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In this tutorial, I am going to walk you
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through the conveyor scene in the ACC
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PLC simulator using the five-step PLC
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program development framework.
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This is a single-axis belt conveyor with
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proximity sensors at each end and a box
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that travels back and forth along the
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By the end, you will have a complete
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working program built step by step the
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same way I approach every PLC project.
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Detailed information contained in this
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video can be found at accautomation.ca.
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A link has been put in the description
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The website offers extensive links,
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references, and coding samples, making
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it a one-stop shop for all your
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Once again, that is accautomation.ca.
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Input and output IO overview.
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The conveyor scene has six IO points,
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four inputs and two outputs.
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X1 is your start push button wired
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normally open. X2 is your stop push
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button wired normally closed. X3 is a
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proximity sensor at the left end of the
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belt. X4 is a proximity sensor at the
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right end. On the output side, Y1
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controls the motor. When Y1 is on, the
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>> Y2 controls direction. When Y2 is off,
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the box travels forward from left to
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right. When Y2 is on, the box travels in
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reverse from right to left.
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Step one, define the task.
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Write down in plain English what the
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system must do before you touch any
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The conveyor must start when the
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operator presses start and stop when the
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operator presses stop. When running, the
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box travels forward from left to right.
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When the box reaches the right sensor,
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the conveyor automatically reverses
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direction. The box then travels in
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reverse from right to left. When the box
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reaches the left sensor, the conveyor
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stops automatically. The operator can
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press start again to repeat the cycle.
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The stop button must stop the conveyor
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at any time regardless of where the box
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Step two, define the IO.
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List every input and with its address
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and description. X1 is start, X2 is stop
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normally closed, X3 is the left sensor,
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X4 is the right sensor, Y1 is motor run,
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Four inputs and two outputs. No analog
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IO is needed for this application. The
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IO map is already defined by the scene,
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so this step is done.
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Step three, develop a flowchart or
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sequence of operations.
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Map out the sequence of operations.
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First, the operator presses start.
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The motor starts with the direction set
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to forward. The box travels left to
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right. The box arrives at the right
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The direction reverses. The box travels
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right to left. The box arrives at the
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left sensor. The motor stops.
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The system is ready for the next cycle.
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The stop button can interrupt the motor
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at any point and immediately stop it.
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Step four, develop the PLC program.
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Translate the flowchart into ladder
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logic. Wrong zero is your motor start
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X1, the start button, is a normally open
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contact in parallel with Y1 for the seal
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in. X2, the stop button, is a normally
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open contact in series with the normally
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Then we add X3, the left sensor, as a
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normally closed contact in series. And
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here's the important part.
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We add X1 in parallel with that normally
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closed X3 contact. The output is Y1,
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motor run. The normally closed X3
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contact is your automatic stop.
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>> When the box arrives at the left sensor,
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X3 goes true. The normally closed
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contact opens and Y1 drops out. But
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after the cycle completes, the box is
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sitting at the left sensor. X3 stays
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true. Without X1 in parallel, the motor
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would never start again.
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With X1 in parallel, pressing start
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bypasses the left sensor and the motor
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>> Wrong one is your direction control.
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X4, the right sensor, is a normally open
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contact. Y2, the direction output, is in
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parallel as a seal in, so the direction
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stays reversed after the box moves away
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from the right sensor.
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Add Y1, motor run, as a normally closed
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contact in series with the seal in
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branch. This [music] resets the
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direction when the motor stops, so the
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next cycle starts in the forward
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The output is Y2, direction.
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If you are enjoying this video, please
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hit the like button below. Keeping up
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hit the subscribe button.
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Remember to hit the bell next to your
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subscription to receive notifications.
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Step five, test the program.
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Connect the conveyor scene and run the
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full test sequence. Put the simulator in
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run mode. Press start.
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The belt starts moving forward. Watch
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the box travel to the right.
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The box hits the right sensor and the
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direction reverses automatically. The
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box travels back to the left. The box
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hits the left sensor and the motor stops
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Press start again and the cycle repeats.
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Now, press stop during travel.
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The motor stops immediately. Test the
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stop button at every stage, forward
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travel, reverse travel, and at each
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sensor position. If any step does not
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work, use step mode in the simulator.
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Toggle the inputs manually and press
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step to see exactly which contacts are
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The conveyor scene introduces IO
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patterns you will see in every material
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Motors, sensors, direction control, and
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automatic sequencing. The five-step
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framework kept our development organized
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from task definition through testing.
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Try modifying the program.
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Add a counter to track how many complete
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cycles the box has made.
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Add a timer to pause for 2 seconds at
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each end before reversing.
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These are fundamental building blocks
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for more complex machines.
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Head over to accautomation.ca/simulator
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to try the conveyor scene yourself.
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The link is in the description.
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If you found this helpful, subscribe to
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ACC Automation for more PLC tutorials.
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And leave a comment telling me what
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program you would like to build next.
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Many PLC manufacturers offer a range of
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hardware and software.
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All programmable logic controllers share
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similar basic features. To see how I
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would approach learning about basic
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Click here to see how you can continue
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programming for free with the ACC PLC
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simulator featuring 3D scenes you can
