Subject to change without notification
Subject to change without notification
24
In stepper-motor mode the drive moves proportionally to an pulse train into the control input
AUXin
. In general terms a pulse at the input corresponds to one step – or 1/256th of a revolu-
tion – of the drive. Since the drive’s rotor may not be driven at very high acceleration rates,
the speed reference given by the pulse train must be modified according to the circumstances.
If a very large speed difference is requested by the pulse-train signal, this may require a
higher response than is permitted by the ramps. In this event the drive will not follow the
pulse-train signal, but will remain within the limits of the acceleration/deceleration ramps.
3.7 Stepper Motor Mode
Command Function Description
contmod
Continuous Mode Normal mode, control via the programmable interface
stepmod
Stepper Motor Mode Stepper motor with position preset
stw
Step width Step width in stepper-motor mode
gstw
Get Step Width Read value of step width
This mode is selected with the command
stepmod
. The motor’s computer counts the incoming
pulses at the
AUXin
input and adopts them as position data. This is used to position the drive.
Every pulse alters the step counter, and the step width is set by the command
stw
.
If
stw 1
is set, then every pulse will add or subtract 1/256th of a revolution to/from the posi-
tion reference.
The acceleration in stepper-motor mode should in general be set as low as possible so as to
avoid large speed perturbations.
ac 500
is a recommended value. Continued pulse signals which
are intended to add to the position count should follow each other as closely as possible.
Depending on the setting of the direction preset (see Chapter
3.5.5
), the position count will
be raised or lowered.
Example:
Using the command
stepmod
, the drive is switched to the mode “stepper-motor
with positioning”, and is at standstill.
smd 1
activates direction preset via the direction switch
and sets the switch to run the drive to the left. Now a three-second rectangular pulse signal
at 2 kHz is applied to the control input
AUXin
. As soon as the pulse train is received, the drive
starts turning, running within the preset acceleration ramp values. After a few seconds the
drive will reach the position 6 000 (= 3 s • 2 000 Hz), and it stops at this position.
If a steadily increasing reference value is input, at constant frequency, the speed value will
fluctuate slightly, as the drive continually accelerates and decelerates. This effect will occur at
intervals of 35 ms, i.e. the scan rate of the position regulator. From the acceleration ramp the
maximum amplitude of the speed fluctuation can be calculated as: _v = a • _t where _t is the
scan rate.
Example:
If a ramp of
ac 10 000
is preset, the speed fluctuation will be:
Δ
v = 10 000
• 35 ms = 350
= 21 000 rpm
U
s
2
U
s
