In this paper, we discuss the finite-time consensus problem for leaderless and leader–follower multi-agent systems with external disturbances. Based on the finite-time control technique, continuous ...distributed control algorithms are designed for these agents described by double integrators. Firstly, for the leaderless multi-agent systems, it is shown that the states of all agents can reach a consensus in finite time in the absence of disturbances. In the presence of disturbances, the steady-state errors of any two agents can reach a region in finite time. Secondly, for the leader–follower multi-agent systems, finite-time consensus algorithms are also designed based on distributed finite-time observers. Rigorous proof is given by using Lyapunov theory and graph theory. Finally, one example is employed to verify the efficiency of the proposed method.
Finite-time boundedness and finite-time weighted L2-gain for a class of switched delay systems with time-varying exogenous disturbances are studied. Based on the average dwell-time technique, ...sufficient conditions which guarantee the switched linear system with time-delay is finite-time bounded and has finite-time weighted L2-gain are given. These conditions are delay-dependent and are given in terms of linear matrix inequalities. Detail proofs are given by using multiple Lyapunov-like functions. An example is employed to verify the efficiency of the proposed method.
For the attitude tracking of quad-rotor system in the presence of disturbances and input saturation, an active finite-time disturbance rejection control method is presented in this paper. ...Specifically, first, based on a second-order attitude model of quad-rotor in the absence of disturbances, a bounded finite-time attitude control algorithm under input saturation is proposed to conquer the saturation constraint for practice system. At the second step, considering the existence of disturbances including constant disturbances or time-varying disturbances, a finite-time disturbance observer is designed to estimate the disturbances. Finally, using the idea of active disturbance rejection, the disturbance is directly compensated through the control input channel in the case of constant disturbance. In the case of time-varying disturbance, an integral sliding mode control method is employed here to handle the disturbance estimating error. Rigorous theoretical analysis is provided to prove that the desired attitude can be tracked in a finite time no matter what kinds of disturbances. Simulation results are given to verify the effectiveness and advantages of the the proposed active finite-time control method.
Thermal models are important in the process of predicting the thermal characteristics and corresponding thermal error of multi-link high-speed precision presses (MLHSPPs) with an oil-lubrication ...system. Previous models only involved the effects of bearing stiffness, temperature change of bearings, flexibility of crank shaft on the heat generation power, while the influences of revolute clearance joint and flexibility of linkage are seldom considered, which inevitably reduces the accuracy of thermal analysis. To overcome this problem, dynamic models of flexible multi-link mechanisms (MLM) with clearance, lubrication, crankshaft-bearing system are constructed, the interaction forces between pin and bushing are obtained to calculate its heat generation power. Then, an improved model of MLHSPP with lubrication is proposed to analyze the temperature evolution and the thermal error between slider and work table at the position of LDP, by considering bearing stiffness, temperature change of bearings, flexibility of crank shaft, linkage, clearance, lubrication and thermal contact resistance all together. Compared with results from traditional models, the simulation data from this improved thermal model agree well with experiment, which proves the validity of the proposed model. Furthermore, the temperature rise and the thermal error of MLHSPP between slider and work table at the position of LDP under different input speeds, lubricating oil flux and contact angles of ball bearing were also studied.
In this paper, the problem of making an input-delay system with saturating actuators finite-time stable by virtue of digital control is investigated. A digital state feedback controller and digital ...observer-controller compensator are designed for two cases: when the state of the input-delay system are available or when it is unavailable. Sufficient conditions which guarantee finite-time stability of a closed-loop input-delay system are given and the proof procedure is presented in a heuristic way by constructing appropriate comparison functions. The condition can be transformed into the intersection of two curves satisfying some constraints, which reveals the relationship between designed parameters clearly. Finally, simulation results are presented to validate the method proposed in this paper.
An optimal fractional order proportional differentiation (FOPD) controller is designed for path tracking control of a specified tractor by taking integral absolute error (IAE) performance index as ...the evaluation criterion. The controller parameters are tuned by two methods: flat phase tuning; or an improved tuning method proposed in this paper, which can compensate for the missing parts of the flat phase method caused by computation. Comparison and analysis of two tuning methods are given. Moreover, the optimal FOPD controller is compared with the optimal integer order proportion differentiation (IOPD) controller tuned by performance indexes through simulations. Simulation results demonstrate that the optimal FOPD controller enables the closed-loop system to have smaller IAE value, and enhances IAE performance allowing less crop to be crushed. The efficiency of the proposed tuning method and the advantages of the FOPD controller are presented.
•Improved parameter tuning to compensate missing parts of flat phase method.•Enables closed-loop system with smaller integral absolute error than IOPD controller.•Enhanced IAE performance can decrease the amount of crop crushed.
Finite-time feedback control of input-delay system with nonlinear saturating actuators is addressed in this paper. First, a state feedback controller is designed to make the closed-loop systems ...finite-time stable. Sufficient conditions which can guarantee finite-time stability of an input-delay system with saturating actuators are given in terms of the comparison function method. For the case where the states cannot be measured, an observer is presented to estimate the unavailable states and the observer-controller compensator strategy is proposed. Finally, an example is employed to illustrate the efficiency of the proposed method. It is not difficult to conclude from the analysis and the simulation results that by virtue of the proposed method the transient characteristics of the closed-loop system can be easily guaranteed to comply with the requirements of the practice.
In traditional models, only the effect of temperature change of bearings on the heat generation power and thermal contact resistance is considered. But the effect of bearing stiffness and flexibility ...of crank shaft on the heat generation power is often neglected, thereby impairing the accuracy of the thermal analysis. Therefore, a better thermal model is demanded to accurately analyse the thermal characteristics of a Multi-link ultra-precision press system (MLUPPS). By combining the effect of stiffness of bearing and flexibility of crank shaft on the heat generation power, an improved thermal model of MLUPPS was developed in this work. The model was based on as-derived kinematic and dynamic equations of Multi-link transmission mechanism (MLTM) and flexible dynamic model of crankshaft-bearing system. The dimension chain of thermal error is constructed to analyse the dimensional error between the slider and the work table at the position of Bottom dead point (BDP). The developed thermal model of MLUPPS and its analysis results from this model are in good agreement with the measurement results, and that is more accurate than the traditional one. The simulation results reveal that the maximum temperature rise of MLUPPS occurs at the crank shaft, and the dimensional error between the slider and the work table at the position of BDP is due to thermal expansion fluctuation before the generation and conduction of heat power reaches balance. The temperature rise and thermal error of MLUPPS under different rotation speeds, piling forces and bearing stiffness were also studied.
The dynamic model is significant for the analysis of the vibrational characteristics of the wheeled tractor system with implement and front axle hydropneumatic suspension. In this work, the nonlinear ...stiffness and damping equations are derived first. The dynamic coupling relationship among cabin, three-point hitch structure, and implement are figured out, and the dynamic model of the half agricultural wheeled tractor/implement system is presented considering the effects of three-point hitch structure, passive silent blocks of cabin, and front axle hydropneumatic suspension together. To validate the model, the power spectral densities (PSDs) of the driver seat, cabin, chassis, and implement acquired from numerical simulations are compared with those from experiments, respectively. Under different forward speeds, two groups of results match well. Based on the model, the influences of passive cabin suspension, implement, and front axle hydropneumatic suspension on the dynamical characteristics of the tractor system are investigated. Results indicate that the front axle hydropneumatic suspension will deteriorate the ride comfort of the driver but improve the handing stability. The passive cabin suspension reduces the operational stability while improving much more ride comfort than the front axle hydropneumatic suspension does. The driver’s comfortableness will be increased due to implement; meanwhile, handling stability will be compromised. Besides, the impacts of initial nitrogen volume, pressure of accumulators, and orifice diameter of throttle valves on the vibration characteristics of the tractor system are also inspected.
Here, classification of rice planthopper (RPH) based on shape descriptors was addressed to solve the low semantics problem of shape features in traditional RPH (mainly including the whiteback ...planthopper (Sogatella furcifera (Horváth)), the brown planthopper (Nilaparvata lugens (Stål)), and the small brown planthopper (Laodelphax striatellus (Fallén))) image classification research. Images of RPH were obtained from rice field by an automatic insect image acquisition device made by ourselves and insect images were divided into single images based on OTSU threshold segmentation algorithm. In terms of the images of RPH after segmentation, Fourier descriptors and Hu moments, which are from two aspects of contour curve and shape area, were extracted to describe shape features of RPH. Then, random forest (RF), an ensemble learning algorithm, was used as the classifier to distinguish RPH efficiently. The optimal number of trees and prediction variables of RF are chosen to be 150 and 4, respectively, by minimising the out-of-bag error. Experimental results show that classification accuracy of RPH based on shape descriptors reaches up to 93.93%. Therefore, it has been verified that the classification with the method presented here is accurate and semantic.
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