Servo Loop Block Diagram - Dual Feedback (Secondary I Only)

The diagram that follows shows the servo loop for a dual feedback secondary I controller.

An alternate method to dual feedback control is shown in Servo Loop Block Diagram - Dual Feedback (Secondary PI). Typically, the Secondary PI method is higher performing, but it requires a relatively high resolution Auxiliary feedback device with a tight structural loop. If it is difficult to get stability with the Secondary PI method, use to the Secondary I Only method, which is more robust.

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 - Dual Feedback Secondary I Only