Abstract:
A camera capable of detecting an abnormality has photographing operation programs, an abnormality detection program, and a checking operation program installed therein. The photographing operation programs cause a plurality of mechanisms included in the camera to act sequentially. The abnormality detection program detects an abnormality in an action of a predetermined one of the plurality of mechanisms. Responsive to detection of the abnormality in the action of the predetermined mechanism, as detected by the abnormality detection program, the checking operation program causes the predetermined mechanism alone to act again for checking of the predetermined mechanism under conditions different from those under which the predetermined mechanism has acted to have the abnormality detected by the abnormality detection program.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a camera, and more particularly, to a sequence of controlling a predetermined action of a camera, which sequence has been executed for performing photography and in which an abnormality has occurred. 
     2. Description of the Related Art 
     Cameras for performing photography generally use system described below to judge whether a shutter unit acts normally during photography. 
     Namely, sectors constituting part of the shutter unit have a slit formed at a predetermined position thereof. A photo-interrupter for detecting the slit is included. When a detection signal is output from the photo-interrupter, it is judged that the shutter unit acts normally. 
     When an output from the photo-interrupter is not detected, it is judged that the shutter unit has an abnormality. If an abnormality is thus detected, control is given so that a camera will be disabled from operating for fear the same event may be repeated, and thus placed in a non-operable state. 
     In a camera disclosed in Japanese Patent Publication No. 2669850, as long as an abnormality in an action is detected once, the camera is not placed in the non-operable state. After an abnormality in a predetermined action is detected a plurality of times, the camera is disabled from operating. As long as an abnormal action is detected only once, the camera remains usable thereafter. This helps a user to become conscious of the abnormal action of the camera thereafter and contributes to improvement in the user&#39;s maneuverability. 
     However, the means disclosed in the Japanese Patent Publication No. 2669850 does not disable the camera from operating as long as an abnormality in the action of the shutter unit is detected only once. Even if the camera malfunctions, the same sequence is executed again. The camera would operate as if it were normal until the abnormality is detected a plurality of times. Other different defects may occur until the camera is placed in the non-operable state because the abnormality in the action has been detected a plurality of times. 
     The above will be described by considering a practical example. That is to say, assume that when a shutter unit fails, an abnormality is detected for the first time. At this time, the camera can still execute operations for the next photography. 
     Normally, prior to photography, a user often actuates a release without loading a predetermined film cartridge (not shown) in a camera body to thus carry out so-called test imaging (blind exposure). 
     If the camera is of a type in which even when an abnormality is detected once, the camera is not disabled from operating immediately, the user will not become aware of the fact that the camera malfunctions and therefore operates abnormally. The user may therefore load a film cartridge in preparations for actual photography. 
     In this case, since the camera is actually abnormal (malfunctions), an abnormality is detected for the second time during photography of the first frame. The camera is then placed in the non-operable state for the first time. 
     According to the system disclosed in the Japanese Patent Publication No. 2669850, discovery of an abnormality in an action of a camera is likely to be delayed. This poses a problem. 
     If this kind of event occurs, the user not only wastes film, but also loses a chance of exposure. Besides, the user who thought that the camera acted normally at the time of test imaging (blind exposure) will be disappointed because the camera has malfunctioned in reality. The user will distrust the camera from that time. This will affect the user&#39;s photographic activity using the camera. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a camera in which when an abnormality is detected in a photographing operation, an appropriate checking operation is executed automatically. It is then judged whether the detected abnormality in the operation is attributable to the malfunction of the camera. A user can therefore accurately recognize the state of the camera. 
     Briefly, according to the first aspect of the present invention, a camera capable of detecting an abnormality has photographing operation section, an abnormality detecting section, and a checking operation section. The photographing operation section causes a plurality of mechanisms included in the camera to act sequentially. The abnormality detecting section detects an abnormality in an action of a certain one of the plurality of mechanisms. Responsive to detection of an abnormality in the action of the certain mechanism achieved by the abnormality detecting section, the checking operation section causes the certain mechanism alone to act again for checking under conditions different from those under which the certain mechanism has acted to have the abnormality detected by the abnormality detecting section. 
     According to the second aspect of the present invention, a camera capable of detecting an abnormality has a photographing section, an abnormality detecting means, a checking operation section, an abnormality judging section, and a photography disabling section. The photographing section executes a series of photographing operations (a photographing sequence). The abnormality detecting section detects an abnormal member during the photographing sequence. Responsive to detection of an abnormal action of said abnormal member, which is involved in any operation belonging to the photographing sequence, achieved by the abnormality detecting section, the checking operation section executes a checking operation for the abnormal member under conditions different from those under which the operation belonging to the photographic sequence is executed. The abnormality judging section judges from the results of the checking operation executed by the checking operation section whether the abnormal member detected by the abnormality detecting section is still abnormal. When the abnormality judging section judges from the results of the judgment made by the abnormality judging section that the abnormal member is still abnormal, the photography disabling section disables the photographic operations of the camera. 
     According to the third aspect of the present invention, a camera capable of detecting an abnormality in an action involved in a photographing operation has an abnormality detecting section, a checking operation section, and an abnormality persistence judging section. The abnormality detecting section detects an abnormality in at least one of a plurality of actions involved in a series of photographing operations (a photographing sequence) initiated with a manipulation performed for initiating the photographing operations. Responsive to detection of an abnormality in the certain action achieved by the abnormality detecting section, the checking operation section forcibly executes a photographing operation involving the action, in which an abnormality is detected, according to predetermined contents immediately after the detection of the abnormality. The abnormality persistence judging section judges from the results of the operation executed by the checking operation section according to the predetermined contents whether the abnormality in the action persists. 
     These and other objects of the present invention and the advantages thereof will be apparent from the description below. 
     According to the present invention, there is provided a camera in which if an abnormality is detected in a photographic operation, an appropriate checking operation is executed automatically. It is reliably judged whether the detected abnormality in the operation is attributed to the malfunction of the camera. A user can therefore accurately recognize the state of the camera. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing a major portion of the electrical internal configuration of a camera in accordance with an embodiment of the present invention; 
     FIG. 2 shows the structure of a shutter unit included in the camera shown in FIG. 1, wherein the shutter unit is closed; 
     FIG. 3 shows the structure of the shutter unit included in the camera shown in FIG. 1, wherein the shutter unit is open; 
     FIG. 4 is a timing chart indicating the relationship between the state of a shutter aperture and an output signal of a photo-interrupter to be attained when a solenoid is powered in order to drive the shutter unit included in the camera shown in FIG. 1; 
     FIG. 5 is a flowchart describing basic operations to be executed when the camera shown in FIG. 1 performs photography; 
     FIG. 6 is a flowchart describing an exposure sequence to be executed in the camera shown in FIG. 1; 
     FIG. 7 is a flowchart describing a checking sequence to be executed when an abnormality is detected in an exposure operation of the camera shown in FIG. 1; 
     FIG. 8 is a flowchart describing a variant of the checking operation to be executed when an abnormality is detected in the exposure operation of the camera in accordance with an embodiment of the present invention; and 
     FIG. 9 is a flowchart describing another variant of the checking operation to be executed when an abnormality is detected in the exposure operation of the camera in accordance with an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A camera in accordance with the present invention has all the components thereof controlled by a control circuit  11  serving as a control means and having a microprocessor. The control circuit  11  controls various operations according to programs stored in advance in a memory such as a ROM. The operations include an exposure operation, film feed operations, a clutch switching operation, a pop-up strobe unit thrust/plunge operation, and a photographic lens drive operation or an automatic open/close type lens barrier open/close operation. The exposure operation involves, for example, the actions of a shutter unit and the actions of aperture blades. The clutch switching operation switches directions of film feed. The photographic lens drive operation involves the power varying action of a zoom lens and the focusing action of a focusing lens. The control circuit  11  also controls input signals originating from various switches. 
     Electrically connected to the control circuit  11  are, as shown in FIG. 1, various kinds of electric circuits, for example, a shutter drive circuit  14 , a shutter detection circuit  13 , a motor drive circuit  16 , and a film detection circuit  15  as well as various kinds of switches, for example, a release switch  31 . The shutter drive circuit  14  drives a plunger or the like included in a shutter unit  17  (to be detailed later). The shutter detection circuit  13  includes a photo-interrupter (PI) for detecting the state of sectors included in the shutter unit  17 . The motor drive circuit  16  drives a film feed motor or the like included in a film feed unit  18  that acts in a predetermined manner to feed a film. The film detection circuit  15  includes a photo-reflector (PR) or the like for detecting the state of the film feed unit  18  or the position of a film. The release switch  31  generates an instruction signal for instructing start of an exposure operation. 
     The film feed unit  18  is a mechanism for feeding a film from a film cartridge loaded at a predetermined position inside the camera. The film feed unit  18  comprises various members including a drive motor, and executes predetermined film feed operations including a film wind operation and a film rewind operation. 
     The shutter unit  17  is a mechanism for adjusting an amount of light to which a picture screen of a film is exposed, and comprises various members including the shutter detection circuit  13 . The various members also include sectors, a solenoid, a plunger, and a photo-interrupter. The shutter unit  17  executes a predetermined exposure operation. 
     Now, the configuration of the shutter unit  17  included in the camera will be described below with reference to FIG.  2 . 
     The shutter unit  17  in the camera comprises various members including a solenoid  27 , a plunger  27   a,  sectors  21  and  22 , a sector lever  25 , part of the shutter detection circuit  13 , and a photo-interrupter  29  serving as an abnormality detector. These various members are located at predetermined positions on a shutter base plate (not shown) fixed to a camera body inside the camera. The shutter base plate has an aperture  20  for exposure. The center of the aperture  20  is aligned with the optical axes of photographic lenses (not shown). 
     Sector pins  23  and  24  are implanted in the shutter base plate near the aperture  20  of the shutter base plate. The sector pins  23  and  24  are fitted into holes bored in the proximal parts of the sectors  21  and  22  formed with two thin plate members shaped substantially like a half moon. The sectors  21  and  22  are thus supported so that they can freely pivot relative to the shutter base plate between closed positions and open positions. At the closed positions, the sectors close the aperture  20 . At the open positions, the sectors open the aperture  20 . 
     Moreover, a sector lever  25  shaped substantially like the letter L is journaled in the shutter base plate near the sectors  21  and  22  so that it can pivot freely. A pin  25   b  is implanted in the tip of one arm of the sector lever  25 . The pin  25   b  is fitted in cam grooves bored in the proximal parts of the sectors  21  and  22 . 
     A pin  25   a  is implanted in the tip of the other arm of the sector lever  25 . The pin  25   a  is located to abut on the distal surface of the plunger  27   a  of the solenoid  27 . 
     An aperture spring  26  is connected between the other arm of the sector lever  25  and a fixed portion of the shutter base plate (not shown). A constraining force exerted by the aperture spring  26  works in a direction of arrow X 1  in FIG. 2 or FIG.  3  and constrains the sector lever  25  to rotate counterclockwise in FIG. 2 or FIG.  3 . The sectors  21  and  22  are constrained to move in directions permitting the aperture  20  to open. 
     A repulsion spring  28  is connected between the plunger  27   a  and a fixed portion of the shutter base plate (not shown). The repulsion spring  28  constrains the plunger  27   a  to move in a direction of repulsion, that is, a direction of arrow X 2  in FIG. 2 or FIG.  3 . The pin  25   a  implanted in the other arm of the sector lever  25  abuts on the distal surface of the plunger  27   a.  The counterclockwise rotation of the sector lever  25  caused by the constraining force of the aperture spring  26  is therefore restricted by the plunger  27   a  constrained to move in the direction of arrow X 2  due to the constraining force of the repulsion spring  28 . 
     When driven by the shutter drive circuit  14  under the control of the control circuit  11 , the plunger  27   a  makes a sucking action or freeing action. This causes the sector lever  25  to rotate in the predetermined direction. The sectors  21  and  22  turn in the predetermined directions accordingly. The aperture  20  is thus opened or closed. 
     The photo-interrupter  29  is secured as an integral part of the shutter base plate at a predetermined position on the shutter base plate at which the photo-interrupter  29  can sense a turn made by the sectors  21  and  22  as shown in FIG. 2 or FIG.  3 . Since the photo-interrupter  29  in the camera of the present embodiment is located at the predetermined position, when the aperture  20  is closed by the sectors  21  and  22  (state shown in FIG.  2 ), detection light is intercepted from the photo-interrupter  29  due to the distal part of one of the sectors  21  and  22 , that is, the sector  21 . Moreover, immediately before the aperture  20  starts being opened by the sectors  21  and  22 , the photo-interrupter  29  is released from a light-intercepted state in which the detection light is intercepted from the photo-interrupter  29 . 
     When the photo-interrupter  29  is released from the light-intercepted state in which the detection light is intercepted from the photo-interrupter  29 , the detection light is transmitted by the photo-interrupter  29 . Now, the photo-interrupter  29  generates an on-state signal. In the camera of the present embodiment, the on-state signal is therefore generated immediately before the aperture  20  starts being opened. The on-state signal is transmitted to the control circuit  11 . The control circuit  11  receives the on-state signal as a triggering signal indicating that an exposure operation should be started. The control circuit then outputs various instructions instructing execution of predetermined processing involved in the exposure operation. 
     Referring to FIG. 2, FIG. 3, and FIG. 4, the relationship among an operation exerted by the shutter unit  17 , the state of the shutter aperture  20 , and an output signal of the photo-interrupter  29  will be described below. 
     To begin with, powering the solenoid  27  included in the shutter unit  17  is started (the solenoid is turned on) (see E in FIG.  4 ). This causes the plunger  27   a  to move in the direction of suction (direction of arrow X 1  in FIG. 2) against the constraining force of the repulsion spring  28 . The sector lever  25  is then rotated counterclockwise in FIG. 2 due to the constraining force of the aperture spring  26 . Accordingly, the pin  25   b  implanted in one arm of the sector lever  25  moves and the sectors  21  and  22  turn in the predetermined directions. The aperture  20  closed by the sectors  21  and  22  to bring the photo-interrupter to the light-intercepted state shifts to an open state. 
     In this case, immediately before the aperture  20  starts being opened, the distal part of the sector  21  withdraws to release the photo-interrupter  29  from the light-intercepted state. The detection light is transmitted by the photo-interrupter  29 . Accordingly, an output signal of the photo-interrupter  29  makes a high-to-low transition (F in FIG.  4 ). The high-level output signal indicates light interception, while the low-level output signal indicates light transmission. The closed state of the aperture  20  attained by the sectors  21  and  22  and associated with the light-intercepted state of the photo-interrupter starts being released at a time instant G (open) in FIG.  4 . The aperture  20  is fully opened at a time instant H (disengaged). The state attained this time is shown in FIG.  3 . 
     Thereafter, powering the solenoid  27  is stopped (the solenoid  27  is turned off) (see J in FIG.  4 ). The plunger  27   a  is then moved in the direction of arrow X 2  in FIG. 3 due to the constraining force of the repulsion spring  28 . This causes the sector lever  25  to rotate clockwise in FIG.  3 . Consequently, the sectors  21  and  22  gradually shift to close the aperture (see K in FIG.  4 ). 
     When the distal part of the sector  21  advances as shown in FIG. 2 to intercept light from the photo-interrupter  29 , the output signal of the photo-interrupter  29  makes a low-to-high transition (L in FIG.  4 ). With the output signal, it is detected that the aperture  20  is fully closed by the sectors  21  and  22 . An operation to be exerted by the normally operating shutter unit  17  has been described so far. 
     The shutter unit  17  acts as mentioned above. If the shutter unit  17  acts abnormally for some reason, an abnormality presumably occurs in the output signal of the photo-interrupter  29 . It is therefore possible to sense an abnormal action of the shutter unit  17  by monitoring the signal output from the photo-interrupter  29  while the shutter unit  17  is in operation. 
     Assume that the shutter unit  17  becomes abnormal for some reason and the sectors  21  and  22  act abnormally. In this case, an abnormality occurs in the output signal of the photo-interrupter  29 . The abnormality in the output signal is thought to manifest itself in three forms described below. 
     In the first form, the output signal of the photo-interrupter  29  is driven low before the solenoid  27  is powered. 
     In the second form, the output signal of the photo-interrupter  29  does not make a high-to-low transition within a predetermined time (S 1  in FIG. 4) after the solenoid  27  is powered. 
     In the third form, the output signal of the photo-interrupter  29  does not go back to high within the predetermined time (see S 2  in FIG. 4) after powering the solenoid  27  is stopped. 
     In the first form, presumably, the sectors  21  and  22  of the shutter unit  17  have failed while being left open. An exposed screen of a film opposed to the aperture  20  is presumably exposed. 
     In the second form, the abnormality is presumably caused by the opening actions of the sectors  21  and  22 , which are included in the shutter unit  17 . An exposure operation may therefore not be executed normally. 
     In the third form, the closing action of the shutter unit is presumably abnormal. Exposure may not be carried out properly. Besides, the shutter unit may be left open and object light may be kept irradiated to an exposed screen of a film. 
     As mentioned above, the control circuit  11  fills the role of a detector for detecting an abnormality in a predetermined action of a camera according to the output signal of the photo-interrupter  29 . 
     Next, a description will be made of a section for judging whether the shutter unit  17  is abnormal. Basic operations involved in photography to be performed by the camera of the present embodiment will be described in conjunction with the flowchart of FIG.  5 . 
     When a barrier member covering the face of the camera is opened, a main power switch interlocked with the barrier member is turned on. Consequently, the camera becomes ready to photograph. 
     Assume that a user of the camera presses a release button (not shown) that is a manipulation member interlocked with a release (REL) switch  31 . An instruction signal (release signal) instructing start of an exposure operation is then generated by the release switch  31 , and then transmitted to the control circuit  11 . The control circuit  11  in turn starts running predetermined photographing operation programs. 
     At step S 1 , photometry is executed. During the photometry, a photometry circuit (not shown) located at a predetermined position inside the camera measures the luminance of an object according to received object light. Based on the luminance of the object, a shutter drive time required for achieving exposure properly is calculated and whether flashlight is needed is determined. When flashlight is needed, a flashing time is calculated. 
     At step S 2 , an automatic focusing section included in the camera (not shown) is used to measure a distance of the camera from a desired object and calculate distances by which photographic lenses should be thrust and thus focused on the object. 
     At step S 3 , the photographic lenses are moved (thrust) to their predetermined positions according to the results of automatic focusing carried out at step S 2 . 
     At step S 4 , an exposure operation or sequence (to be detailed later) (see FIG. 6) is executed. Control is then passed to step S 5 . At step S 5 , the control circuit  11  judges from the output signal of the photo-interrupter  29  whether the exposure operation of step S 4  has terminated normally (see FIG.  6 ). In other words, the control circuit  11  also fills the role of a judging means for judging whether the exposure operation (a photographing operation) has terminated abnormally. 
     If it is judged that the exposure operation has terminated abnormally, control is passed to a non-operable processing sequence of step S 10 . In other words, if the control circuit  11  judges that the exposure (photographing) operation has terminated abnormally, the control circuit  11  operates as an operation disabling means for disabling a predetermined operation of the camera. 
     If it is judged that the exposure operation has terminated normally, control is passed to the next step S 6 . 
     At step S 6 , a lens plunge operation for moving the photographic lenses thrust at step S 3  to predetermined positions is executed. Control is then passed to the next step S 7 . At step S 7 , the control circuit  11  drives the film feed unit  18  using the motor drive circuit  16 . The control circuit  11  then executes a film feed operation for feeding a film by one frame so that a frame to be exposed next will be located at a predetermined position (a film wind operation). 
     At step S 8 , the control circuit  11  judges from an output of the film detection circuit  15  whether the film has come to an end, or in other words, whether the exposure operation executed at step S 4  has been performed on the last frame of the film. If the film has come to an end, control is passed to the next step S 9 . At step S 9 , the control circuit  11  drives the film feed unit  18  using the motor drive circuit  16 . The control circuit  11  then executes the film feed (film rewind) operation for rewinding the exposed film into the film cartridge. Thereafter, the series of operations is terminated (end). 
     In contrast, if it is judged at step S 8  that the film has not come to an end, step S 9  is not executed but the series of operations is terminated. The camera then stands by for the next photography. 
     Next, the exposure sequence to be carried out in the camera will be detailed in conjunction with the flowchart of FIG.  6 . The exposure sequence is a subroutine carried out as step S 4  in FIG.  5 . 
     At step S 71 , the control circuit  11  checks an output signal of the photo-interrupter  29  using the shutter detection circuit  13 . At this time, the shutter unit  17  has not been driven. If operations had been carried out normally, the output signal of the photo-interrupter  29  must be high. 
     If it is confirmed that the output signal of the photo-interrupter  29  is high, control is passed to step S 73 . If it is confirmed that the output signal of the photo-interrupter  29  is low, it means that the shutter unit  17  (sectors  21  and  22 ) is opened at any step before the shutter unit  17  is driven for this exposure operation. It is judged that an abnormality has already occurred in the shutter unit  17 . The exposure operation is then disabled, and control is passed to step S 72 . At step S 72 , history information indicating that an abnormality has occurred in an action of the shutter unit is stored in the predetermined memory (not shown). Control is then passed to a check operation or sequence (to be detailed later) (see FIG. 7) of step S 90 . 
     When control is passed to step S 73  according to the judgment made at step S 71 , the control circuit  11  starts powering the solenoid  27  using the shutter drive circuit  14  at step S 73 . This causes the plunger  27   a  to start suction. Thus, driving for disengaging the sectors  21  and  22  from each other is started. 
     Concurrently with the step S 73 , that is, the start of powering the solenoid  27 , the control circuit  11  causes its own abnormality judgment timer (not shown) to start measuring a time at step S 74 . 
     At step S 75 , the control circuit  11  monitors the state of the output signal of the photo-interrupter  29 . If the output signal of the photo-interrupter  29  is low, that is, if it is sensed that the output signal has made a high-to-low transition, control is passed to the next step S 79 . If it is sensed that the output signal of the photo-interrupter  29  remains high, control is passed to step S 76 . 
     At step S 76 , the state of the abnormality judgment timer started up at step S 74  is checked. The processing of steps S 75  and S 76  is repeated until a predetermined time has elapsed. 
     At step S 76 , if it is confirmed that the predetermined time has elapsed, it is judged that the sectors  21  and  22  are not in action. Control is then passed to the next step S 77 . 
     At step S 77 , execution of subsequent exposure-related actions is disabled, and history information indicating that an abnormality has occurred in an action of the shutter unit is stored in the predetermined memory (not shown). Control is then passed to the next step S 78 . At step S 78 , powering the solenoid  27  is stopped, and then control is passed to the check sequence (see FIG. 7) of step S 90 . 
     Assume that it is sensed at step S 75  that the output signal of the photo-interrupter  29  is driven low and that the sector  21  starts acting normally. In this case, control is passed to step S 79 . At step S 79 , the control circuit  11  allows its own exposure time-in-unit of sec reproduction time (not shown) to start measuring a time. 
     At step S 80 , the control circuit  11  judges from the results of the photometry (step S 1  in FIG. 5) whether flashing is needed. If it is judged that flashlight is needed, control is passed to step S 81 . If it is judged that flashlight is not needed, control is passed to step S 82 . 
     At step S 81 , the control circuit  11  allows a timer for indicating the timing of flashing to start measuring a time, and then passes control to step S 82 . 
     At step S 82 , it is checked if the timer started up at step S 81  has completed measuring a time. If it is confirmed that the timer has completed measuring a time, control is passed to step S 83 . If the timer has not completed measuring a time, control is passed to step S 84 . 
     At step S 83 , the control circuit  11  drives a flashing unit (not shown) using a flashing circuit (not shown) and executes a predetermined flashing action. 
     At step S 84 , it is checked if the shutter timer (exposure time-in-unit of sec reproduction timer) that has started measuring a time at step S 79  has completed measuring the time. If the timer has not completed measuring the time, control is returned to step S 82 . The subsequent processing is then repeated until the timer completes measuring the time. If it is confirmed that the timer has completed measuring the time, control is passed to step S 85 . 
     At step S 85 , the control circuit  11  stops powering the solenoid  27 . This causes the sectors  21  and  22  to start a closing action for closing the aperture  20 . 
     Concurrently, at step S 86 , the control circuit  11  allows its own abnormality judgment timer (not shown) to start measuring a time, and passes control to the next step S 87 . 
     At step S 87 , the control circuit  11  monitors the state of the output signal output from the photo-interrupter  29 . If it is sensed that the output signal of the photo-interrupter  29  is driven high, control is passed to the next step S 91 . If it is sensed that the output signal of the photo-interrupter  29  remains low, control is passed to step S 88 . 
     At step S 88 , it is checked if the abnormality judgment timer that has been started to measure a time at step S 86  has completed measuring the time, that is, if the predetermined time has elapsed. The processing of steps S 87  and S 88  is repeated until the predetermined time has elapsed. 
     If it is confirmed at step S 88  that the predetermined time has elapsed, it is judged that the sectors  21  and  22  have not shifted to close the aperture. Control is then passed to the next step S 89 . At step S 89 , history information indicating that an abnormality has occurred in the closing action of the shutter unit is stored in the predetermined memory (not shown). Control is then passed to the checking sequence (see FIG. 7) of step S 90 . 
     At step S 90 , the control circuit  11  executes the checking sequence for checking an action again. The checking sequence of step S 90  is executed only when any abnormality is identified during the exposure operation. The control circuit  11  thus fills the role of a checking means that executes the checking operation other than the predetermined operations of the camera responsively to detection of an abnormality in an operation. 
     If it is sensed at step S 87  that the output signal of the photo-interrupter  29  is driven high, it means that the exposure operation has terminated normally. Control is then passed to the next step S 91 . At step S 91 , the control circuit  11  initializes abnormality history information in the predetermined memory (not shown), and then terminates (ends) the series of actions. 
     The checking sequence to be executed when the exposure operation of the camera terminates abnormally will be detailed in conjunction with the flowchart of FIG.  7 . The checking sequence is a subroutine to be carried out at step S 90  in FIG.  6 . 
     At step S 101 , the control circuit  11  starts powering the solenoid  27  using the shutter drive circuit  14 . This causes the plunger  27   a  to start suction. Driving for disengaging the sectors  21  and  22  from each other is started. 
     Unlike the aforesaid exposure operation (see FIG.  6 ), the solenoid  27  is powered irrespective of the level of the output signal of the photo-interrupter  29 . If it is judged that an abnormality has occurred at step S 71  within the aforesaid exposure operation, the shutter unit  17  is driven forcibly as described later in the hope that the shutter unit  17  may be restored to its normal state. 
     Concurrently with the processing of step S 101 , that is, the start of powering the solenoid  27 , the control circuit  11  allows it own abnormality judgment timer (not shown) to start measuring a time at step S 102 . The time to be measured by the timer is a relatively long time unlike the one to be measured during the normal exposure operation. The solenoid is thus powered for a longer time because it may facilitate detection of an abnormality and it may give the sectors  21  and  22  of the shutter unit  17  a chance to be restored to their normal states. 
     At step S 103 , the control circuit  11  monitors the state of the output signal output from the photo-interrupter  29 . If it is sensed that the output signal of the photo-interrupter  29  is low, control is passed to the next step S 106 . If it is sensed that the output signal of the photo-interrupter  29  is high, control is passed to step S 104 . 
     If the checking sequence is called because, for example, the shutter unit has failed while being open, the output signal of the photo-interrupter  29  remains low. In this case, control is passed to step S 106 . 
     At step S 104 , the state of the abnormality judgment timer started up at step S 102  is checked. The processing of steps S 103  and S 104  is repeated until the predetermined time has elapsed. 
     At step S 104 , if the control circuit  11  confirms that the predetermined time has elapsed, the control circuit  11  judges that the sectors  21  and  22  have not acted at all despite powering performed at step S 101 , and passes control to the next step S 105 . At step S 105 , the control circuit  11  stops powering the solenoid  27  and terminates the checking sequence. 
     If it is confirmed at step S 103  that the output signal of the photo-interrupter  29  is driven low, the sector  21  is thought to start acting normally. Control is then passed to step S 106 . 
     At step S 106 , the control circuit  11  allows its own checking time-in-unit of sec reproduction timer (not shown) to start measuring a time. The time to be measured is a sufficiently long time that is long enough to open the sectors  21  and  22 . During the long time, the sectors  21  and  22  are driven to move a full stroke in order to check if the sectors act abnormally. 
     At step S 107 , it is checked if the timer started up at step S 106  has measured a predetermined time, that is, the predetermined time has elapsed. If the predetermined time has elapsed, control is passed to the next step S 108 . 
     At step S 108 , the control circuit  11  stops powering the solenoid  27 . This causes the sectors  21  and  22  to start a closing action for closing the aperture  20 . 
     Concurrently, at step S 109 , the control circuit  11  allows its own abnormality judgment timer (not shown) to start measuring a time, and then passes control to the next step S 110 . 
     At step S 110 , the control circuit  11  monitors the state of the output signal of the photo-interrupter  29 . If it is sensed that the output signal of the photo-interrupter  29  is driven high, control is passed to the next step S 112 . If it is sensed that the output signal of the photo-interrupter  29  remains low, control is passed to step S 111 . 
     At step S 111 , it is checked if the abnormality judgment timer started up at step S 109  has measured a predetermined time, that is, the predetermined time has elapsed. The processing of steps S 110  and S 111  is repeated until the predetermined time has elapsed. 
     If it is confirmed at step S 111  that the predetermined time has elapsed, it is judged that the sectors  21  and  22  remain intact with the aperture left open but do not shift to close the aperture. The checking sequence is then terminated. 
     If it is sensed at step S 110  that the output signal of the photo-interrupter  29  is high, it is judged that the sectors  21  and  22  that have shifted to close the aperture and that the shutter unit has been restored to its normal state. Control is then passed to the next step S 112 . At step S 112 , abnormality history information concerning the action of the shutter unit is initialized, and the checking sequence is terminated. 
     As mentioned above, according to the present embodiment, if it is detected that the shutter unit acts abnormally, the checking sequence is executed for tentatively driving the shutter unit  17 . It is checked again if the shutter unit acts abnormally. Consequently, the reliability in judging an abnormality attributable to the failure of the shutter unit  17  can be improved. 
     The checking sequence to be executed when an abnormality occurs during the exposure operation of the camera (subroutine to be carried out at step S 90  in FIG. 6) (see FIG. 7) may be different from the contents of the flowchart of FIG. 7 but may be carried out as described below. 
     FIG. 8 is a flowchart describing a variant of the checking sequence to be executed when an abnormality occurs during the exposure operation of the camera of the present embodiment. According to this variant, if an abnormally is detected during the exposure operation, additional processing is carried out for forcibly opening or closing the shutter unit (sectors  21  and  22 ) repeatedly a plurality of times for a short period of time. Thus, a test operation for giving the shutter unit a chance to be restored to its normal state is added to the checking sequence. The configuration of the camera itself is substantially identical to that of the aforesaid embodiment. The description of this configuration will be omitted. The same reference numerals will be employed, if necessary, in the description below. 
     Assume that the checking sequence is called for at step S 90  in FIG.  6 . As described in FIG. 8, at step S 121 , the control circuit  11  initializes information concerning the output signal of the photo-interrupter  29  stored in the predetermined memory (not shown). In other words, if the output signal of the photo-interrupter  29  is driven low even once to indicate that light is transmitted by the photo-interrupter  29 , the fact is stored in the memory. At step S 121 , history information indicating that the output signal has been driven low is cleared. 
     At step S 122 , the control circuit  11  sets a test counter (not shown) for counting the number of test times by which the opening and closing action of the shutter unit is tested. The test counter is incorporated in, for example, the control circuit  11 . 
     At step S 123 , the control circuit  11  starts powering the solenoid  27  using the shutter drive circuit  14 . This causes the plunger  27   a  to start suction. Driving for disengaging the sectors  21  and  22  from each other is started, that is, the opening and closing action of the shutter unit is started. The opening and closing action of the shutter unit is, unlike the one performed during the normal exposure operation, forcibly executed irrespective of the level of the signal output from the photo-interrupter  29 . 
     Concurrently with the start of powering the solenoid  27  at step S 123 , at step S 124 , the control circuit  11  allows a timer for measuring a powering time (not shown) to start measuring the time. 
     At step S 125 , the control circuit  11  checks the output signal of the photo-interrupter  29  using the shutter detection circuit  13 . If the output signal is low, control is passed to the next step S 126 . If the output signal is high, control is passed to step S 127 . 
     At step S 126 , the control circuit  11  stores information, which indicates that the output signal of the photo-interrupter  29  is low, in the predetermined memory (not shown). If the output signal of the photo-interrupter  29  is driven low even once with the solenoid  27  kept powered in order to indicate that light is transmitted by the photo-interrupter, or in other words, if the sectors  21  and  22  are disengaged from each other, information indicating the fact is stored. 
     At step S 127 , the control circuit  11  checks the timer for measuring a powering time, during which the solenoid  27  is powered, which is started up at step S 124 . If the timer has measured a predetermined powering time, that is, the predetermined powering time has elapsed, control is passed to step S 128 . If the predetermined powering time has not been elapsed, control is returned to the step S 125  and checking the output signal of the photo-interrupter  29  is continued. 
     If the predetermined powering time has elapsed, control is passed to step S 128 . At step S 128 , the control circuit  11  stops powering the solenoid  27 , and then passes control to the step S 129 . 
     Concurrently with the processing of step S 128  (stopping powering the solenoid), at step S 129 , the control circuit  11  starts up an off timer for measuring a powering pause time. 
     At step S 130 , a standby state is attained in order to wait for the off timer started up at step S 129  to complete measuring a time. In short, the shutter unit (sectors  21  and  22 ) acts to close the aperture during the standby period. 
     If the predetermined powering pause time has elapsed, control is passed to step S 131 . At step S 131 , the control circuit  11  judges from the processing of steps S 123  to S 130  that driving the shutter unit to open and close the aperture has completed. The control circuit  11  then decrements the count value of the test counter, which counts the number of test times by which the opening and closing action of the shutter unit is tested, by one. 
     At the next step S 132 , the control circuit  11  checks if the count value of the test counter is a pre-set value, that is, if the opening and closing action of the shutter unit has been tested by a pre-set number of test times. If it is confirmed that the opening and closing action has not been tested by the number of test times, control is returned to step S 123 . The shutter unit is driven again in order to open and close the aperture. If the opening and closing action thereof has been tested by the pre-set number of test times and the count value equals to the pre-set value, control is passed to the next step S 133 . 
     At step S 133 , the control circuit  11  references the history information stored in the memory so as to check if the output signal of the photo-interrupter  29  has been driven low. Assume that while the opening and closing action of the shutter unit is repeated a plurality of times, that is, while powering the solenoid  27  is under way, the sectors  21  and  22  have been disengaged from each other even once. In this case, history information indicating that the output signal of the photo-interrupter  29  has been driven low must have been stored in the memory at step S 126 . 
     If history information indicating that the output signal of the photo-interrupter has been driven low is not found at step S 133 , it means that although the shutter unit has repeatedly been driven to open and close the aperture, the sectors  21  and  22  have not moved to open the aperture. In this case, the shutter abnormality history is left intact, and the checking sequence is terminated. 
     At step S 133 , if the history information indicating that the output signal of the photo-interrupter has been driven low is found, control is passed to step S 134 . At step S 134 , the control circuit  11  allows the abnormality judgment timer to start measuring a time. 
     At step S 135 , the control circuit  11  checks the state of the output signal of the photo-interrupter  29 . If the output signal is high, control is passed to step S 137 . If the output signal remains low, control is passed to step S 136 . 
     At step S 136 , the state of the abnormality judgment timer started up at step S 134  is checked. If it is confirmed that the predetermined time has elapsed, it is judged that the sectors  21  and  22  have not moved to close the aperture. The checking sequence is then terminated. If the abnormality judgment timer has not yet measured the predetermined time, that is, the predetermined time has not elapsed, control is returned to the step S 135 . The output signal of the photo-interrupter  29  is then checked and the abnormality judgment timer is checked. 
     If it is confirmed at step S 135  that the output signal of the photo-interrupter  29  has made a low-to-high transition, control is passed to step S 137 . In this case, it is judged that the sectors  21  and  22  have moved to open the aperture and the shutter unit has been restored to its normal state. At step S 137 , the control circuit  11  therefore initializes the abnormality history concerning the action of the shutter unit and terminates the checking sequence. 
     As mentioned above, according to the above-described variant, the shutter unit  17  is forcibly driven a plurality of times repeatedly for a short period of time. When a frivolous defect caused by, for example, dust or clogging has occurred in the shutter unit  17  or a gear or any other mechanism, the defect can be overcome readily through the repeated driving of the shutter unit. Once such a frivolous defect is overcome during the checking sequence described in FIG. 8, the defect will never affect any subsequent operation. 
     As for the checking operation to be executed when an abnormality occurs during the exposure operation of the camera of the embodiment (subroutine to be carried out at step S 90  in FIG. 6) (see FIG.  7 ), another variant is conceivable. 
     FIG. 9 is a flowchart describing another variant of the checking operation to be executed when an abnormality occurs during the exposure operation of the camera. According to this variant, the processing of checking the solenoid  27  for disconnection according to a voltage developed at a supply battery is added to the checking operation (see FIG.  7 ). The processing of checking the solenoid  27  for disconnection is, as described in FIG. 9, comprised of four steps (steps S 113  to S 116 ) additionally inserted between the step S 101  in FIG.  7  and the step S 102 . The other steps have the same step numbers as those in FIG.  7 . The description of the same steps as those described in relation to the previous embodiment will therefore be omitted. Only the different steps (of checking disconnection) will be described below. 
     The configuration of the camera itself is substantially identical to that in accordance with the first-described embodiment. The description of the configuration will therefore be omitted. The components will be described if necessary with the same reference numerals assigned thereto. 
     At step S 101 , powering the solenoid  27  is started. Thereafter, control is passed to step S 113 . At step S 113 , the control circuit  11  allows a timer, in which a predetermined time required to stabilize the power supply is pre-set, to start measuring a time. 
     At step S 114 , a standby state is attained in order to wait for the timer started up at step S 113  to complete measuring a time, or in other words, to wait until the power supply is stabilized. 
     When it is confirmed using the timer that the predetermined time has elapsed, control is passed to the next step S 115 . At step S 115 , the control circuit  11  measures a voltage developed at the power supply using a supply voltage detection circuit (not shown). The supply voltage detection circuit detects a voltage developed at a battery serving as the power supply for powering all the circuits and actuators in the camera. A fragment of the battery voltage is produced using resistors (not shown) and measured. The measured value is digitized and then output to the control circuit  11 . 
     At the next step S 116 , it is checked if the measured value of the supply voltage that is obtained at step S 115  falls within a range of predetermined standard values. In this case, if the solenoid  27  is not disconnected but is normal, a large current flows. At this time, the supply voltage drops because of an impedance occurring in the battery. When a voltage drop is limited, or in other words, when the supply voltage falls outside the range of predetermined standard values, the solenoid  27  is predicted to be disconnected. 
     If it is found at step S 116  that the measured value of the supply voltage falls outside the range of predetermined standard values (is not a standard value), the solenoid  27  is judged to be disconnected. The checking sequence is then terminated. 
     If it is confirmed at step S 116  that the measured value of the supply voltage falls within the range of predetermined standard values, control is passed to the next step S 102 . The subsequent processing is then executed. 
     As mentioned above, according to the another variant, the processing of checking for an abnormality item to be detected, that is, checking the solenoid  27  for disconnection is added. Consequently, an abnormality detection operation can be carried out with higher precision. 
     In the aforesaid embodiment and variants, a predetermined action of the camera has been described by taking an action of the shutter unit for instance. The predetermined action is not limited to this one. That is to say, the predetermined action may not be any action involved in the exposure operation, such as, the action of the shutter unit or the action of the aperture blades. Alternatively, the predetermined action may be any action involved in the film feed operations, the clutch switching operation for switching destinations of driving force, the pop-up strobe unit thrust/plunge operation, the photographic lenses drive operation, and the automatic open/close lens barrier open/close operation. The photographic lenses drive operation involves the power varying action of a zoom lens and the focusing action of a focusing lens. 
     According to the present invention, it is apparent that a wide range of different embodiments can be formed based on the invention without a departure from the spirit and scope of the invention. This invention will be limited by the appended claims but not restricted by any specific embodiments.