Encoders are sensing devices that operate with high speed and accuracy to provide feedback about the motion of objects to control systems. The feedback allows the control system to determine whether the observed object is being positioned correctly, permitting adjustments as necessary. These devices are also used to measure speed, position, direction, and have the ability to provide a count of the object at hand. Due to their versatile functions, there are many types of encoders, a few of which will be covered in this blog.
Linear encoders are optimal for applications where objects are moving along a designated path or line. It uses a transducer to measure the distance between two points, sometimes implementing a cable for long distances or a small rod for short distances. The cable is typically connected between the transducer and the moving object. When the object moves, the transducer acquires data from the cable and generates an analog that is utilized to determine the object’s position.
Rotary encoders provide feedback about the movement of a rotating object or device. It converts the angular position of the moving object into a digital output signal that establishes an object’s position or speed. Rotary encoders are composed of a series of shafts; however, there is another type known as thru-bore encoders, those of which are capable of being directly mounted on top of a rotating shaft like a motor. Thru-bore encoders are available in a variety of sizes and will feature a clamp or set screw mounting option, enabling them to work with a number of applications.
Like rotary encoders, angle encoders monitor and provide feedback on rotational movement, but offer an enhanced degree of accuracy.
Absolute and Incremental Encoders
The terms “absolute” and “incremental” describe the signal output of an encoder. With this in mind, linear and rotary encoders are available as either absolute or incremental in variation. An absolute encoder generates an output signal in the form of a unique set of digital bits that correspond to the position of the object being measured. They can be especially handy if a signal is lost because the encoder can determine an object’s position as there is a specific digital signal trace for every location.
Rotary absolute encoders are available as either single-turn or multi-turn designs. While single-turn encoders have the ability of providing data about any single shaft rotation, multi-turn encoders can provide information about several shaft rotations. Incremental encoders count the number of pulses a signal emits to establish an object’s position. Due to the fact that these encoders rely on pulses, there is no unique digital signature present to determine the absolute position of an object.
The biggest difference between absolute and incremental encoders relies on the fact that incremental encoders measure relative movement with regard to a specific reference point while absolute encoders measure an object’s position by using a signal code that reveals the position.
Encoders use a few different types of sensing technologies to detect motion or position, and optical encoders are one such type. Rotary optical encoders use a light source and a rotating disk with a series of cloudy lines and alternating colorless grooves. When light makes its way through the rotating disk, a photosensor on one side of the disk senses the light and produces an electrical signal that corresponds to both the presence and absence of light from the grooves and lines. An electrical circuit converts this signal into a square wave signal which is a series of pulses with varying amplitudes. These pulses are then sent to a control circuit that measures the pulse count while the encoder rotates and utilizes the data to determine position or movement.
Magnetic encoders use changes in magnetic flux to establish the movement or position of an object. A magnetic rotary encoder contains a magnetized disk that has a number of magnetic poles located along its exterior. As the disk rotates, a sensor next to it detects a magnetic field when the different poles in the disk surface pass near the sensor. The resulting magnetic field produces an output signal that is converted into a square pulse which can be counted by a control circuit. The sensor that is utilized in these encoders can take advantage of the Hall effect which has the ability to detect change in voltage or can use a magnetoresistive sensor that has the capacity to directly detect changes in a magnetic field.
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