The Observer-based Adaptive Sliding Mode Control of Dual-manipulator System Handling a Flexible Payload
|Course||Control Theory and Control Engineering|
|Keywords||manipulator flexible payload singular perturbation optimal observer vibrationcontrol|
The research of dual-manipulator coordinated operating the flexible payload systemhas been the concern of a growing number of researchers. A very wide range ofapplications includes not only in the industrial field, but also in the unstructuredenvironment. This advantage is particularly evident in the field of space exploration. Thecoordination system of the remote operating dual-manipulator performs orbitconstruction, maintenance and repair work to enable astronauts’ task involvementminimized. In these areas, the load to be manipulated may have excessive weight, toolarge volume, too large flexibility or other adverse operating factors. If the load weightexceeds the carrying capacity of a single manipulator, the coordinating operation ofmulti-manipulator can distribute the weight in order to move the load better. Similarly, ifthe load has certain flexibility, dual-manipulator can be better and more accurate than asingle manipulator to move the load, the same as handling flexible objects with bothhands is faster and better than with one hand. In assembly tasks, multiple manipulatorscollaboration can operate several loads at the same time that will not only improveefficiency but also avoiding the design of specialized assembly equipment. In spaceoperations, the use of dual-manipulator coordination eliminates the need of theworkbench installation for manual operation required. Great practical value promotes thedevelopment of theoretical research. In the field of operating load with dual-manipulator,the most complicated object is the flexible payload. There are still many problems to bechallenged.The inherent flexibility of flexible payload will produce vibration during the systemmotion in turn affecting the stability and accuracy of the operation, so it is necessary tocontrol the dual-manipulator coordinated operation of the flexible payload movementwhile suppress the vibration of the payload. Taking into account the multiple applications,different materials and various specifications of flexible payload, therefore the sensorscan not be mounted in the flexible payload to obtain the vibration information of the load.The need of seeking a more universal and easy way to get the vibration information inorder to suppress the vibration is urgent. In addition the system modeling uncertaintiesand external disturbances will adversely affect the control performance of the system which must be controlled properly.Based on the above mentioned questions, at first with the finite element method, thedynamic model of dual manipulators coordinating the operation of the flexible payload isestablished. In view of the movement of the flexible beam contains the rigid motion andelastic vibration in two parts, and these two motions act in different time domains as therigid motion is considered to be slowly varying system while the elastic vibration isconsidered to be fast-varying system. Therefore, in order that the centroid of the rigid partof the flexible payload tracking the desired trajectory while suppressing the elasticvibration, the introduction of two-time scale theory decomposes the system dynamicsmodel into the slow subsystem and the fast subsystem though singular perturbation. Onaccount of the different time scales, the two reduced-order subsystem controllers can bedesigned separately. The final design of the control inputs are converted to the slow timescale, and the hybrid controller of the whole control system is obtained. In general, thiscontroller design method is successive because the fast subsystem control design is basedon the slow subsystem control design. In this article, the slow subsystem seemed as thesystem of dual-manipulator coordinated operating a rigid load can directly use the moremature control algorithms in the field of the coordinated rigid load operation; for the fastsubsystem as a simple linear time-varying system, the linear control method can beintroduced for controller design.The slow subsystem is still carrying on the foregoing design. For the elastic modeson flexible load are not readily available in the fast subsystem, the manipulator wristmounted force/torque sensors are used to measure the output interaction torques betweenthe end effecter and the flexible payload. The relationship between torques and flexibleload-deflection is derived, and then the observer is designed to estimate the other elasticmodes difficult to obtain. The controller is designed using the estimated state variable. Inaddition, the observer design strategy based on the system linearization is presented. Thelinear model can retain the flexibility movement of the system vibration. The sameforce/torque sensor is used to measure the output torque information and then designobserver to estimate the elastic modes which is applied for the appropriate controllerdesign. The simulation results of two design methods are comparative analyzed. Theparameter uncertainties and external disturbances are estimated by the adaptive control,and given the reasonable control to eliminate the bad effects.The problem mainly solved in this thesis is the system control strategy design ofdual manipulators coordinated operating a flexible payload with uncertainties. There is alarger value of practical application in industrial processes. Considering there may be measurement error and other uncertainties in force/torque sensor in the actual applicationwhere the future research should focus. The second order response of elastic vibrationalso has great value in order to understand the flexible vibration deeper and facilitate theoperation of the flexible load better and more accurate in future. So for the multiplemanipulators coordinated operating of the flexible payload system, there is a lot of workto be completed.