Patent GB-594696-A (GB)
Title: Improvements in or relating to photographic shutters
IPC: G03B9/08
Filed: 1944-05-01
Abstract: 594,696. Photographic shutters. DEHN, F. B. (Mitchell Camera Corporation). May 1, 1944, No. 8149. [Class 98 (i)] The driving mechanism for a photographic rotating blade shutter comprises a spring-driven member and a transmission train, elements being included in the train which are normally in engagement but separable to form a gap upon the spring being wound, the separable elements being re-engaged upon release of the shutter for free movement as a whole. The shutter comprises two rotating units, of high speed and low speed respectively, each having two concentric oppositely rotating apertured discs 25, 25a and 26, 26a with suitable apertures and an occulting blade 27. The elongation of the apertures is 95 degrees for the high speed shutter and 65 degrees for the low speed shutter. The occulting or auxiliary shutter 27 normally closes the exposure aperture, but is swung aside at the beginning of an exposure, i.e. during coincidence of the apertures in the high and low speed shutter discs. This coincidence occurs once in eight revolutions of the high speed unit. The high and low speed shutter discs are driven from a gear 40 and twin gears 44 through suitable trains of gears mounted between upper and lower frame plates 47, 48 supported by brackets, screws and spacers from the main-plate 20. The drive spring 110 is securely anchored at its upper end to a head 112 which is rigid with a dead-shaft 42 and a spacer sleeve 114. The upper end may be wound either by power or by hand, but, as illustrated, a hand crank 132 is rotatably mounted on the upper end of shaft 42 and carries a spring pawl 138 which engages a ratchet disc 136 rotatable on the shaft 42. A clutch jaw 140 on the disc 136 is received between two spaced jaws 141 and 142 projecting from a disc 144 on a sleeve 145. A light coil spring connects discs 136 and 144 and normally holds jaws 140, 141 in engagement. The sleeve 145 is integral with the upper spring head 112 and rotation of the crank thereby drives the upper end of the spring 110. A pawl and ratchet 152 prevents reverse rotation of the spring head 112. The lower end of the spring is anchored to a head 160 which is keyed to a gear sleeve 165, the lower end of which has a clutch jaw connection 166, with the gear sleeve 41 which drives the rotating shutter blades. A coil spring 168 surrounds shaft 42 and engages the jaws 166 to hold them together. The spring relieves the shutter of shock strain by allowing the jaws to separate when the selector mechanism cuts in and stops the lower end of the spring. Selector mechanism.-The gear 151 on the upper part of the drive spring 110 is geared to a gear 174 journalled on a dead-shaft 175. The lower gear 180 is meshed to a gear 183 on the bottom end of shaft 175 and is secured to a sleeve 185 which surrounds shaft 175. An inner sleeve 191 between shaft 175 and sleeve 185 carries a bearing cup 192 which bears upon a flanged disc 201 of an upper sleeve 202 which is journalled on a centrally bored disc 204 keyed in the upper end of sleeve 185. A stop lug 210 on disc 204 extends into a notch with shoulders formed in the lower end of sleeve 202, and a spring 214 maintains the lug 210 normally in contact with one of the shoulders. The disc 201 carries an abutment stop 220 which cooperates with a similar abutment 221 on the underside of gear 174. Splined on sleeve 185 is a circular rack gear 230 meshing with an operating pinion 231 and a crank. The upper end of the rack carries a winding tension selector 246 with a stepped cylindrical wall 248, there being six such shoulders with a drop edge 251 between the highest and lowest. Three vertical shafts 260, 261, 262 extend between spaced mounting plates 265, 266 and the shaft 260 carries at the bottom an arm 220 which is shaped at the tip to engage the teeth of the rack 230 and secure it in its selected vertical position. The arm moves into the spaces between the rack teeth when the selector shoulders are at the right elevation to be engaged by the hooked end 273 of the stop and release latch 272, the arm 270 and catch 272 moving into position together. Operation of the winding crank then rotates the whole mechanism until the latch 272 engages the selected shoulder, whereby the lower end of the drive spring 110 is held fast. Further rotation of the crank tensions the spring 110 until a winding stop 280 on plate 222 engages a latch 281 and prevents further winding. Spring 283 normally urges the latch 281 into locking position (Fig. 11), a stop 284 limiting its movement in that direction. A cam-plate 287 on disc 204 engages a roller 288 (Fig. 12) except when the selector 246 is engaged by the release latch and rock-shaft 261 to withdraw the latch 281 as the disc 204 rotates. When the spring winding has been arrested, the tension will depend on which shoulder of the selector has been engaged by the release latch. When the latch is released just as the auxiliary shutter is moved away, the spring 110 drives the high speed and low speed shutters and performs a single exposure, the speed reached being determined by the strain put upon the spring 110 which again depends on the shoulder 250 which has been selected. Immediately after exposure, the auxiliary shutter closes and the abutments 220, 221 also re-engage, and the whole train is reunited and coasts until its momentum is absorbed by frictional losses or by a friction brake applied to the upper spring head 112. The winding stop 281 is rendered ineffective by the rotating cam 287 during the free wheeling. The spring 214 and the slight displacement of the lug 210 act as a shock-absorber for the stopping or starting of the mechanism. Control mechanism.-When the release latch 272 is moved into selecting position, a locking arm 332 on trip-shaft 262 moves under the influence of a spring 336 and rides over the arcuate edge of the latch tail-piece 330. A spring 338 acts to move latch 272 to its release position. Although the actuation of the shutter release may be by any means, it is preferred to utilize the cranking action. To this end, release shaft carries a hub 290 (Fig. 14) and arm 291 rotatably mounted thereon and engages it through clutch jaws 292, 293. The arm 291 is linked to a.swinging arm 311 pivoted at 312 and carrying a roller 315 which is pressed against discs 136, 144 by a tension spring 316. The peripheries of these two discs are provided each with a scallop 318, 319. These scallops come into register when the crank is actuated and the roller is allowed to move so that the arm 311 rotates, moving the clutch 292 and rotating shaft 260, to move latch 272 and arm 270 into selector engaging position. Subsequent rocking of the roller 315 has no effect due to lost motion between lugs 292 and 293. The hub 294 on release shaft 260 is locked by a latch hook 296 (Fig. 9) which is actuated by a spring 303 but released by the camming action of a pin 300 on the upper side of gear 174 upon the edge 299 of the latch. The pin is so positioned that the latch 297 is released just after the vertical edge 251< >of the selector 246 has passed the release latch hook 273. Rotation of trip shaft 262 before full winding of spring 110 is prevented by a spring-urged latch 342 (Fig. 10) engaging a lug 340 on the shaft. A camming edge 348 on the latch permits the latter to be released by engagement with the edge of the pin 300. When the selector has been set and the crank turned, release shaft 260 is rotated through movement of the roller 315 and engagement of the pin 300 with latch 297. Latch 272 is moved to its advance position and locked by the arm 332 itself locked by latch 342. Continued rotation of the crank brings the stop shoulder 250 up to the release latch and the lower end of spring 110 is held, further rotation tensioning it and separating abutments 220, 221. The winding is stopped by engagement of stops 280, 281. At the same time, the pin 300 releases latch 342, the shaft 262 rocks to release arm 332 permitting latch 272 to be moved by its spring and pressure of the selector to release position. The shutters are then driven until the abutment 220 again strikes abutment 221 and drives gears 174, 151 and disc 144, 136 in free wheeling movement. Lost motion between disc 144, 136 prevents the roller 315 entering the scallops and moving release latch 272 into engagement with the selector. The disc 136 is made slightly smaller than the disc 144 to avoid frictional drag between the former disc and the roller 315. Power actuation and automatic and remote control and timing may be used for actuation of the shutter mechanism. Auxiliary shutter actuation.-The auxiliary shutter 27 may be opened or moved away by the releasing action of the trip shaft. Its arm 33 is secured to a hub which has an arcuate extension 101 engaged by the hooked end of an arm 352 which is connected by linkage to the trip shaft 262. A tension spring normally holds the auxiliary shutter closed. A roller 370 on the frame plate 20 coacts with a cam surface 371 under spring influence and guides the arm 352 in its movement. As the trip shaft rotates, the arm 352 is moved sideways and forwards and swings the auxiliary shutter aside. At this time, the hook end 390 of a latch 391 enters a notch 392 in the arcuate lug 101 and holds the shutter open. A cam 400 on the underside of gear 183 engages a roller 399 towards the end of the movement of the rotating shutters and swings latch 391 away from the lug 101 permitting the auxiliary shutter to return to the closed position. Rebound is prevented by a two-armed latch, a hook 419a of which enters an aperture in the lug 101 and locks the shutter in closed position.