Electromagnetically Operated Shutter Mechanism

The present invention relates to an electromagnetically operated shutter mechanism for use in an optical image producing apparatus, such as a photographic camera or a copying machine, of a type which necessitates a shutter mechanism for selectively closing and opening an exposure aperture provided in the apparatus.

The copending application Ser. No. 725,201, filed on Sept. 22, 1976, now U.S. Pat. No. 4,121,235 the invention of which has been assigned to the same assignee of the present invention, discloses an electromagnetrically controlled shutter mechanism. According to the above described copending application, the shutter mechanism for selectively closing and opening an exposure aperture through which, during opening of the aperture, the incoming light is allowed to pass therethrough, said shutter mechanism substantially comprises, at least shutter member supported in position for movement between an inoperative position, in which the exposure aperture is closed, and an operated position in which the exposure aperture is opened, at least one permanent magnet, a substantially elongated carrier member having the permanent magnet rigidly mounted on one end portion thereof, the other end portion of said carrier member being connected to the shutter member, a solenoid coil supported in position to surround the elongated carrier member and circuit means. The circuit means includes first and second circuit components operable in opposed phase relationship to each other and electrically connected to said solenoid coil. The first circuit component during its operation feeds an electric current from a D.C. power source so as to flow through said solenoid coil in one direction, while the second circuit component during its operation feeds the electric current so as to flow through said solenoid coil in the opposite direction.

The permanent magnet is so positioned that, during the operation of the first circuit component, the shutter member is moved from the inoperative position towards the operated position by the effect of a magnetic force developed between the permanent magnet and the solenoid coil then energized by the current flowing in the one direction, and, during the operation of the second circuit component, the shutter member is returned from the operated position towards the inoperative position by the effect of a magnetic force developed between the permanent magnet and the solenoid coil then energized by the current flowing in the opposite direction.

In the above described copending application, the relation between the magnetic force for moving the shutter member to the operative position and the magnetic force for moving the shutter member to the inoperative position is not disclosed. According to the tests carried out by the present inventors, however, it is found out that the shutter mechanism of the above described type performs quick return of the shutter member from inoperative to operative position or vice versa when the magnetic force for moving the shutter member to the operative position is stronger than the magnetic force for moving the shutter member to the inoperative position, or vice versa. Thus, it is possible to have the above described type of shutter mechanism to open and close the aperture at high shutter speed with optimum stability.

Accordingly, a primary object of the present invention is to provide an improved electromagnetically operated shutter mechanism, in which either one of the two magnetic forces i.e., a first magnetic force produced for moving the shutter mechanism to operated position and a second magnetic force produced for moving the shutter mechanism to inoperated position, is stronger than other magnetic force.

Another object of the present invention is to provide an improved electromagnetically operated shutter mechanism of the type referred to above, wherein said second magnetic force is stronger than said first magnetic force.

Still another object of the present invention is to provide an improved electromagnetically operated shutter mechanism of the type referred to above, wherein a magnetic braking force is applied to the first and second shutter members during their movement from the inoperative positions towards the operated positions to make a relatively high shutter speed available with the solenoid coils compact in size.

A further object of the present invention is to provide an improved electromagnetically operated shutter mechanism of the type referred to above, which is most suited for use in a compact photographic camera.

FIG. 1 is a schematic front elevational view, with portions shown in section, of an electromagnetically operated shutter mechanism according to one embodiment of the present invention, the shutter mechanism being shown in a closed position;

FIG. 2 is a view similar to FIG. 1, showing the shutter mechanism in an opened position;

FIG. 3 is a schematic electric circuit diagram showing a drive circuit for operating solenoid coils employed in the shutter mechanism;

FIG. 4 is a chart showing various waveforms of electric signals appearing in the circuit of FIG. 3;

FIG. 5 is a schematic block diagram showing another form of drive circuit for operating the solenoid coils employed in the shutter mechanism;

FIG. 6 is a chart showing various waveforms of electric signals appearing in the circuit of FIG. 5;

FIG. 7 is a schematic block diagram showing a further form of drive circuit for operating the solenoid coils employed in the shutter mechanism; and

FIG. 8 is a chart showing various waveforms of electric signals appearing in the circuit of FIG. 7.

Before the description of the present invention proceeds, it is to be noted that like parts are designated by like reference numerals throughout the accompanying drawings. It is further to be noted that, for the sake of a better understanding of the present invention, the present invention will be described as applied to a shutter mechanism of a guillotine type used in a photographic camera. However, it is to be understood that the concept of the present invention can equally be applicable not only to the camera shutter mechanism, but also to a shutter mechanism utilized in business machines such as a copying machine for preparing microfiches.

Referring first to FIGS. 1 and 2, a shutter mechanism according to one preferred embodiment of the present invention is shown to comprise first and second shutter members X and Y operatively carried by a camera housing (not shown) in a manner as will be described. It is, however, to be understood that the camera housing has an exposure aperture, shown by the broken circle A, which exposure aperture A is positioned in alignment with the optical axis of an objective lens assembly (not shown) mounted on a lens barrel that is rigidly or interchangeably connected to the camera housing in any known manner.

The first shutter member X is shown to be comprised of a first shutter plate 10 of a shape having a pair of arms 11 and 12 outwardly extending in the opposite directions from the ends of the first shutter plate 10. While the arm 11 has a free end operatively accommodated within a sleeve 30 around which a solenoid coil C.sub.1 is wound, the first shutter member X is supported by the camera housing for movement between inoperative and operated positions by means of a shaft member 31 which extends through a guide slot 13 defined in the arm 12, it being understood that the length of the slot 13 fixes the distance between the inoperative and operated positions of the first shutter member X. An opening 14, which can be brought into alignment with the optical axis of the objective lens assembly and, therefore, the exposure aperture A in the camera housing only when the shutter member X is moved from the inoperative position as shown in FIG. 1 to the operated position as shown in FIG. 2, is defined in the shutter plate 10 at one end portion adjacent the arm 12 and is so positioned as to achieve the alignment thereof with the exposure aperture A in the manner described above.

For the purpose as will become clear from the subsequent description, a connecting lug 15 having a guide slot 15a defined therein is integrally formed with the arm 12 and is shown to extend downwards from said arm 12 in a direction substantially perpendicular to the length-wise direction of the slot 13.

On the other hand, the second shutter member Y is shown to be comprised of a second shutter plate 20 of a shape substantially similar to the first shutter plate 10 and having an arm 21 extending outwardly from the shutter plate 20 and terminating within a sleeve 32 around which a solenoid coil C.sub.2 is wound. This second shutter member Y is supported by the camera housing for movement between inoperative and operated positions by means of the shaft member 31 which also extends through a guide slot 22 substantially defined in the arm 21, it being understood that the length of the guide slot 22 is substantially equal to the length of the guide slot 13. An opening 23 is defined in the shutter plate 20 at one end portion remote from the arm 21 and is so positioned that only when the second shutter member Y is moved from the inoperative position as shown in FIG. 1 to the operated position as shown in FIG. 2 while the first shutter member X is concurrently moved to the operated position, the opening 23 can be aligned to and communicated to the exposure aperture A through the opening 14 in the first shutter member X to allow the incoming light through the objective lens assembly to pass through the openings 14 and 23, then aligned with each other, towards a light sensitive film (not shown) positioned on one side of the shutter mechanism opposed to the side where the exposure aperture A is located. The second shutter member Y has a connecting lug 24 having a guide slot 24a defined therein, which connecting lug 24 is integrally formed with the arm 21 and is shown to extend upwards from said arm 21 in a direction perpendicular to the lengthwise direction of the slot 22.

These shutter members X and Y are operatively associated by a connecting lever 33 pivotally and non-detachably mounted on the shaft member 31 at a substantially intermediate portion thereof. The connecting lever 33 so supported by the camera housing through the shaft member 31, which also supports the shutter members X and Y in the manner described above, has its opposite ends formed with guide pins 34 and 35 which are respectively slidingly engaged in the guide slots 15a and 24a, these guide slots 15a and 24a being so sized that, during the movement of any one of the first and second shutter members X and Y between the inoperative and operated positions, the guide pins 34 and 35 respectively reciprocally move within the slots 34 and 35 while the connecting lever 33 pivots about the shaft member 31.

With the construction so far described, it is clear that, when either one of the first and second shutter members X and Y is moved from the inoperative position towards the operated position, the other of the first and second shutter members X and Y is also moved from the inoperative position towards the operated position, moving in a direction counter to the direction of movement of such either one of the first and second shutter members X and Y. It is, therefore, clear that the connecting lever 33 serves to transmit the movement of either one of the first and second shutter members X and Y to the other of the first and second shutter members X and Y while it reciprocally pivots about the shaft member 31. In view of this, so long as the first and second shutter members X and Y are held in their respective inoperative positions as shown in FIG. 1, the exposure aperture A is closed on one hand and, when the shutter members X and Y are simultaneously moved to the respective inoperative positions as shown in FIG. 2, the exposure aperture A is opened and, therefore, the incoming light entering the exposure aperture A is allowed to pass through the openings 14 and 23 in the respective shutter members X and Y towards the light sensitive film to cause the exposure of the latter to take place.

For effecting the movement of the shutter members X and Y in the manner as hereinbefore described, a pair of permanent magnets 36a and 36b are rigidly mounted on free end of the arm 11, while another pair of permanent magnets 37a and 37b are rigidly mounted on free end of the arm 21. These magnets 36a, 36b, 37a and 37b are respectively operatively associated with the solenoid coils C.sub.1 and C.sub.2 in a manner as will be described later in connection with an electric circuit with reference to any one of FIGS. 3, 5 and 7.

However, for the sake of the description of the present invention, it is to be understood that, as shown in FIGS. 1 and 2, the magnet 36a on the arm 11 of the first shutter member X is shown to have its south and north poles oriented in respective directions close to and away from the exposure aperture A, while the other magnet 36b is positioned adjacent to the magnet 36a and at a substantially intermediate portion of the arm 11 with the south pole thereof facing the south pole of the magnet 36a. On the other hand, the magnet 37a on the arm 21 of the second shutter member Y is shown to have its north and south poles oriented in respective directions away from and close to the exposure aperture A, while the other magnet 37b is positioned adjacent to the magnet 37a and at a substantially intermediate portion of the arm 21 with the south pole thereof facing the south pole of the magnet 37a.

Before the position of any of the magnets 36a, 36b, 37a and 37b relative to the associated solenoid coil is described, a general characteristic of the solenoid coil C.sub.1 or C.sub.2 will now be described. As can readily be understood by those skilled in the art, when an electric current is applied to the solenoid coil C.sub.1 or C.sub.2, unlike poles are developed at the opposite ends of the sleeve 30 or 32 with lines of magnetic force running from the north pole towards the south pole. The magnetic flux density, that is, the number of lines of magnetic force passing across a given surface perpendicular to the longitudinal axis of the sleeve 30 or 32, attains the lowest value at the plane passing through the point intermediate of the length of the sleeve 30 or 32 at right angles to the longitudinal axis of said sleeve and the highest value at the plane perpendicular to the longitudinal axis of said sleeve and spaced a predetermined distance outwards from each of the opposed ends of the sleeve 30 or 32.

With the above in mind, for the sake of the present invention, the plane intermediate of the length of the sleeve 30 or 32 and at right angles to the longitudinal axis of the sleeve, where the magnetic flux density attains the lowest value upon energization of the solenoid coil C.sub.1 or C.sub.2, is shown by the broken line BP and is hereinafter referred to as a boundary plane while the planes adjacent the respective ends of the sleeve 30 or 32 where the highest magnetic flux density is attained upon energization of the solenoid coil C.sub.1 or C.sub.2 are shown by the broken lines P.sub.1 and P.sub.2.

While the characteristic of the solenoid coils C.sub.1 and C.sub.2 are such as hereinabove described, the magnets 36 and 37 on the arms 11 and 21 are so positioned that, when the first and second shutter members X and Y are held in their inoperative positions as shown in FIG. 1, the north pole face of the magnet 36b is aligned with the plane P.sub.2 adjacent the solenoid coil C.sub.1 and the north pole face of the magnet 37b is aligned with the plane P.sub.2 adjacent the solenoid coil C.sub.2, and that when the shutter members X and Y are moved to their operative positions as shown in FIG. 2, the north pole face of the magnet 36a is aligned with the plane P.sub.1 adjacent the solenoid coil C.sub.1 and the north pole face of the magnet 37a is aligned with the plane P.sub.1 adjacent the solenoid coil C.sub.2.

It is to be noted that the stroke of movement of each of the magnets 36a, 36b, 37a and 37b is substantially equal to or slightly smaller than half the difference between the length of each of the solenoid coils or the sleeves and the length of each of the magnets 36a, 36b, 37a and 37b.

In constructing the shutter mechanism according to the present invention, care must be taken that the respective lengths of the slots 13 and 22, which are equal to each other and also to the stroke of movement of any one of the magnets 36a, 36b, 37a and 37b, are to be so selected that, when the shutter members X and Y are respectively held in the inoperative positions as shown in FIG. 1, any portions of the openings 14 and 23 will not overlap with each other in communication with the exposure aperture A. At this time, one of the opposed ends of the slot 13 adjacent the shutter plate 10 and one of the opposed ends of the slot 22 remote from the shutter plate 20 are engaged to the shaft member 31. The operable positions of the shutter members X and Y are respectively defined by the engagement of the other of the opposed ends of the slot 13 and the other of the opposed ends of the slot 22 to the shaft member 31 as shown in FIG. 2.

Furthermore, although not shown, it is to be understood that any suitable guide means may be employed for guiding the relative parallel movement of the shutter members X and Y.

The electric drive circuits, each of which may be employed for operating the shutter mechanism shown in FIGS. 1 and 2 so far described, will now be described.

With reference to FIG. 3, the electric drive circuit shown basically comprises two drive channels and includes a release switch 50, which is normally opened, but is closed in response to depression of a shutter release button (not shown) provided in the camera housing, which depression is effected during actual taking of a photographic picture. Upon closure of the release switch 50, an electric signal indicative of the depression of the shutter release button, the waveform of which is shown by (a) in FIG. 4, is applied to a first one-shot multivibrator 51 having a photocell 51a, such as a CdS cell, the resistance of which photocell 51a varies in proportion to the amount of light reflected onto such photocell from an object to be photographed. The one-shot multivibrator 51 generates an output pulse of a waveform shown by (b) in FIG. 4, the pulse duration of which is determined according to the amount of light received by the photocell 51a. The output pulse from the one-shot multivibrator 51 is subsequently applied in part to a first photo-coupler F.sub.1, composed of a light emitting diode D and a photo-transistor Q, to bring a first switching transistor Q.sub.1 into a conductive state and in part to a second photo-coupler F.sub.2, composed of a light emitting diode D and a photo-transistor Q, to bring a second switching transistor Q.sub.2 into a conductive state. Simultaneous conduction of the first and second switching transistors Q.sub.1 and Q.sub.2 continues for a predetermined time determined by and equal to the pulse duration of the output pulse (b) from the one-shot multivibrator 51. During this conduction of the transistors Q.sub.1 and Q.sub.2, a current from a D.C. power source E flows from the positive terminal thereof towards the negative terminal thereof through the first switching transistor Q.sub.1, then a resistor R and the solenoid coil C.sub.1 and finally the second switching transistor Q.sub.2.

Therefore, during the pulse duration of the output pulse (b) from the one-shot multivibrator 51, the solenoid coil C.sub.1 is energized with a current (b.sub.1) flowing through the resistor R, the amount of which current (b.sub.1) is decreased to a value of h.sub.1, as shown in FIG. 4 in dotted line, in relation to the amount of resistance of the resistor R.

Upon energization of the solenoid coil C.sub.1 thus effected, so far as the magnets 36a and 36b are arranged in the manner as hereinbefore described and shown in FIGS. 1 and 2, the south and north poles are respectively developed at the opposed ends of the solenoid coil C.sub.1 remote from and adjacent the exposure aperture A.

Therefore, by the effect of a magnetic attraction developed between the north pole of the magnet 36a and the south-polarized end of the solenoid coil C.sub.1 remote from the exposure aperture A, the shutter member X is drawn from the inoperative position towards the operated position. The movement of the shutter member X is then transmitted to the shutter member Y through the connecting lever 33 thereby causing the shutter member Y to move from the inoperative position towards the operated position substantially simultaneously with the movement of the shutter member X from the inoperative position towards the operated position. This is possible because the force of the magnetic attraction acting between the north pole of the magnet 36a and the south-polarized end of the solenoid coil C.sub.1 is greater than that acting between the south pole of the magnet 36b and the north-polarized end of the solenoid coil C.sub.1. The first mentioned force of the magnetic attraction gradually increases with decrease of the second mentioned force of the magnetic attraction as the shutter member X, so invited to move, moves from the inoperative position towards the operated position with the north pole of the magnet 36 approaching the plane P.sub.1 where the highest magnetic flux density exists.

On the other hand, the output pulse (b) from the one-shot multivibrator 51 is applied to a second one-shot multivibrator 52 so designed as to generate an output pulse of a waveform shown by (c) in FIG. 4 in response to termination of the pulse duration of the output pulse (b) from the first one-shot multivibrator 51. The second one-shot multivibrator 52 includes a variable resistor 52a, the resistance setting of which variable resistor 52a determines the pulse duration of the output pulse (c) emerging from such one-shot multivibrator 52. This output pulse (c) from the multivibrator 52 is applied in part to a third photo-coupler F.sub.3, composed of a light emitting diode D and a photo-transistor Q, to bring a third switching transistor Q.sub.3 into a conductive state and in part to a fourth photo-coupler F.sub.4, composed of a light emitting diode D and a photo-transistor Q, to bring a fourth switching transistor Q.sub.4 into a conductive state. It is to be noted that, since simultaneous conduction of the third and fourth transistors Q.sub.3 and Q.sub.4 takes place subsequent to the extinguishment of the output pulse (b) from the first one-shot multivibrator 51 as readily be understood from the comparison of the waveforms (b) and (c) in FIG. 4, the first and second switching transistors Q.sub.1 and Q.sub.2 are brought into a non-conductive state at the time the third and fourth switching transistors Q.sub.3 and Q.sub.4 are so brought into the conductive state.

During the conduction of the transistors Q.sub.3 and Q.sub.4 so effected, the current from the D.C. power source E flows from the positive terminal thereof towards the negative terminal thereof through the third switching transistor Q.sub.3, then the solenoid coil C.sub.2 and finally the fourth switching transistor Q.sub.4. Therefore, during the pulse duration of the output pulse (c) from the one-shot multivibrator 52, the solenoid coil C.sub.2 is energized with a current (c.sub.1). The amount of current (c.sub.1) has a value of h.sub.2, as shown in FIG. 4 in dotted line and, is larger than the current (b.sub.1) by the amount of h.sub.3.

Upon energization of the solenoid coil C.sub.2 thus effected, so far as the magnets 37a and 37b are arranged in the manner as hereinbefore described and shown in FIGS. 1 and 2, the south and north poles are respectively developed at the opposed ends of the solenoid coil C.sub.2 adjacent and remote from the exposure aperture A.

Therefore, it is clear that the shutter members X and Y, which have respectively been moved to their operated positions as shown in FIG. 2, can be returned back to their inoperative positions as shown in FIG. 1 by the effect of the magnetic attraction force developed between the coil C.sub.2 and the magnet 37b. It is to be noted that the magnetic attraction force for returning the shutter members X and Y in inoperative position is greater than that for moving the shutter members X and Y in operated position, because, as is understood from the electric drive circuit shown in FIG. 3, the current flowing through the coil C.sub.2 is greater than that flowing through the coil C.sub.1. Thus, the shutter members X and Y are moved to their inoperative position by a quick motion to complete the opening of the exposure aperture in predetermined period of time in high reliance.

Instead of providing resistor R in the drive circuit, it is possible to construct the coil C.sub.2 with a winding lead line having a thick diameter or with a winding lead line in greater number of turns of windings so as to produce such great magnetic attraction force.

From the foregoing, it will readily be seen that the lower the resistance of the photocell 51a, that is, the brighter the object to be photographed, the smaller the time during which the openings 14 and 23 in the respective shutter members X and Y allow the passage therethrough of incoming light from the exposure aperture towards the light sensitive film. On the contrary thereto, the higher the resistance of the photocell 51a, that is, the darker the object to be photographed, the longer the time during which the openings 14 and 23 in the shutter members X and Y allow the passage therethrough of incoming light from the exposure aperture A towards the light sensitive film.

The drive circuit which has been described with reference to FIGS. 3 and 4 is such that pulse (c) for energizing the coil C.sub.2 appears in relation to the extinguishment of the pulse (b). However, the pulse (c) may be produced before the extinguishment of the pulse (b) so as to substantially partially overlap the time durations for the pulses (b) and (c). With such relation between the pulses (b) and (c), the coil C.sub.2 is energized before the coil C.sub.1 is de-energized. Therefore, the movement of the shutter members X and Y towards the operated position may have a braking effect produced before the termination of the shutter members X and Y in the operated position. Thus, the shutter members may not produce a large impact at the moment of termination in the operated position and, can readily and quickly be returned back to the inoperative position. In other words, a comparatively high shutter speed can be obtained. For this purpose, there is provided an alternative drive circuit as shown in FIG. 5.

Referring to FIG. 5, the drive circuit shown includes a shutter release switch 50' so associated with the shutter release button in the camera housing that, upon depression of the release button, the switch 50' is closed to allow passage therethrough of an electric signal of a waveform shown by (a) in FIG. 6 in part towards a set terminal of a flip-flop circuit 53 and in part towards a comparison circuit 54 through a circuit unit composed of a photocell 55, such as a CdS cell, and a capacitor 56. Upon application of the electric signal (a) to the set terminal of the flip-flop circuit 53, the latter is set to generate an output pulse with which a switching transistor SQ.sub.1 of NPN type is brought into a conductive state. Conduction of the switching transistor SQ.sub.1 allows the current from the D.C. power source E to flow from the positive terminal back towards the negative terminal thereof through the solenoid coil C.sub.1 and a resistor R', then the switching transistor SQ.sub.1, thereby energizing the solenoid coil C.sub.1.

Therefore, by the effect of the magnetic attraction developed between the north pole of the magnet 36a and the south-polarized end of the solenoid coil C.sub.1 remote from the exposure aperture A, the shutter member X is drawn from the inoperative position towards the operated position, and also the shutter member Y is moved from the inoperative position towards the operated position substantially simultaneously with the movement of the shutter member X, as in the manner described before.

The comparison circuit 54 has a pair of input terminals; one input terminal being connected to a reference signal generator (not shown) from which a reference signal of a predetermined voltage as shown by (j) in FIG. 6 is applied thereto and the other input terminal being connected to the circuit unit, composed of the photocell 55 and the capacitor 56, from which an electric signal of a waveform as shown by (b) in FIG. 6 is applied thereto. This comparison circuit 54 generates an output signal only when the voltage of the electric signal applied thereto, through the circuit unit composed of the photocell 55 and the capacitor 56, exceeds the predetermined voltage (j) of the reference signal applied thereto from the reference signal generator. The output signal from the comparison circuit 54 has a waveform shown by (c) in FIG. 6. This output signal from the comparison circuit 54 is then applied in part to a one-shot multivibrator 57 and in part to a reset terminal of the flip-flop circuit 53 through a delay circuit 58.

The one-shot multivibrator 57, upon receipt of the output signal from the comparison circuit 54, generates a pulse of a waveform as shown by (g) in FIG. 6 to a second switching transistor SQ.sub.2 of NPN type so that the latter can be brought into a conductive state. Upon conduction of the transistor SQ.sub.2, the current from the D.C. power source E flows through the solenoid coil C.sub.2 and then the switching transistor SQ.sub.2, thereby energizing the solenoid coil C.sub.2. The value of such current flowing through the solenoid coil C.sub.2 is greater than that flowing through the solenoid coil C.sub.1, since there is no resistor connected to the solenoid coil C.sub.2. Therefore, the magnetic force produced by the solenoid coil C.sub.2 is greater than that produced by the solenoid coil C.sub.1. It is to be noted that, at the time the solenoid coil C.sub.2 is energized, the solenoid coil C.sub.1 which has been energized earlier than the solenoid coil C.sub.2 is still energized. De-energization of the solenoid coil C.sub.1 takes place when a reset signal, which is the output signal from the comparison circuit 54 delayed a predetermined time by the delay circuit 58 as shown by (d) in FIG. 6, is applied to the reset terminal of the flip-flop circuit 53.

In the circuit shown in FIG. 5, it is clear that the period during which the solenoid coil C.sub.1, as represented by (f) in FIG. 6 in the form of the current flowing through the switching transistor SQ.sub.1 during the conduction of the latter is energized partially overlap the period during which the solenoid coil C.sub.2, as represented by (h) in FIG. 6 in the form of the current flowing through the switching transistor SQ.sub.2 during the conduction of the latter is energized. This will now be described with particular reference to FIG. 6.

As is well known to those skilled in the art, the circuit unit composed of the photocell 55 and the capacitor 56 serves to determine the gradient of increase of the voltage to be fed to the comparison circuit 54. Specifically, the lower the resistance of the photocell 55 with a relatively high intensity of light received by such photocell 55, the greater the gradient of increase of the voltage to be applied to the comparison circuit 54. Therefore, if the gradient of increase of the voltage to be applied to the comparison circuit 54 is relatively great, the voltage fed from the circuit unit exceeds the reference voltage, applied to the comparison circuit 54 from the reference signal generator, in a relatively short period of time and, therefore, the solenoid coil C.sub.2 is energized earlier than in the case where the resistance of the photocell 55 is relatively high. This means that, before complete travel of the shutter members X and Y from the inoperative positions towards the operated positions, the magnetic attraction takes place between the south-polarized end of the solenoid coil C.sub.2 and the north pole of the magnet 37b which is then moving towards the left, as viewed from FIGS. 1 and 2, together with the shutter member Y, which magnetic attraction so induced serves to impart a braking force to the movement of the magnet 37a and, therefore, the shutter member Y. At this time, the openings 14 and 23 in the shutter members X and Y partially overlap with each other in communication with the exposure aperture A, the extent to which these openings 14 and 23 overlap with each other being determined by the time span between the time at which the solenoid coil C.sub.1 is energized and the time at which the solenoid coil C.sub.2 is energized.

Thereafter, upon de-energization of the solenoid coil C.sub.1 incident to termination of the output from the flip-flop circuit 53, which takes place the predetermined time delayed after energization of the solenoid coil C.sub.2, the shutter members X and Y are returned back towards their inoperative positions by the effect of the magnetic attraction developed between the south-polarized end of the solenoid coil C.sub.2 and the north pole of the magnet 37b.

On the contrary, where the resistance of the photocell 55 is relatively high with a relatively low intensity of light received by said photocell 55, the gradient of increase of the voltage to be applied to the comparison circuit 54 is so relatively small that a relatively long time is required for the voltage from the circuit unit to attain the reference voltage. Therefore, it will readily be seen that energization of the solenoid coil C.sub.2 subsequent to the energization of the solenoid coil C.sub.1 may take place after the shutter members X and Y have moved to their operated positions in which case the openings 14 and 23 may fully overlap with each other in communication with the exposure aperture A.

The waveform (i) shown in FIG. 6 illustrates the operation of the shutter mechanism in timed relation to the various waveforms of the electric signals appearing in the circuit of FIG. 5. In the waveform (i) of FIG. 6, the height of the peak from the base line represents the extent to which the openings 14 and 23 overlap with each other in communication with the exposure aperture A and, therefore, it will readily be seen that, if the voltage from the circuit unit attains the reference voltage in the comparison circuit 54 earlier than that shown by the waveform (c), the height of the peak from the base line is lower than that shown in the waveform (i). This means that the extent to which the openings 14 and 23 overlap with each other, that is, the opening of the shutter mechanism according to the present invention, is smaller than that represented by the waveform (i). It is, however, to be noted that the linear velocity of movement of the shutter members X and Y remains the same irrespective of the opening of the shutter mechanism. This equally applies to the shutter mechanism utilizing the drive circuit of FIG. 3.

Where the de-energization of the solenoid coil C.sub.1 is desired to be effectuated incident to the energization of the solenoid coil C.sub.2, the delay circuit 58 may be omitted and the comparison circuit 54 may be connected to the reset terminal of the flip-flop circuit 53.

While the circuit shown and described with reference to FIGS. 5 and 6 is so designed that the solenoid coils C.sub.1 and C.sub.2 are alternately energized to open and close the shutter mechanism, it is possible to utilize such a drive circuit that the solenoid coils C.sub.1 and C.sub.2 are simultaneously energized by a current flowing in one direction during opening of the shutter mechanism and by a current flowing in the opposite direction during closure of the shutter mechanism. This will now be described with particular reference to FIGS. 7 and 8. It is, however, to be noted that the drive circuit of FIG. 7 is a push-pull circuit based on the circuit of FIG. 5.

Referring now to FIGS. 7 and 8, the push-pull circuit comprises two similar circuit units which operate in an opposite relationship to each other; one circuit unit including first and second flip-flops FF.sub.1 and FF.sub.2 and a first delay circuit Td.sub.1, and, the other circuit unit including third and fourth flip-flops FF.sub.3 and FF.sub.4 and a second delay circuit Td.sub.2.

The first flip-flop FF.sub.1 has a set terminal so connected to the release switch 50' that, upon closure of the shutter release switch 50', that is, in response to depression of the shutter release button in the camera housing, the first flip-flop FF.sub.1 generates from its output terminal a trigger pulse of a duration determined by the output signal to be applied from the comparison circuit 54 to a reset terminal of said flip-flop FF.sub.1. The trigger pulse from the flip-flop FF.sub.1 is applied in part to a switching transistor T.sub.1 of NPN type and in part to a switching transistor T.sub.3 of NPN type, causing these transistors T.sub.1 and T.sub.3 to become conductive. Conduction of these transistors T.sub.1 and T.sub.3 results in energization of the solenoid coil C.sub.1 with the current from the D.C. power source E flowing through the transistor T.sub.1, then the coil C.sub.1 and finally the transistor T.sub.3.

Simultaneously therewith, since the second flip-flop FF.sub.2 also has a set terminal connected to the switch 50' and a reset terminal connected to the comparison circuit 54 through the first delay circuit Td.sub.1, the flip-flop FF.sub.2 also generates a trigger pulse which is in turn applied in part to a switching transistor T.sub.5 of NPN type and in part to a switching transistor T.sub.7 of NPN type, causing these transistors T.sub.5 and T.sub.7 to become conductive. Conduction of the transistors T.sub.5 and T.sub.7 result in energization of the solenoid coil C.sub.2 with the current from the power source E flowing through the transistor T.sub.5, then the solenoid coil C.sub.2 and finally the transistor T.sub.7. Upon energization of the solenoid coils C.sub.1 and C.sub.2 thus effected, so far as the magnets 36a, 36b, 37a and 37b are arranged in the manner as hereinbefore described and shown in FIGS. 1 and 2, the south and north poles are respectively developed at the opposed ends of the solenoid coil C.sub.1 remote from and adjacent the exposure aperture A and, similarly, the south and north poles are respectively developed at the opposed ends of the solenoid coil C.sub.2 remote from and adjacent the exposure aperture A. Therefore, by the effect of the magnetic attraction developed between the north pole of the magnet 36a and the end of the solenoid coil C.sub.1 remote from the aperture A which is then polarized the south and also by the effect of a magnetic attraction developed between the north pole of the magnet 37 a and the end of the solenoid coil C.sub.2 remote from the aperture A which is then polarized the south, the shutter members X and Y are moved from the inoperative positions towards the operated positions, respectively, in the opposed directions relative to each other. This is possible because of the particular positioning of the magnets 36a , 36b, 37a and 37b on the arms 11 and 21 relative to the associated solenoid coils C.sub.1 and C.sub.2, respectively, as hereinbefore described.

It is to be noted that because of the delay circuit Td.sub.1 inserted between the comparison circuit 54 and the reset terminal of the second flip-flop FF.sub.2, the duration of the trigger pulse emerging from the flip-flop FF.sub.2 is, as shown in FIG. 8, longer than that of the trigger pulse from the first flip-flop FF.sub.1, the difference T.sub.2 -T.sub.1 therebetween being substantially equal to the sum of the time required for the voltage charged on the capacitor 56 to attain the reference voltage in the comparison circuit 54 plus the delay time set in the delay circuit Td.sub.1.

On the other hand, the third flip-flop FF.sub.3 is, in response to the output signal applied from the comparison circuit 54 to a set terminal thereof, set to generate a trigger pulse simultaneously with the reset of the flip-flop FF.sub.1, that is, when the voltage charged on the capacitor 56 attains the reference voltage in the comparison circuit 54. The reset of the flip-flop FF.sub.1 results in de-energization of the solenoid coil C.sub.1 with the transistors T.sub.1 and T.sub.3 switched off on one hand and the trigger pulse from the flip-flop FF.sub.3 causes switching transistors T.sub.2 and T.sub.4 of NPN type to become conductive on the other hand. Upon conduction of the transistors T.sub.2 and T.sub.4, the solenoid coil C.sub.1 is again energized. However, the current from the power source E flows through the solenoid coil C.sub.1 in a direction opposite to the direction of flow therethrough of the same current during the conduction of the transistors T.sub.1 and T.sub.3 and prior to the conduction of the transistors T.sub. 2 and T.sub.4. Therefore, the polarities at the opposed ends of the solenoid coil C.sub.1 are reversed so that the shutter member X then being moved towards the operated position is forced to return back towards the inoperative position, the actual return movement of said shutter member X being taken place incident to reset of the flip-flop FF.sub.2 as will now be described. It is, however, to be noted that, prior to the actual return movement of the shutter member X together with the shutter member Y, the current from the power source E flows through the solenoid coils C.sub.1 and C.sub.2 in the opposite directions, respectively, and, therefore, the force of magnetic attraction or repulsion acting on the magnet 36a and 36b to move the shutter member X towards the operated position is substantially cancelled by the force of magnetic attraction or repulsion acting on the magnet 37a and 37b to move the shutter member Y towards the inoperative position. Accordingly, the continued movement of the shutter members X and Y towards the respective operated positions is substantially braked. This may take place either when the openings 13 and 24 partially overlap with each other or when they wholly overlap with each other, depending upon the resistance setting of the photocell 55 which varies in proportion to the amount of light reflected onto said photocell 55 from the object to be photographed.

The flip-flop FF.sub.2 is reset to bring the transistors T.sub.5 and T.sub.7 into a non-conductive state when the output signal from the comparison circuit 54 is, after having been delayed the predetermined time (t.sub.2 -t.sub.1) by the delay circuit Td.sub.1, applied to the reset terminal of said flip-flop FF.sub.2. The delayed output signal from the comparison circuit 54 through the delay circuit Td.sub.1 is also applied to a set terminal of the fourth flip-flop FF.sub.4 and, therefore, simultaneously with the switch-off of the transistors T.sub.5 and T.sub.7, the transistors T.sub.6 and T.sub.8 are brought into a conductive state. Consequently, the current flows through the solenoid coil C.sub.2 in a direction opposite to the direction thereof during the conduction of the transistors T.sub.5 and T.sub.7 and prior to the conduction of the transistors T.sub.6 and T.sub.8. Accordingly, the shutter members X and Y which have been braked as hereinbefore described are returned back towards the inoperative positions with the shutter mechanism closed.

The output signal from the comparison circuit 54 is also, after having been delayed by the delay circuit Td.sub.2, applied to the respective reset terminals of the flip-flops FF.sub.3 and FF.sub.4 to bring the circuit of FIG. 7 into the original, inoperative position in which both of the solenoid coils C.sub.1 and C.sub.2 are de-energized for the subsequent operation. However, the time during which the output signal from the comparison circuit 54 is delayed by the delay circuit Td.sub.2, that is, the difference (t.sub.3 -t.sub.1), is preferably so selected as to be equal to or slightly larger than the sum of the delay time, set in the delay circuit Td.sub.1 and the time required for any one of the shutter members X and Y to complete its movement between the inoperative position and the operated position.

According to such drive circuit as described hereinbefore in connection with FIGS. 7 and 8, the shutter members X and Y are moved into an operative position or into inoperative position, upon receipt of magnetic force simultaneously from the coils C.sub.1 and C.sub.2. Therefore, the shutter members X and Y are placed into their operated and inoperative positions in quick motion with high reliance.

It should be noted that the circuit shown in FIG. 7 can be further provided with a suitable resistor R1 between the emitter of the transistor T.sub.1 and the coil C.sub.1 and also a suitable resistor R2 between the emitter of the transistor T.sub.5 and the coil C.sub.2 for decreasing the current which excites the coils C.sub.1 and C.sub.2 for moving the shutter members X and Y towards the operated position, in comparison with the current which excites the coils C.sub.1 and C.sub.2 for moving the shutter members X and Y towards the inoperative position, whereby the shutter members X and Y can further be quickly returned back to their inoperative position in high speed as described before in connection with FIG. 3 or 5.

Although the present invention has fully been described with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. For example, although in the foregoing embodiments two solenoid coils C.sub.1 and C.sub.2 in cooperation with two permanent magnets for each solenoid coil have been described as employed, it is possible to employ only one permanent magnet in cooperation with each solenoid coil.

Moreover, although the present invention has been described as applied to the shutter mechanism generally known as a guillotine type, the concept of the present invention can equally be applicable to any other shutter mechanism of a type, for example, wherein the first and second shutter members are so supported as to pivot in the opposite directions.

Furthermore, depending upon the purpose for which the shutter mechanism embodying the concept of the present invention is utilized, the openings 14 and 23, which have been described as defined in the first and second shutter members X and Y, respectively, may not be always necessary. In this case, the exposure aperture A may be opened when the shutter plates 10 and 20 are brought into respective positions clear of the exposure aperture A and closed when the shutter plates 10 and 20 overlap with each other. The number of the shutter members may not be always limited to two such as described and shown, but one shutter member may constitute the shutter mechanism according to the present invention.

Where the shutter member includes the only shutter member adapted to selectively close and open the exposure aperture, only one solenoid coil suffices. In this case, the number of the permanent magnets carried by the shutter member may be either one or two.

Accordingly, such changes and modifications are to be understood as included within the true scope of the present invention unless they depart therefrom.