BENJAMIIN C. KUO, FELLOW, IEEE, AND GURDIAL SINGH, MEMBER, IEEE
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. IA.-l, NO. 4, JULY/AUGUST 1975
Professor:王明賢
Class:控晶四甲
Student:蔡景棠
I. INTRODUCTION
THE DC-TYPE hybrid step motor described in this
paper consists of a variable-reluctance (VR) step
motor with a rotor that is wound similar to a dc motor [1].
The development of such a device is nmotivated by the
limited torque capability at higher speeds of existing step
motors. Although the current generation step motors can
generally provide adequate detent torque, the output is
severely limited at higher operating speeds. This limitation
is apparently an inherent problem, since the highly reactive
stator windings have to be sequentially switched to
step the mot-or. As the speed increases, the currents in the
windings simply do not have enough time to build up and
decay sufficiently, thereby reducing the torque capability
of the motor. The use of higher voltages writh series voltagedropping resistors or dual voltage schemes alleviates
the problem to some extent, but the improvement is limited
by practical voltage values and loNwer operating efficiencies.
II. OPERATING PRINCIPLE OF DC-TYPE
HYBRID STEP MOTOR
In order to describe the operation of this type of hybrid motor,
consider a four-phase multiple-stack VR step motor. The end
view of one phase of the mnotor is shown in Fig. 1,and a
longitudinal schemnatic of all four phases is shown in Fig. 2.
With 20 teeth, t,his particular motor has 80 steps per revolution,
or 4.5° per step.
III. DESIGN CONSIDERATIONS
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A. Design of Hybrid Motor by Modifying Existing Step Motor
We shall first consider an existing step motor whose
Configuration will be utilized in the design of a hybrid motor.
Because the step motor portion has already been designed,
the parts that remain to be designed include the rotor winding and
the commiutator. With a fixed number of poles and a given number
of rotor teeth, a double-layer lap winding (progressive or
retrogressive) is generally the only available option. The rotor slots
may have to be modified slightly to better accommodate the
winding coils,although care has to be taken so as not to change the
stepping characteristics (especially, detent torque) too
drastically.
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B. Complete Design of Hybrid M1otor with No Constraints on Configuration
This procedure, which consists of several steps, is now briefly
outlined.
(1) Input Speczfications: These have to be fed to the program first and include data for dc
operation such as rated power output, rotor voltage, rated torque or speed, and the number of
stator poles. In addition, because the motor has to be able to step, information regarding the
number of rotor and stator teeth, the number of phases (stacks), and the nominal air-gap length
have to be provided at this time. In order to insure adequate stepping torque, the minimum rotor
diameter may also be specified if the number of teeth is large.
(2) Design of Rotor Teeth and Rotor Winding: This is the first stage of the design. Fixed slot
width and tooth width ratios are utilized to obtain initial slot and tooth dimensions. Conductor
sizes are automatically selected from a prestored copper wire table, and the rotor winding is
designed.
(3) Initial Magnetic Circuit Analysis and Field Winding Design: Various air-gap flux densities
are selected and a magnetic circuit analysis is performed to determine the
MMF required for the stator and rotor teeth and the air gap. The \I\IF in the remaining portions of
the circuit is estimated and a variety of field structures are designed for each air-gap flux density
chosen previously.
(4) Solution and Final Calculations: From the various designs obtained in step 3), the most
promising one (or more) is selected. The magnetic circuit calculations, includinig leakage flux
calculation, are performed in detail and the densities in each section are checked out. Final
values for output torque, no-load/full-load speed, power output, and efficiency are obtained and
compared with the original specifications. Any major discrepancies or undesirable parameters
are spotted and, if necessary, steps 2) and/or 3) are repeated with modified specifications.
(5) Stepping Torque at-d Other Parameters: In this step the static detent torque is estimated
and the calculations for rotor inertia and the various temperature rises are performed.
Again, if there is any undesirable parameter, the appropriate data changes are made and the
preceding steps are repeated. Since all calculations are performed on a digital computer, the
total computation time needed to repeat steps 2) through 5) is generally just a few minutes.
IV. DESCRIPTION OF PROTOTYPES
Prototype I
This hybrid motor was designed by modifying an
existing step motor. The step motor that was used
has the following characteristic data:
type
number of phases
number of rotor teeth
step size
current rating
static torque
motor outer diameter
motor length
poles per stack
multiple-stack VR
4
20
4.50 (80 steps per revolution)
6 A per phase
750 oz-in per phase at rated
current
4.56 in
12.0 in
4.
This step motor is modified to yield a hybrid motor using the
design procedure of Section III-A. The following additional
characteristic data are obtained:
rotor winding
wire size and material
Insulation
number of conductors
per slot
commutator and
brushes
rated winding current
rated de torque
double layer, simple lap
no. 25 AWG, copper
class type A (heavy formvar)
36
20 segment, copper, 4 brushes
900 apart
2.5 A per conductor, 4 parallel
circuits, - 10 A rated rotor current
330 oz-in.
B. Prototype II
This hybrid motor was completely designed from the first principles and
includes both the dc and stepping aspects of the device. The input
specifications were
torque output
500 oz-in at 4500 r/min
steps per revolution
96 (3.75°/step)
number of phases
4.
Although no static torque was directly specified, the figure of 700 oz-in was
considered desirable.
The computerized design procedure of Section III-B was applied to the
design of this motor. After several iterations the following data were accepted:
V. OPERATING MODES AND TEST RESULTS
A. Stepping Mode
This mode corresponds to normal stepping operation with the rotor left unenergized. The
motor is operating as a regular step motor and any suitable drive scheme may be utilized. In
addition, the motor can be run in either the open-loop mode or the closed-loop mode.
B. DC-Aided Stepping Mode
In this case the stator windings of the motor are stepped normally in an open-loop
scheme and the rotor is also energized from a dc source. The pulsating flux, -which is
established when the stator phases are being stepped, will interact with the rotor current and
produce a pulsating torque in each rotor section. The total torque from all sections, however,
N-ill be relatively uniform, and with the appropriate polarity for rotor current, this torque can be
made to aid the stepping torque. Thus, although the motor is still running open loop, its load
capability is enhanced by adding the de torque to it.
C. DC Mode
In this mode of operation, the hybrid motor is run as a separately-excited dc motor. The
stator windings are all energized with equal currents (If) and the rotor is connected to another
dc supply. The speed of operation is decided, as in a dc motor, by the stator flux, the rotor
voltage, and the load torque.
VI. POINT-TO-POINT CLOSED-LOOP
CONTROL
In this section the application of the hybrid motor for point-to-point
closedloop control is described. The control versatility of the hybrid motor makes
it a particularly effective actuator for point-to-point or fixed-distance
applications.
A closed-loop controller for fixed-distance control with the prototype II
hybrid motor has been designed and constructed. The block diagram of
this controller is shown in Fig. 18. A typical velocity profile generated by
driving the hybrid motor with this controller is shown in Fig. 19. Acceleration
is provided by running the hybrid motor
VII. CONCLUSION
A new hybrid step motor has been described.The feasibility
of an active rotor configuration obtained by winding the rotor of a
VR step motor is demonstrated by two prototypes. Improved
open-loop slewing performance in the dc-aided stepping mode
and substantial running torque at higher speeds in the dc mode
are characteristic of this type of motor. The multimode operation
of this motor also makes it effective as a closed-loop point-topoint actuator. Although more work is needed in developing this
device, the results presented here conclusively indicate its
Feasibility and effectiveness for large power applications.
REFERENCES
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[1l "Electric motor adapted for both stepping and continuous
operation," U. S. patent 3 809 990.
[2] P. N. Budzilovich, "Use of electrohydraulic stepping motors for
all-digital drives," Contr. Eng., vol. 17, pp. 82-88, Jan. 1970.
[3] E. P. Bucher and T. T. Smith, "Stepping motor applications for
machine tool drives," Electromech. Design, vol. 16, pp. 18-21,
Sept. 1972.
[4] M. I. S. Bajwa, "Open-loop control by using electrohydraulic
motors," in Proceedings: Second Annual Symposium on Incremental
Motion Control Systems and Devices, B. C. Kuo, ed.
Urbana, Ill.: Dep. Elec. Eng., Univ. Illinois at Urbana-Champaign,
pp. T1-T18, 1973.
[5] J. Jacquin, "An all-electric high-power step motor," in Proceedings:
Second Annual Symposium on Incremental Motion Control
Systems and Derices, B. C. Kuo, ed. Urbana, Ill.: Dep. Elec.
Eng., Univ. Illinois at Urbana-Champaign, pp. N1-N5, 1973.
[6] A. F. Puchstein, The Design of Small Direct Current Motors.
New York: Wiley, 1961.
[7] A. E. Clayton and N. N. Hancock, The Performance and Design
of Direct Current Machines. London: Pitman, 1969.
[8] M. G. Say, Electrical Engineering Design Manual. London:
Chapman and Hall, 1962.