Abstract:
A method of controlling a plurality of shutter blades activated by a solenoid to move the plurality of shutter blades between an open position and a closed position includes reducing an electrical signal applied to the solenoid while the plurality of shutter blades is in transit between the open position and the closed position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/164,260, filed Nov. 16, 2005, now U.S. Pat. No. 7,513,702, the entire disclosure of which is expressly incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A “SEQUENCE LISTING” 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to shutter assemblies and more particularly to a photographic-type shutter that relies on electromagnetic forces to open and close and which is, in one embodiment, self-damping to reduce impact and rebound when the shutter is opened or closed. 
     2. Description of Related Art 
     Electrically operated lens shutters used in various types of photographic and laboratory equipment are well known in the art. Lens shutters especially adapted for high speed opening and closing can operate in fractions of a second. An open/close cycle can take place in 30-40 milliseconds or less and repeated cycles at frequencies of 30 cycles per second are common. 
     Lens shutters generally are of two types. In one type, a so-called “guillotine” shutter has one or two thin, metal blades or leaves arranged to cover a lens opening. Pivot connections allow each blade to swing between a closed position where the blades cover the lens opening and an open position where the blades are drawn aside from the lens opening. 
     In a second type of shutter a plurality of pivotally mounted blades, usually five, is arranged around the lens opening. Each blade is connected to a rotatable drive ring. In the operation of these shutters, the rotation of the drive ring in one direction causes the blades to swing in unison to an open position. Counter rotation of the ring swings the blades to a closed position over the lens opening after exposure. Generally a linear electric motor is used to activate the shutter. When activated, the linear motor pulls on a lever arm that rotates the drive ring to open the shutter. To close the shutter the motor is deactivated and a spring causes the counter rotation of the drive ring to close the shutter. As noted above, shutters of this sort can cycle open and close 30 times per second. 
     It is common in both types of shutters to provide a shock absorber or damper that absorbs the impact as the blades are pivoted between the open and closed positions. In this respect, reference is made to various U.S. Pat. Nos. 3,595,553; 3,664,251 and 6,652,165 the disclosures of which are incorporated herein by reference. As disclosed in these references, the shock absorber operates to stop the shutter blade very rapidly, yet softly and without damage. There also is little or no bounce as the shutter first is snapped open by the linear electric motor and then is snapped closed by the spring when the motor is deenergized. 
     In some applications, however, it is desirable to hold the shutter open for an extended period to prolong the exposure time. In these cases it has been the practice to keep the motor activated for the duration of the exposure in order to hold the shutter open against the bias of the spring urging the shutter to a closed opposition. 
     Maintaining power to the coil of a linear electric motor for an extended period has its drawbacks due mainly to the resulting generation of heat. If not dissipated, the heat could adversely affect the alignment of the optics, cause image distortion and shorten the life of the motor and other heat sensitive components of the shutter system. A fan, heat sink or heat dissipating fins that normally can solve a heat-generating problem are not appropriate in many applications. For example fans are of little use if the shutter is located in a vacuum environment. In military and space exploration applications weight may be an issue so the use of any additional component such as a heat sink or heat radiating fins is not appropriate. Reference is made to U.S. Ser. No. 11/099,744, as disclosing a shutter assembly that is bi-stable in that it allows the shutter to remain open or closed for long periods without generating excessive heat. 
     In some applications space also is a limitation. Space limitations particularly in the region of the shutter opening dictate the parameters of size and placement of apparatus for holding the shutter open. For example, components placed near the shutter opening must have a relatively low profile so as not to interfere with the cone angle of the light passing through the open shutter. Space limitations also complicate the substitution of one shutter assembly for another as in changing shutter size while maintaining the same base structure. 
     As noted above, most prior art shutter assemblies mechanically couple a linear electric motor to the shutter for opening and closing the lens opening. For proper operation, particularly at high speeds, the mechanical linkage must be precisely made and the movement of the linkage must be dampened. To applicant&#39;s knowledge elimination of a damper system entirely has not been attempted or if attempted, has not been commercially successful. 
     Accordingly, it is an object of the present invention to provide an operating system for a rotary shutter that eliminates the need for a mechanical linkage between an actuator and the shutter to open and close the shutter. 
     Another object of the present invention is to provide is to provide a rotary shutter having an electromagnetic operating system. 
     A further object of the present invention is to provide a method of operating a rotary shutter utilizing electromagnetic energy for opening and closing the shutter. 
     BRIEF SUMMARY OF THE INVENTION 
     In the present invention a shutter operating system is provided that depends on electromagnetic energy to operate shutter blades so that direct mechanical linkage between a drive motor and the shutter blades reduced or is eliminated entirely. In this respect the present invention utilizes a permanent magnet and solenoid system to operate the shutter blade wherein the movement of the magnet causes the shutter blade to move between an open and a closed position over a lens opening. In one embodiment of the invention a single permanent magnet is moved between a pair of spaced coils by selectively energizing first one coil then the other. The movement of the magnet results in the opening and closing of the shutter. In this respect the magnet may be attached directly to a shutter blade or in the case of a rotary shutter, the magnet is attached to a drive ring that in turn is mechanically coupled to the shutter blades. 
     In a preferred embodiment, there are two permanent magnets associated with the shutter blades and there are two fixed coils, one associated with each magnet. The space between the coils is slightly greater than the spacing between the magnets so that if one of the coils is aligned with its associated magnet, the other coil is slightly off set in an outboard direction from its associated magnet. With this arrangement energizing the aligned magnet acts to repel or push away its associated magnet towards the other coil. This moves the shutter blades for example to an open position and also moves the second magnet towards its associated coil. Proper directional movement is assisted by energizing the second solenoid to attract its associated permanent magnet. 
     As the second magnet approaches the second coil it is attracted to the core of the second coil. The movement of the second magnet then is arrested when its magnetic field captures the core of the second coil. This holds the position of the shutter even after power to both solenoids is cut off. 
     To swing the shutter blades in the opposite direction, the second coil is energized with a reversed polarity to repel or push away the second magnet. This moves the shutter blades in the opposite direction or towards a closed position and at the same time the first magnet is moved towards its associated coil. Proper directional movement is assisted by energizing the first coil with a reversed polarity so it acts to attract its associated permanent magnet. 
     As noted above, there is no physical connection between the fixed coils that actuate the shutter and the magnets that cause the shutter blades to move. Accordingly the actuator is mechanically isolated from the shutter blades if the permanent magnets are connected directly to the shutter blades. In cases where the magnets are attached to a drive ring, the number of critical mechanical linkage members is reduced. Also there is no mechanical impacting at the end of travel as the shutter blades open and close so the system is self-damping. Instead the magnetic field of each permanent magnet, as it captures the core of each coil, attenuates the motion of any rebound of the permanent magnet without mechanical damping as it fixes the position of the shutter blades. This does not preclude however the use of a mechanical damper in association with the magnetic damping. 
     Accordingly, the present invention may be characterized in one aspect thereof by a shutter having an isolated actuator comprising: 
     a) a shutter blade movable over a shutter opening to open and close a shutter opening; 
     b) a first control element mechanically connected to the shutter blade, the control element responsive to a magnetic field to move the shutter blade between a shutter open and a shutter closed position; and 
     c) a second control element mechanically isolated from the first control element selectively generating the magnetic field. 
     In its method aspect the present invention is a method for operating a shutter comprising: 
     a) operatively connecting a permanent magnet to a movable shutter blade movable between a shutter open and a shutter closed position; 
     b) mounting an electric coil at a fixed position relative to the permanent magnet mechanically isolated from the permanent magnet; and 
     c) selectively energizing the electric coil so the magnet is alternatively repelled and attracted thereby moving the shutter blade between the open and closed positions. 
     In an additional exemplary embodiment of the present disclosure, a method of controlling a plurality of shutter blades activated by a solenoid to move the plurality of shutter blades between an open position and a closed position includes reducing an electrical signal applied to the solenoid while the plurality of shutter blades is in transit between the open position and the closed position. 
     In still another exemplary embodiment of the present disclosure, a method of controlling a plurality of shutter blades includes moving a permanent magnet from a position adjacent to a first solenoid to a position adjacent to a second solenoid, moving the plurality of shutter blades between an open position and a closed position in response to movement of the permanent magnet, and applying an electrical signal to at least one of the first and second solenoids, while the plurality of shutter blades is in transit between the open and closed positions, to reduce a rate at which the permanent magnet moves. 
     In yet another exemplary embodiment of the present disclosure, a method of controlling a plurality of shutter blades includes selectively energizing at least one of a first solenoid and a second solenoid to magnetically decelerate the plurality of shutter blades while the plurality of shutter blades is in transit between an open position and a closed position. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         FIG. 1  is a plan view of the shutter showing a base plate with components supported by the base plate removed; 
         FIG. 2  is a view of a portion of  FIG. 1  on an enlarged scale with portions broken away; 
         FIG. 3  is a sectional view taken generally along lines  3 - 3  of  FIG. 1 ; 
         FIG. 4  is a sectional view similar to  FIG. 3  only showing the shutter in the open position; 
         FIG. 5  is a view similar to  FIG. 3  only showing another embodiment of the invention; and 
         FIG. 6  is a view similar to  FIG. 3  showing still another embodiment of the invention. 
         FIG. 7  is a sectional view similar to  FIG. 3  only showing another embodiment of the invention with the shutter in a closed position; 
         FIG. 8  is a sectional view similar to  FIG. 7  only showing the shutter of  FIG. 7  in the open position; 
         FIG. 9  is a plan view of still another embodiment of the invention showing the shutter in a closed position; 
         FIG. 10  is a view on a larger scale taken along lines  10 - 10  of  FIG. 9 ; 
         FIG. 11  is a plan view showing the shutter of  FIG. 9  in an open position; and 
         FIG. 12  is a view on a larger scale taken along lines  12 - 12  of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings,  FIG. 1  shows a shutter of the present invention generally indicated at  10 , employing the self-damping activation system. The shutter is a type that can be used in any photographic, scientific or calibration application that requires one or more cycles of opening and closing of a shutter opening by driving one or more shutter blade across the opening. In such systems it is common to provide a shock absorber or damper that absorbs the impact as the blades move, usually by pivoting, between the open and closed positions. In this respect, reference is made to various U.S. Patents including U.S. Pat. No. 3,595,553; No. 3,664,251 and No. 6,652,165 the disclosures of which are incorporated herein by reference. 
     The shutter includes a base plate  12  having a shutter opening  14 . The shutter opening is open and closed by moving a plurality of shutter blades  16  (usually five) in a pivoting action across the shutter opening. In prior art shutters the shutter blades are operated by a linear motor mounted to the base plate. The motor acts through a mechanical linkage to rotate a driver plate wherein the rotation of the driver plate in a to and fro motion acts to open and close the shutter blades. Also mounted to the base plate in the prior art is a damping system that acts as a shock absorber to stop the shutter blade very rapidly, yet softly and without damage. The damping system also produces little or no bounce as the shutter first is snapped open by the action of the linear electric motor and then is snapped closed by a spring mechanism. 
     The present invention also makes use of a conventional drive ring  18 , a portion of which is seen in  FIG. 1  through an elongated opening  20  in the base plate. Carried by the base plate are spaced solenoids  22 ,  24 . The solenoids are positioned over the elongated opening  20  for purposes set out hereinbelow. 
     As shown in  FIGS. 3 and 4 , the drive ring  18  has an opening  26  that aligns with the shutter opening  14 . Extending from the drive ring are pins  28 . These pins extend into a corresponding cam slot  30  formed in each of the shutter blades. With this arrangement, the rotation of the drive ring to and fro about an axis  33  that aligns with the axis of the lens opening will cause the shutter blades to pivot between open and closed positions. 
     Extending from the drive ring  18  and through the opening  26  in the base plate are a pair of posts  32 ,  34 . These posts together with other components described thus far are all formed of a non-magnetic material such as stainless steel. However, supported on each post  32 ,  34  is a permanent magnet  36 ,  38  respectively. The permanent magnets  36 ,  38  are each associated with one of the solenoids  22 ,  24  respectively. 
     As best seen in  FIG. 2 , the spacing between magnets  36 , 38  is slightly less than the spacing between their associated solenoids  22 ,  24 . Accordingly, when the permanent magnet  38  is in axial alignment with the core of its associated solenoid  24 , the permanent magnet  36  is inboard of its solenoid  22 . This difference in spacing is equal to the throw required to move the shutter blades between an open and a closed position. 
     In operation and with the shutter in the closed position as shown in  FIGS. 1 ,  2  and  3  with the solenoids not energized, the permanent magnet  38  is attracted to the core of the solenoid  24  by magnetic attraction and aligns with the axis of the solenoid core. The second magnet  36  is far enough away from its associated solenoid  22  that the attractive force between the two is not enough to overcome the attraction between the magnet  38  and the core of the solenoid  24 . Thus, even with no power applied to either coil, the shutter is stable and is locked in a closed position. 
     To open the shutter, a control  40  operates to energize both solenoids. Solenoid  24  is energized with a polarity that repels magnet  38  while the solenoid  22  is energized with a polarity that attracts its associated magnet  36 . The combination of the repelling action between the solenoid  24 /permanent magnet  38  and the attraction between the solenoid  22 /permanent magnet  36  propels the drive ring  28  in a shutter opening direction. When the magnet  36  comes into alignment with the core of its associated solenoid  22  the motion of the drive ring is arrested and stopped so as to lock the shutter blades in an open position as shown in  FIG. 4 . 
     Deenergizing both solenoids will allow the shutter blades to remain in an open position until the current applied to the solenoids is reversed to reverse the polarity of the solenoids. Accordingly, to close the shutter blades control  40  is operated to energized solenoid  22  with a polarity that repels magnet  36  while the solenoid  24  is energized with a polarity that attracts its associated magnet  38 . The combination of the repelling action between the solenoid  22 /permanent magnet  36  and the attraction between the solenoid  24 /permanent magnet  34  propels the drive ring  28  in the opposite and shutter closing direction. When the magnet  38  comes into alignment with the core of its associated solenoid  24  the motion of the drive ring is arrested and stopped so as to lock the shutter blades in an open position. 
     Delaying the reversal of the current will allow the shutter to remain in the open position for the time of the delay. Conversely, reversing the current soon after opening will cause the shutter to open and close quickly. 
     As noted above, the attraction between a magnet and the core of its associated solenoid arrests the motion of the drive ring and the magnets stops in axial alignment with the core of the solenoid due to magnetic attraction. For example, if on opening the inertia of the system carries the magnet  36  slightly beyond the core of its associated solenoid  22 , the magnetic attraction between the magnet  36  and the core of the solenoid  22  will pull the two back into alignment. In this fashion the motion of the drive ring is arrested and damped without a mechanical damper and the shutter is stable and locked in both the open and closed positions. 
     In the embodiment of  FIGS. 1-4  two permanent magnets and two solenoids are used and the control  40  acts to reverse the current applied to the solenoids to open and close the shutter. In this embodiment the shutter blades are stable in both the open and closed positions when the solenoids are not energized and there is no mechanical damper or stop, that is contacted during opening or closing to absorb the impact produced by the shutter blades on opening and closing. The embodiment of  FIG. 5  utilizes a single solenoid and a single permanent magnet. 
     In this respect  FIG. 5  shows a single magnet  50  carried by a post  52 , which in turn is connected to the drive ring  18 . A single solenoid  54  has its axis off set from the magnet  50 . When no current is applied to the solenoid by the control  40 , the natural magnetic attraction between the core of the solenoid  54  and the magnet  50  pulls the magnet toward the solenoid core. This holds the magnet and therefore the drive ring  18  at one end of its path of travel representing the shutter closed position. In the closed position shown, the end of the path of travel either can be defined by the engagement of the post  52  with one end of the opening  20  through the base plate  12  as shown, or by a mechanical damper (not shown). 
     To open the shutter, the controller  40  energizes the solenoid  54  to produce a polarity that is the same as that of the permanent magnet  50 . Accordingly the magnet  50  is repelled away from the solenoid  54 . Repelling the magnet causes the drive plate  18  to rotate to a shutter open position. When the controller  40  removes current from the solenoid the magnetic attraction between the magnet  50  and the core of the solenoid  54  returns the drive ring to the shutter closed position. 
     This embodiment is primarily useful in situations where the shutter is open only for a short period or where several rapid cycles are desired. This is because holding the shutter open requires either that the solenoid stay energized or a mechanical latching mechanism be employed. Also the timing of both applying a current to the solenoid and cutting off power may be such as to prevent the shutter blades from over opening or over closing so that no mechanical damper is required. For example, on opening, the power to the solenoid may be cut off prior to the shutter blades being at the full open position so as to allow the inertia of the blades to move them to the full open position and not beyond. Conversely, as the shutter is closing, the solenoid can be energized to repel the magnet prior to the time that the shutter blades reach the full closed position. 
     Still another embodiment is illustrated in  FIG. 6 . This embodiment utilizes two permanent magnets and two solenoids but eliminates the need to reverse the polarity of the solenoids as in the embodiment of  FIGS. 3 and 4 .  FIG. 6  also illustrates that the magnets  60 ,  62  can be disposed to either side of the centerline  63  of the shutter opening  14  instead of on the same side as shown in the previous embodiments. 
     In the  FIG. 6  embodiment one of the magnets indicated at  60  is slightly offset from the core of its associated solenoid  64  whereas the magnet  62  is separated from the core of its associated solenoid  66  by a greater distance. With the shutter blades  16  in a closed position the distance between magnet  62  and solenoid  66  is too great to overcome the attraction of the magnet  60  to the core of solenoid  64  so the shutter remains stable and in the closed position with no power supplied to either coil. 
     To open the shutter blades, current is applied only to solenoid  64  so as to produce a polarity in the solenoid that acts to repel the magnet. The desired direction of motion is induced by the offset so the magnet  60  moves to the position shown in dotted line. This rotates the drive plate to pivot the shutter blades to an open position. Once the magnet  60  is repelled away, it is too far from the core of its associated solenoid  64  to be pulled back by magnetic attraction when current to the solenoid  64  is shut off. 
     As the drive plate rotates, it carries the magnet  62  closer to its associated solenoid  66  until it reaches the dotted line position, which is the end of travel. In this position the magnet  62  is held to the core of its associated solenoid  66  by magnetic attraction and the shutter blades remain locked in the open position even when no power is applied to either solenoid. 
     To close the shutter and return the shutter blades to the  FIG. 6  position power is applied to solenoid  66  to produce a polarity that repels the magnet  62  so as to move it back to the solid line position. This also moves the magnet  60  back to its solid line position where it is held by magnetic attraction to the core of its associated solenoid  64 . 
     While the embodiment of  FIG. 6  uses an electromagnetic force to open and close a rotary shutter, it is not preferred as the system would require a mechanical damping system. 
     Still another embodiment is illustrated in  FIGS. 7 and 8 . This embodiment uses one permanent magnet  78  and two solenoids  82 ,  84  together with two mechanical dampers  74 ,  76  that engage the permanent magnet  78  at the open and closed ends of its range of travel. 
     In the  FIG. 7  embodiment, in which the shutter is shown closed, the magnet indicated at  78  is resting against the stop surface of a damper  76 . Associated solenoid  84  is offset from the rest position of the magnet  78  so that the magnetic field created by the solenoid  84  continues to attract the magnet  78  in its rest position. 
     An opposing damper  74  is disposed in a corresponding position relative to the position of the magnet  78  when the shutter is in the open position as shown in  FIG. 8 . In the open position, the magnet  78  rests against a stop surface of the damper  74  and the associated solenoid  82  is positioned so that when energized it continues to attract the magnet  78  causing it to come to a stop resting against the stop surface of the damper  74 . The second solenoid  82  is positioned so that the magnetic field created by the solenoid  82  continues to attract the magnet  78  causing it to move into a position resting against the stop surface of the damper  74 . 
     Referring again to  FIG. 7 , to open the shutter blades, current is applied to the solenoid  84  to create a field that repels the magnet  78  while substantially simultaneously, current is applied to the solenoid  82  to create a magnetic field that attracts the magnet  78 . It will be understood that while applying current to both solenoids  82 ,  84  substantially simultaneously provides an effective opening action, it isn&#39;t necessary that the currents be applied simultaneously. For example, current could be applied first to solenoid  84  to create a repelling magnetic field and then subsequently, as the magnet  78  moves towards the other damper  74 , current could then be applied to the solenoid  82  to create an attracting magnetic field. The current to solenoid  84  could either be maintained or cut off depending on the characteristics of the opening motion desired. Energizing both solenoids  82 ,  84  creates the largest force on the magnet  78  while sequentially energizing the solenoids or in the alternative energizing only one of the solenoids to either attract or repel the magnet  78 , provides less force to the drive ring  18 . In addition, the current to the solenoids  82 ,  84  can be modulated to control the movement of the magnet  78  between the shutter open and shutter-closed positions. For example, pulses of varying width could be applied to the two solenoids  82 ,  84 , the polarity of the current applied to the solenoids  82 ,  84  could be reversed at various points during the movement of the magnet  78  to either accelerate the magnet  78  or decelerate the magnet  78 , or the movement of the magnet  78  could be controlled so as to, for example, increase the size of the shutter opening  14  linearly over time or according to any other desired characteristic. 
     While the embodiment of the invention shown in  FIGS. 7 and 8  shows a single set of solenoids  82 ,  84  and a single magnet  78 , multiple magnets and multiple pairs of solenoids may be coupled to the drive ring  18  at various radial positions around the shutter opening. Using multiple sets of solenoids and magnets reduces the amount of current that must be applied to each solenoid to generate the same force on the drive ring  18 . 
     It will also be appreciated that while the embodiment shown in  FIGS. 7 and 8  shows a set of solenoids  82 ,  84  associated with a single magnet  78 , variations on this arrangement can also be employed. For example, multiple magnets can be provided at radially spaced positions around the shutter opening  14  and one solenoid  82  or  84  can be associated with each magnet  78 . In one example, solenoid  82  could be associated with the first magnet and solenoid  84  associated with the second magnet. Since the magnets are mechanically coupled by the drive plate, a multiplicity of arrangements can be contemplated. 
     Similarly, it is not necessary that the dampers be physically associated with the magnet or with the magnet that is driven. Any of the dampers known to those skilled in the art could be coupled to the drive ring at a location remote from the magnet and solenoids and still provide effective damping action. 
     Another embodiment of the invention is shown in  FIGS. 9 ,  10 ,  11 , and  12 . Referring first to  FIG. 9 , a shutter in accordance with this invention is illustrated in a top plan view. Shutter  10  includes a base plate  12 , a shutter opening  14  and a plurality of shutter blades  16 . A pair of solenoids  22  and  24  are arranged on the base plate in radially spaced apart locations on opposite sides of the shutter opening  14 . As may be more clearly seen in  FIG. 10  which is a section taken a long line  10 - 10  of  FIG. 9 , first and second magnets  60  and  62  are coupled to a drive ring  18  which is in turn coupled to the shutter blades  16 . Magnets  60  and  62  are mounted on the drive ring in oppositely pulled configurations, that is to say, the north pole of magnets  60  is on top while the north pole of magnets  62  is on the bottom, or vice versa. 
     Solenoid  24  includes a core  25  of magnetic material such as a ferrous material surrounded by a coil  27  wound on a bobbin  29 . Preferably, in this and the other embodiments, core  25  is made from a material with a low coercive force such as M6 grain oriented 3.3% silicon steel, manufactured by Magnetic Metals of Camden N.J. under the trademark Microsil, to allow the coil  27  to quickly revert to an unmagnetized state when the coil is deenergized and to allow the coil to switch polarity relatively rapidly from one magnetic orientation to the other while retaining only minimal residual magnetism. By applying a signal of appropriate polarity to coil  27 , core  25  can be temporarily forced to assume a magnetic state in which the North Pole is either on the top or on the bottom depending on the polarity of the signal. For example, if magnet  60  is arranged with its north pole up, and solenoid  24  is energized so that its north pole is on the bottom, core  25  will repel magnets  60  and attract magnet  62 . This is the configuration shown in  FIG. 10 . This arrangement causes the magnets  60  and  62  to drive the drive ring from the position shown in  FIG. 10  to the position shown in  FIG. 12 . This arrangement uses both the attractive and repulsive forces existing between solenoid  24  and magnets  60  and  62  to move the drive ring and to move the shutter from the closed position shown in  FIG. 9  to the open position shown in  FIG. 11 . Once the shutter reaches the configuration shown in  FIG. 12 , power is removed from solenoid  24 . Because core  25  is made from magnetic material, magnet  62  is attracted to core  24  even when the core is not energized and this maintains the shutter in the open position. 
     To move the shutter from the open position shown in  FIGS. 11 and 12  to the closed position shown in  FIGS. 9 and 10 , the solenoid is energized so that its south pole is on the bottom. This repells magnet  62  and simultaneously attracts magnet  60  thereby rotating the base plate to the position shown in  FIG. 10  and closing the shutter. When the magnet sizing signal is removed from coil  27 , magnet  60  continues to be attracted to core  25  and this holds the shutter in the closed position. 
     To move from the open position shown in  FIG. 12  to the closed position shown in  FIG. 10 , a signal is applied to solenoid  24  that is opposite in polarity from the signal just discussed. This causes core  25  to be temporarily magnetized 
     Optionally, a second solenoid  22  and a second pair of magnets can be provided for increasing the force on the base plate and thereby increasing the speed at which the shutter opens and closes, or decreasing the power that must be applied to the coil to produce the same opening/closing speed as can be produced by a single coil. 
     Preferably, the shutter  10  is provided with a damper  70 . The damper  70  includes a slot  72  formed in the base plate  12  through which a pin  73  a projects upwardly. The slot is preferably provided with damping material such as a ring  75  surrounding the slot, or blocks of energy absorbing plastic or similar material at the ends of the slot. Examples of suitable damping material are described in U.S. Pat. No. 6,652,165. The damper increases the life cycle of the shutter by softening the shock that would otherwise occur as a solenoid moves to shutter from the fully open to the fully closed position. In addition, the damper quiets the shutter which may be important in certain applications. 
     The damper may be arranged in a variety of ways. While it is possible for the shutter blades themselves to be directly coupled to the damping system if the shutter blades are relatively sturdy, this is presently not preferred if the shutter blades are very thin and susceptible to damage on impact. Preferably, the damper is separate from the solenoid actuator and from the magnets as shown in  FIGS. 9 through 12 . 
     Alternatively, the damper may be arranged to directly engage the magnets. The configuration of the damper would be substantially the same as the configuration shown in  FIGS. 9 and 11  but the damper  75  would be arranged with respect to one or both of the magnets  60  and  62 , to provide the same sort of damping action provided with respect to pin  73  in  FIGS. 9 and 11 . 
     As another alternative, the damper may be arranged to dampen motion between the base plate and the drive ring. 
     Preferably, in all arrangements of the damper, the damper material is arranged to engage the magnet or pin at a position at least slightly before the position that the magnet or pin would reach if the damper were not present. This ensures that the damper controls the end position rather than the combination of the magnet and solenoid controlling the end position. It also ensures that when the magnet is retained in his position by virtue of the magnetic force between the magnet and the solenoid core, that position is fixed by the damper and known in advance. 
     Accordingly, it should be appreciated that the present invention accomplishes its intended objects in that it provides an operating system for a shutter that eliminates the need for a mechanical linkage to open and close the shutter. It also provides a shutter that is opened and closed by an electromagnetically driven operating system and which, in at least one embodiment eliminates the need for mechanical damping. 
     Having described the invention in detail, what is claimed as new is: