Photography – Attitude sensing
Reexamination Certificate
1999-06-29
2001-02-06
Perkey, W. B. (Department: 2851)
Photography
Attitude sensing
C396S358000
Reexamination Certificate
active
06185373
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a mirror control apparatus for a mirror in a single lens reflex camera.
2. Description of the Related Art
A single lens reflex (SLR) camera has a mirror disposed in a camera body and supported for reciprocal rotation between a first position in a photographing light path and a second position out of the photographing light path. The mirror is normally positioned at the first position, at which it is angled at forty-five degrees, serving to reflect light coming through the lens onto the viewing screen of a viewfinder.
The mirror is driven by a mirror control apparatus for quick rotation from the first to the second position and then from the second to the first position, so that it tends to impact onto a part of the camera body when reaching either of the positions. In order to prevent any harmful shocks to the mirror and/or to the camera body, as will as bounces of the mirror, from occurring when the mirror reaches these positions, cushions are typically used to receive the mirror at these positions so as to absorb the shocks. The shock absorbing capability of such cushions are, however, relatively limited. More effective shock absorption may be achieved by using a mirror brake mechanism which produces brake power against rotation of the mirror.
Typical mirror brake mechanisms include a friction brake comprising a disk operatively connected to and rotatable in synchronism with the mirror and a brake shoe for applying frictional brake force to the disk when the mirror is travelling in a selected angular position range. The brake shoe is urged to and in frictional contact with the peripheral edge of the disk only in a selected sectorial region thereof, which corresponds to the selected angular position range of the mirror. The selected angular position range is the range the mirror travels through when it is reaching the second position. The friction brake therefore provides brake power against the rotation of the mirror only when the mirror is reaching the second position. This facilitates smooth stopping of the mirror at the second position so as to avoid any harmful shocks and bounces.
Unfortunately, such type of mirror brake mechanisms suffer from certain inconveniences. Although the brake power to be produced by the friction brake is carefully chosen to have a desired value, the desired value itself may change depending on various factors affecting rotation of the mirror.
Such factors include, for example, temperature in the environment of the camera and orientation of the camera relative to the gravity. Specifically, when the camera is subjected to a low temperature, the viscosity of lubricant applied to pivots and sliding parts in the camera increases, resulting in an increase in resistance caused by lubricant against motions of moving parts. This in turn leads to a reduction in velocity of the mirror being rotated, and thus to a reduction in the desired brake power. In such case, lower brake power is desirable or, in other words, the actual brake power is too high to ensure appropriate motion of the mirror. Further, the brake power to be produced by the friction brake is chosen to be at an appropriate level just when the camera is in its normal orientation, where the mirror will snap up against the gravity during rotation from the first to the second position. Thus, if the camera is held by the photographer, for example, with its right or left side oriented up or down, the mirror will rotate about a vertical axis and thus not against the gravity. In such case, the velocity of the mirror when reaching the second position is relatively high so that higher brake power is desirable, and therefore the actual brake power is too low to achieve appropriate motion of the mirror.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide a mirror control apparatus for a mirror in a single lens reflex camera, the mirror being supported for reciprocal rotation between a first position in a photographing light path and a second position out of the photographing light path, in which appropriate brake power may be always produced against rotation of the mirror in order to effectively avoid any harmful shocks to and bounces of the mirror under different conditions of the single lens reflex camera which may occur.
In accordance with one aspect of the present invention, there is provided a mirror control apparatus for a mirror in a single lens reflex camera, in which the mirror is supported for reciprocal rotation between a first position in a photographing light path and a second position out of the photographing light path. The mirror control apparatus comprises a drive mechanism and a brake mechanism. The drive mechanism is operatively connected to the mirror for applying drive power to the mirror for rotation between the first and second positions. The brake mechanism is operatively connected to the mirror for producing brake power which varies depending on at least one of factors affecting rotation of the mirror, the brake power serving as resistance against rotation of the mirror.
The brake mechanism may preferably produce brake power only when the mirror is travelling through at least one predetermined partial region within its rotational stroke between the first and second positions.
In such case, the brake mechanism may preferably produce brake power when the mirror is reaching the second position. Further, the brake mechanism may preferably produce brake power when the mirror is reaching each of the first and second positions.
The brake mechanism may preferably produce brake power which varies depending on temperature in the camera. Additionally or alternatively, the brake mechanism may preferably produce brake power which varies depending on orientation of the camera relative to the gravity.
In one embodiment, the brake mechanism comprises a friction brake. The friction brake may comprise a disk operatively connected to and rotatable in synchronism with the mirror, a brake shoe supported by a stationary part of the camera for movement toward and away from the disk and capable of contact with the disk; and an urging device for urging the brake shoe toward the disk with a variable urging force compensated for a change in temperature in the camera.
In another embodiment, the brake mechanism comprises an induction brake unit and control circuitry associated with the induction brake unit. The control circuitry may comprise an angular position sensor for detecting angular position of the mirror relative to the camera and providing an angular position signal indicative of detected angular position of the mirror, a temperature sensor for detecting temperature in the camera and providing a temperature signal indicative of detected temperature in the camera, an orientation sensor for detecting orientation of the camera relative to the gravity and providing an orientation signal indicative of detected orientation of the camera, and a brake unit controller responding to the angular position signal, the temperature signal and the orientation signal by controlling the induction brake unit so as to control brake power to be produced by the induction brake unit.
In accordance with another aspect of the present invention, there is provided a mirror control apparatus for a mirror in a single lens reflex camera, in which the mirror is supported for reciprocal rotation between a first position in a photographing light path and a second position out of the photographing light path. The mirror control apparatus comprises a drive mechanism and a brake mechanism. The drive mechanism is operatively connected to the mirror for applying drive power to the mirror for rotation between the first and second positions. The brake mechanism is operatively connected to the mirror for producing brake power serving as resistance against rotation of the mirror. Further, the brake mechanism comprises an induction brake unit and control circuitry associated with the induction brake unit.
Asahi Kogaku Kogyo Kabushiki Kaisha
Greenblum & Bernstein P.L.C.
Perkey W. B.
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