstructural and mechanical behavior of Na0.4K0.1Bi0.5TiO3 ferroelectric ceramics

Na_0.4K_0.1Bi_0.5TiO₃ (NKBT) solid solution was synthesized by the conventional solid-state route. X-ray diffraction pattern of poled NKBT ceramic was refined by the Rietveld technique to determine the structural phases (Rhombohedral and Tetragonal) present in the solid solution. High density (98% of theoretical density) ceramics exhibited an average grain size of 1.2 μm from the SEM analysis. EDS spectra and elemental mapping were recorded to confirm the formation of exact stoichiometric composition in the prepared ceramic. The hardness of the NKBT ceramic was measured by nano-indentation and Vickers microhardness techniques. Young's modulus was measured by nano-indentation, ultrasonic echo pulse tester, compression tests and compared. The effect of mechanical stress on piezoelectric properties of pre-poled NKBT ceramic was studied at room temperature. Fracture toughness (1.45 MPa m^1/2) and compressive strength (250 MPa) of the ceramic were determined to ensure its candidature for actuator application from a mechanical perspective. The phenomena of mechanical depolarization were explained through the domain rotation concept.     

A theoretical model for the bending of a laminated beam with SMA fiber embedded layer

A theoretical model for the bending of a laminated beam bonded with shape memory alloy (SMA) fiber reinforced layer is presented. The constitutive relations of the SMA layer are obtained by using the method of micromechanics. The bending of the laminated beam is then discussed, and the relationship between bending moment, curvature and temperature are provided. The governing relationships obtained in this paper can be used for theoretical predications of thermomechanical properties of beam-like SMA actuators.     

Effect of Thermoelastic Coupling on Thermally Induced Plate Parametric Vibrations

Vibration control for linear elastic plate due to time-dependent in-plane forces in the presence of raised temperature is presented. Transverse inertia, modified terms corresponding to adiabatic deformations and a viscous external damping are taken into account. The coupled partial differential equations describing the transverse plate motion and the electric potential are used. The two piezoelectric layers are placed symmetrically as actuators. When voltages of equal magnitude but opposite phase are applied to the upper and the lower piezoelectric layers of the plate, induced strains are resulting in flexure action. The piezoelectric sensor is used to measure plate deformations. The derived coupled equations are applicable to stability analysis of plate parametric vibration. The control law is derived using the Liapunov approach with a functional as a sum of the modified mechanical plate energy and the energy of electric field. Influence of the thermoeleastic effect and feedback gain factor on stability domain is shown.     

On actuators number in distributed systems

The aim of this brief paper is to give original results regarding inputs for abstract distributed parameter systems. More precisely we show that if we increase the number of actuators exciting a system, the transfer cost functional will be cheaper. Until now this intuitive result has only been noticed in numerical simulations and for certain classes of distributed parameter systems. The principle of the approach consists to introduce the notion of extended actuators. The results are given for various cases where the actuators can be internal, pointwise or boundary.     

新型液粘调速器及其在电厂中的应用

在分析现有液粘调速器存在的问题的基础上,详细介绍了笔者研制成功的一种直动式液粘调速器及其应用实例。     

Degradation of PZT-4D hard piezoceramics under moderate heating

The changes produced in the dielectric permittivity, the transverse piezoelectric coefficient, the k₃₁ coupling factor, the s₁₁^E elastic compliance and the mechanical quality factor of PZT-4D hard piezoceramics by heating have been investigated. The ceramics were then repoled, and the reversible and irreversible components of the changes quantified. The results showed that depolarisation began at 150°C. A high level of poling was retained even after heating at 300°C (d₃₁=−83×10⁻¹² C N⁻¹ and k₃₁=0.225), only 20°C below the transition temperature. However, a significant irreversible degradation of the mechanical quality factor, Q_m, occurred at a temperature as low as 100°C. Experiments on thinned specimens showed that the degradation of Q_m took place in the Ag doped layer produced by the electrodes. Indentation surface cracks were also introduced into the ceramics to investigate the behaviour of cracks during the thermal treatments.