Electricity: motive power systems – Synchronous motor systems – Synchronization systems
Reexamination Certificate
2000-03-17
2001-08-28
Ip, Paul (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
Synchronization systems
C318S661000, C388S842000, C359S369000, C382S181000
Reexamination Certificate
active
06281657
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-080023, filed Mar. 24, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to an image detecting apparatus and method used to observe and measure the shape of microstructures or three-dimensional structures of specimens.
Conventionally, confocal microscopes have been used as image detecting apparatus. A typical confocal microscope is one that uses a disk having a large number of pinholes arranged in the form of spirals, i.e., a Nipkow disk. In such a confocal microscope, in order to produce a confocal image of a specimen, it is scanned with a beam of light by rotating the Nipkow disk. If, when the confocal image of the specimen is captured by a CCD camera or the like, scanning of the specimen by the disk and image capture by the camera are not properly synchronized with each other, then light and dark bars may be produced on captured images.
To solve such a problem, a method has been proposed which synchronizes the disk rotation with the CCD camera using a video signal from the camera as disclosed in Japanese Unexamined Patent Publication No. 9-297267.
Most of the conventional apparatuses use a brushless DC motor that is comparatively inexpensive and easy to use. Usually, the speed control of such a brushless DC motor is performed by controlling the magnitude of a motor drive signal input to a motor driver and thereby changing the magnitude of current in the motor stator coil. As the magnitude of the drive signal increase, the motor speed increases with increasing motor stator coil current and vice versa.
As an invention regarding control of motor stator coil current for motor speed control, there is a motor control device as disclosed in Japanese Unexamined Patent Publication No. 7-250492.
FIG. 1
shows the arrangement of such a device. A brushless DC motor (hereinafter referred to simply as a motor)
111
is provided with delta-connected stator coils
112
a
,
112
b
and
112
c
and a rotor
113
formed with four magnetic poles. Hole elements
114
a
,
114
b
and
114
c
are placed opposite to the motor stator coils
112
a
,
112
b
and
112
c
, respectively. Hall signals E
1
, E
2
and E
3
are output from the Hall elements
114
a
,
114
b
and
114
c
, respectively. Each of the Hall signals is inverted every 180 degrees with movement of the magnetic poles of the rotor
113
past the corresponding Hall element. The Hall signals are displaced in phase with respect to one another by 60 degrees.
A motor controller
115
comprises a digital signal processor. The motor controller has a sinusoidal amplitude control section
116
for controlling the motor
111
in the steady state after start. The control section, in conjunction with a timing generator
117
provided as an external circuit, controls the amplitude of a sinusoidal signal for keeping the motor at a specified speed on the basis of the Hall signals from the Hall elements
114
a
to
114
c
DA converters
118
a
,
118
b
and
118
c
are connected to the motor controller
115
, which convert three-phase sinusoidal amplitude digital data having a phase deviation of 60 degrees output from the control section
116
into analog signals.
The DA converters
118
a
,
118
b
and
118
c
are connected to separation circuits
119
a
,
119
b
, and
119
c
, respectively, which separate sinusoidal signals E
16
, E
17
and E
18
from the respective DA converters into drive signals. The driving signals are signals for driving pairs of switching elements of opposite driving polarity provided in a driver circuit
120
. The driver circuit is provided with three series circuits, each of a P-channel FET and an N-channel FET, in correspondence with the stator coils
112
a
,
112
b
and
112
c
of the DC motor
111
. A switching circuit
121
is equipped with six analog switches
121
a
to
121
f
. The switching circuit
121
is connected at its terminals a to the separation circuits
119
a
to
119
c
and at its terminals b to a starting controller
122
. The switching circuit
121
has its respective switches placed to the b position at the start of the motor by the motor controller
115
, applying drive signals from the start controller
122
to the driver circuit
120
.
When the motor reaches a specified speed as a result of the start control by the start controller
122
, a speed lock signal is obtained from that controller. In response to the speed lock signal, the motor controller
115
moves the switches in the switching circuit
121
to a position. As a result, the drive signals are applied from the separation circuits
119
a
to
119
c
to the driver circuit
120
.
The start controller
122
is provided with a rectangular-pulse amplitude control section
123
, which, in response to the Hall signals E
1
to E
3
from the Hall elements
114
a
to
114
c
, controls the amplitude of rectangular pulses to obtain the specified motor rotation. The amplitude gain of the rectangular pulse signals is controlled so that the difference between the actual rotation detected via the Hall signals and the predetermined reference rotation based on a reference clock becomes zero.
The sinusoidal amplitude control section
116
itself in the motor controller
115
provides no control gain. A drive signal E
11
output from the start controller
122
and having its amplitude gain controlled according to the Hall elements
114
a
to
114
c
is fed through an AD converter
124
into the motor controller
115
. The sinusoidal amplitude control section
116
considers the amplitude of the drive signal E
11
to be the control gain for the motor
111
and determines the amplitudes of sinusoidal signals.
Thus, the speed of the brushless DC motor is changed by changing the motor stator currents in analog fashion. Thereby, the motor is allowed to rotate at a target speed.
However, trying to implement the motor speed control by changing the motor stator currents inevitably results in the need of analog circuits. Even if a high-speed digital signal processor is used to detect the difference between specified speed and current speed and to produce digital drive signals, it becomes necessary to change the motor stator coil currents in analog manner in the final stage. Thus, analog circuits, such as DA converters, become necessary. Usually, the motor driver circuit is susceptible to strong noise that arises from the brushless DC motor itself and various components. Analog signals are easy to be distorted by noise. Control of currents in the stator coils of the brushless DC motor by distorted analog signals results in failure to cause desired currents to flow in the stator coils, making the rotation of the DC motor unstable.
Reducing the stator coil currents in the brushless DC motor allows the rotating speed of the motor to be reduced; however, at the same time, the rotation torque will also be reduced. Thus, there arises a problem that the number of rotations of the DC motor varies greatly with varying torque.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image detecting apparatus which is noise-resistant and permits the rotation speed of a motor to be regulated against variations in torque.
It is another object of the present invention to provide an image detecting method which is noise-resistant and permits the rotation speed of a motor to be regulated against variations in torque.
According to an aspect of the present invention there is provided an image detecting apparatus comprising:
a rotating body having a light-transmission pattern; rotating state detecting mechanism producing a signal indicative of the rotating state of the rotating body;image capture mechanism capturing an image transmitted through the light-transmission pattern and providing an image signal; a motor mounted to the rotating body for rotating the rotating body at a given speed; a motor driver for driving the motor; and a
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Ip Paul
Leykin Rita
Olympus Optical Co,. Ltd.
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