Electricity: motive power systems – Positional servo systems
Reexamination Certificate
2000-12-27
2003-09-09
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
C318S132000, C318S245000, C318S254100, C318S434000, C318S685000
Reexamination Certificate
active
06617816
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS AND PUBLICATIONS
This application claims priority and contains subject matter related to Japanese Patent Application No. 11-371936 filed in the Japanese Patent Office on Dec. 27, 1999 and the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus wherein a DC (direct current) motor is used to provide the driving force for performing mechanical operations, and wherein stabilization of the rotational speed of the DC motor and control of cumulative rotation numbers of the DC motor are required. More particularly, the present invention relates to a rotation detecting apparatus and a rotation control apparatus for the DC motor wherein rotational operations of the rotor of the DC motor are controlled by detecting at least one of the rotational direction, the rotational speed, the cumulative rotation number, and the rotational position of the rotor.
2. Discussion of the Background
A brush-using DC motor is often used to provide the driving force for mechanical operations in a camera, for example: in zooming operations, wherein photographic lenses including a zoom lens are zoomed; in focusing operations, wherein at least one of a photographic lens and an imaging device is moved along an optic axis of the photographic lens for focusing based on the distance from an object to an image focusing point; and in film feeding operations, wherein a photographic film is wound and rewound.
In the brush-using DC motor, plural fixed magnetic poles are formed in a stator by employing a permanent magnet, etc. A DC drive current is switched corresponding to the rotational angle of the rotor, and is applied to plural rotor coils forming plural magnetic poles of the rotor through a commutator which rotates together with the rotor and through a brush which is in sliding contact with the commutator. Thereby, the rotor rotates.
There are, for example, five types of apparatuses using a motor as a driving force: (1) the type where uni-directional rotations of the motor are used, and the rotational speed of the motor is required to be kept constant; (2) the type where uni-directional rotations of the motor are used, and cumulative rotation numbers of the motor, that is, the total driving amount of the motor, are required to be controlled; (3) the type where bi-directional rotations of the motor (i.e., a forward rotation and a reverse rotation) are used, and the rotational speed only on uni-directional rotations of the motor is required to be kept constant; (4) the type where bi-directional rotations of the motor are used, and each rotational speed on bi-directional rotations of the motor is required to be kept constant; and (5) the type where bi-directional rotations of the motor are used, and cumulative rotation numbers on uni-directional rotations of the motor are required to be controlled.
With regard to the rotation control method of the motor in an apparatus, there are, for example, two types of apparatuses according to their uses and operation environmental conditions: (1) the type where the rotational speed of the motor is controlled by changing a drive voltage for driving the motor; and (2) the type where the rotational speed of the motor is controlled by a chopping control wherein a drive voltage is intermittently applied to the motor.
As an example of the above-described brush-using DC motor,
FIG. 30
illustrates a three-pole motor. In the three-pole motor, electricity is fed to a commutator CM
0
which is in sliding contact with a pair of electrode brushes B
01
and B
02
from a DC drive power supply E
0
through the paired electrode brushes B
01
and B
02
. The paired electrode brushes B
01
and B
02
are brought into contact with the commutator CM
0
on rotational angle positions different by 180°. The commutator CM
0
includes three pieces which form a cylindrical surface and rotates together with a rotor of the DC motor. The three pieces of the commutator CM
0
are separated at equally angled interval of about 120°. Three rotor coils are connected to each other between the adjacent pieces of the commutator CM
0
, and thereby three rotor magnetic poles are formed therebetween. The polarity of these rotor magnetic poles varies depending on the contact state of each piece of the commutator CM
0
and the electrode brushes B
01
and B
02
which changes corresponding to the rotational angle of the rotor. Thereby, a rotational driving force is generated between, for example, a pair of stator magnetic poles of a permanent magnet at the side of a stator (not shown).
With the rotation of the rotor, respective rotor magnetic poles oppose to respective stator magnetic poles in order, and the contact state of each piece of the commutator CM
0
and the electrode brushes B
01
and B
02
changes. Thus, by the variance of the polarity of each rotor magnetic pole in order, the rotor continually rotates.
Specifically, when a voltage is applied to the paired electrode brushes B
01
and B
02
from the power supply E
0
, the current flows from one of the electrode brushes B
01
and B
02
to another through the rotor coils. The magnetic field is generated by the rotor coils, and thereby the rotor magnetic poles are formed. By the action of the magnetic field generated by the rotor coils and the magnetic field generated by the stator magnetic poles, the rotor rotates.
As a method of detecting the rotation of the above-described motor, a rotary encoder method is known. Specifically, in the rotary encoder method, a rotational slit disk having slits on the circumferential surface thereof is provided on a rotation output shaft of the motor or in a power transmission mechanism rotated by the rotation output shaft. The rotation of the motor is detected by the method of detecting the slits on the circumferential surface of the rotational slit disk with a photointerrupter. Although the rotary encoder method allows an accurate detection of the rotation of the motor, space and cost for the rotary encoder constructed by the rotational slit disk, the photointerrupter, and etc. are inevitably increased.
Further, another method of detecting the rotation of the motor from the drive voltage ripple of the motor is described referring to
FIGS. 31 and 32
. In
FIG. 31
, a resistor R
0
is connected in series to electrode brushes B
01
and B
02
in a power supplying line for supplying the motor drive current to the electrode brushes B
01
and B
02
from a drive power supply E
0
, and the voltage between both terminals of the resistor R
0
is detected. In such a way, the ripple waveform of 60°-period of the drive current as illustrated in
FIG. 32
is obtained.
Because the ripple waveform corresponds to the rotational angle position of the rotor, the pulse signal corresponding to the rotational angle position can be obtained by suitably rectifying (shaping) the ripple waveform. Although this another rotation detecting method is advantageous in cost and space, detection errors due to noise, etc. may be caused, so that this another rotation detecting method may be disadvantageous in detection accuracy.
For example, Japanese Laid-open Patent Publication No. 4-127864 describes a method for detecting the rotational speed of a DC motor wherein a rotation detecting brush is provided in addition to a pair of electrode brushes. Similarly, as in the paired electrode brushes, the rotation detecting brush is brought into sliding contact with a commutator so as to extract a voltage applied to the commutator. The rotational speed of the DC motor is detected based on the signal generated by the rotation detecting brush.
Specifically, Japanese Laid-open Patent Publication No. 4-127864 describes a DC motor control circuit illustrated in FIG.
33
. Referring to
FIG. 33
, a rotation detecting brush BD
0
is provided to a motor M
0
in addition to a pair of electrode brushes B
01
and B
02
. The rotation detecting brush BD
0
is connected to a differentiating circuit
101
, a time constant reset circuit
10
Koyama Kenji
Ohno Yoshimi
Tsurukawa Ikuya
Nappi Robert E.
Ricoh & Company, Ltd.
Smith Tyrone
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