Rotary encoder zero position - Solutions - Huaqiang Electronic Network

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Rotary encoders are photoelectric devices that convert angular displacement into digital signals, typically in the form of high-speed pulse outputs. They are widely used in industries such as machine tools, elevators, servo motors, textile machines, packaging systems, printing equipment, and lifting machinery. These devices play a crucial role in motion control, position tracking, and speed measurement.

There are two main types of rotary encoders: incremental and absolute. Incremental encoders generate periodic electrical signals that correspond to the movement, and the number of pulses indicates the distance or angle moved. Absolute encoders, on the other hand, assign a unique digital code to each position, allowing for direct position reading without needing to return to a reference point.

The key difference between the two is how they determine position. Incremental encoders rely on counting pulses from a zero reference point, while absolute encoders provide an immediate and accurate position reading based on their internal code. This means that even after power loss, an absolute encoder retains its position information, whereas an incremental encoder must re-find its zero point before operation can resume.

Figure A (Structural principle): Photosensitive elements are typically made up of phototubes, which detect light patterns generated by the encoder's code disk.

Figure B (With inverter wiring)

Figure C (Incremental type)

Figure D (Absolute type)

In most industrial applications, incremental encoders are preferred because they can directly interface with PLCs through high-speed counters. However, absolute encoders are often used in applications where maintaining position data during power cycles is essential.

Setting the zero position is a critical step when using incremental encoders. There are several methods to achieve this:

1. Rotating the encoder shaft to align with the zero position during installation.
2. Adjusting the housing to set the zero point, commonly used in compact mounted flanges.
3. Powering the system and aligning the machine to the encoder’s zero position.
4. Using offset calculation, where the encoder reading is adjusted based on known mechanical positions.
5. Utilizing external zero functions provided by intelligent encoders, such as buttons or software settings.
6. For absolute encoders, it's important to note that the zero position corresponds to the maximum value of the encoding cycle. Improper setup may lead to sudden jumps in readings due to overshoot or inertia.

Best practices for setting zero include choosing a non-zero position with some margin for error and using a midpoint offset method. This ensures stable operation and avoids position jumps during rotation.

Encoders can also be classified based on how the code wheel is engraved:

• Incremental Encoders: Generate pulses at regular intervals, usually with A, B, and Z phases. The A and B signals are quadrature pulses, and the Z signal marks a single revolution.
• Absolute Encoders: Provide a unique binary code for each position, allowing for precise position tracking over multiple revolutions.

Connection example between encoder and PLC:

Note: Power supply can vary between DC 5V and DC 24V depending on the application.

Common issues with encoders include:

• Internal component failure leading to incorrect output signals.
• Cable faults such as open circuits, short circuits, or poor connections.
• Low +5V power supply voltage, causing unstable operation.
• Loose installation affecting accuracy and potentially triggering overload alarms.

In addition to position feedback, encoders can also provide speed signals to frequency converters, enabling precise motor control.

When an encoder fails, the inverter may not function properly, resulting in slow operation or protection mechanisms being triggered. The display might show “PG disconnection,” indicating a problem with the encoder signal connection. Proper configuration of the PG interface is essential to ensure compatibility between the encoder and the inverter.

In summary:

• Rotary encoders use high-precision metering gratings as detecting components.
• They convert mechanical angular displacement into digital codes using LED light sources and grating code disks.
• They can measure angular displacement, velocity, and acceleration accurately.

1: Light source (LED) 2: Lens 3: Indicating grating 4: Disk 5: Receiver (ASIC)

The light from the LED is refracted by the lens into parallel beams, which pass through the grating and code disk. As the code disk rotates, the light pattern changes, and the receiver converts these optical signals into electrical pulses. These pulses represent the physical motion in terms of displacement, velocity, and acceleration.