Backstepping control of flexible joint manipulator based on hyperbolic tangent function with control input and rate constraints

In this paper, we investigate the trajectory tracking problems of the link angle and angle speed of the flexible joint manipulator model based on external disturbance, the control input and rate constraints. The controller of the flexible joint manipulator model is designed using the backstepping control scheme. To achieve this objective, the smooth hyperbolic tangent function is used to solve the problems of control input and rate constraints, and the stability is proved using Lyapunov function in the design procedure of the backstepping control scheme. Finally, the effectiveness of the proposed backstepping controller is verified by numerical simulation.     

Controllability of Boolean control networks with state-dependent constraints状态依赖约束下布尔网路的能控性

This paper investigates the controllability of Boolean control networks (BCNs) with state-dependent constraints. A kind of input transformation is proposed to transfer a BCN with state-dependent input constraints into a BCN with free control input. Based on the proposed technique, a necessary and sufficient condition for controllability is obtained. It is shown that state-dependent constraints for the state can be equivalently expressed as input constraints. When a BCN has both input and state constraints, there is a possibility that the sets of admissible controls for some states are the empty set. To treat this kind of BCN, a variation of the input transformation is proposed and the problem of controllability is solved. An illustrative example is provided to explain the proposed method and results.     

Thresholded and Optimized Histogram Equalization for contrast enhancement of images

A novel technique, Thresholded and Optimized Histogram Equalization (TOHE) is presented in this paper for the purpose of enhancing the contrast as well as to preserve the essential details of any input image. The central idea of this technique is to first segment the input image histogram into two using Otsu’s threshold, based on which a set of weighing constraints are formulated. A decision is made whether to apply those constraints to any one of the sub-histograms or to both, with respect to the input image’s histogram pattern. Then, those two sub-histograms are equalized independently and their union produces a contrast enhanced output image. While formulating the weighing constraints, Particle Swarm Optimization (PSO) is employed to find the optimal constraints in order to optimize the degree of contrast enhancement. This technique is proved to have an edge over the other contemporary methods in terms of Entropy and Contrast Improvement Index.     

Adaptive fault-tolerant control for a class of flexible air-breathing hypersonic vehicles

In this paper, a novel adaptive fault-tolerant control (FTC) scheme is proposed for a class of flexible air-breathing hypersonic vehicles with unknown inertial and aerodynamic parameters and even input constraints. The fault model under consideration covers the case that all actuators suffer from unknown time-varying faults. In the controller design and stability analysis, we introduce new Lyapunov functions, some differentiable auxiliary functions, a bound estimation approach, and a Nussbaum function, which help us successfully circumvent the obstacle caused by the faults, input constraints, and flexible modes. In addition to higher reliability, the proposed scheme is able to ensure that all closed-loop signals are globally uniformly bounded and to steer the tracking errors of altitude and velocity into predefined arbitrarily small residual sets. As a result, the tracking accuracy can be designated in advance. Simulation results illustrate the effectiveness of the proposed scheme.     

Constrained physical design tuning

Existing solutions to the automated physical design problem in database systems attempt to minimize execution costs of input workloads for a given storage constraint. In this work, we argue that this model is not flexible enough to address several real-world situations. To overcome this limitation, we introduce a constraint language that is simple yet powerful enough to express many important scenarios. We build upon a previously proposed transformation-based framework to incorporate constraints into the search space. We then show experimentally that we are able to handle a rich class of constraints and that our proposed technique scales gracefully. Our approach generalizes previous work that assumes simpler optimization models where configuration size is the only fixed constraint. As a consequence, the process of tuning a workload not only becomes more flexible, but also more complex, and getting the best design in the first attempt becomes difficult. We propose a paradigm shift for physical design tuning, in which sessions are highly interactive, allowing DBAs to quickly try different options, identify problems, and obtain physical designs in an agile manner.     

One step at a time: animating virtual characters based on foot placement

Especially in a constrained virtual environment, precise control of foot placement during character locomotion is crucial to avoid collisions and to ensure a natural locomotion. In this paper, we present an extension of the step space: a novel technique for generating animations of a character walking over a set of desired foot steps in real time. We use an efficient greedy nearest-neighbor approach and warp the resulting animation so that it adheres to both spatial and temporal constraints. We will show that our technique can generate realistic locomotion animations over an input path very efficiently even though we impose many constraints on the animation. We also present a simple footstep planning technique that automatically plans regular stepping and sidestepping based on an input path with clearance information generated by a path planner.     

状态与输入受限的二阶多输入多输出非线性系统自适应控制

针对含有状态和输入受限的二阶多输入多输出非线性系统的控制问题,提出了一种自适应控制策略.通过综合利用障碍Lyapunov函数和动态面控制方法的特性,使得系统的状态满足约束条件而且能够减少计算量.此外,为了处理输入约束和系统中的不确定性的影响,分别设计了辅助系统和自适应算法.通过理论分析表明,闭环系统的所有状态都是有界的,而且系统的状态和输入都满足约束条件.最后,通过一个数值仿真算例和一个实际的航天器姿态控制系统的仿真来验证所提出的自适应控制策略的有效性.     

Quasi-min-max output-feedback model predictive control for LPV systems with input saturation

In the research field of model predictive control (MPC), an output-feedback-type MPC method is consistently required for controlling a wide range of constrained systems. In this paper, we propose a two-stage control strategy for polytopic linear parameter varying (LPV) systems subject to input constraints. This strategy consists of a modified quasi-min-max output-feedback MPC method and a novel terminal output-feedback robust control technique. The proposed control mechanism involves the system states to be first controlled via the MPC method to be driven into a prescribed neighborhood of the origin, and then, the terminal output-feedback robust control method guaranteeing the input constraints is applied to make such states converge to the origin. It is also verified that our control method guarantees the closed-loop stability and feasibility in the presence of model uncertainties and input constraints. Finally, a numerical example is given to demonstrate its effectiveness.     

Using stable input-output inversion for minimum-time feedforward constrained regulation of scalar systems

The paper approaches the feedforward minimum-time smooth control of non-minimum-phase linear scalar systems for set-point regulation. The aim is to synthesize a bounded input subject to non-saturating constraints on the input and its derivatives till a prespecified arbitrary order. The provided solution relies on a stable input-output dynamic inversion technique and an ad hoc parameterized family of output transition functions. The synthesized minimum-time input that exhibits pre- and post-actuation is determined by means of easily-implementable closed-form expressions. Examples are given to illustrate the methodology.     

A disturbance model for control/structure optimization with output feedback control

This paper deals with a technique for the integrated optimization of structure and control in the design of flexible systems. The current approach uses the concept of response to dynamic constraints to establish a concise variational methodology to total system optimization, and eliminates the need to specify rather arbitrary trade-offs between control energy and structural mass. Results give an explicit dependency between structural stiffness (hence mass), disturbance magnitude, available control energy, and deflection constraints. The current paper presents results for direct output feedback and dynamic filter compensation with optional positive real constraints on the filters. The key element of the design approach is to formulate a set of response constraints that bound the allowable deflections and a set of constraints that bound the allowable control energy. The results for model structures indicate the importance of the control-structure interaction in a light-weight structure and the trade-offs between controller complexity, energy and structural mass.     

An extension of singular value analysis for assessing manipulated variable constraints

A new approach called feasible output radius analysis for linear or linearised models is introduced to address the problem of scaling dependency. This problem arises when assessing the effect of manipulated variable constraints (MVCs) on the closed-loop performance of chemical processes prior to carrying out control designs. The new indicators, and can be used to rank alternative control schemes on the basis that the larger and , the better the closed-loop performance in the presence of control constraints. These indicators are determined from extending the concept of the ‘feasible output amplitude region’ and are independent of the input scaling chosen. Theoretical analysis shows that this method is an extension of the more traditional singular value analysis approach and is more flexible in dealing with various kinds of manipulated variable constraints. A case study, i.e. a two-CSTR process, is investigated using the new method. Via the case study, some superior characteristics of the new technique are demonstrated, such as ease of calculation, and flexibility in coping with different kinds of constraints.     

Trajectory following for a flexible probe with state/input constraints: An approach based on model predictive control

This paper describes the trajectory following algorithm developed for a bio-inspired flexible probe, the direction of which can be controlled by means of an offset between interlocked probe segments which make up its body. The control approach employs model predictive control (MPC) to explicitly consider input and state constraints which arise from the unique mechanism of motion of the probe. For the sake of fast computation, a tracking error model is modified so that the nonlinear kinematic model of the probe is linearized, and the model is used to convert the optimization problem into a well-known quadratic programming (QP) problem. The input and state constraints are also converted into an inequality to be integrated into the QP problem. Simulated results demonstrate that the linearized tracking error model and the MPC control strategy are appropriate, handling large perturbations robustly, while satisfying all constraints. Experimental results in a gelatine sample, carried out with a 12 mm outer diameter prototype, demonstrate satisfactory two-dimensional trajectory following performance (0.52 mm average tracking error, with 1.49 mm STD). The experimental results also show that, given the probe’s constraints, the proposed controller provides more robust performance against large insertion perturbations than previously published control strategies developed for the probe.     

复杂约束下的挠性航天器姿态参考管理控制

本文提出了一种基于显式参考管理与模态观测器的挠性航天器姿态机动控制方法. 首先, 采用改进的罗德里格斯参数建立了航天器的运动学和动力学模型, 分析了存在的控制约束和角速度约束. 在此基础上, 设计了基于显式参考管理的约束挠性航天器姿态重定向控制算法. 由于挠性模态不能直接测量, 内层设计了模态观测器, 并将观测器观测得到的模态坐标作为内层无约束控制器的输入. 随后, 外层导航模块根据所需满足的约束条件设计了相应的动态路径, 该路径可以根据当前状态以合适的速率收敛到最终状态, 通过跟踪该路径, 航天器姿态就可以在满足约束的情况下快速到达期望位置. 通过构造合适的李雅普诺夫函数, 严格证明了该挠性航天器显式参考管理姿态控制算法的稳定性. 最后, 仿真结果进一步验证所设计算法的约束处理效果与振动抑制能力.     

Natural motion animation through constraining and deconstraining at will

This paper presents a computational technique for creating whole-body motions of human and animal characters without reference motion. Our work enables animators to generate a natural motion by dragging a link to an arbitrary position with any number of links pinned in the global frame, as well as other constraints such as desired joint angles and joint motion ranges. The method leads to an intuitive pin-and-drag interface where the user can generate whole-body motions by simply switching on or off or strengthening or weakening the constraints. This work is based on a new interactive inverse kinematics technique that allows more flexible attachment of pins and various types of constraints. Editing or retargeting captured motion requires only a small modification to the original method, although it can also create natural motions from scratch. We demonstrate the usefulness and advantage of our method with a number of example motion clips.     

Radial Pole Paths SVSC for Linear Time Invariant Multi Input Systems with Constrained Inputs

In this article a novel soft variable structure control method is proposed to reduce the settling time of liner time‐invariant multi‐input systems with constrained inputs. The method is a generalized pole placement technique which extends the desired pole locations to radial pole paths to reduce settling time while satisfying input constraints. The control signal obtained by this method is soft and is therefore suited to industrial applications. The paper provides a test for the stability of the control system based on the multivariable circle criterion and the Kalman‐Yakubovich‐Popov lemma. Simulation results where the method is applied to an aviation example, and comparison with pole placement, demonstrate how the method significantly increases the speed of response in spite of the input constraints.     

Adaptive input shaping for manoeuvring flexible structures using an algebraic identification technique

Input shaping is an efficient feedforward control technique which has motivated a great number of contributions in recent years. Such a technique generates command signals with which manoeuvre flexible structures without exciting their vibration modes. This paper presents a novel adaptive input shaper based on an algebraic non-asymptotic identification. The main characteristic of the algebraic identification in comparison with other identification methods is the short time needed to obtain the system parameters without defining initial conditions. Thus, the proposed adaptive control can update the input shaper during each manoeuvre when large uncertainties are present. Simulations illustrate the performance of the proposed method.     

针对执行器非光滑反向间隙-饱和的柔性立管边界控制

研究了针对执行器非光滑反向间隙-饱和约束特性的深海柔性立管系统振动控制和全局稳定问题.为了实现控制效果和品质,引入辅助系统和函数设计边界控制策略,以抑制立管系统振动并消除混合的反向间隙-饱和输入非线性影响.采用严格的分析且无需求助于模型降阶,所研发的控制器确保闭环系统在Lyapunov意义下的一致有界稳定性.通过选取恰当的设计参数,仿真结果验证了所设计控制器的控制性能.能.     

Scalability issues with using FSMWeb to test web applications

Web applications are fast becoming more widespread, larger, more interactive, and more essential to the international use of computers. It is well understood that web applications must be highly dependable, and as a field we are just now beginning to understand how to model and test Web applications. One straightforward technique is to model Web applications as finite state machines. However, large numbers of input fields, input choices and the ability to enter values in any order combine to create a state space explosion problem. This paper evaluates a solution that uses constraints on the inputs to reduce the number of transitions, thus compressing the FSM. The paper presents an analysis of the potential savings of the compression technique and reports actual savings from two case studies.     

Robust input shaping control for multi-mode flexible structures

Input shaping provides an effective method for suppressing residual vibration of flexible structure systems. However, robustness is not possible without a time penalty. In this paper, a robust input shaping method is developed for suppressing residual vibration of multi-mode flexible structure systems with parameter uncertainties and external disturbances. The proposed scheme integrates both input shaping control and sliding mode output feedback control. The input shaper is designed for the reference model and implemented outside of the feedback loop to reduce the residual vibration. In the feedback loop, the SMOFC technique is employed to make the closed-loop system behave like the reference model with input shaper, where the residual vibration is suppressed. The selection of switching surface and the existence of sliding mode have been addressed. The knowledge of upper bound of uncertainties is not required. Furthermore, it is shown that increasing the robustness to parameter uncertainties does not lengthen the duration of the impulse sequence. Simulation results demonstrate the efficacy of the proposed control scheme.     

Generating semantically valid test inputs using constrained input grammars

ContextGenerating test cases based on software input interface is a black-box testing technique that can be made more effective by using structured input models such as input grammars. Automatically generating grammar-based test inputs may lead to structurally valid but semantically invalid inputs that may be rejected in early semantic error checking phases of a system under test.ObjectiveThis paper aims to introduce a method for specifying a grammar-based input model with the model’s semantic constraints to be used in the generation of positive test inputs. It is also important that the method can generate effective test suites based on appropriate grammar-based coverage criteria.MethodFormal specification of both input structure and input semantics provides the opportunity to use model instantiation techniques to create model instances that satisfy all specified constraints. The input interface of a subject system can be specified using a high-level specification scheme such as attribute grammars, and a transformation function from this scheme to an instantiable formal modeling language can generate the desired model instances.ResultsWe propose a declarative grammar-based input specification method that is based on a variation of attribute grammars and allows the user to specify input constraints in addition to input structure. The model can be instantiated automatically to generate structurally and semantically valid test inputs. The proposed method has the capability to specify test requirements and coverage criteria and use them to generate valid test suites that satisfy test coverage criteria requirements.ConclusionThe work presented in this paper provides a black-box test generation method for grammar-based software inputs that can automatically generate criteria-covering test suites.