Compared with traditional additive manufacturing technology (3D printing), 4D printing technology (four-dimensional printing) increases the time dimension. The structure prepared by 4D printing process can change its shape and configuration with the external environment (i.e. light, heat, magnetism, electricity, etc.), which has a broad application prospect. This paper introduces several typical implementation methods of 4D printing in combination with the typical research results of 4D printing in recent years. The printing materials, design methods, and simulation methods of current 4D printing technology are summarized. Finally, the possible development directions of 4D printing technology and its application prospects in the fields of biomedicine, soft robotics, aerospace, etc. are introduced, and some problems of 4D printing technology are discussed.
Abstract: To meet the requirements of improving work efficiency, the rotating machinery represented by gas turbines reduces the gap between rotor and stator, making rub-impact occur frequently. However, a few researchers combined with the current gas turbine condition monitoring concluded that it could diagnose the rub-impact fault. In this study, the vibration features that can help diagnose the compound fault of rotor unbalance and rub-impact are researched. Taking the Jeffcott rotor system as the research object, the mathematical model is constructed considering the coupling of radial and torsion, and the Runge-Kutta method is used to solve the differential equation. Through the analysis of the model results, it is concluded that the compound fault can be diagnosed by the vibration features-reduction of the fundamental frequency amplitude. Finally, the correctness of the model is verified by experiments. At the same time, the vibration features of the rotor and stator are compared to show the consistency of vibration features, which shows that the proposed features can diagnose this compound fault.
Abstract: The processed surface integrity of the propeller has a vital impact on the performance, efficiency, and noise of the entire power energy conversion device, and the bionic micro-structured surface is conducive to improving the noise reduction performance of the working parts. In this paper, the microstructure of the propeller blade surface is machined by precision abrasive belt grinding. Based on the surface roughness detection and 3D morphology analysis results, a univariate model of propeller surface groove with V-shaped section is established. The flow field analysis, numerical analysis of cavitation, and noise performance analysis of general marine propellers and bionic marine propellers are also carried out. The results show that the maximum noise of the propeller with the bionic grooved surface is 94.7 decibels, and the maximum noise of the general propeller is 146 decibels. The noise reduction effect is increased by 35%, which provides a new method of precision abrasive belt grinding for the noise reduction of the propeller.
Abstract: Space particle suspension transport has the advantages to avoid adsorption loss, contact pollution, and signal interference, and has potential applications in the fields of cell self-assembly, controllable distribution of nanoparticles, and micro-Led mass transfer. Here, an ultrasonic array device was developed to obtain space particle levitation transport, and explore the suspension mechanism of the specific impact of the modulation signal on the space transmission and the mechanism of using the phase modulation signal to control the opposed linear transducer array to realize the space transportation. The suspension and directional transportation of ultrasonic standing waves are both non-contact and important means for processing without a certain container, and have a very broad application prospect in the fields of mechanical manufacturing, biochemical trace analysis, and droplet dynamics and so on. In this paper, aiming at the imperfect mechanism of space transportation and the complicated method of space transportation, we propose a new method of using phase modulation signals to control the array of opposite linear transducers to realize the space transportation of solid pellets. The transportation acceleration is used to characterize the stationarity in the transportation process, and the specific deviations of different phases of the modulation signal are set, so that the curves of acceleration change and position change of solid pellets in the transportation cycle can be drawn. The results show that when the phase deviation is π/2, it is the best to realize the stability of lateral transportation. When the phase deviation of coaxial array elements is set to π in longitudinal transportation, stable and long-distance transportation based on cycle period can be realized. The parametric model of 3D finite element is established, and the specific distribution of instantaneous sound pressure of dynamic sound field in space transportation is simulated. By comparing the experimental phenomena with different simulation results, we can find that the transportation process of solid balls is in good agreement with the movement of sound pressure nodes in sound field.
The vision-guided robotic machining accuracy highly depends on the hand-eye calibration accuracy between robot and vision equipment. In order to address the problem of less parameter constraints in existing hand-eye calibration methods, in this paper a hand-eye calibration algorithm of binocular stereo vision is proposed based on multi-pixel 3D geometric centroid relocalization. The algorithm mainly includes three steps:1) the checkerboard relocalization images of multiple sets of fixed-point pose transformations are captured by the binocular stereo vision; 2) the robot tool center point (TCP) coordinates in the binocular coordinate system are obtained by an iterative reweighted least squares algorithm based on sub-pixel corner extraction, and 3) the hand-eye transformation matrix between the binocular system and the robot is obtained by the singular value decomposition (SVD). The experimental results show that both the average error and the mean square error of the proposed hand-eye calibration algorithm can reach 0.45mm and 0.21mm, respectively, which are much smaller than the existing algorithms and can meet the accuracy requirements of robotic positioning and machining.