Page 685 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 671
Integral electrical receplacle provides high retention
Neodymium-iron-boron All-in-one molded force of mating connector—8 flying leads are
rotor magnets stator assembly standard option
Exposed laminations aid
thermal dissipation Rugged end bell, encapsulated
windings and electrical connector
utilize high-tech polymer
Class B insulation
New end bell runs cooler:
Many drive shaft encoder life is enhanced
modifications available
Optional encoders and
rear shaft extensions
Largest available shaft Precision ground rotor
diameter (0.375”) on a OD and honed stator ID
NEMA 23 stepper for concentric air gap
withstands high radial
and axial loads, supports Octagonal shape simplifies
numerous shaft modifications automated assembly
Oversized 30 mm bearings
increase bearing fatigue
NEMA size 23 mounting life (L w ) 400% over typical
22 mm bearings
FIGURE 8.46: Cross-sectional view of a four stack hybrid type stepper motor.
Source: Reproduced with permission from Parker Hannifin.

The most significant advantages of step motors are their low cost, simplicity of design,
and ruggedness. The disadvantages are that step motors have mechanical resonance and
step loss problems, although most of these drawbacks have been largely eliminated by the
“microstepping drive” technology. Figure 8.46 shows a picture of the most common type
of stepper motor (hybrid-stepper motor). Figure 8.47 shows the construction of the rotor,
where laminations with teeth are assembled over an axially magnetized permanent magnet
pole pair. Furthermore, the north pole group of laminations is mounted on the rotor with
one half pitch of a tooth angular phase from the south pole group of the laminations.
A stepper motor has a rotor (Figure 8.47) and stator (Figure 8.46). The rotor and
stator are made of laminations of soft iron material. Each stator pole has a concentrated

Phase 1, Pole 1
12 o'clock position

1
2
8

7 3
N S

4
6
5
Magnet
Laminated core Space for coils
Stator poles with teeth
Rotor with teeth
Phase 1, Pole 5
6 o'clock position
FIGURE 8.47: Rotor of a hybrid permanent magnet stepper motor: permanent magnet is
polarized axially (north pole on one side and south pole on the other side along the shaft) and
laminated iron core with teeth. Source: Reproduced with permission from Parker Hannifin.