In a nutshell, an encoder is a sensing device that provides feedback. Encoders convert motion into an electrical signal that can be read by some type of control device in a motion control system, such as a counter or PLC. The encoder sends a feedback signal that can be used to determine position, count, speed, or direction. A control device can use this information to send a command for a particular function. For example:
In a cut-to-length application , an encoder with a measuring wheel tells the control device how much material has been fed, so the control device knows when to cut.
In an observatory , encoders tell actuators what the position of a moving mirror is by providing positioning information.
In rail car jacks, motion precision feedback is provided by the Encoders, so that the jacks lift simultaneously.
In an elevator, encoders tell the controller when the car has reached the correct floor, in the correct position. That is, the motion feedback from the encoder to the elevator controller makes sure that the open elevator doors are level with the ground. Without the Encoders, you may find yourself looking in or out of an elevator, rather than simply walking out on level ground.
On automated assembly lines, Encoders give motion feedback to robots. On an automotive assembly line, this could mean ensuring that robotic welding arms have the correct information to weld in the correct places.
In any application, the process is the same: a count is generated by the encoder and sent to the controller, which then sends a signal to the machine to perform a function.
Enocoders use different types of technologies to create a signal, including: mechanical, magnetic, optical, and resistance – optical is the most common. In optical sensing, the encoder provides information based on light interruption.
The graphic to the right describes the basic construction of an incremental rotary encoder with optical technology. A beam of light emitted by an LED passes through the code disk, which is patterned with opaque lines (much like the spokes on a bicycle wheel). As the encoder shaft rotates, the LED light beam is interrupted by opaque lines on the code disk before being picked up by the Photodetector Assembly. This produces a pulse signal: light = on; no light = off. The signal is sent to the counter or controller, which in turn will send the signal to produce the desired function.