Servo Loop Block Diagram - Single Feedback PI

The diagram that follows shows the servo loop for a single feedback PI controller. It is for spring-like systems such as flexure-based piezo stages and the Yaw (Theta) axis of a rigid H-bridge gantry.

The units of the servo loop output depend on the type of axis being controlled. Refer to the table that follows.

Table: Servo Loop Axis Type, Output, and Units

Axis Type	Servo Loop Output and Units
Piezo axis	Amplifier command in Volts.
Stepper axis	Commutation The action of steering currents to the proper motor phases to produce optimum motor torque/force. In brush-type motors, commutation is done electromechanically via the brushes and commutator. A brushless motor is electronically commutated using a position feedback device such as an encoder or Hall effect devices. Stepping motors are electronically commutated without feedback in an open-loop fashion. angle in microsteps.
All other axes	Current command in Amps. When the servo loop output is a current command, the current loop is used to generate the amplifier command in Volts. For more information, refer to Digital Current Loop Block Diagram.

 

Figure: Servo Loop Block Diagram - Single Feedback PI