四层电梯控制系统英文文献
物流管理专业排名-湖南省城市学院
Elevator Control System
EET 275
Experiment #9
Instructor: Roger A. Kuntz
Office: 174
REDC
May 1, 2008
Richard Baker
Mike Penfield
Eric Williams
Table of Contents:
Executive Summary………………………………………………….3
Discussion of the Nine Step Process of
Programming………………3
Modular
Options…………………………………………………….4
Discussion
of the Design…………………………………………….5
Discussion of Teamwork…………………………………………….10
Conclusion…………………………………………………………...11
Wiring Schematic……………………………………………………12
Program……………………………………………………………..13
2
Executive Summary
The purpose
of this lab was to design and implement a three
floor elevator control
system. The system was
implemented using the nine step procedure for
programming
PLCs from the EET 275 text book.
Each floor was to have its own illuminated
pushbutton to call the elevator to a demanded
floor. The elevator door was to be
simulated
with the use of a 12VDC bench-top mounted motor
that opened, stayed open,
and reversed after
ten seconds at each floor after being called. A
12VDC motor was used
to hoist the elevator and
IR sensors were used to indicate when the elevator
was at the
floor in position to open. The
entire system included a master start-stop circuit
to ensure
that the operation could be
completely shutdown for emergencies or repair.
The final
aspect of this experiment was to
intelligently organize the ladder logic to make
troubleshooting easier. To do this, all of
the subroutine jumps were placed in the second
ladder and the actual subroutines in its
respective ladder.
Discussion of the
Nine Step Process of Programming
The
first step of the nine step procedure of
programming PLCs is to define the
process to
be controlled. As stated in the executive
summary, there were three floors, a
simulated
door opened and closed when the IR sensor was
engaged, and a master start-
stop circuit
stopped the hoist system.
The second step
of the process is to make a sketch of the process
operation.
Fig. 9-1, System Layout Sketch
3
Creating a written step
sequence list for the process is the third step of
planning a PLC
program. Ladder two in the
program ladder diagram explains step three well.
The way
the subroutines are ordered is the
order in which we intended on working through the
experiment. The first in the process was the
jump to the floor sensor subroutine for all of
the floors. The next jump went to the floor
which housed the code for the call buttons.
The hoist subroutine was next in line which
actually controlled the hoisting motor. After
the elevator was hoisted, the door subroutine
commenced. The last subroutine in the
program
was a master reset subroutine which reset all of
the used timers.
The fourth step is to add
any sensors to the sketch, and the only sensors
which
were used were on each of the floors to
stop the elevator. The fifth step is to ad manual
controls. The manual controls used in the
design were an emergency stop button, a start
button to start the process, and the call
buttons for all three floors.
The sixth
step makes the point to consider safety and make
additions and
adjustments as necessary.
Safety is a large concern in an elevator process
however this
model did not really represent
many of the extra processes to protect the riders.
Such
processes may be an overweight for the
car protection, emergency call button, telephone,
and even fall protection. This emergency stop
also satisfies step seven, to include master
stop switches to ensure a safe shutdown.
After the first seven steps, a rough version
of the ladder logic diagram was created
for
step eight of the process. Step nine instructs to
consider the “what ifs” where the
process
sequence may go astray. There were many what if
questions asked during this
lab experiment.
One of which was what if more than one call
buttons were pressed at
once, another was if
the third floor were called before the second and
the car was on the
first, would the car stop
at the second before the third, or continue
traveling to the third
and come back down for
the second.
Modular Options:
There were a total of eight modular options
presented in the experiment
instructions.
These options consisted of a door interference
limit switch, an elevator stop
switch for
loading and unloading, an alarm push button, a set
of floor queue lights, up or
down tones for
sightless passengers, a faulty sensor or button
monitor and detector, a
floor number
enunciator LED display, and finally a fire
operation switch.
The door limit switch
would have been hard to emulate with the provided
equipment however it would have been possible
if the motor were either geared down or
slowed
to a lower RPM. The elevator stop switch for
loading and unloading would
temporarily stop
the door motor after being opened to allow for the
extra time needed for
boarding. The function
of the alarm switch would sound an alarm if there
was a
functional problem with the elevator
system which was not picked up by any pre coded
alarms. For example, if the motor stopped,
the passenger could sound an alarm manually
for assistance. The floor queue lights would
display that the elevator was on a floor and
stopped temporarily. Two different
frequencies would be needed to produce the
sightless
passenger tones. Possibly the “up”
sound would be a higher frequency than the “down”
tone. The faulty sensor protection would be
written into the code to trip if the elevator
were operating wrongly. The floor numbers
would display the floor of which the
elevator
was on every floor and the fire operation switch
would be a manual override.
4
Discussion of the System
Five
different functions were required for the elevator
to work properly and after
a function was
completed the next could start. After a floor is
sensed by the sensor, the
elevator car could
be called to another floor. With a floor called,
the car hoist motor
could operate, lifting the
car up or letting it down. When the car sensor
sensed that the
car was at the correct floor,
the door openclose function could run. The last
function
reset the system so the elevator
could be called to a different floor. Since there
are five
functions, five different subroutines
were put in place in the program.
In
the main ladder, Fig. 9-2, a startstop seal
circuit was put in place to control the
system.
Fig. 9-2, Main Ladder
Diagram
With the system started, the
first subroutine, floor sense, could operate. As
in Fig. 9-3,
when a sensor senses the car, its
output coil activates, and when a floor is sensed,
the
subroutine returns to the main ladder.
5
Fig. 9-3, Floor Sense
Subroutine
Next, the elevator car
could be called to a specific floor when the call
floor
subroutine, Fig. 9-4, operates.
Fig. 9-4, Call Floor Subroutine
When
the First, Second, or Third floor call button is
pressed, its output coil turns on,
sealing the
button. The output also deactivates the other two
floor’s rungs. With a floor
called, the
program returns to the main ladder diagram.
6
The master stopstart seal circuit was
included in the hoist subroutine, Fig. 9-5, to
stop all action since this subroutine worked a
moving part. Since the car could go up or
down, it was obvious that the only direction
the car could go from the first floor was up,
and likewise, the car could only go down from
the third floor. The difficult part of this
subroutine was to discriminate which direction
the car would go from the second floor.
The
floor sense output aided with this problem. When
the second floor sensor sensed the
car, the
second floor sensed output deactivated the second
floor call button. So that if
first is called
from the second floor, the motor let the car down,
or if the third floor is
called, the motor
pulled the car up. When the floor called and the
floor sensor of the
floor called is true, the
hoisting complete output turns on and deactivates
the up and down
outputs, it also allows the
program to return to the main ladder.
Fig. 9-5, Hoist Subroutine
Once
the car reached the floor it was called to, the
doors had to open, stay open
for ten seconds
and then close. Three timers and a master timer
used in this subroutine,
7
Fig.
9-6. When the floor that was called was sensed, a
five second timer was activated.
While the
timer was timing, the motor would run, opening the
doors. The done bit of the
first timer
activated the next timer, which held the doors
open for ten seconds. The done
bit from that
timer activated the motor to close the doors. The
master timer started its
twenty seconds when
the first timer started, when the twenty second
timer was done, it
allowed a return from the
doors subroutine.
Fig. 9-6, Doors
Subroutine
8
The
completion of the doors subroutine signified that
the process was over and
needed to be reset.
The next subroutine of the program reset the
outputs so that a new
floor could be called
and reset all the timers, Fig. 9-7. When these
resets were complete,
the whole process was
finished, awaiting new orders for a floor.
Fig. 9-7, Reset Subroutine
9
Discussion of Teamwork
One of
the key objectives of this experiment was to
demonstrate the advantages of
working together
as a team. The three major components for the
successful execution of
this lab were the
planning, the programming, and the wiring of the
PLC. It was decided
that we would share
responsibility for all components of the lab.
First, we came up with
our own ideas
individually and then came together and work
towards a common solution
together. For the
most part, our final solution was the combination
of all of our ideas
instead of each person
being responsible for their own component.
During the planning portion of our project we
all came up with the needed inputs
and outputs
and wrote a PLC program individually. We then
compared notes and
discussed what the best
solution would be and why. It was decided to take
this project
one step at a time instead of
trying to program and wire it all at one time. In
past
experiments we had felt a little
overwhelmed trying to program and wire the
complete
project on the first try.
First, we programmed and wired the PLC to
operate the hoist motor and the door
motor
only and tested their operation. Next we analyzed
the operation of the floor
sensors by
measuring the output voltage of the sensor while
holding a white piece of
paper in front of the
sensor and also by observing the output with
nothing in from of the
sensor. After we were
confident of the operation of the sensors, we
added them to the
PLC program. Next the call
buttons were wired so that the lamp would light
when the
user pressed the pushbutton to call
the elevator. Finally, after all of the external
wiring
was finished and its operation verified
we programmed all of the subroutines needed to
successfully demonstrate the operation of the
elevator into the PLC. This idea of taking
this complex project step by step in small
increments enabled us to understand the
operation of the elevator more completely.
This practice of team building goes a
long way in promoting collaboration and
understanding across technical disciplines.
It also promotes cross training so that if one
person in the team goes down, the others can
pick up the project and proceed with
minimal
interruption or down time. The ability to be a
flexible member of a team is an
absolute must
to be competitive in today’s manufacturing
environment and working
together on this
experiment was a good example of how to do it
successfully.
10
Conclusion
This lab was very interesting to partake
in, in a sense that a modeled elevator was
taken and programmed to operate much like a
real world functioning elevator. The
greatest
point learned from the experiment was to
understand the great complexity of
something
that many people take for granted. An elevator
system is extremely complex
and experiment
nine only modeled the core functions. To do so,
the nine step process of
PLC design was
followed from start to finish allowing for a
thoroughly complete system.
The elevators
logic was designed in accordance to the
instruction list however the
addition of other
modular options were not applied to the system but
observed as possible
inputs to further the
system. Teamwork has been a large part of every
lab experiment and
lab #9 was no exception.
Tasks were divided up accordingly, and
communication within
the group on the
processes taken place was vital to the completion
of the elevator system.
As far as the nine
step process went, all of our personal sketches
and drawings of
the setup and prospected
design of the electronics were saved for reference
for the actual
design process. Having
strictly followed the process in this lab, the lab
group seemed
more organized than usual.
However, during previous labs the process was
followed,
maybe not that strictly, but the
main steps, especially making a sketch and writing
the
process sequence, were followed. This
ended up working out well for the group due to
the complexity of the elevators system and
many features provided.
With all intentions
of creating an exact elevator system, the
guideline specs were
followed carefully.
However, not every aspect of the elevator was
covered by the final
design. An example of
this is how only one floor can be traveled to at
one time by the
elevator car. What this means
is that if two buttons were pressed at one time,
the first
floor in which the car arrived at
would also be the last until another button were
hit. This
would pose a large problem in real
life because the call buttons could only be hit
after the
doors have been shut and the system
has been reset. If this problem were solved
earlier
on in our experiment, it would have
been nice to apply some of the modular options to
the overall program. Although these options
were not completed, there is no doubt that
any
one of the extra applications could have been
completed successfully.
The final part of
this experiment which played a large role in its
completion was
how well the team worked
together. Communication within the group was most
important in taking the design from our ideas,
to paper, to the computer, and finally to
wiring up the overall system. We worked
efficiently and affectively on this lab and are
proud of the overall performance of the
elevator. A lot was learned from this experiment
by every member; from how the core operation
of an elevator works as well as the
potential
“add-ons” to make the system work better and
safer. Even though this was a
scaled model,
it is interesting to think of how closely related
the designed system is with
say an 80 floor
elevator system. Experiment nine was a great test
of the knowledge
learned in the EET 275 class.
11
IO
Diagram
12