Encoders – also called rotary encoders, protractors or angle encoders – originate from communications engineering as well as from drive engineering and each designate somewhat different things. Whereas in communications engineering an encoder is the first converter or transducer for digital or analog signals, in drive engineering encoders are used to generate signals from mechanical movements. The encoders detect the position of a drive unit (shaft) and output this as an electrical signal (pulse generator).
Encoders are connected to the rotating element by various attachments such as grooves or bores. A distinction is made between rotary and linear encoders. Rotary encoders are used on rotating components (e.g. a motor shaft) and are thus used for measuring rotation. Linear encoders, on the other hand, are usually used on components with straight movements.
Encoders have incremental (not absolute measuring) or absolute measuring standards. Absolute measuring encoders (so-called absolute encoders) work on the basis of measuring standards that assign a clear signal pattern to each position. Incremental encoders, i.e. encoders that do not measure absolutely, are mounted on motor shafts, for example, to set parameters such as volume or to manually regulate motor movements on CNC controls.
With their output signal, encoders enable drive units to perform reproducible movements. If the encoder is an absolute encoder, the machine can also be returned precisely to the starting position. Incremental encoders, on the other hand, require an additional encoder, such as a limit switch, to find the starting position. Linear incremental encoders are used, for example, for optically sampling line patterns in a printer. They enable the print carriage to execute a precise movement along the line.
As far as the differences in mechanical design are concerned, a distinction is made between rotary encoders with integral bearing and those without integral bearing. Whereas encoders with integral bearing are either plugged directly onto the shaft to be measured or connected with a separate shaft coupling, encoders without integral bearing (for example built-in encoders or panel meters) are mounted directly on the shaft to be measured at their rotor. For this purpose, the stator is aligned to the machine.
In addition, there are some differences in the type of signal evaluation:
Incremental encoder: Incremental encoders provide information about position, angle and number of revolutions. This information is generated by measuring the number of pulses per revolution that the encoder passes on to the controller. This in turn calculates the current position by counting the pulses that are passed on. Incremental encoders are ideal for factory, logistics and process automation, for example. By mounting them on the motor of an automated guided vehicle, for example, they can provide information about the direction of travel and speed of the system.
Absolute encoders: This type of encoder measures the rotary motion of a shaft in angular increments, each of which is assigned a unique code pattern. In some cases, other information can also be recorded, such as speed or diagnostic data. Absolute encoders are used in automation technology in factories and logistics to record horizontal or vertical rotary motion. In palletizing systems, they measure the exact position of the grippers.
Safety encoders: These incremental encoders are used in combination with safe evaluation units, especially in factory and logistics automation. For example, they are used to monitor the speed of stationary machines and minimize the risk of injury during maintenance operations by slowing down the machine, thus enabling the operator to intervene in the hazardous area.
Draw-wire encoders: These encoders are an interaction of encoder and wire draw mechanics. They are used to measure the drum rotation proportional to length and to output the corresponding data. They are thus used for positioning on linear measuring paths. Draw-wire encoders are also used in industrial environments, for example in logistical processes in the automotive industry. In this context, wire-draw encoders ensure, for example, the correct positioning of lifters that transport goods over several levels.
Linear encoder: Linear encoders consist of a sensor, i.e. a read head, and the reference scale. They operate without contact and are therefore used for wear-free positioning. For example, the encoders determine the position of the trolleys of cranes as well as their travel path positioning.
Measuring wheel encoders: Measuring wheel encoders detect linear movements of a wheel and translate these into speed or position values. They are used, for example, in printing machines. They measure the speed of the print medium and use this information to make a decisive contribution to the correct position of the print and the print quality.
Inclination sensors: Inclination sensors monitor the position of a wide variety of objects and measure their angle of inclination in relation to the earth’s gravity. For harvesters, for example, it is essential that the machine’s inclination angle adapts to the ground as best as possible.
Encoders measure movements and map these in electrical signals. In addition to optical encoders, there are also those that operate magnetically or mechanically with contacts.
Incremental encoders measure the number of pulses per revolution by means of a magnetic wheel, graduated disk or gear flanks. A zero pulse repeated with each revolution serves as a reference. By evaluating two different tracks offset by a quarter pulse, the direction of rotation is read out in addition to the speed.
Absolute encoders, on the other hand, use an encoding disk to record rotations and angles of rotation. On this, each position is unique, so no reference is needed. A connected gear or pulse wire sensors measure the number of revolutions.
Encoders measure pulses and thus motion quantities or quantities that define the state of an object in progressive motion. The pulse frequency that occurs at the encoder is determined by the maximum speed and results from its resolution per revolution. The maximum speed must already be known in advance, since encoders cannot accommodate arbitrary speeds.
In very general terms, a decoder is a system for decoding data. In a modern technological environment in which information must be constantly transmitted, stored and interpreted, both encoders and decoders therefore play a key role.
While the encoder converts or encodes information from one format (binary code) to another, the decoder is the component that reverses the process. It converts the data back into its original or another accessible form. This means that for every encoding process there is an equivalent decoding system. This is the only way to retrieve information.
Since encoders are particularly well suited for exact position determination in automation technology, they are used primarily in industry. They measure both rotational speed and velocity as well as the acceleration of components or drive shafts very reliably.
Even in complex application areas, high-resolution optical and magnetic encoders work perfectly together and enable precise measurements. These include all areas of the manufacturing industry and metal construction, especially the use in lathes and milling machines, CNC machines, motors and many other machines. Their accuracy is also important in the production of industrial spare parts.
Whether digital or analog device, computer or software system – the transmission, storage and evaluation of information play a central role in the operation of electronics-based systems. For this reason, rotary encoders are used in all areas of industry. A distinction is made between rotary and linear measuring tasks. While linear encoders measure linear movements, their position and synchronization, rotary encoders control rotary movements. The latter are divided into incremental and absolute encoders. In linear measurement technology, there are wire-draw and linear encoders with a measuring scale as well as inclination sensors that can measure angles without contact.
