基于PLC的电梯控制系统的设计英文文献
庐山导游词-北京工商大学嘉华
2008 Workshop on Power Electronics and
Intelligent Transportation System
Design and
Practice of an Elevator Control System Based on
PLC
Xiaoling Yang
1, 2
, Qunxiong
Zhu
1
, Hong Xu
1
1
College of Information Science &Technology,
Beijing University of Chemical Technology,
Beijing 100029, China
2
Automation College
of Beijing Union University,Beijing,100101, China
yxl_lmy@ , zhuqx@,
Abstract
This paper describes the development of 2
nine-storey
elevators control system for a
residential building. The
control system
adopts PLC as controller, and uses a
parallel
connection dispatching rule based on
waiting
time
paper gives the basic structure, control
principle and
realization method of the PLC
control system in detail.
It also presents the
ladder diagram of the key aspects of
the
system. The system has simple peripheral circuit
and
the operation result showed that it
enhanced the
reliability and performance of
the elevators.
The electric power driving
system includes: the
elevator car, the
traction motor, door motor, brake
mechanism
and relevant switch circuits.
Here we adopted
a new type of LC series AC
contactors to
replace the old ones, and used PLC’s
contacts
to substitute the plenty of intermediate relays.
The circuits of traction motor are reserved.
Thus the
original control cabinet’s
disadvantages, such as big
volume and high
noise are overcome efficiently.
2.2.
Signal control system
The elevator’s
control signals are mostly realized by
PLC.
The input signals are: operation modes, operation
control signals, car-calls, hall-calls,
safetyprotect signals,
door openclose signal
and leveling signal, etc. All control
functions of the elevator system are realized
by PLC
program, such as registration, display
and elimination of
hall-calls or car-calls,
position judgment of elevator car,
choose
layer and direction selection of the elevator,
etc.
The PLC signal control system diagram of
elevator is
showed in Figure 1.
1.
Introduction
With the development of
architecture technology, the
building is
taller and taller and elevators become
important vertical transportation vehicles in
high-rise
buildings. They are responsible to
transport passengers,
living, working or
visiting in the building, comfortable
and
efficiently to their destinations. So the elevator
control system is essential in the smooth and
safe
operation of each elevator. It tells the
elevator in what
order to stop at floors, when
to open or close the door and
if there is a
safety-critical issue.
The traditional
electrical control system of elevators is
a
relay-controlled system. It has the disadvantages
such as
complicated circuits, high fault ratio
and poor
dependability; and greatly affects
the elevator’s running
quality. Therefore,
entrusted by an enterprise, we have
improved
electrical control system of a relay-controlled
elevator in a residential building by using
PLC. The result
showed that the reformed
system is reliable in operation
and easy for
maintenance.
This paper introduces the basic
structure, control
principle and realization
method of the elevator PLC
control system in
detail.
2. System structure
The
purpose of the elevator control system is to
manage movement of an elevator in response to
user’s
requests. It is mainly composed of 2
parts:
Figure 1 PLC signal
control system diagram
2.3. Requirements
The goal of the development of the control
system is to
control 2 elevators in a 9-storey
residential building.
For each elevator, there
is a sensor located at every
floor. We can use
these sensors to locate the current
2.1.
Electric power driving system
978-0-7695-3342-108 $$25.00 © 2008 IEEE
DOI
10.1109PEITS.2008.44
94
position of
the elevator car. The elevator car door can be
opened and closed by a door motor. There are 2
sensors
on the door that can inform the
control system about the
door’s position.
There is another sensor on the door can
detect
objects when the door is closing. The elevator
car’s
up or down movement is controlled by a
traction motor.
Every floor, except the first
and the top floor, has a
pair of direction
lamps indicating that the elevator is
moving
up or down.
Every floor, has a seven segment
LED to display the
current location of the
elevator car.
The first step for the
development of the elevator
control is to
define the basic requirements. Informally, the
elevators behavior is defined as follows.
(1) Running with a single elevator
Generally, an elevator has three operation
states:
normal mode, fire-protection mode and
maintenance
mode. The maintenance mode has the
highest priority.
Only the maintenance mode is
canceled can the other
operation modes be
implemented. The next is
fire-protection mode,
the elevator must return to the
bottom floor
or base station immediately when the fire
switch acts. The elevator should turn to
normal operation
mode when the fire switch is
reset. Under normal
operation mode, the
control system’s basic task is to
command each
elevator to move up or down, to stop or
start
and to open and close the door. But is has some
constraints as follows:
Each elevator has
a set of 9 buttons on the car control
panel,
one for each floor. These buttons illuminate when
they are pressed and cause the elevator to
visit the
corresponding floor. The
illumination is canceled when
the
corresponding floor is visited by the elevator.
Each floor, except the first and the top
floor, has two
buttons on the floor control
panel, one to request an up-
elevator, one to
request a down-elevator. These buttons
illuminate when they are pressed. The
illumination is
canceled when an elevator
visits the floor, then moves in
the desired
direction.
The buttons on the car control
panel or the floor
control panel are used to
control the elevator’s motion.
The elevator
cannot pass a floor if a passenger wants to
get off there.
The elevator cannot stop at
a floor unless someone
wants to get off there.
The elevator cannot change direction until it
has served
all onboard passengers traveling in
the current direction,
and a hall call 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
simultaneously. It 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 not. It 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.
3. Software design
Due to the random nature of call time,
call locations
and the destination of
passengers, the elevator control
system is a
typical real-time, random logic control system.
Here we adopted collective selective control
method with
siemens PLC S7-200 CPU226 and its
extension modules.
There are 46 input points
and 46 output points in the
system. The IO
points are showed in Table1 and Table 2.
Table
1 Input points
description address
1-8
floor up hall-call I0.0-I0.7
2-9 floor down
hall-call I1.0-I1.7
1-9 floor car-call
I2.0-I2.7, I3.0
1-9 arrival sensor I3.1-I3.7,
I4.0-I4.1
door open button I4.2
door close
button I4.3
door close location switch I4.4
door open location switch I4.5
up leveling
sensor I4.6
down leveling sensor I4.7
fire
switch I5.0
driver operation switch I5.1
touch panel switch of car door I5.2
overload I5.3
Forced speed changing
switch I5.4
full load I5.5
Table 2 Output
points
description address
1-8 floor
up hall-call lamp Q0.0-Q0.7
2-9 floor down
hall-call lamp Q1.0-Q1.7
1-9 floor car-call
lamp Q2.0-Q2.7, Q3.0
up moving lamp Q3.1
down moving lamp Q3.2
Seven segment LED
display of Q3.3-Q3.7
elevator’s position
Q4.0-4.1
door opening Q4.2
door closing
Q4.3
up moving Q4.4
down moving Q4.5
full load lamp Q4.6
high speed operation
Q4.7
low speed operation Q5.0
acceleration
of starting Q5.1
deceleration of braking
Q5.2-Q5.4
alarm beeper Q5.5
About software
designing, we adopt the modularized
method to
write ladder diagram programs. The
information
transmission between modules is achieved by
intermediate register bit of PLC.
95
The whole program is mainly
composed of 10 modules:
hall-call registration
and display module, car-call
registration and
display module, the signal combination
module,
the hall-call cancel module, the elevator-location
display module, the floor selection module,
the moving
direction control module, the door
openclose module, the
maintenance operation
module and the dispatching
module under
parallel running mode.
The design of the
typical modules is described as follows:
3.1. Hall-call registration and display
There are two kinds of calls in an elevator:
hall-call
and car-call. When someone presses a
button on the floor
control panel, the signal
will be registered and the
corresponding lamp
will illuminate. This is called
hall-call
registration.
When a passenger presses a
button in the elevator car,
the signal will be
registered and with the corresponding
lamp
illuminated. This is called car-call registration.
Figure2 shows the ladder diagram of up hall-
calls
registration and display. The self-lock
principle is used to
guarantee the calls’
continuous display.
Figure 2 up hall-call
registration and display
Figure 3 The combination of the
calls
3.2. The collective selection
of the calls
Here the collective
selection control rules are used. As
showed in
Figure3, M5.1-M5.7, M6.0 and M6.1 are
auxiliary relays in PLC. They denote the
stopping request
signal of 1
st
to
9
th
floor respectively. The auxiliary
relay
M6.2 denotes the elevator driver’s
operation signal. When
there is a call in a
certain floor, the stopping signal of
corresponding floor will output. When the
elevator is
operated by the driver, the hall-
calls will not be served.
And the elevator
cannot pass a floor at which a passenger
wishes to alight.
3.3. The
cancellation of the calls
The program of this
module can make the elevator
response the
hall-calls which have the same direction as
the car’s current direction, and when a hall-
call is served,
its registration will be
canceled. The ladder diagram of up
hall-calls’
cancellation is showed in Figure4.
In Figure4, the auxiliary relay M4.0 is the up
moving
flag of the elevator. When the current
direction of the
elevator is up, M4.0’s
contacts are closed; on the contrary,
when the
current direction of the elevator is down, M4.0’s
contacts are opened. M0.1 to M0.7 denotes the
car-calls’
stopping request signal of floor 2
to floor 8 respectively.
This program has two
functions:
(1) Make the elevator response the
normal down
hall-calls when it is moving down,
and when a down
hall-call is served, its
registration is canceled.
(2) When the
elevator is moving up, the corresponding
floor’s down hall-call it passing by is not
served and the
registration is remained.
Figure 4 The cancellation of up calls
96
The cancellation of down hall-
calls is reversed with up
hall-calls.
3.4.
Elevator’s direction
The elevator may be
moving up or down, depending
on the
combination of hall-calls and car-calls. The
following ladder diagram in Fig.5 illustrates
that the
elevator will move up.
Figure5 shows that when the calls
corresponding floor
is higher than the
elevator’s current location, the elevator
will
go up. Here the auxiliary relay M4.0 is used as
the
up-moving flag. When the elevator is
moving up, the
up-moving lamp is illuminated,
so the M4.0 is connected
on. When the elevator
arrives the top floor, the up-moving
lamp is
off and the timer starts. After 0.2s, the M4.0 is
disconnected, the up-moving display is off.
Here we used
M4.0 to replace Q3.1 which can
ensure the cancellation’s
reliability.
Figure 5 Up moving of the elevator
3.5. Elevator’s floor-stopping
Figure6 shows the ladder diagram of the
elevator’s
floor-stopping function.
As
showed in Figure6, M6.4 is the flag of
floor-
stopping signal. M6.6 is the floor-stopping signal
sent by the driver. M7.0 is the fire signal
sent by the fire
switch. And M6.7 is the
forced speed changing signal.
When either of
these contacts act, the system should send
out
the floor-stopping signal.
4. Minimum
waiting time algorithm
In traffic of
elevator systems, there are two types of
control task usually. The one is the basic
control function
to command each elevator to
move up or down, to stop or
start and to open
and close the door. The other is the
control
of a group of elevators.
The main requirements
of a group control system in
serving both, car
and hall calls, should be: to provide even
service to every floor in a building; to
minimize the time
spent by passengers waiting
for service; to minimize the
time spent by
passengers to move from one floor to
another;
to serve as many passengers as possible in a
given time
[1]
.
Figure 6 The elevator’s
floor-stopping
There are many
dispatching algorithms for elevator’s
group
control. Such as Nearest-neighbor
Algorithm
[2]
,
which the elevator
always serve the closet request next;
Zoning
Algorithm
[3]
which by analyzing the
traffic of
elevator system with unequal floor
and population
demand to dispatch the
elevator; and Odd-even rule,
which an elevator
only serves the odd floor and the other
only
serves the even floor.
The Nearest-neighbor
Algorithm minimizes the length
of the
elevator’s empty move to the next request. it
usually has very small average waiting times,
but
individual waiting times can become quite
large[2]. The
Zoning Algorithm usually used in
buildings which has
heavy traffic situations,
such as the office building at
lunch time.
Compared to the office building and shopping
mall,
the traffic flow of residential
buildings is relatively low
97
and
even in every floor. Secondly, people usually
think of
elevators as purely functional
objects and the experience
of riding an
elevator is time waited for most of them.
Furthermore, there exist immense problems when
attempting to satisfy all requirements.
Considering all of the reasons above, we
adopted the
“minimum waiting time” algorithm
to realize the 2
elevators’ parallel
running
[4]
.
4.1. Evaluation
function
The goal of the “minimum waiting
time” algorithm is
to predict the each
elevator’s response time according to
all
calls, and select the elevator which has the
shortest
response time to serve.
When
there is a call, the system calculates out the
function values of each elevator according the
evaluation
function showed in (1) and (2):
J(*)=Min[J(1),J(2),…,J(n)] (1)
J(i)=T
r
(i)+KT
d
(i)+KT
o
(
i) i=1,2,...,n (2)
J(i) is the
evaluation index of each elevator; T
r
(i)
denotes the time of the elevator directly
moving to the
destination corresponding the
latest call from its current
floor;
T
o
(i) denotes the additional acceleration
and
deceleration time of a floor-stop of the
elevator; T
d
(i)
denotes the average
time of the passenger boarding and
alighting
the elevator; and K is the sum of hall-calls and
car-calls. But when a hall-call and a car call
corresponds
the same floor, the K is only
calculated one time.
4.2. Calculation of
minimum waiting time
In equation (2), K
is a certain value, T
o
and T
d
can
be
obtained by means of statistics. T
r
= T*L, where T denotes
the average time of the
elevator passing by one floor; L
denotes the
desired floors of the elevator from current
floor to the hall-call floor.
In order to
calculate the L value, we defined the 2
elevators are A and B respectively;
Y
A
,Y
B
denotes the
current
floor of elevator A and B respectively. H is the
corresponding key value when a hall-call
button is
pressed, and H=floor number of the
hall-call.
We defined 4 tables for the PLC
realization: up
hall-call registration table,
down hall-call registration
table, car-call
registration table of A and car-call
registration table of B. When a certain call
button is
pressed, its floor value is recorded
in corresponding table.
Here we take elevator
A as an example. First, define
the variable
M
A
, M
B
and M
W
. Where
M
A
, M
B
denotes the
extreme
value of car-calls with same direction of A or B’s
movement respectively.
When elevator A is
up-moving, set M
A
is equal to the
maximum value in car-call registration table
A; when
elevator A is down-moving, set
M
A
is equal to the
minimum value in
car-call registration table A.
M
W
denotes the extreme value of hall-calls with same
direction of A’s movement.
When elevator A
is up-moving and up-hall-call
value≥Y
A
, set M
W
=0; otherwise,
set M
W
is equal to the
minimum value
in up-hall-call registration table A. When
elevator A is down-moving and up-hall-call
value≤Y
A
, set
M
W
=0; otherwise,
set M
W
is equal to the maximum value
in down-hall-call registration table A .
Thus, we can determine the L value according
to Y
A
, H,
M
A
and M
W
.
There are 3 situations:
(1) When the hall-
call’s direction is opposite to
elevator A’s
movement:
L=|Y
A
-M
A
|+|M
A
-H|
(3)
(2) When the hall-call’s direction is same
as elevator
A’s movement and it is in the
front of elevator A:
L=|Y
A
-H|
(4)
(3) When the hall-call’s direction is same
as the
elevator A’s movement and it is in the
back of elevator A:
L=|Y
A
-M
A
|+|M
A
-M
W
|+|H-M
W
|
(5)
So the i-th floor’s minimum waiting time
can be
calculated by (6) as follows:
Time(i)=TL(i)+KT
d
(i)+KT
o
(i)
i=1,2,...,n (6)
When the calls change
during the operation of
elevators, the system
calculates the minimum waiting
time of each
elevator. Then it allocates the current call to
the elevator which has small value. When the
each
elevator has the same value, then the
current call is prior
to elevator A.
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
98
the up-
moving lamp of elevator A, and the car-calls
extreme value is saved in VB120.
Figure 7 The car-calls extreme value
calculation
of elevator A
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 (1998). “A
Fuzzy Elevator Group Controller With Linear
Context
Adaptation”. IEEE World Congress on
Computational
Intelligence. Vol. 12, No. 5,
pp.481-486.
[2] Philipp Friese, Jorg Rambau
(2006). “Online-optimization
of multi-elevator
transport systems with reoptimization
algorithms based on set-partitioning models”.
Discrete
Applied Mathematics .No. 154,
pp.1908-1931.
[3] Zheng Yanjun, Zhang Huiqiao,
Ye Qingtai, Zhu
Changming. (2001). “The
Research on Elevator Dynamic
Zoning Algorithm
and It's Genetic Evolution”. Computer
Engineering and Applications, No. 22,
pp.58-61.
[4] Xiaodong Zhu, Qingshan Zeng
(2006). “A Elevator Group
Control Algorithm
for Minimum Waiting Time Based On
PLC”.
Journal of Hoisting and Conveying Machiner, No. 6,
pp.38-40
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 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)
Average Maximum
Down–peak 63.20 240.33
Up–peak 52.78
235.26
Other 43.25 215.43
Table 4
Average and maximum waiting time(reformed)
Average Maximum
Down–peak 30.12 203.33
Up–peak 27.81 195.20
Other 37.32 186.43
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