Technical Manual PD4-E-M (EtherCAT)
5 General concepts
5 General concepts
5.1 Control modes
5.1.1 General
The control mode of systems without feedback is called open loop, the mode with feedback is called
closed loop. In the closed loop control mode, it is initially irrelevant whether the fed back signals come
from the motor itself or from the influenced process.
For controllers with feedback, the measured control variable (actual value) is constantly compared
with a set point (set value). In the event of deviations between these values, the controller readjusts
according to the specified control parameters.
Pure controllers, on the other hand, have no feedback for the value that is to be regulated. The set
point (set value) is only specified.
Open loop operating mode
Closed loop operating mode
Motor Controller
Motor
Process
Target value
Motor Controller
Motor
Process
Target value
Actual value
In addition to the physical feedback systems (e.g., via encoders or Hall sensors), model-based
feedback systems, collectively referred to as sensorless systems, are also used. Both feedback
systems can also be used in combination to further improve the control quality.
Motor Controller
Operating mode
Open loop
Operating mode
Closed loop
Physical
feedback systems
Encoder/hall
Sensorless
Model-based
feedback systems
Summarized in the following are all possible combinations of control modes and feedback systems with
respect to the motor technology. Support of the respective control mode and feedback is controller-
specific and is described in chapters Pin assignment and Operating modes.
Control mode
Stepper motor
BLDC motor
Open Loop
yes
no
Closed Loop
yes
yes
Feedback
Stepper motor
BLDC motor
Hall
no
yes
Encoder
yes
yes
Version: 1.0.1 / FIR-v1748
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