Design and Implementation of a Statechart Based Reconfigurable Elevator Controller.doc

编号： 毕业设计(论文)外文翻译（原文）学 院： 机电工程学院 专 业： 电气工程及其自动化 学生姓名： 梁君剑 学 号： 0800120121 指导教师单位： 机电工程学院 姓 名： 范兴明 职 称： 副教授 2012年5月20日2011 6th International Conference on Industrial and Information Systems, ICIIS 2011, Aug. 16-19, 2011, Sri LankaDesign and Implementation of a Statechart BasedReconfigurable Elevator ControllerH.P.A.P. Jayawardana, Student Member, IEEE, H.W.K.M. Amarasekara, Student Member, IEEE,P.T.S. Peelikumbura, W.A.K.C. Jayathilaka, S.G. Abeyaratne, Member, IEEE and S.D. DewasurendraAbstract- This paper presents a simple and clear method to design and implement a reconfigurable elevator controller using an FPGA, which can be implemented for an elevator with any (N) number of floors, with specified inputs and outputs. A model based design approach was followed. We started from a state chart model developed for a prototype elevator with three floors. Extension of the model for a variable number of floors was considered. Controller for the prototype system was implemented in ladder logic on a PLC and the limitations of that approach with regard to re-configurability were identified: viz., in the extension of elevator controller for N no of floors. Next VHDL code was developed for a reconfigurable elevator controller where, by changing a variable corresponding to the required number of floors, the suitable code can be generated. The controller thus generated can be implemented in an FPGA. The method was successfully tested on a Xilinx Spartan 3ANFPGA. Index Terms- Elevator, FPGA, PLC, Reconfigurable, State Chart, VHDLI. INTRODUCTIONIn control and automation industry, Programmable Logic Controllers (PLCs) are commonly used to implement controls for complex reactive systems, primarily because of their easy programming environments based on IEC-61131-3. However,they are meant for sequential event processing and not for hard real-time reactive environments which require parallel processing capabilities. In contrast, Field Programmable Gate Arrays (FPGAs), which are inherently parallel, can be used to develop controls for more complex systems with large number of inputs and outputs. In addition to reconfigurability, it consumes less power and it can provide comparatively low response times and flexibility in expansion of designs. This paper presents the work carried out to design and implement a reconfigurable elevator controller, which can be implemented for an elevator with any number of floors (N) in a simple and user friendly manner. With this design, which was implemented using a Field Programmable Gate Array a controller suitable for an elevator with any number of floors, H.P.A.P. Jayawardana, H.W.K.M. Amarasekara, P.T.S. Peelikumbura, and W.A.K.C. Jayathilaka are final year undergraduates in the Department of Electrical, Electronic Engineering, Faculty of Engineering, University of Peradeniya, Sri Lanka. Dr. S.G. Abeyaratne is a Senior Lecturer in the department of Electrical, Electronic Engineering, Faculty of Engineering, University of Peradeniya, Sri Lanka Dr. S.D. Dewasurendra, MIMechE is a Senior Lecturer in the department of Computer Engineering, Faculty of Engineering, University of Peradeniya, Sri Lanka. with some specified inputs and outputs, can be implemented simply by changing a variable N corresponding to number of floors. When designing controls for any event driven, complex reactive systems, development of a method for formal specification of the control at the initial stage facilitates easy implementation in later stages. Therefore such an approach is essential in developing controls for a system like the elevator which has a fairly large number of sensors and which needs to continuously react to several inputs. This becomes more pronounced for systems with large numbers of floors, for the added complexity. Therefore, this elevator controller was also developed using a model based design approach, in which a statechart model was developed for the prototype elevator at the initial stage. A verification of the design can also be done at the development stage with this approach. The objectives of the research presented in the current paper are:1. Demonstrate the development of a statechart model for the prototype elevator that permits extension of the model for N number of floors and simulate in MATLAB SIMULINK STATEFLOW, to validate the architecture.2. Implementation of a controller for the prototype system using a Programmable Logic Controller (PLC) and development of a methodology to extend the controller for any number of floors in a user friendly manner: using IEC- 61131-3 languages.3. Validate the reconfigurable design process through implementation of the reconfigurable controller using a FPGA in a convenient and user friendly approach: with VHDL (IEC 61691) as the HDL.II. DEVELOPMENT OF PROPOSED STATECHART MODELA. Statechart DesignFollowing our model based design approach, at the initial stage we developed a state chart model for the prototype elevator and simulated it with MATLAB SIMULINK STATEFLOW, which permitted us to verify the design at the development stage, before going for costly and time consuming hardware implementation. With that simulation, which clearly indicates the state transitions of the system, it was easy to identify the system behavior. Thereafter, we investigated the extension of this model to N no of floors so that the behavior of such system could be understood clearly. In designing the state chart model for the prototype elevator, we mainly identified four main components of it. Considering those, we basically identify three orthogonal sub states of the system namely; Inputs, Car and Lights. After that, the total system was divided into sub states with AND or OR decompositions, considering their behaviors as shown in Fig.1. The relevant state transitions were applied with appropriate conditions and simulated. State chart diagrams for three main sub states with their state transitions are shown in the Fig.2, Fig.3 and Fig.4. Reference 1 clearly illustrates basics of the state chart. Although methods of modeling elevators using state charts are presented in recent work, the proposed method in this paper has reduced number of states and the model is error free as it is simulated with relevant transition conditions 2.B. Extension of the Statechart ModelWith the simulation of state chart model explained in section A, it was easy to identify the system behavior. In our study on expansion of the model to an elevator with N no of floors, we identified that the state configurations of Inputs and Lights sub states only needed to be changed, while state configuration of Car sub state could remain the same. However, it was not possible to extend the simulation for N no of floors. But, with this study we were able to identity how the conditions for state transition should be adjusted and it helps us to identify the logic behind expansion of the controller.III. HARDWARE FOR CONTROLLER IMPLEMENTATIONPrototype elevator, for which the controllers were implemented, consists of 3 floors as shown in Fig 5. For any controller used for this elevator gets inputs from 3 proximity sensors, 2 limit switches, push button inputs (Hall Call Buttons and Car Call Buttons) and 3 door position sensors. To drive the elevator car it is needed to provide 2 control outputs to main inverter as inputs to the inverter which can drive the main induction motor to forward and reverse direction. In the same time it is needed to release the electric brake activating a solenoid to provide 3 control signals for another inverter. Therefore each controller design was based on the coordination of these inputs/ outputs.Fig 1: Division of Systems into StatesFig 2. State Transitions of Input Sub StateFig 3: State Transitions of Car Sub StateFig 4: State Transitions of Light Sub StateFig 5: Overview of the Prototype ElevatorIV. CONTROLLER DEVELOPMENT WITH PLCA. Implementation of a controller for the prototype elevatorAs most real time systems are commonly implemented using PLCs, in the first stage of our work we tried to develop the controller using a PLC. For that we used, TWDLCDE40DRF Telemachanique PLC. Initially we tried to develop a controller for the prototype elevator using ladder diagrams. We identified that we have to basically develop two kinds of ladder diagrams for the forward and reverse motion of the elevator car, in addition to other features like door and lights. To illustrate the logic behind that, let us consider the ladder diagrams we developed for the forward motion of the prototype elevator. As shown in Fig 6, we develop a separate rung for forward motion from floor0 to floor1, and another for forward motion from floor 0 to floor2 and floor1 to floor2. According to the motion required by the passenger, a memory bit is set and all those outputs are considered for overall system forward motion of the car as shown in the ladder shown in Fig 7. Similarly, we have to develop sixteen rungs for the development of a controller for prototype elevator with three floors. We programmed the PLC using the developed ladder program and we successfully implemented the controller. Fig 6: Ladder Diagrams for Forward MotionFig 7: Ladder for Overall System Forward MotionB. Extension of the Controller for N no of FloorsAfter implementation of the controller for prototype elevator, we studied about extension of the controller for an elevator with any number of floors. For that we will consider the following inputs; Car Buttons : CCB0,CCB1,CCB(N-1) Hall Call Buttons:HCB0U,HCB1D,HCB1U,.,HCB(N-1)D Proximity Sensor Inputs:PROX0,PROX1,.,PROX(N-1) Similar to the way that we developed the ladders for prototype elevator, we have to basically consider forward and reverse motion of the car. To illustrate the method for extension, let us again consider the forward motion. Similar to the method for prototype elevator, two types of ladders has to be developed. As shown in the Fig 8, a separate ladder diagram is needed for the forward motion to (N-1) floor. In addition, (N-2) no of ladder diagrams have to be drawn for the forward motion to floor 1,.,(N-2), as shown in Fig 9. At the same time, overall system Ladder has to be edited as shown in Fig 10.P- Proximity Sensor InputsH-Hall Call Button InputsC-Car Call Button InputsD-Door Sensor InputsL-Limit Switch InputsFig 8: Ladder Diagram for Forward Motion to (N-1) FloorFor X= 1 to (N-2)Fig 9: (N-2) No of Ladder Diagrams for Forward Motion to Floor1,., (N-2)Fig 10: Ladder Diagram for Forward MotionEven though, we can draw the ladder diagramcorresponding to a controller for an elevator with N no of floors using the explained method, as the no of floors increases the ladder diagrams become more complex. This is because, according to the explanation given above, we need to draw more than 2N no of ladder diagrams for that. PLC ladder programming does not provide support to simplify the design in any clear way. Otherwise, we could have developed a method to adjust the programs accordingly, when the number of floors changes, as will be shown to be possible with FPGAs (in section V). Therefore, if we follow this method, we have to manually construct the ladder diagrams as explained above, draw them with the relevant software for the PLC and program the controllers individually, as required for each elevator with a particular number of floors. This May be very Difficult for an elevator with large no of floors. Therefore, we need to find a simple method to develop a controller for an elevator with N no of floors. We can accomplish that task in a simple way using an FPGA. In addition to its reconfigurablity, FPGAs also provide reduced response times and flexibility in expansion.V. IMPLEMENTATION OF A RECONFIGURABLECONTROLLER FOR AN ELEVATOR WITH N NO OF FLOORSWith PLCs we have to use separate input/output cards with increasing of no of input/outputs. The power consumption is also considerably high when compared to FPGAs. Also programming a FPGA using VHDL or Verilog is very descriptive and can be spread for a wider range of concepts or logics in programming rather than trying the same logic in PLCs using ladder diagrams or sequential function charts. Therefore this program which is used for a controller of an elevator with N number of floors was implemented using VHDL for an FPGA. Our main aim was to obtain a program where we can simply change the no of floors and achieve the required performance: i.e., the program will automatically generate inputs outputs. Fig 11 shows the logic behind the corresponding code. Unlike in the PLC, FPGAs have inputs/outputs that we can even use as bit vectors in programming directly. We use this property to develop the program. The logic behind this was input data vectors. In this program we define data vectors containing bits equal to number of floors: these vectors will be generated automatically when the number of floors is given. Eg.: If number of floors is 3 an input vector will be 000 Here in this program we define three input data vectors as follows;Proximity sensor inputsCar call button inputsHall call button inputsPROX: in std_logic_vector (n-1