rotary encoders

Basic Components

Every rotary encoder contains several essential components, which include:

• Shaft: The rotating part in the device that connects with the application.
• Code Disk: Depending on the type, it has patterns or tracks to detect rotation.
• Light Source: Used in optical encoders to illuminate the disk.
• Photodetector: Detects light changes for optical types.
• Electrical Circuit: Processes signals to generate readable output.

Types of Rotary Encoders

Rotary encoders are categorized into two main types based on their operation and output signal:

• Incremental Encoders: Produce digital signals for tracking relative motion. They use A and B signals to determine direction and incremental position.
• Absolute Encoders: Provide a unique digital code for each shaft position, ensuring accurate location tracking even after power cycling.

Applications of Rotary Encoders

Rotary encoders find usage in various fields, including:

• Consumer Electronics: Used in volume controls and position sensors for input devices.
• Industrial Automation: Essential in robotics, CNC machines, and assembly lines for precise position and speed control.
• Automotive Industry: Used in throttle position sensors and steering angle sensors for vehicle dynamics control.
• Medical Equipment: Applied in devices requiring precise movements, like MRI machines.

Rotary Encoder Working Principle

The working principle of a rotary encoder involves converting the angular motion into an electrical signal that can be read by a digital circuit. This is achieved through the actions of different internal components depending on the type of encoder.

Incremental Encoder Operation

Incremental encoders work by generating pulses as the shaft rotates. These pulses are produced by the movement of a patterned disk between a light source and a detector. Based on the detected light interrupts, the encoder outputs signals corresponding to increments of movement. Some key aspects include:

• A and B Channels: Two separate output channels offset by 90 degrees, used for determining direction and distance.
• Signal Processing: The controller counts pulses to measure movement and can also determine the direction based on the phase difference between A and B channels.

Absolute Encoder Operation

Absolute encoders provide a distinct signal for each position of the encoder shaft, making it possible to determine its exact position at any time. They use a disk divided into a complex code pattern that represents a unique binary number for each position. This feature allows them to provide position feedback even after a power loss. Key features include:

• Single-turn or Multi-turn: Single-turn encoders track position only within a single rotation, while multi-turn can provide a unique position code over multiple rotations.
• Binary Coding: Each position is mapped with a unique binary code, enabling precise location tracking.

Types of Rotary Encoders

Rotary encoders are vital components in many electromechanical systems. They are primarily categorized into two types: Absolute Rotary Encoders and Incremental Rotary Encoders, each serving distinct functions in automation and control applications.

Absolute Rotary Encoder

Absolute rotary encoders provide a unique position value for each rotational position of the shaft. These encoders use a binary code mapped onto a disk, which is read by sensors to determine the exact angle.Here are some characteristics:

• Unique Positioning: Each angle position corresponds to a specific code, eliminating the need for reference runs after power outages.
• No Increment Counting: Unlike incremental encoders, these do not require counting pulses to determine the position, making them ideal for applications where exact positioning is crucial.

Incremental Rotary Encoder

Incremental rotary encoders generate a series of pulses as the shaft rotates, requiring pulse counting to determine position. Unlike absolute encoders, they do not have a distinct value for each shaft position.The primary features include:

• Pulsed Output: Each complete rotation generates a set number of pulses, often using two channels (A and B) to determine direction and speed.
• Simple Construction: Typically involves fewer components leading to cost-effective solutions for basic positioning applications.

• Position Calculation: If \(P\) is the position, the formula \(P = N \times R\) can be used, where \(N\) is the number of counted pulses, and \(R\) is a resolution factor.
• Phase Quadrature: Utilizes two signals 90 degrees out of phase for determining rotation direction by recognizing leading signal, i.e., if A leads B or vice versa.

Rotary Encoder Techniques

Understanding the various techniques employed by rotary encoders is crucial for selecting the right encoder for your application. These techniques dictate how the encoders generate and process signals to provide information about rotational position and motion.

Optical Rotary Encoders

Optical rotary encoders are among the most commonly used due to their precision. They utilize a light source (LED) and a photodetector array to read a code pattern on a disk. This interaction converts the mechanical motion into an electrical signal.Key Elements of Optical Encoders:

• Grating Disk: A transparent or reflective disk with an intricate pattern of lines or slits that modulates the light intensity detected by the sensors.
• Interference Absorption: A technique used to enhance accuracy by minimizing external light interference.

Magnetic Rotary Encoders

Magnetic rotary encoders operate using magnetic fields generated by magnets. These encoders use magnetic sensors to detect the field changes as the encoder rotates. This technique is beneficial for environments where dirt and dust might affect optical encoders.Characteristics of Magnetic Encoders:

• Robustness: Unaffected by debris, water, or oil, making them ideal for harsh conditions.
• Lower Resolution: Typically less precise than optical encoders, but still sufficient for many industrial applications.

Encoding Techniques for Signal Processing

The signals generated by rotary encoders must be processed to be useful. Techniques for signal processing include:

• Phase Detection: Used to determine rotation direction by comparing the phase relationship between channels A and B.
• Interpolation: Enhances resolution by generating additional points between detected positions through mathematical calculations.
• Digital Filtering: Removes noise from signals to ensure that output remains clear and accurate.