Smart Hydraulic Support (SHS) Improvement by Finite Element Analysis (FEA) and Control System Design in Mining Industry

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1 Smart Hydraulic Support (SHS) Improvement by Finite Element Analysis (FEA) and Control System Design in Mining Industry Weijiang Chen a, Peng Zhang b 1 School of Computer Science, Engineering and Mathematics, Flinders University Adelaide, Australia a Weijiang.Chen@flinders.edu.au; b pengzhang871024@hotmail.com Abstract- Based on study and analysis of the working condition in fully mechanized coal mine, a smart hydraulic support control system (SHS) is designed to control breaking processon top coal and to help operatorsincreasing the efficiency in development. The Finite Element Analysis (FEA) method is applied in mechanical design and simulation in the initial stage. Based on real-time pressuremonitored by pressure sensors, the smart control system offers different working orders to actuators in SHS acting motions. All actuators and sensors are intergraded and connected with a host computer which provides high speed signal processing. When the signal comparison progresses completed in SHS, the control unit send commands to hydraulic cylinders acting new motion immediately. SHS offers higher productivity working environment, more reliable mechanical system and faster response control unit in mining industry. Keywords- FEA; Hydraulic Cylinder; Automation Control System I. INTRODUCTION The productivity and efficiency of Chinese coal mine increased exponentially since fully mechanized sub-level caving machine was used in However, there are still many factors influencing efficiency of coal mine. One of the most important issues is how to raise mining ratio. Currently only approximately 80 percent of mine can be exploited. While comparing all possible methods, improving top coal breaking ratio is the one of best options [1]. At present, hydraulic support in China is mainly manual. Two potential problems can be listed, the first one is that operators are required all 24 hours within a day staying at coal face and the other is that operations are fully depending on operators' experience. As it is impossible to control top coal breaking directlybecause we cannot put any kind of sensors into the layer of coal to measure or observe breaking situations of top coal [2]. There are two communication spaces exist in coal mine environment [3], the first communication space is used for the majority coal mining using coal cutter, and the second communication space is for human movement and top coal breaking operation, as in Figure 1. Figure 1 Two communication spaces of coalface In this paper, a mechanical structure of smart hydraulic support (SHS) is designed and analyzed in Workbench which provides pressure and stress analysis at the beginning.then finite element analysis (FEA) is used for building dynamic simulation and collecting the pressure and stress from mechanical system in real time. [4]. Based on the results, a hydraulic support control system is implemented to control the status of hydraulic supports automatically. II. SYSTEM DESIGN A. Mechanical System Modeling 129

2 The support system is shown in Figure 2. A working platform, hydraulic cylinders and a fixed base are three most significant parts to be analyzed in this paper. Figure 2 Working Environment [4] 1-Working Platform 2- hydraulic cylinders 3-fixed base In mechanical system, two smart hydraulic cylinders, three pressure sensors, a support base and a working platform are constructed in Computer Aided Engineering (CAE) software. In smart control system, a pressure sensor is located at the bottom of the platform (Sensor A) and two monitoring sensors (Sensor B, Sensor C) are attached in both hydraulic cylinders. In SHS, Sensor A receives the pressure applied in working platform. Sensor B and Sensor C monitor the pressure of two hydraulic cylinders individually in Figure 3. Figure 4 shows the advanced mesh system hired in mechanical system analysis. The mechanical structure is divided into 176,353 elements with 302,760 nodes in Workbench which provides high quality mesh system in order to supply the high standard results in final stage [6]. In this project, the pressure located on sensors is a significant element which provides conditions as system inputs during the control system design. In order to improve the accuracy in data collection of sensor, the variable-sized elements in FEA are applied. Figure3. Components in support design B. Finite Element Analysis (FEA) Cutting edge technologies in mechanical design and analysis such as Finite Element Analysis (FEA) are widely applied in rapid engineering project [5]. In this project, FEA provides dynamic simulation and real time results to meet the stress and strain requirements. 1) System mesh progress Figure 4 High quality mesh with variable sizes in FEA 2) Mechanical System Environment (Static) According to the support working environment in Figure 5, three basic mechanical conditions applied are: 1)Gravitation potential of earth 2) Working forces 3) Fixed supported base 130

3 The Gravitation condition is applied into the mechanical system as shown in yellow arrow. The working force is indicated in red arrow which locates on the top of the working platform. On the base, the fixed supported part is shown as blue tag which means the element will hold the whole equipment during operation progresses to hold bodies in steady condition [7]. 3) Mechanical System Environment (Dynamic) Based on current research data, the working force for hydraulic support is shown in Figure 6[1]. Seven critical Figure 5 System environments in Static (A: Gravitation B: Fixed support C: Working force) points are selected from Figure 6 as dynamic force inputs in FEA. Generally speaking, there are 5 working situations in operation. 1) Platform lifting (Touching) The high pressure fluid inside the hydraulic cylinders converts to mechanical force to lift the working platform to the required height. Figure 6 Dynamic workforce with working time 2) Platform Crashing When the platform touches the coal layer, the hydraulic cylinders continue to supply the extra force in order to smash the coal body into small particles. 3) Holding process 131

4 After the crashing process is done, the working platform is held by the hydraulic cylinder for a while to keep the coal layer stable. 4) Platform release The final working state is releasing the working platform from holding process. The working platform is going to be set back to the original point 5) Support remove The support move to the new location to repeat working situation (1) to (4) Table 1 shows input forces in different stages. TABLE 1. PLATFORM WORKING FORCE IN DIFFERENT STAGES Process Name Force Required(KN) Time (s) 1)Platform Lifting (Touching) 0<F=< )Platform Crashing 2500<F< )Holding process )Platform release 360<F< )Support remove 0<F< ) Location of sensors Due to pressure collection requirement, two sensors (Sensor B, Senor C) are designed in FEA simulation in order to record dynamic pressure in hydraulic cylinders during variable stages. The Figure7 shows dynamic pressure monitoring system attached with hydraulic cylinders. 5) FEA results According to feedback from pressure sensorsin high quality meshed system, the real time pressure for two sensors located on hydraulic cylinders are given in Figure 8.They are Figure7.The Sensor location of hydraulic cylinders (Sensor B,Sensor C) used to show pressure changes in different mining processes [8]. The total working time for SHS following the design requirement is 7200 seconds.the maximum pressure in hydraulic cylinders is set as 175MPa (in holding process). Figure 8 Pressure monitoring in two sensors 132

5 III. SMART HYDRAULIC SUPPORT (SHS) CONTROL SYSTEM DESIGN In this paper, dynamic pressure of sensor B is selected as the plant to be controlled. Table 2 shows three conditions of top coal breaking related to feedback pressure on the sensor. A. Control System Data Flow The control system data flow chart is shown in Figure 9. When the pressure data from sensor B is received, the computer is going to compare the value from the sensor with values in table 2. There are three scenarios: 1. Pressure value is greater or equals to 175MPa: 2. Pressure value is between 150MPa and 175MPa 3. Pressure value is below 150MPa: TABLE 2. BREAKING CONDITIONS AND BREAKING RATIO [9] system will let hydraulic support release the platform and move to the next area. When the feedback sensor pressure is between 150MPa and 175MPa, this means that only part of top coal has broken. Therefore, the system will release the platform and then process platform lifting, crashing and pressure holding statuses again to check whether the pressure is greater than 175MPa. The hydraulic support will move to the next area if feedback pressure is greater than 175MPa or three full period of pressure holding status have operated. If feedback sensor pressure is below 150MPa, which is the initial pressure supplied to hydraulic support, it indicates that some errors have occurred in the hydraulic support. Then a warning will be given to inform operators to check the working conditions of the hydraulic support. Top coal break Breaking Pressure Received(MPa) condition ratio Fully break 175MPa <= P 90% - 100% Partly break 150MPa <= P < 175MPa 0% - 90% No break P <= 150MPa 0% B. Structure of the smart hydraulic control system Figure 10 shows control system structure in SHS. Smart hydraulic support control system mainly contains control units, a host computer and safety network. The control unit connects to each other by cable. It includes sensor, controller and also connect to the electromagnetic valve. Host computer monitors all controllers through the CAN bus network. Safety network connects all control units and host computer by signal isolators. The controller uses pressure sensor, get the feedback of the pressure in the hydraulic cylinder, and then transfer data to the host computer. A host computer will make decision to control the working condition of hydraulic support automatically [10]. Figure10. Smart hydraulic support control system structure IV. CONCLUSION Based on existing systems used in Chinese coal mine, a smart hydraulic support control system is designed to control and monitor the top coal breaking condition automatically. Compared to normal top coal breaking methods, several advantages can be listed. Firstly, the time consumption of each processing cycle reduced. Secondly, safety issues involved in operating top coal breaking minimized due to change the operation from manually to automatically. Furthermore, the percentage of top coal breaking no longer depends on the experience of operators, but could be controlled by computer. However, some more practical issues need to be considered before using this system in practice. For example, we need to specify the initial condition for different coal mines in China; initial pressure may vary due to sophisticated geological conditions. Potential issues need to be justified and analyzed in the future. REFERENCE Figure9. Smart Hydraulic support control system design data flow [11] When the feedback sensor pressure value is greater than 175MPa, it means that approximately 90% of top coal already broke, which we regard as full break condition. Then the [1] W. J. Wang and X. H. Liu, (2000) Study on Mechanism of Breaking Top Coal in Caving Mining, Ground pressure and state control, vol. I, pp [2] P. Zhang, W. Chen and Z. Zhao,(2012) Research of Fuzzy Recognition System for Hydraulic Support in Working Status 133

6 with FEA Analysis, International conference on control engineering and communication technology. [3] P. Zhang, S. Zhang and Y. Yang, (2011) Coalface WSN Sub-area Model and Network Deployment Strategy, 2011 International Conference on Computer Communication and Management, vol. 5, pp [4] P Ausiello, S Rengo, CL Davidson(2004). Stress distributions in adhesively cemented ceramic and resin-composite Class II inlay restorations: a 3D-FEA study. Dental Materials,vol. 20(9), pp [5] A. N. EI. Kholy, M. A. Kamel and M. O. Mousa, FiniteElement Analysis of Stresses Caused by External Holes in Hydraulic Cylinders, International Journal of Mechanical Engineering.Vol. 2(2), pp [6] "Customized Design: Roof Support Systems", Available: 44 (Accessed: 2012, October 8). Weijiang, Chen is a Ph.D candidate at Flinders University, Australia. He received his B.Eng (Mechanical Engineering) in 2008 from The University of Adelaide, Adelaide, Australia and M.Project Management in 2010 from The University of Adelaide, Adelaide, Australia. As a mechanical engineer, he has 2 years of experience in industry for mechanical system design, manufacturing and project management in international companies. He also has 5 years of experience in university teaching and project research. His areas of research interests include Mechanical system design, FEA, CFD analysis, Modern control systems and engineering project management. [7] Ţ. Ă. Lu, and D.L.Mihai, (2010). A Finite Element Analysis of Hydraulic Cylinder of Linear Hydraulic Motor from Horizontal. Journal of Engineering Studies and Research, vol. 16(4), pp [8] L. Chen, G. Y. Meng, and Y. C. Niu, Hydraulic Support Pressure Detection System based on CAN and Wireless Sensor Technology, Coal Engineering, vol. VI, 2010, pp [9] F. Litvin, FL Litvin, A Fuentes, Q Fan, RF Handschuh. (2002). Computerized design, simulation of meshing, and contact and stress analysis of face-milled formate generated spiral bevel gears. Mechanism and Machine Theory. Vol. 37 (5), pp [10] B.X. Huang, H.T.Li and et.al, Rational cutting height for large cutting height fully mechanized top-coal caving, Ming Ccience and Technology(China), 2011, vol. 21. pp [11] W. Zhang, Stateflow Logic System Modeling, Xian electrical technology university press, Peng. Zhang was born on 24 th Oct, He is currently doing his internship in Flinders University, Australia. He finished his bachelor of Engineering in The University of Adelaide awarded with honours degree in 2010, and got his master of Electrical and Electronic Engineering from The University of Adelaide, Australia in As a professional engineer, he has around 2 years of experience in real industry. His areas of research include Advanced Control Systems, Electronic Hardware System Design and System Modeling and Simulation. Mr. Zhang is a Graduate Student Member of IEEE and had won several medals in painting. 134