2015 Vol. 41, No. 8

  Previous Issue | Next Issue 
Display Method:
Cover Catalogue
Novel cable measurement while drilling device used for directional drilling in coal mine
FANG Jun, SHI Zhijun, LI Quanxin, GAO Jun
2015, 41(8): 1-5. doi: 10.13272/j.issn.1671-251x.2015.08.001
<Abstract>(84) <PDF>(6)
Abstract:
In order to solve problems of short usage time, poor signal stability, high fault ratio and high maintenance cost of existing cable measurement while drilling device for coal mine drilling which was powered by battery in hole, a technology scheme was proposed which used explosion-proof computer to power supply measuring tube in hole. By researching design of constant voltage source and signal demodulation of explosion-proof computer, design of parameter measurement, secondary power supply and signal carrier transmission work of measuring tube and development of measurement software, a cable measurement while drilling device was developed which was powered by explosion-proof computer. Measurement accuracy test of the device is taken in a professional organizations as well as work stability test in Shizuishan No.2 Coal Mine and depth test in Sihe Coal Mine. The tests results show that the device is feasible with higher measuring accuracy than the design value, and has strong working stability with drilling transmission distance of 1 881 m. The device can meet need of directional drilling with different types in coal mine.
Online monitoring and pre-alarming system for surrounding rock pressure of coal mine tunneling roadway
MENG Qingyong
2015, 41(8): 6-9. doi: 10.13272/j.issn.1671-251x.2015.08.002
<Abstract>(58) <PDF>(7)
Abstract:
For problems of difficult realization of effective monitoring and poor pre-alarming ability of existing surrounding rock pressure monitoring technologies for coal mine tunneling roadway, a kind of online monitoring and pre-alarming system for surrounding rock pressure of coal mine tunneling roadway was designed by use of wireless sensor technology, and structure, principle, data transmission mode, functional module and pre-alarming flow of the system were introduced in details. The application shows that the system achieves real-time monitoring of roof separation, stress and acoustic emission of tunneling roadway, and the comprehensive pre-alarming flow with multi-parameter improves pre-alarming.
Supervision method of software effectiveness of in-use coal mine safety monitoring and control system
ZHAO Liang
2015, 41(8): 10-12. doi: 10.13272/j.issn.1671-251x.2015.08.003
<Abstract>(50) <PDF>(6)
Abstract:
Key points and methods of basic function supervision of software of in-use coal mine safety monitoring and control system were summrized. A supervision method of software effectiveness of in-use coal mine safety monitoring and control system was proposed by data consistent check, including software real-time performance consistent check, software history data consistent check, software dual computer data consistent check, software and networking system consistent check and mine duty record and monitoring main computer duty record.
Monitoring system of suspension type single hydraulic prop for underground forepoling
CHEN Xin, HAN Zhengtong, HAO Jingbin, LI Baoli
2015, 41(8): 13-16. doi: 10.13272/j.issn.1671-251x.2015.08.004
<Abstract>(41) <PDF>(5)
Abstract:
A monitoring system of suspension type single hydraulic prop for underground forepoling was introduced, and working principle and design scheme of the system were focused on. The system can realize pressure and bending deformation detection of hydraulic prop, LED warning and wireless data transmission. The experimental result based on a type of hydraulic prop shows that the error between measurement value of the system and the theoretical one is small, which verifies that the system can actually reflect bending deformation degree of suspension type single hydraulic prop when the hydraulic prop suffers different stress from roof and provide accurate data for safety warning of forepoling.
Design and implementation of communication module of remote control system of electrical traction shearer
ZHANG Xuhui, XIA Hongbo, WU Haiyan, ZHAO Youjun, LOU Lingli
2015, 41(8): 17-21. doi: 10.13272/j.issn.1671-251x.2015.08.005
<Abstract>(83) <PDF>(6)
Abstract:
The paper designed a communication module between controller of electrical traction shearer based on DSP and peripheral equipment through analyzing problems existing in communication among shearer core controller and touch screen, frequency converter and remote control computer, and introduced hardware and software design of the communication module in detail. The test results show that the module has stable communication and good real-time performance, and solves the disunity problems of communication interface and communication protocols of controller and peripheral equipment of electrical traction shearer based on DSP.
Application of SOI pressure sensor to working resistance monitoring of hydraulic support
FU Dongbo
2015, 41(8): 21-24. doi: 10.13272/j.issn.1671-251x.2015.08.006
<Abstract>(68) <PDF>(5)
Abstract:
In order to improve reliability of monitoring of hydraulic support working resistance, a new silicon SOI pressure sensor was developed. The sensor fuses strain meter with double-deck resistance grid and stainless steel elastomer, the control circuit uses sampling mode with constant value and time to ensure effectiveness and coherence of the data. The field application results show that the new silicon SOI pressure sensor can get accurate monitoring data and can be used to analysis of mine roof supports crushing accident.
Design of signal acquisition system of mine-used electronic belt scale
FAN Lijun, TIAN Bailin
2015, 41(8): 25-28. doi: 10.13272/j.issn.1671-251x.2015.08.007
<Abstract>(70) <PDF>(4)
Abstract:
In view of problems that weighting signal and speed signal of mine-used electronic belt scale has slower speed of signal acquisition and data processing and lower accuracy of data sampling, a design scheme of signal acquisition system of mine-used electronic belt scale based on FPGA was proposed. The system is built with FPGA as control core. In the system, the weighing signal is processed by A/D conversion and digital filtering and the pulse signal of speed is collected and processed. The processed data is transferred to electronic belt scale through RS485 bus. The testing result shows that the system has high speed of signal acquisition and data processing, high precision and strong anti-jamming capability.
Study on mine emergency command communication mode based on emergency rescue model
ZHENG Wanbo
2015, 41(8): 29-34. doi: 10.13272/j.issn.1671-251x.2015.08.008
<Abstract>(88) <PDF>(7)
Abstract:
In view of problems of non-unified communication mode, being difficult to connect with emergency command communication technology platform and poor adaptability of disaster environment existed in mine emergency command communication system in China, current mine emergency command communications systems were analyzed based on technology framework of dotted and planar emergency rescue models, so as to get 6 kinds of mine emergency command communication mode, which can provide effective technical basis for rescue team to select rescue communication equipment.
Study on vibration intensity distribution of boom-type hard rock roadheader
HU Yulong, YANG Yang, WU Miao
2015, 41(8): 35-37. doi: 10.13272/j.issn.1671-251x.2015.08.009
<Abstract>(42) <PDF>(5)
Abstract:
In order to get vibration intensity distribution of boom-type hard rock roadheader working underground, mine-used potable vibration recorder and vibration acceleration sensor were applied to collect vibration signal of the boom-type hard rock roadheader under coal mine actual working conditions. Characteristic parameters of time domain index were counted based on the measured data, and vibration intensity distribution of the whole roadheader and the same part at different vibration directions were got, that is, vibration of cutting unit is the most intense, while vibration of main frame is minimal, and vibration intensity of each part at different vibration directions are less different which show that the roadheader runs stably.
Characteristic analysis of acoustic emission monitoring signal in coal seam hydraulic fracturing
LI Baolin, WANG Enyuan, LI Nan, GAO Qinqiong, ZHOU Ming
2015, 41(8): 38-42. doi: 10.13272/j.issn.1671-251x.2015.08.010
<Abstract>(47) <PDF>(3)
Abstract:
In order to promote application of acoustic emission monitoring technology in effect evaluation of coal seam hydraulic fracturing, coal seam hydraulic fracturing process was monitored by use of coal and rock dynamic disaster acoustoelectric monitor, and characteristics of acoustic emission signals collected in the process were analyzed through fourier transformation and wavelet packet analysis. The field test results show that main frequency of effective acoustic emission signals of coal seam hydraulic fracturing is in 470-1 700 Hz, which is lower than main frequency of underground noise interference signal. Energy distribution of the effective acoustic emission signals of coal seam hydraulic fracturing is concentrated in 0-5 000 Hz with proportion 86.5%-95.4%, and the energy distribution of effective signals is concentrated in low frequency band such as 312.5-625, 625-937.5, 937.5-1 250, 1 875-2 187.5 Hz.
Comparative analysis of application of mobile operating system in coal mine
ZHANG Bing
2015, 41(8): 42-45. doi: 10.13272/j.issn.1671-251x.2015.08.011
<Abstract>(45) <PDF>(5)
Abstract:
Current main mobile operating systems such as Android, iOS and Windows were compared and analyzed from aspects of technology level, application cost and security, combined with specific technology requirements of mobile device used for coal mine enterprise, a conclusion was got that Android is the most suitable for application in ground and underground of coal mine, Windows is second to Android, and iOS can only be applied in ground.
Water inrush prediction of coal floor based on adaptive robust evidence theory
CHEN Xiaolei, LI Fenglian, ZHANG Xueying, JIAO Jiangli, LI Yuanyua
2015, 41(8): 46-51. doi: 10.13272/j.issn.1671-251x.2015.08.012
<Abstract>(35) <PDF>(3)
Abstract:
For low prediction accuracy of D-S evidence theory used in water inrush prediction of coal floor because of poor robust and fusion effect under the condition of large conflict probability of evidence source, an adaptive robust evidence theory was proposed based on robust evidence theory. A water inrush prediction model of coal floor was established by combining the adaptive robust evidence theory and multiple neural networks. The model was experimentally researched by use of real hydrogeololgy data of a coal mine working face. The experimental result shows that the model has high prediction accuracy and good stability.
Prediction of uncertainties of gas emission quantity based on RVM
WANG Xiaolu, LI Guomin, TANG Shancheng, HUANG Jia
2015, 41(8): 51-55. doi: 10.13272/j.issn.1671-251x.2015.08.013
<Abstract>(31) <PDF>(2)
Abstract:
In order to evaluate uncertainties of prediction results of gas emission, an estimation approach based on relevant vector machine was proposed. The sparse relevant support vector and its corresponding hyper parameters were calculated on sample space of gas emission by sparse Bayesian learning model. The mean and variance of prediction results were worked out, so probability distribution and confidence interval of prediction results of gas emission quantity can also be obtained. The analysis results show that the mean prediction error of three group testing samples is 1.74%, and real gas emission quantities are all in confidence interval of 97%. The prediction result is consistent with actual situation, it shows that the proposed approach can be used to get probability distribution of prediction result of gas emission, and has high prediction accuracy and requires less support vectors.
Timing synchronization algorithm of OFDM symbols for mine through-the-earth communication system
LU Yuan, HAO Jianjun, DING Xiaoming
2015, 41(8): 56-59. doi: 10.13272/j.issn.1671-251x.2015.08.014
<Abstract>(31) <PDF>(4)
Abstract:
In view of problem that existing timing synchronization algorithm of OFDM symbols has training sequence with complex structure and low timing accuracy, a timing synchronization algorithm based on linear frequency modulation sequence was proposed. The algorithm uses linear frequency modulation sequence and its negative conjugate sequence to constitute frames structure of sequence, so as to achieve the OFDM symbols timing synchronization. Matlab simulation results show that the synchronization algorithm has training sequence with sharper correlation peak, and can determine starting position of OFDM symbols more accurately. Finally, DSP chip was used to design a simple OFDM baseband communications system, and correction of the proposed synchronization algorithm was verified by consistency of sending data and receiving data.
Design of cognitive algorithm for mine-used accurate positioning system
WU Wei, HUANG Qian, TANG Lijun
2015, 41(8): 60-64. doi: 10.13272/j.issn.1671-251x.2015.08.015
<Abstract>(38) <PDF>(2)
Abstract:
In view of problem of high power consumption and data generation rate of existing mine-used accurate positioning system, a cognitive algorithm for mine-used accurate positioning system was designed. The recognition algorithm reasonably reconfigures transmitter power of target node and location data sampling interval by sensing changes of moving speed and position of target node and using reconstruction method of decision-making, achieves optimization of system power and data generation rate. The simulation results show that the cognitive algorithm can effectively reduce power consumption and data generation rate of accurate positioning system without affecting track performance of positioning system to node trajectory.
Theoretical calculation of gas pipeline of beam tube monitoring system and its experimental verificatio
XING Zhen
2015, 41(8): 65-67. doi: 10.13272/j.issn.1671-251x.2015.08.016
<Abstract>(23) <PDF>(2)
Abstract:
For problems that the choice of pumping time and pump type of beam tube monitoring system with long gas pipeline lacks theoretical support and only depends on experience, so as to lead large error, flow conductance of beam tube and effective pumping speed and pumping time of beam tube vacuum system were calculated through discriminating gas flow state in gas pipeline. Three kinds of vacuum pump and gas pipeline with four length were selected for combination experiment to verify accuracy of theoretical calculation conclusion. Based on calculation and experiment results, suggestions for selecting gas pipeline and pump in beam tube monitoring system are put forward.
Experimental study on purification by pressure ventilation of coal mine refuge chamber
HE Tingmei
2015, 41(8): 68-71. doi: 10.13272/j.issn.1671-251x.2015.08.017
<Abstract>(37) <PDF>(2)
Abstract:
Relationship formula between average concentration of harmful gas and pressure ventilation supply volume in refuge chamber was given, CO2 concentration distribution in refuge chamber under conditions of different pressure ventilation supply volume and air outlet layout were analyzed through refuge experiment with 50 people. The experimental results show that when air supply volume per person is 84 L/min, CO2 volume fraction in refuge chamber could be controlled under 1%; CO2 concentration distribution is uneven when only one air outlet is set in refuge chamber, air outlets should be evenly arranged in both sides of long passage of refuge chamber, and CO2 concentration distribution is more even with more air outlets.
Effect of moisture content on resistivity of coal or rock
XU Zhaoyong, SONG Dazhao, WANG Enyuan, QIU Liming
2015, 41(8): 72-76. doi: 10.13272/j.issn.1671-251x.2015.08.018
<Abstract>(47) <PDF>(4)
Abstract:
By establishing real-time monitoring system of resistivity variation regularities of loaded coal, real-time resistivity variation law of natural raw coal samples and raw coal samples with different moisture content in uniaxial compressive failure process was tested and studied, and the effect of porosity of the process on the resistivity was analyzed. The testing results show that resistivity of natural raw coal samples increases dramatically when a large-scale destruction of rupture crack, although resistivity of raw coal samples with different moisture content also increases during burst damage, but compares to the natural raw coal samples is more gentle; porosity of raw coal samples with moisture content has a significant impact on resistivity change in damage process, resistivity and porosity change of raw coal samples with moisture content is negative linear correlation before severe damage.
Research of electrostatic field characteristics of liquid-solid two-phase flow inside slurry pipeline
WANG Pai, WANG Mei, MA Xianmi
2015, 41(8): 76-81. doi: 10.13272/j.issn.1671-251x.2015.08.019
<Abstract>(24) <PDF>(2)
Abstract:
This paper adopted finite element method to set up an electrostatic field model of liquid-solid two-phase flow inside slurry pipeline, and made qualitative research on soft field characteristics of liquid-solid two-phase flow by taking sensitivity as a medium. It analyzed impact on the soft field characteristics from flow rate, size of solid particles, deposit and concentration and got the following conclusion: the slower the ore pulp flows, the more uneven the sensitivity distributes; the larger the solid ore pulp particle is, the more uneven the sensitivity distributes; the thicker the deposit scales, the more uneven the sensitivity distributes. The greater the concentration of ore pulp changes, the greater the impact occurs on the sensitivity. The conclusion provides technical support for the visualization test on the liquid-solid two-phase flow inside slurry pipeline.
An image compression method for coal mine undergroud
YANG Lei, HUANG Yourui, TANG Chaoli, QU Liguo, CHEN Zhenping, HAN Tao
2015, 41(8): 82-84. doi: 10.13272/j.issn.1671-251x.2015.08.020
<Abstract>(58) <PDF>(2)
Abstract:
For difficult transmission and storage of a large of video monitoring image data of coal mine underground, an image compression method was proposed which was based on improved compressive sending algorithm. Firstly, collected images data are spared by Coiflet2 wavelet transform principle. Secondly, the spared data is measured by measurement matrix to get measurement data. Finally, the images are refactored by orthogonal matching tracking algorithm and inverse transformation. The experimental results show that the method can effectively compress image and reconstruct the image.
Analysis of transmission characteristics of magnetically-coupled resonant wireless power transmission system
ZHANG Guoyuan, WANG Xi, ZHAO Duan
2015, 41(8): 85-88. doi: 10.13272/j.issn.1671-251x.2015.08.021
<Abstract>(38) <PDF>(3)
Abstract:
A circuit model of magnetically-coupled resonant wireless power transmission system was established, and relationships between transmission power, transmission efficiency and input frequency, transmission distance and load were analyzed. The simulation and experimental results show that transmission power and transmission efficiency achieve the maximum when input frequency of the system is the same as resonant frequency of excitation coil loop without frequency offset; transmission power increases then decreases with increase of transmission distance, and there is the optimum transmission distance to get the maximum transmission power, while transmission efficiency increases with decrease of transmission distance; transmission power and transmission efficiency increases then decreases with increase of load, and there is the optimum matched load to get the maximum transmission power and transmission efficiency.
Modeling and transmission efficiency analysis of three coil system for wireless power transmissio
WU Rong, WANG Chao, ZHANG Shang, XU Lisha
2015, 41(8): 89-92. doi: 10.13272/j.issn.1671-251x.2015.08.022
<Abstract>(146) <PDF>(18)
Abstract:
Based on the theory of magnetic resonance coupling, a model of three coil system for wireless power transmission was established, and the transmission efficiency formula was derived by applying equivalent circuit theory and two port network theory. Cross coupling coefficient between transmitting and receiving coils was analyzed theoretically by using the formula. The theoretical analysis results show that the transmission efficiency of the system should decrease if cross coupling coefficient is large enough. The simulation results verify the correctness of the theoretical analysis.
Novel database keyt management method for coal mine safety monitoring and control system
DING Ruiqi, ZHANG Weiguo
2015, 41(8): 93-95. doi: 10.13272/j.issn.1671-251x.2015.08.023
<Abstract>(33) <PDF>(2)
Abstract:
Advantages and disadvantages of existing data keyt management methods were analyzed. A database keyt management method for coal mine safety monitoring and control system was proposed which was based on double dynamic password, and principle, realization and key technologies of the method were introduced. The method improves security and operability of database through identity authentication agent software and dynamic password generation algorithm. Key words:
Protection technology of coal mine power based on GOOSE network with information sharing
YAO Fuqiang, BAI Meng, ZOU Wenbing
2015, 41(8): 96-99. doi: 10.13272/j.issn.1671-251x.2015.08.024
<Abstract>(43) <PDF>(2)
Abstract:
For problems of override trip in short-circuit fault and fault line selection in single-phase earth fault of coal mine power system, a protection technology of coal mine power based on GOOSE network with information sharing was proposed. The technology realizes anti-override trip with blocking signal and line selection in single-phase earth protection with zero sequence full current vector information based on GOOSE network. On the basis of existing gigabit industrial Ethernet of coal mine and high-speed real-time communication mechanism of GOOSE, fault information can be shared between protection devices, which can realize anti-override trip effectively and improve accuracy of fault line selection in single-phase earth fault.
Design of on-line monitoring and early warning system of balancing tail rope of hoist based on machine visio
CHANG Hao
2015, 41(8): 100-104. doi: 10.13272/j.issn.1671-251x.2015.08.025
<Abstract>(43) <PDF>(4)
Abstract:
In view of problems of difficult detection and high risk in manual vision inspection of balancing tail rope failures of hoist, an on-line monitoring and early warning system of balancing tail rope of hoist based on machine vision was designed. The system uses CCD camera to real-timely collect on-site images of tail ropes of hoist, extracts characteristic parameters of the image by integration projection and Hu invariant moment, and adopts image feature classifier to do pattern recognition to get fault information and judge fault. Meanwhile, the system can remote monitor state of the tail rope of hoist by local area network and Ethernet, and can find out failures of the hoisting tail ropes, such as twisted rope, broken rope, the disproportional spacing and bending deformation of tail ropes, which solves problem of long detection cycle and fail to find fault of tail ropes timely.
Research of underground mobile application system platform
CHEN Xiaoli
2015, 41(8): 104-107. doi: 10.13272/j.issn.1671-251x.2015.08.026
<Abstract>(25) <PDF>(3)
Abstract:
The development way, deployment and architecture of current underground mobile applications are not unified, and the transmission method between ground server and the applications is various, it makes multiple professional applications on a mobile terminal cannot share data and cannot be unified login, and forms a new mobile information island. To solve above problems, a construction idea and solution of underground mobile application system platform was put forward combining with coal mine application scenarios and special environment. The system platform adopts design ideas of shared libraries and modular application, and achieves standard development mode of underground mobile application, so as to solve the problems of data sharing, automatic deployment and rapid development of the underground mobile application.
Design and application of coal mine intelligent warehousing and logistics transportation management system based on Internet of Things
ZHENG Jiasong, MENG Wei
2015, 41(8): 108-112. doi: 10.13272/j.issn.1671-251x.2015.08.027
<Abstract>(115) <PDF>(16)
Abstract:
In order to slove the problems of backward technology and low efficiency existed in warehousing and logistics transportation management of coal enterprises, a coal mine intelligent warehousing and logistics transportation management system based on Internet of Things was designed. The system adopts technologies of Internet of Things and RFID, and achieves precise management of cargo warehousing, increases storage capacity, warehouse utilization and speed of entry-and-exit of cargoes. Meanwhile, the system can realize closed-loop management of distribution, transportation and recycling of goods and materials in the whole process.
Design and application of ion potentiometer
QIN Haiming
2015, 41(8): 112-115. doi: 10.13272/j.issn.1671-251x.2015.08.028
<Abstract>(27) <PDF>(2)
Abstract:
In order to achieve quick identification of mine water bursting source and flood forecasting, an ion potentiometer used for water quality analysis was designed. The ion potentiometer uses ion selective electrode to transfer corresponding ion in water sample to voltage, and the voltage is amplified by signal conversion circuit and converted to digital value by 24 bit high-precision AD converter. Finally the ion potentiometer uses TFT LCD screen to display ion species, ion concentration and other related information, and it has high measurement accuracy of ion content and is easy to use.
Design of internal measuring system of hydraulic cylinder stroke
WU Laijie, LI Yafeng, CHEN Qi, LI Xuebin, LONG Qing
2015, 41(8): 116-119. doi: 10.13272/j.issn.1671-251x.2015.08.029
<Abstract>(32) <PDF>(6)
Abstract:
In view of problems of large space occupation and complex structure existed in current internal measuring method of hydraulic cylinder stroke, internal measuring systems of hydraulic cylinder stroke which are respectively based on optical mouse and wheel pulse were designed, work principle and hardware and software design of the systems were introduced. The test results show that the optical mouse mode measuring system is suitable for short stroke of hydraulic cylinder, and the wheel pulse mode measuring system is suitable for long stroke of hydraulic cylinder.
Design of wireless monitoring system of battery charging and discharging
MU Lili, LIU Cheng, LIU Zhenhe
2015, 41(8): 119-122. doi: 10.13272/j.issn.1671-251x.2015.08.030
<Abstract>(39) <PDF>(3)
Abstract:
In view of problems of huge volume, complex wiring and small data throughput existed in battery charging and discharging monitoring system of coal mine, a wireless monitoring system of battery charging and discharging based on CC1101 wireless communication module was designed. Synchronous monitoring of multi battery sets is realized through frequency-hopping function of CC1101. Fast continuous transfer of big data packet and automatic recognition of sending end are realized through threshold characteristic of CC1101. The test result verifies validity and stability of the system.
Research on correction coefficient of relationship formula of shearer parameters and coal rock hardness
YANG Jianjian, LI Xu, FU Shichen, WU Miao
2015, 41(8): 123-126. doi: 10.13272/j.issn.1671-251x.2015.08.031
<Abstract>(26) <PDF>(1)
Abstract:
In view of problem that current shearer on fully-mechanized coal mining face ca't automatically and accurately identify coal petrography character, the paper analyzed relationship formula between cutting motor parameters and Protodyaknove's coefficient reflecting coal and rock hardness, and obtained that they were approximately proportional and have linear relationship. Value range of correction coefficient was obtained by measured data, and finally it was validated by practical application that the Protodyaknove's coefficient inferred according to correction coefficient was consistent with the actual situation.
Understanding of mine automation of German based on survey on Ruhr Group
CHEN Xiaojing
2015, 41(8): 127-130. doi: 10.13272/j.issn.1671-251x.2015.08.032
<Abstract>(50) <PDF>(3)
Abstract:
Current situations of mine in German and its automation were summarized and application of some new technologies was introduced through survey and technical exchange about automatic mining technology in Ruhr Group of German. Components and key technologies of automation system of Ruhr Mine of Ruhr Group were focused on. Some understanding about mine automation of German was discussed combining current situation of mine automation in China and work practice of the writer. The paper provides some reference for further development of mine automation of China.

苏ICP备 05016349号-2

Supported by: Beijing Renhe Information Technology Co. Ltd.  Visits：