ee301 answer2

What are incremental encoders? Are they useful to us in any way?
Optical encoders are devices that convert a mechanical position into a representative electrical signal by means of a patterned disk or scale, a light source and photosensitive
elements. With proper interface electronics, position and speed information can be derived.

Incremental encoders

The disk of an incremental encoder is patterned with a single track of lines around its periphery. The disk count is defined as the number of dark/light linepairs that occur per revolution ("cycles / revolution" or "c/r").As a rule, a second track is added to generate a signal that occurs once per revolution (index signal), which can be used to indicate an absolute position.
To derive direction information, the lines on the disk are read out by two different photo-elements that "look" at the disk pattern with a mechanical shift of 1/4 the pitch of a linepair between them. This shift is realized with a "reticle" or "mask" that restricts the
view of the photo-element to the desired part of the disk lines. As the disk rotates, the two photo-elements generate signals that are shifted 90° out of phase from each other. These are commonly called the quadrature "A" and "B" signals. The clockwise direction for most encoders is defined as the "A" channel going positive before the "B" channel.




If the readout of the disk is obtained by a single photoelement for each of the A and the B channels, it is called a "single-ended" readout. This type of readout generates signals that are very susceptible to disk runout ("wobble"), slight imperfections in disk etching, etc. A much more effective and accurate readout system is called "push-pull" where the A and B channels are generated by two photo elements for each channel.

Incremental encoders are used to track motion and can be used to determine position and velocity. This can be either linear or rotary motion. Because the direction can be determined, very accurate measurements can be made.
Rotary encoders are often used to track the position of the motor shaft on permanent magnet brushless motor, which are commonly used on CNCmachines,robots, and other industrial equipment. In these applications, the feedback device (encoder) plays a vital role in ensuring that the equipment operates properly. The encoder synchronizes the relative rotor magnet and stator winding positions to the current provided by the drive.

Reference:
en.wikipedia.org