The word "encoder" is of English origin. It came from the word encode, which means "transform." The most famous world manufacturers of these devices are such well-known brands as Siemens, SKB IS, HEIDENHAIN RLS, Baumer, SICK AG, Balluff, Schneider electric (Autonics Telemecanique), OMRON.
Scope and purpose of application
An encoder is a sensor used in the industrial field to convert a controlled quantity into an electrical signal. Using it, for example, the position of the shaft of an electric motor is determined. Due to the fact that each device in which rotation is used must necessarily be equipped with a device that controls the accuracy of the torque, popular applications for such converters are precise movement systems. The main purpose for which the encoder is used is to measure the angle of rotation of the object during rotation. Encoders are indispensable in the production process at machine-tool enterprises, in work equipment complexes. They are also used in many modern measuring instruments, which require the registration of high-precision measurements of angles, rotations, turns and inclinations.
Encoder Ranking
All currently known encoders are divided into absolute and incremental, resistor, magnetic and optical, working through industrial networks or a bus interface.
Depending on the general principle of operation, absolute encoders and incremental encoders are distinguished. The difference between the two is in the tasks they perform. The list of tasks of the absolute encoder is much wider than the list, which is covered by the incremental encoder.
Incremental encoders
This is a pulse sensor. In the process of turning the object at its outputs are recorded pulses, the number of which is directly proportional to the angle of rotation of the object. Typically, incremental converters are used in the machine tool industry to record the angular movement of the shaft or in automated systems in the feedback circuit to measure and record the speed of rotation of the shaft.
An incremental encoder is a device that operates on the basis of data from pulses generated during rotation. The number of pulses per unit of revolution - this is the main working parameter of this device. The current value is determined by the sensor by the method of counting the number of pulses from the reference point. In order to bind reference systems on the pulse encoder, reference marks are set, which are the starting marks after turning on the equipment. Data determination with an incremental converter is only possible during rotation or rotation. When rotation stops, all encoder data is reset. As a result, upon subsequent activation, the previous counter data will be unknown. For the convenience of its operation should bring the shaft to its original position. The incremental encoder is ideally suited to the task of measuring the speed of rotation. By counting the number of pulses from the reference mark, you can also accurately determine the current coordinate of the rotation angle of the object.
Absolute encoders
So called an absolute position sensor. Typically, in such encoders, more complex processes of electronic signal processing are observed and there is an optical circuit. But then they give out the details of the object immediately after switching on, which is often mandatory for the correct functioning of the system as a whole. Compared to incremental, the use of absolute encoders allows to solve a much wider range of problems, since the measurements are carried out not with the help of fixing pulses, but with special digital codes. The unit of measurement of such an apparatus is the number of unique digital codes per unit of rotation (1 revolution).
Due to the fact that all the digital codes issued by the sensor are unique, it is not difficult to determine the current coordinate of linear displacement immediately after turning on the device without using a reference mark. At the moment of switching on, a code of numbers appears on the sensor outputs. It is the designation of the current position of the angle of rotation of the object. Thus, the absolute encoder copes not only with the task of tracking the speed of rotation (rotation) of an object, but also gives the correct data about its exact location at a given time, regardless of whether it is connected or not.
Varieties of absolute encoders
Depending on the characteristics of the characteristics, axial encoders can differ in the type of fastening, the presence of a through or through, hollow or protruding shaft. The range of such devices is also very diverse in terms of external characteristics: length, diameter of the case and so on. In addition, it is known that absolute position measurement sensors during rotation are multi-turn and single-turn. Single-turn ones determine the current coordinate within 1 revolution, and multi-turn ones are capable of recognizing a few more additional turns.
Optical encoder - what is it?
This converter is a disk made of glass rigidly fixed to the shaft. The optical encoder, in contrast to the above-described sensors, is additionally equipped with an optical raster, which during rotation of the shaft moves and converts the torque into a stream of light, which is subsequently received by the photosensor.
This type of converter captures the rotation angles, where each unique position corresponds to a special unique code of numbers. It, together with the number of revolutions, is the unit of measurement for the sensor. The connection of the encoder and the principle of its operation are identical to the operation of the incremental device described above.
Types of sensors depending on the principle of operation
According to the characteristics of the work, the encoders are divided into magnetic and photoelectric.
The physical principle of the first is based on the application of the Hall effect, discovered in 1879 by E. Hall. In this case, the potential difference arises only when the direct current conductor is placed in the magnetic field region.
In terms of resolution and accuracy, the magnetic encoder is inferior to the photoelectric, but its implementation is simpler. It is much less demanding on spaces and operating conditions.
The representative magnetic encoder is a device that records the cycle of passage of the magnetic pole of a rotating magnet located near the sensing element. The expression of the transmitter data also has the form of a digital code.
A photoelectric encoder is a sensor that operates on the basis of the photoelectric effect, which is observed as a result of the action of light on a substance. This principle was discovered in 1887 by G. Hertz. In the process of operation of a sensor of this type, a constant conversion of the light beam into an electrical signal is observed.
A synonym for photoelectric encoder are optronic, optical and optoelectronic. Sensors of this type are more demanding on the characteristics of production, operation, and much more than other encoders, but this is justified, since the potential for their accuracy is much higher than that of competitors.