Patent GB-1422301-A (GB)
Title: Shutter mechanism for a camera
IPC: G03B9/58
Filed: 1974-01-17
Abstract: 1422301 Shutter mechanisms SEIKO KOKI KK 17 Jan 1974 [19 Jan 1973] 02195/74 Heading G2A A camera shutter mechanism has means for moving the shutter blades from a closed to an open position and vice versa, with an electromagnet for maintaining the blades in the open position during an exposure, and has a first spring 19 for biasing the magnet armature into contact with the electromagnet and a second spring 24 for biasing it out of contact, such that when the blades are moved, from closed to open, the force applied by the first spring exceeds that applied by the second spring so that the armature is maintained in contact with the electromagnet, and when the blades are moved from open to closed the force applied by the second spring exceeds that applied by the first so that the armature is moved away from the electromagnet. Fig. 1 shows the shutter elements in the cocked position, the setting lever 4 having been rotated clockwise until an abutment 4b thereon has latched behind a bent-over end 5a of the release lever 5. The armature 23 is biased away from the electromagnet Mg by the second spring 24, but biased towards it by the first spring 19, acting via intermediate lever 17 and holding lever 20. Spring 19 is stronger than spring 24, so that in the position shown the armature is held against the magnet. A switch lever 26 carrying an insulated pin 26a is biased clockwise by a spring 28, but is retained in the Fig. 1 position, against the spring, by a pin 4a on lever 4. A switch 30 has three terminals a, b, c, which normally take the Fig. 1 position, in which terminal b, because of its natural resilience, lies in contact with terminal a. The switch is part of an exposure time control circuit Fig. 4 (not shown), and in this position is "open". When the release lever 5 is pivoted clockwise, the shutter mechanism is released to effect an exposure. End 5a of lever 5 disengages from abutment 4b of lever 4, freeing it for rotation. A main driving cam 12 is mounted on a shaft 13, and has a forked portion 12a which receives a pin 3b fixed on a sector ring 3, the sector ring being in direct driving connection with the shutter blades 2. The cam 12 has a pin 12b which is engaged by one end of the main driving spring 14, its other end engaging a - bent-over portion 1 lc of the main driving lever 11. The cam also has a projection 12c which is latched behind an arm 15b of a driving pawl 15 spring- biased anti-clockwise. As the freed lever 4 rotates anti-clockwise, it rotates a gear 6 which engages and pivots pawl 15 clockwise. This frees arm 15b from projection 12c and allows cam 12 to rotate rapidly clockwise under the action of spring 14. Sector ring 3 is thus driven anti-clockwise, and the shutter blades open. At the same time pin 4a disengages from arm 26b of lever 26, so allowing lever 26 to be pivoted clockwise by spring 28. Insulated pin 26a then closes the switch 30 by changing over terminal b from terminal a to terminal c, so energizing the electromagnet Mg. Also at the same time, a pin 12b on cam 12 engages and pivots lever 17, which thus disengages and frees holding lever 20. This therefore no longer applies any holding force to the armature 23, which nevertheless remains in contact with the electromagnet because this is now energized. The mechanism is now in the "shutter open" position of Fig. 2. After an exposure, the shutter is closed by the energy stored in a closing spring 9 acting on a closing lever 8, urging it clockwise. A toothed portion 8a of lever 8 meshes with a toothed portion of driving lever 11, urging it anti-clockwise, but it cannot so move because it is latched by a claw 16. After the exposure, as controlled by the switching circuit (S), is terminated, the electromagnet is de-energized, so that the armature 23 is no longer retained, and the lever 22 on which it is mounted is pivoted clockwise by spring 24. Lever 22 engages and pivots claw 16 out of engagement with driving lever 11, which can now rotate anticlockwise, and, through its engagement with sector ring 3, closes the shutter blades. At the same time an arm 8c of closing lever 8 disengages from an arm 27a of a lever 27 which is interlocked by a spring 29 with switch lever 26. Lever 27 can now pivot anti-clockwise, and takes lever 26 with it. Terminal a is thus released from contact with terminal c, and returns to terminal b. The mechanism is now in the position of Fig. 3 (not shown). In order to cock the mechanism again, setting lever 4 is moved clockwise, back to its Fig. 1 position, which rotates the main driving lever 11 and the main driving cam 12 back to their Fig. 1 positions, and re-tensions the main driving spring 14 and the closing spring 9.