The principles of incremental photoelectric encoders are: When a encoder disk rotates, (1)it will produce the pulse signal
proportional to the angle; (2) it will also produce the sensing signal of identifying the rotation direction.
The way that the existing incremental photoelectric encoders determine the rotation direction is: one encoder disk has 3
code channels: 'A', 'B' and 'Z'. On both 'A' and 'B' code channels, there are a number of evenly distributed grid holes, and
they have the same cycle, but with one quarter cycle difference in phase between channel 'A' and 'B'. When disk rotates
clockwise, signal phase from 'A' channel is a quarter cycle ahead of that from 'B'; Similarly, when disk rotates
counterclockwise, 'B' signal phase will be a quarter cycle ahead of 'A'. Based on the above phenomena, a circuit can
identify the rotation direction, which is known as 'Kam-Phase Method'.
The mechanism of the new direction recognition method is: When the encoder disk rotates , it continuously generates
three kinds of state binary information sequentially. These three states are defined as state 1, state 2, state 3. While rotating
clockwise, the state changes in the order of state 1, state 2, state 3, state 1.....; While rotating counterclockwise, the state
changes in the sequence of state 1, state 3, state 2, state 1..... The new theory differentiate the digitized state changing
sequence between the clockwise and counter clockwise to determine the rotation direction.This method is called as 'Digital
The advantages of applying the digital method for the rotation direction determination in incremental photoelectric
encoder are: the code channel structure is simpler and there is no accumulative errors and so on.