Skip to Content
All case studies
Case studiesCasesBottle labelling
Talk to an engineer

Case study · Bottle labelling · Arduino PLC

Label bottles in motion, while the line speed changes.

An encoder, a photocell and two stepper motors on one Arduino based PLC.

See the architectureDiscuss a similar project
2stepper motors: label roll and conveyor
2interrupt inputs read the conveyor encoder
6digital outputs: pulse, direction and enable for two drivers
1photocell detects the position of each bottle

Bottles arrive when they arrive.

The label follows the conveyor.

This case describes a real labelling conveyor. We do not name the customer. Bottles on a conveyor belt run through a labelling mechanism that applies a label to each bottle. Nobody regulates the gap between the bottles, and the conveyor can slow down, speed up or stop at any time. One Arduino based PLC from Industrial Shields controls two stepper motors: the first one moves the large label roll, the second one moves the conveyor. A rotary encoder on the conveyor gives the speed of the line. A photocell gives the position of each bottle.

The challenge

Put a label on a moving bottle. At any speed, with any gap.

The customer listed five requirements: apply labels accurately to bottles in motion, allow a variable conveyor speed, allow an inconsistent distance between bottles, pull the label web through the dispenser, and label smoothly and consistently at all speeds. A fixed time delay is not enough when the speed changes. The label has to follow the real movement of the belt.

01

Bottles in motion

The label goes on while the bottle moves. It has to land in the same place on every bottle.

02

Speed changes at any time

The conveyor can slow down, speed up or stop at any moment. The labelling has to follow it.

03

Irregular gaps

Nobody regulates the spacing between the bottles. The system has to find each bottle on its own.

A heavy label roll

The label web comes from a large roll and goes through the dispensing head. The motor needs enough torque and speed to overcome the friction of the head and the inertia of the roll.

How it works

Two loops: measure the line, then meet each bottle.

Move the slider and press the buttons. The panels show the general pattern: what the PLC reads, what it drives and when. They are illustrative simulations. They do not show the program, the speeds or the data of the installation.

Loop 1 · Line speed

The encoder is the reference. Not a timer.

A rotary encoder is mounted on the conveyor. Its two signals go to two interrupt inputs of the PLC, I0.5 and I0.6. Each pulse is a small piece of belt travel. The PLC refers all the speeds and distances of the label roll to this count. When the conveyor slows down, speeds up or stops, the reference changes with it. With interrupts, the PLC does not have to ask the encoder for data all the time.

  • Rotary encoder on the conveyor, on interrupt inputs I0.5 and I0.6
  • Encoder supplied with 24 V and GND, as in the original diagram
  • All speeds and distances of the label roll refer to the encoder
  • Stepper motor 2 moves the conveyor through driver 2
I0.5I0.6PLC0Encoder
80 %
0Encoder count
0Line speed (example)
0Label roll reference

Illustrative simulation. Example speeds and encoder counts, scaled in time. The real encoder resolution and line speeds of the installation are not published.

RelatedHow to use interrupt inputs with industrial Arduino boardsSolution Library: pulse counter with interrupts (ESP32 PLC)

Loop 2 · Label cycle

The photocell finds the bottle. The label meets it at line speed.

A photocell detects the position of each bottle before the labelling head. The gaps are not regular, so each bottle starts its own label cycle. The PLC commands the label motor to accelerate to line speed at the moment the first edge of the label touches the bottle. The motor keeps line speed until the full label is on the bottle. Then it slows to a stop and waits for the next bottle.

  • Start photocell: position of each bottle at the time of labelling
  • Stepper motor 1 pulls the label web from the large roll through the dispenser
  • Accelerate, hold line speed, slow down, stop, wait
  • Goal of the customer: smooth, consistent labelling at all speeds
PhotocellLabel roll

Yellow line: label motor speed. Grey dashed line: line speed from the encoder.

WaitAccelerateLine speedStop
0Labelled bottles
0Last gap (example)
0Label motor

Event log (example)

    Illustrative simulation. Example distances, gaps, speeds and ramps, scaled in time. Where the ramp starts is an example. The real values of the installation are not published.

    RelatedStepper motor speed control with an Arduino based PLC and a rotary encoder

    System architecture

    How does one Arduino PLC synchronise a label roll with a conveyor?

    The rotary encoder goes to two interrupt inputs. Three digital outputs drive each stepper driver: pulse, direction and enable. Driver 1 moves the label roll, driver 2 moves the conveyor. The start photocell gives the position of each bottle. This diagram follows the original wiring diagram of the case, shown below it.

    Bottle labelling conveyor automation with an Arduino based PLC, a rotary encoder and two stepper motorsArduino PLCM-Duino24 V · GNDI0.5 · I0.6 (INT)Q0.0 PUL · Q0.1 DIR · Q0.2 ENADriver 1PUL · DIR · ENAQ1.0 PUL · Q1.1 DIR · Q1.2 ENADriver 2PUL · DIR · ENAA+ A- B+ B-Stepper motor 1label rollA+ A- B+ B-Stepper motor 2conveyorLabel rollCONVEYOREncoderPhotocellinput pin not shownBased on the original wiring diagram of the case. The photocell input pin and the models of drivers, motors and sensors are not published.EncoderI0.5 · I0.6 (INT)Photocellinput pin not shownArduino PLCM-DuinoQ0.0 · Q0.1 · Q0.2Q1.0 · Q1.1 · Q1.2Driver 1PUL · DIR · ENADriver 2PUL · DIR · ENAA+ A- B+ B-Stepper motor 1label rollStepper motor 2conveyorCONVEYORBased on the original wiring diagram of the case.Photocell input pin: not shown in it.
    Sensor signals: encoder and photocellDigital outputs: PUL, DIR, ENAMotor phases A+ A- B+ B-24 V supply
    Signals
    SignalBetweenTypePurpose
    Encoder signalsBetweenRotary encoder → I0.5 and I0.6TypeDigital inputs with interruptPurposeLine speed and belt travel, without constant polling
    Encoder supplyBetween24 V and GND → rotary encoderTypePowerPurposeSupplies the encoder, as in the original diagram
    Bottle positionBetweenStart photocell → PLCTypeDigital input (pin not shown in the diagram)PurposePosition of each bottle at the time of labelling
    Label motor: pulse, direction, enableBetweenQ0.0, Q0.1, Q0.2 → driver 1TypeDigital outputsPurposeSteps, direction and enable of stepper motor 1 (label roll)
    Conveyor motor: pulse, direction, enableBetweenQ1.0, Q1.1, Q1.2 → driver 2TypeDigital outputsPurposeSteps, direction and enable of stepper motor 2 (conveyor)
    Driver returnsBetweenPUL-, DIR-, ENA- of both drivers → GNDTypeCommon referencePurposeCloses the input circuits of the drivers
    Motor phasesBetweenDriver → stepper motorTypeA+, A-, B+, B-PurposeTwo phases per motor
    Original wiring diagram of the labelling case: Arduino based PLC, two stepper drivers, two stepper motors, start photocell and rotary encoder on a bottle conveyor
    Original wiring diagram of the case: encoder on I0.5 and I0.6, driver 1 on Q0.0 to Q0.2, driver 2 on Q1.0 to Q1.2. Open the full size diagram

    Why it works

    One distance reference. Simple signals.

    Interrupts for the encoder

    The encoder uses two interrupt inputs. The PLC does not ask the encoder for data all the time: the pulses come to it.

    Three outputs per motor

    Each stepper driver takes three digital outputs: pulse, direction and enable. The same PLC drives the label roll and the conveyor.

    Speed and distance, not time

    The label roll follows the encoder, and each bottle starts from the photocell. The cycle adapts when the speed or the gap changes.

    Hardware used

    One Arduino based PLC on the DIN rail.

    M-Duino 42+, industrial Arduino PLC with Ethernet for the DIN rail

    M-DUINO ETHERNET PLC ARDUINO 42

    An industrial PLC built around an original Arduino Mega 2560. It has the pins of the original diagram: interrupt inputs I0.5 and I0.6, and digital outputs Q0.0 to Q0.2 and Q1.0 to Q1.2. You program it in C++ with the Arduino IDE.

    Inputs
    26: 12 analog/digital (0-10 V), 14 digital optoisolated (5 to 24 Vdc), 4 with interrupt
    Outputs
    16: 6 analog/digital/PWM (0-10 V), 10 digital optoisolated (5 to 24 Vdc)
    Network and serial
    Ethernet 10/100 (RJ45), RS-485, RS-232, I2C, SPI
    Built in
    Real-time clock, microSD slot
    Power supply
    12 to 24 Vdc
    Mounting
    DIN rail TS35, IP20

    The case does not publish the exact PLC model. The image and the link show the M-Duino 42+ (reference IS.MDuino.42+), a current model with all the pins of the diagram. The case does not publish the models of the drivers, the motors, the encoder or the photocell. Before you wire a stepper driver, check that its inputs accept the output voltage of the PLC.

    See the M-Duino 42+M-Duino family datasheet

    Questions about this case

    How does the label stay in sync when the conveyor speed changes?

    A rotary encoder on the conveyor measures the belt travel. The PLC refers all the speeds and distances of the label roll to the encoder, not to a timer. When the line slows down or speeds up, the reference changes with it.

    Why is the encoder on interrupt inputs?

    The encoder goes to two interrupt inputs, I0.5 and I0.6. This way the PLC does not have to make constant requests to get the encoder data. Each pulse triggers a short routine that updates the count.

    What does the label motor do for each bottle?

    The photocell detects the bottle. The PLC commands the label motor to accelerate to line speed at the moment the first edge of the label touches the bottle. The motor holds line speed until the full label is applied, then slows to a stop and waits for the next bottle.

    Stepper motors or servo motors?

    The case uses two stepper motors: the introduction and the wiring diagram both say so. They run with pulse, direction and enable drivers. The hardware text of the case also speaks of a servo system, because the label motor needs torque and speed for the dispensing head and the large roll. Many servo drives also accept pulse and direction inputs.

    Which PLC was used?

    An Arduino based PLC from Industrial Shields. The case does not name the model. The diagram uses interrupt inputs I0.5 and I0.6 and outputs Q0.0 to Q0.2 and Q1.0 to Q1.2. The M-Duino 42+ has all of them.

    Do I need to program in Arduino?

    The PLC is programmed in C++ with the Arduino IDE. You start from your machine, not from the code: tell us the sequence, the signals and the motors, and our engineers will tell you how to build it.

    Download the case study

    4-page PDF with the challenge, the logic, the architecture and the hardware. No form required.

    Download PDF

    Similar project?

    Tell us your line and your labels. An engineer will answer.

    Tell us what you label, how the products arrive, how the line speed changes and which motors and drivers you use. We will tell you how to connect the encoder, the sensor and the drives, and which controller fits.

    • You get an answer from our technical team
    • I/O count for your machine
    • Arduino, ESP32 or Raspberry Pi based PLCs
    Send to an engineer