Hsi Stepper Motor Theory, SILNIKI KROKOWE
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HSI Stepper Motor Theory
Motors convert electrical energy into mechanical energy. A
stepper motor converts electrical pulses into specific rotational
movements. The movement created by each pulse is precise and
repeatable, which is why stepper motors are so effective for posi-
tioning applications.
Permanent Magnet stepper motors incorporate a
permanent magnet rotor, coil windings and magnetically
conductive stators. Energizing a coil winding creates an
electromagnetic field with a north and south pole as
shown in figure 1. The stator carries the magnetic field
which causes the rotor to align itself with the magnetic
field. The magnetic field can be altered by sequentially
energizing or “stepping” the stator coils which generates
rotary motion.
N
S
Figure 1.
Magnetic field
created by energizing a coil
winding
Figure 2 illustrates a
typical step sequence for a
two phase motor. In Step 1
phase A of a two phase
stator is energized. This
magnetically locks the rotor
in the position shown, since
unlike poles attract. When
phase A is turned off and
phase B is turned on, the
rotor rotates 90
Phase A
Phase A
S
Phase B
N
S
Phase B
Phase B
N
S
•
N
S
Phase B
N
Step 1
Step 2
Phase A
Phase A
clockwise.
In Step 3, phase B is turned
off and phase A is turned on
but with the polarity re-
versed from Step 1. This
causes another 90
Phase A
Phase A
N
Phase B
S
N
Phase B
Phase B
S
N
S
N
Phase B
rotation.
In Step 4, phase A is turned
off and phase B is turned
on, with polarity reversed
from Step 2. Repeating this
sequence causes the rotor to
rotate clockwise in 90
°
S
Step 3
Step 4
Phase A
Phase A
steps.
Figure 2.
“One phase on” stepping sequence for
two phase motor.
Page 1 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 3)
•
°
•
•
°
Stepper Motor Theory: Continued
The stepping sequence illustrated in figure 2 is called “one phase on” stepping.
A more common method of stepping is “two phase on” where both phases of the
motor are always energized. However, only the polarity of one phase is switched
at a time, as shown in figure 3. With two phase on stepping the rotor aligns itself
between the “average” north and “average” south magnetic poles. Since both
phases are always on, this method gives 41.4% more torque than “one phase on”
stepping.
Phase A
Phase A
S
N
Phase B
N
S
Phase B
Phase B
N
S
Phase B
N
S
Phase A
Step 1
Phase A
Step 2
Phase A
Phase A
N
S
Phase B
S
N
Phase B
Phase B
S
•
N
Phase B
S
N
Step 3
Phase A
Step 4
Phase A
Figure 3.
“Two phase on” stepping sequence for two phase motor.
Page 2 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 4)
Stepper Motor Theory: Continued
The stepping sequence illustrated in figure 2 is called “one phase on” stepping.
A more common method of stepping is “two phase on” where both phases of the
motor are always energized. However, only the polarity of one phase is switched
at a time, as shown in figure 3. With two phase on stepping the rotor aligns itself
between the “average” north and “average” south magnetic poles. Since both
phases are always on, this method gives 41.4% more torque than “one phase on”
stepping, but with twice the power input.
Half Stepping
on each half step, figure 4. However, half
stepping typically results in a 15% - 30% loss of torque depending on step rate
when compared to the two phase on stepping sequence. Since one of the wind-
ings is not energized during each alternating half step there is less electromagnetic
force exerted on the rotor resulting in a net loss of torque.
stepping motor would move 45
°
Phase A
Phase A
Phase A
S
N
Phase B
N
S
Phase B
Phase B
N
S
•
N
S
Phase B
Phase B
N
S
Phase B
N
S
Phase A
Step 1
Phase A
Step 2
Phase A
Step 3
Phase A
Phase A
Phase A
N
N
Phase B
S
N
Phase B
Phase B
S
N
Phase B
Phase B
S
N S
•
N
Phase B
S
S
Step 4
Step 5
Step 6
Phase A
Phase A
Phase A
Phase A
Phase A
S
S
Phase B
S
•
N
Phase B
Phase B
N
S
•
Phase B
N
N
Phase A
Step 7
Phase A
Step 8
Figure 4.
Half-stepping – 90
°
step angle is reduced to 45
°
with half-stepping.
Page 3 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 5)
The motor can also be “half stepped” by inserting an off state between
transitioning phases. This cuts a stepper’s full step angle in half. For example, a
90
°
•
Bipolar Winding
The two phase stepping sequence described utilizes a “bipolar coil winding.”
Each phase consists of a single winding. By reversing the current in the windings,
electromagnetic polarity is reversed. The output stage of a typical two phase bipo-
lar drive is further illustrated in the electrical schematic diagram and stepping se-
quence in figure 5. As illustrated, switching simply reverses the current flow
through the winding thereby changing the polarity of that phase.
BLACK
N S
Bipolar
Step
1
2
3
4
1
RED
Q2-Q3
ON
OFF
OFF
ON
ON
Q1-Q4
OFF
ON
ON
OFF
OFF
Q6-Q7
ON
ON
OFF
OFF
ON
Q5-Q8
OFF
OFF
ON
ON
OFF
GREEN
+V
BLUE
+V
Q1
Q2
Q5
Q6
Q3
Q4
Q7
Q8
Figure 5.
Wiring diagram and step sequence for bipolar motor.
Unipolar Winding
Another common winding is the unipolar winding. This consists of two
windings on a pole connected in such a way that when one winding is energized a
magnetic north pole is created, when the other winding is energized a south pole is
created. This is referred to as a unipolar winding because the electrical polarity,
i.e. current flow, from the drive to the coils is never reversed. The stepping se-
quence is illustrated in figure 6. This design allows for a simpler electronic drive.
However, there is approximately 30% less torque available compared to a bipolar
winding. Torque is lower because the energized coil only utilizes half as much
copper as compared to a bipolar coil.
BLACK
N S
Unipolar
Step
1
2
3
4
1
Wh
Q1
ON
OFF
OFF
ON
ON
Q2
OFF
ON
ON
OFF
OFF
Q3
ON
ON
OFF
OFF
ON
Q4
OFF
OFF
ON
ON
OFF
+V
RED
Wh
BLUE
GREEN
Q1
Q2
Q3
Q4
Figure 6.
Wiring diagram and step sequence for unipolar motor.
Page 4 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 6)
Other Step Angles
motor has 12 pole pairs and each pole plate has
12 teeth. There are two pole plates per coil and two coils per motor; hence 48
poles in a 7.5
°
°
motor in a cut away view. Of course, multiple steps can be combined to provide
larger movements. For example, six steps of a 7.5
°
per step motor. Figure 7 illustrates the 4 pole plates of a 7.5
°
stepper motor would deliver a
45
°
movement.
Figure 7.
Partial cut away showing pole plates of a 7.5
°
step angle motor.
Accuracy
The accuracy for can-stack style steppers is 6 - 7% per step, non-cumulative.
of theoretical position for every step, regardless
of how many steps are taken. The incremental errors are non-cumulative because
the mechanical design of the motor dictates a 360
°
stepper will be within 0.5
°
movement for each full
revolution. The physical position of the pole plates and magnetic pattern of the
rotor result in a repeatable pattern through every 360
°
rotation (under no load
conditions).
Page 5 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 7)
In order to obtain smaller step angles, more poles are required on both the
rotor and stator. The same number of pole pairs are required on the rotor as on
one stator. A rotor from a 7.5
A 7.5
°
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HSI Stepper Motor Theory
Motors convert electrical energy into mechanical energy. A
stepper motor converts electrical pulses into specific rotational
movements. The movement created by each pulse is precise and
repeatable, which is why stepper motors are so effective for posi-
tioning applications.
Permanent Magnet stepper motors incorporate a
permanent magnet rotor, coil windings and magnetically
conductive stators. Energizing a coil winding creates an
electromagnetic field with a north and south pole as
shown in figure 1. The stator carries the magnetic field
which causes the rotor to align itself with the magnetic
field. The magnetic field can be altered by sequentially
energizing or “stepping” the stator coils which generates
rotary motion.
N
S
Figure 1.
Magnetic field
created by energizing a coil
winding
Figure 2 illustrates a
typical step sequence for a
two phase motor. In Step 1
phase A of a two phase
stator is energized. This
magnetically locks the rotor
in the position shown, since
unlike poles attract. When
phase A is turned off and
phase B is turned on, the
rotor rotates 90
Phase A
Phase A
S
Phase B
N
S
Phase B
Phase B
N
S
•
N
S
Phase B
N
Step 1
Step 2
Phase A
Phase A
clockwise.
In Step 3, phase B is turned
off and phase A is turned on
but with the polarity re-
versed from Step 1. This
causes another 90
Phase A
Phase A
N
Phase B
S
N
Phase B
Phase B
S
N
S
N
Phase B
rotation.
In Step 4, phase A is turned
off and phase B is turned
on, with polarity reversed
from Step 2. Repeating this
sequence causes the rotor to
rotate clockwise in 90
°
S
Step 3
Step 4
Phase A
Phase A
steps.
Figure 2.
“One phase on” stepping sequence for
two phase motor.
Page 1 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 3)
•
°
•
•
°
Stepper Motor Theory: Continued
The stepping sequence illustrated in figure 2 is called “one phase on” stepping.
A more common method of stepping is “two phase on” where both phases of the
motor are always energized. However, only the polarity of one phase is switched
at a time, as shown in figure 3. With two phase on stepping the rotor aligns itself
between the “average” north and “average” south magnetic poles. Since both
phases are always on, this method gives 41.4% more torque than “one phase on”
stepping.
Phase A
Phase A
S
N
Phase B
N
S
Phase B
Phase B
N
S
Phase B
N
S
Phase A
Step 1
Phase A
Step 2
Phase A
Phase A
N
S
Phase B
S
N
Phase B
Phase B
S
•
N
Phase B
S
N
Step 3
Phase A
Step 4
Phase A
Figure 3.
“Two phase on” stepping sequence for two phase motor.
Page 2 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 4)
Stepper Motor Theory: Continued
The stepping sequence illustrated in figure 2 is called “one phase on” stepping.
A more common method of stepping is “two phase on” where both phases of the
motor are always energized. However, only the polarity of one phase is switched
at a time, as shown in figure 3. With two phase on stepping the rotor aligns itself
between the “average” north and “average” south magnetic poles. Since both
phases are always on, this method gives 41.4% more torque than “one phase on”
stepping, but with twice the power input.
Half Stepping
on each half step, figure 4. However, half
stepping typically results in a 15% - 30% loss of torque depending on step rate
when compared to the two phase on stepping sequence. Since one of the wind-
ings is not energized during each alternating half step there is less electromagnetic
force exerted on the rotor resulting in a net loss of torque.
stepping motor would move 45
°
Phase A
Phase A
Phase A
S
N
Phase B
N
S
Phase B
Phase B
N
S
•
N
S
Phase B
Phase B
N
S
Phase B
N
S
Phase A
Step 1
Phase A
Step 2
Phase A
Step 3
Phase A
Phase A
Phase A
N
N
Phase B
S
N
Phase B
Phase B
S
N
Phase B
Phase B
S
N S
•
N
Phase B
S
S
Step 4
Step 5
Step 6
Phase A
Phase A
Phase A
Phase A
Phase A
S
S
Phase B
S
•
N
Phase B
Phase B
N
S
•
Phase B
N
N
Phase A
Step 7
Phase A
Step 8
Figure 4.
Half-stepping – 90
°
step angle is reduced to 45
°
with half-stepping.
Page 3 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 5)
The motor can also be “half stepped” by inserting an off state between
transitioning phases. This cuts a stepper’s full step angle in half. For example, a
90
°
•
Bipolar Winding
The two phase stepping sequence described utilizes a “bipolar coil winding.”
Each phase consists of a single winding. By reversing the current in the windings,
electromagnetic polarity is reversed. The output stage of a typical two phase bipo-
lar drive is further illustrated in the electrical schematic diagram and stepping se-
quence in figure 5. As illustrated, switching simply reverses the current flow
through the winding thereby changing the polarity of that phase.
BLACK
N S
Bipolar
Step
1
2
3
4
1
RED
Q2-Q3
ON
OFF
OFF
ON
ON
Q1-Q4
OFF
ON
ON
OFF
OFF
Q6-Q7
ON
ON
OFF
OFF
ON
Q5-Q8
OFF
OFF
ON
ON
OFF
GREEN
+V
BLUE
+V
Q1
Q2
Q5
Q6
Q3
Q4
Q7
Q8
Figure 5.
Wiring diagram and step sequence for bipolar motor.
Unipolar Winding
Another common winding is the unipolar winding. This consists of two
windings on a pole connected in such a way that when one winding is energized a
magnetic north pole is created, when the other winding is energized a south pole is
created. This is referred to as a unipolar winding because the electrical polarity,
i.e. current flow, from the drive to the coils is never reversed. The stepping se-
quence is illustrated in figure 6. This design allows for a simpler electronic drive.
However, there is approximately 30% less torque available compared to a bipolar
winding. Torque is lower because the energized coil only utilizes half as much
copper as compared to a bipolar coil.
BLACK
N S
Unipolar
Step
1
2
3
4
1
Wh
Q1
ON
OFF
OFF
ON
ON
Q2
OFF
ON
ON
OFF
OFF
Q3
ON
ON
OFF
OFF
ON
Q4
OFF
OFF
ON
ON
OFF
+V
RED
Wh
BLUE
GREEN
Q1
Q2
Q3
Q4
Figure 6.
Wiring diagram and step sequence for unipolar motor.
Page 4 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 6)
Other Step Angles
motor has 12 pole pairs and each pole plate has
12 teeth. There are two pole plates per coil and two coils per motor; hence 48
poles in a 7.5
°
°
motor in a cut away view. Of course, multiple steps can be combined to provide
larger movements. For example, six steps of a 7.5
°
per step motor. Figure 7 illustrates the 4 pole plates of a 7.5
°
stepper motor would deliver a
45
°
movement.
Figure 7.
Partial cut away showing pole plates of a 7.5
°
step angle motor.
Accuracy
The accuracy for can-stack style steppers is 6 - 7% per step, non-cumulative.
of theoretical position for every step, regardless
of how many steps are taken. The incremental errors are non-cumulative because
the mechanical design of the motor dictates a 360
°
stepper will be within 0.5
°
movement for each full
revolution. The physical position of the pole plates and magnetic pattern of the
rotor result in a repeatable pattern through every 360
°
rotation (under no load
conditions).
Page 5 HAYDON SWITCH & INSTRUMENT MOTORS / THEORY (CAT. REF. 7)
In order to obtain smaller step angles, more poles are required on both the
rotor and stator. The same number of pole pairs are required on the rotor as on
one stator. A rotor from a 7.5
A 7.5
°
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