Processing and Transmission Strategy of Elevator Cage Terminal Based on Low‐power ZigBee Technology

www.seipub.org/ijepr International Journal of Engineering Practical Research (IJEPR) Volume 3 Issue 4, November 2014 doi: 10.14355/ijepr.2014.0304.07

Processing and Transmission Strategy of Elevator Cage Terminal Based on Low‐power ZigBee Technology Jian Yang*1,2, Zhe Ou3 South China University of Technology, No. 381, Road Wushan, Guangzhou Guangdong 510640, China

*1

School of electronic and information, Guangdong Polytechnic Normal University, No.293 Zhongshandadao, Tianhe district, Guangzhou Guangdong 510665, China 2

Hitach Elevator (China) Co., Ltd., Guangzhou Guangdong, China

3

*1,2

yj_sanshengshi@sohu.com; 3ouzhe@hitachi‐helc.com

Abstract The paper aims to realize long‐distance wireless two‐way communication between cage terminal and the master terminal without changing traditional electromechanical structure of elevator system. Firstly, modelling of a small‐ power Zigbee‐based wireless elevator communication system is presented and a unified data structure of wireless elevator communication system is proposed in the paper.

Secondly, signal transmission line between the cage terminal and the master terminal is set up by utilizing rotary encoder readings to determine position of elevator cage and combine with routing forwarding function of floor terminals. Finally , functions and logics of the ʺspecial callʺ, ʺcage callʺ, and ʺcage call and button lamp onʺ are analyzed, based on which data processing and information transmission strategies are established accordingly, processing algorithm and transmission procedure are concluded and time delay characteristics of information are analyzed. Research shows that common transmission of diversified wireless information could be achieved in spite of hoistway environment as long as reasonable data processing measures and transmission methodologies are adopted with partial correction on electric parts.

Keywords Elevator; Zigbee; Cage Call; Cage Call Button Lamp; Cage Position Detection; Data Processing; Transmission Strategy

Introduction Introduction of wireless technology to elevator control system would not only reduce installation and maintenance costs, but also has attractive prospects where its combination with the Internet of things would expand elevator operating and monitoring function, marching towards intelligent processing of elevator and eventual integrate into intelligent building system. Wireless transformation on elevator

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operating system has been in progress for a long time.

At present, there are mainly three types of applications.

The first one is to include wireless technology into the existing elevator hierarchical control system for remote monitoring of the elevator. The second one lies in identification of passenger status outside the hall.

Both of them are known as wireless applications outside the elevator control system. On the opposite, the third is to integrate the wireless technology as a part of control system, to function in the entire machine operation. The acquisition and wireless transmission of such information as ʺspecial callʺ, ʺcage callʺ and ʺcage call and button lamp onʺ focused in this paper are typical cases of the third type of application.

Literature proposed in 2003 an elevator wireless call solutions based on Bluetooth technology, which stayed in a vision and not yet realized.

In spite of the price advantage of Bluetooth device, its short transmission range and limited number of devices simultaneously activated have confined its practical prospect. Distinctive from literature which only presents proposals, literature showed that in 2002, Hitachi, Ltd., Tokyo applied for and obtained the invention patent of elevator wireless signal communication system in the United States.

Enterprise‐oriented modification and research accomplished by the company fit more to the actual industrial application.

In electromechanical structure of traditional elevator system, master control cabinet and motor are placed in the machine room outside the hoistway top while the elevator cage position constantly changes due to its ʺcall answeringʺ among all passenger call related

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information. This have caused the communication between the elevator cage and the master control cabinet to become the most difficult issue for wireless transformation. To solve this problem, literature has changed electromechanical structure of traditional elevator system, placing the master controller along with the motor on the counterweight in the hoistway, as opposed to the cage in the direction. This act certainly has a more reliable communication than placing the master terminal outside the hoistway in the traditional practices. What’s more, the opposite directional running of elevator cage and the master terminal, except some special and casual occasions, the worst case in which one is at the top and the other is at the bottom, they are more often close to each other, making the wireless module meet transmission requirement and do not need of too much power.

The structure proposed in Literature can indeed solve the problem of limited transmission range of low power wireless module. However, this has led to a dilemma, that is, changes in the mechanical and electrical structure will cause a change in hoistway, and the corresponding costs of mechanical parts modification, installation and commissioning will also increase, which further affects practical use of the product.

In economic and practical terms, the processing and transformation of the elevator wireless communication system must base on a premise, that is, to achieve the goal of reliable low‐power wireless signal transmission by utilizing only partial minor correction of electrical parts and combining with the reasonable method of data processing and information transmission mechanism, with no changes or minor changes on the traditional mechanical structure. The most important and difficult part lies in the two‐way communication between the cage terminal and the master terminal when they are furthest away from each other.

This paper attempts to, on the basis of the traditional electromechanical structure, modify the model proposed in literature and re‐establish the small‐ power ZigBee module‐based elevator wireless communication system. It presents research on the data processing and transmission strategies of diversified information from the cage terminal that is furthest away from the master controller, and finally achieves the minimal cost transformation of wireless elevator cage call system.

Definitions of Wireless Communication System Model and Data Structure Wireless Communication System Model Traditional elevator system is designed in a way that frequency converter, master controller, motors and guide wheel are all placed in the machine room outside the hoistway top, with elevator cage and the counterweight on each side of the guide wheel, moving opposite to each other in the hoistway. Hall call boxes are installed on each floor, and connected through the cable to the master controller in a serial or parallel way. Call boxes are also installed inside the elevator cage on each floor, along with the safety circuit, power supply voltage and the like, connected to the master controller through independent cable.

Without changing the electromechanical structure, the small‐power ZigBee module‐based elevator wireless communication system is designed as shown in Fig. 1.

Its basic development concept is as follows: simulate serial communication mode, and pass all call instructions, including cage call instructions, floor by floor, to complete in ʺserialʺ way the long‐distance two‐way communication between the node terminal and the master terminal.

FIG. 1 WIRELESS ELEVATOR COMMUNICATION SYSTEM

For the convenience of description, the public parameters are defined as follows: Set the floor table as F={floor1,…,floor n}={Node1, Router2, …, Router n}; Set the floor indicator as In={Indicator1,…indicator16, Indicator c}; Set the floor ascending instruction as UP={1UP,…(n‐1)UP},the floor descending instruction as DN={2DN,…,nDN}.

As shown in Fig. 1, the two‐way signal transmission function of the wireless communication system is

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completed by the floor terminal, the cage terminal, and the master terminal.

Definition of Information Priority Levels and Data Type Table 1 gives clear definitions on the priority and data type of 6 groups of information with steady flow in the elevator wireless communication system.

TABLE 1 DEFINITIONS OF INFORMATION PRIORITY AND DATA TYPES

Priority

Information category

Type

Source Route Destinatio terminal terminal n terminal

00

Special call

000

Cage

Hall and floor

Master terminal

01

Cage call

001

Cage

Hall and floor

Master terminal

01

Cage position and traveling direction display

010

Master terminal

10

Cage call and button lamp on

011

Master Hall and terminal floor

Cage

10

Hall call button lamp on

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Master Hall and terminal floor

Hall and floor

11

Hall call

101

Hall and Hall and floor floor

Master terminal

Hall and Hall and floor floor/cage and cage

In consideration of transmissions of different information between terminals in the same period of time, conflict among information might cause information channel jammed. To avoid this, firstly, prioritize the information based on sequence of processing and sending into four levels from high to low by taking into account passengers’ real mentality and importance of functions. The highest priority is represented by ʺ00ʺ, indicating the data in need of rapid transmission under emergency or special circumstances; ʺ01ʺ is for the second priority, and ʺ10ʺ for the third, indicating the data requires a shorter path to do transmission; the lowest level is in ʺ11ʺ, which means the general data transmitted floor by floor under normal conditions.

Secondly, define the data type with ʺ000ʺ to ʺ101ʺ. The concrete meaning of the ʺdata contentʺ of data with the same priority needs to be determined by the ʺdata typeʺ. Different information has different roles and also different length of data content. Emergency information like ʺspecial callʺ, for instance, only needs

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1 bit to ʺtriggerʺ the signal. The shorter the data, the less power consumed and the faster the transmission speed; on the contrary, general information like ʺhall callʺ under normal operation could be delivered in the time as long as passengers can endure, and therefore has a relatively longer data length.

As shown in Table 1, the cage terminal needs to deal with and send information including ʺspecial callʺ, ʺcage callʺ, ʺcage call and button lamp onʺ and ʺcage position and travel direction displayʺ etc. Only ʺcage position and travel direction displayʺ is forwarded as a role of route, while the others act simply as the ʺsource terminalʺ or ʺtarget terminalʺ. However, ʺcage position detectionʺ is sent from hall terminal, though, it is closely related to the cage terminal, making it a factor that must be considered in the cage terminalʹs information sending and receiving.

Strategies for Data Processing and Transmission between the Cage Terminal and the Master Terminal Set up the Transmission Line Between the Cage Terminal and the Master Terminal The cage that keeps running in the hoistway, only stays near the upper part of the hoistway for a very short time. In this way it fails to keep continuous direct contact with the master terminal. It needs to take use of the routing function of floor terminals to realize indirect implementation of two‐way communication between the cage terminal and the master terminal. To set up the information transmission line, we must decide on the floor routing terminal for forwarding, and hence the cage position has to be determined. On the basis of analysis on information transmission logics of the cable system, the idea for transmission line setup is determined as follows: the master controller reads the motorʹs rotary encoder readings to determine the cage position and traveling direction, and then sends this information via the master terminal to the floor terminal. After the floor terminal which the cage is approaching receives the information, it forwards to the cage terminal to prompt it that the forward routing function can be completed. When the cage terminal receives the relevant information, on one hand, it displays the information on the screen; on the other hand, it sets the rest of the forward routing addresses as the corresponding floor terminals, and finally completes the transmission line establishment between the cage terminal and the master terminal.

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① Rotary

Determine position of cage

Cage position

① information

①

Master controller

Master terminal

②

①

②

① Floor terminal k

Floor terminal n

Cage position

①

② Cage terminal

Floor terminal 1

Set floor k as routing address, send other information of cage

FIG. 2 DETECTION OF CAGE POSITION AND INFORMATION TRANSMISSION PATH

Fig. 2 displays the detection of elevator cage position and information transmission path in the elevator wireless communication system.

As long as the motor keeps running, the master controller is able to detect the cage location at any time.

Forwarding by floor terminal helps to determine the routing line for the cage terminal, and further build the information transmission line between the cage terminal and the master terminal.

As the cage keeps changing its location, it is difficult to determine the time needed to set up the transmission line. Supposing it takes T1 for the master controller of a 16‐storey elevator to read the rotary encoder data and send the information, T2 for the master terminal to receive and forward the information, T3 for uncertain floor terminal to process and forward the information, T4 for certain floor terminal to process and forward the information, and T5 for the cage terminal to receive and confirm the routing terminal address. Select when the cage parks is at the top floor and the 2nd floor (ground floor is the terminal node without routing function, so the lowest routing terminal that the cage terminal can borrow is Floor 2), and determine value scope of the time needed for transmission line establishment T1∑ {T1min, T1max} as follows: i) If the cage parks at the top floor, then T1min =T1+T2+T4+T5 (1) ii) If the cage parks at the bottom floor, then T1max =T1+T2+14T3+T4 +T5 (2) The time difference concluded by (2) – (1) is: ΔT1= T1max‐ T1min =14T3 (3) For a elevator of n floors, (3) can be simplified as: ΔT1= (n‐2)T3 (4) (3) and (4) show that the time consumed by the middle floors to process and forward information, with different cage positions, determines the time duration required to establish transmission line between the cage terminal and the master terminal. To reduce the impact of forwarding, set the information priority

level as ʺ01ʺ, second only to ʺspecial callʺ information.

Data Processing and Transmission Strategies for Cage Terminal Once the transmission line is established between the cage terminal and the master terminal, they come to deal with various information associated with the cage terminal and discuss the transmission strategies.

(1) From cage terminal to the master terminal: ʺspecial callʺ, ʺcage callʺ 

“Special call” is highly prioritized information under emergency or special circumstances, such as ʺfire fightingʺ, ʺearthquakeʺ, special ʺVIPʺ service or ʺtroubleshootingʺ function. Such information needs rapid transfer to the master terminal, enjoying the highest priority when conflicting with other signals.



“Cage call” is the choice of target floor made by passengers in the cage. It needs to decide the validity of such choice according to the floor number where passengers get on the cage, as well as the cage traveling direction. For example, when the cage is traveling upward, and passengers get on the cage from Floor 4, then possible options are limited to 5 ~ 16 floors;

Both information is delivered from the sensing device outside, requiring a number of processing inside the terminal, including A/D conversion and single‐chip microcomputer. After the processing, they are forwarded via a floor terminal and enjoy a higher priority than the signals sent from the terminal on its own, which includes skipping the floor and immediate forwarding. Two kinds of information share the same processing but distinct priority levels. Once conflict happens, ʺspecial callʺ information is dealt first.

Fig. 3 indicates the processing and transmission process for the two types of data. The data sent from the cage terminal to the master terminal through floor terminals only contains two types of priority levels, ʺ00ʺ and ʺ01ʺ. While information of the rest priority levels are beyond the scope of the paper, they are only labelled as ʺother informationʺ.

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and data type of the information it receives and then its processing strategies and steps. If information of different priority levels is received at the same time, then processing will be carried out in accordance with the priority levels from high to low (for simplicity, this step serves as a part of the common mechanism, and is not specified in the implementation strategy of specific functions). The processing and transmission strategies for the two types of information are:

Start

Collect "special call" or "cage call" status

Data processing

Set address information



Step 1 Collect ʺspecial callʺ or ʺcage callʺ status;

Send data to the designated Cage terminal station terminal

Step 2 Data processing: set priority level, data type and data content;

Floor terminal Receiving the information by floor terminal

Step 3 Set address information: source address, routing address (of the adjacent floor), target address (master terminal);

Abandon the information yes

Is it the destination address?

Other information

Cage terminal

Step 4 Send data;

no



no

Is it the routing address?

Floor terminal

Step 1 Receive data;

yes

Step 2 Is it the destination address? If yes, the data belongs to other information; if not, go to the next step;

no

Is the priority level 00/01?

Step 3 Judge the validity of data: is it the routing address? If yes, go to the next step; if not, the data has nothing to do with this floor terminal. Abandon it and wait to receive new information;

Other information

no

yes

Is the data type 010? no

Modify the routing address (+2) then send data.

"cage position and traveling direction display" information

Step 4 Judge the priority level: is it 00/01? If yes, go to the next step; if not, the data belongs to other information; Step 5 Judge the data types: is it 010? If yes, the data is ʺcage position and traveling direction displayʺ information; if not, the data belongs to the two kinds of information mentioned above, then go to the next step;

Floor 15/16 terminal receives the data

Set the routing address directly as the coordinator, and then send the data.

Step 6 Modify the routing address (+2), and send immediately skipping the floor;

Master terminal Receive the data

Step 7 If this floor is Floor 15/16, then set the routing address as the coordinator (master terminal), and send directly;

After processing, send the data into the master controller

 End

FIG. 3 DATA PROCESSING & TRANSMISSION STRATEGIES

Although the cage terminal only sends two types of information, ʺ00ʺ and ʺ01ʺ, the information sent from the floor terminal to the master terminal includes more.

Floor terminal needs to determine the priority level

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Master terminal

Step 1 Receive data; Step 2 After processing, send the data into the master controller.

(2) Analysis of information transmission time Similar to transmission line setup in the previous stage,

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the time needed for the processing and transmission of the two information is also difficult to determine. One of the most major delays occurs in the forwarding among floor terminals. In comparison with that, the time needed for cage terminal end signal acquisition, data processing, information sending, as well as master terminal end receiving and forwarding to the controller can be determined. Said that it takes T6 for the cage terminal of a 16‐store elevator to collect, process and send ʺspecial callʺ information, T7 for ʺcage callʺ information, T8 for the floor terminal to receive, process and forward, T9 for the master terminal to receive and forward the information. Select particularly the two extreme scenarios where the cage parks at Floor 16 and Floor 2 and determines the value scopes of time needed for ʺspecial callʺ information transmission T2∑{T2min, T2max} and ʺcage callʺ information transmission T3∑ {T3min, T3max} as: i)

If the cage parks at Floor 16, then T2min =T6+T8+T9 (5) T3min =T7+T8+T9 (6)

ii)

If the cage parks at Floor 2, then T2max =T6+8T8+T9 (7) T3max =T7+8T8+T9 (8)

Generally, ʺSpecial callʺ works as an emergency button, and thus only needs to handle 1 bit of data content, whereas ʺcage callʺ needs to face the choice of all floor data on the whole panel, therefore, the equations above also satisfy the following conditions: T7 >T6 (9) Time differences can be concluded by (7)‐(5) and (8)‐(6) respectively are: ΔT2= T2max‐ T2min =8T8 (10) ΔT3= T3max‐ T3min =8T8 (11) For a elevator of n floors, (10) can be simplified as:

terminal, the transmission of ʺspecial callʺ information takes not much time.

Conclusions A long history has been witnessed in the course of wireless transformation on elevator operation system.

With exception of the elevator monitoring model based on wireless sensor mentioned in Literature, no wireless products have ever been seen integrated into the elevator operation system on the market.

Investigation shows that the primary reason lies in too many changes in the elevator wireless transformation and too high cost which have affected its practical uses.

Based on the point of view of industrial application, and giving consideration to the practical demands of economy and performance, the paper proposes minor corrections on electrical components without changing the electromechanical structure. Long‐distance two‐ way communication function between the cage terminal and the master terminal is so realized by adding the low‐power ZigBee module and through reasonable data processing strategies and transmission method, which are cost effective and of practical significance.

The paper has established the low‐power ZigBee technology based wireless elevator system model, proposed a unified data structure of elevator wireless communication system. It also creates the signal transmission line between the cage terminal and the master terminal, serving as a basis for the research on information transmission and data processing strategies between the cage terminal and the master terminal. Time limit of all kinds of information processing and transmission is analyzed, and priority levels and transmission methods for diverse information are accordingly set up. The research results could provide ideas for developing solutions for other information processing and transmission, and pave the way for wireless transformation of the elevator control system circuit, like safety circuit.

ΔT2= (n/2) T8 (12) For a elevator of n floors, (11) can be simplified a ΔT3= (n/2) T8 (13) It can be seen from the calculation results of (11) and (12) that, due to the same skip‐the‐floor transmission approach, the two pieces of information take the same time in floor terminal processing and forwarding.

Through the observation on (5), (6), and (9), we can get that thanks to the short processing time of cage

ACKNOWLEDGMENT

Joint work with LIU Wen‐ji (South China University of Technology). With advice from HUANG Dao‐ping (South China University of Technology).

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Jian Yang, Hainan, China, May 21, 1973, received the B.S. degree in electrical electronic instruments and measurement technology from University of Electronic Science and Technology of China, in 1995, and the M.S. and the Ph.D degrees in control theory and control engineering from South China University of Technology, Guangdong, China, in 2002 and 2007, respectively.

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