Incremental encoders
Incremental encoders from FAULHABER measure the shaft rotation and enable both the precise measurement of speed as well as the highly accurate positioning of the drive. Most brushless DC-motors from FAULHABER are offered with fully integrated, analog Hall sensors that can replace the function of an incremental encoder. For the other motors as well as for applications that require a higher level of accuracy, suitable incremental encoders are available. They have an extremely compact design and add only minimal length to the given drive solution.
Encoders detect the rotary movement of a shaft. The rotation is divided into pulses of smaller or larger size depending on their resolution. An incremental encoder does not detect the absolute position of a motor shaft but instead detects it only relative to a reference position. It, thus, counts how many pulses the current position is from the reference. Position data can be derived from this value. FAULHABER offers incremental encoders with optical and magnetic measurement principle.
The device uses sensors to detect changes to a magnetic field. A sensor magnet on the motor shaft supplies the magnetic field that moves with the motor rotation. The sensors are placed on the PCB of the encoder and detect this rotary movement.
In addition to the electronics, an optical incremental encoder consists of three key components: light source, code disc and photosensor. The bundled light beam of the light source is directed at the code disc, which rotates with the motor shaft. The disc is divided into fields with different optical properties.
With reflective encoders, there are alternating reflective and black fields. The light is reflected by the reflective fields; light source and photosensor are located on the same side of the code disc. Light source, photosensor and electronics can be accommodated here on the same PCB or even on the same chip, thereby enabling an especially compact design. With transmissive incremental encoders, on the other hand, the disc is divided by slits through which the light beam falls. Light and sensor are separate here.
In both cases, the photosensor detects the light pulses from the code disc. The analysis of the pulse sequence provides the information about speed and relative position. Optical encoders are characterized by a very high position accuracy and repeatability and a very high signal quality. Furthermore, they are insensitive to magnetic interference.
FAULHABER offers incremental encoders with optical or magnetic measurement principle. With the optical devices, a light beam is divided into pulses by a code disc. These are detected by a photosensor and serve as the basis for the encoder signal. Optical incremental encoders from FAULHABER are based mainly on the reflective process as it enables especially compact solutions.
Magnetic incremental encoders use sensors to detect the changes of a magnetic field resulting from the motor rotation.
Special electronic components process the pulses of the optical or magnetic sensors and generate the standardized output signals of the encoders. They can also interpolate the sensor signals. Multiple pulses can thereby be generated from a single physically measured pulse. This allows the physical resolution of the incremental encoder to be increased many times over.
The encoders can be equipped with two or three channels. Devices with three channels determine an index on each revolution. With optical encoders, it comes from a differently designed field on the code disc; with magnetic encoders, it comes from an additional small magnet or a change of the existing magnet at a defined point. Because an incremental encoder does not detect any absolute positions but instead only relative, an external sensor for referencing is necessary for positioning. An absolute position (zero point) is thereby detected once by the external sensor.
Most incremental encoders from FAULHABER are optionally equipped with a line driver to eliminate electromagnetic interference during signal transmission. Such interference can occur, above all, if encoder signals are transmitted over distances of 0.5 meters in length. The line driver generates an additional differential signal for all channels. The signals are combined again in the controller with a receiver module.
Which variant offers the optimal solution is dependent on the operating conditions and on the requirements for accuracy.
Because magnetic incremental encoders require no optical signals, they are less sensitive to dust. Moreover, they are simpler from a mechanical perspective and more robust than optical encoders. Most magnetic incremental encoders from FAULHABER have a modular design and allow an application-specific adaptation of the resolution. Accuracy and signal quality of the magnetic incremental encoders are sufficient for most applications.
Optical incremental encoders are insensitive to magnetic interference. Moreover, the use of a code disc allows a higher physical resolution to be achieved than with a sensor magnet. This is the basis for a very high position accuracy and repeatability and a very high signal quality. FAULHABER thus offers, e.g., an optical incremental encoder whose code disc divides a revolution into 625 signal periods. Through interpolation, a pulse count of 10,000 with 40,000 individual edges can thereby be achieved. This corresponds to an angular resolution of 0.009 degrees.
Incremental encoders are always part of a drive solution and must be suitable for the motor. All incremental encoders from FAULHABER were developed for combination with selected motor families. For nearly every motor from the FAULHABER product line there is, thus, at least one suitable incremental encoder available.
With our Drive Calculator, you can quickly find the drive solution that best matches your requirements. You can also add an encoder there. Learn exactly what is important when selecting an encoder in our Encoder selection webinar.
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