Technical Manual PD4-E-M (EtherCAT)
5 General concepts
Feedback
Stepper motor
BLDC motor
Sensorless
yes
yes
Various operating modes can be used depending on the control mode. The following list contains all
the types of operation that are possible in the various control modes.
Operating mode
Control mode
Open Loop
Closed Loop
Profile Position
yes
yes
Velocity
yes
yes
Profile Velocity
yes
yes
Profile Torque
no
1)
yes
Homing
yes
2)
yes
Interpolated Position Mode
yes
3)
yes
Cyclic Synchronous Position
yes
3)
yes
Cyclic Synchronous Velocity
yes
3)
yes
Cyclic Synchronous Torque
no
1)
yes
Clock-direction
yes
yes
1) The Profile Torque and Cyclic Synchronous Torque torque operating modes are not possible in
the open loop control mode due to a lack of feedback.
2) Exception: Homing on block is not possible due to a lack of feedback.
3) Because ramps and speeds in operating modes Cyclic Synchronous Position and Cyclic
Synchronous Velocity follow from the specified points of the master, it is not normally possible to
preselect these parameters and to ascertain whether a step loss can be excluded. It is therefore not
advisable to use these operating modes in combination with open loop control mode.
5.1.2 Open Loop
Introduction
Open loop mode is only used with stepper motors and is, by definition, a control mode without
feedback. The field rotation in the stator is specified by the controller. The rotor directly follows the
magnetic field rotation without step losses as long as no limit parameters, such as the maximum
possible torque, are exceeded. Compared to closed loop, no complex internal control processes are
needed in the controller. As a result, the requirements on the controller hardware and the controller
logic are very low. Open loop mode is used primarily with price-sensitive applications and simple
movement tasks.
Because, unlike closed loop, there is no feedback for the current rotor position, no conclusion can be
drawn on the counter torque being applied to the output side of the motor shaft. To compensate for any
torque fluctuations that arise on the output shaft of the motor, in open loop mode, the controller always
supplies the maximum possible (e.g., specified by parameters) set current to the stator windings over
the entire speed range. The high magnetic field strength thereby produced forces the rotor to assume
the new steady state in a very short time. This torque is, however, opposite that of rotor's inertia. Under
certain operating conditions, this combination is prone to resonances, comparable to a spring-mass
system.
Commissioning
To use open loop mode, the following settings are necessary:
Version: 1.0.1 / FIR-v1748
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