How Does a Rotary Encoder Work?


Quick Answer

Rotary encoders digitize a signal determined by the intermittent passing of light from a light-emitting diode through a spinning disc attached to a motorized shaft. Thus, encoding information about the rotational motion of the shaft.

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Full Answer

Rotary optical encoders are composed of the rotating shaft connected to a motor providing the torque, a code disc connected to the rotating shaft, a light source, optical detectors, as well as circuitry connected to the optical detectors (which translate the light signals from the original source into digital information describing the shaft's motion). First, a light-emitting diode is used to emit light from a steady source toward the code disc. This light then passes through the spinning code disc en route to the optical sensors.

The code disc contains alternating opaque and translucent surfaces, which interrupt or allow the light's passage from point A to point B. The code disc makes complete revolutions or incremental revolutions. This is done according to the rotational speed of the shaft, and the light signal passing through the disk measures the rotational accelerations or decelerations per unit of time by analyzing the intermittent light signals (which are allowed to pass through according to the patterns hard-coded to the disk).

Rotary encoders typically come in two different types - incremental and absolute. Incremental rotary encoders are so named for their measurements of relative motion and calculations between incremental rotations. Absolute rotary encoders use an absolute positioning system, so that the axis of the shaft can be measured by a fixed point at all times.

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