Stability of Iterative Learning Control with Data Dropouts via Asynchronous Dynamical System

In this paper, the stability of iterative learning control with data dropouts is discussed. By the super vector formulation, an iterative learning control （ILC） system with data dropouts can be modeled as an asynchronous dynamical system with rate constraints on events in the iteration domain. The stability condition is provided in the form of linear matrix inequalities （LMIS） depending on the stability of asynchronous dynamical systems. The analysis is supported by simulations.

Robust Attitude Control for Reusable Launch Vehicles Based on Fractional Calculus and Pigeon-inspired Optimization

In this paper, a robust attitude control system based on fractional order sliding mode control and dynamic inversion approach is presented for the reusable launch vehicle RLV during the reentry phase. By introducing the fractional order sliding surface to replace the integer order one, we design robust outer loop controller to compensate the error introduced by inner loop controller designed by dynamic inversion approach. To take the uncertainties of aerodynamic parameters into account, stochastic robustness design approach based on the Monte Carlo simulation and Pigeon-inspired optimization is established to increase the robustness of the controller. Some simulation results are given out which indicate the reliability and effectiveness of the attitude control system. © 2014 Chinese Association of Automation.

A New Tuning Method for Two-Degree-of-Freedom Internal Model Control under Parametric Uncertainty

Internal model control （IMC） yields very good performance for set point tracking, but gives sluggish response for disturbance rejection problem. A two-degree-of-freedom IMC （2DOF-IMC） has been developed to overcome the weakness. However, the setting of parameter becomes a complicated matter if there is an uncertainty model. The present study proposes a new tuning method for the controller. The proposed tuning method consists of three steps. Firstly, the worst case of the model uncertainty is determined. Secondly, the parameter of set point con- troller using maximum peak （Mp） criteria is specified, and finally, the parameter of the disturbance rejection con- troller using gain margin （GM） criteria is obtained. The proposed method is denoted as Mp-GM tuning method. The effectiveness of Mp-GM tuning method has evaluated and compared with IMC-controller tuning program （IMCTUNE） as bench mark. The evaluation and comparison have been done through the simulation on a number of first order plus dead time （FOPDT） and higher order processes. The FOPDT process tested includes processes with controllability ratio in the range 0.7 to 2.5. The higher processes include second order with underdarnped and third order with nonminimum phase processes. Although the two of higher order processes are considered as difficult processes, the proposed Mp-GM tuning method are able to obtain the good controller parameter even under process uncertainties.

A Neuro-fuzzy-sliding Mode Controller Using Nonlinear Sliding Surface Applied to the Coupled Tanks System

The aim of this paper is to develop a neuro-fuzzy-sliding mode controller （NFSMC） with a nonlinear sliding surface for a coupled tank system. The main purpose is to eliminate the chattering phenomenon and to overcome the problem of the equivalent control computation. A first-order nonlinear sliding surface is presented, on which the developed sliding mode controller （SMC） is based. Mathematical proof for the stability and convergence of the system is presented. In order to reduce the chattering in SMC, a fixed boundary layer around the switch surface is used. Within the boundary layer, where the fuzzy logic control is applied, the chattering phenomenon, which is inherent in a sliding mode control, is avoided by smoothing the switch signal. Outside the boundary, the sliding mode control is applied to drive the system states into the boundary layer. Moreover, to compute the equivalent controller, a feed-forward neural network （NN） is used. The weights of the net are updated such that the corrective control term of the NFSMC goes to zero. Then, this NN also alleviates the chattering phenomenon because a big gain in the corrective control term produces a more serious chattering than a small gain. Experimental studies carried out on a coupled tank system indicate that the proposed approach is good for control applications.

Hybrid Adaptive Compensation Control Scheme for High-Precision Servo System

In this paper,a hybrid adaptive compensation control scheme is proposed to compensate the friction occurrence and other nonlinear disturbance factors that exist in the high-precision servo system.An adaptive compensation controller with a dual-observer structure is designed,while the LuGre dynamic friction model with non-uniform parametric uncertainties characterizes the friction torque.Considering the influence of the periodic disturbance torque and parametric uncertainties,fuzzy systems and a robust term are employed.In this way,the whole system can be treated as a simple linear model after being compensated,then the proportional-derivative (PD) control law is applied to enhancing the control performance.On the basis of Lyapunov stability theory,the global stability and the asymptotic convergence of the tracking error are proved.Numerical simulations demonstrate that the proposed scheme has potentials to restrain the impact of disturbance and improving the tracking performance.

Periodic Motion Planning and Control for Double Rotary Pendulum via Virtual Holonomic Constraints

Periodic motion planning for an under-actuated system is rather difficult due to differential dynamic constraints imposed by passive dynamics, and it becomes more difficult for a system with higher underactuation degree, that is with a higher difference between the number of degrees of freedom and the number of independent control inputs. However, from another point of view, these constraints also mean some relation between state variables and could be used in the motion planning.We consider a double rotary pendulum, which has an underactuation degree 2. A novel periodic motion planning is presented based on an optimization search. A necessary condition for existence of the whole periodic trajectory is given because of the higher underactuation degree of the system. Moreover this condition is given to make virtual holonomic constraint(VHC) based control design feasible. Therefore, an initial guess for the optimization of planning a feasible periodic motion is based on this necessary condition. Then, VHCs are used for the system transformation and transverse linearization is used to design a static state feedback controller with periodic matrix function gain. The controller gain is found through another optimization procedure. The effectiveness of initial guess and performance of the closed-loop system are illustrated through numerical simulations.

On iterative learning control design for tracking iteration-varying trajectories with high-order internal model

In this paper, iterative learning control （ILC） design is studied for an iteration-varying tracking problem in which reference trajectories are generated by high-order internal models （HOLM）. An HOlM formulated as a polynomial operator between consecutive iterations describes the changes of desired trajectories in the iteration domain and makes the iterative learning problem become iteration varying. The classical ILC for tracking iteration-invariant reference trajectories, on the other hand, is a special case of HOlM where the polynomial renders to a unity coefficient or a special first-order internal model. By inserting the HOlM into P-type ILC, the tracking performance along the iteration axis is investigated for a class of continuous-time nonlinear systems. Time-weighted norm method is utilized to guarantee validity of proposed algorithm in a sense of data-driven control.

Robust iterative learning control for nonlinear systems with measurement disturbances

The iterative learning control （ILC） has been demon-strated to be capable of considerably improving the tracking perfor-mance of systems which are affected by the iteration-independent disturbance. However, the achievable performance is greatly degraded when iteration-dependent, stochastic disturbances are pre-sented. This paper considers the robustness of the ILC algorithm for the nonlinear system in presence of stochastic measurement disturbances. The robust convergence of the P-type ILC algorithm is firstly addressed, and then an improved ILC algorithm with a decreasing gain is proposed. Theoretical analyses show that the proposed algorithm can guarantee that the tracking error of the nonlinear system tends to zero in presence of measurement dis-turbances. The analysis is also supported by a numerical example.

Research on robust control strategy of single DOF supporting system of MLDSB based on H∞ mixed-sensitivity Method

Because of hydraulic-electromagnetic double supporting forms,the supporting capacity and stiffness of magnetic-liquid double suspension bearing(MLDSB)can be improved sharply and then it is more suitable for medium speed,heavy load and frequent-starting occasions.Due to the multiple uncertainty,such as the coupling,the unmodeled dynamics,the parameter perturbation and the external disturbance perturbation,the robust stability and stiffness of control system of MLDSB are hard to meet the design requirements.Firstly,the structural features and the regulation mechanisms of MLDSB are presented and the radial 4-DOF kinetic equations are established.Secondly,the influence factors of the control system's coupling on unbalanced vibration caused by the deviation of the rotor center of mass are revealed,and then the weighting function of suppressing the unbalanced vibration can be obtained.Finally,H∞ controller of MLDSB is designed with H∞ mixed-sensitivity method,and the control performances of H∞ controller is compared with the state feedback controller.The simulation results show that single degree of freedom(DOF)supporting system of MLDSB with H∞ controller has good robust stability,stiffness and the ability to suppress unbalanced external disturbances.This study can provide the theoretical reference for stabilized suspension and control of MLDSB.

Control and Implementation of 2-DOF Lower Limb Exoskeleton Experiment Platform

In this study,a humanoid prototype of 2-DOF(degrees of freedom)lower limb exoskeleton is introduced to evaluate the wearable comfortable effect between person and exoskeleton.To improve the detection accuracy of the humanrobot interaction torque,a BPNN(backpropagation neural networks)is proposed to estimate this interaction force and to compensate for the measurement error of the 3D-force/torque sensor.Meanwhile,the backstepping controller is designed to realize the exoskeleton's passive position control,which means that the person passively adapts to the exoskeleton.On the other hand,a variable admittance controller is used to implement the exoskeleton's active followup control,which means that the person's motion is motivated by his/her intention and the exoskeleton control tries best to improve the human-robot wearable comfortable performance.To improve the wearable comfortable effect,serval regular gait tasks with different admittance parameters and step frequencies are statistically performed to obtain the optimal admittance control parameters.Finally,the BPNN compensation algorithm and two controllers are verified by the experimental exoskeleton prototype with human-robot cooperative motion.

Stable Flocking of Multiple Agents Based on Molecular Potential Field and Distributed Receding Horizon Control

A novel distributed control scheme to generate stable flocking motion for a group of agents is proposed.In this control scheme,a molecular potential field model is applied as the potential field function because of its smoothness and unique shape.The approach of distributed receding horizon control is adopted to drive each agent to find its optimal control input to lower its potential at every step.Experimental results show that this proposed control scheme can ensure that all agents eventually converge to a stable flocking formation with a common velocity and the collisions can also be avoided at the same time.

Function Observer Based Event-triggered Control for Linear Systems with Guaranteed L_∞-Gain

This paper is devoted to event-triggered control design for linear systems based on function observer. More specifically, the main purpose is to design event-triggered mechanisms that trigger transmissions when the difference between the current value of the system and its previously transmitted value which includes the plant output or the function observer output exceeds an additional threshold. For such an eventtriggered mechanism, we derive conditions in terms of matrix inequality to guarantee the stability as well as longer inter-event time. We propose two approaches to investigate the closed-loop model, namely, reformulating the event-triggered control system as a hybrid system and interpreting the event-induced error as exogenous disturbance. Furthermore, the minimum inter-event time is guaranteed to be strictly positive. An example is presented to illustrate the feasibility and efficiency of the theoretic results. © 2014 Chinese Association of Automation.

Possible Mosquito Control by Silver Nanoparticles Synthesized by Soil Fungus (<i>Aspergillus niger 2587</i>)

Here, we have synthesized the silver nanoparticles (AgNPs) by using the soil fungus Aspergillus niger 2587. The results recorded from UV-vis spectrophotometer and transmission electron microscopy (TEM) support the biosynthesis and characterization of AgNPs. The synthesized silver nanoparticles have also been tested against the larvae and pupae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti. The efficacy test was performed at different concentrations for a period of different hours by the probit analysis. The larvae of Cx. quinquefasciatus have shown the 100% mortality to the synthesized AgNPs after 1 h of exposure, while the larvae of An. stephensi and Ae. aegypti were found less susceptible to the synthesized AgNPs. The pupa of Ae. aegypti has shown the efficacy LC50 4, LC90 12 and LC99 19 ppm after 2 h of exposure of the synthesized AgNPs, while, the pupae of Cx. quinquefasciatus and An. stephensi were found less susceptible to the synthesized AgNPs. By this approach, it is suggestive that this rapid synthesis of nanoparticles would be proper for developing a biological process for mosquito control.

Digital Control Design for the Boiler Drum BDT921

A boiler drum BDT921 that is installed in the Control Laboratory, Department of Mechatronics and Robotics Engineering, Faculty of Electric and Electronic Engineering, Universiti Tun Hussein Onn Malaysia （UTHM） is being used as a model plant to achieve the digital control system since its analog. Implementing a digital system to boiler quite a though work. This paper covers analysis from the experiment done to match with digital design that will be implemented to the real system. The digital control design will come up with the mathematical model and will be analyzed with MATLAB and SIMULINK software named as ＂Discrete Analysis ofBDT921 Simulation＂. A proportional integral and derivative （PID） controller is being chosen as the control element in discrete form as the real system is using the same control element. The output responses behave as the second order system with a bit difference in rise times and peak times compared with data obtained from experiment. With regarding to the analysis done, the digital control can be implemented and for further viewing, to be controlled digitally with computer in the control room.

Gold: A Unique Pigmentation Defective Laboratory Strain of the Lady Beetle

A laboratory colony of Coleomegilla maculata (De Geer) was selected for a novel phenotypic color trait. The phenotype was paler in color than the wild type, although not as pale as a previously described mutant strain, yellow (ye), and retained dark pigmentation in the eyes. This selected strain was named gold. Mendelian breeding experiments indicate a recessive biallelic inheritance. The strain has decreased fitness characteristics based on measurements of egg production and pupa size.

Characteristics of a Laboratory Strain of Coleomegilla maculata with a Novel Heritable Wing Spot Pattern Trait

The lady beetle Coleomegilla maculata is a common New World insect that is naturally colored pink to red or orange with black spots on the forewings of the adult stage. Previous laboratory in-breeding resulted in selection for a strain lacking red pigment in the cuticle and eyes. An additional strain selected for a novel spotting pattern is described here. The inheritance of the new trait, “ten spotted” (10sp), was determined by classical crossing experiments. Inheritance of the trait was autosomal and exhibited incomplete dominance. Bionomic strain measurements were compared to the parental strains and were similar overall. Two expressed sequences from C. maculata that may be related to the new phenotype were compared to model insect genes encoding a melanin biosynthesis enzyme and a patterning transcription factor.

New Approach to the Diagnosis of Control Hydraulic Systems

A dynamical hybrid system is described by a set of continuous variables and a set of discrete events interacting mutually. The reality imposes to take into account the failures of the components or the uncertainties on the knowledge of the system. Therefore, the systems can work in several modes. Some of these modes correspond to a normal functioning and the others represent failing modes. In this article, we are interested in the evaluation of the probability of occurrence of the failing events in a hybrid dynamic system. Furthermore, we propose an approach to detect on line the failed states and try to find the components responsible for this fault. This approach is based on the knowledge in priori of the system, at least from the point of view of the state of its components in normal functioning. This approach is here described through a simple case study taken from literature.

Dynamic Target Enclosing Control Scheme for Multi-Agent Systems via a Signed Graph-Based Approach

Dear Editor,This letter investigates the target enclosing control problem of multi-agent systems.A signed graph-based control strategy is presented,where the agents are steered to enclose the dynamic target from both sides as they move.This is inspired by the phenomenon that signed networks exhibit bipartite clustering if the underlying graph is structurally balanced,so that the agents may naturally enclose the zero point from opposite sides(+and.)if proper controllers are applied.By adopting a distributed observer to estimate the information of dynamic target。