Tag Archives: ladder logic development

PLC Programming Example – Paint Spraying

We will look at a PLC basic tutorial of a paint spraying station. Following the 5 steps to program development this PLC programming example should fully explain the procedure for developing the PLC program logic. Ladder will be our PLC programming language.

We will be using the Do-more Designer software which comes with a simulator. This fully functional program is offered free of charge at automation direct.

Define the task:

What has to happen?
Paint Station 01

Paint spraying system where boxes are fed by gravity through a feeder magazine one at a time onto a moving conveyor belt. Upon the start signal, boxes are pushed towards the conveyor by valve 1. This is a cylinder which extends and retracts which operates switches S1 and S2 respectfully. A spraying nozzle paints each box as it passes under the paint spray controlled by valve 2. A sensor (S3) counts each box being sprayed. When 6 boxes have been painted the valve 2 shuts off (paint spray) and valve 1 (cylinder) stops moving boxes onto the conveyor. Three seconds later the conveyor stops moving and the hopper with its load moves forward (valve 3) where it is emptied. Ten seconds later the hopper returns to the original position. The cycle is then complete and waits for a start signal again.

Define the Inputs and Outputs:

Inputs:
Start Switch – On/Off (Normally Open) – NO
Stop Switch – On/Off (Normally Closed) – NC
S1 – Valve 1 (cylinder retract) On/Off – NO
S2 – Valve 1 (cylinder extend) On/Off – NO
S3 – Box Detected- On/Off – NO
Outputs:
Motor – On/Off (Conveyor Run)
Valve 1- Cylinder to feed boxes – On/Off
Valve 2- Paint Spray – On/Off
Valve 3- Cylinder to move hopper – On/Off

Develop a logical sequence of operation:

Fully understanding the logic before starting to program can save you time and frustration.

Sequence Table: The following is a sequence table for our paint spraying application.

Sequence Table
1 – Input / Ouput ON
0 – Input / Output OFF
x – Input / Output Does not Matter
When power goes off and comes on the sequence will continue. This means that we must use memory retentive areas of the PLC. The stop pushbutton will stop the sequence. The start will resume until the end.

Develop the PLC program:

The best way to see the development of the programmable logic controller program is to follow the sequence table along with the following program. You will see the direct correlation between the two and get a good understanding of the process.

This is the main process start and stop bit. V0:0 is used because it is memory retentive.
Paint Stn Program 1

Control of the Motor (Conveyor) and the paint spray is done with the V0:0 contact in front of the actual PLC output. The conveyor and paint spray will stop when the timer 0 is done. This is the delay after the last box is detected to allow the box to be painted and loaded onto the hopper.
Paint Stn Program 2

Control of the box movement onto the conveyor. As long as we have the process start and the hopper count is not complete this will allow the cylinder to put boxes on the conveyor.
Paint Stn Program 3

Count number of boxes in the hopper via S3. The counter is memory retentive.
Paint Stn Program 4

Timer to stop the conveyor and spray after the last box is detected for the hopper. This will allow time for the box to be sprayed and loaded into the hopper.
Paint Stn Program 5

Hopper movement to load and unload the boxes.
Paint Stn Program 6

The hopper unload timer is to unload the boxes and will then trigger the reset conveyor timer, box counter and the process start bit (V0:0).
Paint Stn Program 7

Test the program:

Paint Spraying
Test the program with a simulator or actual machine. Make modifications as necessary. Remember to follow up after a time frame to see if any problems arise that need to be addressed with the program.

Watch on YouTube : PLC Programming Example – Paint Spraying
If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

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PLC Programming Example – Shift Register (Conveyor Reject)

Allot of times when programming a PLC you need to track what has previously happened. Shift registers allow you to do just that. We will look at a PLC basic tutorial of a conveyor belt and reject station. Following the 5 steps to program development this PLC programming example should fully explain the function of shift registers. Ladder will be our PLC programming language.

We will be using the Do-more Designer software which comes with a simulator. This fully functional program is offered free of charge at automation direct.

Define the task:

What has to happen?
Conveyor Reject 0

A start pushbutton (NO) is used to start the conveyor and a stop pushbutton (NC) is used to stop. Sensor B detects product on the conveyor belt and sensor A will detect if it is too large and needs to be rejected. The product is tracked along the conveyor belt and when under the reject station the Reject Blow Off will expel the bad product. Product is randomly placed on the conveyor belt, so an incremental encoder is used to track the conveyor movement. The reset pushbutton (NO) will signal that all of the product on the conveyor has been removed between the sensors and reject blow off.

Define the Inputs and Outputs:

Inputs: Start Switch – On/Off (Normally Open) – NO Stop Switch – On/Off (Normally Closed) – NC Reset Switch – On/Off – NO Motor Encoder – On/Off – This will give a discrete signal when the conveyor is moving. It picks up the movement of the free wheel. Sensor A (Part Reject) – On/Off – NO Sensor B (Part Present) – On/Off – NO

Outputs: Motor – On/Off (Conveyor Run) Air Blow Off – On/Off (Reject)
Inputs_Outputs

Develop a logical sequence of operation:

Fully understanding the logic before starting to program can save you time and frustration.

Sequence Table: The following is a sequence table for our conveyor reject application.
Sequence Table

It is a simple sequence table, but clarifies the following: When power goes off and comes on the sequence will continue. This means that the shift sequencer must be memory retentive. Sensor A and B must be on to get tracked with a shift register.

Shift Registers: The Shift Register (SR) instruction shifts data through a predefined number of BIT locations. These BIT locations can be a range of BITs, a single Word or DWord, or a range of Words or DWords. The instruction has three inputs. Data, Clock and Reset. The data input will load the beginning bit with a ‘1’ if it is on or ‘0’ if it is not. Clock input is used to shift the data through the shift register. In our example, we will be using the encoder on the conveyor to track the reject container. So each pulse of the clock represents a distance on the conveyor. The last input is the reset. It will place ‘0’ in all of the bits within the shift register.
Shift Register

Develop the PLC program:

Start and stop of the conveyor motor.
Program Conveyor Reject 1

Shift register to track the rejected parts. This will move the bits with each pulse of the encoder. Note that the ‘V’ memory is used because it is memory retentive.
Program Conveyor Reject 2

This will look at the bit in front of the reject station. We can measure and count off the length (conveyor) and then find out what the bit location will be at the reject location.Program Conveyor Reject 3

Test the program:

Test the program with a simulator or actual machine. Make modifications as necessary. Remember to follow up after a time frame to see if any problems arise that need to be addressed with the program.

Conveyor Reject

Notes: Sometimes you can use multiple shift registers in your program. This can be helpful if you want to actually track the container as well as the rejects. You could also use bit shift right (BSR) and bit shift left instructions (BSR) to do the same thing as we did with the shift register instruction. In the Do-more PLC it is rotate left (ROTL) and rotate right (ROTR) instructions. Always check your instruction set of the controller that you are working with before starting to program.

Watch on YouTube : PLC Programming Example – Shift Register (Conveyor Reject)

Additional information on shift registers can be seen at the following URL:
http://accautomation.ca/plc-programming-example-sorting-station-shift-register/
This PLC programming example will look at sorting coloured tags into three different exits. The 3D simulation will use three different shift registers to trigger when to direct the correct colour tag.
Watch the sequence of operation video below.
Watch on YouTube : PLC Programming Example – Sorting Station Testing

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.

PLC Programming Example – Process Mixer

We will apply the five steps to PLC Program development to our next programming example of a process mixer.

1 – Define the task:

PLC Prgramming Example - Process Mixer
A normally open start and normally closed stop pushbuttons are used to start and stop the process. When the start button is pressed, solenoid A engergizes to start filling the tank. As the tank fills, the empty level sensor switch closes. When the tank is full, the full level sensor switch closes. Solenoid A is de-energized. Mixer motor starts and runs for 3 minutes to mix the liquid.  When the agitate motor stops, solenoid B is engergized to empty the tank. When the tank is completely empty, the empty sensor switch opens to de-engergize solenoid B. The start button is pressed to repeat the sequence.

2 – Define the Inputs and Outputs:

Inputs:
Start Pushbutton – Normally Open – On/Off
Stop Pushbutton – Normally Closed – On/Off
Empty Sensor Switch – On/Off
Full Sensor Switch – On/Off
Timer 3 minutes done bit – On/Off (Internal)

Outputs:
Mixer Motor – On/Off
Solenoid A – Fill – On/Off
Solenoid B – Empty – On/Off
Timer 3 minutes – (Internal)

3 – Develop a logical sequence of operation:

A flow chart or sequence table is used to fully understand the process.  It will also prompt questions like the following.

What happens when electrical power and/or pneumatic air is lost? What happens when the input / output devices fail? Do we need redundancy?

This is the step where you can save yourself allot of work by understanding everything about the operation. It will help prevent you from continuously re-writing the PLC logic. Knowing all of these answers upfront is vital in the development of the PLC program.

Process Mixer - Sequence Table

4 – Develop the PLC program

Since we need to continue the sequence when the power goes off then memory retentive locations in the PLC must be used. In our example we will use the ‘V Memory’ locations.

The first thing in our program is to control the start and stop functions. This is done through a latching circuit. From the sequence table we know that to reset the sequence we need to have the timer done and the empty sensor off.Process Mixer Program 1

The filling of the tank is done through Solenoid A. It is turned on by the start signal and off by the full sensor switch. (Sequence Table) You will notice that we have a memory retentive output and the actual output to active the solenoid.Process Mixer Program 2

The memory retentive timer will start timing when we have the start sequence signal and when the empty and fill sensors are on. The timer will reset when the empty and fill sensors are off. Mixing motor will be on when the timer is timing and when the timer is not done.Process Mixer Program 3

Solenoid B turns on to empty the tank when the timer is done and the full and empty sensors are on. It will reset when the empty sensor switch goes off.Process Mixer Program 4

5- Test the program

PLC Programming Example - Process Mixer

Test the program under many conditions. Check to see what happens when power is removed.

Using this five step to program development technique will shorten your programming time. The result will be a better defined logic and easier to understand program, because it has within the documentation the logic flow chart or sequence table.

Watch on YouTube : PLC Programming Example – Process Mixer

Factory IO provides a 3D simulation of the process. Testing of the program is important and should be done in a variety of ways. Factory IO provides a straight forward method of seeing your program in action before you wire your application.

We will be using the BRX PLC Modbus TCP Server (Slave). Factory IO will be the Modbus TCP Client (Master). When the tank fills up we will start a dwell time instead of the mixer time for the simulation.
Here is the mapping of the inputs and outputs using Factory IO.

Factory IO Website is at the following URL:
https://factoryio.com/
Documentation is well done. Start at the ‘Getting Started’ at the following URL:
https://factoryio.com/docs/

You can download the PLC program and Factory IO scene here.

Watch the following video to see this simulation in action.

Watch on YouTube : Process Mixer Test Simulation
If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.