Festo MTRE-ST42-48S Serie Instrucciones De Utilizacion página 30

MTRE−ST42−48S−..
Phase current
Phase current is the current that flows through strand of a winding. At the maxi
mum phase current, the stepping motor has its maximum holding torque. The
phase current should be adjusted to the load. That is, it does not always make
sense to set the motor's maximum phase current. If the motor is run without load
or with a torque lower than its nominal torque, it can also carry out steps too far or
begin to resonate (see above), which is equivalent to a loss of step.
The set phase current flows at all times through the active coils of the motor, even
when the motor is standing still. An advantage of this is that the motor has a cer
tain resting torque and can be loaded with its holding torque during standstill.
Also, the motor is warmed even at standstill. If this holding torque is not needed in
standstill, it makes sense to reduce the phase current when the motor is at stand
still. The Festo stepping motor controller SEC−ST−48−6−P01 offers this option.
With these attributes of the stepping motor considered, it provides an economical
positioning variant with adequate precision.
Procedure for correctly adjusting the stepping motor
Determining the possible speed with known load
If the torque of the load on the drive is known, the possible speed can be deter
mined from the speed−torque characteristic curve. (see Chapter "Characteristic
curves").
It should be noted that the usable speed range above the speed is about 80% of
the maximum. Beyond that, the motor's loss of torque is so great that the danger
of losing steps increases.
Increased incidence of resonance can be expected in full−step operation. Since this
always depends on the system, it cannot always be precisely determined where
resonance will occur. Here it is necessary to test.
In general, it is advantageous to run at half−step to reduce resonance. Current
should be reduced when the motor is run without load. Current that is set too high
can also cause resonance and thus a loss of step.
30
Festo MTRE−ST42−48S−.. 0407a English