IM483H/IM805H Rev. R032206
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IM483H/IM805H Rev. R032206
Hybrid stepping motors combine the features of the PM stepping motors with
the features of another type of stepping motor called a variable reluctance mo-
tor (VR), which is a low torque and load capacity motor that is typically used
in instrumentation. The IM483H/IM805H cannot be used with VR motors as
they have no permanent magnet.
On hybrid motors, the phases are wound on toothed segments of the stator as-
sembly. The rotor consists of a permanent magnet with a toothed outer surface
which allows precision motion accurate to within ± 3 percent. Hybrid stepping
motors are available with step angles varying from 0.45° to 15° with 1.8° being
the most commonly used. Torque capacity in hybrid steppers ranges from 5
- 8000 ounce-inches. Because of their smaller step angles, hybrid motors have
a higher degree of suitability in applications where precise load positioning and
smooth motion is required.
S i z i n g a M o t o r f o r Yo u r S y s t e m
The IM483H/IM805H is a bipolar driver which works equally well with both
bipolar and unipolar motors (i.e. 8 and 4 lead motors, and 6 lead center tapped
motors).
To maintain a given set motor current, the IM483H/IM805H chops the voltage
using a constant 20kHz chopping frequency and a varying duty cycle. Duty
cycles that exceed 50% can cause unstable chopping. This characteristic is
directly related to the motor’s winding inductance. In order to avoid this situ-
ation, it is necessary to choose a motor with a low winding inductance. The
lower the winding inductance, the higher the step rate possible.
W i n d i n g I n d u c t a n c e
Since the IM483H/IM805H is a constant current source, it is not necessary to
use a motor that is rated at the same voltage as the supply voltage. What is
important is that the IM483H/IM805H is set to the motor’s rated current. See
Section 7: Interfacing to the IM483H/IM805H
for more details.
As was discussed in the previous section,
Power Supply Requirements,
the
higher the voltage used the faster the current can flow through the motor wind-
ings. This in turn means a higher step rate, or motor speed. Care should be
taken not to exceed the maximum voltage of the driver. Therefore, in choosing
a motor for a system design, the best performance for a specified torque is a
motor with the lowest possible winding inductance used in conjunction with
highest possible driver voltage.
The winding inductance will determine the motor type and wiring configuration
best suited for your system. While the equation used to size a motor for your
system is quite simple, several factors fall into play at this point.
The winding inductance of a motor is rated in milliHenrys (mH) per Phase.
The amount of inductance will depend on the wiring configuration of the motor.
