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Rotary Encoders

A rotary encoder is a type of sensor that detects position and speed by converting rotational mechanical displacement into electrical signals. It works by translating the movement of a rotating shaft into a series of digital pulses that can be used to determine the position and speed of the shaft.

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Types of Rotary Encoders

Rotary encoders come in two main types: incremental and absolute. Incremental encoders generate a series of digital pulses that correspond to the relative position of the shaft, while absolute encoders provide an absolute position measurement that does not rely on any previous position information.

All Incremental Rotary Encoders

An incremental rotary encoder provides excellent speed and distance feedback and are both simple and inexpensive.

All Absolute Rotary Encoders

Absolute rotary encoders are best where accuracy for both speed and position is required and fail tolerance is required.

Specialized Rotary Encoders

Key Features of Rotary Encoders:

  • Provides high accuracy and reliability
  • Can be used in a variety of industrial automation applications
  • Can be incremental or absolute
  • Has a long lifespan and requires minimal maintenance
  • Can be customized to meet specific requirements
  • Provides real-time feedback for closed-loop control systems.

Types of Rotary Encoder Technologies

Rotary encoders can be further classified into different types based on the technology they employ.

  • Optical Rotary Encoders: There are optical rotary encoders that use a light source and photoelectric sensors to detect the position of the shaft.

  • Magnetic Rotary Encoders: Magnetic rotary encoders, on the other hand, use a magnetic field to detect the position of the shaft and are immune to dust and other environmental contaminants.

  • Capacitive Rotary Encoders: Capacitive rotary encoders use changes in capacitance to detect position and are highly accurate but sensitive to temperature changes.

  • Inductive Rotary Encoders: Inductive rotary encoders use changes in inductance to detect position and are often used in harsh environments due to their durability.

  • Each type of rotary encoder technology has its own unique advantages and disadvantages, making it important to choose the right type for a particular application.


How to Select a Rotary Motor Encoder:

To select a rotary encoder, you need to consider several factors, including:

  • The required resolution and accuracy, which will help you choose between incremental or absolute encoders
  • The type of output signal you need, such as open-collector, voltage, or current output
  • The environmental conditions, such as temperature, humidity, and vibration, and choose an encoder that can withstand those conditions
  • The mechanical interface, such as a shaft size, mounting style, and connector type, that is compatible with your system

    It is important to consult the encoder's datasheet and follow the manufacturer's recommendations to ensure that you choose the right encoder for your application.

Operating Principles of Rotary Encoders

Rotary encoders operate on the principle of converting the mechanical motion of a rotating shaft into an electrical signal that can be processed by a digital system. An encoder typically consists of a rotating disc or shaft with evenly spaced marks, which can be detected by a sensor. As the disc or shaft rotates, the sensor detects the position and direction of rotation by counting the number of marks that pass by. The electrical signal generated by the sensor is then processed by a digital circuit to provide an accurate measurement of the shaft's position and speed.

The resolution and accuracy of the encoder depend on the number of marks on the disc or shaft and the precision of the sensor used. Rotary encoders are used in a variety of applications, such as robotics, industrial automation, and machine tools, where precise position and speed control are critical.

Frequently Asked Questions about Rotary Encoders

 What is a rotary encoder?

A rotary encoder, often referred to as simply a shaft encoder, is an electro-mechanical device that converts angular positioning into output signals. Rotary encoders can be broadly segmented by their feedback type as incremental or absolute.

Learn more about absolute rotary encoders here

Learn more about incremental rotary encoders here

How do rotary encoders work?

Rotary encoders translate the mechanical rotational motion of an object such as a motor shaft into an electronic signal. Optical rotary encoders measure rotation by shining a LED light through a disc with markings onto an optical sensor to detect motion. Magnetic rotary encoders use a similar principle but measure motion as a magnetized wheel turns and is detected by a magnetic sensor. 

Learn more about optical rotary encoders here

Learn more about magnetic rotary encoders here

What is the output of a rotary encoder?

Incremental rotary encoders output a stream of ubiquitous pulses over 360 degrees of rotation, hence the term pulses per revolution of PPR. Incremental rotary encoders can have one channel output (A), two channel output (AB, known as quadrature) as well as an optional index channel (Z).

Learn more about incremental rotary encoder output here

Absolute rotary encoders output a unique digital word or bit for each position over 360 degrees of rotation. This digital word must be communicated in the same language as the controlling system with options including parallel, serial, field bus and ethernet based communication protocols.

Learn more about absolute encoder protocols here

When should you use a rotary encoder?

Rotary encoders should be used in any application that requires precision motion control. While a power can be supplied to a motor to make it turn, to control exactly how fast it actually turns  requires real time feedback so that the controlling device can increase or decrease power to achieve a consistent motor speed or shaft position. Rotary encoders are therefore indispensable in precision motion control applications including servo motor feedback, robotics, factory automation and more.

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What is a Rotary Encoder vs Potentiometer?

A rotary encoder generates an electrical signal corresponding to the position and direction of a shaft. It is used in applications requiring high accuracy and resolution. A potentiometer is a variable resistor that changes resistance in response to shaft rotation and is used in applications requiring a variable resistance, such as audio equipment and sensors.

Do Rotary Motor Encoders Need Diodes?

Rotary encoders don't always need diodes, but they may be required in some cases. Diodes are used to protect the encoder's electronics from voltage spikes and reverse voltage. If there is a risk of voltage spikes or reverse voltage, diodes can be used to prevent damage to the encoder's electronics. However, if the encoder is powered by a stable and clean power supply, diodes may not be necessary. It is important to consult the encoder's datasheet and follow the manufacturer's recommendations to determine if diodes are needed.