Electricity: motor control systems – Closed loop speed control system for dc motor with commutator
Reexamination Certificate
2001-01-04
2003-09-30
Nappi, Robert E. (Department: 2837)
Electricity: motor control systems
Closed loop speed control system for dc motor with commutator
C318S132000, C318S245000, C318S254100, C318S432000, C318S434000, C318S434000, C318S685000, C318S800000, C318S801000, C318S802000
Reexamination Certificate
active
06628893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus wherein a DC (direct current) motor is used as a driving force for performing mechanical operations, and stabilization of the rotation speed of the DC motor and control of cumulative rotation number of the DC motor are required, more particularly relates to a DC motor rotation detecting apparatus and a DC motor rotation control apparatus wherein rotational operations of a rotor of the DC motor are controlled by detecting at least one of a rotational direction, a rotation speed, a cumulative rotation number, and a rotational position of the rotor.
2. Discussion of the Background
A brush-use DC motor is much used as a driving force for mechanical operations in a camera, such as, for example, zooming operations wherein photographic lenses including a zoom lens are zoomed, 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 information of distance from an object to an image focusing point, and film feeding operations wherein a photographic film is wound and rewound.
In the brush-use DC motor, plural fixed magnetic poles are formed in a stator employing a permanent magnet, etc. A DC drive current is switched corresponding to rotation angle of a 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) uni-directional rotations of the motor are used, and a rotation speed of the motor is required to be kept constant; (2) uni-directional rotations of the motor are used, and a cumulative rotation number of the motor, that is, a total driving amount of the motor, is required to be controlled; (3) bi-directional rotations of the motor (i.e., a forward rotation and a reverse rotation) are used, and a rotation speed only on uni-directional rotations of the motor is required to be kept constant; (4) bi-directional rotations of the motor are used, and each rotation speed on bi-directional rotations of the motor is required to be kept constant; and (5) bi-directional rotations of the motor are used, and a cumulative rotation number on unidirectional rotations of the motor is required to be controlled.
With regard to a rotation control method of a motor in an apparatus, there are, for example, two types of apparatuses according to their uses and operation environmental conditions; (1) a rotation speed of the motor is controlled by changing a drive voltage for driving the motor, and (2) a rotation 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-use DC motor,
FIG. 22
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 rotation 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 an 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 rotation angle of the rotor. Thereby, a rotation 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 rotation 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 rotation 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 rotation slit disk, the photointerrupter, 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. 23 and 24
. In
FIG. 23
, 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 the way, the ripple waveform of 60°-period of the drive current as illustrated in
FIG. 24
is obtained.
Because the ripple waveform corresponds to the rotation angle position of a rotor, the pulse signal corresponding to the rotation 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 cause inaccuracies. Thus, this rotation detecting method is disadvantageous.
Japanese Laid-open patent publication No. 4-127864 describes another method for detecting a rotation speed of a DC motor wherein a rotation detecting brush is provided in addition to a pair of 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 rotation speed of the DC motor is detected based on the signal generated by the rotation detecting brush.
Further, Japanese Laid-open patent publication No. 4-127864 describes a DC motor control circuit illustrated in FIG.
25
. Referring to
FIG. 25
, 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
102
, and a time constant circuit
103
in order. In a comparator
105
, the voltage of the output signal from the time constant circuit
103
is applied to a non-inversion input terminal (i.e., +side) of the comparator
105
, and the voltage of the output signal from a reference voltage generating device
104
is applied to an inversion input terminal (i.e., −side) of the comparator
105
. The output signal from the comparator
105
is connected to one terminal of exciting coils of a relay
107
through a diode
106
. Another terminal of the exciting coils of the relay
107
is connected to one termi
Koyama Kenji
Ohno Yoshimi
Tsurukawa Ikuya
Nappi Robert E.
Ricoh & Company, Ltd.
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