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Conveyor Encoder Tracking Scaler

Determine encoder scale factor for vision-guided robotics.

Encoder & Conveyor Setup

If using 4X quadrature, use PPR × 4.

Use 1 if directly mounted to the roller shaft.

Tracking Resolution

12.73 counts / mm
Linear Distance per Count 0.0785 mm
Roller Circumference 314.16 mm
info
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Conveyor Encoder Tracking Basics

To effectively track a conveyor using a rotary encoder, you must understand the mathematical relationship between the physical rotation of the encoder, the electrical pulses it generates, and the resulting linear movement of the conveyor belt. This allows a PLC to translate raw encoder counts into real-world units like millimeters or inches.

Key Terminology

  • PPR (Pulses Per Revolution): The number of electrical pulses an encoder generates on one channel during a full 360° rotation.
  • CPR (Counts Per Revolution): In quadrature encoders, a controller can count both the rising and falling edges of channels A and B, effectively multiplying the PPR by four (4x decoding).
  • Scaling Factor: The multiplier used by the controller to convert encoder pulses into a linear distance.

Calculating Linear Resolution

To determine how much linear distance each pulse represents, follow these steps:

1. Determine Linear Distance per Revolution

Calculate the distance the conveyor belt moves for one full rotation of the encoder shaft. If the encoder is mounted on a measuring wheel or roller, this is the circumference of that roller:

Circumference = π × Diameter of Roller

2. Calculate Linear Resolution (Distance per Pulse)

With the circumference and the encoder’s total counts per revolution (PPR or CPR depending on decoding), the distance per pulse is:

Linear Resolution = Circumference / Total Counts per Rev

3. Calculate the Scaling Factor (Pulses per Unit)

If your controller requires a scaling factor to convert pulses into a specific length unit (e.g., pulses per meter):

Pulses per Meter = Total Counts per Rev / Circumference (in meters)

Implementation Tips

  • Mounting Location: For the highest accuracy, mount the encoder on a non-driven (idle) roller or use a dedicated measuring wheel. Mounting on the drive motor shaft introduces errors from belt slip and gear backlash.
  • Frequency Limits: Ensure the maximum pulse frequency at the conveyor’s top speed does not exceed the input limits of your PLC’s high-speed counter. Max Frequency = (Max RPM × PPR) / 60.
  • Integer Math: PLC counters handle integers best. Design your mechanical measuring wheel diameter to yield a clean integer for pulses per unit to prevent cumulative rounding errors.