采摘机械臂自适应输入整形控制研究

采摘机械臂在夹住柔性果茎后运输果实时,执行器末端的加减速运动使得果实在移动过程中产生摆动,易引发掉落,进而导致采摘失败.本文以单个西红柿作为负载,将果茎近似为柔性连杆.由于每一个果实的质量是不同的,因此,针对机械臂抓取可变柔性负载移动过程中的振动抑制问题,提出了自适应输入整形控制方法.当系统模型由于负载的不确定性发生变化后,传统的输入整形算法无法抑制柔性连杆移动过程中产生的振动.因此采用自适应输入整形算法,实时计算脉冲的幅值和时间.构造二次性能指标函数,通过对机械臂移动的加速度和负载的摆角实时数据进行迭代运算,达到零残余振动的目的.仿真实验结果表明,在变负载情况下,自适应输入整形算法有良好的末端振动抑制能力,获得满意的控制效果.     

A STABLE ON‐LINE SELF‐TUNING OPTIMAL PID CONTROLLER FOR A CLASS OF UNKNOWN SYSTEMS

In this paper, a novel self‐tuning method of optimal PID control laws is proposed for both continuous‐time systems and discrete‐time systems. The controlled plant is assumed to be unknown except the system order (or system delay) and the direction of transmitting control input. Through the minimization of PID gains subject to the Lyapunov stability based reaching condition, the tuning of the three PID control gains is transformed to solve the inequality constraint optimization problem. An unknown SISO nonlinear system subject to a unit step input, and the tracking control problem of the piezoelectric actuator (PZA) with unknown dynamics are simulated. The simulation results show that the excellent tracking performance can be achieved.     

Active vibration isolation based on model reference adaptive control

High-performance instruments are very sensitive to vibrations and jitters. In this article, a new approach towards multi-degree-of-freedom (DOF) active vibration isolation and its application in spacecraft jitter suppression are presented. Model reference adaptive control (MRAC) with acceleration feedback is used to isolate random disturbances. However, a side effect of this algorithm is that displacements at low frequencies are amplified. Thus, the MRAC is augmented with proportional–integral–differential (PID) displacement feedback to suppress vibration displacements. The MRAC-PID composite control is applied to a 4-leg platform to isolate vibrations and suppress tip/tilt jitters. The scheme is also used to isolate 6-DOF vibrations and steer the payload of a flexible spacecraft. Satisfactory performance of vibration isolation and jitter attenuation has been observed.     

Multivariable norm optimal iterative learning control with auxiliary optimisation

The paper describes a substantial extension of norm optimal iterative learning control (NOILC) that permits tracking of a class of finite dimensional reference signals whilst simultaneously converging to the solution of a constrained quadratic optimisation problem. The theory is presented in a general functional analytical framework using operators between chosen real Hilbert spaces. This is applied to solve problems in continuous time where tracking is only required at selected intermediate points of the time interval but, simultaneously, the solution is required to minimise a specified quadratic objective function of the input signals and chosen auxiliary (state) variables. Applications to the discrete time case, including the case of multi-rate sampling, are also summarised. The algorithms are motivated by practical need and provide a methodology for reducing undesirable effects such as payload spillage, vibration tendencies and actuator wear whilst maintaining the desired tracking accuracy necessary for task completion. Solutions in terms of NOILC methodologies involving both feedforward and feedback components offer the possibilities of greater robustness than purely feedforward actions. Results describing the inherent robustness of the feedforward implementation are presented and the work is illustrated by experimental results from a robotic manipulator.     

基于相控投切技术的无功补偿装置

为了减小煤矿电网在无功补偿时随机投切电容器组给电网带来的涌流及过电压,设计了一套以具有发展前景的"软开关"技术即相控技术为根基的无功补偿装置,采用寿命长、成本低的带有永磁机构的真空接触器作为投切开关,该机构较传统的弹簧机构和电磁机构动作分散性小,为满足动作时间高度一致,对真空接触器动作时间的分散性进行有效补偿,并采用模块化的思想理念建立系统整体结构,采取适当的控制策略完成预期位置投切.最后本系统进行了仿真,并在某矿6kv电网中进行了实验测试,仿真和实验结果都表明本系统能有效的补偿系统无功,有一定的应用价值.     

VIBRATION CONTROL OF A SMART STRUCTURE USING PERIODIC OUTPUT FEEDBACK TECHNIQUE

Active vibration control is an important problem in structures. One of the ways to tackle this problem is to make the structure smart, adaptive and self‐controlling. The objective of active vibration control is to reduce the vibration of a system by automatic modification of the system's structural response. This work features the modeling and design of a Periodic Output Feedback (POF) control technique for the vibration control of a smart flexible cantilever beam system for a Single Input Single Output case. A POF controller is designed for the beam by bonding patches of piezoelectric layer as sensor/actuator to the master structure at different locations along the length of the beam. The entire structure is modeled in state space form using the Finite Element Method by dividing the structure into 3, 4, 5 elements, thus giving rise to three types of systems, viz., system 1 (beam divided into 3 finite elements), system 2 (4 finite elements), system 3 (5 finite elements). POF controllers are designed for the above three types of systems for different sensor/actuator locations along the length of the beam by retaining the first two vibratory modes. The smart cantilever beam model is developed using the concept of piezoelectric bonding and Euler‐Bernouli theory principles. The effect of placing the sensor/actuator at various locations along the length of the beam for all the three types of systems considered is observed and the conclusions are drawn for the best performance and for the smallest magnitude of the control input required to control the vibrations of the beam. The tip displacements with the controller is obtained. Performance of the system is also observed by retaining the first 3 vibratory modes and the conclusions are drawn.     

Development of a linear vibration motor with fast response time for mobile phones

This research investigated the magnetic and mechanical characteristics of a linear actuator by using structural and magnetic finite element analyses as well as experimental verification. The response time to reach the steady state of vibration was investigated through the equivalent mass–spring–damper system of the linear actuator. The response time can be reduced by increasing the magnetic force or by decreasing the mass. In the case of decreasing the mass, the spring constant should also be decreased in order to maintain the same natural frequency. However, reduction of both the mass and stiffness decreases the vibration magnitude because it is proportional to the spring constant. The results show that the ideal method to reduce response time without decreasing vibration magnitude is to increase magnetic force. Finally, this research proposes a novel design of a linear actuator with a large magnetic force to reduce the response time.     

An inverse-model approach to multivariable norm optimal iterative learning control with auxiliary optimisation

Motivated by the commonly encountered problem in which tracking is only required at selected intermediate points within the time interval, a general optimisation-based iterative learning control (ILC) algorithm is derived that ensures convergence of tracking errors to zero whilst simultaneously minimising a specified quadratic objective function of the input signals and chosen auxiliary (state) variables. In practice, the proposed solutions enable a repeated tracking task to be accurately completed whilst simultaneously reducing undesirable effects such as payload spillage, vibration tendencies and actuator wear. The theory is developed using the well-known norm optimal ILC (NOILC) framework, using general linear, functional operators between real Hilbert spaces. Solutions are derived using feedforward action, convergence is proved and robustness bounds are presented using both norm bounds and positivity conditions. Algorithms are specified for both continuous and discrete-time state-space representations, with the latter including application to multi-rate sampled systems. Experimental results using a robotic manipulator confirm the practical utility of the algorithms and the closeness with which observed results match theoretical predictions.     

Adaptive actuator fault compensation control for a rigid-flexible manipulator with ODEs-PDEs model

In this paper, the actuator fault problem is studied for a two-link rigid-flexible manipulator system in the presence of boundary disturbance and state constraint. The system consists of a rigid beam, a flexible beam and a payload at the end, which are described by hybrid ordinary differential equations–partial differential equations. The novel controller includes a proportional-derivative feedback structure, a disturbance observer and a fault-tolerant algorithm, which can regulate the joint positions and eliminate vibration of flexible beam, on circumstance of boundary disturbance and actuator fault. With the help of Barrier Lyapunov Function, the states will not be violated. It is proved that the closed-loop system has asymptotic stability by LaSalle Invariance Principle. Simulations are provided to demonstrate the effectiveness of the proposed controller.     

Vibration suppression for mass‐spring‐damper systems with a tuned mass damper using interconnection and damping assignment passivity‐based control

This paper considers a vibration suppression control method using feedback for a mass‐spring‐damper system with a tuned mass damper. For vibration suppression, we adopt the interconnection and damping assignment passivity‐based control, whereby the system is transformed to a system with a skyhook damper with an artificial structure matrix. The feedback law includes no accelerometer signal and uses only information on relative displacements and velocities. The proposed control method can simultaneously suppress the influences of the floor vibration and the disturbance force acting on the main body. A guideline for choosing parameters of the desired system is shown. The proposed method can be easily extended to nonlinear cases, which is demonstrated for a nonlinear‐spring case. We also show the input‐to‐state stability property of closed‐loop systems for linear cases and nonlinear cases. Copyright © 2015 John Wiley & Sons, Ltd.     

Dynamic analysis of structures containing nonlinear springs

An efficient algorithm is presented for the solution of the dynamics problem of a linear structure containing springs with nonlinear force-deflection characteristics. The method is based upon the Newmark Direct Integrator, and uses an iterative procedure in each time step to account for the nonlinear spring behavior. Convergence criteria are derived for the iteration.     

机器人串联弹性关节驱动器的刚度控制方法

机器人关节的柔顺性在人机协作过程中具有重要作用，然而固定的关节柔性无法满足动态变化的人机协作需求，因此对机器人的关节驱动器提出了具有刚度调节能力的要求.本文采用阿基米德螺旋线平面涡卷弹簧作为机器人关节的柔性元件，并提出一种可用于具有固定刚度的串联弹性驱动器的刚度控制方法.根据关节刚度的定义，将测量得到的弹簧输出端角度用于计算弹簧的输入端转角，使得机器人关节驱动器的等效刚度可以被调整到所期望的大小.该方法以电机位置控制为内环，关节刚度控制为外环，简化了控制器设计，并实现了解耦控制.对所设计的刚度控制器进行了分析.最后在自主设计的单自由度薄型串联弹性驱动器实验平台上进行了刚度调节实验，包括刚度的双向阶跃、零刚度和正弦变化的刚度，实验结果表明关节等效刚度能准确跟踪期望值，验证了该方法的有效性.     

欠驱动TORA系统的自耦PID控制策略

针对欠驱动旋转激励平移振荡器(translational oscillations with a rotational actuator,TORA)系统的控制问题,使用一种自耦PID(self-coupling proportional-integral-differential,SCPID)控制方法.该方法首先利用坐标变换使TORA系统的质心映射为Huygens振动中心,以实现新系统控制输入解耦,避免零动态不稳定问题;然后对Huygens振动中心设计平移位置的SCPID控制器,同时获得小球偏转角度的虚拟指令,进而设计小球偏转角度的SCPID控制器,从而实现TORA系统的平衡点跟踪控制;最后在复频域对闭环控制系统的稳定性进行严格的数学分析和证明.仿真及与其他方法的结果对比表明,所设计的控制算法简单高效,在欠驱动控制系统领域具有实际的应用价值.     

On controller tuning for a flexible-link manipulator with varying payload

In this article experimental results are presented for system identification and control of a single-link flexible manipulator carrying an unknown, varying payload. The control objective is to maintain endpoint position accuracy in the presence of flexure effects after rapid movement due to a rigid body slew-angle commanded position. Various time-domain parameter estimation techniques are used to identify ARMA model representations to be employed in controller tuning schemes for vibration compensation. Only endpoint acceleration measurements and motor shaft angle measurements are utilized in relatively simple PID control schemes, which are tuned as dictated by a varying, unknown payload.     

数字式电子调速器动态特性的研究

本论文介绍的数字式电子调速器,是用步进电机作为执行器,以AT89C51单片机为主控芯片,通过编制相应的控制程序,实现了汽油机的数字调速。通过减小瞬时调速率成为全面提高汽油机调速性能的关键。采用PID控制算法,按汽油机过渡过程各阶段转速变化的情况,确定PID各项的系数,调节节气门开度的变化量。实验结果表明,瞬时调速率达到5.6%,稳定时间1.64s,瞬时调速率和稳定时间都有很大的提高,该方法对改善电子调速器的动态特性有明显的效果。     

模糊神经网络PID在电动舵机控制中的应用

研究电动舵机控制系统优化问题。针对传统控制器响应速度慢,由于系统本身是多变量非线性的复杂系统,存在时滞问题,系统参数不易整定,为了优化电动舵机控制系统的快速性性能,设计了一种改进的模糊神经网络PID控制器,提出了分离学习算法,利用自组织学习整定隶属度函数参数和误差反向传播学习整定加权系数。将算法用于电动舵机控制,实现对舵机以及导弹姿态的快速控制。仿真结果表明,改进控制器的响应时间达到4.8ms,优于传统的PID控制器和模糊PID控制器,为电动舵机控制系统快速性、高精度的设计提供了依据。     

高速列车非线性系统的分数阶有限时间控制器设计

针对具有输入非线性, 不确定的气动阻力, 未知的车间力, 外部扰动以及未知的执行器故障等特征的高速列车非线性系统, 结合分数阶稳定性原理以及有限时间控制理论, 本文设计了一种分数阶有限时间控制器以实现高速列车更快速且更高精度的跟踪控制. 该控制器能够直接补偿高速列车的不确定性和非线性以及执行器故障而不需任何“试错”过程, 且稳定时间可由控制参数的不同选择来调整. 仿真研究验证了所设计控制器的有效性和优越性.     

On the relationship of natural frequency,damping, and feedforward acceleration with transient vibrations of track-seek control

The relationship between natural frequency, damping, the waveform of a feedforward acceleration input, and the transient vibrations of track-seek control is derived theoretically and a target for vibration design of the head actuator of a hard disk drive (HDD) is discussed from the viewpoint of the transient vibrations. When the acceleration feedforward input of the track-seek control is expressed as a polynomial function of time, the transient response of a single degree of freedom system is solved by applying integral by parts to the Duhamel’s integral repeatedly. The results show the transient vibrations are generated at the initial and terminal times of the input and their amplitude depends on the lowest orders of non-zero derivatives of the polynomial. They also show that increasing the damping ratio effectively reduces the transient vibrations for fourth and sixth order polynomials but not for fifth and seventh order polynomials. The results were confirmed by performing a continuous time simulation and analyzing the shock response spectrum. Also discussed is the relationship between the transient vibrations and the seek time and track pitch, which are key parameters associated with the data access time and the HDD capacity. This relationship indicated the requirements needed for vibration design of the head actuator to increase HDD performance and capacity.     

Modified PID Control of a Single-Link Flexible Robot

The use of flexible links in robots has become very common in different engineering fields. The issue of position control for flexible link manipulators has gained a lot of attention. Using the vibration signal originating from the motion of the flexible-link robot is one of the important methods used in controlling the tip position of the single-link arms. Compared with the common methods for controlling the base of the flexible arm, vibration feedback can improve the use of the flexible-link robot systems. In this paper a modified PID control (MPID) is proposed which depends only on vibration feedback to improve the response of the flexible arm without the massive need for measurements. The arm moves horizontally by a DC motor on its base while a tip payload is attached to the other end. A simulation for the system with both PD controller and the proposed MPID controller is performed. An experimental validation for the control of the single-link flexible arm is shown. The robustness of the proposed controller is examined by changing the loading condition at the tip of the flexible arm. The response results for the single-link flexible arm are presented with both the PI and MPID controller used. A study of the stability of the proposed MPID is carried out.     

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.