Rotary encoder zero position - Solutions - Huaqiang Electronic Network

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Rotary encoders are photoelectric devices that convert angular displacement directly 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 machinery, packaging, printing, and lifting equipment.

There are two main types of rotary encoders: incremental and absolute. An incremental encoder produces a periodic electrical signal that is converted into counting pulses. The number of pulses indicates the magnitude of the displacement. On the other hand, an absolute encoder assigns a unique digital code to each position, making its readings independent of the measurement process. This means that even after power loss, the absolute encoder retains its position information, while an incremental encoder must re-find the zero point after restart.

The difference between the two lies in how they determine position. Incremental encoders rely on counting pulses from a reference point (zero), whereas absolute encoders read a unique code at each position, ensuring accuracy without needing a reset. Here’s a breakdown:

• Incremental Encoder: Position is calculated based on the number of pulses from a known starting point.
• Absolute Encoder: Each position corresponds to a specific digital code, so it can report the exact position without needing to return to a zero point.

Below are some schematic diagrams illustrating the structure and operation of different types of encoders:

Figure B (with inverter wiring)

C picture (incremental type)

D picture (absolute type)

In many applications, especially with PLCs, incremental encoders are commonly used. Their pulse output can be directly connected to a PLC's high-speed counter to measure displacement accurately. However, for accurate positioning, the zero point must be set correctly.

There are several methods to set the zero point:

1. Shaft rotation: Align the encoder shaft with the zero position during installation.
2. Housing rotation: Rotate the encoder housing to set the zero point, often used in compact mounting scenarios.
3. Power-on alignment: Set the zero point by aligning the machine and encoder when powered on.
4. Offset calculation: Adjust the encoder reading using a pre-determined offset based on the actual position.
5. External zero setting: Some advanced encoders have built-in buttons or software functions for zero calibration.
6. Direction consideration: For absolute encoders, ensure correct rotation direction to avoid sudden jumps in data.
7. Best practice: Set a non-zero position with a margin and use offset correction for more stable results.

Encoders can also be classified based on their code wheel engraving method:

• Incremental Encoders: Generate pulse signals per unit angle, with A, B, and Z phase outputs for direction and position tracking.
• Absolute Encoders: Provide a unique binary code for each position, enabling precise multi-position measurement.

Connection diagram between encoder and PLC:

Encoder-----------PLC
A-----------------X0
B-----------------X1
Z------------------X2
+24V------------+24V
COM------------ -24V-----------COM
    

^{tangram_guid="TANGRAM__38"} Note: Power supply can be DC 5V or DC 24V.

Common issues include:

• Encoder failure: Internal components may fail, requiring replacement or repair.
• Cable faults: Open circuits, short circuits, or poor connections are common causes of malfunction.
• Powder supply drop: If +5V is too low, the encoder may not function properly.
• Loose installation: Can cause inaccurate positioning and system alarms.

Rotary encoders can also provide speed feedback to frequency converters, helping regulate motor performance. If the encoder fails, the inverter may display “PG disconnection” and become unstable.

In summary, rotary encoders are essential in precision control systems. They convert mechanical motion into digital signals, allowing for accurate measurement of position, speed, and acceleration. Their design typically involves a light source, lens, grating, and receiver to process optical signals into electrical pulses.

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

The LED emits light that is focused through a lens onto the grating and code disk. As the disk rotates, the pattern of light changes, and the receiver translates these optical variations into electrical signals, which represent the physical motion in terms of displacement, velocity, and acceleration.