Vibration control of smart structures using an array of Fiber Bragg Grating sensors

Optical strain gauges, such as Fiber Bragg Grating (FBG) sensors, are widely used to monitor the health of structures and their state of deformation. This paper proposes exploiting the measurements of these sensors as feedback for active vibration control applications. The advantages of this solution are the possibility of monitoring a large number of sensors (to approximate distributed measurements) and of embedding them in carbon fiber structures with negligible load effects. Experimental tests confirm that smart structures with embedded FBG sensors can be profitably designed to suppress vibrations.     

Adaptive neuro-fuzzy control of a flexible manipulator

This paper describes an adaptive neuro-fuzzy control system for controlling a flexible manipulator with variable payload. The controller proposed in this paper is comprised of a fuzzy logic controller (FLC) in the feedback configuration and two dynamic recurrent neural networks in the forward path. A dynamic recurrent identification network (RIN) is used to identify the output of the manipulator system, and a dynamic recurrent learning network (RLN) is employed to learn the weighting factor of the fuzzy logic. It is envisaged that the integration of fuzzy logic and neural network based-controller will encompass the merits of both technologies, and thus provide a robust controller for the flexible manipulator system. The fuzzy logic controller, based on fuzzy set theory, provides a means for converting a linguistic control strategy into control action and offering a high level of computation. On the other hand, the ability of a dynamic recurrent network structure to model an arbitrary dynamic nonlinear system is incorporated to approximate the unknown nonlinear input–output relationship using a dynamic back propagation learning algorithm. Simulations for determining the number of modes to describe the dynamics of the system and investigating the robustness of the control system are carried out. Results demonstrate the good performance of the proposed control system.     

Active vibration control of a flexible one-link manipulator using a multivariable predictive controller

This article presents a new application of model-based predictive controller (MPC) for vibration suppression of a flexible one-link manipulator using piezoceramic actuators. Simulation and experimental studies were conducted to investigate the applicability of the MPC strategy to control vibration of the flexible structure having multiple inputs and multiple outputs (MIMO). The performance of the proposed technique was assessed in terms of level of vibration reduction. The results demonstrated that the proposed predictive control strategy is well suited for multivariable control of vibration suppression on flexible structures.     

弯曲增敏型光纤曲率传感器的优化分析

为一种直接检测弯曲曲率的光强调制型光纤曲率传感器—它采用弯曲增敏技术提高光纤对弯曲的灵敏度,能区分正向弯曲和负向弯曲,具有线性范围宽、成本低和适合薄结构的埋入式检测等优点建立了数学模型。基于这个模型,讨论了敏感区的光强的调制原理,推导出了光功率损耗与光纤弯曲半径、敏感区几何参数的关系,并通过实验验证了理论分析的有效性,为传感器结构的优化提供了定量依据。     

Inertial vibration damping control of a flexible base manipulator

A rigid (micro) robot mounted serially to the tip of a long flexible (macro) robot is often used to increase the reach capability, but flexibility in the macro-manipulator can make it susceptible to vibration. A rigid manipulator attached to a flexible but unactuated base was considered as an analogous problem. The interaction forces and torques acting at the base of the robot are used to damp the vibration. Appropriate control gain limits are established to ensure the inertia effects, or those directly due to accelerating the links of the rigid robot, have the greatest influence on the interactions. By commanding the link accelerations out of phase with the base velocity, vibrational energy will be removed from the system. This signal is then added to the rigid robot position controller, providing combined rigid robot position and vibration control of the base.     

Adaptive control of a flexible linear array

A system has been constructed which adaptively corrects for an applied phase error along the length of a flexible linear array. The system utilises resistance strain gauges and electrically controlled ferrite phase shifters. Results at 9.4 GHz are presented, in the form of radiation patterns, to provide an illustration of the system performance.     

Force control of a very lightweight single-link flexible arm based on coupling torque feedback

In this paper, a feedback control law is proposed for regulating the contact force exerted by a very lightweight single-link flexible manipulator when it comes into contact with a motionless object. This control law is based on a lumped-parameter model. The tracking of the desired contact force is obtained by using a feedback loop control of the coupling torque between the motor and the flexible arm. To achieve a good performance on the force control it is only necessary to measure the coupling torque at the root of the arm. Neither the contact force sensor nor the angular position sensor of the motor are used in the control method. A modified PID controller is proposed for this control law. In this work the force control problem is studied for both free and constrained motions of the flexible manipulator, and a collision detection algorithm is also described.     

Robust control of a planar manipulator for flexible and contactless handling

Many industries require non-contact and flexible manipulation systems, such as magnetic or pneumatic devices. In this paper, we describe a one-degree-of-freedom position control of an induced-air flow surface. This device allows to convey objects on an air cushion using an original aerodynamic traction principle. A model of the system is established and the parameters are identified experimentally. A H_∞ robust controller is designed and implemented on the device in order to control the object position. Experiments with objects of various dimensions and materials are conducted and showed the robustness capabilities of the controller.     

All-digital demodulation system of interferometric fiber optic sensors using an improved PGC algorithm based on fundamental frequency mixing

In this paper,the optimum supercontinuum(SC)spectrum generation in a dispersion decreasing fiber is presented.Three normalized parameters for the pump pulse and SC fiber are introduced.It is found that the shape of an SC spectrum is uniquely specified by the input soliton order,the normalized dispersion slope and the normalized effective fiber length.For a pumping condition with a given input soliton order and a given normalized dispersion slope,by optimizing the normalized effective fiber length,the residual spectral peak in the SC spectrum can be suppressed effectively,and a broad SC spectrum with optimum spectral flatness can be obtained.     

Interaction control of an industrial manipulator using LPV techniques

This paper presents the design and implementation of a hybrid force/motion control scheme on a six-degrees-of-freedom robotic manipulator employing a gain-scheduled linear parameter-varying (LPV) controller. A nonlinear dynamic model of the manipulator is obtained and the unknown parameters are estimated. The manipulator is decomposed into an inner and a wrist submodel, and a practical way is proposed to investigate the coupling between them. The motion control part of the hybrid controller which is the main focus of this paper is formed by a combination of an LPV controller and a model-based inverse dynamics controller for the inner submodel and the wrist joints, respectively. A quasi-LPV model with a reduced number of scheduling parameters is derived for the inner submodel, and a polytopic LPV gain-scheduled controller is synthesized in a two-degrees-of-freedom structure including feedback and feedforward parts, which is augmented by a friction compensation term. A PD controller with a feedforward path is designed to control the interaction force. The proposed hybrid force/motion scheme is implemented on the 6-DOF CRS A465 robotic manipulator to perform a writing task. Comparison of the results with those of a hybrid force/motion controller with a plain model-based inverse dynamics motion control and the same force control shows that the proposed controller improves the position tracking performance significantly.     

Hybrid learning control schemes with input shaping of a flexible manipulator system

The paper describes a practical approach to investigate and develop a hybrid iterative learning control scheme with input shaping. An experimental flexible manipulator rig and corresponding simulation environment are used to demonstrate the effectiveness of the proposed control strategy. A collocated proportional-derivative (PD) controller utilizing hub-angle and hub-velocity feedback is developed for control of rigid-body motion of the system. This is then extended to incorporate iterative learning control with acceleration feedback and genetic algorithms (GAs) for optimization of the learning parameters and a feedforward controller based on input shaping techniques for control of vibration (flexible motion) of the system. The system performance with the controllers is presented and analysed in the time and frequency domains. The performance of the hybrid learning control scheme with input shaping is assessed in terms of input tracking and level of vibration reduction. The effectiveness of the control schemes in handling various payloads is also studied.     

A local approach for the LPV identification of an actuated beam using piezoelectric actuators and sensors

This paper considers the identification of structural dynamics by identifying its frequency response functions (FRFs) – a mathematical representation of the relationship between the vibration response at one location and excitation at the same or another location. The spatially-varying characteristics of the FRFs at various input and output locations are explored, and lead to a spatial linear parameter varying (LPV) representation. A local LPV identification technique for lumped systems is adapted here to spatially-interconnected systems. The identification of a spatial LPV model facilitates the experimental work, and also simplifies the controller synthesis. The proposed approach is applied to identify an actuated beam equipped with an array of collocated piezoelectric actuators and sensors for performance illustration.     

Interrogation of an integrated optic modulator over a low-birefringence fiber using polarization tracking

The remote operations of an integrated optic Mach-Zehnder modulator via a low-birefringence fiber link using an input polarization control scheme is demonstrated. The polarization tracking scheme actively maintains the state of polarization arriving at the modulator in the state required for optimum operation of the device. As the feedback signal is determined by the overall optical throughput of the modulator, no modulation is itself required for the modulator to be set for optimum performance.<>     

布里渊散射的分布式光纤温度传感器的研究进展

提要：基于布里渊散射的分布式光纤温度传感技术凭借着其独特的优点,在国内外引起了广泛的关注,成为了一大热点研究,本文综述了基于布里渊散射的分布式光纤温度传感技术的研究现状。在简单介绍了布里渊测温原理的基础上,针对目前布里渊散射的光纤温度传感器存在的在测量范围以及空间分辨率上的缺陷、不足,重点介绍了布里渊散射的分布式光纤温...     

Multiplexing of optical fiber sensors using a frequency-modulated source and gated output

A novel method is proposed and demonstrated for multiplexing fiber-optic interferometric sensors using the FMCW technique. The method uses a gas laser whose optical frequency is modulated sinusoidally by an external modulator. The use of gating and appropriate signal processing can achieve low crosstalk between sensors. Experiments on two and three sensor systems are reported. The minimum detectable signal measured is 1 mrad/sqrt{Hz}and the crosstalk factor achieved is -35 dB. The major causes of crosstalk are also analyzed.     

Reduced phase error of a fiber optic gyroscope using a polarization maintaining photonic crystal fiber

We report the first measurement of the polarization crosscoupling of a 900-m length of quadrupolar-wound sensing coil for the fiber optic gyroscope (FOG) using polarization maintaining photonic crystal fibers (PM-PCFs). The crosscoupling is analyzed with the Optical Coherence Domain Polarimeter (OCDP). Also the polarization extinction ratio (PER) of the PM-PCF coil is measured. For comparison, a standard panda fiber coil with nearly the same length is examined. The results show that PER of the PM-PCF coil is ～10 dB larger than the panda fiber coil, and polarization crosscoupling in the PM-PCF coil is ～10 dB less than in the panda fiber coil. Moreover, based on measurements, a 4-fold reduction in phase error is demonstrated numerically in a FOG made of the PM-PCF coil, compared to the same gyro operated with a similar coil of panda fiber. These findings have important benefits in a higher measurement precision and stability of FOG.     

Motion control of a tendon-based parallel manipulator using optimal tension distribution

This paper presents the motion control of a six degree-of-freedom tendon-based parallel manipulator, which moves a platform with high speed using seven cables. To control the motion of the platform along desired trajectories in space, nonlinear feedforward control laws in the cable length coordinates are used. Taking account of the effect of redundancy on actuation, the optimal tension distribution should be considered to the advantage of the control laws. Using a method based on the analysis of the workspace condition, tension constraints and limiting torque constraints of actuators, an analytical solution for optimum tension distribution was found and used to compute the force in each cable for compensation of dynamic errors. It is experimentally demonstrated that the proposed control laws reduce the energy consumption of the actuators and satisfy the path tracking accuracy.     

Vibration control of flexible rotors using a passive magnetic device working on the principle of electromagnetic shunt damping

Excessive rotor vibration can propagate the micro-cracks and hence the premature failure of the rotor system. A passive magnetic device working on the principle of electromagnetic shunt damping (EMSD) is proposed to passively control the rotor vibrations. Although, these EMSD-based damping systems are quite common in the literature, however, there is not even a single article available in the literature, showing the application of such a device passively controlling the rotor vibrations from a distance. Due to the flow of flux between the rotor, stator, and air gap, the modeling procedure for such an EMSD-based system changes completely and is not available in the literature. Due to rotor movement, there is a variation in the magnetic flux provided by the permanent magnets placed in the device. Due to electromagnetic interactions, electric currents are induced in the windings provided in the device. When these currents are allowed to pass through electrical resistance, damping forces are generated. In this way, vibration energy is converted into heat energy. In this research, it is observed that the damping effect is maximum for an optimal value of electrical resistance. The effect of several turns in the windings and permanent magnet thickness is also investigated in terms of the production of damping forces. The efficiency of the device is mathematically proved through simulations. Further, experimental results verify the effectiveness of the proposed device.     

引入曲率与角度校正的柔性机构三维形状多芯光纤重构方法

为提高柔性机构三维位形参数光纤测量精度,提出了基于曲率与角度校正的多芯光纤三维形状重构方法。通过引入方向角和曲率校正系数,改进了柔性三维形变多芯光纤重构算法;利用准分子激光器和相位掩膜法制备了多芯光纤光栅传感阵列,建立了多芯光纤三维形状重构实验系统;实验测量了不同曲率比例因子下的形状重构误差,分析了曲率与角度校正前后形状重构误差;通过对应变进行了三次样条插值,并对方向角和曲率进行了校正,得到了形状重构误差平均值为0.74 mm、最大值为1.64 mm;利用校正后的多芯光纤传感系统进行三维螺旋形变重构实验,得出重构精度提高了10.2%。研究结果表明,基于曲率与角度校正的多芯光纤三维形状重构方法具有更高精度,在柔性机构三维位形实时监测中具有应用前景。     

Code reusuable optical CDMA system using an array of superstructured fiber Bragg gratings

We have proposed a user extensible optical CDMA system which employs a repeated use of codes in the encoders and the decoders. In this study, we report the user-extension effect by using an array of superstructured fiber Bragg grating (SSFBG) as an encoder and a decoder through the simulations and the experiments. We performed the experiments by using 4 SSFBGs in each encoder and decoder. We have shown that the capable number of users can be increased up to ₆₃C₁?₆₃C₁?₆₃P₂ when 63 orthogonal codes are used.