Photography – Single lens reflex camera – With mirror support or drive
Patent
1999-09-27
2000-09-26
Perkey, W. B.
Photography
Single lens reflex camera
With mirror support or drive
396463, 396508, G03B 902, G03B 1912, G03B 908
Patent
active
061234664
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an electromagnetic displacement means for effecting cyclic displacement of a mechanical system, such as a shutter mechanism, mirror mechanism, and the like, 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 results in the mirror being accelerated during its entire movement and therefore reaching 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 the camera to shake, thereby giving rise to a blurred picture. The high velocity of the mirror also creates 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 while decreasing the lifespan of the camera.
Many partial solutions to the above-described problem have been proposed. For example, PCT Application No. WO 93/025935 provides a solution for effecting cyclic displacement of a mechanical system, such as a mirror mechanism, shutter mechanism, and the like in a camera, between two end positions, which avoids the risk of bounce, requires a minimal amount of energy and which is simpler than previous solutions. This is achieved by including spring means for biasing the system towards a neutral position or zone between these end positions, and drive means, activated during displacement of the system, for ensuring that the system sequentially reaches these end positions. This arrangement can also be used for cyclic displacement of a mechanical system, such as a mirror mechanism, shutter mechanism, and the like in a camera, between two end positions. The solution consists of the following steps: positions; biasing to ensure that the system reaches the other of the two end positions; biasing to ensure that the system reaches the one end position.
Since the system is biased towards a neutral position or zone between the end positions, the maximum velocity of the component occurs at this neutral position or zone during movement from one end position to the other. Similarly, the velocity of the system, and therefore its kinetic energy, tends to zero when approaching the end positions. As such, no complicated braking or damping system is necessitated and latching is simplified.
One disadvantage of this sol
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Johansson Tomas
Persson Kjell-Anders
Wihlander Johan
Perkey W. B.
Victor Hasselblad AB
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