Modern Media PLCs User Manual
Beginner’s Guide
to
PLC
Programming
How to Program a PLC (Programmable Logic Controller)
By Neal Babcock
modernmediaonline.com
Copyright 2008 Modern Media
Table of Contents
Introduction to PLCs.....................................................................................................................3
Ladder Logic.................................................................................................................................3
The Dialect of PLCs .....................................................................................................................5
Equivalent Logic ...........................................................................................................................7
Scan Time ....................................................................................................................................9
The Automated Drill Press..........................................................................................................10
Sequence of Operation...............................................................................................................11
Operator Station .........................................................................................................................13
I/O Listing ...................................................................................................................................14
Inputs......................................................................................................................................14
Outputs ...................................................................................................................................15
Internal Coils...........................................................................................................................15
The Program ..............................................................................................................................16
Machine Safeties ....................................................................................................................16
Pilot Light Test ........................................................................................................................18
Indicate The System Is Operational........................................................................................19
Machine Operation Mode........................................................................................................19
Run The Spindle Drive Motor..................................................................................................20
Indicate The Spindle Drive Is Running....................................................................................20
Run The Infeed Conveyor.......................................................................................................21
Ensure There Are No Parts In The Machine ...........................................................................21
Ensure All Components Are At Home..................................................................................... 22
Begin The Cycle .....................................................................................................................22
Lower The Stop Gate.............................................................................................................. 23
Run The Main Conveyor .........................................................................................................23
Indicate The Part Is In Place...................................................................................................24
Clamp The Part In Place.........................................................................................................24
Lower The Spindle..................................................................................................................25
Drilling Operation Is Complete ................................................................................................ 26
Return The Spindle To Its Home Position...............................................................................27
Machine Cycle Is Complete ....................................................................................................28
Fault Detection And System Diagnostics ................................................................................29
Personnel Safety Guard Door.................................................................................................29
Low Compressed Air Pressure ...............................................................................................30
Motor Starter Overload ...........................................................................................................31
Latch The Motor Overload Detection ......................................................................................32
Indicate A Motor Overload Condition ......................................................................................32
Jammed Part Detection ..........................................................................................................33
Latch The Part Jammed Detection .........................................................................................34
Indicate A Part Jammed Condition .........................................................................................34
Monitor The Drill Time.............................................................................................................35
Summarize The Fault Conditions............................................................................................ 36
13 Marks Of A Well Written Program .........................................................................................37
General PLC Tips.......................................................................................................................38
The Automated Drill Press in Rockwell Automation’s RSLogix 500 ...........................................39
Beginner’s Guide to PLC Programming How to Program a PLC (Programmable Logic Controller)
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2
Introduction to PLCs
Nearly all the industrial equipment that you find in a modern manufacturing facility shares one
thing in common - computer control. The most commonly used controller is the PLC, or the
Programmable Logic Controller, using a programming language called Ladder Logic. The
language was developed to make programming easy for people who already understood how
switches, relay contacts and coils work. Its format is similar to the electrical style of drawing
known as the “ladder diagram”.
Originally, there were only a few functions available in this language, but as times have
progressed, many more higher-level functions have been introduced. We are going to stick to
the basic, commonly used functions here. Also, this text will not replace the user's manual that
comes with a PLC, but it will give you a big head start if you have never programmed a PLC.
This course is intended to provide an introduction to the programming methods used in PLCs
and give the reader a solid, basic understanding of the language of Ladder Logic.
After you complete this course, you may be interested in learning about hardware-specific
software and programming techniques. Modern Media offers a book entitled PLC Programming
Techniques How to Program an Allen-Bradley SLC 500 with Rockwell Automation’s RSLogix.
This ebook shows, step-by-step, how to create a program from scratch in Allen-Bradley’s
RSLogix 500. To learn more, please visit http://www.modernmediaonline.com.
Ladder Logic
I have summarized the terms and techniques you need to know if you are going to work with
ladder logic. It is not a comprehensive summary, as that would take volumes of text, but if you
are just starting out, the information in this book will be very helpful. Every PLC programmer, no
matter what skill level, must have learned the principles described in this book at one point in
time. There is simply no way around it.
I have included a program for a simple machine that lets you really understand how Ladder
Logic works.
To effectively write a program, or even edit one, the programmer must know how to visualize the
effects of the changes he will make. In other words, you have to be able to look at the logic “on
paper” and imagine how it will work when it is entered into the PLC. This course will teach you
how to do that.
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There are many types of PLCs, and differences among PLCs, but what is discussed here should
be common to all types. After you read and understand this, you will have a clear understanding
of the structure of this type of programming. In the real world of industrial automation, the
methods presented in this document may be all that many people will ever need to know.
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The Dialect of PLCs
Lets' define some terms and symbols:
BIT - an address within the PLC. It can be an input, output or internal coil, among others.
RUNG - A section of the PLC ladder program that terminates in an output function of some type.
HARDWIRED INPUT - a physical connection to the PLC from an input device (switch or sensor,
etc.)
A hardwired input is labeled INPUT in our example.
HARDWIRED OUTPUT - a physical connection from the PLC to an output device (relay or pilot
light, etc.)
A hardwired output is labeled OUTPUT in our example.
INTERNAL COIL
This is a programmable bit used to simulate a relay within the PLC. The internal coil has no
connection to the outside world. It does not connect to an output card. Internal coils are used to
store information. The “contacts” of this “relay” can then be used multiple times in other parts of
the program.
An internal coil is labeled COIL in our example.
--] [-- Normally Open Contact
When used with a hardwired input, this instruction is off until there is a voltage applied to the
input. The bit address then goes high, or on, and the instruction becomes “true.” It works the
same way when it has the same address as an internal coil, except that the coil must be turned
on by logic in the program.
--]/[-- Normally Closed Contact
This is an inverted normally open contact. When used with a hardwired input, this instruction is
"true" until there is a voltage applied to the input. It then goes low, or off, and becomes “false.” It
also can be used with an internal coil, becoming true when the coil is off and becoming false
when the coil is on.
-( )- Output Coil
When used with a hardwired output, this function is off until the logic in the program allows it to
turn on. It then becomes “true”, and will energize the device that is wired to the respective
output. If it is used as an internal coil, it will toggle the instructions associated with it. That is, it
will close a normally open instruction and open a normally closed instruction.
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+---------+
TIMER |
+-- SEC---+ Timer
This function is used to supply a programmable delay. It requires the use of its "timer finished"
bit, like a time delay relay uses its contact.
+---------+
COUNTER |
+-- 000---+ Counter
The counter function is used to count events. It could be used to keep track of machine cycles,
count parts, etc. It can be programmed with a preset value that triggers another event when the
count is reached.
TRUE - An indication the a bit is “on”. If you press a pushbutton switch that is wired to an input,
then the bit is said to be true. Also, if the logic in a rung turns on the output of the rung, then the
rung is said to be true.
FALSE - Without stating the obvious, this is the opposite of true.
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Equivalent Logic
In its elementary form, PLC logic is very similar to the hard-wired logic you would find in an
electrical ladder diagram.
For example, if you wanted to turn on a light with a momentary pushbutton, you would wire it like
the circuit below.
When you press PB1, the pilot light PL1 lights up.
Now let's do the same thing in a PLC. To duplicate the hardwired circuit on a PLC, you would
wire the switch PB1 to an input and wire the light PL1 to an output. Each PLC manufacturer
gives you the details of wiring their particular modules. The I/O (hardwired inputs and outputs) is
set up like this:
- There is a “PB1” pushbutton switch wired to INPUT1 of the PLC.
- There is a “PL1” pilot light wired to OUTPUT1 of the PLC.
|
| INPUT1 OUTPUT1
[---] [------------------------------------------------------( OUT )
|
PB1 PL1
Now let’s examine the sequence of events. When you first turn on the PLC, the PB1 pushbutton
is off, or false. Therefore, the PL1 output is off. Pressing PB1 will make INPUT1 true,
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OUTPUT1 will come on and the light will be energized. It will stay on only as long as you hold
the button in. Just like electrical current has to flow through the switch to turn on the light in the
hardwired circuit, the logic has to "flow" through the normally open instruction (which is closed
when you press the switch) of INPUT1 to energize the output that turns on PL1.
The programming terminal display will look something like this as you hold in PB1. The yellow
highlight indicates the bit, or address, is “on” or “true”.
|
| INPUT1 OUTPUT1
[---] [------------------------------------------------------( OUT )
|
PB1 PL1
Let's look at how a timer works. Suppose you want to delay running a motor for 2 seconds after
you turn on a switch. You can use the input from the switch to run a timer. Program the timer for
the duration you want and then use the "timer finished" bit to turn on your motor. In this
instance, we have configured an "on delay" timing sequence. Two seconds after INPUT1 is on,
the TIMER1 will turn on its "finished" bit and the motor will run.
Note that there is no "off delay" here. As soon as the start switch is released, the "timer finished"
bit will drop out and the motor will stop. With a little creativity, you can combine timers to provide
any timing function you need.
|
|
|
|
[---] [---------------------------------------------------+--2SEC------+
|
|
|
|
|
|TIMER1 OUTPUT1
[---] [-------------------------------------------------------( OUT )
Start +--Motor -+
Motor | Start |
PB1 | Delay |
INPUT1 TIMER1 |
Motor
Start Run
Delay Motor
One nice feature of PLCs is that you can document each bit in the program. In the example
above, “INPUT1” is somewhat meaningless on its own. After you add the descriptive text “Start
Motor PB1”, things make more sense.
Most PLCs are programmed via a Windows based terminal. Editing, deleting or adding to the
ladder logic is usually pretty straightforward. You use the arrow keys or the mouse to add
instructions, change addresses or comments, etc. We won’t cover the specifics of keystrokes
here, but will concentrate on understanding the ladder logic.
These terminals will usually have the capability of programming online or offline. If you are
making changes in online mode, be aware that any changes you make and save (or upload) will
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alter the program that is being used to run the machine. This requires great care and a full
understanding of what will happen when you make the change.
Scan Time
One critical difference between a PLC program and the equivalent electrical circuit is the issue
of scanning. It works like this in most PLCs:
The PLC looks at the state of the inputs and stores that information in a temporary buffer. Then,
it ignores what is happening electrically at the inputs. The PLC will use the information in the
temporary buffer to execute the logic in the program. It will solve the logic from top to bottom,
determining the truth of each rung, and turn on or turn off the appropriate addresses in the
temporary buffer. When it reaches the last rung in the program, the PLC will use the data in the
temporary buffer to turn on or turn off the corresponding outputs. The scan cycle is complete,
and the PLC will once again look at the inputs. The amount of time this takes is called scan
time, and is measured in milliseconds.
Stated more simply, the PLC reads the inputs, performs the logic and adjusts the outputs as
needed.
In some newer PLCs, such as Rockwell’s ControlLogix platform, it doesn’t work that way. The
inputs are updated during the program scan. In high-speed applications, such as bottling or
pharmaceutical lines, this can cause problems.
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The Automated Drill Press
Now let’s jump right into a project. The best way to learn a programming language is to look at a
real world example. However, before you can do any programming, you must have a clear
understanding of how the machine works. Let’s say a furniture manufacturer needs to drill a 3/8”
hole in a certain spot on a piece of wood. The entire process needs to be automatic. The
mechanical and electrical engineers bring you an isometric drawing like the one shown here.
Mechanical details have been omitted for clarity, as is often the case in a “concept” drawing.
The main conveyor will transport the part into the machine where the part will meet a
pneumatically actuated stop gate. At that time, another pneumatic cylinder will actuate a clamp
that will push the part back against the conveyor wall. This will hold the part in place during the
drilling process. Photocells will verify that the part is in position; the spindle will lower and
proceed to drill a hole in the part. After the hole has been drilled and the spindle has retracted to
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its home position, the clamp will release, the stop gate will raise and the part will exit. The cycle
then repeats itself for each part that comes down the line.
Sequence of Operation
Here is a more detailed explanation of the drilling process:
When the machine starts, the stop gate lowers
and the part is moved into position by the main
conveyor.
Optical sensors (photoeyes) determine when
the part is in place.
When the part is positioned correctly, a clamp
extends to hold the part in place.
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The spindle of the drill press is lowered, and
the hole is drilled in the part.
A sensor in the drill press spindle tells the PLC
when the spindle has reached the end of its
travel.
After the hole is drilled, the spindle retracts,
the clamp retracts, the stop gate is lifted and
the part is carried out of the machine by the
main conveyor.
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Operator Station
An operator station for the machine might look like this. Though the device name, such as PB1,
would not show up on the actual station, it is a good idea to show them on your drawing.
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I/O Listing
It is important to define the I/O (inputs/outputs) before you begin to program. Do not skip this
crucial step. Listed below is the I/O arrangement for the Automated Drill Press program.
Inputs
Address Device Name Device Type Description
INPUT1 PB1 pushbutton switch Reset System
INPUT2 PB2 pushbutton switch Start System
INPUT3 PB3 pushbutton switch Stop System
INPUT4 SS4 selector switch System in Auto Mode
INPUT5 CR1 relay Emergency Stop Cleared
INPUT6 PB6 pushbutton switch Start Press
INPUT7 PB7 pushbutton switch Stop Press
INPUT10 PB10 pushbutton switch Raise Spindle
INPUT11 PB11 pushbutton switch Lower Spindle
INPUT12 PB12 pushbutton switch Hold Part In Place
INPUT20 MS1AUX aux contacts on motor starter Infeed Conveyor Running
INPUT23 MS2AUX aux contacts on motor starter Main Conveyor Running
INPUT24 MS5AUX aux contacts on motor starter Drill Press Running
INPUT26 LS26 limit switch Guard in Place
INPUT27 PS27 air pressure switch Air Pressure Normal
INPUT31 PSC31 photo-electric switch Placed in X-Axis
INPUT32 PSC32 photo-electric switch Placed in Y-Axis
INPUT33 PSC33 photo-electric switch Part at Home
INPUT34 PSC34 photo-electric switch Part Cleared
INPUT35 PRS35 proximity switch Spindle Raised
INPUT36 PRS36 proximity switch Spindle Lowered
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Outputs
Address Device Name Device Type Description
OUTPUT1 MS1 motor starter Run Infeed Conveyor
OUTPUT2 MS2 motor starter Run Main Conveyor
OUTPUT5 MS5 motor starter Run Drill Press
OUTPUT6 DRV1 variable speed drive Raise Spindle
OUTPUT7 DRV1 variable speed drive Lower Spindle
OUTPUT11 SOL11 solenoid Hold Part in Place
OUTPUT12 SOL12 solenoid Lower Drilling Stop Gate
OUTPUT20 PL20 pilot light System Running
OUTPUT21 PL21 pilot light Drill Press Running
OUTPUT22 PL22 pilot light Part in Place
OUTPUT23 PL23 pilot light Part Jammed
OUTPUT24 PL24 pilot light Motor Overload Detected
OUTPUT25 PL25 pilot light Guard Open
OUTPUT26 PL26 pilot light Low Air Pressure
Internal Coils
Address Description
COIL1 System Running
COIL2 Pilot Light Test
COIL4 System in Auto Mode
COIL5 System in Manual Mode
COIL20 No Part In Machine
COIL21 Machine at Home
COIL22 Machine in Cycle
COIL23 Drilling Operation Complete
COIL24 End of Machine Cycle
COIL34 Part Jam Detected
COIL35 Excessive Drill Time Detected
COIL40 Motor Overload Detected
COIL50 System Fault
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The Program
Now that you understand what has to be done and how it is to be accomplished by the
mechanical equipment, you can begin writing the program.
The text in the fixed font is basically the information that you would see if you were looking
at the monitor of the computer or a printout. In actual practice, the fonts used in PLC software
vary widely. For the purposes of this book, we want to easily differentiate the program logic from
our explanations of the logic.
A series of asterisks (*****) indicates a "rung comment." This is descriptive text added to the
program, and is seen on the programming monitor, but has no affect on the logic. For purposes
of this manual, I have placed additional explanations between rungs.
Use a title to name the program and include any general information.
|
| | |
| | AUTOMATIC DRILL PRESS MACHINE CONTROL |
| | PRODUCTION LINE #3 |
| | REVISION 2 |
| |__________________________________________________________|
Machine Safeties
It is best to start a program by evaluating any safety switches and setting a master bit. This type
of bit is what we call an internal coil. It has no hardwired connection to the outside world. In this
case, a latch is used to set an internal “System Running” bit. The “latch” is accomplished by
putting a normally open contact around the Start System pushbutton input.
If the emergency stop is clear, and the machine guard is in place, and there is no system fault
the operator may press the start button to set the latch. If the stop button is pushed or a
previous conditions ceases to exist, the “System Running” latch will drop out.
Most of the time, the order of the bits in a rung doesn't matter. We could have rearranged any of
the bits in this rung, though we would still have to put the latch around the Start pushbutton. The
PLC wouldn't care and the output coil would still respond the same. However, to make the rung
easier to read, I try to place bits from left to right in order of importance. If the E-Stop is not
cleared, then nothing else should matter anyway. Having the safety guard in place is more
important than a system fault. Now, if those requirements have been met, we can press the start
button. And we don't care about the stop button until we have pushed the start button.
Note the instruction used for the input of PB3, the Stop System bit. It may seem backwards at
first, since a hard-wired circuit would use the normally closed contacts of the switch. In fact, the
____________________________________________________________
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switch is wired in the failsafe position, using the normally closed contacts as the input to the
PLC.
The E-Stop and the guard limit switch are called "safety interlocks." NEVER rely on a PLC to
stop a machine if a contact of a safety interlock is open. ALWAYS use an interlock in a
hardwired, fail-safe circuit. Use additional contacts from the switches and wire them to inputs of
the PLC so that it knows the machine is to be stopped, or has stopped.
It is very important to label the bits properly. Arrange the verbs and nouns correctly. If you do,
the rung will read like a sentence. You can look at this rung and say “If the Emergency Stop is
Cleared and the Guard is in Place and there is no System Fault and the Start System button is
pressed and the Stop System button is not pressed the System Running coil will turn on and
latch itself”.
There are some simple rules that I always follow when I am writing a description for a bit:
-
Descriptions for bits portray an action.
-
Descriptions are written to describe the “normally open” condition of the bit.
-
The description is true when the normally open instruction of the bit is on.
-
The description is false when the normally open instruction of the bit is off.
| ***** Ensure all machine safeties have been made to allow
| the system to be enabled.
|
|
|Cleared Place System System System System
|CR1 LS26 Fault PB2 PB3 Running
|
1 [---] [--------] [--------]/[----+----] [----+----] [----------( OUT )
| | |
| | |
| |
| |
| |
| +----] [----+
EmergStop Guard in Start Stop
INPUT5 INPUT26 COIL50 INPUT2 INPUT3 COIL1
System |
Running |
COIL1 |
The main reason for setting a master “System Running” bit is to simplify the program. For
example, we don’t want the spindle motor to run if the e-stop has been pressed, or if the guard
is not in place, or if there is a system fault. Rather than putting all of these bits in the rung that
controls the spindle motor, we can summarize all of these bits and make the “System Running”
bit. We can then place just that bit in the rung that controls the spindle motor and know that we
have met all the criteria to allow the spindle motor to run.
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Pilot Light Test
The next two rungs provide a pilot light test. The idea is to turn on all the pilot lights for a couple
of seconds so you can verify that all the lights work. This feature is very handy when you are
troubleshooting a machine.
When the Emergency stop is first cleared, Timer 0 is started.
| ***** Perform a pilot light test upon clearing the
| emergency stop.
|
|
| +- |
|
|
|
2 [---] [----------------------------------------------------+--2SEC--+
|
|
|
EmergStop | Light |
Cleared | Test |
CR1 | Time |
INPUT5 TIMER0 |
Pilot-+
During the period when the Emergency Stop is clear but the timer is not finished, the Pilot Light
Test bit is on. The result is that all the pilot lights will turn on for two seconds after the E-Stop is
cleared. This bit is then used throughout the program.
|
|
|
|Cleared Light Light
|CR1 Test Time Test
|INPUT5 TIMER0 COIL2
3 [---] [-------]/[----------------------------------------------( OUT )
|
EmergStop Pilot Pilot
***** Test the pilot lights.
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Indicate The System Is Operational
Let the operator know that the safeties have been made and the machine is ready to run.
|
|
|
|
|
|
|
|
4 [---] [---+----------------------------------------------------( OUT )
| |
|
|
|
|
[---] [---+
|
|
System Running
Running PL20
Pilot |
Light |
Test |
COIL2 |
***** Indicate the system is operational.
System
COIL1 OUTPUT20
Machine Operation Mode
Here we look at the Manual/Auto Mode selector switch to set the machine mode. You want to
enable certain machine functions in Auto Mode, and disable some in Manual Mode, and vice
versa. Notice how the System Running bit is used. If we lose that bit, such as when the
emergency stop is pressed or the machine guard is opened, neither mode is valid.
The state of the bits below indicates that the System Mode Selector switch is in “Auto”.
|
|
|
|
|
|System Auto Mode Manual
|Running SS4 Mode
| COIL1 INPUT4 COIL5
5 [---] [-------]/[--------------------------------------------( OUT )
|
|
|
|
|System Auto Mode System in
|Running SS4 Auto Mode
| COIL1 INPUT4 COIL4
6 [---] [-------] [--------------------------------------------( OUT )
|
***** Determine the mode of machine operation.
System In System in
System In
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Run The Spindle Drive Motor
This rung turns on the drill press spindle motor. It will come on immediately in automatic mode,
but it can also be controlled by the “Start Press” and “Stop Press” switches in manual mode.
|
| manual mode is provided to allow ease of set-up.
|
|
|
|System in Press
|Auto Mode MS5
| COIL4 OUTPUT5
7 [---] [-----------------------+----------------------------( OUT )
| |
|
|
|Mode PB6 PB7 |
| COIL5 INPUT6 INPUT7 |
[---] [---+---] [---+---] [---+
| | |
| |
| |
| |
| |
| +---] [---+
|
SystemIn Start Stop |
Manual Press Press |
***** Run the spindle drive motor of the drill press. A
Run Drill
Run Drill|
Press |
MS5 |
OUTPUT5 |
Indicate The Spindle Drive Is Running
Turn on the pilot light to let the operator know the motor is running.
|
|
|
|
|
|Press Running
|MS5 PL21
| OUTPUT5 OUTPUT21
8 [---] [---+------------------------------------------------( OUT )
| |
|
|
|
|
[---] [---+
Run Drill DrillPres
Pilot |
Light |
Test |
***** Indicate the drill press is running.
COIL2 |
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Run The Infeed Conveyor
Run the conveyor all the time when the machine is in auto mode. Note the use of the “System In
Auto Mode” bit to ensure all machine safety conditions have been met.
|
|
| in automatic mode.
|
|
|
|
|Auto Mode MS1
| COIL4 OUTPUT1
9 [---] [---------------------------------------------------( OUT )
|
|
System in Conveyor
***** Run the infeed conveyor if the machine is
RunInfeed
Ensure There Are No Parts In The Machine
You want to make sure there are no parts in the machine before you start a cycle. These
photoeyes are positioned so that if they "see" a part, they will turn on the input. A part will break
the beam, the input will turn on and you know you have a part present.
In this rung, we want to make sure there is no part in the machine. The rung will only be true if
all the photoeyes indicate there is not a part present.
|
|
| drilling cycle.
|
|
|
|X-Axis Y-Axis Home Cleared In
|PSC31 PSC32 PSC33 PSC34 Machine
|
10 [---]/[---------]/[---------]/[---------]/[-------------------( OUT )
|
|
Placed in Placed in Part at Part No Part
***** Ensure there are no parts in the machine to start the
INPUT31 INPUT32 INPUT33 INPUT34 COIL20
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Ensure All Components Are At Home
Make sure all the moving parts of the machine are at their initial or "home" position before you
allow any automatic motion to begin. This is standard on most machines.
| ***** Ensure all components are at home.
|
|
|
|In Place Stop Gate Raised Machine
|
|OUTPUT11 OUTPUT12 INPUT35 COIL21
11 [---]/[---------]/[---------] [--------------------------( OUT )
|
Hold Part Drilling Spindle
SOL11 SOL12 PRS35 At Home
Begin The Cycle
Here is the rung that starts the machine's automatic cycle. When the operator goes to Auto
Mode, and there are no parts in the machine, and the machine components are at home, the
cycle will begin. You might ask, "If there is a part in the press, wouldn't the machine start
running as soon as the operator took the part out?" The answer has to be no. You don't want
this machine to start running when someone clears a part. In our case, to remove a part the
operator would have to open the machine guard door in order to physically remove the part, and
that would kick the machine out of automatic mode. He would have to close the guard and start
the machine again.
|
|
| and all components are at home. Bit coil22 will stay on
| during the entire drilling cycle and drop out when an end of cycle
| signal is generated.
|
|
|
|
|
|
12 [---] [---+---] [-------] [---+---]/[--------------------------( OUT )
| | |
| | |
| |
| |
| |
| +---] [-------------+
|
***** Begin the cycle when the part has cleared the machine
No Part End of
System in In Machine Machine Machine
Auto Mode Machine At Home Cycle In Cycle
COIL4 COIL20 COIL21 COIL24 COIL22
Machine |
In Cycle |
COIL22 |
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Lower The Stop Gate
Lower the stop gate when the machine is in cycle.
| ***** Lower the stop gate to stop the part under the
| spindle.
|
|
|
|
|
|
13 [---] [-----------------------------------------------( OUT )
|
Machine Stop Gate
In Cycle SOL12
COIL22 OUTPUT12
Drilling
Run The Main Conveyor
Bring the part into position by running the conveyor in the press. Note that the PLC will stop the
conveyor after the part has been clamped in place (Rung 16), but until that happens, the
conveyor will run.
|
|
|
|
|
|
|
|
14 [---] [---------]/[-----------------------------------------( OUT )
|
System in In Place Conveyor
Auto Mode SOL11 MS2
***** Run the main conveyor unless a part is being clamped.
Hold Part Run Main
COIL4 OUTPUT11 OUTPUT2
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Indicate The Part Is In Place
The photoeye PSC33 is physically placed so that the part will block the beam of the photoeye
when the part is in place. This rung will let the operator know that.
|
|
|
|
|
|
|
15 [---] [---------------------------+-------------------------( OUT )
| |
|
|
|
|
[---] [---------------------------+
Part at Part In
Home Place
PSC33 PL22
INPUT33 OUTPUT22
Pilot |
Light |
Test |
***** Indicate the part is in place and ready to be drilled.
COIL2 |
Clamp The Part In Place
When the part is in position, the PLC will clamp it in place. Since the “Hold Part In Place” bit is
used in Rung 14, the main conveyor will stop running.
Also, a manual method of holding the part has been provided for machine set-up.
|
|
|
|
|
|
|
|
|
16 [---] [---------] [-----------------------------+-------( OUT )
| |
|
|
|
|
[---] [---------] [-----------------------------+
|
|
Machine Home In Place
In Cycle PSC33 SOL11
System in Hold Part |
Manual In Place |
Mode PB12 |
***** Clamp the part in place after it has reached the
proper position.
Part at Hold Part
COIL22 INPUT33 OUTPUT11
COIL4 INPUT12 |
Beginner’s Guide to PLC Programming How to Program a PLC (Programmable Logic Controller)
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24
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