Optimized Locations Of Actuator/Sensor And Active Control Of Structures

In active structural control, the degrees of freedom of system are usually very large, but the number of sensors and actuators applied in the system is often small. So to control structures is actually to control the system with large degrees of freedom by applying finite number of sensors and actuators. So here come two questions regarding the placement of sensors or actuators on the structure. When the sensors are placed at improper locations, the output of the sensors cannot synthesize the modal coordinates exactly, i.e., the unobserved mode responses are embedded into the observed mode responses and the sensors cannot give a clear picture of the structural vibration, which will result in observation spillover. When the actuators are misplaced, they may stimulate responses from the uncontrolled modes, which will cause control spillover. Both control spillover and observation spillover may deteriorate control performance or even make the control system unstable. As active control technique has wide applications in many high-tech engineering areas, such as aerospace, aviation and robotics, the study of optimal locations of sensors and actuators is of importance both theoretically and practically.To determine locations of sensors and actuators is in fact an optimization problem which can be solved by optimizing a certain index function by some optimization algorithm. The index function is to evaluate the optimum of the structure when sensors and actuators are placed at different locations on the structure. The extremum of the index function corresponds to the optimal position of the sensor and actuator, while the optimization algorithm is to get the extremum as fast as possible. Therefore the optimization problem of sensors and actuators consists of the selection of an index function and the selection of an optimization algorithm. For the index function, controllable and observable Gramian matrices are often used as objective function to optimize the locations of actuators and sensors. Among modern optimization algorithms, the Particle Swarm Optimizer (PSO) is a random optimization algorithm based on swarm intelligence. For its simplicity to use, high calculation efficiency, fast convergence rate and strong paralleling ability, it has found applications in various scientific problems such as the optimization of continuous nonlinear function, the training of artificial neural network weights, fuzzy control, etc. PSO proves effective and efficient in all these applications.This dissertation presents the theoretical and experimental studies of the optimal locations of sensors and actuators for the flexible plate and trussed structure by means of PSO algorithm. This research was funded by the National Natural Science Foundation of China (Grant No. 10472065), the Key Project of Ministry of Education of China (Grant No's. 10772112, 107043), the Key Project of Ministry of Education of China (107043) and the Specialized Research Fund for the Doctoral Program of Higher Education of China (107043). Some achievements are acquired both in theory and applications and a few highlights are as follows:(1) Ongoing researches on the optimized locations of the sensor and the actuator are comprehensively reviewed. The research extent and contents of this dissertation are thus put forward.(2) The optimized locations of sensors and actuators on the flexible plate are studied in this dissertation, where piezoelectric patch is used as an actuator. The dynamic equation is firstly presented using the Finite Element Method and the continuous modal function is fitted using the least square method. Then the PSO algorithm is applied to optimize the locations of sensors and actuators. Finally active controller is designed using the optimal control method. Simulation results indicate that the PSO is effective in determining the optimal locations of sensors and actuators and is especially fit when multiple actuators are involved. The efficiency of PSO is evidently higher than that of the idiomatic traverse algorithm.(3) This dissertation discusses the optimal positions of actuators for a flexible trussed structure, where piezoelectric stack is used as an actuator. It also presents the controller design and the modeling of the trussed structure. Numerical simulations are done to show the validity of the presented method.(4) Based on DSP control board, the experimental study is performed on active control of the flexible plate and trussed structure. The experiment scheme is also designed and some practical problems such as signal difference and transformation of acceleration signal are solved in this paper. Theoretical results are verified by the experiment.The topic of optimal positions of sensors and actuators is challenging both in mechanics and in control engineering, where many aspects need further study and more efforts. At conclusion, a summary of work done in this dissertation is given and some problems of interest are also brought forward for future research.