This post covers the topic of what is a working principle of digital position encoder. A digital position encoder is a sensor that generates a digital signal that is proportional to the position of the device. The most frequent application of this device is motion control applications, for example robotics.

We must make a distinction between a shaft encoder and a linear encoder, which responds to rotation and line motion relatively. There are two types of encoders that exist – incremental and absolute.

Incremental encoders generate a series of impulses in response to the motion. This sensor does not have a memory function. In contrary, absolute encoders generate multi-bit digital signals and can detect the actual position directly. These sensors are characterised by the memory function.

Incremental sensors are mostly used for position and speed control, where the lack of a start point is not very important, so the sensor can reset every time after the power break. Absolute encoders can also sense position and speed, but this sensor has a memory option of the start point, so it can memorise the last point before power off.

These types of encoders are very popular in manufacturing applications. Optical encoders are the most popular and wide spread, especially rotary encoders. They are used in electromechanics to detect parameters of engines.

Rotary optical encoders consist of a light source, light detector, code disk and signal processor. The disk has transparent and non-transparent segments between the light source and the detector. The light goes through the code disk patterns, making specific signal patterns on the optical detectors, creating signals A and B.

There is also a Z signal that should correspond to the zero position. The detector sends this information to the processor that identifies information about rotational motion. The manufacturer, CUI, offers different kinds of rotary encoders – incremental, absolute, communicational encoders. Figure 1a depicts the panel mount optical encoder C14, 1b are output waveforms.

working principle of digital position encoder
Figure 1. a – is the incremental optical panel mount encoder C14 from CUI, b is output waveforms.
working principle of digital position encoder
Figure 2 depicts an absolute rotary encoder, the optical shaft MAS36 Serier from CUI
Figure 2. An absolute optical shaft encoder MAS36 Series from CUI
Figure 2. An absolute optical shaft encoder MAS36 Series from CUI

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Signal sources, noise sources, coupling mechanisms


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