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Hybrid stepping motors combine the features of the PM stepping motors
with the features of another type of stepping motor called a Variable
Reluctance Motor (VR). A VR motor is a low torque and load capacity
motor typically used in instrumentation. The IB series drivers 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 assembly. 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 range 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 IB series drivers are bipolar drivers which work 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 IB drive 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 situation, 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 IB drive 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
drive is set to the motor’s rated current. Precise current control settings are
explained in the sections of Part II of this document that pertain to the model IB
drive which you purchased.
As was discussed in the previous section,
Selecting a Power Supply ,
the higher the
voltage used the faster the current can flow through the motor windings. 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.
Содержание IB S Series
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