JPH058407B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a program shutter, and more specifically, to a program shutter in which the opening and closing operations of shutter blades are performed by a step motor.

(Prior art) A program shutter that uses a step motor to open and close the shutter blades inputs a drive pulse with a fixed period to the step motor through a release operation, rotates the motor in the forward direction, and gradually opens the sector. The structure is such that the phase of the drive pulse is switched when the step rotation corresponds to the amount of exposure, the step motor is reversed, the sector is closed, and proper exposure is obtained.

By the way, the maximum rotational speed of the step motor used in this shutter is low, at most 500 to 1000 pulses/second, which limits the minimum time required for one step of rotation, resulting in large errors, especially in short-second exposures. This has disadvantages in that it may cause problems, and it may not be possible to obtain an optimum exposure step, which is a serious problem, especially in the current situation where the sensitivity of film is becoming increasingly high.

Of course, such problems can be solved by reducing the slope of the opening line of the shutter or by using a step motor with a high rotation speed, but as the mechanism becomes more complicated and the cost of the motor increases, new problems arise. cause problems.

(Objective) In view of the above-mentioned problems, it is an object of the present invention to provide a program shutter that not only can shorten the exposure time but also can obtain exposure steps with fine grains.

(Structure) That is, the feature of the present invention is that the number of rotational steps and interpolation amount of the step motor are determined according to the exposure amount corresponding to the brightness of the subject, and the step drive is performed in accordance with this number of steps when the shutter is opened. The sector is driven in steps by pulses, and the direction of rotation is switched when a time corresponding to the amount of interpolation has elapsed from the time when the final step drive pulse is output, and the interpolation is performed by subdividing the steps between steps. It is in.

Therefore, details of the present invention will be explained below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a base plate to which a front plate 2 for positioning a lens is attached, and a sector chamber 3 is provided between the front plate 2 and the front plate 2. It forms and houses sectors 4,4. Reference numeral 5 denotes a sector ring that drives the sectors 4, 4 to open and close, and has degree-determining portions 5a, 5 formed on the outer periphery.
The range of rotation is restricted by the pin 6 installed in the front plate 1 and the base plate 1, and the spring 7 applied between the front plate 1 and the base plate 1 imparts levorotation to the front plate 2 so that it can rotate around the outer periphery of the front plate 2. It is attached by a retaining ring 8. Two sector pins 5b, 5b are implanted on the surface of the base plate side of this sector ring 5 so as to be symmetrical with respect to the optical axis, and are engaged with the two sectors 4, 4, respectively, and teeth are provided on the outer periphery. 5
c, and is connected to a pinion 21 of a step motor 11, which will be described later, via wheel trains 9 and 10.

FIG. 2 shows an embodiment of the above-mentioned step motor 11 which is capable of forward and reverse rotation, and 12 is
Mounting holes 13 are drilled in the motor base plate to engage with the base plate 1 of the shutter body using screws, and the two stators 16, 16 can be moved up and down using pillars 14, 14 and guide pins 15, 15 planted on the surface. The motor upper plate 17 is placed opposite to the pillar 1.
4 and 14 with screws 18 and 18, and a rotor 19 made of a permanent magnet is fixed to the motor base plate 12 and the upper plate 1.
7 to rotatably support the rotary shaft 20 from one side.
The transmission gear 21 is attached so that the transmission gear 21 is protruded. Note that the symbols L ₁ and L ₂ in the figure indicate the first and second drive coils wound around the stators 16 and 16, respectively.

Therefore, the following description will be given of the control device which constitutes the characteristic part of the present invention.

FIG. 3 shows an embodiment of a device for controlling the shutter mechanism described above, and is designated by reference numeral 31 in the figure.
34 is a photometry start pulse generating circuit that detects the operation of a switch 32 linked to a release button (not shown) and outputs a photometry start pulse; Clock CK for luminance data
1. A frequency dividing circuit that generates a step driving clock CK2 and an interpolation clock CK3 whose frequency is higher than that of the clock CK2. 35 is a brightness detection circuit that outputs a clock CK1 according to the brightness of the subject. It starts operating when a pulse is input, and the light receiving element 4 such as CdS installed in the camera body
Logarithmically compresses the subject brightness detected by step 9, and clocks the brightness data clock CK for a time proportional to this value.
1 is output to a counter circuit 36, which will be described later. 36 is the aforementioned counter circuit which is cleared by the photometry start pulse and at the same time counts and holds the luminance data clock CK1 from the luminance detection circuit 35; 37 is the exposure amount calculation circuit which calculates the film sensitivity set by the switch group 38; The configuration is such that the optimum exposure amount is calculated based on the information and the contents counted by the counter circuit 36. Reference numeral 39 is an exposure amount data storage circuit that stores step motor drive data corresponding to the exposure amount in advance, and stores data on the number of steps by which the step motor should rotate and subdivides one step in order to correct exposure errors caused by this number of steps. It is configured to output interpolated data. Reference numeral 40 denotes a step drive pulse generation circuit that sets the rotational speed of the step motor per step.
Step drive clock CK input via _G1
Step drive pulse Ps with a constant period based on 2
is configured to output. 42 is a presettable first down counter for controlling step drive, which presets the number of steps from the exposure amount data storage circuit 39 and controls step drive pulses.
The counter is sequentially subtracted by 1 by Ps, and when the counter contents reach zero, a signal is output from the output gate _G2 . 43 is a presettable second down counter that controls the interpolation drive, and a gate G that presets the interpolation data from the exposure data storage circuit 39 and opens when the content of the first down counter 42 reaches zero. ₃ is sequentially subtracted by 1 by interpolation clock CK3,
It is configured to output a signal from the output gate _G3 when the content becomes zero. 44 is a forward/reverse switching circuit that detects the point in time when the contents of the first counter 42 and the second counter 43 both become zero, outputs an inverted signal, and switches the exposure data from the exposure calculation circuit 37 again. The step number can be called and preset in the first counter 42, or the step drive pulse generation circuit 4 can be called up via the reset pulse generation circuit 45.
0 again, and furthermore, it is configured to switch the direction of pulse movement of a pulse motor drive circuit 46, which will be described later. Reference numeral 46 designates the aforementioned pulse motor drive circuit, which consists of a so-called ring counter in which the terminal that outputs the signal moves one by one each time a pulse signal is input. Output terminal Q ₁ ~
It is configured to rotate the step motor 11 in the forward or reverse direction by switching the moving direction of the pulse from _Q4 . In addition, the number 4 in the figure
Reference numeral 7 indicates a drive circuit that amplifies the signal from the drive circuit 46 and supplies power to the stator coils L ₁ and L ₂ of the step motor 11 .

Next, the operation of the apparatus configured as described above will be explained based on the waveform diagram shown in FIG.

After turning on the power switch (not shown) and pressing the release button on the camera body to the first depressed position, the switch 32 turns on and the counter circuit 36 is cleared, and at the same time the brightness detection circuit 3
5 to a fixed number of clocks CK1 according to the subject brightness
is output and stored in the counter circuit 36. The exposure calculation circuit 37 calculates an appropriate exposure determined based on the contents of the counter circuit 36 and the film sensitivity, and outputs it to the exposure data storage circuit 39. The exposure amount data storage circuit 39 receives the exposure amount from the arithmetic circuit 37 and stores the number of steps that can cover the rotation amount of the sector and the interpolation data for correcting this step rotation in first and second data, respectively. is output to down counters 42 and 43 to set the exposure amount.

When you have finished setting the exposure amount, push the release button to the second position and the switch 41 will release.
ON, the step drive pulse generation circuit 40 operates, and the step drive pulse Ps is sent to the first counter circuit 42 and the aforementioned pulse motor drive circuit 4.
Output to 6. As a result, each time a step drive pulse is inputted, the step motor 11 rotates in the positive direction by one step and begins to open the sectors 4, 4 (FIG. 1), and at the same time, the first down counter 42 moves to 1 It is subtracted by one by one. When the fixed number step drive pulse preset to the first counter 42 is output in this way, the step motor is rotating toward the final step, and the first
The counter circuit 42 outputs a signal from the gate _G2 , opens the gate _G3 , and inputs the interpolation clock CK3 to the second down counter 43. As a result, the rotation continues while one step is subdivided according to the pulse interval of the interpolation clock CK3. When the number of interpolation clocks CK3 matches the preset number of the second counter 43, a signal is output from the gate _G4 to activate the forward/reverse switching circuit 44 to output an inverted signal, and the arithmetic circuit 37 outputs an exposure signal. Quantity data storage circuit 3
At step 9, the previous exposure amount is output again to preset the number of steps in the first counter 42, and at the same time, the pulse movement direction of the pulse motor drive circuit 46 is switched, and the short pulse width output just before switches its phase. output and step motor 1
1 is forced to be reversed. Due to this reverse rotation of the pulse motor, the sectors 4, 4 gradually begin to close, rotate step by step every time a drive pulse is input, and when the first counter 42 reaches zero, gate _G1 is closed and step drive starts. The pulse stops, and at the same time sectors 4 and 4 return to their original positions, closing the optical path. When the above operations are completed, the release button returns to its original position, and the power switch (not shown) is turned off to prepare for the next photograph.

Needless to say, since the correction amount becomes zero at a location where the step rotation position of the step motor and the exposure amount match, it is possible to immediately shift to reverse driving without performing interpolation.

FIG. 5 shows a second embodiment of the present invention, in which the charging voltage from a capacitor 48b that is charged with a constant current via a transistor 48a that is turned off by a pulse from a photometry start pulse generation circuit 31, and A comparator 48d compares the terminal voltage of a logarithmic compression diode 48c connected in series with a light receiving element 49 such as CdS, and when the switch 32 is activated, the gate 48e is opened and the clock CK1 from the frequency dividing circuit 34 is input to the counter circuit 36. The gate 48e is output by the inversion of the comparator 48d.
By closing the clock CK1 and stopping the output of the clock CK1, digitized subject brightness data is output.

In the above-described embodiment, rotation step number data and interpolation amount data corresponding to the exposure amount are used and stored in advance in the storage means, but the calculation means,
For example, a division circuit may be used to perform calculations using the exposure amount as the dividend and the exposure amount per one step rotation as the divisor, the quotient as step number data, and the remainder as interpolation amount data, producing the same effect.

(Effects) As explained above, according to the present invention, the number of rotational steps of the step motor and the interpolation amount are determined according to the exposure amount, and the motor is step-driven in the forward direction in accordance with the number of steps. Since the step drive is performed in the opposite direction when the corrected time has elapsed since the last step drive, the shutter charge mechanism is not required and the release operation can be made lighter, which is an advantage.
Regardless of the inter-step movement speed of the step motor, the exposure amount can be precisely controlled, and the exposure accuracy, especially at short seconds, can be dramatically improved.

[Brief explanation of the drawing]

1A and 1B are a plan view and a sectional view showing an example of a shutter mechanism to which the present invention is applied, and FIGS. 2A and 2B are a plan view and a sectional view showing an example of a step motor used in the same device, and 3 is a block diagram of a circuit constituting an embodiment of the control device according to the present invention for operating the shutter mechanism, FIG. 4 is an explanatory diagram showing the operation of the above device, and FIG. FIG. 3 is a block diagram of a circuit constituting another embodiment of the control device according to the invention. 4, 4...Sector, 11...Pulse motor,
L ₁ , L ₂ ... Drive coil, 46 ... Pulse motor drive circuit.

Claims (1)

[Claims] 1. A shutter mechanism equipped with a sector that forms a lens aperture, a step motor that can be rotated forward and backward to open and close the sector, a calculation circuit means that calculates an exposure amount according to the brightness of the subject, and output circuit means for outputting the number of rotational steps and interpolation amount of the step motor; a motor drive means for rotating the motor in a forward direction and a reverse direction in correspondence with the number of steps from the circuit means; and from the drive means. A program shutter equipped with a control section comprising a switching circuit means for switching the direction of rotation and driving the shutter in reverse when a time corresponding to the interpolation amount has elapsed from the time when the last pulse was output.