查看更多>>摘要：The reliable estimation of the wavenumber space(k-space)of the plates remains a long-term concern for acoustic modeling and structural dynamic behavior characterization.Most current analyses of wavenumber identification methods are based on the deterministic hypothesis.To this end,an inverse method is proposed for identifying wave propagation characteristics of two-dimensional structures under stochastic conditions,such as wavenumber space,dispersion curves,and band gaps.The proposed method is developed based on an algebraic identification scheme in the polar coordinate system framework,thus named Algebraic K-Space Identification(AKSI)technique.Additionally,a model order estimation strategy and a wavenumber filter are proposed to ensure that AKSI is successfully applied.The main benefit of AKSI is that it is a reliable and fast method under four stochastic conditions:(A)High level of signal noise;(B)Small perturbation caused by uncertainties in measurement points'coordinates;(C)Non-periodic sampling;(D)Unknown structural periodicity.To validate the proposed method,we numerically benchmark AKSI and three other inverse methods to extract dispersion curves on three plates under stochastic conditions.One experiment is then performed on an isotropic steel plate.These investigations demonstrate that AKSI is a good in-situ k-space estimator under stochastic conditions.
查看更多>>摘要：Traditional single-acting piezoelectric-hydraulic hybrid actuators usually have the prob-lem of inertial force caused by flow pulsation of the liquid,which degrades their output perfor-mance.To suppress or solve the associated inertial force and enhance its output capabilities,this paper proposes a new type of double-acting piezoelectric-hydraulic hybrid actuator with four check valves acting as mechanical diodes.The new hybrid actuator was fabricated and its output perfor-mance was tested.When the voltage is 700 Vp-p and the bias pressure is 2 MPa,the pulsation rates δof the new actuator at 400 Hz,500 Hz and 600 Hz are 2.29,2.08 and 1.78,respectively,while b of the single-acting hybrid actuator under the same conditions are 10.98,11.05 and 17.12.Therefore,the liquid pulsation rate of the new hybrid actuator is significantly reduced,which is beneficial for improving the flow uniformity and weakening the influence of inertial force on the hybrid actuator.This strategy ultimately leads to a maximum no-load velocity of 168.1 mm/s at 600 Hz and a max-imum blocking force of 141 N at 450 Hz for the new hybrid actuator.In addition,this strategy has the potential to be used in other electrohydrostatic actuators to improve their performance.
查看更多>>摘要：Geometric error is the main factor affecting the machining accuracy of hybrid machine tools.Kinematic calibration is an effective way to improve the geometric accuracy of hybrid machine tools.The necessity to measure both position and orientation at each pose,as well as the instability of identification in case of incomplete measurements,severely affects the application of traditional calibration methods.In this study,a kinematic calibration method with high measure-ment efficiency and robust identification is proposed to improve the kinematic accuracy of a five-axis hybrid machine tool.First,the configuration is introduced,and an error model is derived.Further,by investigating the mechanism error characteristics,a measurement scheme that only requires tool centre point position error measurement and one alignment operation is proposed.Subsequently,by analysing the effects of unmeasured degrees of freedom(DOFs)on other DOFs,an improved nonlinear least squares method based on virtual measurement values is proposed to achieve stable parameter identification in case of incomplete measurement,without introducing additional parameters.Finally,the proposed calibration method is verified through simulations and experiments.The proposed method can efficiently accomplish the kinematic calibration of the hybrid machine tool.The accuracy of the hybrid machine tool is significantly improved after calibration,satisfying actual aerospace machining requirements.
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