Photography – Camera shake sensing – Having stabilization system
Reexamination Certificate
2002-09-16
2004-06-29
Adams, Russell (Department: 2851)
Photography
Camera shake sensing
Having stabilization system
C396S052000, C348S208400
Reexamination Certificate
active
06757488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in the signal controller for a vibration detecting unit mounted on an optical apparatus such as a compact camera.
2. Description of the Related Art
In current cameras, since all important operations for taking pictures such as exposure determination and focusing are automated, even a person unfamiliar with camera operations is very unlikely to fail in taking intended pictures.
In addition, systems for preventing camera shake have been under study recently, and factors inducing picture mistakes by a photographer have been practically eliminated.
A brief description will now be made of a system for preventing camera shake.
Camera shake at the time of picture taking typically involves vibrations of 1 Hz to 10 Hz in frequency. As a basic principle to allow pictures to be taken with no blur even with such camera shake occurring when a shutter is released, vibrations of a camera due to the camera shake must be detected to move a correcting lens in accordance with the detection value. Thus, taking pictures including no image blur even with camera shake requires exact detection of vibrations of the camera firstly, and correction of a change in optical axis due to the camera shake secondly.
The detection of vibrations (camera shake) can be performed in principle by providing the camera with a vibration detecting apparatus comprising of a vibration detecting sensor for detecting accelerations, angular accelerations, angular velocities, angular displacements or the like, and a control/arithmetic section for appropriately processing the output from the sensor to correct the camera shake. Based on the detection information, a correcting lens for decentering an optical axis for picture taking is driven to suppress picture blur.
FIG. 7
is a perspective view showing the outward appearance of a compact camera having a vibration preventing system. The camera has a function of correcting vertical camera shake and horizontal camera shake indicated by arrows
42
p
,
42
y
with respect to an optical axis
41
. In the following description, “p” means the vertical direction and “y” means the horizontal direction.
A camera body
43
has a shutter release button
43
a
, a mode dial
43
b
(including a main switch), a retractable electronic flash
43
c
, and a viewfinder
43
d.
FIG. 8
is a perspective view showing the internal structure of the camera shown in
FIG. 7
, in which reference numeral
44
shows a camera body,
51
a vibration correcting unit,
52
a correcting lens,
53
a support frame for freely driving the correcting lens
52
in directions
58
p
,
58
y
in
FIG. 8
to correct image blur in the directions indicated by the arrows
42
p
,
42
y
in
FIG. 7
, details of which are later described. Reference numerals
45
p
,
45
y
show vibration detecting devices such as angular velocity meters, angular accelerometers or the like for detecting vibrations about axes as indicated by the arrows
46
p
,
46
y.
Outputs from the vibration detecting devices
45
p
,
45
y
are converted by arithmetic devices
47
p
,
47
y
, later described, into target values for driving the correcting lens
52
in the vibration correcting unit
51
and input to coils
510
p
and
510
y
included in the vibration correcting unit
51
to correct image blur. Reference numeral
54
shows a base plate. Reference numerals
56
p
,
56
y
show permanent magnets. The permanent magnets
56
p
and
56
y
, and coils
510
p
and
510
y
constitute part of components of a driver for driving the correcting lens
52
.
FIG. 9
is a block diagram showing details of the arithmetic devices
47
p
,
47
y
. Since both devices have the same configurations, description is made in
FIG. 9
only for the arithmetic device
47
p.
The arithmetic device
47
p
comprises a DC cut filter
48
p
, a low pass filter
49
p
, an analog-digital converting circuit (hereinafter referred to as “A/D converting circuit”)
410
p
, a driver
419
p
, and a camera microcomputer
411
surrounded by a broken line, all of which are surrounded by a dash dotted line.
The camera microcomputer
411
comprises a storage circuit
412
p
, a differential circuit
413
p
, a DC cut filter
414
p
, an integrating circuit
415
p
, a storage circuit
416
p
, a differential circuit
417
p
, and a PWM duty changing circuit
418
p.
A vibration gyro for detecting the angular velocity of camera shake is used as the vibration detecting device
45
p
. The vibration gyro is driven in synchronization with turn-on of the main switch of the camera to start detection of the angular velocity of camera shake.
An output signal from the vibration detecting device
45
p
is input to the DC cut filter
48
p
formed of an analog circuit which cuts a DC bias component superimposed on the output signal. The DC cut filter
48
p
has a characteristic of cutting signal components at frequencies equal to or lower than 0.1 Hz, so that no influence is exerted on a frequency band of camera shake from 1 to 10 Hz. Such a characteristic of cutting frequencies of 0.1 Hz or lower, however, presents a problem that it takes nearly 10 seconds from the input of the vibration signal from the vibration detecting device
45
p
to the completion of the DC cut. To address the problem, the DC cut filter
48
p
is set to have a small time constant (for example, to have a characteristic of cutting signal components at frequencies equal to or lower than 10 Hz), for example for 0.1 seconds after turn-on of the main switch, to cut DC components in a short time period of approximately 0.1 seconds. Then, the time constant is set to be larger (to have a characteristic of cutting frequencies of 0.1 Hz or lower). In this manner, deterioration of a vibration angular velocity signal due to the DC cut filter
48
p
is prevented.
An output signal from the DC cut filter
48
p
is input to the low pass filter
49
p
formed of an analog circuit which appropriately amplifies the signal in accordance with the resolution of the A/D converting circuit
410
p
and cuts noise at high frequencies superimposed on the vibration angular velocity signal. This is performed for the purpose of preventing the noise in the vibration angular velocity signal from causing erroneous reading of the signal sampled by the A/D converting circuit
410
p
when the signal is input to the camera microcomputer
411
. An output signal from the low pass filter
49
p
is sampled by the A/D converting circuit
410
p
and acquired by the camera microcomputer
411
.
While the DC bias components have been cut by the DC cuter filter
48
p
, the amplification by the low pass filter
49
p
causes DC bias components to be again superimposed on the vibration angular velocity signal. Thus, DC cut must be performed again in the camera microcomputer
411
.
For example, a vibration angular velocity signal sampled 0.2 seconds after the turn-on of the switch of the camera is stored in the storage circuit
412
p
, and then the differential circuit
413
p
determines a difference between the stored value and the vibration angular velocity signal from the A/D converting circuit
410
p
to perform DC cut. This operation can only achieve rough DC cut (since the vibration angular velocity signal stored 0.2 seconds after the turn-on of the main switch of the camera includes not only DC components but also actual camera shake), so that the DC cut filter
414
p
formed of a digital filter in a subsequent stage performs adequate DC cut.
The DC cut filter
414
p
has a changeable time constant similarly to the analog DC cut filter
48
p
, in which the time constant is gradually increased in a time period of 0.2 seconds after the lapse of 0.2 seconds from the turn-on of the main switch of the camera. Specifically, the DC cut filter
414
p
has a characteristic of cutting frequencies of 10 Hz or lower when 0.2 seconds has elapsed since the turn-on of the main switch, and thereafter, the frequency cut by the filter
414
p
is reduced to 5 Hz, 1 Hz, 0.5 Hz, and 0.2 Hz each time 50 millise
Robin Blecker & Daley
Smith Arthur A
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