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Segmented Constrained Layer Damping Treatment And Its Application On Vibration Suppression For Space Robotic Arm

Posted on:2017-03-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:S T TianFull Text:PDF
GTID:1108330482991308Subject:Mechanical Manufacturing and Automation
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The space robotic arm is considered a promising approach for space station missions such as assembling and repairing. Vibration in the launched robotic arm is inevitably provoked due to the flexibility of arms. Constrained layer damping treatments promise to be an effective method to control vibration in flexible structures. The principle involved is related to dissipation of vibratory energy in the form of heat due to shear deformation in the viscoelastic core. Cutting both the constraining layer and the viscoelastic layer, which leads to segmentation, increases the damping efficiency. However, this approach is not effective for all treatments. In this study, damping characteristics of segmented constrained layer damping treatments was studied. Taking the fine small arm of China’s space station robotic arm system as an example, applications of constrained layer damping treatments to structural vibration control are discussed.First, a finite element model capable of handling treatments with extremely thin viscoelastic layer was developed on the basis of interlaminar continuous shear stress theories. Loss factor results of the present model and a model that neglects interlaminar continuous shear stress theories is compared. It is shown that adopting extremely thin viscoelastic layers could not lead to optimal structural damping capacity and the point is verified by means of experiments. The loss factor, which is calculated through the modal strain method, is used for quantitative assessment of system damping.The volume of viscoelastic material and the shear strain field in the viscoelastic layer have direct impact on the structural damping efficiency. Other design parameters act on the damping efficiency through their influence on the shear strain field. Segmentation, which could create a high-shear region in the viscoelastic layer, is not always effective. Using the developed method, influence of segmentation and change in design parameters on the shear strain field was analyzed and optimal cut arrangements were obtained by adopting a genetic algorithm. It is shown that thickness variance of the viscoelastic layer has different effects on the applicability of segmentation. Segmentation is found to be suitable for tr eatments with relatively thin viscoelastic layer while the shear strain in the viscoelastic layer is at a high level. However, structural damping rate is relatively low for treatments with relatively thin viscoelastic layer. Provided that optimal viscoelastic layer thickness was selected, placing cuts would only be applicable to treatments with low shear strain inside the viscoelastic layer. Increasing stiffness of the two face layers or adopting relatively soft viscoelastic material would result in higher levels of shear strain in the viscoelastic layer. The shear strain level in the viscoelastic layer is low when the treatment is deformed in the form of first-order mode shape. Thus, segmentation is always effect in improving first-order modal damping. As for high-order modal damping, segmentation is applicable for very flexible structures. In this study, a novel method to segment the constraining layer is presented and the method is characterized by not segmenting the constraining layer thoroughly. The new method is effective in improving high-order modal damping and this feature is proven by experiments.Segmentation has an impact on active constrained layer damping treatments, which adopted piezoelectric ceramics as the constraining layer. Piezoelectric ceramics produce mechanical strain when subjected to an electric field and the mechanical strain could further improve the shear in the viscoelastic layer. A proportional derivative control law is applied on the piezoelectric ceramics. Effects of control gain and other design parameters have been investigated. Influence of segmentation is also discussed. It is shown that the actuation ability of piezoelectric ceramics is reduced due to the viscoelastic layer. Segmentation is applicable only when the base layer is relatively thin. For solving many engineering problems, techniques for modeling active constrained layer damping treatments in the commercial software MSC/Nastran are discussed. MSC/Nastran offers no piezoelectrical coupled-field elements and an analogy is drawn between piezoelectric strains and thermal strains. The control strategy is implemented using the TF module in MSC/Nastran. Furthermore, the method is illustrated with an engineering application example.Cylindrical shells are applied to the design of arms. Constrained layer damping treatments could enhance the damping capacity of arms. A cylindrical constraining layer would limit the deformation of viscoelastic layer while segmentation creates a high-shear region in the viscoelastic layer. Thus, segmentation had wide applicability to cylindrical constrained layer damping treatments. Two different methods, which respectively segment the treatment along the longitudinal direction and along the circumferential direction, are compared. It is shown that segmentation along the circumferential direction is superior to that along the longitudinal direction. The finite element model of the robotic arm is developed and then verified by vibration test in the state of launch. Two different solutions to bond constrained layer damping to the arms is proposed, which are respectively active constrained layer damping and segmented passive constrained layer damping. Frequency response analysis results show that constrained layer damping treatments could suppress the vibration at the end-effector under the condition that the mass and the rigidity of the arm is not changed significantly. Moreover, the reliability of the method is high.
Keywords/Search Tags:space robotic arm, segmented constrained layer damping treatment, vibration suppression, viscoelastic material, finite element method
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