JP2007101994A - Camera focal plane shutter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera focal plane shutter capable of absorbing mechanical dispersion of individual products. <P>SOLUTION: The camera focal plane shutter includes: a shutter base plate with an aperture; blades for opening/closing the aperture; an arm, one end of which is pivotally supported by the shutter base plate, and with the blades pivotally supported toward the other end; an actuator 19 which is connected to the arm and actuated in reply to the power supply to rotate the arm; and a driving circuit 40 which supplies the power to the actuator 19 and drives the actuator 19 to control the opening/closing of the aperture. The power supply is started by the driving circuit 40 at a first level of voltage/current, after a lapse of a first period, the energizing voltage/current is changed to a second level lower than the first level, then, the power is continuously supplied, and after a lapse of a second period, the power supply is ended. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a focal plane shutter for a camera. More specifically, the present invention relates to a drive control technique for an actuator that drives a shutter.

The focal plane shutter for a camera basically includes a shutter base plate, blades, an arm, an actuator, and a drive circuit. The shutter base plate has an aperture for exposure. The blade opens and closes this aperture to perform the exposure operation. One end of the arm is pivotally attached to the shutter base plate, and the blade is pivotally supported toward the other end. The actuator is connected to the arm and operates in response to energization to rotate the arm. The drive circuit controls opening and closing of the aperture by energizing the actuator and driving it. A focal plane shutter for a camera having such a configuration is disclosed in Patent Document 1, for example.
JP2001-281730

  The focal plane shutter opens and closes the aperture according to the time set in accordance with the subject brightness, thereby obtaining an appropriate exposure. The drive circuit supplies a constant current or a constant voltage to the actuator for a predetermined time. In response to this, the actuator drives the arm with a certain amount of force to open and close the wings. A constant current drive or a constant voltage drive is used to make the force of the actuator constant, so that the exposure amount does not vary among the individual shutter devices.

  However, the actuator is electrically driven but contains mechanical components. Further, the torque of the actuator is transmitted to the blades via connecting parts such as an arm. Since the focal plane shutter is composed of mechanical parts, there is a variation among individual products, and there is a problem that the exposure amount actually varies even if constant current driving or constant voltage driving is performed.

  In view of the above-described problems of the conventional technology, an object of the present invention is to provide a focal plane shutter capable of absorbing mechanical variations of individual products. In order to achieve this purpose, the following measures were taken. That is, the present invention provides a shutter base plate having an aperture, blades for opening and closing the aperture, an arm having one end pivotally attached to the shutter base plate and pivotally supporting the blade toward the other end, and coupled to the arm In the focal plane shutter for a camera, comprising: an actuator that operates in response to energization to rotate the arm; and a drive circuit that energizes and drives the actuator to control opening and closing of the aperture. The drive circuit starts energization at the first level voltage or current, changes the energization voltage or energization current to the second level lower than the first level after the first period, and continues energization until the second period elapses. The post-energization is terminated.

  Specifically, the actuator can be driven in both the forward and reverse directions to open and close the aperture, and the drive circuit is energized by one or both of forward drive and reverse drive. Is changed from the first level to the second level. In addition, the drive circuit can variably adjust both or one of the first period and the second level. The blade is divided into a leading blade and a trailing blade, and an actuator is provided separately correspondingly.

  According to the present invention, when the focal plane shutter is activated, energization is started at a relatively high first level voltage or current, and then the energization voltage or energization current is changed to a relatively low second level until the end of the operation. To stop the shutter operation. As a general trend, the effects of mechanical variations appear especially at startup, causing mechanical delays. In order to minimize this mechanical delay as much as possible, energization is performed at a high level of voltage or current during startup. As a result, it is possible to start up quickly regardless of mechanical variations of individual products. After that, when the shutter blades shift to stable running, the energization level is changed downward to end the shutter operation. At that time, the mechanical characteristics can be corrected more effectively by variably adjusting the second level of energization in accordance with the mechanical variation of each product. That is, a shutter that travels stably with a relatively light torque may set the second level lower, while a shutter with a relatively heavy torque may set the second level higher.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic plan view showing an overall configuration of a first embodiment of a focal plane shutter for a camera according to the present invention. As shown in the drawing, the focal plane shutter 1 is assembled using a main plate 2. A rectangular aperture 2a (indicated by a one-dot chain line) is provided at the center of the main plate 2. In the resting state, the four leading blades 3 partially overlap each other to shield the aperture 2a. Although not shown, the rear blade group is disposed below the front blade group. Unnecessary movement of the tip of each shutter blade is regulated by the blade presser 30. A pair of arms 5 and 6 is pivotally supported at the left end of the main plate 2 while maintaining a parallel relationship with each other. Each leading blade 3 is locked to a pair of arms 5 and 6 at its tip. Similarly, the rear blade group is locked by a pair of arms (not shown). The main arm 5 is provided with a long hole 18, and the long groove 4 is provided in the main plate 2 along the movement locus of the long hole 18 accompanying the rotation of the main arm 5. Although not shown, the long hole 18 is engaged with a drive pin that penetrates the main plate 2 through the long groove 4. Although not shown, this drive pin is driven by an actuator. When a shutter release button (not shown) is pressed, the actuator is activated, and the drive pin moves upward along the long groove 4 provided in the main plate 2. Along with this, the main arm 5 engaged with the drive pin in the elongated hole 18 and the slave arm 6 interlocked therewith rotate upward. By this rotation, the leading blade 3 runs vertically and opens the aperture 2a. Next, a rear blade group (not shown) travels longitudinally to shield the aperture 2a and the exposure is completed. In order to drive the rear blade group, another actuator (not shown) is mounted on the main plate. In order to execute such an exposure operation, the shutter 1 is equipped with a drive circuit and controls both actuators.

  As is apparent from the above description, the focal plane shutter 1 for this camera basically includes the shutter base plate 2, the blade 3, the arms 5 and 6, the actuator, and the drive circuit. The shutter base plate 2 has an aperture 2a. The blade 3 opens and closes the aperture 2a. One end of each of the arms 5 and 6 is pivotally attached to the main plate 2, and the blade 3 is pivotally supported toward the other end. The actuator is connected to the arm 5 via a drive pin and operates in response to energization to rotate the arms 5 and 6. The drive circuit energizes the actuator to drive it, thereby controlling the rotation of the actuator. As a feature of the present invention, the drive circuit starts energization at the first level voltage or current, changes the energization voltage or current after the first period to the second level lower than the first level, and continues energization. And energization is complete | finished after 2nd period progress. Preferably, the actuator can be driven in both the forward and reverse directions to open and close the aperture 2a. In this case, the drive circuit changes the energization from the first level to the second level in one or both of the forward drive and the reverse drive. Preferably, the drive circuit can variably adjust both or one of the first period and the second level. In the present embodiment, the blade is divided into a leading blade and a trailing blade, and corresponding actuators are also provided separately.

  According to the present invention, energization is started at a relatively high first level at startup. As a result, the shutter can be activated quickly regardless of the mechanical variation of individual products, so that no mechanical delay occurs. After that, when the blades reach stable running, the energization level is lowered to maintain stable running. At this time, the mechanical variation can be finely corrected by variably adjusting the second level in accordance with the difference in mechanical characteristics of individual products. In some cases, the length of the first period may be variably adjusted according to mechanical variations. For example, an individual with a high starting torque can set a long first period, and conversely, an individual with a low starting torque can set a short first period so that the total exposure time does not vary.

  FIG. 2 is a circuit diagram showing a specific configuration example of the drive circuit for the focal plane shutter according to the present invention. In order to simplify the explanation and facilitate understanding, a case will be described in which the blades are driven to open and close by rotating in both forward and reverse directions, focusing on one actuator. As shown in the figure, the drive circuit 40 basically includes a bridge circuit 41 and a pair of level change circuits 42O and 42C. The bridge circuit 41 includes four transistors Tr1 to Tr4, and drives the motor 19 in both forward and reverse directions. The motor 19 is an actuator for opening and closing the shutter blades. When the transistors Tr2 and Tr3 are turned on, the motor 19 rotates in the forward direction and opens the shutter. Conversely, when the transistors Tr1 and Tr4 are turned on, the motor 19 rotates in the reverse direction and closes the shutter. A control signal LC is supplied to the base of the transistor Tr1 via the inverter I1. Further, another control signal LO is supplied to the base of the transistor Tr2 via the inverter I3. These control signals LC and LO are used to control the rotation direction of the motor 19. The bridge circuit 41 is connected between the power supply potential VB and the ground potential. A resistor RL for detecting a drive current flowing through the motor 19 is connected between the bridge circuit 41 and the ground potential.

  The level change circuit 42O is a circuit for switching the level of the drive current when the motor 19 rotates in the forward direction. Basically, the level changing circuit 42O is a constant current circuit, and the driving current flowing through the transistor Tr3 is controlled to be constant using the operational amplifier A. For this reason, the output terminal of the operational amplifier A is connected to the base of the transistor Tr3. The drive current level detected by the detection resistor RL is input to one input terminal of the operational amplifier A. A predetermined reference voltage is supplied to the other input terminal. This reference voltage is obtained by dividing the voltage supplied from the reference voltage source 43 by resistance. The operational amplifier A is in an operating state when the motor 19 is driven in the forward direction. For this reason, the control signal LO is supplied to the operational amplifier A through the inverter I4 and the transistor Tr5.

  The reference voltage supplied from the reference voltage source 43 is resistance-divided by the series resistors R1 and R2, and the first reference voltage level is supplied to the operational amplifier A. The timing for supplying the first reference voltage is controlled by the control signal OIA1 through the transistor Tr6 and the inverter I5. The reference voltage supplied from the reference voltage source 43 is resistance-divided by the series resistors R1 and RV and supplied to the operational amplifier A as the second reference voltage level. The timing for supplying the second level is controlled by a control signal OIA2 supplied through the transistor Tr4 and the inverter I6. The level changing circuit 42O enters an operating state in response to the control signal LO when rotating the motor 19 in the forward direction, and switches the level of the reference voltage input to the operational amplifier A in accordance with the control signals OIA1 and OIA2. As a result, the level changing circuit 42O can switch the level of the forward current flowing through the transistor Tr3 in two stages. That is, the operational amplifier A performs constant current control of the transistor Tr3 so that the detection voltage appearing at the resistor RL matches the first reference voltage level or the second reference voltage level. The resistor RV is a variable resistor, and the level of the second reference voltage supplied to the operational amplifier A can be individually adjusted.

  The level change circuit 42C has basically the same configuration as the level change circuit 42O. The level changing circuit 42C is placed in an operating state when the motor 19 rotates in the reverse direction. For this reason, the control signal LC is input to the level changing circuit 42C via the inverter I2. Control signals CIA1 and CIA2 are input to the level changing circuit 42C in order to switch the level of the driving current during reverse rotation.

  The operation of the drive circuit 40 shown in FIG. 2 will be described with reference to FIG. FIG. 3 is a timing chart showing the opening / closing state of the shutter, the logic level of each control signal, and the level change of the driving current of the motor along the common time axis T. As shown in the figure, in the standby state before entering the timing T1, all the control signals LO, LC, OIA1, OIA2, CIA1, and CIA2 are at the low level, the shutter is in the closed state, and the motor drive current is 0. is there.

  When activation is started at timing T1, the control signal LO rises to high. As a result, the transistors Tr2 and Tr3 of the bridge circuit 41 are turned on, and a forward current flows through the motor. At this time, since the control signal OIA1 becomes high, the reference voltage input to the operational amplifier of the level changing circuit 42O becomes the higher first level, and the first level with a higher drive current flows. As a result, the motor starts rotating forward with a large torque, and the shutter rises from the closed state to the open state with a slight delay.

  Subsequently, at timing T2, the control signal OIA1 returns to low and OIA2 rises to high. As a result, the reference voltage is switched from the high first level to the low second level, so that the level of the forward drive current also decreases. The period from timing T1 to T2 is appropriately set in advance. In some cases, the period T1 to T2 may be variably adjusted in accordance with the load torque of the shutter according to individual differences. For example, the period from the timing T1 to T2 may be lengthened as the load torque required when starting the shutter is larger. Further, although the level of the forward drive current is appropriately set in advance, depending on the case, the second level of the forward drive current may be variably adjusted depending on the difference in load torque. For this purpose, a variable resistor RV is incorporated in the level changing circuit 42O.

  After the shutter reaches the fully open state, the control signals LO and OIA2 return to the low level at timing T3. As a result, the supply of the forward current is stopped, and the rotation of the motor is stopped.

  Thereafter, the control signal LC rises at timing T4 when a predetermined time has elapsed. As a result, the transistors Tr1 and Tr4 are turned on, and the reverse drive current starts to flow through the motor 19. At this time, since the control signal CIA1 becomes a high level, the reverse direction drive current is set to a relatively high first level.

  The shutter starts to return from the open state to the closed state in conjunction with the reverse rotation of the motor 19. At timing T5 in the process, the control signal CIA1 falls to the low level, while CIA2 rises to the high level. As a result, the reverse drive current is switched from the relatively high first level to the relatively low second level. Thereafter, the shutter is completely closed, and the control signals LC and CIA2 return to the low level at the timing T6. Thus, one opening / closing operation of the shutter is completed.

  A second embodiment of the focal plane shutter according to the present invention will be described with reference to FIGS. FIG. 4 shows a state where the set operation is completed and the aperture is opened, and FIG. 5 shows a state where the exposure operation is completed and the aperture is closed. This embodiment is applied to a digital camera, and its configuration is such that one blade is operated by one drive circuit using one actuator. In order to facilitate understanding, parts corresponding to those of the first embodiment shown in FIG. 1 are denoted by corresponding reference numerals.

  In this embodiment, when the locking member 20 is rotated in one direction by the motor 19, the transmission member 21 is engaged with the driven portion 13 of the driving member 10, so that the driving member 10 is subjected to the urging force of the spring member 11. The blade 3 rotates against the opening, and the blade 3 opens the aperture 2a. The locking member 20 locks the driving member 10 against the urging force of the spring member 11. Thereafter, when the locking member 20 is further rotated in the same direction, the locking of the drive unit 10 by the locking member 20 is released immediately after the cam surface 24 reaches the tooth surface 14, and the driving member 10 is a spring member. 11 and the blade 3 closes the aperture 2a.

  In the case of a focal plane shutter used in a digital camera, several types are known depending on the camera specifications. One of them is that the aperture is opened and a CCD or the like is opened except when shooting is performed. By exposing the entire imaging surface of the imaging device to the subject light, it can be displayed on an image display means such as a liquid crystal monitor. In shooting, when the release button is pressed, a shooting start signal is output to electrically control the image sensor, and the aperture is closed by a blade after a predetermined exposure time from the shooting start signal. To do. Thereafter, when the recording of the subject image on the storage medium is completed, the blade opens the aperture so as to prepare for the next photographing, and there are some which can display on the display means. Therefore, a case where such a digital camera is adopted will be described.

  First, FIG. 4 shows a state in which the setting operation is completed. That is, since the driving member 10 is locked by the locking member 20 and the blade 3 is operated above the aperture 2a, the aperture 2a is opened. A control unit (not shown) is in a state where the motor 19 is turned off and stopped by a detection signal from the light receiving unit of the photosensor 26. Therefore, in this set state, since the image sensor is exposed, display by an image display means such as a liquid crystal monitor is possible.

  Next, when the release button of the camera is pressed in such a set state, the control circuit on the camera side (not shown) is automatically switched from the display mode for the display means to the shooting mode, and at the same time, Imaging of an image is started, and counting of the exposure time is started using the start signal as a trigger signal. Then, after the count ends and a predetermined exposure time elapses, the motor 19 is energized by the count end signal. The drive member 10 is unlocked by the locking member 20, and the blade 3 closes the aperture 2a. Thereafter, the drive pin 18 comes into contact with a buffer member (not shown) at the lower end of the long hole 4 and the impact is absorbed to stop. FIG. 5 shows a state in which the blade 3 closes the aperture 2a and stops the motor 19 in such a manner.

  In this state, when the subject image is recorded on the storage medium, the exposure operation ends. For this reason, the above-described control circuit on the camera side (not shown) performs the setting operation simultaneously with switching from the shooting mode to the display mode. That is, the operation from such a state to the set state causes the blade opening / closing drive mechanism 7 to perform the set operation, and the blade 3 is operated to the position where the aperture 2a is opened. Then, when the locking member 20 locks the driving member 10 and the photo sensor 26 detects the locked state, the motor 19 is stopped, and it is prepared for the next photographing while being held at the set position. FIG. 4 shows a state in which a series of exposure operations is completed in this way, and returns to the set position.

It is a typical top view showing a 1st embodiment of a focal plane shutter for cameras concerning the present invention. It is a circuit diagram which shows the specific structural example of the drive circuit integrated in the focal plane shutter for cameras concerning this invention. 3 is a timing chart for explaining the operation of the drive circuit shown in FIG. 2. It is a typical top view which shows 2nd Embodiment of the focal plane shutter for cameras concerning this invention. It is a typical top view showing a 2nd embodiment similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Focal plane shutter for cameras, 2 ... Shutter base plate, 2a ... Aperture, 3 ... Blade, 5 ... Arm, 6 ... Arm, 19 ... Motor, 40 ...・ Drive circuit 41... Bridge circuit 42 O... Level change circuit 42 C.

Claims (4)

A shutter base plate having an aperture, a blade for opening and closing the aperture, an arm having one end pivotally attached to the shutter base plate and pivotally supporting the blade toward the other end, and connected to the arm and operated in response to energization In the focal plane shutter for a camera, comprising: an actuator that rotates the arm; and a drive circuit that controls opening and closing of the aperture by energizing and driving the actuator.
The drive circuit starts energization at a first level voltage or current, changes the energization voltage or current after the first period to a second level lower than the first level, and continues energization for a second period. A focal plane shutter for a camera, wherein energization is terminated after elapse of time. The actuator can be driven in both forward and reverse directions to open and close the aperture,
2. The focal plane shutter for a camera according to claim 1, wherein the drive circuit changes the energization from the first level to the second level in one or both of forward drive and reverse drive.   2. The focal plane shutter for a camera according to claim 1, wherein the drive circuit is capable of variably adjusting both or one of the first period and the second level.   2. The focal plane shutter for a camera according to claim 1, wherein the blade is divided into a front blade and a rear blade, and an actuator is provided separately corresponding to the blade.

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