Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-04-19
2003-08-12
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156320, C310S156360, C310S268000, C310S114000, C310S090500
Reexamination Certificate
active
06605883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to a construction of a multi-phase flat-type PM (Permanent Magnet) stepping motor and a driving circuit thereof. Particularly, the present invention relates to an improvements of a high-resolution and high-accuracy PM stepping motor and a driving circuit thereof that are suitable for OA equipment, which requires accurate positioning during high speed operation, such as a printer, a high speed facsimile or a PPC copying machine.
2. Prior Art
FIG. 23
is a longitudinal sectional side view of one example of this kind of conventional multi-phase flat-type PM stepping motor (referred to as a “motor” in the following description), and
FIG. 24
is a front view of the main portion from a XXIV—XXIV line in FIG.
23
.
In the drawing, a reference
1
denotes a stator,
2
denotes air-core coils and
3
denotes a magnetic disc on which permanent magnets
4
are attached. The magnetic disc
3
is fixed to a rotation axis
8
, and this rotation axis
8
is rotatably supported by bearings
7
fixed to the stator
1
through brackets
1
B. The permanent magnets
4
alternatively magnetized in N-pole and S-pole that are radially arranged. Each of the permanent magnets
4
constitutes a magnetic pole. The pitch of the permanent magnets
4
corresponds to that of the coils
2
.
FIG. 25
shows a connection example of a conventional 6-phase motor with twenty-four coils, and
FIG. 26
shows a driving circuit for the connection of FIG.
25
.
In
FIG. 25
, &PHgr;
1
through &PHgr;
24
denote the coils, A through F denote terminals at one end side of the coils connected in series for each of the phases and A′ through F′ denote terminals at the other end side of the coils.
In
FIG. 26
, T
1
through T
24
are switching elements such as switching transistors to excite the respective coils, &PHgr;AA′ through &PHgr;FF′ are the coil groups in which the coils of the same phase are serially connected as shown in
FIG. 25. A
reference V represents a power supply.
Four switching elements form bridge connection for each phase and each terminal of the coil groups is connected to the intermediate point of the serial connection. In other words, the first switching element T
1
and the second switching element T
13
are connected, the third switching element T
2
and the fourth switching element T
14
are connected, and the terminals A and A′ of the coil group of the first phase shown in
FIG. 25
are connected to the connection points of the switching elements.
In this connection, when the first switching element T
1
and the fourth switching element T
14
are conducting, an electric current passes in a direction EC
1
from the terminal A to the other terminal A′, which energizes the coil group of the first phase. In this way, the motor rotates as the respective phases are sequentially excited by bringing the respective switching elements into conduction in order.
FIG. 27
is a connection diagram of a 10-phase motor that includes forty coils and
FIG. 28
shows a driving circuit for the coils shown in FIG.
27
. In
FIG. 27
, &PHgr;
1
through &PHgr;
40
denote the coils, A through T denote terminals in one end side of the coils connected in series for each of the phases and A′ through T′ denote terminals in the other end side of the coils. A reference V represents a power supply.
In
FIG. 28
, T
1
through T
40
are switching elements such as switching transistors to excite the respective coils, &PHgr;AA′ through &PHgr;TT′ are the coil groups in which the coils of the same phase are serially connected as shown in FIG.
27
. Four switching elements form bridge connection for each phase, each coil group is connected to the intermediate points of the bridge connection.
In other words, the first switching element T
1
and the second switching element T
21
are serially connected and the third switching element T
2
and the fourth switching element T
22
are serially connected. The terminals A and A′ of the first phase coil group are connected to the connection points of the switching elements.
In this connection, when the first switching element T
1
and the fourth switching element T
22
are conducting, an electric current passes in a direction EC
1
from the terminal A to the other terminal A′, which energizes the coil group of the first phase. In this way, the motor rotates as the respective phases are sequentially excited by bringing the respective switching elements into conduction in order.
A step angle is a rotation angle of one step rotation of the stepping motor when the coil groups are sequentially excited phase by phase and it is determined by the structure of the motor. Accordingly, it is necessary to minimize the step angle to obtain a motor having high resolution and a good control performance.
The step angle &thgr; of the multi-phase flat-type stepping motor is represented by &thgr;=360°/(m×Pr), where m is phase number and Pr is a total number of magnetic poles of the rotor including N-poles and S-poles. Therefore, it is necessary to increase the phase number m or the magnetic pole number Pr in order to decrease the step angle &thgr;.
In order to increase the phase number, it is required to increase the number of coils on the stator. For instance, while a 6-phase motor operates with two coils per phase (12 coils in total) in principle, the stable operation requires 24 coils. In the same manner, a 10-phase motor requires 40 coils in total.
However, since the coil has a predetermined width, when all the coils are arranged in the same magnetic disc as the prior art, a number of the coil is limited, and the number of phase cannot be enough large.
On the other hand, the magnetic pole number Pr of the rotor should be increased in order to decrease the step angle without increasing the phase number. However, the magnetic pole number Pr of a rotor is fixed by precision ability of a magnetizing device and cannot be enough large. The minimum step angle of the conventional 6-phase flat-type PM stepping motor was 15°.
A micro-step driving is needed to get a resolution higher than the step angle determined by the phase number and the magnetic pole number. However, since the stop position of the rotor is determined by the relative values of electric current applied to the respective phases under the micro-step driving, it was difficult to improve the accuracy of the resolution due to variation of the values of electric current applied to the respective phases, variation of characteristics of switching elements, or the like. Further, since a complicated driving circuit was need for the micro-step driving, there was a problem that the cost rises.
Further, the conventional driving circuits shown in
FIGS. 26 and 28
require four switching element for each phase. Therefore, 24 switching elements are needed for driving the 6-phase motor and 40 switching elements are needed for driving the 10-phase motor. This complicates the driving circuit and increases the cost thereof.
It is the fact that the multi-phase flat-type stepping motor is hardly available in the market due to the above-described reasons.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above described problems of the conventional motor and to provide a high-resolution, high-accuracy multi-phase flat-type PM stepping motor with employing a multi-unit construction. Another object of the present invention is to provide a simple and low-cost driving circuit for the multi-phase flat-type PM stepping motor.
A multi-phase flat-type PM stepping motor of the present invention described in claim 1 comprises a first motor unit that comprises a first stator unit and a first rotor unit, and a second motor unit that comprises a second stator unit and a second rotor unit. The first stator unit has a plurality of air-core coils that are radially arranged on a first isolating magnetic disc. The first rotor unit has a plurality of permanent magnets that are alternatively magne
Isozaki Kouki
Rokunohe Junji
Tsuda Yuichi
Japan Servo Co. Ltd.
Mohandesi Iraj A
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ramirez Nestor
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