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Encoders are a group of devices used to precisely measure rotary motion. The principle of encoders is to convert the measured rotary motion into an electrical signal to determine the number of revolutions, displacement and angular position.
Basic information about encoders
Encoders is a small device that provides precise information about the angular connection of an object (such as a shaft) in motion, as well as the direction of rotation and the distance separating the encoder and the moving element. The principle of optical encoders is based on the use of photoelectric phenomenon. Selected encoders are equipped with a rotating disc with notched slots. Other models, on the other hand, have a transparent dial and printed apertures. On one side of the dial is a light source. Most often it is an energy-saving LED. On the opposite side is mounted a light-sensitive element (such as a photodiode). As the dial begins to rotate, the emitted light in the form of pulses reaches the photosensitive part.
In this way, an impulse voltage is generated. Other types of encoders use other technologies to produce an electrical signal, such as resistive, magnetic and mechanical.
Selected types of encoders
There are several types of encoders, which differ from each other, among others. mode of action and application. In addition to the optical encoder described earlier, there are also magnetic models, which are used to precisely measure linear or rotary motion by taking advantage of magnetic phenomenon. Devices of this type consist of, among other things. a magnetic rotating disc and a sensor whose main task is to respond to the changing magnetic field. Applications of the magnetic encoder include. Industrial automation (precise position monitoring of shafts and other rotating elements). In addition, they are used in robotics, transportation and even medicine.
A resistive encoder, on the other hand, uses changes in resistance to produce output signals based on mechanical movements. Devices of this type are built, among other things. of a variable resistance path, a slider and terminals to which the wires are connected.
How does a resistive encoder work? As the slider moves along the resistive path, there is a change in resistance between one of the terminals and the slider. The change in resistance is proportional to the current position of the slider. The generated output (electrical) signal is proportional to the change in resistance. Applications of resistive encoders include. potentiometers, position sensors, controllers and joysticks.
What are mechanical encoders and how do they work?
Mechanical encoders use physical contact to produce an output signal. In other words, they convert rotary motion into an electrical signal. The design of the mechanical encoder includes, among other things. a disc with paths or sectors with different conductive properties, sliding contacts and a shaft. The operating principle of this type of device is to move the sliding contacts along the code disc. Depending on the specific position of the contacts on the dial, the circuit is broken or closed. This is how the generation of the corresponding electrical signal takes place.
Applications of mechanical encoders include. positioning systems and clocks. Devices of this type have certain limitations due to, for example, wear and tear of contact elements and potential interference caused by, among other things. dust.
What is an absolute encoder and what is it used for?
An absolute encoder is a specific type of digital rotary angle encoder. This device gives precise information on the angle of rotation of a moving component based on a one-time fixed position. The absolute encoder, or more precisely, its resolution mostly does not exceed 25 bits. In addition, cyclic Gray code can be used in such converters. Due to their characteristics and the ability to indicate the angle of rotation, even in the event of a power cut, encoders are used, among other things. In industrial automation and CNC machines.
In addition, they are used in industrial robots and other equipment where precise positioning of moving parts is crucial. The absolute encoder is also used in medical applications, such as in CT scanners and surgical robots, where it is responsible for precise positioning. In transportation, on the other hand, such devices are used to monitor the position of wheels on trains and cars. The next industry is energy, where the encoder is used, among other things. For monitoring the performance of wind turbine blades.
Absolute encoder - additional information
Where did the name absolute encoders come from? Devices of this type convert the current position into digital values. They use Gray code, BCD or binary code for this. Each encoder position is one unique value in digital form. This is where the name absolute encoder came from.
The most popular communication interface is SSI, or synchronous serial interface. The principle of this interface is to transmit digital information directly to the data bus in a single way, i.e. one bit at a time synchronized to the so-called clock input.
Selected models of absolute encoders can be easily connected to microcontrollers (such as the popular Arduino series) and minicomputers (such as Raspberry Pi). Mostly they require a power supply in the range of 3.3 V to 5 V.
For absolute rotary encoders, we distinguish between single-turn and multi-turn devices. For single-turn models, rotating the shaft 360° gives the same digital value as the initial value. The absolute multi-turn encoder is equipped with a gear system to provide a unique digital value. Models capable of accurately recognizing more than one number of revolutions are distinguished by their higher overall resolution. This value is the product of the number of items per turn and the number of turns.
