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What is an ENCODER - Linear and Rotary encoder - Incremental and Absolute encoder

An encoder is a communication device that controls the motion of an operating device.
Encoders are used to translate rotary or linear motion into a digital signal helping to determine the speed or position of a motor or other moving equipment.
Basically, an encoder acts as a measuring system for moving parts.

There are two different types of encoders: linear and rotary. A linear encoder responds to motion along a path, while a rotary encoder responds to rotational motion.
Within this two categories, we can list different encoder measurement types such as: Absolute encoders which are capable of providing unique position values from the moment they are switched on. And Incremental encoders that instead generate an output signal each time the shaft rotates a certain amount.
Encoder also differ in electromechanical technologies such as: Optical, Magnetic, Inductive, Capacitive and Laser.

In this video we will focus on the most popular encoder technology: the optical encoder.
We will see different types of optical encoders and their applications.

Let’s start from the linear encoder, which is basically a transducer paired with a scale that encodes position. The transducer reads the scale in order to convert the encoded position into an analog or digital signal, which can then be decoded into position by a motion controller. It is normally used for linear measurements in order to detect the translational motion of an object. These encoders in fact can use a rod or a cable that is run between the encoder transducer and the object that will be measured for movement.

Let’s move on to the rotary encoder, also known as shaft encoder. Unlike the linear encoder, the rotary encoder collects data and provides feedback based on the rotation of an object or in other words, a rotating device. Since it converts the angular position or motion of its shaft to analog or digital output signals.

Basically, both linear and rotary encoders do the same thing. They produce an electrical signal. When this signal is properly processed by the electronic circuits, it produces analog or digital output signals which are translated into angular movements, linear and rotational motion as well as in rotation speed and accelerations.

More than 10 years in industrial supplies, have led JAES to become a qualify partner for some of the most important industrial automation companies, offering a wide range of different encoder types.

As we have said before, both linear and rotary encoders can perform "absolute" or "incremental” measurements.

Absolute Rotary Encoders can measure “angular” positions while Incremental Encoders can measure things such as distance, speed, and position.
Here an example of Absolute Rotary Encoder. We can see inside that a slotted disc on a shaft is used in conjunction with a stationary pickup device. When the shaft rotates, the disc is rotated in a beam of light such as an LED, and the markings on the disc act as shutters blocking and unblocking the light. Thanks to this, a unique code pattern is produced. This means that each position of the shaft has a pattern and this pattern is used to determine the exact position.

If the power to the encoder was lost, and the shaft was rotated, when power is resumed, the encoder will record the absolute position, as demonstrated by the unique pattern transmitted by the disc and received by the pickup device. Absolute measurement encoders can be single turn or multi turn.

“Single turn” absolute encoders are used for measurements of short distance, while “multi-turn” absolute encoders would be more suitable for longer distances or more complex positioning requirements.

Incremental rotary encoders create an output signal every time that the shaft rotates a certain amount. This output signal is then interpreted based on the number of signals per revolution. This encoder begins its count at zero when powered on. So, there are no safeguards regarding the position. Because unlike the absolute encoder, the incremental encoder begins its count at zero in startup or power disruption, for this reason, it is necessary to determine a reference point for all tasks requiring positioning.

The most common type of incremental encoder uses two output channels (A and B) to sense position and direction of rotation. Using two code tracks with sectors positioned 90 degree out of phase, the two output channels of the encoder indicate both position and direction of rotation. If A leads B, for example, the disk is rotating in a clockwise direction. If B leads A, then the disk is rotating in a counter-clockwise direction.

Some types of incremental encoders with integrated commutation signals, are normally used as motor feedback. These additional signals simulate the Hall phases, which are usually employed in brushless motors, as you can see in our previous video. Linear encoders, on the other hand, can be used inside a milling machine, in order to obtain direct control over the exact position of the material.

We can find encoders in many robotic devices for multi-Axis Synchronization control, but also we can find them in common printers. Absolute encoders can be used inside the pitch control system of wind turbines, allowing the blades angle to be adjusted according to wind speed. An absolute encoder is often the preferred solution when the device is inactive for long periods of time or moves at a very slow rate such as flood gate control.

Due to their many advantages, optical encoders are used in many industrial sectors, specifically where high precision is most needed. Like in the healthcare sector, where this type of encoder can be used for precision medical equipment.