Incremental encoders

The incremental encoders are constructed according to optical or magnetic principles as well as in a single-chip version. Available at the encoder outlets are two 90°e phase-shifted square wave signals with up to 10,000 pulses as well as one index pulse per motor revolution in the 3-channel version.

Incremental encoders transmit a specific number of uniformly distributed lines per revolution. All FAULHABER Incremental encoders have at least two channels: A and B. Both channels supply a square wave signal, shifted by 90°e with respect to one another, i.e., one quarter cycle C. Through this shift of the pulses, the motor’s direction of rotation can be determined.

Functionality of incremental encoders

An incremental encoder does not measure absolute positions, but rather relative positions. So incremental encoders determine a position relative to another reference position. For this purpose, the signal edges must be counted forward or backward by the motor control using a quadrature counter according to their edge sequence.

This position value of an incremental encoder, however, will be lost if the power supply is interrupted. A positioning system must therefore move to a defined reference position during commissioning or after a power interruption to initialise the position counter. This process of an incremental encoder is referred to as homing. For the determination of the reference position in incremental encoders, an additional, external sensor, such as a reference switch or limit switch, is usually used.

Incremental encoders from FAULHABER - Features and benefits

To determine the reference position with an especially high level of accuracy, the FAULHABER 3-channel incremental encoders have an additional channel – the index. Here, a single index pulse is generated once per revolution. External reference switches or limit switches can have a comparably high position error due to environmental influences and can sometimes trigger a little earlier, sometimes a little later. To nevertheless accurately determine the reference position, the drive system can move back after the limit switch until the first signal edge of the index pulse occurs. This point can then be used as an exact reference position.

Incremental encoder with integrated Line Driver

Some of the FAULHABER incremental encoders are equipped with a Line Driver. The Line Driver generates an additional differential signal Ā , B̅ and Ī for all channels, A, B and I. Electromagnetic interference in incremental encoders can thereby be eliminated using this method during signal transmission. Especially if the encoder signals must be transmitted over long distances of 5 m and more and for position control, the use of a Line Driver is recommended.

On the control side, these differential signals of an incremental encoder must be combined again with a receiver module. The Line Drivers from FAULHABER are TIA-422 compatible. TIA-422, also known as EIA-422 or RS-422, is an interface standard for cable-based, differential and serial data transfer.