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Aiming at problems of poor information perception ability and low decision level in coal mine safety production, a coal mine information comprehensive perception and intelligent decision system was proposed, which was composed of capsule network layer, data transmission layer and cloud service layer. The capsule network layer is composed of personnel position and behavior perception capsule, equipment status perception capsule and environment perception capsule to realize comprehensive perception of 'person, machine and ring' in coal mine. The data transmission layer adopts method of combining wireless sensor network and wired network to realize reliable data transmission in underground coal mine. The cloud service layer provides guarantee for efficient and reliable decision for coal mine production through intelligent decision mechanism based on random forest. The experimental results verify effectiveness of the system.

Aiming at the problem of speed fluctuation caused by the hard dot arrangement of the automobile double cross shaft universal joint steering system,the layout of hard spot how to ensure universal constant velocity transmission is studied,and taking the double cross shaft universal joint transmission structural optimization of a car as example,by using ADAMS / view software,the parametric dynamics model of double cross shaft universal joint transmission mechanism is built.Taking the variable in structure as design variable,taking the interaxial angle between intermediate shaft and the input shaft,the output shaft is not less than 155° as constraint condition,taking the angular difference of interaxial angle between intermediate shaft and the driving,driven shaft as the optimization target,and setting the steering intermediate shaft phase angle,the best hard spot layout program of double cross shaft universal joint steering system is acquired,and the steering transmission without fluctuation.

A lot of mechanical parts are subject to failure due to the deterioration. Usually the preventive maintenance is taken to ensure the safety and reliability. Therefore, it is very important to study the gradual reliability design of the mechanical part for improving the gradual reliability of the mechanical system under the condition of considering the preventive maintenance. Beta distribution is employed to describe the randomness of the mechanical part state after the preventive maintenance. The deterioration process of the mechanical part is modeled using the nonstationary Gamma process. The gradual reliability model before the first preventive maintenance is proposed according to the gradual failure principle and using the initial state distribution and the properties of Gamma process. Then, the gradual reliability model between any two times of preventive maintenance is also derived. Subsequently, the sensitivity equations of the proposed gradual reliability model to each parameter are given. The application process and practicality of the proposed approach are described by a numerical example. This work solved the problem where the maintenance has not been well considered in the reliability design of the mechanical part and contributed to the theory and method of improving the safety and reliability operation of the mechanical system.

Material extrusion (ME), one of the most rapidly developing additive manufacturing techniques, has been widely used in the field of aerospace, medical, industrial design, and so on. Since the working environment is increasingly complex, it is urgent to study the ME products' dynamic performances to determine their reliability. In this article, a finite element theoretical model of ME thin plate was established with the porosity defect taken into account. A modal test system was set up and the multiple-input single-output method was used to obtain the measured data. The scanning electron microscopy (SEM) analysis on the samples confirmed that the dynamic characteristic was improved as the extrusion temperature increased. In addition, the sensitivity analysis was carried out on the model to predict how the samples' elastic modulus, Poisson's ratio, and density affect their dynamic characteristics. The results show that the proposed model is reliable to give accurate predictions on the dynamic characteristics of ME thin plates. With the increase of extrusion temperature, the samples' natural frequency will increase, and the vibration response will decrease. The sensitivity analysis indicates that increasing elastic modulus or Poisson's ratio can increase the natural frequency of ME thin plate but decrease the vibration response. While increasing the density will decrease both the natural frequency and vibration response. KEYWORDS extrusion temperature, dynamic characteristic, finite element theoretical model, material extrusion, sensitivity analysis, 1 | INTRODUCTION Additive manufacturing is an advance manufacturing technology that accumulates materials (such as filaments, liquids, etc.) to produce parts layer by layer according to a predetermined path. [1,2] [...]