Fault diagnosis for a class of active suspension systems with dynamic actuators’ faults

In this paper, a new fault diagnosis and fault-tolerant control method for a class of active suspension systems with actuator faults is proposed. The considered actuators have uncertain dynamic characteristics, which are the electromagnetic actuators made up with a motor control system and a ball screw transmission mechanism. To detect such suspension system actuator faults, dynamic fault diagnosis observers are designed for the actuators to estimate the possible faults. The actuators are analyzed to first and second order dynamic models, respectively, whose output can be measured but the rate is non-measurable. Then, the fault diagnosis method is developed for these two kinds of models to obtain the fault information. Using the fault estimation and adaptive control technique, a robust fault-tolerant controller is constructed to guarantee the performance of the rail vehicles in the faulty case. Finally, using the parameters of a practical suspension system, a simulation study is conducted to show the effectiveness of the proposed method.     

A magnetic fluid actuator

This paper describes an omni-directional walking robot, which has six legs and can move in any direction. The mechanism consists of a parallel link mechanism connecting the two frames with three linear actuators. Legs are attached to each frame. The relative position and angle of the two frames are selected arbitrarily in accordance with the length of three actuators. The walking mechanism is composed by combining them with extendable legs. The mechanism and control method of this robot are presented. Walking and inclination experiments were performed with an experimental prototype model, and desired movement is attained.     

Recursive modelling in dynamics of Agile Wrist spherical parallel robot

Recursive matrix relations for kinematics and dynamics of the 3-RRR Agile Wrist spherical parallel robot are established in this paper. The prototype of the robot is a three-degrees-of-freedom mechanism with three identical legs. Controlled by concurrent torques, which are generated by some electric motors, the active elements of the robot have three independent rotations. Knowing the rotation motion of the moving platform, we develop first the inverse kinematical problem and determine the velocities and accelerations. Further, the principle of virtual work is used in the inverse dynamic problem. Matrix equations offer iterative expressions and graphs for the power requirement comparison of each of three actuators in two computational complexities: complete dynamic model and simplified dynamic model.     

Dynamics and genetic fuzzy neural network vibration control design of a smart flexible four-bar linkage mechanism

In this paper, a dynamic modeling method and an active vibration control scheme for a smart flexible four-bar linkage mechanism featuring piezoelectric actuators and strain gauge sensors are presented. The dynamics of this smart mechanism is described by the Discrete Time Transfer Matrix Method of Multibody System (MS-DTTMM). Then a nonlinear fuzzy neural network control is employed to suppress the vibration of this smart mechanism. For improving the dynamic performance of the fuzzy neural network, a genetic algorithm based on the MS-DTTMM is designed offline to tune the initial parameters of the fuzzy neural network. The MS-DTTMM avoids the global dynamics equations of the system, which results in the matrices involved are always very small, so the computational efficiency of the dynamic analysis and control system optimization can be greatly improved. Formulations of the method as well as a numerical simulation are given to demonstrate the proposed dynamic method and control scheme.     

Simulation‐based actuator selection for redundantly actuated robot mechanisms

This article presents a simulation‐based strategy for sizing the actuators of a redundantly actuated robotic mechanism. The class of robotic mechanisms we consider may contain one or more closed loops and possess an arbitrary number of active and passive joints, and the number of actuators may exceed the mechanism's kinematic degrees of freedom. Our approach relies on a series of dynamic simulations of the mechanism, by applying Taguchi's method to systematically perform the simulations. To efficiently perform each of the dynamic simulations, we develop, using tools from modern screw theory, new recursive algorithms for the forward and inverse dynamics of the class of redundantly actuated mechanisms described. © 2002 Wiley Periodicals, Inc.     

事件驱动的网络化系统最优控制

针对随机事件驱动的网络化控制系统, 研究其中的有限时域和无限时域内最优控制器的设计问题. 首先, 根据执行器介质访问机制将网络化控制系统建模为具有多个状态的马尔科夫跳变系统; 然后, 基于动态规划和马尔科夫跳变线性系统理论设计满足二次型性能指标的最优控制序列, 通过求解耦合黎卡提方程的镇定解, 给出最优控制律的计算方法, 使得网络化控制系统均方指数稳定; 最后, 通过仿真实验表明了所提出方法的有效性.

     

磁悬浮刚性转子系统振动机理分析与动力学建模

磁悬浮惯性执行机构采用磁轴承支承,可通过主动控制实现极微振动,但磁悬浮惯性执行机构仍存在频谱分量丰富的振动.首先在转子动静不平衡和Sensor Runout振动机理分析的基础上,重点分析了Magnet Runout产生振动机理;然后,建立包含多振动源的系统动力学建模,并将整个动力学模型分解为平动和转动子系统,分析表明转子动静不平衡、Sensor Runout和Magnet Runout是通过不同的途径产生振动,不仅产生同频振动还包含倍频振动;最后,提出磁悬浮刚性转子系统主动振动控制的要求,为以后的主动振动控制研究奠定基础.     

Dynamic compensation method for multivariable control systems withsaturating actuators

This paper proposes a dynamic compensation method for multivariable control systems with saturating actuators to cope with the reset windup phenomenon. A dynamic compensator is explicitly determined based on a performance index of controller states. The proposed method is applicable to any open-loop stable plants with saturating actuators whose controller has been determined by some design technique. A simulation example is included to illustrate the effectiveness of the proposed method     

Design and control methodology of a 3-DOF flexure-based mechanism for micro/nano-positioning

A 3-DOF (X–Y–θ_Z) planar flexure-based mechanism is designed and monolithically manufactured using Wire Electro-Discharge Machining (WEDM) technology. The compact flexure-based mechanism is directly driven by three piezoelectric actuators (PZTs) through decoupling mechanisms. The orthogonal configuration in the x and y directions can guarantee the decoupling translational motion in these axes. The rotational motion and translational displacement in the x direction can be decoupled by controlling the piezoelectric actuators in the x axis with the same displacement values in same and opposite motion directions, respectively. The static and dynamic models of the developed flexure-based mechanism have been developed based on the pseudo-rigid-body model methodology. The mechanical design optimization is conducted to improve the static and dynamic characteristics of the flexure-based mechanism. Finite Element Analyses (FEA) are also carried out to verify the established models and optimization results. A novel hybrid feedforward/feedback controller has been provided to eliminate/reduce the nonlinear hysteresis and external disturbance of the flexure-based mechanism. Experimental testing has been performed to examine the dynamic performance of the developed flexure-based mechanism.     

Matrix modelling in dynamics of a 2-DOF orienting gear train

Recursive matrix relations for kinematics and dynamics analysis of a 2-DOF orienting gear train are established in this paper. The mechanism is a parallel system with five moving links and three bevel gear pairs controlled by two electric motors. Knowing the rotation motion of the end-effector, the inverse dynamic problem is solved using an approach based on the principle of virtual work and have verified the results in the framework of the Lagrange equations of the second kind. Finally, some graphs for the input angles of rotation, the forces and the powers of the actuators are obtained.     

生物启发的无线传感执行网络协同方法

本文针对无线传感执行网络(wireless sensor and actor network,WSAN),在昆虫生物种群协作机理的启发下,提出了一种WSAN协同方法,以改善网络传输可靠性、节能与执行效率.首先,针对传感器节点与执行器节点之间的协作,提出以信息传递能耗和剩余能量衡量中继节点选择概率的效能协同机制,以及包含区域中继、影响因子和学习因子3个保障单元的组织协同机制.进而,针对执行器--执行器间的协作,引入学习因子作为组织协同机制中的一个保障单元.最后,给出了算法执行的流程,并通过仿真验证了方法的优越性.仿真结果表明,采用本文提出的协同机制,不但优化了WSAN信息传递路径,而且在执行器节点间协作中选择优势节点参与信息处理和决策,降低了网络能耗,同时提高了网络执行效率.     

Reliable computation of minimum-time motions for manipulators moving in obstacle fields using a successive search for minimum-overload trajectories

In this paper we present a practical method for finding obstacle-free minimum-time motions for manipulators subject to the limits of velocity-dependent actuator forces. An optimal motion-planning problem is converted into a finite-dimensional nonlinear programming problem by means of parameter optimization with quintic B-splines. We introduce the concept of the minimum-overload trajectory in which the motion time is specified to be faster than the actuators can handle, and the actuator overloads are minimized with the motion time fixed. By successive searches for minimum-overload trajectories, minimum-time motions are determined for three example manipulators without simplifying any of the kinematic, dynamic or geometric properties of the manipulators or the obstacles. In the resultant minimum-time motions, almost all of the joint actuators are close to saturation during the motions. © 2005 Wiley Periodicals, Inc.     

Design,modeling and test of a novel compliant orthogonal displacement amplification mechanism for the compact micro-grasping system

In the compact micro-grasping system, the combination of precisely orthogonal movement transformation, displacement amplification and simple structure is important. The typical solution of the combination issue requires bidirectional symmetric input forces/displacements. However, under a certain driving condition, numerous actuators used in micro-manipulation only supply unidirectional input froce/displacement for the driven mechanism, which makes the typical solution infeasible. In this study, a novel compliant orthogonal displacement amplification mechanism (DAM) is proposed to solve the combination issue for numerous actuators used in micro-grasping. The proposed mechanism is a triangulation amplification-based mechanism with undetermined structural parameters. The number of the undetermined parameters and the solution principle are analyzed. The design process is presented. Finite element analysis (FEA) is used to verify the design method. The FEA results show that, for the design examples, the errors evaluating the orthogonal movement transformation are smaller than 0.56 % and 0.15 % respectively, and the displacement amplification ratios are larger than 4.6. The orthogonal displacement amplification is realized. A precise model of the displacement amplification ratio is derived. The dynamic performances of the proposed orthogonal DAM are modeled and FEA verified. Furthermore, a microgripper utilizing the proposed mechanism is presented. The performances of the gripper, including the displacement amplification and the parallel movement of the jaws, are verified by FEA and experiments.

     

Design and control of a 6-degree-of-freedom precision positioning system

This paper presents the design and test of a 6-degree-of-freedom(DOF) precision positioning system, which is assembled by two different 3-DOF precision positioning stages each driven by three piezoelectric actuators (PEAs). Based on the precision PEAs and flexure hinge mechanisms, high precision motion is obtained. The design methodology and kinematic characteristics of the 6-DOF positioning system are investigated. According to an effective kinematic model, the transformation matrices are obtained, which is used to predict the relationship between the output displacement from the system arrangement and the amount of PEAs expansion. In addition, the static and dynamic characteristics of the 6-DOF system have been evaluated by finite element method (FEM) simulation and experiments. The design structure provides a high dynamic bandwidth with the first natural frequency of 586.3 Hz. Decoupling control is proposed to solve the existing coupling motion of the 6-DOF system. Meanwhile, in order to compensate for the hysteresis of PEAs, the inverse Bouc-Wen model was applied as a feedforward hysteresis compensator in the feedforward/feedback hybrid control method. Finally, extensive experiments were performed to verify the tracking performance of the developed mechanism.     

Swing-arm-type PZT dual actuator with fast seeking for optical disk drive

 In this paper, a swing-arm-type dual positioning mechanism using a voice coil motor (VCM) and bimorph PZT actuators is proposed for the possible application to the future optical disc drive actuator. A VCM is used as a coarse motion actuator, and a set of piezoelectric actuators is used for fine motion. The two pairs of PZT actuators are arranged in parallel and are carefully designed to deflect in `S' shape such that tension and compression forces are generated simultaneously and thus the hysteresis is minimized. The static and dynamic analyses are performed and the parameter studies on the key dimensions of the set of PZT actuators are investigated. For fast seeking motion, time optimal control scheme combined with PD algorithm is adopted for the fast seeking motion of VCM. Positive position feedback (PPF) control is used to suppress residual vibration for the PZT actuator beams by activating it at the end of VCM swing motion. The feasibility of the suggested actuator system and the control scheme is demonstrated through simulations and experiments. Received: 5 July 2001/Accepted: 21 December 2001     

Shape optimization and dynamic characterization of multiple-electrostatically deformable microbridges

The nonlinear nature of electrostatic fields in micromachined structures, such as, cantilevers, bridges or plates, makes it difficult to achieve desired deflection shapes. An analytical approach to predict the static deflection and dynamic behavior of a microbridge subjected to electrostatic fields of multiple electrostatic actuators is presented in this paper. The boundary support conditions of the micromachined structures are nonhomogeneous in nature and are modeled with artificial translational and rotational springs. The static and dynamic behaviors of the microbridge are investigated by the Rayleigh–Ritz method using boundary characteristic orthogonal polynomials. The deflection of the microbridge and the natural frequencies under certain applied voltages are also presented. Least-squares fitting method is used to optimize the applied voltage of actuators in order to generate the desired static deflection. The proposed method is simple and can be easily extended to complicated configurations which are suitable for adaptive optics applications.     

Matrix modeling of inverse dynamics of spatial and planar parallel robots

Recursive matrix relations for kinematics and dynamics analysis of two known parallel mechanisms: the spatial 3-PRS and the planar 3-RRR are established in this paper. Knowing the motion of the platform, we develop first the inverse kinematical problem and determine the positions, velocities, and accelerations of the robot’s elements. Further, the inverse dynamic problem is solved using an approach based on the principle of virtual work, and the results can be verified in the framework of the Lagrange equations with their multipliers. Finally, compact matrix equations and graphs of simulation for power requirement comparison of each of three actuators in two different actuation schemes are obtained. For the same evolution of the moving platform, the power distribution upon the three actuators depends on the actuating configuration, but the total power absorbed by the set of three actuators is the same, at any instant, for both driving systems. The study of the dynamics of the parallel mechanisms is done mainly to solve successfully the control of the motion of such robotic systems.     

动态迟滞Hammerstein系统的改进卡尔曼状态估计

迟滞特性具有非光滑、多值映射等复杂特性.而在实际的工程中,当输入电压变化频率超过一定的范围时,迟滞的特性是随着输入频率的改变发生变化,使得整个系统的状态估计工作更复杂.本文首先提出一种新的描述动态迟滞的方法,进而描述了动态迟滞Hammerstein系统的状态空间方程,根据此系统在传统卡尔曼滤波器的基础上进行改进得到一种新的非光滑卡尔曼滤波器.最后通过仿真和实验,比较了在输入信号变化频率比较大时,用动态迟滞Hammerstein系统来描述压电陶瓷和采用静态迟滞Hammerstein系统来描述压电陶瓷的特性,非光滑卡尔曼滤波器对这两种含有噪声的模型进行滤波,结果表明由于静态迟滞Hammerstein系统的建模不能很好的描述压电陶瓷的特性,模型存在着误差,因此对系统状态估计的结果也没有用动态Hammerstein系统的误差小,从而说明当输入电压频率变化比较大时研究动态的迟滞Hammerstein模型是很有意义的.     

Robust sliding mode control of redundantly actuated parallel mechanisms with respect to geometric imperfections

The paper deals with the modeling and control of redundantly actuated parallel mechanisms. The redundant actuation means the redundant number of actuators, that is, more actuators than degrees of freedom of the mechanism. These machines bring the possibility of removing the backlash by the so-called antibacklash control. However, control of such a structure suffers from several new control problems like the danger of mutual fighting of the redundant actuators. This is especially problematic if the geometric imperfections appear. The presented solution is based on the usage of robust sliding mode control for uncertain dynamics. The paper explains classic approach of sliding mode control and its new modification based on the uniform usage of all actuators replaced by the fictitious auxiliary drives. The verification of the proposed algorithms is presented by two planar mechanisms with four actuators and three degrees of freedom. The first one is the fiber-driven mechanism, and the second one is the rigid 4RRR mechanism “Crosshead.”