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Realization of face feature point recognition based on cascaded convolutional neural network ZHANG Yun, LI Lan Journal of Lanzhou University of Technology    2020, 46 (3): 105-109.   Abstract （531）      PDF（pc） （862KB）（1791）       Knowledge map    Save If a face image is interfered by redundant information, the accuracy of the extracted effective feature points from the image is not high enough. To solve this problem, a face feature point detection algorithm based on a cascade convolutional neural network is proposed in this paper. The algorithm reads in information of an original image via the input-function first, then extracts local features of the image through neurons in a receptive domain, and inputs all local features into a pooling domain. After doing that, the algorithm is able to average all captured local features stored in the pooling domain, and further do down-sampling to the pooling domain, and reduce the dimension of the convolution results, and finally output detection results of those feature points by virtual of iterative training. In this study, Python language is used to program the algorithm, and simulation experiments are carried out with the help of face data set. Simulation results show that the algorithm has a high recognition rate for face feature points. Reference | Related Articles | Metrics

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Analysis of thrust and velocity variation of permanent magnet synchronous linear motor under variable load SHEN Hao, ZHANG Wang, TAN Wei-rong, DANG Sheng-hui Journal of Lanzhou University of Technology    2021, 47 (2): 54-59.   Abstract （721）      PDF（pc） （1152KB）（1286）       Knowledge map    Save Taking the permanent magnetic synchronous linear motor as the research object, its force was analyzed; mathematical model was established, and the simulation model of the linear motor by using Matlab/Simulink in order to study the thrust and speed change of the linear motor when different loads are applied. The results show that with the increase of the workpiece’s mass, the state response time and maximum deviation of the linear motor increased; the response time curve of the speed is flat; the response time curve of thrust changed obviously; the overshoot curve of thrust increase flatly; the overshoot curve of velocity increased stably, the overshoot curve of speed is obvious.When the quality of the workpiece is 240 kg, the over-adjusting amount of motor speed exceeds 30%, which seriously affects the operation of the motor. In order to reduce the effect of load change on linear motor stability, the maximum load quality and maximum motor thrust are calculated. Reference | Related Articles | Metrics

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Effect of impeller exit width on performance and pressure fluctuation of centrifugal pump ZHAO Wei-guo, ZHAI Li-jing, XIAN Li-xia, MA Liang-liang Journal of Lanzhou University of Technology    2020, 46 (2): 62-68.   Abstract （843）      PDF（pc） （6499KB）（949）       Knowledge map    Save Taking a single-stage end-suction centrifugal pump as study object and assuring the inlet and outlet setting angle and diameter and as well as other parameters unchanged, five sets of pump models with different outlet width of impeller were designed respectively, their numerical simulation was carried out one after another and the influence of impeller outlet width on the performance and pressure fluctuation was analyzed. It was shown by the study result that with the increase of impeller outlet width, the lift and shaft power would increase to different extent, the efficiency curve would be hump shaped, indicating that there would be an optimum impeller outlet width to make the flow loss minimum; increasing the width of the impeller outlet, flow separation phenomenon in flow channel would be enhanced, blocking phenomenon there would decrease hydraulic loss would decrease thereby, indicating that an appropriate width of impeller outlet would be effective for reducing the energy loss of centrifugal pump. With progressive decrease of impeller outlet width, the shaft frequency peak would change obviously, assuming progressive increase trend, indicating that an excessive narrow impeller outlet width would easily lead to flow blocking in flow passage and hinder the development of the flow mode, At the same time, the impeller outlet width would also have a greater effect on pressure pulsation in centrifugal pump. Reference | Related Articles | Metrics

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Discussion on calculation method of active earth pressure for limited soils ZHU Yan-peng, WEI Peng-yun, MA Xiao-rui, LI Geng, LIU Xin Journal of Lanzhou University of Technology    2020, 46 (2): 133-137.   Abstract （455）      PDF（pc） （2711KB）（927）       Knowledge map    Save Based on the sliding plane hypothesis of Coulomb’s earth pressure theory and the limit equilibrium theory, a modified formulation for active earth pressure is derived according to the relationship between limited soils’ width b 0 (a distance between a supporting structure and an existing building) and triangular sliding wedge’s width b. Assumptions of formulation are that the limited soil is in horizontal and the support structure is in vertical. In addition, the formulation takes into account not only the adhesion between the supporting structure and soils but also the cohesion between the static soils and sliding soils. It is then analyzed that the impact of the external friction angle as well as the adhesion between the supporting structure and soils on the sliding soil mass’ cracking angle (failure angle of sliding soils) and active earth pressure. A viewpointabout generalized active earth pressure coefficient is also put forward in this paper. All results gaining from our calculated examples show that the formulation becomes more effective in practices. Evidently, taking the impact of the external friction angle into account in the formulation will reduce cost indeed. Reference | Related Articles | Metrics

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Design and implementation of transmitting and receiving circuits in wireless laser data communication system WANG Hui-qin, MA Yu-kun, CAI Hong-liang, ZHANG Yue, CAO Ming-hua Journal of Lanzhou University of Technology    2021, 47 (3): 91-96.   Abstract （374）      PDF（pc） （4255KB）（904）       Knowledge map    Save Wireless laser communication has numerous advantages that include high transmission rate, strong anti-jamming ability, low power consumption, etc. In this paper, the red light with the wavelength of 650 nm is used as the signal carrier to design a transceiver circuit for wireless laser communication. And we elaborate the designed principles and methods of laser transmitting circuit and photoelectric receiving circuit. In proposed system, the transmitting circuit has the functions of automatic power control, fault indication and current monitoring, while the receiving circuit has the functions of signal amplification, photocurrent monitoring and automatic noise. Furthermore, the performance of proposed circuit is tested by using the experimental platform, and the correctness and rationality of designed circuit are verified. The exprimental results showed that the designed circuit can achieve reliable transmission when the transmission rate is 16 Mbit/s. Reference | Related Articles | Metrics

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Structural design and modeling simulation of standing-to-lying changing angle swing head of five-faced body machining center YAN Chang-feng, LI Hui-long, LI Qiang, GAO Gang-gang, GOU Wei-dong Journal of Lanzhou University of Technology    2020, 46 (2): 35-40.   Abstract （429）      PDF（pc） （4323KB）（901）       Knowledge map    Save Aimed at the problem of five-face body machining center that the transmission chain was excessive long and unfavorable for improving the machining accuracy in the case of standing-to-lying change, a novel project of angle swing head for standing-to-lying change was proposed. In this project, the measure of transmission was dropped, where the angle swing head employed individual set of power supply for cutting power transmission and also for standing-to-lying change, and a simple set of power supply was used either for cutting power transmission or for standing-to-lying change, so that the transmission chain was contracted extremely. A three-dimensional mechanical structure model of the assembly of angle swing head, spindle and its key components was established with software SolidWorks. The software Romax was used to conduct the modelling of the driven system of the angle swing head, and the reliability of the driven system was analyzed under different working conditions. The result showed that under given operation conditions the design of the drive system would be reasonable and the operational reliability would meet the design requirements. To ensure rigidity and stability of the standing-to-lying change spindle of angle swing head, the modality analysis was carried out by using the ABAQUS. The result showed that the spindle would not resonate within the range of rated operating speed. Reference | Related Articles | Metrics

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Cleaning and modeling of abnormal data of wind farm power curve CAO Li-xin, LIU Wei-min, GUO Hu-quan Journal of Lanzhou University of Technology    2022, 48 (4): 64-70.   Abstract （510）      PDF（pc） （3178KB）（880）       Knowledge map    Save The wind speed and power data of wind farms usually contain a large number of abnormal data, which is difficult to reflect the real working conditions of wind turbines, affect the accuracy of wind power prediction, and then cause certain economic losses. To solve this problem, the characteristics of abnormal data are analyzed, a slip-quartile abnormal data elimination method is proposed, and the wind speed power curve of the eliminated data is modeled by using high-order polynomial and Logistic function. Finally, the applicability and effectiveness of this method are verified by variance, root means square error and determination coefficient. The analysis in the example shows that the method is simple, efficient and versatile, and can significantly improve the accuracy of wind turbine power characteristic analysis. Reference | Related Articles | Metrics

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General model for kinematic analysis of swash plate axial piston pump WANG Jian-sen, CAO Wei-dong, HE Xin-long, WANG Zheng-rong, ZHANG Zhi-wei Journal of Lanzhou University of Technology    2021, 47 (5): 59-64.   Abstract （608）      PDF（pc） （3701KB）（822）       Knowledge map    Save Based on the comprehensive consideration of swash plate angle, cross angle and piston inclination angle of the swash plate axial piston pump, the general piston kinematics model is established by coordinate transformation method. The analysis results show that the cross angle of swash plate and the inclination angle of piston will increase the maximum amplitudes of displacement, velocity and acceleration of piston, and then increase the displacement of pump, the maximum transient flow velocity in the piston chamber and the inertia force of piston; the cross angle of swash plate will change the phase of piston movement and make the internal and external dead points deflect, which will change the pre-compression and pre-expansion angle of valve plate; the inclination angle of piston will affect the movement of the piston, the smaller the inclination angle of the plunger, the closer the movement of the plunger is to the simple harmonic motion, on the contrary, the larger the deviation is, the maximum deflection angle of internal and external dead center is 90°, the smaller the absolute value of the cross angle is, the smaller the deflection angle of internal and external dead center changes in the range of big swash plate angle, and the greater the gradient of change when swash plate angle is close to zero displacement. Reference | Related Articles | Metrics

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Influence of high rate charge and discharge cycle on the electronic performance and thermal safety of lithium ion battery LI Dong-qi, ZHANG Qing-song, ZHENG Shao-shuai Journal of Lanzhou University of Technology    2023, 49 (3): 30-35.   Abstract （549）      PDF（pc） （2624KB）（780）       Knowledge map    Save Lithium-ion batteries are widely used in electric vehicles and various energy storage devices. In this paper, cyclic aging and thermal runaway experiments under different charge-discharge rates were carried out, and the effects of large-rate charging and discharging on the performance and thermal safety of single lithium-ion batteries were studied. The results showed that the actual capacity of single lithium-ion battery is attenuated under the large-rate charge-discharge cycle, and the degree of attenuation is positively relevant to the charge-discharge rate. With the charge-discharge rate increasing, the constant current ratio is stepwise attenuation, but the coulombic efficiency still maintains in the range of 99%-100%, indicating that the reversible performance of lithium-ion batteries is normal. With the increase of the magnification, the thermal runaway trigger time, explosion pressure and jet flame temperature first increase and then decrease. The average surface temperature of the battery during explosion is 655.8 ℃, which is close to the melting point of aluminum. The explosion injection powder products are mainly metal aluminum, graphite and lithium cobalt oxide. Reference | Related Articles | Metrics

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Anti-sway design of overhead crane based on model predictive control TANG Wei-qiang, HUANG Xiao-li, LONG Wen-kun, SUN Li-juan Journal of Lanzhou University of Technology    2020, 46 (2): 92-96.   Abstract （632）      PDF（pc） （1787KB）（774）       Knowledge map    Save Aimed at the sway problem of lifted weight in the working process of overhead crane, an electronic anti-swing design method is proposed based on predictive control strategy. Firstly, dynamic analysis is carried out for the overhead crane, and a control-oriented mathematical model is established by using Lagrange equation, Secondly, according to the historical information of the object and the future input, the future output is predicted and a control rule is obtained by optimizing the performance function combined with prediction error compensation. Finally, it is shown by simulation result that the designed anti-sway system can be used to realize rapid positioning of the trolley and effective restriction of the swing angle of lifted weight. Compared with an optimal anti-sway control, the system overshoot and swing angle amplitude will be greatly reduced, manifesting the superiority of this anti-sway method; When a parameter perturbation or measurement noise is added onto this system, the anti-sway system can still achieve the control purpose very well, showing that this anti-swing method has a better robustness. Reference | Related Articles | Metrics

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A machine learning methods for identifying the properties of Chinese medicinal materials from infrared spectrum data TIAN Chun-ting, ZHAO Ning, QIN Jian-wei, MENG Xiao-feng Journal of Lanzhou University of Technology    2023, 49 (3): 55-59.   Abstract （325）      PDF（pc） （2953KB）（771）       Knowledge map    Save There are great differences in the characteristics of near-infrared and mid-infrared spectra of different kinds of traditional Chinese medicine. Due to the different chemical components such as inorganic elements and organic substances, even if the origin of the same traditional Chinese medicine is different, the labeling effect under near-infrared and mid-infrared spectral irradiation will have different spectral characteristics which can be used to classify Chinese herbal medicine and identify the origin of Chinese herbal medicine. With the help of MATLAB software tool and K-means clustering algorithm in SPSS classification tool, unsupervised machine learning is carried out on traditional Chinese medicine to classify traditional Chinese medicine; Using SPSS neural network multilayer perceptron and the random forest algorithm provided by Python language, 70% of the data set is used as the training set and 30% as the verification set to train the supervised machine learning model which is finally used to identify and predict the origin of traditional Chinese medicine. Reference | Related Articles | Metrics

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Effect of sample area on load characteristics of AZ31B magnesium alloy treated by micro-arc oxidation WANG Sheng, HAUANG Zhi-jie, LAN Ye-feng, LIU Kang-kang WANG Xiao-long, MA Ying Journal of Lanzhou University of Technology    2020, 46 (5): 7-12.   Abstract （204）      PDF（pc） （2599KB）（761）       Knowledge map    Save In order to clarify the effect of sample area on the load characteristics and film properties of micro-arc oxidation, four AZ31B magnesium alloy samples with different areas were treated by micro-arc oxidation in unipolar pulse power supply mode. In the treatment, the equivalent resistance and equivalent capacitance of the load are collected by a LCR tester, the voltage and current waveforms of the load are recorded by oscilloscope, and the load voltage waveform is fitted by using software MATLAB, so as to investigate the effect of sample area on the load characteristics in the process of micro-arc oxidation. Our results indicate that with the increase of treatment voltage, the equivalent capacitance of all loads decreases continuously, the equivalent resistance increases continuously, and the discharge time constant of the loads increases continuously as well. The increase of the equivalent resistance indicates that the thickness of the film increases with increase of the treatment voltage. In addition, with the increase of the treated area, the equivalent resistance of the loads decreases, the load capacitance increases, and the discharge time constant of the loads decreases either. This indicates that the growth of the film becomes slower with increase of the treated area, and the larger the treated area is, the closer the load waveform is to the square wave. Therefore, it is more practical for the unipolar pulses. The equivalent resistance of the loads can reflect the thickness of the film. Reference | Related Articles | Metrics

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Nitrogen doping of tubular hard carbon as conjugate microporous polymer and its lithium storage performance ZHANG Qing-tang, BAI Yong-bao, LI Meng Journal of Lanzhou University of Technology    2020, 46 (1): 71-76.   Abstract （997）      PDF（pc） （4508KB）（753）       Knowledge map    Save Conjugate microporous polymer (CMP) and nitrogen-contained conjugate microporous polymer (NCMP) were synthesized with chosen different monomers and the tubular hard carbon(THC) and N-doped tubular hard carbon(NTHC) were prepared by means of pyrolysis of those two kinds of CMP. The morphology and structure of the two tubular hard carbons were characterized with SEM, TEM and BET and it is shown that the materials of THC and NTHC have similar morphology and specific surface area. Further, The electrochemical property of THC and NTHC then compared with that of common carbon nanotube(CNT) was analyzed by constant current charge and discharge method and the result showed that the lithium storage performance of NTHC would be the best and it would have a high reversible lithium storage capacity of 541.2 mAh/g at 0.1 A/g and its specific capacity would retain around 458 mAh/g at 0.6 A/g after 500 cycles. Reference | Related Articles | Metrics

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Experimental study of heat loss of heat storage tank in solar heating system of northwest region LI Jin-ping, LIU Run, CUI Wei-dong, HUANG Juan-juan, WANG Chuan-long Journal of Lanzhou University of Technology    2020, 46 (4): 67-72.   Abstract （324）      PDF（pc） （877KB）（735）       Knowledge map    Save Taking the solar heating system in an 117.07 m 2 northwest China as investigation object and the day of December 15 th as an example, it is concluded that the heat loss of heat storage tank occurs mainly during the natural cooling period, the total heat loss of the heat storage tank is 9.49 MJ when its daily total heat loss coefficient is 5.68 W/℃. Then the test data of other 11 typical days is chosen to carry out the fitting of several factors of influence on total heatloss coefficient and total heat loss of the heat storage tank. It is shown that the total heat loss of the heat storage tank will be influenced by the ambient temperature and outdoor wind speed, leading to the change of the temperature of the heat storage tank. Decrease of every 1 ℃ of average ambient temperature will increase the total heat loss of heat storage tank by 0.067 MJ and the increase of every 1 m/s of outdoor wind speed will increase the total heat loss of the heat storage tank by 0.042 MJ, The increase of temperature of 1 ℃ of heat storage tank will increase the total heat loss of heat storage tank by 0.068 MJ. The increase of the temperature of 1 ℃ of heat storage tank will increas the total heat loss of the heat storage tank by 1.641 MJ. Aimed at the analysis of heat loss of heat storage tank and the present situation of indoor thermal environment, it is presented that a suggestion on indoor location of heat storage tank can be taken into consideration to enhance the heat storage capacity of heat storage tank and improve the indoor comfortableness of the building. Reference | Related Articles | Metrics

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Preparation and adsorption properties of corncob based biochar WEI Hui-ge, LI Dai-yuan, MA Jun-hui, ZHOU Deng-feng, CUI Da-peng Journal of Lanzhou University of Technology    2020, 46 (6): 77-84.   Abstract （822）      PDF（pc） （2593KB）（732）       Knowledge map    Save Using agricultural waste corncob as raw material, biochar with low cost and high performance was prepared by hydrothermal carbonization (HTC) at different temperatures. The biochar has mesoporous structure and abundant oxygen-containing functional groups on its surface, such as —OH, C ==O, C—O and so on. Methylene blue (MB) was used as model adsorbent to further study the adsorption properties of the biochar. Results from the study of adsorption kinetics show that the adsorption behavior is in accordance with the pseudo second-order kinetics model, and the biochar obtained under the hydrothermal condition of 225 ℃ has the maximum adsorption capacity (41.37 mg/g) and the maximum adsorption rate. The adsorption equilibrium data agree well with the Langmuir isotherm model, indicating that the adsorption of MB on biochar belongs to monolayer adsorption, and the interaction between oxygen-containing functional groups on the surface of the biochar and the MB molecule is helpful to the adsorption process. Reference | Related Articles | Metrics

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Energy performance prediction of single-stage single-suction centrifugal pump under multiple operating conditions YANG Jun-hu, JI Ya-ya, LIN Bin, MA Qi-hang, LUO Yu-tong, LI Zhi-fan Journal of Lanzhou University of Technology    2020, 46 (2): 48-54.   Abstract （323）      PDF（pc） （2022KB）（730）       Knowledge map    Save In order to predict accurately the energy performance of centrifugal pumps under different working conditions, their hydraulic loss models are established based on the existing theoretical and empirical formulas at home and abroad. The linear regression method is used to find out the functional relationship between the impeller inlet angle of attack and the impact loss, so that the impact loss formula is revised. Thereby, to verify the accuracy of this model in predicting the energy performance of centrifugal pumps under different working conditions, a centrifugal pump with a specific speed of 92.8 is selected to calculate the head, efficiency and shaft power at nine operating points, and the result is compared with that of experiment and analyzed. The results show that the prediction results of the head will be basically consistent with the test results. The error between the predicted head and the test head at nine operating points will be less than 5%. This shows that the hydraulic loss equation can be used to predict the energy performance of centrifugal pumps well under different working conditions. Reference | Related Articles | Metrics

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Fatigue strength analysis of high-strength bolts for tower flange of wind turbine LIANG Yuan, WANG You-liang, WEI Tai, LIU Jian-hui Journal of Lanzhou University of Technology    2023, 49 (2): 65-69.   Abstract （267）      PDF（pc） （1391KB）（729）       Knowledge map    Save An analysis method for high-strength bolts of wind turbine tower flange was established by considering the influence of external load on fatigue damage. Firstly, the maximum load section was determined with the aid of the tower equivalent model according to the damage parameters of the stress state on the connection section. Secondly, the external load on any sector of the tower was obtained by Schmidt-Neuper algorithm. Afterwards, the fatigue damage distribution model of high-strength bolts was established and the relationship between the external load and the internal stress of high-strength bolts was explored based on the finite element model. Finally, the optimal bolt pretightening force was determined with comparing the fatigue cumulative damage values with different bolt pretightening forces by considering the influence of pretightening forces. The results show that the positions of the maximum fatigue cumulative damage of flange bolts were －4.17° and 175.87°, and the bolt pretightening force was the most suitable value when the bolt pretightening force ratio was 70%. Reference | Related Articles | Metrics

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Importance identification method of complex network nodes based on betweenness and degree entropy LU Peng-li, GUO Xu-dong, DONG Men, CAO Le Journal of Lanzhou University of Technology    2020, 46 (2): 111-115.   Abstract （437）      PDF（pc） （3156KB）（719）       Knowledge map    Save Existent complex networks will usually be subject to random attacks and deliberate attacks, resulting in reduced reliability of complex network topologies. In order to solve the above-mentione problems, a new attack strategy is proposed based on graph entropy and incorporated with the betweenness centrality of nodes and the degree centrality of all their neighbor nodes, namely the betweenness and degree entropy (BE), which is used to identify important nodes in the network and protect them. Experimentally, the efficiency of attack strategies of three standard network models and three real networks is evaluated under condition of static attacks and dynamic attacks. By means of comparison, it is found that the betweenness and degree entropy will have higher attack efficiency than the traditional attack strategy. Reference | Related Articles | Metrics

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Numerical simulation of stress and deformation for Al/steel sheet welding by trailing cooling of argon gas FAN Ding, HAN Miao-miao, ZHAO Jin-long, YU Xiao-quan, GAO Ming-jiang Journal of Lanzhou University of Technology    2020, 46 (4): 22-26.   Abstract （288）      PDF（pc） （3548KB）（715）       Knowledge map    Save The numerical simulation of butt brazing process of Al/steel dissimilar metal sheet under different welding conditions was carried out by using finite element analysis software ANSYS. Two models are established for TIG arc heat source and cold source respectively. Comparative analyses of residual stress and deformation reveal that the argon quenching at low temperature in the process of welding can effectively reduce longitudinal residual stress and deformation in the weld, resulting in apparent reduction by 32.8% and 48.1%, respectively. In order to verify the validity and prove the accuracy of our finite element simulation results, a welding test of Al/steel dissimilar metal sheet was carried out. Through analytical comparisons of the predicted results of temperature field and stress field and with tested ones, it is verified the effectiveness of the numerical model. It has been shown that the residual stress and deformation in Al/steel sheet welds can be effectively controlled by argon quenching technology. Reference | Related Articles | Metrics

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Dynamic output feedback control of networked system with communication constraints ZHU Chao-qun, LI Liu-yang, JIN Hui Journal of Lanzhou University of Technology    2021, 47 (1): 83-90.   Abstract （242）      PDF（pc） （1124KB）（713）       Knowledge map    Save In this paper, the design of dynamic output feedback controller in networked control systems is studied for a class of networked control systems with access constraints and time-varying delays. Considering that the media access constraint obeys Markov distribution and the upper bound of time-varying delay is less than one sampling period, the networked control system should be built into a kind of uncertain time-discrete Markov jump system in modeling of the system. According to the Lyapunov stability theory and the state augmentation method, the sufficient conditions for the asymptotic stability of the closed-loop networked control system are therefore given, and a dynamic output feedback controller may be designed to make the closed-loop system asymptotically stable. Finally, a numerical example is provided to demonstrate the correctness and effectiveness of the proposed modeling method. Reference | Related Articles | Metrics