Previous Control Designs Research Articles

A novel finite-time stability criteria and controller design for nonlinear impulsive systems

The issue of a novel finite-time stability and stabilization design for a class of nonlinear impulsive systems is discussed in this paper. In previous finite-time control designs for impulsive systems, the convergence rate of these control strategies is even less rapid than the exponential convergence rate when the initial state is distant from the origin. To overcome this problem, two sufficient conditions for the novel finite-time stability of impulsive systems are presented, in which the stabilizing impulses and the destabilizing impulses are considered, respectively. Meanwhile, the upper bound of the settling-time is evaluated. In addition, combining Lyapunov functions theory with impulsive control, we design a controller for impulsive dynamical systems to satisfy the novel finite-time stability. Finally, two simulation examples are given, in which the first example demonstrates the superiority of the proposed finite-time stability criterion for nonlinear impulsive systems by comparing it with traditional finite-time stability, and the second example verifies the effectiveness of the presented controller.

Enhanced High-Gain Observer for Blood and Micro-robot Velocity Estimation in Magnetic Drug Targeting

Micro-robots have a promising prospect to be used in healthcare and bioengineering applications due to their capability to access hard-to-reach areas, allowing them to overcome the limitations of many conventional clinical methods. Controlling these micro-robots in blood vessels is an essential technology for several applications such as targeted drug delivery. One approach is to use a magnetic resonant navigation control strategy which allows precise manipulation of the micro-robot by adjusting the frequency and intensity of the magnetic field. The accuracy and robustness of this technique rely on the knowledge of some parameters such as blood and micro-robot velocities. In previous control designs, the blood velocity was assumed to be known and its pulse was supposed to be constant. This assumption did not reflect reality and reduced the feasibility of the control system. Considering this fact, this paper addresses the problem of estimating the velocity of the blood and micro-robot using an enhanced high-gain observer. Simulation results are carried out in MATLAB/Simulink to demonstrate the effectiveness of the proposed observer with comparisons to the standard high-gain observer.

Understanding the stability of deep control policies for biped locomotion

Achieving stability and robustness is the primary goal of biped locomotion control. Recently, deep reinforcement learning (DRL) has attracted great attention as a general methodology for constructing biped control policies and demonstrated significant improvements over the previous state-of-the-art control methods. Although deep control policies are more advantageous compared with previous controller design approaches, many questions remain: Are deep control policies as robust as human walking? Does simulated walking involve strategies similar to human walking for maintaining balance? Does a particular gait pattern affect human and simulated walking similarly? What do deep policies learn to achieve improved gait stability? The goal of this study is to address these questions by evaluating the push-recovery stability of deep policies compared with those of human subjects and a previous feedback controller. Furthermore, we conducted experiments to evaluate the effectiveness of variants of DRL algorithms.

Adaptive Control with Quantized Inputs Processed by Lipschitz Logarithmic Quantizer

In this paper, the design of adaptive control for a class of control systems with quantized inputs is investigated. According to the stability analysis result of adaptive control design, the quantized errors act as a great potential unstable risk for a class of sophisticated multi-channel system with quantized inputs. Thus, we establish Lipschitz logarithmic quantizer considering package loss problem in data transmission to eliminate quantized errors, and the superiority of this new quantizer is then proved by the asymptotically convergent mathematic expectation of quantized errors. Especially, a typical under-actuated multi-channel system, quadrotor UAV, is introduced to exhibit the effectiveness of the whole control scheme and the advancement compared with previous quantized control designs.

Neural-networks-based adaptive quantized feedback tracking of uncertain nonlinear strict-feedback systems with unknown time delays

We develop a quantized-feedback-based adaptive delay-independent control design for systems with unknown strict-feedback nonlinearities and time-varying delays. It is assumed that full state variables quantized by uniform quantizers are only available for the feedback control design. Compared with the previous adaptive control designs of lower-triangular nonlinear time-delay systems, the major contribution of this paper is to develop quantized-states-basedmemoryless adaptive control and stability analysis strategies to deal with unmatched and unknown time-delay nonlinearities. An adaptive neural network controller and its adaptive laws are designed via quantized state variables where neural networks are employed to compensate for unknown time-delay nonlinear effects. By deriving theoretical lemmas on the boundedness of quantization errors of the closed-loop signals, the stability of the resulting closed-loop system and the convergence of the tracking error are analyzed. Finally, simulation results are provided to validate the effectiveness of the theoretical result.

Static output feedback control of positive linear systems with output time delays

ABSTRACTIn this paper, we discuss a new problem of static output feedback controllers design for positive systems with delayed output measurements. When delayed output measurements are exclusively used as feedback control signals, previous control design methods for positive systems relying on the so-called delay-independent positivity and stability conditions are unable to synthesise a stable static output feedback controller for positive systems. A new method based on delay-dependent positivity and stability conditions is proposed in this paper to tackle this issue. We show that the synthesis of static output feedback controllers for positive systems under the effect of delayed output measurements is feasible under the newly proposed design method. Numerical examples are given to demonstrate the effectiveness of the new result.

Adaptive finite‐time tracking control of 6DOF spacecraft motion with inertia parameter identification

This study deals with the problem of relative motion control with 6 degrees of freedom (6DOF) for spacecrafts without a priori knowledge of the inertia parameters. Considering the system natural couplings, the integrated rotational and translational dynamics of the spacecraft are achieved. By a series of first-order filter operations, an expression of the parameter estimation error is derived and then used for the design of an integrated finite-time tracking controller applying adaptive backstepping technique. Proven by the Lyapunov theory, the proposed controller can guarantee that the errors of trajectory tracking and parameter identification simultaneously converge to zero in finite time. Furthermore, to be applied in practice, the controller is adapted for the spacecraft subject to external disturbance and input saturation. Compared with the previous control designs, the proposed control strategy can realise inertia parameter identification together with tracking of command position and attitude in finite time, in the presence of input saturation and external disturbance. The effectiveness of the control law is finally demonstrated by numerical simulations.

An Improved Wave-Variable Based Four-Channel Control Design in Bilateral Teleoperation System for Time-Delay Compensation

Good transparency performance (including position tracking and force feedback) is a significant issue for teleoperation control design. The four-channel control approach, which is based on the impedance matching between the master and slave, is an effective method to achieve the perfect transparency performance of teleoperation system. However, the obvious drawback of this design is that the time delay existing in the communication channel is neglected and thus the stability of this design under time delay cannot be guaranteed. Some passivity based control approaches such as wave-variable are developed to handle the stability problem of teleoperation system under time delay, and have been tried to add into four-channel control design. Though the stability under time delay is achieved for this kind of design, the transparency performance may largely decrease since the traditional wave-variable may essentially suffer some performance limitations (e.g., wave reflection). Thus, simultaneously realizing the stability and good transparency performance for four channel teleoperation system is still a challenging issue. In this paper, an improved wave-variable based four-channel control design is developed for bilateral teleoperation system to guarantee stability and further improve transparency performance. Under four channel control architecture, the passivity based time-delay compensator by the modified wave transform and the local force feedback are provided to compensate the distortion by reducing wave reflection and further enhance the stability and transparency of teleoperation system. The experiment is carried out, and the results show the great improvement of the proposed method to achieve the good transparency performance compared to the previous four-channel control designs.

A Design of a Hybrid Non-Linear Control Algorithm

One of the high energy consuming devices in the buildings is the air-conditioning system. Designing a proper controller to consider the thermal comfort and simultaneously control the energy usage of the device will impact on the system energy efficiency and its performance. The aim of this study was to design a Multiple-Input and Multiple-Output (MIMO), non-linear, and intelligent controller on direct expansion air-conditioning system The control algorithm uses the Fuzzy Cognitive Map method as a main controller and the Generalized Predictive Control method is used for assigning the initial weights of the main controller. The results of the proposed controller shows that the controller was successfully designed and works in set point tracking and under disturbance rejection tests. The obtained results of the Generalized Predictive Control-Fuzzy Cognitive Map controller are compared with the previous MIMO Linear Quadratic Gaussian control design on the same direct expansion air-conditioning system under the same conditions. The comparative results indicate energy savings would be achieved with the proposed controller with long-term usage. Energy efficiency and thermal comfort conditions are achieved by the proposed controller.

Adaptive Backstepping Control of Spacecraft Rendezvous and Proximity Operations With Input Saturation and Full-State Constraint

This paper presents a six-degree-of-freedom relative motion control method for autonomous spacecraft rendezvous and proximity operations subject to input saturation, full-state constraint, kinematic coupling, parametric uncertainty, and matched and mismatched disturbances. Relative rotational and relative translational controllers are developed separately based on a unified adaptive backstepping technique. Both element-wise and norm-wise adaptive estimation techniques are used for handling parametric uncertainties, kinematic couplings, and matched and mismatched disturbances, where the bounds of disturbances are unknown. Two auxiliary design systems are employed to deal with input saturation in the relative rotational and relative translational control designs, and the stability of the saturated control solution is verified. Full-state constraint of the relative pose motion is handled by using barrier Lyapunov functions while achieving a satisfactory control performance. All signals in the closed-loop system are guaranteed to be uniformly ultimately bounded, and the relative motion states are all restricted within the known constraints. Compared with the previous control designs of spacecraft rendezvous and proximity operations, the proposed control strategy in this paper can simultaneously deal with input saturation, full-state constraint, kinematic coupling, parametric uncertainty, and matched and mismatched disturbances. Experimental simulation results validate the performance and robustness improvement of the proposed control strategy.

Model validation and feedback controller design for a dielectric elastomer actuator

Tubular dielectric elastomer actuators have been utilized for a number applications where bi-directional positioning is required, for example, positioning of loads and haptic interfaces. Previous model validation and control design research carried out by the authors on extendable metal electrode–based actuators (which need no internal stressing) has concentrated on the design of open-loop type model-based controllers to reject both measurable and unmeasurable vibration disturbances on a prototype tubular actuator developed by Danfoss A/S. A developed electromechanical model and its linearized form were important components in the control design work carried out previously. This work examines the design and implementation of a closed-loop controller on a second-generation extendable metal electrode dielectric elastomer tubular actuator. This actuator has the same strain characteristics as the original prototype but contains more rolled material leading to greater push–pull force capability. Electromechanical model validation of the larger actuator is initially carried out for a range of different operating conditions both with and without loading. Additionally, the increased capacitance of this actuator, due to a greater amount of dielectric elastomer material, could have implications for the accuracy of the gain scheduling term (which is used to linearize the model), when there is dynamic input voltage stimuli. The overall popularity of the proportional, integral and derivative controller, due to its transparency and simple structure, made it the obvious choice for the feedback controller to be considered here. Model-based design of the proportional, integral and derivative controller, via the internal model control design procedure, is then achieved using a reduced-order linear representation of the linearized electromechanical model. The real-time performance of the designed controller is examined to changes in desired position of the payload (servo performance) and its ability to reject periodic vibratory base disturbances to try and maintain the payload in a fixed position.

Simple Fuzzy PID Controllers for DC-DC Converters

A fuzzy PID controller design method is proposed for precise robust control of DC-DC buck converters. The PID parameters are determined reflecting on the common control engineering knowledge that transient performances can be improved if the P and I gains are big and the D gain is small at the beginning. Different from the previous fuzzy control design methods, the proposed method requires no defuzzification module and the global stability of the proposed fuzzy control system can be guaranteed. The proposed fuzzy PID controller is implemented by using a low-cost 8-bit microcontroller, and simulation and experimental results are given to demonstrate the effectiveness of the proposed method.

Robust decentralized direct adaptive output feedback fuzzy control for a class of large-sale nonaffine nonlinear systems

In the previous work of Huang et al., a decentralized direct adaptive fuzzy H ∞ tracking controller of large-scale nonaffine nonlinear systems is obtained predicated upon the assumption that the mismatching error dynamics stay squared integrable. In this note, we focus in the absence of the conservative assumption upon developing a robust decentralized direct adaptive output feedback fuzzy controller. By combination of a state observer, a fuzzy inference system and robust control technique, the previous controller design is modified and no a priori knowledge of bounds on lumped uncertainties is required. All the signals of the closed-loop large-scale system are proved to be uniformly ultimately bounded. The effectiveness of the developed scheme is demonstrated through the simulation results of interconnected inverted pendulums.

Adaptive observer-based switched control for electropneumatic clutch actuator with position sensor

AbstractIn this paper we extend previous control design applied to an electropneumatic clutch actuator. A dual-mode switched nonlinear controller design and an adaptive nonlinear observer design are combined to achieve position control of the clutch actuator with only position measurements available. The observer provides estimates of position, velocity, chamber pressures, friction state and parameters, and clutch load characteristic parameters. The paper focus on design for implementation in a heavy duty truck system, and focus on performance evalution using simulations. Performance is tested with a simulation model which is validated against experimental results from a heavy duty test truck, showing no significant loss of performance due to lack of a pressure sensor.

Applied periodic l ∞ control: Presenting prototype designs for a real sprayform tooling process

This paper presents the design and implementation of prototype periodic l ∞ control systems for governing the temperature profile of a spray-form tooling process that is used in rapid manufacture of tooling. The controllers are based on discrete time varying l ∞ theory for periodic/almost periodic linear systems. After a brief description of the process in study and its mathematical modelling, the paper formulates the control problem and investigates its design and characteristic features. The theoretical issues are accompanied with simulation and experimental studies on a real spray-form apparatus. The paper shows that the performance of the proposed controllers is better than previous control designs. This is the first ever application of l ∞ control systems for spray-form tooling processes, something that reflect their characterization as prototypes.

MULTIVARIABLE H∞ CONTROLLER DESIGN AND TESTING FOR A 2.4M TELESCOPE

This paper considers high performance motion control systems for the Azimuth axis of a 2.4m Altitude-Azimuth telescope manufactured by Telescope Technologies Limited (TTL). Tracking performance is paramount and the telescope is designed to operate with no surrounding enclosure; wind disturbances that could degrade the tracking performance are a major consideration. Previous robust control designs have used a single-input-single-output (SISO) architecture for position tracking, and this paper will assess the stability and performance of a multi-input-multi-output (MIMO) controller using simulations and test data from the real telescope. Simulations indicate that the MIMO design offers better wind disturbance rejection, and the test data show that the implementation of a MIMO control architecture is feasible.

A test of imitative learning in starlings using a two-action method with an enhanced ghost control

Imitative learning, in which an individual learns to reproduce the behaviour pattern of another, has attracted considerable attention as a potentially powerful form of social learning. Despite extensive research, however, it has proved difficult to demonstrate in nonhuman animals. We investigated the ability of European starlings, Sturnus vulgaris, to imitate the behaviour of a conspecific. Subjects watched a trained conspecific manipulating a plug for access to a food reward, using either a pushing or a pulling action. When later tested with the same apparatus these birds completed the task using the same action they had previously observed. In a second experiment, a separate group of starlings saw the plug move upwards or downwards automatically and a nearby conspecific obtain a food reward. When given access to the task these starlings failed to move the plug in the direction they had seen. Our experiment is an improvement on previous bidirectional control designs and provides strong evidence that starlings are capable of imitation. We advocate further use of this experimental design in attempts to demonstrate imitative learning. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Theoretical Control and Experimental Verification of Carded Web Density. Part IV: Computer-Aided On-Line Control of Carded Web Density

This paper presents a new on-line control system that is implemented for controlling carded web density. The control system is based on the previous controller design of the worker-stripper group presented in Parts I, II, and III of this series. Theoretically, these aforementioned control methods can make a corresponding closed-loop system for efficient and precise system control, but the design effort is meaningful only when tested by experiment. In this part of the series, the well-designed analog controller can be discretized and used as a digital controller for experimental verification. The worker-stripper group control system successfully operates based on our experimental implementation and agrees well with theoretical analyses.

Exponential stabilization of a class of unstable bilinear systems

Considers the control design of bilinear systems with multiplicative control inputs. Previous control designs for such systems normally assume that the open-loop bilinear system is (neutrally) stable. In this paper, a nonlinear control design is proposed for open-loop unstable bilinear systems. The new control stabilizes the bilinear system globally and exponentially if a sufficient stability condition, which can be checked by off-line computer simulations in advance of the control, is satisfied.

An Active Control Design for a Class of Parametrically Excited Systems Based on the Gradient Algorithm

This paper introduces a new control design for a dynamic system subject to stationary or nonstationary parametric excitations. In this new design, the system dynamics is transformed into one with a null system matrix using the variation of parameters method. A stabilizing state feedback control can then be immediately obtained by following the gradient algorithm that is originally developed for the parameter identification purpose. Such a design has the advantage that the control requires only past and present information of the time-varying parametric excitations while previous control designs usually require prediction of future information of the excitations. The closed-loop system stability is guaranteed if the open-loop state response does not diverge too fast. The control design approach can also be applied to the observer design in case where there is only partial observation of the system state.