【正文】 l cannot be served by a car going in the reverse direction. If an elevator has no requests,it remains at its current floor with its doors closed. (2)Parallel running with two elevators In this situation,there are two elevators to serve the building runs at 7am to 9am and 5pm to 7pm every day. When an elevator reaches a level,it will test if the stop is required or will stop at this level when the stop is required. At the same time,to balance the number of stops,the operation of two elevators will follow a certain dispatching principle. An elevator doesn’t stop at a floor if another car is already stopping,or has been stopped there. The normal operation of elevators is implemented by cooperation of its electric power driving system and logic control system. design 4 Due to the random nature of call time,call locations and the destination of passengers,the elevator control system is a typical realtime,random logic control system. Here we adopted collective selective control method with siemens PLC S7200 CPU226 and its extension modules. There are 46 input points and 46 output points in the I/O points are showed in Table1 and Table 2. Table 1 Input points Table 2 Output points About software designing,we adopt the modularized method to write ladder diagram information transmission between modules is achieved by intermediate register bit of PLC. The whole program is mainly posed of 10 modules: hallcall registration and display module,carcall registration and display module,the signal bination module,the hallcall cancel module,the elevatorlocation display module,the floor selection module,the moving direction control module,the door open/close module,the maintenance operation module and the dispatching module under parallel running mode. The design of the typical modules is described as follows: 5 registration and display There are two kinds of calls in an elevator:hallcall and someone presses a button on the floor control panel,the signal will be registered and the corresponding lamp will is called hallcall registration. When a passenger presses a button in the elevator car, the signal will be registered and with the corresponding lamp is called carcall registration. Figure2 shows the ladder diagram of up hallcalls registration and selflock principle is used to guarantee the calls’continuous display. Figure 2 up hallcall registration and display collective selection of the calls Here the collective selection control rules are showed in Figure3, and are auxiliary relays in denote the stopping request signal of 1st to 9th floor auxiliary relay denotes the elevator driver’s operation there is a call in a certain floor,the stopping signal of corresponding floor will the elevator is operated by the driver,the hallcalls will not be served. And the elevator cannot pass a floor at which a passenger wishes to alight. cancellation of the calls The program of this module can make the elevator response the hallcalls which have the same direction as the car’s current direction,and when a hallcall is served, its registration will be ladder diagram of up hallcalls’cancellation is showed in Figure4. 6 Figure 3 The bination of the calls Figure 4 The cancellation of up calls In Figure4,the auxiliary relay is the up moving flag of the the current direction of the elevator is up,’s contacts are closed。on the contrary, when the current direction of the elevator is down,’s contacts are to denotes the carcalls’ stopping request signal of floor 2 to floor 8 respectively. This program has two functions: (1)Make the elevator response the normal down hallcalls when it is moving down,and when a down hallcall is served,its registration is canceled. (2)When the elevator is moving up,the corresponding floor’s down hallcall it passing by is not served and the registration is remained. The cancellation of down hallcalls is reversed with up hallcalls. ’s direction The elevator may be moving up or down,depending on the bination of hallcalls and following ladder diagram in illustrates that the elevator will move up. 7 Figure 5 Up moving of the elevator Figure5 shows that when the calls corresponding floor is higher than the elevator’s current location,the elevator will go the auxiliary relay is used as the upmoving the elevator is moving up,the upmoving lamp is illuminated,so the is connected the elevator arrives the top floor,the upmoving lamp is off and the timer ,the is disconnected,the upmoving display is we used to replace which can ensure the cancellation’s reliability. ’s floorstopping Figure6 shows the ladder diagram of the elevator’s floorstopping function. As showed in Figure6, is the flag of floorstopping is the floorstopping signal sent by the is the fire signal sent by the fire is the forced speed changing signal. When either of these contacts act,the system should send out the floorstopping signal. waiting time algorithm In traffic of elevator systems,there are two types of control task one is t