Encoder Research - Keyon

Owned by
k2jerome@uwaterloo.ca
Jun 01, 2021


What's an encoder?

"A sensing device that provides feedback." They convert motion to a signal that can be read by a control device in a motion control system.

An encoder can send back a signal that can be used to determine position of the motor's spin, rotation count, the speed, or direction.

What are the different types of encoders?

Mechanical, magnetic, resistive, and optical, with optical being the most common. In an optical encoder, the encoder provides its feedback based on the interruption of light.

What's the difference between an absolute encoder and an incremental (relative) encoder?

An incremental signal from an encoder does not tell you the position of the shaft in its rotation. It just tells you that the position has changed.

Absolute encoders tell you that the position has changed, as well as the exact position of the shaft, and how many rotations have been completed.

This translates to the position of a shaft as it spins, or, for example, which way an end effector is facing.

In order for an incremental encoder to tell number of rotations and the position of the shaft accurately, it must be "reset" to a known position before it's turned on. Think of this like manually backdriving a shaft to its original position for testing. An absolute encoder doesn't need to be reset; when the power is turned back on, it picks back up where it was before and can tell you the exact # of rotations, and the shaft's current position, without a reset.

In this way, absolute encoders are better for an application like a robotic arm where it might be difficult to manually bring the arm back to a starting position between power cycles.

General Encoder Stats:

  • What does the "Pulses Per Revolution" stat mean?
    Pulses Per Revolution determines the "precision" of the encoder. It is the number of "ticks" in the circle as the shaft spins around. If there are 4096 ticks (4096 pulses per revolution, PPR), then you can tell where the shaft is in its rotation with about 1/4096 precision.

  • What does the "Detent" stat mean?

    If an encoder has detent, it just means that it makes a "click" when it turns.

AMT:

Mounting the AMTs:
- There are several mounting holes that come with the AMT base (which comes with the AMT encoder's kit). If your gearbox/shaft output has a hole that's in range of it, screw the AMT in with that: https://www.digikey.ca/short/7r5dfbjt
- Drawing of the AMT base (mounting gear):  https://www.digikey.ca/htmldatasheets/production/2288685/0/0/1/amt-b0-s-drawing-.html
- Example mounting video: https://www.digikey.com/en/videos/c/cui/mounting-the-amt-modular-encoder-series
- Otherwise, the AMTs will need to be glued in place.
- Different AMT series encoders (1XX vs 2XX) come with different mounting bases.

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