US3688674A

US3688674A - Electronic shutter device

Info

Publication number: US3688674A
Application number: US884569A
Authority: US
Inventors: Yoshio Kuramoto; Toshio Kobori
Original assignee: Minolta Co Ltd
Current assignee: Minolta Co Ltd
Priority date: 1968-12-25
Filing date: 1969-12-12
Publication date: 1972-09-05
Anticipated expiration: 1989-09-05
Also published as: DE1964863A1

Abstract

A focal plane shutter includes a front screen and a rear screen, the latter being locked in a cocked position by an electromagnet through a locking lever while the electromagnet is energized. The locking lever is biased in a direction to contact the electromagnet and lock the rear screen. When the electromagnet is de-energized after a time period controlled by an electric circuit, the rear screen is driven against the bias of the locking lever.

Description

United States Patent Kuramoto et al.

[54] ELECTRONIC SHUTTER DEVICE [72] Inventors: Yoshio Kuramoto, Sakai-shi; Toshio Kobori, Izumiotsu-shi, both of Japan [73] Assignee: Minolta Camera Kabushlki Kaislia,

- Minami-ku, Osaka, Japan [22] Filed: Dec. 12, 1969 [21] Appl. No.: 884,569

[30] Foreign Application Priority Data Dec. 25, 1968 Japan ..43/112562 52 US. Cl. ..95/53 E, 95/57 51 Int. Cl. ..G03b 9/62 [58] Field 61 Search ..95/57, 55, 10 c, 53 E, 53 EB [56] References Cited UNITED STATES PATENTS g 3,277,806 10/1966 Wagner et al. .;.....95/55 3,391,627 7/1968 Leuschke ..95/57 3,498,195

3/1970 Ono.- ..95/57 X 1 51 Sept. 5, 1972 3,442,190 5/1969 Erickson ..95/10 c 3,349,678 10/1967 Suzuki et al ..95/10 C 3,241,471 3/1966 Burgarella ..95/55 FOREIGN PATENTS OR APPLICATIONS 260,015 2/1968 Austria ..95/52 EB 4/1968 Great Britain ..95/53 E Primary Examiner-Samuel S. Matthews Assistant Examiner-Russell B. Adams, Jr Attomey-Watson, Cole, Grindle & Watson 57 ABSTRACT A focal plane shutter includes a front screen and a rear screen, the latter being locked in a cocked position by an electromagnet through a locking lever while the electromagnet is energized. The locking lever is biased in a direction to contact the electromagnet and lock the rear screen. When the electromagnet is deenergized after a time period controlled by an electric circuit, the rear screen is driven against the bias .of the locking lever. f

4Claims,4DrawingFigures PATENTED'SEP 51912 3.688374 SHEET 2 BF 2 FIG.3

mmmu INVENTOR [214,5 @{JM Ms;

A ORNEY BACKGROUND OF THE INVENTION The present invention relates to a focal plane shutter device in which the closing operation is started by deenergization of an electromagnet. It is well known to electrically control the closing of camera shutters, specifically focal plane shutters having a rear screen. The control for such operations normally consists of an RC timing network where a capacitor is charged via a photoresistive element. The rate at which the capacitor is charged is therefore dependent upon the amount of light falling on the photoresistive element.

The potential across the capacitor usually controls a Schmidt trigger circuit which in turn controls an electromagnetic actuator for shutter closure. Generally, there are two types of design for such an electrically controlled shutter. The electromagnetic actuator may be (I) magnetized by the Schmidt circuit to effect shutter closure or it may be (2) demagnetized to effect shutter closure. Both types of control have'a minimum number of moving parts therefore they are both generally immune from damage due to vibration shock. However, the first type of control relies on the attrac tion of an armature by an electromagnet. Since magnetic force varies by the inverse square of the distance, a strong electromagnet is required. This entails a large coil or a large current supply.

In .the second type of control, a spring is required to pull the armature away from the electromagnet. This system also requires a strong electromagnet to overcome the pull of the spring.

SUMMARY OF THE INVENTION so as to increase the displacement angle of the arresting member against the force of spring when the travel of rear screen is finished and to do a braking operation at the time when the travel of rear screen is finished.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a wiring diagram showing an example of a .control circuit for an electric shutter used in the DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a wiring diagram showing a control circuit for the well known electric shutter used in the present invention, and variable resistance R and condenser C are connected in series to electric power source E a through power switch S1.

The present invention is directed to a demagnetization type electric shutter wherein the rear screen is released by demagnetization of an electromagnet. The armature of the arresting member is held in contact with the electromagnet by a spring which urges the member in the direction for arresting the movement of the rear. A rear screen check plate cooperates with said arresting member and for that purpose is provided with a notched portion engaging said arresting member and a sliding contact portion disposed in series with said notched portion. Thus, when said arresting member engages said notched portion said armature is in contact with said electromagnet. The sliding contact portion causes said armature of the arresting member to separate from said electromagnet against said spring bias and simultaneously said arresting member slides in contact thereon so as to permit said rear screen arresting'plate to turn.

An important object of the present invention is to provide an electronic shutter device wherein the release mechanism for the rear screen is spring biased into contact with an electromagnet. As a result, the electromagnet may be of a small capacity.

Another object of the present invention is to provide a camming contact portion on the rear screen arresting plate whereby the arresting member is moved against the bias of the spring to the position where the armature of said arresting member is separated from the electromagnet.

A further object of the present invention is to provide means to prevent the rear screen from springing back by forming said contact portion into a cam shape When said variable resistance is taken to be a photoconductive element such as a CdS cell, the resistance is changed in accordance with the brightness of an object. By setting up variable resistance R manually for the resistance value it is possible to make a manually set up type. A timing switch S2 is provided in parallel with condenser C for short-circuiting the latter. And, connecting point-P between variable resistance R and condenser C is connected to the base of transister Trl and its collector is connected to the base of second transistor Tr2 to form a Schmidt trigger circuit, and in the collector circuit of said second transistor Tr2 electromagnetic coil M is disposed. r1 and r2 are respectively an adjusting resistance and a set up for the trigger voltage of said Schmidt trigger circuit..

And, when the voltage of point P comes to a certain value transistor Trl is turned over from the cut off state and into the conductive state and in opposition transistor Tr2 is formed to turn to the cut off state from the conductive state. I

In FIG. 2 showing an embodiment in accordance with the present invention, front screen 1 of a focal plane shutter is fixed rigidly on one end thereof to front screen winding drum 2 fixed'to shaft 3 integral with front screen pinion 4. The other end of screen 1- is wound around a take-up drum urged to take-up screen 1 through a strong spring force (not shown in the drawings). v

To front screen gear 5 meshed with said front screen pinion 4 there is fixed front screen check plate 6 having notched arresting portion 6a, and to said front screen plate 6 there is provided a connecting pin 7 extending upwardly therefrom.

Front screen arresting lever 8 which has, on one end thereof, an arresting pawl 8a for engaging with notched arresting portion 6a of said front screen check plate 6. Lever 8 has, on the other end thereof, an insulating pin 11 disposed for coming into contact with the contact piece of timing switch S2 which is normally closed.

Lever 8 is connected to a camera body rotatably on pin 9 and biased in a clockwise direction by spring 10. Said arresting pawl 80 engages with said notched arresting portion 6a, and said insulating pin 1 1 is disposed to permit timing switch S2 to remain in the closed condition.

Rear screen 12 is fixed on one end thereof to rear screen winding drum 13 fixed to shaft 14 integral with rear screen pinion 15 and the other end thereof is wound around a screen take-up drum urged to take-up screen 12 through a strong spring force not shown in the drawings.

To rear screen gear 16 which is meshed with said rear screen pinion 15, a rear screen check plate 17 is fixed. Said rear screen-check plate 17 is fonned into a cam shape and is provided with notched step portion 17a for engaging with arresting pawl 19a of rear screen arresting lever 19 which is a rear screen arresting member described hereinafter, and sliding contact portion 17b provided in succession to said notch step portion 170 andfor allowing said arresting pawl 19a to slide in touch thereon, and under rear screen gear 16 there is provided wind up pin 18 for engaging with said connecting pin 7.

Said rear screen arresting lever 19 is connected to the camera body rotatably on pin 20 and on one arm thereof weak spring 21 is provided for giving the counterclockwise turning tendency to said arresting lever 19, that is, armature 22 on one arm thereof is connected to the pole of electromagnet M and arresting pawl 19a of the other arm thereof is biased so as to engage with notched step portion 17a of rear screen check plate 17.

Therefore, when plate 17 turns, arresting pawl 19a is pushed out from notched step portion 17a against spring 21 was to slide in contact on sliding contact portion 17b. 4

FIG. 2'shows the state at the time when the shutter is cocked, and in this state arresting pawl 80 of front screen arresting lever 8 is in arresting engagement with notched arresting portion 6a of front screen check plate 6. In, and in notched step portion 17a of rear screen check plate 17 of rear screen gear 16, there is fitted arresting pawl 19a of rear screen arresting lever 19 which turns counter-clockwise by means of spring 21 and armature 22 is in contact with the pole of electromagnet M. In this case, in FIG. 1, power switch S1 is opened, timing switch S2 is closed, and condenser C is short-circuited. Therefore, electromagnet M is demagnetized and rear screen gear 16 is arrested because wind up pin 18 thereof is in engagement'with connecting pin 7.

In this state, when a shutter button (not shown in the drawings) is pushed down, power switch S1 is closed by means of a well known mechanism also not shown in the drawings and transistor Tr2 becomes conductive to energize electromagnet M, and armature 22 is attracted by electromagnet M and arresting pawl 19a is held in notched step portion 17a, and thereby the arresting operation of the rear screen gear remains in effect.

Then, the shutter button turns front screen arresting lever 8 counter-clockwise through a well known mechanism not shown in the drawings and breaks the engagement of arresting pawl 8a and notched arresting portion 6a of front screen check plate 6, so that front screen starts to travel and simultaneously timing switch S2 is opened to start to charge condenser C with the current running through photoconductive element R corresponding to the brightness of an object.

Thus, the engagement of connecting pin 7 and roll up pin 18 is broken but electromagnet M is still in, the excited state so rear screen arresting lever 19 prevents rear screen check plate 17 from turning and rear screen 12 remains motionless.

When the charging voltage in condenser C comes to a predetermined valuethe Schmidt trigger circuit is operated and transistor Tr2 becomes non-conductive and electromagnet M is demagnetized. Therefore, rear screen arresting lever 19 is held against plate 17 by only the force of weak spring 21, so that by means of rear screen 12 which is pulled by the winding drum having a strong spring, rear screen check 17 turns while pushing arresting pawl 19a of rear screen arresting lever 19 out from notched step portion 17a against the bias of spring 21, allowing said arresting pawl 19'to slide in contact as shown in FIG. 3, and thus the shutter is closed.

After an exposure is finished, by turning front screen 5 by means of the shutter wind up lever not shown in the drawings, connecting pin 7 pushes wind up pin 18 to turn rear screen gear 16 to cock the shutter, and when rear screen arresting pawl 19a comes to notched step portion 170, rear screen arresting lever 19 turns counter-clockwise by means of spring 21 and armature 22 comes in to contact with electromagnet M, so that in the next shutter release the attraction at the time when power switch S1 is closed is increased. Rear screen gear 16 is checked in the cocked position through wind up pin 18 by means of connecting pin 7 of front screen check plate 6 which is arrested by front screen arresting lever 8.

In the embodiment shown in FIG. 4, the rear screen check plate acts also as a brake during the terminal portions of travel of the rear screen.

On rear screen check plate 17 there are provided notched step portion 17'a, sliding contact portion 17'b provided in series with said notched step portion 17'a, and rising portion 17'c provided on the terminal portion of said sliding contact portion 17'b, namely, near the terminal portions of turning during travel of the rear screen. And, when arresting lever 19' is turned farther clockwise from the position where it comes into contact with sliding contact portion 17'b by riding on portion 17'c, protrusion l9'b formed on arresting lever 19' comes into contact with contact portion 24a of brake lever 24 to turn said brake lever 24 counterclockwise, and the braking operation is effected by means of the well known delayed mechanism (not shown in the drawings provided on said brake lever 24, and thereby it is possible to prevent the light break due to spring back of the rear screen on the terminal position of travel of said rear screen.

We claim:

1. A shutter mechanism for a focal plane camera comprising:

a front screen and a rear screen, each of which is driven by a respective spring for film exposure;

an electromagnet means for locking the rear screen in cocked position against the bias of its spring while energized;

an electric circuit for controlling the time interval during which the electromagnet is energized;

a first stopper member mechanically connected with the front screen to be moved therewith;

a first locking element engageable with the first stopper member for preventing movement of the first stopper member to thereby lock the front screen in a cocked condition against the bias of its spring;

a second stopper member mechanically connected with the rear screen to be moved therewith;

an interlock means for interlocking the first and second stopper members during the shutter cocking operation and for locking the rear screen by the first locking member through the interlock means until the front screen is released;

a second locking element having an armature mounted thereon, said second locking element being engageable with the second stopper member for preventing movement of the latter to thereby lock the rear screen in a cocked condition against the bias of its spring,

said second stopper member comprising a rotatable cam provided with a circumferentially extending camming surface including a stopper portion,

said second locking element including a segment disposed for continuously contacting said camming surface during rotation of the cam; and

a biasing member connected to the second locking element for urging said segment into continual engagement with the camming surface and urging the armature into contact with the electromagnet means, said electromagnet means being disposed to cooperate with thebiasing member for holding said segment against said stopper portion to thereby lock the rear screen through the second 6 locking element while the electromagnetmeans is energized.

2. A shutter device as set forth in claim 1 wherein the stopper portion of the cam and the segment of the second locking element are configured to cause the same to separate during movement of the cam with the rear screen when the latter is driven to terminate exposure of the film, the spring of the rear screen having a bias which is stronger than the bias of the biasing member whereby the rear screen is released against the engagement of the second locking element with the stopper portion of the cam when the electromagnet is demagnetized.

3. An electrically controlled shutter device as set forth in claim. 1, wherein is provided a brake member disposed in the pathof the second locking element, the cam being provided with a rising portion on its camming surface for rotating the second locking element to cause the latter to come into contact with the brake member so that the movement of the rear screen may be braked before termination of the shutter closing operation of the rear screen.

4. An electrically controlled shutter device as set forth in claim 1, wherein said front and rear screens are each connected to and wound around a respective wind-up drum mounted on a wind-up shaft having a pinion fixed thereon, said cam being fixed on a rear screen gear meshing with the pinion of the rear screen wind-up shaft, said first stopper member being fixed on a from screen gear meshing with the pinion of the front screen wind up shaft, said gears being disposed concentrically but independently of o e another, sai interock means comprising a pair 0 mterengageab e plllS,

each pin being fixed on a respective gear.

l II i I I!

Claims

1. A shutter mechanism for a focal plane camera comprising: a front screen and a rear screen, each of which is driven by a respective spring for film exposure; an electromagnet means for locking the rear screen in cocked position against the bias of its spring while energized; an electric circuit for controlling the time interval during which the electromagnet is energized; a first stopper member mechanically connected with the front screen to be moved therewith; a first locking element engageable with the first stopper member for preventing movement of the first stopper member to thereby lock the front screen in a cocked condition against the bias of its spring; a second stopper member mechanically connected with the rear screen to be moved therewith; an interlock means for interlocking the first and second stopper members during the shutter cocking operation and for locking the rear screen by the first locking member through the interlock means until the front screen is released; a second locking element having an armature mounted thereon, said second locking element being engageable with the second stopper member for preventing movement of the latter to thereby lock the rear screen in a cocked condition against the bias of its spring, said second stopper member comprising a rotatable cam provided with a circumferentially extending camming surface including a stopper portion, said second locking element including a segment disposed for continuously contacting said camming surface during rotation of the cam; and a biasing member connected to the second locking element for urging said segment into continual engagement with the camming surface and urging the armature into contact with the electromagnet means, said electromagnet means being disposed to cooperate with the biasing member for holding said segment against said stopper portion to thereby lock the rear screen through the second locking element while tHe electromagnet means is energized.

3. An electrically controlled shutter device as set forth in claim 1, wherein is provided a brake member disposed in the path of the second locking element, the cam being provided with a rising portion on its camming surface for rotating the second locking element to cause the latter to come into contact with the brake member so that the movement of the rear screen may be braked before termination of the shutter closing operation of the rear screen.

4. An electrically controlled shutter device as set forth in claim 1, wherein said front and rear screens are each connected to and wound around a respective wind-up drum mounted on a wind-up shaft having a pinion fixed thereon, said cam being fixed on a rear screen gear meshing with the pinion of the rear screen wind-up shaft, said first stopper member being fixed on a front screen gear meshing with the pinion of the front screen wind-up shaft, said gears being disposed concentrically but independently of one another, said interlock means comprising a pair of interengageable pins, each pin being fixed on a respective gear.