US3810692A

US3810692A - Photographic film-handling appliance

Info

Publication number: US3810692A
Application number: US00159698A
Authority: US
Inventors: J Drasch; R Scheiber; H Wessner
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-07-06
Filing date: 1971-07-06
Publication date: 1974-05-14
Anticipated expiration: 1991-05-14
Also published as: DE2127062A1; JPS5524087B1; AT298980B

Abstract

An electric motor is energizable to rotate a rotary shutter. A release switch is movable between an operative position and an inoperative position. A power supply circuit is adapted to energize the motor when the release switch is in the operative position. Electric braking means are energizable to stop the shutter. Fully electric brake control means are operatively connected to the shutter and arranged to de-energize the braking means when the release switch is in its operative position and to energize the braking means at least temporarily so as to stop the shutter in a predetermined position when the release switch has moved from its operative position to its inoperative position.

Description

United States Patent [1 1 Drasch et al.

[4 1 May 14, 1974 [73] Assignees: Karl Vockenhuber; Raimund Hauser, both of Vienna, Austria Filed: July 6, 1971 Appl. No.: 159,698

Foreign Application Priority Data July 6, 1970 Austria 6112/70 References Cited UNITED STATES PATENTS 7/1942 Fuller t 1. 352/176 X 8/1968 Schrader 352/179 X Int. Cl. G03b 1/00 1,880,106 9/1932 Robinson 352/30 3,567,316 3/1971 Wilharm 352/178 X FOREIGN PATENTS 0R APPLICATIONS 1,120,101 7/1968 Great Britain... 352/174 U.S.S.R 1. 352/176 Primary ExaminerMonroe H. Hayes 5 7] ABSTRACT An electric motor is energizable to rotate a rotary shutter. A release switch is movable between an operative position and an inoperative position. A power supply circuit is adapted to energize the motor when the release switch is in the operative position. Electric braking means are energizable to stop the shutter. Fully electric brake control means are operatively connected to the shutter and arranged to de-energize the braking means when the release switch is in its operative position and to energize the braking means at least temporarily so as to stop the shutter in a predetermined position when the release switch has moved from its operative position to its inoperative position.

10 Claims, 12 Drawing Figures 1 PHOTOGRAPHIC FILM-HANDLING APPLIANCE This invention relates to a photographic or cinematographic recording or reproducing appliance, preferably a motion picture camera, which comprises an electric motor for driving a shutter, a release switch having an operative position, in which the electric motor is energized, and an inoperative position, in which the electric motor is de-energized, and exclusively electric means which are connected to the release switch and serve to arrest the shutter in a predetermined position.

It is known that such appliances, particularly motion picture cameras, can be de-energized so that the shutter is in a desired position if a stop is provided, which is moved into the path of a cooperating stop that is connected to the drive means. To avoid a detrimental reaction on the drive motor in such arrangements, the drive means may comprise an overload coupling. Such overload coupling in most cases requires a large space and for this reason is inconsistent with a compact structure. A camera is known which comprises an exclusively electric means for arresting the shutter in a predetermined position. In that camera, an oscillator operating at a variable frequency delivers pulses to a ring counter, which orders said pulses to provide a phase voltage of a three-phase system. That phase voltage is amplified and then fed to a rotating field induction motor having a magnetic rotor. A so-called starting storage device ensures that the motor is electrically stopped always at the same phase angle and started always with the same phase, which succeeds said phase angle. That design is mostexpensive and for this reason cannot be used in appliances used by amateurs.

The invention eliminates these difficulties in that means are provided which are connected to the shutter and operated in dependence on the position of the shutter and which in a manner known per se render an eddy current brake and/or counter-current brake operative at least temporarily and particularly short-circuit the motor. Said means are controlled by the releaseswitch in such a manner that the means are operative when the release switch is in its inoperative position and the means are inoperative when the release switch is in its operative position. Whereas cinematographic appliances are known which comprise an eddy current brake, said eddy current brake served only to control the speed of the motor. it is also known to short-circuit the motor for operating a zoom lens when the motor has been de-energized. According to a proposal which has not been disclosed in a printed publication, it has already been'attempted to short-circuit thedrive motor.

of a camera when the motor has been deenergized. That arrangement, however, does not provide for a proper synchronization with the position of the shutter so that the need for mechanical means for stopping the shutter could not be eliminated.

In the simplest case, the eddy current brake may cooperate in known manner with a sector-shaped'conducting disc whereas the release switch consists of a change-over switch. in this case, the release switch energizes either the motor or the eddy current brake and the action of the eddy current brake is initiated when the shutter is in the desired position because the sectorshapcd'disc hasa corresponding configuration or the pole pieces of the eddy current brake have a corre sponding configuration. In this arrangement, a particularly good braking action will be obtained if the sectorshaped disc is driven by a speed-increasing transmission. In this case, however, a plurality of pole pieces of the eddy current brake in a numberwhich corresponds to the transmission ratio must be spaced around the disc. It is simpler to provide a rotary shutter disc consisting of a conducting disc. A further simplification may be obtained in that the winding of the eddy current brake is formed by the stator winding of the motor.

According to a preferred feature of the invention, at least one circuit is provided which by-passes the release switch and comprises a by-pass switch, which is adapted to be closed for a time which is shorter than one cycle of the shutter, and said circuit comprises, if desired, a resistor for braking the motor. Said by-pass switch maybe connected to the shutter responsive to the position thereof in such a manner that the by-pass switch is closed and the brake-actuating switch is open when the shutter has moved beyond its predetermined position, whereas the two switches are in their respective opposite positions before the shutter has reached that predetermined position and, if desired, both switches are open when the shutter is in its predetermined position. In order to prevent a movement of the shutter beyond its predetermined position when the release switch has been opened, it is a feature of the invention that the closing of the by-pass switch when the release switch is open causes the motor to be reversed, e.g., by means of a reversing switch connected to the release switch. Particularly when electronic switching circuits are used, the by-pass switch consists preferably of a photodetector, e.g., a photodiode, which is illuminated in dependence on the position of the shutter.

In an arrangement according to the invention, a special problem resides in the provision for single frame operation. For this purpose, the above-mentioned bypass switch or an additional by-pass switch may be desirable if the single frame operation is enabled by means for closing the by-pass switch or another switch which bypasses the release switch and is adapted to be closed for a short time. In such arrangement, the bypass switch controlled by the shutter may be supplemented by a pulse-generating switch, which may be operated to supply a current pulse to the motor. In many known cameras and also in projectors, a mode control switch for changing between continuous operation and single frame operation is provided. In such arrangement, the release switch itself may consist of a pulse generating switch and the mode control switch may be connected to means for holding the motor circuit closed when the release switch is closed for continuous operation. This concept may be realized in various ways. For instance, the means connected to the mode control switch maybe formed by a locking device, which holds the pulse-generating switch in its unstable position. lna preferred arrangement, however, the release switch when closed is connected to a contact that is included in the circuit of an interrupter that is controlled by the mode control switch. Alternatively, said by-pass switch may be closed in that a starting device is provided, which serves to mechanically rotate the drive means until the by-pass switch has been closed.

In cameras having a circuit which is adapted to be energized by a main switch, the arrangement according to the invention affords the special advantage that there is no need for additional means which prevent an inadvertent opening of the main switch when the release switch is closed. This object will be accomplished if the main switch, which is preferably arranged to be closed by the inserted film cartridge, is connected between the power source and the release switch because in that case the by-pass switch ensures that the shutter will assume its predetermined position in any case before or after the release switch has returned to its opened position, even when the main switch is open. When the film cartridge has been removed, the presence of the bypass switch which might prevent a permanent deenergization of the motor when it has run up because the load on the drive means is reduced and the by-pass switch iscontinually closed. This phenomenon will be prevented if the main switch is arranged to be closed by the insertion of the film cartridge.

Electronic components may be used to advantage in an arrangement according to the invention. For instance, the pulse-generating switch for single frame operation may be formed by a 'monostable multivibrator stage, which is adapted to be driven by a time constant circuit. One of the transistors of such multivibrator stage may serve as a switching transistor for the motor. In this case, a preferred feature-resides in that this switching transistor may serve at the same time as a final control element of the speed control system for the motor, the switch for controlling the brake may also consist of a transistor having an emitter-collector path which shunts the motor. In this way, at least part of'the switching circuits may easily be made as integrated circuits. v

Further details of the invention will become apparent from the following description of embodiments which are shown diagrammatically and by way of example in the drawings, in which FIG. I is a sectional view showing a camera according to the invention,

FIG. 2 is a sectional view taken on line IIlI in FIG.

FIG. 3 is a diagrammatic representation of a simplified embodiment of the invention,

FIG. 4 is a sectional view which is similar to FIG. 1 and shows a detail of another embodiment,

FIG. 5 is a diagrammatic representation of a further embodiment, I

FIGS. 6 to 9 show various positions of a further embodimen't,

FIGS. 10, 11 are circuit diagrams of two embodiments of means for enabling single frame operation, and

FIG. 12 shows an embodiment of an arrangement according to the invention which is composed of electronic components.

A camera 1 provides a light path from a diagrammatically indicated lens 2 through a rotary shutter 3 and an exposing aperture 4 to a film 5, which is disposed be hind the exposing aperture 4. A pull-down claw 6 is provided to move the film 5 and is driven by a pulldown cam 7. The pull-down cam is mounted on the same shaft 8 as the rotary shutter 3. That shaft 8 carries also a gear 9, which is driven by 'a pinion mounted on the shaft of a motor 11. The shaft 8 is mounted at one end on the plate 12 which defines the exposing aperture 4 and at the other end on another plate 13. The plate I3 carries a printed circuit, which comprises slip rings that cooperate with sliding contacts l4, 15 on the gear Wheel 9. A microswitch 16 is soldered to the plate 13. That microswitch 16 consists of a change-over switch and forms the release switch of the camera 1. The release switch 16 is operable by a release member 17 in such a manner that the movable contact 18 moves from an inoperative position, which is shown in FIG. I and in which the contact 18 engages a normally closed contact 19, to its operative position, in which the movable contact 18 engages a normally open contact 20.

It is apparent from FIG. 2 that the sliding contacts l4. 15 are conductively interconnected. The contact I9 is engaged by the movable contact 18 when the release switch 16 is in its inoperative position and is connected to an intermediate slip ring 21 on the plate 13. The movable contact 18 is connected to a motor terminal 22, which is directly soldered to the printed circuit. The other motor terminal 23 is directly connected to one terminal of a power source 24 and is also connected to an outer half-ring 25 on the plate 13. The half-ring 25 and another half-ring 26 form together a complete ring. The half-ring 26 is connected to the other terminal of the power source 24 and to the normally open contact 20.

Upon an operation of the release member 17, the movable contact 18 engages the normally open contact 20 so that the motor 11 having a terminal 23 connected to one terminal of the power source 24 is now connected by its terminal 22 and the

contacts

18, 20, also to the other terminal of the power source 24. When the release member 17 is then released, the release switch 16 assumes is inoperative position, in which the movable contact 18 engages the normally closed contact 19. When the shutter 3 and with it the gear 9 carrying the sliding contacts l4, 15 are in the position shown in FIG. 2, the motr II is short-circuited by the terminal 23 and by the half-ring 25, the two sliding contacts l5, 14, the slip ring 21, the contacts l9, l8, and the terminal 22 so that the motor is braked quickly. When the shutter 3 is in a position to expose the exposing aperture 4, the sliding contact 15 engages the half-ring 26 to connect the latter through the sliding contact 14 and the

contacts

19, 18 to the motor terminal 22. Because the motor is connected by its terminal 23 to one terminal of the power source 24 and is connected by its terminal 22, the contacts l8 19, the slip ring 21, the sliding contacts l5, l4 and the half-ring 26 to the other terminal of the power source 24, the energization of the motor 11 is continued until the shutter 3 has rotated to its predetermined position, in which it is braked by the then short-circuited motor 11. Hence, the half-ring 26 and the sliding

contacts

14, 15 form a by-pass switch for temporarily by-passing the release switch 16.

FIG. 3 shows that the invention may be embodied in much simpler arrangements. In FIG. 3, parts having the same function are designated with the same reference characters as in the preceding Figures. The rotary shutter 3 consists of a conducting disc, which cooperates with an eddy current brake 27. In this embodiment, the eddy current brake 27 is energized as soon as the release switch 16 has moved to its inoperative position shown in FIG. 3. A braking action will not be exerted by the eddy current brake 27, however, until the conducting disc 3 moves between the pole pieces of the eddy current brake 27. Hence, there will be no braking action as long as the shutter disc 3 exposes the exposing aperture 4 because the sector-shaped part of the disc 3 is not disposed between the pole pieces of the eddy current brake; these pole pieces are disposed adjacent to the exposing aperture 4. The eddy current brake 27 will not become effective until the shutter disc 3 assumes its predetermined position, in which the disc 3 covers the exposing aperture 4. It will depend substantially on the dimensioning of the eddy current brake 27 at what point of the path of the shutter disc 3 the eddy current brake is actually disposed. The braking action will be increased if the eddy current brake cooperates with a sector-shaped disc which is driven by a speedincreasing transmission. The design of the disc and of the eddy current brake will then be selected in view of the transmission ratio.

FIG. 4 shows an embodiment which enables a single frame operation. All parts not required for an under standing of this embodiment have been omitted in F IG.; 4. In the embodiment of FIG. 4, the release member 17 operates the movable contact 18 of the switch 16 by a slider 28 rather than directly. The latter comprises slots 29, 30, which are passed through by stationary pins.31, 32. The release member 17 comprises two

nipples

33, 34 for the connection ofa cable release. The nipple 33 is used for continuous operation and the nipple 34 for single frame operation. The nipple 33 is in register with the slider 35, which is also guided by the

pins

31, 32 but has a much larger opening 36 adjacent to the pin 32. The slider 35 is formed with a shoulder 37, which is engaged by an extension 38 of the slider 28 under the actionof a coiled torsion spring 39. The other end portion of the spring 39 directly engages the slider 35.

When a cable release screwed into the nipple 34 is operated to push the slider 35 to the right of FIG. 4,.the movement of the slider 35 is transmitted by the shoulder 37 and the extension 38 to the slider 28. The latter moves the movable contact 18 of the switch 16 into engagement with the normally open contact 20. At the same time, an extension 40 of the slider 35 is moved into the path of a hook 4-1, which is connected to the pulldown claw 6 and which engages the extension 40 during the upward movement of the pull-down claw 6. The enlarged opening 36 permits the slider 35 to follow the movement of the pull-down claw 6 to its upper dead center. so that the slider 35 is pivotally moved about the pin 31. That pivotal movement causes the shoulder 37 to disengage the extension 38 so that the spring 39 causes the slider 28 to return to its left-hand end position so as to return the release switch 16 to its inoperative position.

FIG. 5 shows a slip ring half 42, which is connected to the shutter 3 and cooperates with stationary sliding contacts 43 to 46. The sliding

contacts

43, 44 are connected to respective terminals of the power source 24. The sliding

contacts

45, 46 are connected one to the other.

When the release switch 16 is in its operative position, the motor 11 is directly connected to the power source 24. When the release switch 16 is in its inoperative position, shown on the drawing, and the half-ring 42 connected to the shutter 3 connects the sliding

contacts

44, 46, the motor 11 is short-circuited by its terminal23 and by the sliding

contacts

44, 46, the contacts 18, I9, and the terminal 22. When the shutter 3 is in the position in which the exposing aperture 4'is exposed, the half-ring 42 connects the sliding

contacts

43, 45 so that the normally open contact of the release switch 16 is bypassed because the terminal 22 of the motor 11 is then connected to one terminal of the power source 24 through the

contacts

18, 19 and the sliding

contacts

43, 45.

According to FIG. 5, the power source 24 feeds the motor circuit and an exposure control circuit 47. As in numerous known appliances. a main switch 48 is provided to prevent a flow of current through the exposure control circuit 47 when the appliance is inoperative. Previously, mechanical locking means were required to prevent'an inadvertent opening of the main switch of the appliance while the motor was running because such opening would cause the shutter to stop in an uncontrolled position so that an ingress of light into the film cartridge could not be prevented. That problem maybe solved with simpler means in that the main switch 48 is included in the circuit which is by-passed by the circuit including the by-

pass switch

43, 45 so that even when the main switch 48 is opened inadvertently, the shutter 3 can still move to its predetermined position, in which the shutter 3 covers the exposing aperture 4.

Another embodiment which enables a single frame operation is shown in FIG. 5. In this embodiment, the

contacts

43, 45 are connected to energize the motor 11 so that the movement of the shutter 3 is continued for one revolution. A mechanical starting device is provided to connect the

contacts

43, 45. That device comprises a slider 50, which is biased by a spring 49 and guided by a pin 52, which extends through a slot 51, and by a guide pin 53. A pawl 54 is provided at one end of the slider 50 and can cooperate with a ratchet wheel 55, which is secured to the shaft 8. For this purpose, the slider 50 is moved in the direction of the arrow E by a cable release, not shown, against the action of the spring 49, so that the pawl 54 engages the ratchet wheel 55 and rotates the same together with the shutter 3 until the slip ring 42 connects the

contacts

43, 45. The motor 11 is now enrgized and the shutter 3 is driven until the motor 11 is again short-circuited by the

contacts

44, 46 so that the shutter 3 is stopped in a predetermined position.

. In order to prevent a continual movement of the shutter beyond its predetermined position when the load on the drive means is insufficient so that the bypass switch continually turns on the motor 11, means for energizing an eddy current brake may be provided. Such means are shown in FIGS. 6 to 9. In the embodiment shown by way of example, the shutter 3 is provided with four sliding

contacts

56, 57 and 58, 59, which may be connected in pairs like the sliding

contacts

14,15 in FIGS. 1 and 2. These sliding contacts 56 to 59 cooperate with sliding contacts which are carried by a plate, not shown, and which have the same form as the illustrated sliding contacts. That plate which is not shown is similar to the plate 13 shown in FIGS. 1 and 2. A release switch 60 comprises two

movable contacts

61, 62, which are connected to respective terminals of the voltage source. When the release switch 60 is in its inoperative position, shown in FIGS. 6 to 9, the

center contacts

61, 62 are connected to

stationary contacts

63, 64. The contact 63 is connected to the left-hand, outer slip ring 65. A further quadrant arc 65a is coupled by a braking resistor 66 to the slip ring 65. The remaining outer'quadrant and three quadrants of the adjacent inner slip ring are connected to the negative terminal of the power source by the

contacts

64, 62. The two

terminals

22, 23 of the motor 11 are soldered to respective additional

inner slip rings

68 and 69, and when the releaseswitch is in operative position are directly connected by

stationary contacts

70, 71 to the two terminals of the voltage source. Since current flows through the slip rings 68, 69, the sliding contacts 56'to 59 and the remaining slip rings when the release switch is in its operative position, there will be no effeet, particularly because the. connection to the contacts 63, 64is interrupted. When the release switch 60 and the shutter 3' are in their inoperative position, shown in FIG. 6, the sliding

contacts

56 and 59 are insulated from the current-carrying

slip rings

65 and 67, respectively so that the motor ll is at rest.

When the release switch 60 has returned from its operative position to its inoperative position, the

contacts

70, 71 will be by-passed when the shutter disc 3' is in a position shown in FIG. 7. For this reason, the full energization of the motor 11 is continued through the

contacts

61, 63, the slip ring 65, the sliding

contacts

59, 58 and the slip ring 68, on the one hand, and through the

contacts

62, 64, the slip ring 67, the sliding

contacts

56, 57 and the slip ring 69, on the other hand. The current thus supplied will be reduced as soon as the shutter disc 3 assumes the position shown in FIG. 8 because the sliding contact 59 then slides on the quadrant arc 65a, which is connected to the current-carrying slip ring 65 by the braking resistor 66. This will prepare the braking of the motor 11. Within the scope of the invention, the'slip rings might be designed and connected so that the braking is initiated by a short-circuiting of the motor 11.

Owing to its flywheel effect, the shutter disc 3' having left the quadrant arc 65a obviously will not stop in its inoperative position shown in FIG. 6 but will move to a position such as shown in FIG. 9, lll'.WlllCh a reverse current flows through the motor 11 because the sliding contact 59, which previously cooperated with the

slip ring

65, 65a connected to the positive terminal of the power source now contacts the slip ring 67, which is connected to the negative terminal of the voltage source. At the same time, the sliding contact 56 has moved from the slip ring 67 to the slip ring 65 so that the motor 11 is supplied with reverse current. As a result. the shutter disc 3' is first braked and then returned to its inoperative position shown in FIG. 6. There may be a slight hunting until the shutter disc 3 finally remains in its predetermined position. That hunting is damped particularly because only a low current flows through the quadrant arc 65a.

FIGS. 4 and 5 show embodiments which enable a single frame operation. Modifications of these embodiments are shown in FIGS. 10 and 11. A switchgear block 72 represents the bypass switch and the braking switch, which may be designed as shown in FIG. 5, for instance. in both modifications, means are provided which cause the shutter disc to rotate through a small angle until the by-pass switch is closed. That small rotation of the shutter disc is effected in. both embodiments by a short current pulse.

According to FIG. 10, the circuit of the motor 11 includes a release switch 73 and a single frame switch 75, which is operable by a single frame release 74. The single .frame switch consists of a pulse-generating switch and has two inoperative positions, in which the movable contact member 76 of the switch engages

stops

77 and 78, respectively. The operation of the single frame release 74 causes the movable-contact member 76 to move from one inoperative position to the other. During this movement the contact member 76 is in contact for a short time with a stationary contact strip 79. The

length of the Contact strip 79 is sufficient to ensure that the by-pass switch cooperating with the rotary shutter will be reliably closed during the pivotal movement of the contact member 76.

Cinematographic appliances are often provided with a mode control switch, which may be set to positions for continuous operation and for single frame operation. In the embodiment shown in FIG. 1], such mode control switch may be connected to a switch 80 for a change between continuous operation and single frame operation. The switch 80 may be opened for a taking or reproduction of single frames and closed for continuous operation. Regardless of the position of the switch 80, the motor ll is always started by the operation of a release 81, which cooperates with a release switch 82, which consists of a pulse-generatingswitch. When the release switch 82 is in its operative position, the movable contact member 83 contacts a stationary contact 84, which corresponds to the normally closed contact 19 of the release switch 16. Another stationary contact 85 in the circuit of the switch 80 corresponds to the normally open contact 20 of the release switch 16. A contact strip 86, which corresponds to the contact 79 (FIG. 10) is disposed between the two

contacts

84, 85.

When the switch 80 has been opened to set the appliance for single frame operation and the release member 81 is operated so that the contact member 83 slides over the contact strip 86, a switch 87 disposed behind the contact strip 86 will be opened at the same time. The movable contact member 83 finally engages the stationary contact 85, which is in circuit with the open switch 80. During the movement of the contact member 83 in contact with the contact strip 86, the motor 11 has moved through an angle which is just sufficient to cause the closing ofthe by-pass switch, which cooperates with the shutter. As a result, the motor 11 is braked after one revolution. When the contact member 83 is returnd toward the normally closed contact 84, the contact member 83 again slides on the contact strip 86. Because the switch 87 has been opened during the release, the motor 11 remains de-energized and the contact member 83 returns to its inoperative position while closing the switch 87.

FIG. 12 shows how the invention can easily be realized by' means of integrated switching circuits. The switching elements for switching the motor 11 comprise a single frame switch 88, a release switch 89, a bypass switch 90 consisting of a photodetector, a monostable multivibrator comprising two

transistors

91 and 92, and another transistor 93. One transistor 92 of the multivibrator serves as a switching transistor for the motor 11 and conducts only when one of the

switches

88, 89, and 90 is closed. For instance, when the release switch 89 is closed, the switching transistor 92 conducts so that the motor 11 is in normal operation. A speed control circuit 94 may have an output which is connected to the base of the switching transistor 92 so that the latter serves also as a final control element of the speed control system. The shutter disc may be or may not be in its predetermined position before the exposing aperture when the release switch 89 is opened. This is detected by the photodetector 90, which is disposed behind the rotary shutter adjacent to the exposing aperture or receives light from the light-reflecting surface of the shutter disc. Unless the shutter disc covers the exposing aperture, the photodetector 90 is illuminated and constitutes a closed by-pass switch so that the switching transistor 92 remains conducting. As soon as the illumination of the photodetector 90 ceases, the switching transistor 92 is blocked and the transistor 91 is rendered conducting as well as the transistor 93. Because the emitter-collector path of the transistor 93 shunts the motor 11 and thus connects the two terminals of the motor 11, the latter is braked.

To enable a single frame operation, a capacitor 95 is provided as well as a time constant circuit including a capacitor 96. The capacitor 95 is in circuit with the single frame switch 88. When the latter is closed, the ca pacitor 95 is closed. During the charging of the capacitor 95, the capacitor 96 is charged too. During that time, the switching transistor 92 is rendered conducting for a short time. This is sufficient for an angular movement of the shutter disc until the photodetector 90 is illuminated and holds the switching transistor 92 con ducting until the shutter disc has returned to its prede termined position of rest, in which it is braked by the transistor 93 when the transistor 92 has been blocked.

What is claimed is:

1. In a photographic film-handling appliance means defining an optical path,

a shutter arranged on said optical path and having an open'position and a closed position, i

an electric motor drivingly connected with said-shutter to control its position,

a power supply circuit to energize said motor,

a braking circuit including fully electric brake means to stop said motor,

release switch means having a first position for interrupting said braking circuit, and a second position for interrupting said power supply circuit, v

a bypass circuit disposed to by-pass said release switch means in said second position,

by-pass switch means arranged within said by-pass circuit and operated by said motor, said by-pass switch means for interrupting said by-pass circuit in said'closed position of said shutter and being closed in said open position of said shutter,

braking switch means arranged within said braking circuit and operated by said motor, said braking switch means for interrupting said braking circuit in said open position of said shutter and being closed in said closed position of said shutter,

said electric brake means for being energized only with said braking switch means being closed and with said release switch in'said second position.

2. The appliance, as set forth in claim 1, wherein said by-pass circuit includes a braking resistor for said motor,

3. The appliance, as set forth in claim I, wherein said by-pass switch means comprise a photoelectric transducer and means for transmitting light to said transducer only with saidshutter in open position.

4. The appliance, as set forth in claim 1, further comprising manually operable means'to close forcibly said bypass switch means'for a period corresponding in a maximum to the period of said open position of said shutter when said shutter is standing still in said closed position and said motor is de'energized.

5. The appliance, as set forth in claim 4, wherein Said manually operable means comprise means to totate saidshutter until said by-pass switch means are closed.

6. The appliance. as set forth in claim I, wherein said release switch means comprise a release switch anda brake control switch. said switches being operatively interconnected.

7. An appliance, as set forth inclaim 6, wherein said brake control switch means comprises a switching transistor having an emitter-collector path shunting said motor.

8. In a photographic film-handling appliance means defining an optical path,

a shutter arranged on said optical path and having an open position and a closed position,

an electric motor drivingly connected with said shutter to control its position,

a power supply circuit to energize said motor,

a braking circuit including fully electric brake means to stop said motor,

I release switch means having a first position for inter rupting said braking circuit, and a second position for interrupting said power supply circuit,

7 a first by-pass circuit to by-pass said release switch means in said second position,

first by-pass switch means arranged within said first by-pass circuit and operated by said motor, said first by-pass switch means for interrupting said bypass circuit in said closed position of said shutter and being closed in said open position of said shutter,

a second by-pass circuit to by-pass said release switch means in said second position,

second by-pass switch means arranged within said second by-pass circuit,

manually operable means for closing said second bypass switch means for a period corresponding in a maximum to the period of said open position of said shutter.

9. The appliance, as set forth in claim 8, wherein said second by-pass switch means comprise a wiping contact switch.

10. An appliance, as set forth in claim 8, wherein said second by-pass switch means comprise,

a monostable multivibrator,

a time constant circuit to control said multivibrator and including an interrupter, said time constant circuit having a time constant corresponding in a maximum to the time period of said open position of said shutter.

Claims

1. In a photographic film-handling appliance means defining an optical path, a shutter arranged on said optical path and having an open position and a closed position, an electric motor drivingly connected with said shutter to control its position, a power supply circuit to energize said motor, a braking circuit including fully electric brake means to stop said motor, release switch means having a first position for interrupting said braking circuit, and a second position for interrupting said power supply circuit, a by-pass circuit disposed to by-pass said release switch means in said second position, by-pass switch means arranged within said by-pass circuit and operated by said motor, said by-pass switch means for interrupting said by-pass circuit in said closed position of said shutter and being closed in said open position of said shutter, braking switch means arranged within said braking circuit and operated by said motor, said braking switch means for interrupting said braking circuit in said open position of said shutter and being closed in said closed position of said shutter, said electric brake means for being energized only with said braking switch means being closed and with said release switch in said second position.

3. The appliance, as set forth in claim 1, wherein said by-pass switch means comprise a photoelectric transducer and means for transmitting light to said transducer only with said shutter in open position.

4. The appliance, as set forth in claim 1, further comprising manually operable means to close forcibly said by-pass switch means for a period corresponding in a maximum to the period of said open position of said shutter when said shutter is standing still in said closed position and said motor is de-energized.

5. The appliance, as set forth in claim 4, wherein said manually operable means comprise means to rotate said shutter until said by-pass switch means are closed.

6. The appliance, as set forth in claim 1, wherein said release switch means comprise a release switch and a brake control switch, said switches being operatively interconnected.

7. An appliance, as set forth in claim 6, wherein said brake control switch means comprises a switching transistor having an emitter-collector path shunting said motor.

8. In a photographic film-handling appliance means defining an optical path, a shutter arranged on said optical path and having an open position and a closed position, an electric motor drivingly connected with said shutter to control its position, a power supply circuit to energize said motor, a braking circuit including fully electric brake means to stop said motor, release switch means having a first position for interrupting said braking circuit, and a second position for interrupting said power supply circuit, a first by-pass circuit to by-pass said release switch means in said second position, first by-pass switch means arranged within said first by-pass circuit and operated by said motor, said first by-pass switch means for interrupting said by-pass circuit in said closed position of said shutter and being closed in said open position of said shutter, braking switch means arranged within said braking circuit and operated by said motor, said braking switch means for interrupting said braking circuit in said open position of said shutter and being closed in said closed position of said shutter, a second by-pass circuit to by-pass said release switch means in said second position, second by-pass switch means arranged within said second by-pass circuit, manually operable means for closing said second by-pass switch means for a period corresponding in a maximum to the period of said open position of said shutter.

10. An appliance, as set forth in claim 8, wherein said second by-pass switch means comprise, a monostable multivibrator, a time constant circuit to control said multivibrator and including an interrupter, said time constant circuit having a time constant corresponding in a maximum to the time period of said open position of said shutter.