Shotcrete spray is an indispensable process in tunnel construction. At present, the construction of tunnels in China is mainly depend on labor or mobile concrete sprayer, which has lots problems like timeconsuming, low precision, and labor intensive. An intelligent detection method for tunnel shotcrete spraying is proposed in this article. There are two main issues need to be solved, one is the modeling of tunnel in real-time to monitor the thickness of shotcrete and other is the detection of spraying area in the tunnel. The LiDAR can obtain a 3D model of tunnel after performing necessary preprocess on it in real-time. On the other hand, the spraying areas are usually divided by arches in the tunnel, so we can detect the position of arches to determine the spraying areas. Inspired by the YOLO algorithm, we proposed a novel neural network structure to detect the approximate bounding boxes of the arches and a line-detection algorithm is used to determine the final positions of the spraying area in the image. The size of the weight file of our neural network is only 2.57 MB after the use of some deep compression tricks, which means our model is device friendly. After that, the object detection results in the image will be projected to the point cloud data. The experimental results suggest that our method performed well in the detection for tunnel shotcrete spraying, and the mAP for spraying area detection was found to be 91.4%. INDEX TERMS 3D point cloud, deep learning, object detection, tunnel shotcrete.
In an eccentric rotating system driven by two hydraulic motors without synchronous gears, vibration coupling may help render motion stable. In order to investigate how vibration coupling influences the motion, the coupling characteristics of the vibration system were studied regarding the differences between two motors such as leakage network, coulomb damping network, and pressure loss network, and the sensitivity of the influence factors was also studied. The influence of tiny differences between the two motors, tiny differences in the motion pair structure, in the oil temperature and in the resistance coefficient on the coupling motion were discovered, and the criterion for synchronous motion were obtained consequently. The results show that the influence of the resistance coefficient difference on system motion stability is the greatest, accounting for 46.7%, and the influence of the difference in motion pair structure (e.g. motor piston clearance) is the second, accounting for 32.8%. For motors with displacement 80 ml/r, the condition of self-synchronization is that the difference in piston clearance between the two motors is equal to or smaller than 6 μm. Experiments have proved the correctness of the theory and showed that the synchronization can be achieved by leakage compensation, damping compensation, and back-pressure compensation of the external system by means of control when the motors rotate slowly enough for system response. The study shows that the coupling synchronous model can reduce the force of the gear for the eccentricity rotary system with synchronous gear, and that the synchronous stability can be improved for the eccentricity rotary system without synchronous gear.
In view of the abnormal phenomena in the movement of the 4-stage hydraulic cylinder, this paper establishes the basic motion model of the multi-stage hydraulic cylinder by melting point nodal cavity method, and analyses the variation law of its external load. On this basis, the erection process of the multi-stage hydraulic cylinder is simulated and analyzed by AMESim, and it is found that the sudden change of pressure at the change of the stage will cause the vibration of the multi-stage. Found that the abnormal vibration of the third piston occurs during the retraction process of the hydraulic cylinder, which is caused by the insufficient guide distance of the 3 stage piston of the multi-stage hydraulic cylinder. The sealing conditions of the piston and the guide sleeve are improved by increasing the guide length of the piston appropriately, and the correctness of the improved scheme is verified by the way of simulation, that is, it can effectively suppress the vibration of the third piston. Vibration occurs during retraction. Some improvement suggestions are provided for vibration reduction of multi-stage hydraulic cylinder.
Referring to the structure and parameters of the actual multi-way valve, the CAD software SOLIDWORKS was used to establish the three-dimensional geometric model of the internal flow passage of the hydraulic multi-way valve, and the model was calculated and analyzed by CFD software Star CCM+. By studying the flow field distribution in the valve chamber, the pressure distribution at each monitoring point in the chamber and the change of the overall flow rate were obtained, and the steady-state hydrodynamic force of the valve core was calculated. The effects of flow rate and the opening of the valve core on the pressure distribution and steady-state hydrodynamic force in the valve chamber were analyzed under various working conditions. The results show that the steady-state hydraulic force on the valve core increases with the increase of flow rate and decreases with the increase of valve opening. The pressure loss at the inlet and outlet of the slide valve is mainly caused by the throttling characteristics of the oil at the throttle port. The smaller the opening, the greater the inlet pressure and the greater the pressure at all points in the valve chamber.
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