Encoder
Encoder is a instrument which detects device movement and converts it into analog or digital electrical signal. There are many different types of encoders which can detect different types of movement. Most prevalent difference between them is how they are presenting that position change, and which type of position change they can detect. That is why encoders can be listed into two groups. When it comes to change of position value there are two groups: absolute and incremental encoders. Second difference is the way position is measured and that is: linear and rotary. Encoder we had at our disposal during bachelor thesis is the incremental rotary encoder from SCANCON Industrial encoders.
Figure 6: 2RMHF rotary encoder
Rotary incremental encoders are meant to detect rotary motion and then report it back to the user by incrementing its value. Rotary motion usually of a motor shaft is converted to analog or digital signal and reported back to the user. Important to note is that rotary incremental encoders do not report absolute position, instead they show the change in position that has happened compared to the reference point. It achieves this task by utilizing two signals, A and B. When position is changed encoder sends two square shaped signals which increment the position value according to change. There is also a third signal Z. It's purpose is to determine a particular reference point encoder is positioned at. Faze difference between signal A and B determines direction that position value is going to be incremented towards. That way it is possible to know which direction encoder is spinning. Subsequently speed can be determined by a rate of change.
Resolution of the encoder is also very instrumental considering how precise one needs to track shaft position. Different encoders are going to have different resolutions. Grater the precision which is required, greater the resolution encoder must operate at in order to achieve that precision. If robot is considered, that is tracking of robot joint position, in that case encoder with greater resolution should be considered, standard would be from 3000 - 7000 pulses per revolution.
Figure 7: Differential output waveforms from an incremental encoder