Photography – Camera shake sensing
Reexamination Certificate
1999-12-21
2002-05-21
Perkey, W. B. (Department: 2851)
Photography
Camera shake sensing
Reexamination Certificate
active
06393215
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus for image blur correction, which is applied to image blur correction devices for correcting an image blur occurring in optical equipment such as cameras and the like.
2. Related Background Art
In the cameras which are available presently, the important works for photography, including determination of exposure, focusing, etc., all are automated, and thus even those inexperienced in manipulation of camera have only a minimal possibility of causing a failure of photography.
In recent years research also has been conducted on systems for preventing hand vibration exerted on the camera and there are few factors to induce a photographer's mistake in photography.
A system for preventing the hand vibration will be described below briefly.
The hand vibration of camera during photography is normally vibration in the frequency range of 1 Hz to 10 Hz, and a basic idea for permitting a photograph without an image blur to be taken even with such hand vibration upon release of the shutter is to detect vibration of the camera due to the above hand vibration and displace a correction lens according to a detected value thereof. For taking a photograph without an image blur even under the camera vibration, therefore, the first requirement is to accurately detect the vibration of the camera and the second requirement is to correct variation of the optical axis due to the hand vibration.
The detection of this vibration (camera vibration) can be implemented theoretically by providing the camera with a vibration detection device which is comprised of a vibration detection sensor for detecting acceleration, angular acceleration, angular velocity, angular displacement, or the like, and a calculation portion for calculating an output therefrom in order to correct the camera vibration on necessary occasions. Then the image blur is restrained by driving a correction means which decenters the photographing optical axis, based on this detection information.
FIG. 30
is a perspective view of appearance of a compact camera having the blur prevention system, which has the function of effecting the vibration correction for vertical vibration and horizontal vibration of camera indicated by arrows
42
p,
42
y
with respect to the optical axis
41
.
In the camera body
43
, reference symbol
43
a
designates a shutter release button,
43
b
a mode dial (including the main switch),
43
c
a retractable flash (strobe), and
43
d
a finder port.
FIG. 31
is a perspective view to show the internal structure of the camera illustrated in FIG.
30
. Reference numeral
44
denotes the camera body,
51
the correction means,
52
a correction lens, and
53
a support frame which is arranged to freely drive the correction lens
52
in directions
58
p,
58
y
in the figure to correct the vibration in the directions of the arrows
42
p,
42
y
of FIG.
30
and which will be detailed hereinafter. Reference symbols
45
p
,
45
y
represent vibration detection devices such as angular velocity sensors, angular acceleration sensors, or the like, which detect the vibration about the arrows
46
p,
46
y,
respectively.
An output from each of the vibration detection devices
45
p,
45
y
is converted into a drive target value of the correction means
51
through a calculation device
47
p
or
47
y,
described hereinafter, and the target value is entered into a corresponding coil of the correction means
51
to effect the blur correction. Reference symbol
54
indicates a base plate,
56
p
and
56
y
permanent magnets, and
510
p
and
510
y
coils.
FIG. 32
is a block diagram to show the details of the above-stated calculation devices
47
p,
47
y.
Since these devices have like structure, the figure will be explained using only the calculation device
47
p.
The calculation device
47
p
is composed of a DC cut filter
48
p,
a low pass filter
49
p
, an analog-to-digital conversion circuit (hereinafter referred to as an A/D conversion circuit)
410
p,
a driving device
419
p,
and a camera microcomputer
411
indicated by a dashed line, which are enclosed in a chain line. The camera microcomputer
411
is composed of a memory circuit
412
p,
a differential circuit
413
p,
a DC cut filter
414
p
, an integration circuit
415
p,
a memory circuit
416
p,
a differential circuit
417
p,
and a PWM duty variation circuit
418
p.
In this case, the vibration detection device
45
p
is a vibration gyro which detects the angular velocity of vibration of the camera. The vibration gyro is driven in synchronization with on of the main switch of the camera to start detection of the angular velocity of vibration exerted on the camera.
An output signal of the vibration detection device
45
p
is supplied to the DC cut filter
48
p
constructed as an analog circuit, which cuts off the DC bias component superimposed on the output signal. This DC cut filter
48
p
has such a frequency characteristic as to cut the signal at the frequencies of not more than 0.1 Hz and does not affect the frequency band of the hand vibration ranging from 1 Hz to 10 Hz on the camera. This characteristic to cut the component at and below 0.1 Hz, however, poses a problem that approximately ten seconds are necessary for completely having cut the DC component since input of the vibration signal from the vibration detection device
45
p.
For this reason, the time constant of the DC cut filter
48
p
is set to a small value (for example, such a characteristic as to cut the signal at the frequencies of not more than 10 Hz), for example, up to 0.1 second after on of the main switch of the camera, whereby the DC component is cut off in the short time of about 0.1 second. Thereafter, the time constant is increased to a large value (such a characteristic as to cut the signal only at the frequencies of not more than 0.1 Hz) in order to prevent the DC cut filter
48
p
from degrading the angular velocity signal of vibration.
An output signal from the DC cut filter
48
p
is supplied to the low pass filter
49
p
constructed as an analog circuit, which properly amplifies the output signal so as to match it with resolving power of the A/D conversion circuit
410
p
and which cuts noise of high frequencies superimposed on the angular velocity signal of vibration. This is for avoiding occurrence of a read error due to the noise in the angular velocity signal of vibration, in sampling by the A/D conversion circuit
410
p
when the angular velocity signal of vibration is entered into the camera microcomputer
411
. The output signal from the low pass filter
49
p
is sampled by the A/D conversion circuit
410
p
to be read into the camera microcomputer
411
.
Although the DC cut filter
48
p
has cut the DC bias component, the amplification thereafter by the low pass filter
49
p
again causes the DC bias component to be superimposed on the angular velocity signal of vibration. Therefore, the DC component has to be cut again inside the camera microcomputer
411
.
The cut of the DC component is carried out, for example, by storing the angular velocity signal of vibration sampled 0.2 second after on of the main switch of the camera, in the memory circuit
412
p
and obtaining a difference between the thus stored value and the angular velocity signal of vibration by the differential circuit
413
p.
Since this operation permits only rough cut of DC (or since the angular velocity signal of vibration stored 0.2 second after on of the main switch of the camera also includes the actual hand vibration as well as the DC component), adequate DC cut is effected by the DC cut filter
414
p
constructed of a digital filter in the subsequent stage. The time constant of this DC cut filter
414
p
is also variable, similar to the analog DC cut filter
48
p,
and the time constant is gradually increased during the period of 0.2 second from 0.2 second after on of the main switch of the camera. Specifically, this DC cut filter
414
p
has such a filter characteristic as to cut the sig
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Perkey W. B.
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