When an elevator is wrong or not in service, the system can exit the dispatching algorithm and turns to a single elevator running mode. 4.3 Algorithm realization
Compared with single elevator running mode, the parallel running mode is mainly different at the processing method about hall-calls. The former uses collective selective control method, and the latter uses dispatch rule combined with collective selective control method.
Here the system is to control a 9-storey building, so we choose two Siemens S7-200 PLCs(CPU226) and its Extensive Modules to control the single elevator respectively. And by using PPI Protocol to realize the communication between 2 PLCs.
The PPI Protocol adopts master-slave communication mode, so we defined elevator A as the master and elevator B as the slave. By communication program, the 2 PLCs can exchange the massage such as the current position, hall-calls or car-calls and moving direction. Then by using “minimum waiting time” algorithm, the system realizes the optimal operation of 2 elevators.
Figure7 shows the ladder program of the car-calls extreme value calculation of elevator A.
In Figure7, VB121～VB130 is the register address of elevator A’s car-call corresponding to each floor, Q3.1 is the up-moving lamp of elevator A, and the car-calls extreme value is saved in VB120.
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Figure 7 The car-calls extreme value calculation of elevator A
5. Conclusions
In this paper, we have improved an old elevator control system by using PLC, and realized the group control of 2 elevators. The new control system has been operated for 1 year, and its operation scenarios are as follows:
(1) Down–Peak
This traffic condition concerns people out of the building in the morning between 7am to 9am.
(2) Up–Peak
This condition concerns people entering the building between 5pm to 7pm. (3) Other
It covers the day from 6:00 to 0:00 except the two situations above. And in this
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situation, there is only one elevator running.
The results are expressed via an average waiting time and maximum waiting time(both given in seconds) are collected in Tables 3 and 4.
Table 3 Average and maximum waiting time(before reformed) Down–peak Up–peak Other
Down–peak Up–peak Other Average 63.20 52.78 43.25 Average 30.12 27.81 37.32 Maximum 240.33 235.26 215.43 Maximum 203.33 195.20 186.43 Table 4 Average and maximum waiting time( reformed) Due to the nonparallel running before the reform, so the average waiting time and maximum waiting time of down–peak and the up–peak are very longer than the reformed. The practice results have showed the better performance of the improved control system.
References
[1] Ricardo Gudwin, Fernando Gomide, Marcio. A Fuzzy Elevator Group Controller With Linear Context Adaptation[M]. IEEE World Congress on Computational Intelligence, 2006.
[2] Philipp Friese, Jorg Rambau. Online-optimization of multi-elevator transport systems with reoptimization algorithms based on set-partitioning models[M]. Discrete Applied Mathematics, 2005.
[3] Zheng Yanjun, Zhang Huiqiao, Ye Qingtai, Zhu Changming. The Research on Elevator Dynamic Zoning Algorithm and It's Genetic Evolution[M]. Computer Engineering and Applications, 2008.
[4] Xiaodong Zhu, Qingshan Zeng. A Elevator Group Control Algorithm for Minimum Waiting Time Based On PLC[M]. Journal of Hoisting and Conveying Machiner, 2001.
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