Camera mechanism displacement means

Photography – Camera detail – Shutter

Patent

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Details

396496, 396358, G03B 910

Patent

active

055982441

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a camera, more particularly to means for effecting cyclic displacement of a mechanical system, such as a shutter mechanism, mirror mechanism, etc., in the camera, between two end positions. The invention further relates to a method for achieving cyclic displacement of a mechanical system, such as a mirror mechanism, shutter mechanism, etc., in a camera, between two end positions.


BACKGROUND OF THE INVENTION

Most cameras are provided with one or more mechanical systems which, during the sequence of taking a picture, are displaced from one end position to another, and thereafter returned to the first end position in readiness for the taking of a subsequent picture. Such systems include, for example, the viewing mirror mechanism of a single lens reflex camera, and/or the shutter mechanism and/or the diaphragm mechanism.
In terms of the viewing mirror mechanism, a common displacement means includes a return setting member, a mirror-up spring and an associated return spring, a latch and a mirror-up mechanism. A shutter charging operation energizes both the mirror-up spring and the return spring while bringing the return setting member to its set position where it is locked by the latch. A shutter release causes the mirror-up member to be initially actuated under the influence of the mirror-up spring to drive the mirror upward. Immediately after termination of shutter operation the return setting member is unlocked from the latch, thereby allowing the setting member to be returned under the influence of the return spring until the mirror returns to its original position.
The above-described mechanism suffers from many disadvantages. Firstly, to guarantee that the mirror will indeed reach its end positions, even if the camera in which it is fitted is operated in an inverted state, the two springs must be sufficiently tensioned to overcome mechanical losses so that the mirror arrives at the end positions with at least some tension remaining in the springs. This implies that the mirror is accelerated during its entire movement and therefore reaches its end positions at a maximum velocity for that movement. At the end positions the kinetic energy of the mirror and driving mechanism must be absorbed and, due to the relatively high velocity, the deceleration forces can be sufficiently high to cause shake of the camera, thereby giving rise to a blurred picture. The high velocity of the mirror also imposes problems with latching of the mirror at its end positions since the mirror can bounce back before the latch engages. The requisite high deceleration forces lead to increased noise levels and vibration whilst decreasing the life-span of the camera.
Many partial solutions to the above-described problem have been proposed. For example, in U.S. Pat. No. 4,192,598 a damping mechanism for reducing noise and shock is provided either on an element moving integrally with the mirror or on the driving lever. In U.S. Pat. No. 4,385,820 the mirror is raised and lowered by means of a gear train, one gear of which engages a sector-shaped gear integral with a mirror supporting member. Due to the weight of the mirror, large inertial forces have to be overcome and thus a greater driving force is necessary. In order to avoid bounce of the mirror at its end positions, U.S. Pat. No. 4,385,820 proposes a mechanical brake system for applying a braking force to the gear mechanism during the latter stages of the mirror's movement.
Whilst the systems described above may reduce the levels of noise and vibration, they also add to the complexity of the camera and occupy valuable space. In addition, the energy consumption of such systems is relatively high since, on the one hand, the relatively strong springs must be reenergized after each sequence and, on the other hand, not all of the energy in the springs is utilized.
A recent development in the field of mirror mechanisms makes use of a link mechanism driven by an electro-mechanical transducer, normally a d.c. motor. When a picture is

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