Encoders are sensing devices whose purpose is to provide feedback about the motion of objects to control systems. This feedback allows the control system to establish whether the object being monitored is being correctly moved or positioned and permits adjustments to be made or actions to be taken based on the movement and position of the object.
Encoders typically are used to measure one or more specific parameters about the object, such as its speed, position, and direction, or to provide a count of the object or some related value. A simple example of how an encoder might be used is in a cut-to-length application. Imagine a cutting operation or machine that is designed to regularly produce material of a certain fixed length. The raw material, such as fabric, is continuously fed into the machine from a spool.
Types of Encoders
There are several different ways in which encoders can be characterized for motion control applications. The most common approach is to characterize these devices by the type of movement being monitored, whether that be linear or rotational. The three most common types of encoders are linear encoders, rotary encoders, and angle encoders.
Linear encoders deal with the movement of objects along a path or line, such as in the cut-to-length application mentioned earlier. This type of encoder makes use of a transducer to measure the movement or distance between two points, sometimes employing a cable or a small rod. In these cases, a cable is run between the encoder transducer and the moving object. As the object moves, the transducer gathers data from the cable and produces an analog or digital output signal that is used to establish the object’s movement or position.
Rotary encoders are used to provide feedback about the movement of a rotating object or device, such as the shaft of a motor. The rotary encoder converts the angular position of the moving shaft into an analog or digital output signal that will then enable a control system to establish the shaft’s position or speed.
Rotary encoders may contain shafts or can be of a design that is known as thru-bore encoders, meaning that they are capable of being directly mounted on top of a rotating shaft such as that of a motor. Thru-bore encoders are available with a wide variety of sizes and feature clamp or set screw mounting options making them suitable for attachment in machine design applications. Flanges are used to position the encoder and to keep it from rotating with the moving shaft.
Angle encoders are similar to rotary encoders in that they monitor and provide feedback on rotational movement, but they are different in that angle encoders tend to offer higher accuracy.