How Do A and B Signals Determine Motor Direction in Incremental Encoders?

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Discussion Overview

The discussion revolves around the functioning of incremental encoders, specifically how the A and B signals, which are 90 degrees out of phase, determine the direction of motor rotation. Participants explore the relationship between the order of these signals and the direction of rotation, addressing both theoretical and practical aspects of encoder outputs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant expresses confusion about how the order of A and B signals indicates motor direction and seeks clarification.
  • Another participant suggests that the sequence of signals differs based on the direction of rotation, describing a pattern where A is followed by B with varying pauses depending on the direction.
  • A third participant provides a technical overview of the quadrature outputs of the encoder, emphasizing their phase relationship.
  • A later reply explains that the state of signal B when signal A rises can indicate the direction of rotation, proposing a method to connect these signals to an up-down counter for position detection.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specifics of how the order of signals indicates direction, with some providing differing interpretations of the signal patterns. The discussion remains exploratory and unresolved regarding the precise mechanics of signal interpretation.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about signal timing and the definitions of "high" and "low" states, which may vary based on specific encoder designs. The mathematical relationships and signal processing steps are not fully detailed.

tomizzo
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So I've been trying to read up a little on incremental encoders and have been looking at the outputted signals typically labeled A and B. These signals are 90 degrees out of phase. Apparently, the purpose of having both of these signals is for identifying motor direction. However, I'm kind of confused as to how the order of the A and B signals are able to show direction.

I've searched the web and physics forums database but was not able to find any discussion in how direction effects the order of signal outputs. Any help?
 
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A and B detect the rotation of something?

In one direction, the signal will look like A(short pause)B(long pause)A..., in the other the long pause is after A and the short one is after B.
 
Basically if you look at the level of the B when A rises you will see it is high in one direction of rotation and low in the other. Connect A to the clock of an up-down counter and B to the up-down control and you get a relative position detector.
 

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