Intelligent phase plane switching control of a pneumatic muscle robot arm with Magneto-Rheological Brake

Pneumatic cylinders are one kind of low cost actuation sources which have been applied in industrial and robotics field, since they have a high power/weight ratio, a high-tension force and a long durability. To overcome the shortcomings of conventional pneumatic cylinders, a number of newer pneumatic actuators have been developed such as McKibben Muscle, Rubber Actuator and Pneumatic Artificial Muscle (PAM) Manipulators. However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion. In addition, the nonlinearities in the PAM manipulator still limit the controllability. Therefore, it is not easy to realize motion with high accuracy and high speed and with respect to various external inertia loads. To overcome these problems, a novel controller which harmonizes a phase plane switching control method (PPSC) with conventional PID controller and the adaptabilities of neural network is newly proposed. In order to realize satisfactory control performance a variable damper, Magneto-Rheological Brake (MRB), is equipped to the joint of the robot. The mixture of conventional PID controller and an intelligent phase plane switching control using neural network (IPPSC) brings us a novel controller. The experiments were carried out in a robot arm, which is driven by two PAM actuators, and the effectiveness of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with 1PPSC and without regard for the changes of external inertia loads.     

Sliding mode control of the inchworm displacement with hysteresis compensation

This paper proposes a new modeling scheme to describe the hysteresis and the preload characteristics of piezoelectric stack actuators in the inchworm. From the analysis of piezoelectric stack actuator behavior, the hysteresis can be described by the functions of a maximum input voltage and the preload. The dynamic characteristics are also identified by the frequency domain modeling technique based on the experimental data. The hysteresis is compensated by the inverse hysteresis model for precise control of inchworm displacement. Since the dynamic stiffness of an inchworm is generally low compared to its driving condition, the mechanical vibration may degrade accuracy of the inchworm. Therefore, the SMC (Sliding Mode Control) and the Kalman filter are developed for the motion control of the inchworm. The feasibility of the proposed modeling scheme and the control algorithm is tested and verified experimentally.     

Theoretical Investigation of the Viscous Damping Coefficient of Hydraulic Actuators

The viscous damping coefficient(VDC) of hydraulic actuators is crucial for system modeling,control and dynamic characteristic analysis.Currently,the researches on hydraulic actuators focus on behavior assessment,promotion of control performance and efficiency.However,the estimation of the VDC is difficult due to a lack of study.Firstly,using two types of hydraulic cylinders,behaviors of the VDC are experimentally examined with velocities and pressure variations.For the tested plunger type hydraulic cylinder,the exponential model B=αυ~(-β),(α0,β0)or B=α_1e~(-β_1υ)+α_2e~(-β_2υ)(α_1,α_20,β_1,β_20),fits the relation between the VDC and velocities for a given pressure of chamber with high precision.The magnitude of the VDC decreases almost linearly under certain velocities when increasing the chamber pressure from 0.6 MPa to 6.0 MPa.Furthermore,the effects of the chamber pressures on the VDC of piston and plunge type hydraulic cylinders are different due to different sealing types.In order to investigate the VDC of a plunger type hydraulic actuator drastically,a steady-state numerical model has been developed to describe the mechanism incorporating tandem seal lubrication,back-up ring related friction behaviors and shear stress of fluid.It is shown that the simulated results of VDC agree with the measured results with a good accuracy.The proposed method provides an instruction to predict the VDC in system modeling and analysis.     

压电陶瓷作动器非对称迟滞建模与内模控制

压电陶瓷作动器被广泛应用于精密定位和控制中,但其本身存在的非对称迟滞非线性特性,严重影响了系统的定位和控制精度。针对这一问题,提出了一种基于广义Bouc-Wen模型的非对称迟滞建模方法,并利用差分进化算法辨识模型参数;基于所建的广义Bouc-Wen模型构建了其具有解析形式的迟滞逆模型,并设计了内模控制方案实现对压电陶瓷作动器的精密跟踪控制;最后在压电陶瓷作动器实验平台,对所提出的建模和控制方案进行了实验验证。对压电陶瓷作动器的建模结果表明,系统建模误差均小于0.051 0,比经典Bouc-Wen模型的建模误差降低约21%～46%;对100 Hz内幅值为20μm的期望位移信号的控制实验结果表明,所提出的控制方法具有良好的实时跟踪性能和跟踪控制精度。对100 Hz期望信号的跟踪控制均方根误差为0.491 6μm,相对误差为0.040 2μm,可以很好地满足实际工程需要。     

Performance improvement of pneumatic artificial muscle manipulators using magneto-rheological brake

A novel pneumatic artificial muscle actuator (PAM actuator), which has achieved increased popularity to provide the advantages such as high strength and high power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source, inherent safety and mobility assistance to humans performing tasks, has been regarded during the recent decades as an interesting alternative to hydraulic and electric actuators However, some limitations still exist, such as the air compressibility and the lack of damping ability of the actuator bring the dynamic delay of the pressure response and cause the oscillatory motion Then it is not easy to realize the performance of transient response of pneumatic artificial muscle manipulator (PAM manipulator) due to the changes in the external inertia load with high speed In order to realize satisfactory control performance, a variable damper — Magneto-Rheological Brake (MRB), is equipped to the joint of the manipulator Superb mixture of conventional PID controller and a phase plane switching control method brings us a novel controller This proposed controller is appropriate for a kind of plants with nonhnearity, uncertainties and disturbances. The experiments were carried out in practical PAM manipulator and the effectiveness, of the proposed control algorithm was demonstrated through experiments, which had proved that the stability of the manipulator can be improved greatly in a high gain control by using MRB with phase plane switching control method and without regard for the changes of external inertia loads     

螺栓结合部切向动力学行为辨识方法

首先,以螺栓结合部切向动力学特性为研究对象,基于频响函数的子结构综合法为理论主线,建立结合部切向动力学行为辨识基本方程,推导其切向动刚度Za的理论表达式;其次,联合奇异值分解与最小二乘法,优化辨识结合部切向等效刚度ka与阻尼ca,由此建立螺栓结合部切向动力学数值模型;最后,利用该模型计算结构测点频响函数,进而将其与实测值进行对比。结果表明,二者吻合程度较高,且特征峰对应频率误差分别为1.38%,1.51%和0.84%,验证了所提方法能有效辨识螺栓结合部切向动力学行为,所得等效动力学参数精度较高,可为机械系统整机精准建模提供理论参考与数据支撑。     

压电陶瓷微位移器件控制模型的研究

从不同角度介绍了压电陶瓷微位移器件的两种控制模型.首先,借助于统计物理学分析,结合数学建模方法,建立了一个简单实用的压电陶瓷的迟滞数学模型.其次,借助于弹性体变形理论,介绍了压电/电致伸缩陶瓷的归一化控制模型,从理论上说明了采用电极化强度的方法可以有效减小迟滞的观点.并设计了两种实验系统,对两种控制模型进行了实验验证,实验结果表明,所建立的两种模型可有效减小压电陶瓷的迟滞非线性误差,提高压电陶瓷微位移的控制精度,有助于实现压电陶瓷驱动器的高精度开环微位移控制.     

基于APDL的柔性铰链位移放大机构

针对压电陶瓷微位移驱动器输出位移范围小的局限性,应用柔性铰链位移放大原理,设计了一种柔性铰链微位移放大机构,提出了柔性铰链杠杆放大机构的参数化数学建模方法,并采用ANSYS参数化程序设计语言（APDL）编写了柔性铰链杠杆放大机构的建模和仿真分析程序。仿真试验表明,所设计的柔性铰链杠杆放大机构的输入位移与输出位移线性度高,实际放大位移与理论值相差5％,完全可以满足机构的微位移放大要求。     

Comparative study of modeling and identification of the pneumatic artificial muscle (PAM) manipulator using recurrent neural networks

The paper deals with the PAM manipulator modeling and identification based on autoregressive recurrent neural networks. For the first time, the most powerful types of neural-network-based nonlinear autoregressive models, namely, NNARMAX, NNOE and NNARX models, will be applied comparatively to the PAM manipulator identification. Furthermore, the evaluation of different nonlinear neural network auto-regressive models of the PAM manipulator with different number of neurons in hidden layer is completely discussed. On this basis, the merits of each identified model of the highly nonlinear PAM manipulator have been analyzed and compared. The results show that the nonlinear NNARX model yields better performance and higher accuracy than the other nonlinear NNARMAX and NNOE model schemes. These results can be applied to model and identify not only the PAM manipulator but also to control other nonlinear and time-varying industrial systems.     

气动人工肌肉外骨骼机器人位置跟踪控制

针对以气动人工肌肉作为关节驱动器的外骨骼机器人关节位置跟踪控制问题进行了研究。首先,在动力学模型的基础上,设计了上层控制器,并结合自适应控制和滑模控制方法降低了动力学参数不准确和扰动项未知对外骨骼机器人的影响;其次,基于无模型方法设计了底层关节力矩控制器,调整外骨骼机器人的关节力矩;最后,针对上述控制方案设计仿真实验与外骨骼机器人的穿戴实验。结果表明,该控制方法对气动人工肌肉外骨骼机器人的关节位置跟踪控制是有效的。     

Faulty measurement substitution and control reconfiguration by using a multivariate flow control loop

A two-tank multivariate loop was designed and built to support research related to instrumentation and control, equipment and sensor monitoring. This test bed provides the framework necessary to investigate and test control strategies and fault detection methods applicable to sensors, equipment, and actuators, and was used to experimentally develop and demonstrate a fault-tolerant control strategy using six correlated variables in a single-tank configuration. This work shows the feasibility of using data-based empirical models to perform fault detection and substitute faulty measurements with predictions and to perform control reconfiguration in the presence of actuator failure in a real system. These experiments were particularly important because they offered the opportunity to prove that a system, such as the multivariate control loop, could survive degraded conditions, provided the empirical models used were accurate and representative of the process dynamics.     

MIMO model of an interacting series process for Robust MPC via System Identification

This paper discusses the empirical modeling using system identification technique with a focus on an interacting series process. The study is carried out experimentally using a gaseous pilot plant as the process, in which the dynamic of such a plant exhibits the typical dynamic of an interacting series process. Three practical approaches are investigated and their performances are evaluated. The models developed are also examined in real-time implementation of a linear model predictive control. The selected model is able to reproduce the main dynamic characteristics of the plant in open-loop and produces zero steady-state errors in closed-loop control system. Several issues concerning the identification process and the construction of a MIMO state space model for a series interacting process are deliberated.     

Modeling of hysteresis in piezoelectric actuators using neural networks

For the application of neural networks to the approximation of hysteresis which is characterized of multi-valued mapping and non-smooth nonlinearities, a novel modeling technique based on a transformation of one-to-one mapping is proposed in this paper. In this method, a special hysteretic operator is introduced to describe the change tendency of the hysteresis with regard to its input. Then an expanded input space is constructed for hysteresis with the introduction of such hysteretic operator, on which the multi-valued hysteresis is decomposed into a one-to-one mapping. Thus, neural networks model for hysteresis is derived, avoiding the calculation of the gradient of hysteresis. Subsequently, for approximation of rate-dependent hysteresis in piezoelectric actuators which is caused by the dynamic voltage excitations, a hybrid model, i.e. the dynamic extension of the proposed neural hysteresis submodel is developed. In the model, a linear dynamic block is introduced in series with the proposed neural model to allow for rate-dependent dynamics of the piezoelectric actuator simultaneously. Also the corresponding optimization algorithm by use of the modified Levenberg–Marquarqt (MLM) method is given. Finally, the experimental validation results of applying both the proposed neural hysteresis model and hybrid model to a piezoelectric actuator are presented.     

软体机器人研究现状综述

软体机器人由柔韧性材料制成,可在大范围内任意改变自身形状、尺寸在侦察、探测、救援及医疗等领域都有广阔的应用前景。综述软体机器人结构类型、驱动方式、物理建模技术和加工制造方法等问题。其结构模仿生物的静水骨骼结构和肌肉性静水骨骼结构,采用形状记忆合金、气动、电活性聚合物等物理驱动方式或将化学能转化为机械能的化学驱动方式。软体机器人建模困难,主要采用试验分析或使用超冗余度机器人建模方法近似研究。制造中的问题包括柔性本体制造、柔性致动器制造以及可伸展电路的制造,采用形状沉积、激光压印、智能微结构等新型制造工艺。软体机器人是一种全新的机器人,对它的研究刚刚起步,涉及材料科学、化学、微机电、液压、控制等多学科,从材料、设计、加工、传感到控制、使用均存在着一系列问题需要继续研究。     

Investigation of vibration modes excited upon reversal in gaps of cyclic mechanisms connected with a common actuator

A dynamic model of a ring structure for investigating vibrations excited in cyclic drive mechanisms of long actuators upon reversal in gaps is proposed. From theoretical analysis and computational modeling of the obtained set of nonlinear differential equations with variable parameters, the amplitude level of vibrations, the dominant vibration mode, and the conditions of its degeneracy are determined. Analytical criteria of rational dynamic synthesis are proposed.     

基于回归模型的SDBD-PA击穿特性试验研究

近年来,表面介质阻挡放电等离子体激励器（Surface dielectric barrier discharge plasma actuator,SDBD-PA）已经成为流动控制领域的研究热点。为研究SDBD-PA的击穿特性,为SDBD-PA相关研究的参数区间选取提供参考,首先采用控制变量法研究各激励器参数对SDBD-PA击穿电压和放电稳定性的影响,然后选取对击穿电压有影响的激励器参数,基于DOE方法进行试验,使用Isight软件建立二次回归模型并分析激励器参数对击穿电压的影响。研究结果表明,对SDBD-PA击穿电压和放电稳定性有影响的参数包括频率f、电极间隙d₁和激励器长度L;拟合所得三元二次回归模型经验证具有良好的精确度,可作为SDBD-PA击穿电压的预测模型;对SDBD-PA击穿电压影响最大的参数是f,其次为L和d₁;f和L对击穿电压的影响为负效应,d₁对击穿电压的影响为正效应;d₁和f之间以及f和L之间的交互作用对击穿电压也有很大影响,d₁和L之间的交互作用对击穿电压的影响非常小。     

压电智能桁架作动器配置的优化设计

利用优化设计的思路来探讨作动器的优化配置,并将优化模型分为两类:待控模态数目固定前提下优化作动器的数目和位置;固定作动器的数目,优化作动器的位置以控制更多的模态数目。并根据该类优化问题为多目标优化的性质,提出了一种基于模糊逻辑推理的多目标遗传算法,构造了一个能与适应度相对应的评价个体优劣的评价体系,以引导处理多目标问题的遗传算法的进化过程。数值算例结果表明了所提方法是正确的和有效的。     

Estimation of oscillation period/switching time for electrostatically actuated microbeam type switches

The undamped dynamic response of step-voltage driven parallel-plates, cantilever, and fixed-fixed type electromechanical switches is numerically investigated. In each case, application of energy technique yields the threshold values of the amplitude and the applied voltage beyond which the oscillatory motion of the movable electrode ceases to exist. These critical values are identified as the dynamic pull-in parameters of the corresponding microactuator model. For all three microactuator configurations, empirical expressions for the switching time and oscillation period are developed. These empirical relations are applicable over a wide range of applied voltage, and the estimates obtained using the proposed empirical relations correlate very well with the previously published results. Furthermore, the phase portraits of these actuators have been thoroughly investigated in order to examine the role of static pull-in point in a dynamic setting and also to propose the design rules to build faster microswitches.     

基于机群的电动汽车柔性实时仿真平台的研究与构建

为了解决电动汽车研究中控制策略的实时仿真,非线性元件建模和整车控制器快速原型开发等关键技术问题,采用机群技术和硬件在环仿真技术建立了电动汽车柔性实时仿真平台。结合燃料电池汽车开发实例,运用平均值建模方法实现了异步驱动电动机、主DC／DC及其控制系统动态模型的实时仿真:针对蓄电池模型精度差的特点,实现了蓄电池的在环仿真,从而构造了与真实车辆更为接近的仿真环境。最后,通过道路试验初步验证该平台的有效性,并对蓄电池在环仿真的应用进行阐述。     

MODEL IMPROVEMENT AND EXPERIMENT VALIDATION OF PNEUMATIC ARTIFICIAL MUSCLES

According to the deficiency of the present model of pneumatic artificial muscles (PAM), a serial model is built up based on the PAM's essential working principle with the elastic theory, it is validated by the quasi-static and dynamic experiment results, which are gained from two experiment systems. The experiment results and the simulation results illustrate that the serial model has made a great success compared with Chou's model, which can describe the force characteristics of PAM more precisely. A compensation item considering the braid's elasticity and the coulomb damp is attached to the serial model based on the analysis of the experiment results. The dynamic experiment proves that the viscous damp of the PAM could be ignored in order to simplify the model of PAM. Finally, an improved serial model of PAM is obtained.