INTRODUCTION
Three developing stages of the interlocking and control system at railway stations are went through, which are mechanical-interlocking control system, electronic-centralized interlocking control system and computer interlocking control system . The computer interlocking control system, which is used presently, is a system whose operation realizes by computer and execution outcome is taking out by safety relays[1].
Although different typed computer interlocking system reserves different amount relays, some problems are caused to maintenance department. They have to maintain the relays as well as computer systems. Especially, when the number of computer interlocking systems is increasing, the problem will be more serious. It will be hard to increase benefit with less people and also difficult to realize the goal of factory construction.
Hence, digitalization, networking, intelligence and integration must be updated in technology [2]. With the development of micro-electronics technology, computer technology and information technology along with the enhancement of security and fault tolerance [3], it is possible to realize functions and performance indexes of safety relays by using intellectualized all-electronic execution and safety unit.
2. EXISTING SYSTEM
The computer interlocking control system, which is used presently, is a system whose operation realizes by computer and execution outcome is taking out by safety relays. It consists of five parts:
2.1 Console and Displaying Machine
The console is very convenient for users to adapt station layout changes. Users do not have to modify any hardware, only pictures of station and the graphic that displayed on the screen need modifications. The function of consoles is to collect commands and to communicate with controlling and supervising computer.
Both consoles and displaying machines are located in operator room. All information of the system is displayed on the displaying machine screen, including the station graphic, all routes, train moving, any change of outside equipment and the status of interlocking system, Chinese information of route and error message.
2.2 Controlling and Supervising Computer
The controlling and supervising computer is made up of two industrial computers. It is used as a man-machine interface of the interlocking control system. It receives commands from operators through console, provides station graphic displayed on the displaying machine, selects route based on the command from console, communicates with the interlocking computer, and Constitutes local area network contacting with other system.
2.3 Interlocking computer
They perform four main functions. The first one is to support communications with the controlling and supervising computer and the extending I//O computer, which is implemented by query -response protocols. If the communication is not successful, the overtime alarming will be issued and the next query will be made. Moreover, when the standby interlocking computer works in the state of hot standby, it sends queries to the main in time. They exchange and compare information with each other. The second function is to support interlocking logical of all signal equipments, and perform the task of route selection, route lock, signal clearance and running point.
The third function is to collect outdoor signal equipment status, including track circuits, point positions, signal status etc. The last function is to output dynamic commands and control outside equipments by special bias plate relays.
2.4 Extending I/0 Computer
The extending I/O computer has the same structure with the interlocking computer, and each function module has a hot standby module, too. By Communicating with the interlocking computer, it sends the collected information of the outdoor signal equipment status to the interlocking computer and executes the output command issued by the interlocking computer to control outside equipments.
2.5 Maintenance Computer
For the sake of the convenience of maintaining the interlocking control system, the system uses a maintenance computer. It is an industrial computer, featuring easy operation and clarity. It obtains the interlocking computer's real time information by communicating with the controlling and supervising computer.
All the information of operation, site statues and error numbers in a month are recorded and stored. In order to provide reliable scientific proof to search and analyze failures, the information can also be reappeared by graph mode directly on line. Additionally, it can supply the interfaces to computer testing system, remote diagnosing system and dispatch supervision system etc.
PROPOSED MODEL
The summarization of electronic
execution unit (EEU)
EEU is the execution and displaying circuit of computer interlocking system, which replaces relays. It is made of various kinds of electronic modules (EM) which are designed with electronic circuit and have different functions. Because there are many different types of control and collection objects such as switch, signal and track circuit and so on, EM is designed using independent unit module structure. EM has many functions such as order execution, signal pickup, monitor, fault protection and so on. EEU has discrimination pins that can prevent from inserting into wrong position. CAN-Bus interfaces are used for communication between EEU and the interlocking computer. Monitor computer is set up in EEU and is connected with one CAN-Bus interface between EM. Monitor computer is not only used for monitoring the process and status of EM, but also measuring the data of outdoor equipments such as the switch current.
Figure 1. Simple block representation of proposed system
3.2 The characters of EEU
The core of EEU is the EM and EEU is divided into signal module, switch module, railway track module and so on. Signal module is used to control different kinds of signals and signal repeaters. According to the difference among signals that are controlled by signal module, the signal module can be divided into two types such as one-drive-one train signal module and one-drive-four shunting signal module and so on.
Switch module can be divided into DC type, three-phase AC type, single-phase AC type. One switch module can control one group of switch circuit.
The track circuit module can be divided into AC480 type and 25HZ phase detecting track circuit module. Every track circuit module has four groups of track current collecting circuit, which is used to replace the functions of four groups of track relays. The interface of EEU is showed in Fig. 2.
Figure 2. The interface of EEU
4. THE CHARACTERS OF CAN BUS
Controller area network (CAN or CAN-bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. CAN is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment. CAN offers an efficient communication protocol between sensors, actuators, controllers, and other nodes in real-time applications, and is known for its simplicity, reliability, and high performance.
The CAN protocol is based on a bus topology, and only two wires are needed for communication over a CAN bus. CAN bus is multimaster. CAN bus offers remote transmit request (RTR), which means that one node on the bus is able to request information from the other nodes. CAN bus communication speed is not fixed. Any communication speed can be set for the devices attached to a bus. Here this CAN Bus is used to establish communication between the interlocking system and EEU.
5. APPLICATIONS
Using this EEU various railway functions like providing signal clearance to trains, detecting the track circuits, controlling the speed of the trains, switching operations can be controlled.
To explain and design the technical features of EEU the following explains are:
Giving the signal clearance and controlling the speed of the train according to the signal given.
The track circuits are checked and according to the route request the signal are provided.
When the signal is given the speed of the train is automatically made to control.
Also the accidents occurring in the railways due to train collision and derailment can be prevented by sensing the problem.
A single EEU are used to perform these functions simultaneously replacing relays in computerized interlocking system. When relays are used, then for every operation separate relays should be used. To avoid this complex circuitry a single EEU can be used, so that all operations can be done simultaneously using a single system.
CAN Bus is used, so that any number of EEU can also be connected to the same interlocking system. This adds more advantages to the proposed model.
6. ADVANTAGES OF EEU
EEU have the same function as the traditional interlocking execution layer. For intelligent control chips are adopted, EEU has some advantages as following.
• The wiring of EEU is simpler than the traditional interlocking execution layer, which can reduce the failure rate.
• EEU has the function of outside short circuit protection and all fuses are taken away which is easily aging.
• EEU is easy to realize area interlocking and unattended operation. For EEU is established on the network transmission platform, it is easy to realize remote control and area interlocking control without the need of setting execution and displaying machine in the remote stations.
• Space decreases obviously. Take a station with 40 switches for example, electric centralization will use 20 unit block assembly rack, while the system with EEU only has 5 cabinets(2 of them are interlocking cabinets), and the area is one out of five of the electric centralization. This is suitable for improving route and mending, and it can save housing investment.
• The engineering design is brief and conventional because the method of modularized designing is used to replace the job of station planning.
7. CONCLUSION
The successful utilization of EEU will not only offer a new set of equipment for railway control system, but also will have a profound influence on the maintenance of railway signal.
