Incremental photoelectric encoder basic waveform and circuit
Incremental s are sensors that are output in the form of pulses. Their code disks are much simpler and have higher resolution than those of s.Generally, only three bar code channels are needed. In fact, the code channels here no longer have the meaning of absolute encoder code channels, but generate counting pulses.
The outer channel and the middle channel of its code disk have the same number of transparent and opaque sector (grating) evenly distributed, but the two sectors stagger half of each other.As the dial rotates, its output signals are phase A and Phase B pulses with A phase difference of 90° and pulse signals generated by A third channel with only one transparent slit (which serves as the reference position of the dial and provides an initial zero signal to the counting system).
The direction of rotation can be judged from the phase relation (lead or lag) of the two output signals A and B.As can be seen from FIG. 3 (a), the a-channel pulse waveform is more /2 advanced than the B-channel pulse when the code disk is in positive rotation, while the A-channel pulse is more /2 delayed than the B-channel pulse when it is reversed.FIG. 3 (b) is an actual circuit, in which the positive pulse generated by the monostable pulse triggered by the lower edge of the A-channel shaping wave is' matched 'with the B-channel shaping wave. When the code disk is turning in A positive direction, only the forward port pulse is output, and conversely, only the reverse port pulse is output.
Therefore, the determines the rotation direction and relative angular displacement of the code disk according to the output pulse source and pulse count.In general, if the encoder has N (code channels) output signals, the phase difference is/N, and the countable pulse is 2N times the number of gratings, now N=2.Figure 3 circuit fault is sometimes mistake pulse generated error, this situation occurs when a signal in a 'high' or 'low' level, and the other a signal is in the midst of the "high" and "low" change state, back and forth between the encoder while not produce displacement, but the single direction of the output pulse is produced.For example, when the code disk jitters or is manually aligned (as you can see below during gravimeter measurements).