Encoders are so called because they "encode" the mechanical
position of a tool or system into an electrical signal. Optical
rotary encoders perform this encoding by means of a patterned disk.
Put the system into motion and, in addition to position (with the
support of the appropriate electronics), encoders can also determine
speed, rate, velocity, distance, or direction of rotation. In a
typical application, one or more encoders provide these parameters
as feedback to the controller in a motion control system. EPC's
rugged reliable encoders are particularly suited to the most challenging
applications in process and machine control, motor feedback, factory
automation, robotics, web tensioning, etc. In addition to these
applications, rotary optical encoders can also provide electronic
commutation in brushless servo systems.
There are two types of rotary optical encoders-incremental and absolute.
Incremental encoders are the simpler and by far the most popular,
having as an output a series of square wave pulses generated as
the code disk, when its evenly spaced opaque radial lines, moves
past a light source. The number of lines on the disk determines
the encoder's resolution, expressed as cycles per revolution (CPR),
or for some models pulses per revolution (PPR). The most basic incremental
encoder, which is sometimes called a tachometer, has just one output
and is most often used in unidirectional applications that just
need position or speed information. As incremental encoders increase
in complexity through bi-directional to quadrature to quadrature
with index, more types of information can be provided.
Since incremental encoders provide only relative position, the position
count can be lost in the event of a power failure. Therefore incrementals
usually use the Channel Z index pulse to reestablish the home position.
Another way is to use an absolute encoder. Absolute rotary encoders
provide a unique output in the form of a binary word for every position.
An absolute encoder retains the exact position information if power
fails and eliminates the need to return to "home" position.
This feature is particularly useful in applications where the equipment
runs infrequently and/or has power turned off between uses.