Abstract:
A diaphragm control device for a camera capable of controlling a diaphragm member with a high level of precision is disclosed. The camera and diaphragm control device are equipped with a mirror member that moves from the down position to the up position during shooting of a subject, a mirror driving device to drive the mirror member, a diaphragm mechanism connected with the mirror member to control light rays from the subject, a diaphragm driving device to drive the diaphragm mechanism, a stopping device to stop the diaphragm driving device, and a control device to control the diaphragm driving device and the stopping device to stop the diaphragm mechanism at about a predetermined position. A correction device correct changes in the stopping characteristics of the stopping device to precisely stop the diaphragm mechanism at the predetermined position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a diaphragm control device for a camera, in particular, a diaphragm control device for a camera suited for use in a camera which drives a diaphragm of a camera with a motor. 
     2. Description of the Related Art 
     A camera is equipped with a diaphragm mechanism to control light rays from the subject by varying the size of the aperture to record an image of the subject with the proper amount of light. 
     This diaphragm mechanism functions by connecting with a mirror which moves from the down position to the up position during shooting of a subject. 
     With the rapid progress of electronic cameras in recent years, cameras which use motors to drive the above-mentioned aperture mechanism and mirror are being proposed. 
     The diaphragm control mechanism driven by a motor is controlled by the control device to assume a specified diaphragm step number (hereafter AV value). 
     FIG. 7 is a drawing of a timing chart to control the diaphragm mechanism and the mirror using the above-mentioned control device. Hereinafter control operation of a related art control device will be explained with reference to FIG. 7. 
     A sequence motor to drive a mirror rotates, by command from the control device, in the normal direction to move the mirror up and in the reverse direction to move the mirror down between first and second positions in and away from an optical axis of said camera. 
     A sequence switch turns on and off by connection with the motion of the mirror. 
     A diaphragm pulse is a pulse to transmit the position data of the diaphragm mechanism to the control device. 
     A diaphragm magnet is a magnetic member acting as a stopping device to stop the motion of the diaphragm mechanism. The magnetic member receives electric current from the control device. 
     The control device recognizes a delay time from the reception of electric current by the diaphragm magnet to the actual stopping of the diaphragm mechanism as an adjustment value and controls the flow of electric current to the diaphragm magnet as follows. 
     The control device computes an estimated overrun pulse based on the period of the diaphragm pulse and the above-mentioned adjustment value and controls the flow of electric current to the diaphragm magnet in such a manner that the target diaphragm position is realized ultimately by adding the estimated number of overrun pulses to the diaphragm pulse generated. 
     However, in the diaphragm control device for a related art camera, the problem occurs that, due to changes in the voltage applied to the motor to drive the diaphragm magnet and the diaphragm mechanism, the time for the diaphragm magnet to stop the diaphragm changes, resulting in a failure to control the diaphragm precisely. 
     Moreover, even if the voltage applied to the diaphragm magnet is uniform, the acceleration of the diaphragm mechanism during the diaphragm pulses period is not uniform, resulting in a failure to control the diaphragm mechanism precisely. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a diaphragm control device for a camera capable of controlling a diaphragm member with a high level of precision regardless of changes in voltage and the period of the diaphragm pulses. 
     To solve the above and other problems, the diaphragm control device for a camera of the present invention is equipped with a mirror member which moves from the down position to the up position during shooting of a subject, a mirror driving device to drive the mirror member, a diaphragm mechanism connected to the mirror member to control light rays from the subject, a diaphragm driving device to drive the diaphragm mechanism, a stopping device to stop the diaphragm driving device, and a control device to control the diaphragm driving device and the stopping device to make the diaphragm of the diaphragm mechanism equal to the specified diaphragm value, and further includes a correction device to correct the actuation time of the stopping device. 
     In a modified diaphragm control device of the present invention, the power source to drive the mirror driving device and the stopping device are the same, and the correction device corrects changes in the actuation time of the stopping device based on the moving time of the mirror member. 
     In a second embodiment of the present invention, the diaphragm control device further comprises a voltage detection member to detect the voltage applied to the stopping device, and the correction device corrects the actuation time of the stopping device based on the detection results of the voltage detection member. 
     The diaphragm control device for a camera of the present invention is equipped with a mirror member which moves from the down position to the up position during shooting of a subject, a mirror driving device to drive the mirror member, a diaphragm mechanism connected with the mirror member to control light rays from the subject, a diaphragm driving device to drive the diaphragm mechanism, a stopping device to stop the diaphragm driving device, and a control device to control the diaphragm driving device and the stopping device to make the diaphragm of the diaphragm mechanism equal the specified diaphragm value, and further includes a correction device to correct the actuation time of the stopping device based on the driving characteristics of the diaphragm mechanism. 
     In the diaphragm control device for a camera of the present invention, the correction device corrects the actuation time of the stopping device, enabling the diaphragm mechanism to assume a specified diaphragm value with a high level of precision. 
     In the diaphragm control device for a camera of a first embodiment of the present invention, the correction device corrects changes in the actuation time of the stopping device based on the moving time of the mirror member, enabling the diaphragm mechanism to assume a specified diaphragm value with a high level of precision. 
     In the diaphragm control device for a camera of the second embodiment of the present invention, the correction device corrects changes in the stopping characteristics of the stopping device based on the detection results of a voltage detection element, enabling the diaphragm mechanism to assume a specified diaphragm value with a high level of precision. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following figures in which like reference numerals refer to like elements, and wherein: 
     FIG. 1 is a block diagram of a camera according to a first embodiment of the present invention; 
     FIG. 2 is a schematic diagram of a portion of the camera of FIG. 1; 
     FIG. 3 is a flow chart for operation by the microcomputer unit (MCU) of the camera of FIG. 1; 
     FIG. 4 is a timing chart of various electrical outputs to control the mirror and control the diaphragm mechanism of the camera of FIG. 1; 
     FIG. 5 is a block diagram of a camera according to a second embodiment of the present invention; 
     FIG. 6 is block diagram of a modified example of a camera according to the present invention; and 
     FIG. 7 is a timing chart of various electrical outputs of a related art mirror and diaphragm mechanism control device. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A first embodiment will be explained with reference to FIG. 1-FIG. 4. 
     The mirror member 1 is driven to the up position and the down position by a mirror driving motor 2. The mirror member 1 takes the down position to guide light rays from the subject to an unpresented finder unit and takes the up position during shooting. 
     A sequence switch 3 detects the position of the mirror member 1 and outputs the results of the detection to the microcomputer 9 (hereafter MCU 9) to be explained later. 
     A diaphragm mechanism 4 is driven by a diaphragm driving motor 5. Moreover, driving of the diaphragm mechanism 4 connects with the mirror member 1 for being driven together. 
     A diaphragm encoder 6 monitors the movement of the diaphragm mechanism 5, and the results of this monitoring are outputted to a microcomputer unit (MCU) 9 to be explained later. 
     The magnetic member 7, the stopping device, stops the driving of the diaphragm mechanism 4. In the present embodiment, power is supplied to the mirror driving motor 2, the diaphragm driving motor 5, and the magnetic member 7 by the power source unit 8. 
     The MCU 9 controls the entire camera. In particular, it controls the mirror driving motor 2, the diaphragm driving motor 5, the diaphragm encoder 6, and the magnetic member 7. Moreover, the MCU 9 computes the time from the down position to the up position of the mirror 1 based on the position data of the mirror member 1 outputted from the sequence switch 3 and stores the results of the computation in a memory device 10. 
     In addition, the MCU 9 enters the necessary data from the memory device 10 and an APEX algorithm unit 11. 
     The memory device 10 stores the up-time with the power source unit 8 in normal voltage, the delay time until the magnetic member 7 receives electric current with the power source unit 8 in normal voltage, and the previous mirror-up time. 
     The APEX algorithm unit 11 computes the diaphragm step number or position determining the size of the diaphragm opening (hereafter AV value) of the diaphragm mechanism 4 and outputs the results of the computation to the MCU 9. 
     Moreover, even if the AV value is specified manually, the APEX algorithm unit 11 outputs the specified AV value to the MCU 9. 
     The other components of the camera in the present embodiment are the same as in cameras that are known. Therefore, explanation of these components will be omitted here. 
     Next, explanation of the operation of the camera in the present embodiment will be given. 
     FIG. 3 is a flow chart describing the operation of the MCU 9. 
     With reference to FIG. 3, the flow chart begins upon receiving release signals from the unpresented release switch. 
     The MCU 9 reads the computed AV value from the APEX algorithm unit 11 (step 101). 
     After reading the AV values, the MCU 9 converts the AV value into a number of pulses (step 102). 
     The MCU 9 reads the up-time with the power source unit 8 in normal voltage, the delay time until the magnetic member 7 receives electric current with the power source unit 8 in normal voltage, and the previous mirror-up time for moving the mirror member 1 from the first position to the second position (step 103). 
     MCU 9 computes target diaphragm pulses based on the number of pulses determined at step 102 and the three data read in step 103 in order to set the diaphragm mechanism 4 to the AV value outputted from the APEX algorithm unit 11 (step 104). 
     FIG. 4 is a drawing describing a comparison between control of the diaphragm mechanism 4 with the power source unit in normal voltage and control of the diaphragm mechanism 4 with the power source unit 8 having a decreased voltage. 
     In FIG. 4, if the power source unit 8 is in normal voltage, the MCU 9 can compute the target diaphragm pulses by taking the above-mentioned delay time into consideration to set the diaphragm mechanism 4 to the AV value outputted from the APEX algorithm unit 11 precisely. 
     However, if the voltage of the power source unit 8 drops, the magnetic member 7 takes more time than normal to stop the diaphragm mechanism 4. Hence, the MCU 9 fails to set the diaphragm mechanism 4 to the AV value outputted from the APEX algorithm unit 11 precisely. 
     In the present embodiment, because the mirror driving motor 2 and the magnetic member 7, the stopping device, use the same power source unit 8, if the voltage of the power source unit drops, the mirror-up time becomes longer than usual (see FIG. 4). 
     Therefore, the MCU 9 corrects the actuation time of the stopping device, magnetic member 7, by outputting the target diaphragm pulses taking the previous mirror-up time into consideration. Hence, the MCU 9 can set the diaphragm mechanism 4 to the AV value outputted from the APEX algorithm unit 11 with a high level of precision even if the voltage of the power source unit 8 drops. 
     Following the flow chart in FIG. 3, the MCU 9 begins the mirror-up operation of the mirror member 1 (step 105). 
     The diaphragm encoder 6 outputs diaphragm pulses synchronized with the mirror-up operation. 
     The MCU 9 causes electric current to flow in the magnetic member 7 based on the results of the computation in step 104 and the diaphragm pulses from the encoder 6, and stops the diaphragm mechanism 4 (step 106). 
     FIG. 6 is a block diagram describing a modified example of the present invention in which the mirror member 1 and the diaphragm mechanism 4 are driven by the same motor (mirror driving motor 2). 
     Next, the second embodiment of the present invention will be explained with reference to FIG. 5. The components of FIG. 5 which are the same as in the block diagram of FIG. 1 will be denoted by the same symbols and explanation thereof will be omitted. 
     With reference to FIG. 5, a voltage detection device 12 monitors the voltage of the power source unit 8 and outputs the results to the MCU 9. 
     In the second embodiment, the MCU 9 computes the target diaphragm pulses by detecting the voltage of the power source unit 8 instead of detecting the mirror-up time. 
     Hence the MCU 9 can set the diaphragm mechanism 4 to the AV value outputted from the APEX algorithm unit 11 precisely, even if the voltage of the power source unit 8 fluctuates. 
     Through detection of the voltage of the power source unit 8, the voltage applied to the magnetic member 7 can be detected regardless of whether the mirror driving motor 2 and the magnet 7 use a common power source unit or separate units. 
     Moreover, even if the voltage of the power source unit 8 is uniform, if the acceleration of driving the diaphragm mechanism 4 is not uniform, the period of the diaphragm pulses outputted by the diaphragm encoder 6 fluctuates. Hence, the MCU 9, acting as a control device, fails to control the diaphragm mechanism 4 to stop at a desired predetermined position with a high level of precision. 
     In this case, even if the acceleration during the driving of the diaphragm mechanism 4 is not uniform, compensation for the varying acceleration can be made. By storing data of the characteristics of the acceleration during the driving of the diaphragm mechanism 4 in the memory device 10 beforehand, the MCU 9 can control the diaphragm mechanism 4 precisely. 
     As described above, the diaphragm control device for a camera can set the diaphragm mechanism to a specified diaphragm value precisely because the correction device corrects the time of actuation of the stopping device. 
     In the diaphragm control device for a camera according to the first embodiment of the present invention, the correction device included in MCU 9 corrects the time of actuation of the stopping device based on the moving time of the mirror member 1. Hence, the diaphragm mechanism 4 can be set to a specified diaphragm value with a high level of precision. Moreover, correction of the time of actuation of the stopping device or magnetic member 7 is executed without measuring the voltage of the power source unit because the mirror driving device 2 and the magnetic member 7 use the same power source unit 8. Hence, changing of the stopping characteristics of the stopping device is realized with a simple structure. 
     In the diaphragm control device for a camera according to the second embodiment of the present invention, the correction device included in MCU 9 corrects the actuation time of the stopping device based on the detection results of the voltage detection device 12. Thus the diaphragm mechanism is set to a specified diaphragm value with a high level of precision. Moreover, the control device is easy to use because it can be used regardless of whether the mirror driving device and the stopping device use the same power source unit. 
     In the diaphragm control device for a camera according to the present invention, the correction device corrects the actuation time of the stopping device of the diaphragm mechanism, enabling setting of the diaphragm mechanism to a specified diaphragm value precisely. 
     While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.