90-Degree Box Pusher

Purpose of the Mechanism

Production lines often need to move a box from one conveyor to another conveyor positioned at a 90-degree angle.

The box travels along the main conveyor until it reaches a mechanical stop. Once the box is in the transfer position, it covers a sensor. The controller waits for a short delay and then activates a pneumatic pusher. The pusher transfers the box onto the cross conveyor.

This learning example uses a minimal set of equipment: one sensor, one digital output, and two timers.

System Components

The example assumes a monostable pneumatic valve with one coil. When the output is energized, the cylinder extends. When the output is de-energized, the valve returns by spring force and the cylinder retracts.

Operating Sequence

1. The Box Reaches the Stop

The box travels along the main conveyor, reaches the mechanical stop, and covers sensor B1.

B1 = TRUE

2. The Delay Starts

The sensor signal is connected to the input of TON timer T1.

For this learning example:

T1.PT = 500 ms

The delay gives the box enough time to reach the stop completely, stop moving, and settle into a stable position.

If the sensor turns off before the delay expires, the TON output will not turn on and the pusher will not operate.

3. The Push Pulse Is Generated

After the delay expires, output T1.Q becomes TRUE. This rising edge starts TP timer T2.

For this learning example:

T2.PT = 1000 ms

The T2 output remains active for the preset time regardless of the subsequent TON output state, according to the TP semantics implemented in the simulator.

4. The Pusher Transfers the Box

Output T2.Q controls output Y1.

Y1 = TRUE

The pneumatic valve coil is energized. The pneumatic cylinder extends and transfers the box onto the cross conveyor.

5. The Pusher Returns

When the T2 time expires, output Y1 turns off.

Y1 = FALSE

The coil is de-energized. The monostable valve returns to its normal position and the cylinder retracts.

6. The System Prepares for the Next Cycle

After the box leaves the position, the sensor is clear:

B1 = FALSE

The TON timer resets. A new cycle can begin after the next transition of the sensor from FALSE to TRUE.

FBD Diagram

B1 — box sensor
        |
        v
T1 — TON, 500 ms delay
        |
        v
T2 — TP, 1000 ms pulse
        |
        v
Y1 — pneumatic valve coil

The logic chain consists of four blocks:

IN → TON → TP → OUT

TON provides the delay before movement starts. TP generates a fixed-duration pulse and limits how long the pneumatic valve remains energized.

Timer Settings

The values of 500 ms and 1000 ms are intended for learning. On real equipment, the parameters must account for:

• main conveyor speed;
• box mass and dimensions;
• distance to the mechanical stop;
• pneumatic cylinder speed;
• air pressure;
• valve switching time;
• receiving conveyor width.

The T1 delay must be long enough to position the box correctly.

The T2 duration must allow the cylinder to push the box completely, but it should not delay cylinder return without a reason.

How to Test the Example in the Simulator

• 1. Open the example in the simulator.
• 2. Start program execution.
• 3. Set input B1 to TRUE.
• 4. Confirm that Y1 does not turn on immediately.
• 5. Wait for the T1 delay to expire.
• 6. Confirm that Y1 turns on for approximately 1000 ms.
• 7. Return B1 to FALSE.
• 8. Set B1 to TRUE again and verify a new cycle.

Actual timing accuracy depends on the simulator's logical scan time.

Limitations of the One-Sensor Diagram

The minimal diagram cannot determine:

• whether the cylinder has fully extended;
• whether the cylinder has returned to its home position;
• whether the box has actually left the transfer position;
• whether the cross conveyor is clear;
• whether a jam has occurred;
• whether the next box is in a hazardous area.

A real industrial system would usually add:

• a cylinder home-position sensor;
• a cylinder extended-position sensor;
• a transfer-position clear sensor;
• a ready signal from the receiving conveyor;
• motion timeout monitoring;
• air-pressure diagnostics;
• emergency interlocks.

This learning FBD diagram demonstrates only the basic control algorithm. It does not replace functional-safety engineering. Emergency stops, protective guards, and safe de-energization of actuators must be implemented with separate hardware and software measures that meet the requirements of the specific equipment.