2
Product description
Festo – GDCP-CMMO-ST-EA-SY-EN – 2017-05c – English
19
Step motor and encoder
If a step motor is operated without an encoder the motor must always be operated
below
its perform
ance limits. If for example the motor is operated by the driving mass to its performance limit during
fast acceleration, this can have the following consequences:
–
The rotor may no longer be able to follow the rotary field (load torque > motor torque).
–
The resultant step losses lead to incorrect position values.
If a step motor is controlled by an encoder, it can be loaded up to its performance limit. The encoder
must have the same rotor position and it reports this back to the position controller. This prevents
imprecise positioning caused by step losses.
The motor controller supports
–
Step motors with encoder in closed-loop operation (optional: in open-loop operation)
–
Step motors without encoder in open-loop operation
Motor configuration
Function
Motor with encoder
Controlled operation
(closed-loop operation)
Only the energy needed to move the load is
directed into the motor. The motor works in
an energy-optimised way and produces less
heat. The motor is position-controlled when
stationary. Standstill monitoring is active.
Motor without encoder
Controlled operation
(open-loop operation)
The motor is always operated with the set
driving current when travelling. When at a
standstill, the motor is maintained in its posi
tion at the set holding current.
The following functions are
not
supported:
–
Homing/driving to stop
–
Force Comparator
–
Force mode
1)
For specific applications, the “open-loop operation” function can be set with FCT. This function corresponds to that of a motor
without encoder.
Tab. 2.8
Motor configuration: encoder
