Modern warehouses rely on fast conveyors, sorting gates, scanners, motors, and robots that must act at the right place and the right time. A rotary encoder attached to a roller or motor shaft converts rotation into electrical pulses that reveal position, speed, and direction. A programmable logic controller, or PLC, reads those signals and uses them to control the warehouse equipment.
This feedback loop helps packages move accurately through sorting, routing, and handling systems.
Key Facts
- Encoder pulse count per revolution is called PPR, and angle per pulse = 360 degrees / PPR.
- If an encoder has PPR pulses per revolution and rotates at f revolutions per second, pulse frequency = PPR x f.
- Conveyor speed can be found from v = pi d N, where d is roller diameter and N is rotations per second.
- Distance traveled per encoder pulse = pi d / PPR for a roller directly driving the belt.
- A PLC scan cycle usually follows input read, logic solve, output update.
- Closed-loop control compares measured motion to desired motion, then adjusts outputs to reduce error.
Vocabulary
- Rotary encoder
- A sensor that converts shaft rotation into electrical signals that represent position, speed, or direction.
- PLC
- A programmable logic controller is an industrial computer that reads inputs, runs control logic, and switches outputs.
- PPR
- Pulses per revolution is the number of signal pulses an encoder produces during one full shaft rotation.
- Quadrature signal
- A pair of encoder signals offset in phase so a controller can determine both motion amount and direction.
- Actuator
- A device such as a motor, gate, solenoid, alarm, or robot joint that performs a physical action when controlled.
Common Mistakes to Avoid
- Using motor RPM as belt speed without checking roller diameter is wrong because linear conveyor speed depends on circumference, v = pi d N.
- Ignoring encoder resolution is wrong because low PPR creates larger distance steps and can make sorting gates trigger too early or too late.
- Wiring only one encoder channel when direction matters is wrong because a single pulse train gives speed and count but not reliable direction.
- Assuming the PLC output changes instantly is wrong because input filtering, scan time, communication delays, and actuator response all add timing delay.
Practice Questions
- 1 A conveyor roller has diameter 0.10 m and turns at 5 revolutions per second. What is the belt speed in m/s?
- 2 A rotary encoder has 1024 PPR and is mounted on a roller with diameter 0.08 m. How far does the belt move per pulse?
- 3 A package must be diverted by a sorting gate exactly 1.2 m after passing a sensor. Explain how encoder feedback and PLC logic can trigger the gate more accurately than using only a fixed time delay.