In machine and machine building, the most recent and accurate positional data is constantly required ensuring the correct positioning of movement control systems. Due to its ability to assign exact and unambiguous positional values to any angular position or displacement position at any time, absolute encoders have become one of the most important connecting links between the mechanical part of the machine and its control unit.
The history of the creation of the first absolute rotation encoder and the main differences from incremental
The first absolute sensor, the principle of which was based on the optoelectronic reading of encoded rasters, was developed by the German company FRABA in 1973. While incremental sensors determine the position only relative to a certain position, in absolute sensors the information on the angular position is encoded mechanically, for example, on an optical disk in the form of a raster containing a unique code for each shaft position. Thus, the absolute encoder provides information about the position of the shaft, i.e. about the current coordinate, immediately after switching on and generates a signal both during rotation and at rest.
The absolute encoder does not lose its value in the event of a power loss, and if the encoder shaft was turned off by a certain angle or a certain number of revolutions, when the voltage appears, the encoder will immediately display a new, actual angular position of the shaft and the actual revolution number. Due to this property, it is not necessary to move the mechanical parts of the machine to the starting position or, as it is customary to call the reference position, after each switching on the system, which is an indisputable advantage of absolute encoders over incremental (pulse) ones.
Absolute Encoder Benefits for the Business
The advantage of an absolute encoder is also that it is not susceptible to interference. In cases where the signal from the disk cannot be fully read by the encoder, for example, if the shaft rotates too fast, the exact rotation angle will be recorded when the rotation speed decreases. But even with rapid rotation of the shaft, position registration is possible, albeit with less accuracy. For this, only information coming from the higher ranks is simply taken into account, i.e. distorted (due to the high rotation speed) information coming from the lower digits is simply ignored. The absolute encoder is resistant to vibrations and other kinds of interference, as an error resulting from the calculation of “false” pulses resulting from, for example, vibration, is excluded.
For a clearer understanding of the principle of operation of absolute encoders, in particular, the grounds for the need to use special methods of encoding signals when constructing absolute encoders, it will be appropriate to recall some basics of digital technology, including types / methods of encoding numbers / signals described below.
The term “binary” in meaning is consisting of two parts, components. Thus, binary codes are codes that consist of only two symbolic states, for example, black or white, light or dark, a conductor or insulator. A binary code in digital technology is a way of representing data (numbers, words, and others) in the form of a combination of two characters, which can be designated as 0 and 1. Signs or units of the BC are called bits. One of the justifications for the use of BC is the simplicity and reliability of the accumulation of information in any medium in the form of a combination of only two of its physical states, for example, in the form of a change or constancy of the light flux when read from an optical code disk.