Page 254 - Mechatronic Components Roadmap to Design

Case Studies Chapter 16 233

Case 8: Encoder selection
If the mechatronic application requires the system to be positioned and/or speed
controlled, the direction, the amount, and the speed of the rotation should be
measured. An encoder is a sensor that measures direction and amount of rota-
tion and with calculation the speed of rotation can be found. From the structural
perspective there are two types of encoders: absolute and incremental. An abso-
lute encoder can provide output for the specific position and if the power is cut,
the system does not forget where it was when the power comes back. An Incre-
mental encoder has a disc with multiple cuts and a light source and light detector
can count the number of cuts to find the amount of rotation. In order to calculate
the speed of the rotation the amount of rotation is divided into time intervals. If
the time is too long (depends on the application), this division will not be able to
catch any change in the speed and will just average it. If the time interval taken
is too short, it causes computational load.