Shutter control device for a camera

Abstract: [OBJECT] When a trapezoid control is carried out for plural diaphragm values, an opening-time control for each of the plural diaphragm values is performed. In addition, an error correction inherent to a shutter can be easily carried out. [CONSTRUCTION] An aperture area (h1) for a prescribed diaphragm value of a shutter, times (t1, t2) required for opening and closing operations, data on an opening time (t) and correction amount inherent to the shutter are beforehand stored in the EEPROM or the like, and an opening time (t') for a set diaphragm value is calculated on the basis of the above data and an aperture area (h2) for the set diaphragm value. [EFFECT] Storage of the opening-time data every diaphragm value is not required, and a small amount of data is sufficient to a shutter control operation, so that a data ROM having small capacity can be used. In addition, various errors such as an error of the opening time due to the dispersion of the diaphragm area, an error due to the deviation in linearity of the opening and closing operations, etc. can be easily corrected, and thus the shutter control operation can be accurately performed.

Description: [DETAILED DESCRIPTION OF THE INVENTION] [FIELD OF INDUSTRIAL APPLICATION] This invention relates to a shutter control device for a camera according to the preamble of claim 1, and particularly to a device for controlling an opening time of a shutter for a camera in a diaphragm-priority mode. [PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION] An exposure amount (Ev) of a camera is generally dependent on a diaphragm value of a shutter and an opening time therefor, that is, the exposure amount is a function having the diaphragm value of the shutter and the opening time therefor as independent variables. Therefore, an opening time of the shutter is determined by setting desired exposure amount and diaphragm value. An operation of driving the shutter is schematically shown in Fig. 3. Abscissa and ordinate of the graph of Fig. 3 represent an aperture area and a time, respectively. In Fig. 3, the shutter starts its opening motion at a point A, is fully opened at a point B, starts its closing motion at a point C after an opening time t elapses, and then is completely closed at a point D. Here, the area of a trapezoid which is closely surrounded by the points A, B, C and D, corresponds to an exposure amount (Ev) for this shutter driving operation. The shutter driving operation which provides such a trapezoidal waveform for the opening and closing operations of the shutter is referred to as "a trapezoid control". In a conventional method for controlling the opening time of the shutter in which the exposure amount is controlled by a stepping motor, etc., the relationship between an exposure amount (Ev) and an opening time is beforehand stored as a data table as shown in Fig. 6 in a storing unit of a control device, and an opening time for a desired shutter driving operation is determined on the basis of the data table. For example, a data table as shown at the left side of Fig. 6 is used for a shutter driving operation for a full-opened diaphragm (hereinafter referred to as "diaphragm full-opening operation"). In a case where the trapezoid control is carried out in the diaphragm-priority mode, the opening time is varied in accordance with a diaphragm value. For example. if the diaphragm value is set to a value smaller than a value for the full-opened diaphragm in the graph of Fig. 3. the opening time must be set to be longer to obtain the same exposure amount as set for the diaphragm full-opening operation. Therefore, in order to control the opening time with the data table, the data table must be individually prepared in accordance with each of various diaphragm values, for examples, diaphragm values such as F4, F5.6, F8, etc., and thus the number of the data table is greatly increased. In addition. the linearity of a trapezoidal waveform representing opening and closing operations of a shutter for a camera is ordinarily dispersed in accordance with each shutter, and it has been hitherto very difficult to correct the dispersion of the linearity of the trapezoidal waveform. [OBJECT] A shutter control device for a camera according to the preamble of claim is known from DE-A-40 21 803. This known shutter device comprises a control means including a table in which exposure values are associated with control values for controlling the shutter. Furthermore, the control means includes calculating means for calculating control values by interpolating between control values stored in the table. Using this calculating means, the number of values stored in the table can be reduced. It is the object of the present invention to provide a shutter control device for a camera according to the preamble of claim 1, which is further improved with respect to the number of values to be stored in a storing means. This object is achieved by the features as set forth in claim 1. [BRIEF DESCRIPTION OF THE DRAWINGS] [Fig. 1] is a block diagram of an embodiment of the shutter control device for a camera according to this invention. [Fig. 2] is a graph showing a shutter driving operation and a driving state of a motor. [Fig. 3] is a graph showing shutter driving operations for a diaphragm full-opening operation and an opening operation of a small diaphragm value. [Fig. 4] Is a graph showing a shutter driving operation which requires correction. [Fig. 5] shows an example of a data table used in this invention. [Fig. 6] shows a data table which is required for a conventional shutter control. [DESCRIPTION OF REFERENCE NUMERALS] 1 Shutter 2 Exposure amount setting means 3 Diaphragm value setting means 4 Opening-and-closing control means 5 Opening-time control means 6 Control means 7 Shutter driving means 8 Storing means [EMBODIMENT] An embodiment of the shutter control device for a camera according to this invention will be described hereunder with reference to the accompanying drawings. As shown in Fig. 1, the shutter control device for a camera according to this invention includes setting means comprising exposure amount setting means 2 for setting an exposure amount of a shutter 1 and diaphragm setting means 3 for setting a diaphragm value, control means comprising opening-and-closing control means 4 for controlling opening and closing operations of the shutter, opening-time control means 5 for controlling an opening time of the shutter and control means 6 for performing a prescribed calculation on the basis of signals from the exposure setting means 2 and the diaphragm value setting means 3 to control the opening-and-closing control means 4 and the opening-time control means 5, and shutter driving means 7 for driving the shutter 1 on the basis of signals from the opening-and-closing control means 4 and the opening-time control means 5. The shutter driving means 7 comprises an AC motor, a motor such as a stepping motor, and a motor driver. The shutter 1 is a lens shutter which also serves as a diaphragm, and includes plural sectors whose opening and closing operations are carried out by a rotational motion of the motor of the shutter driving means 2 in forward and reverse directions.The shutter driving means 7 serves to carry out the opening and closing operations of the shutter sectors through the control of the opening-and-closing control means 4 and the opening-time control means 5. The exposure and diaphragm operations are carried out by keeping the shutter 1 at an opening state with a prescribed aperture for a prescribed time. The exposure amount setting means 2 detects various information such as brightness of an object, a film sensitivity, an exposure correction, etc., and outputs a signal representing an exposure amount to the control means 6 through a calculation of the exposure amount or a manual setting. The diaphragm value setting means 3 sets a diaphragm value through a manual setting, or detects various conditions to automatically set the diaphragm value, and outputs a signal representing the diaphragm value to the control mean 6. The control means 6 carries out a calculation as described later on the basis of the signals from the exposure amount setting means 2 and the diaphragm value setting means 3 to determine a forward/reverse rotation amount of the motor and an opening time for the diaphragm value and the exposure value which have been set, and outputs signals representing the determined rotation amount of the motor and opening time to the opening-and-closing control means 4 and the opening-time control means 5, respectively. The control means 6 is preferably equipped with non-volatile storing means 8 such as an EEPROM, in which data required for the calculation, such as an opening time for each exposure amount in a shutter full-opening operation, a shutter aperture area for each diaphragm value, a correction value inherent to the shutter. etc., are beforehand stored. The opening-and-closing control means 4 controls a driving time for each of the forward and reverse rotational motions, or a driving voltage, a driving current, a pulse of the motor if the motor is a stepping motor, etc. on the basis of the signal representing the forward/reverse rotation amount of the motor which is supplied from the control means 6, and outputs an instruction to the shutter driving means 7. The opening-time control means 5 controls a timing for a switching operation between the forward and reverse rotational motions of the motor on the basis of the signal representing an opening time which is supplied from the control means 6. A driving operation of the shutter thus constructed will be described with reference to Fig. 2. representatively using an embodiment where the driving operation is carried out by a stepping motor. Abscissa and ordinate of the graph of Fig. 2 represent a time and an aperture area of the shutter (a value corresponding to a diaphragm value). The motor is first driven in a forward rotational direction on the basis of the signal from the opening-and-closing control means 4, and the shutter sectors start their opening motion. Here, the forward rotational motion of the motor is carried out while the phases (Φ 1 , Φ 2 ) of the motor are alternately switched to each other, and the opening area of the shutter is determined on the basis of the number of switching pulses for the phase switching operation of the motor. The shutter sectors continue their opening motions until the motor is rotated by a prescribed rotation amount and the shutter has an aperture area which is set by the diaphragm setting means 3. Thereafter, the rotational motion of the motor is stopped, and the two phases (Φ 1 , Φ 2 ) are retained for a prescribed period on the basis of the signal from the opening-time control means 5. Subsequently, the alternate switching operation between the phases (Φ 1 , Φ 2 ) is restarted to drive the motor in the reverse rotational direction until the shutter is completely closed. Here, in Fig. 2, representing a point where the shutter starts its opening motion, a point where the shutter is opened at a prescribed amount, a point where the shutter starts its closing motion, and a point where the shutter is completely closed by A, B, C and D, the area which is surrounded by the four points A, B, C and D and the abscissa corresponds to an exposure amount. The control means 6 determines an opening time in such a manner that through the calculation as described below the exposure amount is equal to a value set by the exposure setting means 2, and controls the opening-time control means 5 on the basis of the calculated opening time. The calculating operation of the control means 6 will be described hereunder. Fig. 3 is a graph showing a driving operation of the shutter which is similar to that of Fig. 2. In Fig. 3, a trapezoid ABCD represents an opening waveform in a diaphragm full-opening operation; a trapezoid A'B'C'D',an opening waveform for a set diaphragm value (a small diaphragm value): h1 and h2, maximum aperture areas for the trapezoids ABCD and A'B'C'D', respectively; t and t', opening times in maximum opening state for the trapezoids ABCD and A'B'C'D', respectively; t1 and t'1, times required for a shift from the opening-start state till the maximum-opening state for the trapezoids ABCD and A'B'C'D'. respectively; and t2 and t'2, times required for a shift from the maximum opening state till the completely-closing state for the trapezoids ABCD and A'B'C'D', respectively. Here, representing total times of the shutter from the opening-start time till the completely-closing time for the trapezoids ABCD and A'B'C'D' by T and T' respectively, the following equations are satisfied: T = t + t1 + t2, T' = t' + t'1 + t'2 Here, assuming that the exposure amount (Ev) for a full-opened diaphragm is equal to the exposure amount (Ev) for a set diaphragm value, the following equation is satisfied: Ev = t + T 2 X h1 = t' + T' 2 X h2 Here, if a motor driving condition set by the opening-and-closing control means 4 is identical between the trapezoids ABCD and A'B'C'D', an inclination between a line AB is equal to an inclination of a line A'B' and an inclination between a line CD is equal to a line C'D', and in addition h1 : h2 = t1 : t'1 = t2 : t'2. From this relation and the above equation, the following equations are satisfied: 2t + t1 + t2 2 X h1 = 2t' + h2/h1 t1 + t2 2 X h2 t' = h1 h2 t + h1 1 - h2 2 2h1h2 t1 + t2 Therefore, the opening time t' for the set diaphragm value can be obtained with the aperture area h2 for the set diaphragm value, and the opening area h1, the opening time t and (t1 + t2) for the full-opened diaphragm. In this case, h1 and (t1 + t2) are data for the full-opened diaphragm, and thus may be beforehand obtained as values inherent to the shutter. The opening time t is determined by a desired exposure amount (Ev), and thus an opening time data for each exposure amount may be beforehand stored as a data table as shown in Fig. 5 in the storing means 8 of the control means 6, or it may be calculated as a function of the exposure amount. The aperture area h2 is a value for the set diaphragm value (Av), and thus an aperture-area data for each diaphragm value may be beforehand stored in the storing means 8 of the control means 6 like the opening time data, or it may be calculated as a function of the diaphragm value. The control means 6 outputs a signal representing the opening time t' for the set diaphragm value to the opening-time control means 5, and controls the shutter opening operation. The shutter driving operation as described above is satisfied in an ideal case where no dispersion occurs in the linearity of the opening waveforms. However, in an actual exposure operation, the dispersion of the opening area and nonlinearity of the opening and closing operations frequently occur. A correcting operation for these actual cases will be next described. Fig. 4 is a graph showing an operation of the shutter similar to that of Fig. 3. In Fig. 4. a solid line represents an opening waveform of an actual shutter which is deviating from an ideal state as indicated by a broken line. A figure abcd is an opening waveform for a full-opened diaphragm. and another figure a'b'c'd' is an opening waveform for a set diaphragm value. The same reference numerals as those of Fig. 3 represent the same elements. Assuming that an exposure amount for the full-opened diaphragm is equal to that for the set diaphragm value, the following equation is satisfied: Ev = (area of abe) + (area of bcfe) + (area of cdf) = (area of a'b'e') + (area of b'c'f'e') + (area of c'd'f') Here, assuming that ΔEv = {(area of abe) + (area of cdf)} - {(area of a'b'e') + (area of c'd'f')}, (area of bcfe) = h1 X t. and (area of b'c'f'e') = h2 X t'. and thus t' = (h1 X t + ΔEv)/h2. Here, h1 and ΔEv are values inherent to the shutter, and obtained through an actual measurement, t represents an opening time for the set exposure amount in the diaphragm full-opening operation, and it may be beforehand stored as a data for each exposure amount in the storing means 8 of the control means 6 or may be calculated as a function of the exposure amount. The aperture area h2 is a value corresponding to the set diaphragm value (Av), and it may be beforehand stored as a data for each diaphragm value in the storing means 8 of the control means 6 or may be calculated as a function of the diaphragm value. Therefore, by beforehand storing values of ΔEv in the storing means 8, the correction can be easily performed, and thus a shutter control can be accurately carried out. Here, the area of ab'e' of ΔEv is set in consideration of a phenomenon occurring from the point a to the point b' where a shutter bound is stabilized, and thus an inherent error for each aperture area can be corrected. In this embodiment, the opening time t' in the maximum opening state of the shutter is calculated, however, in place of this calculation an effective opening time for which the shutter starts its opening motion and completes its closing motion may be calculated. [EFFECT OF THE INVENTION] As is apparent from the above embodiment, according to the shutter control device for a camera and the shutter controlling method for a camera of this invention, the trapezoid control for plural diaphragm values can be performed with a small amount of data, and thus a data from haxing small capacity can be used. In addition. according to this invention, the correction to various errors such as an error of the opening time due to the dispersion of a diaphragm or aperture area, an error due to the deviation in linearity of the opening and closing operations. etc. can be easily made by beforehand storing a correction amount inherent to the shutter in an EEPROM or the like, and the shutter control can be accurately performed.

Claims: A shutter control device for a camera, comprising setting means (2, 3) for setting an exposure amount (Ev) of a camera and a diaphragm value (Av) of a shutter, control means (4, 5, 6) for controlling opening and closing operations for the shutter on the basis of said set diaphragm value (Av) of the shutter and a calculated opening time for the shutter, shutter driving means (7) for driving the shutter on the basis of a signal from said control means (4, 5, 6) and storing means (8), characterized in that the storing means (8) are arranged to store an aperture area (h1) corresponding to a predetermined diaphragm value of the shutter and first and second time values (t1, t2) required for the opening and closing operations of the shutter corresponding to said predetermined diaphragm value of the shutter, and in that said control means are arranged to perform a calculation of the opening time (t') for obtaining said set exposure amount (Ev) of the camera at said set diaphragm value (Av) of the shutter on the basis of following parameters: the opening time (t) for obtaining said set exposure amount (Ev) of the camera at said predetermined diaphragm value of the shutter, said stored aperture area (h1), said stored time values (t1, t2) required for the opening and closing operations of the shutter corresponding to said predetermined diaphragm value and an aperture area (h2) corresponding to said set diaphragm value (Av) of the shutter. The shutter control device as claimed in claim 1, wherein said storing means (8) is further arranged to store the opening time (t) corresponding to every exposure amount (Ev) of the camera at said predetermined diaphragm value of the shutter and/or stores the aperture area (h2) corresponding to every diaphragm value (Av) of the shutter. The shutter control device as claimed in claim 1, wherein said control means (4, 5, 6) is further arranged to perform a calculation of said opening time (t) on the basis of said set exposure amount (Ev) of the camera and/or said aperture area (h2) on the basis of said set diaphragm value (Av) of the shutter. The shutter control device as claimed in claim 1, wherein said storing means is further arranged to store a correction value (ΔEv) inherent to the shutter, said control means is further arranged to calculate the opening time (t') for obtaining said set exposure amount (Ev) of the camera at said set diaphragm value (Av) of the shutter on the basis of said parameters and said stored correction value inherent to the shutter.

Inventors: AKIMOTO KAZUO, FUJITA HIROKO, IWAMATSU YOSHIYUKI, KAKUTA MITSUHIRO, MIYATA SHINJI, NAKAMURA TOMOKI, AKIMOTO, KAZUO, FUJITA, HIROKO, IWAMATSU, YOSHIYUKI, KAKUTA, MITSUHIRO, MIYATA, SHINJI, NAKAMURA, TOMOKI, AKIMOTO, KAZUO C/O SEIKOSHA CO. LTD CHIBA OFFICE, Fujita, Hiroko, c/o Siekosha Co.,Ltd. Chiba Office, IWAMATSU, YOSHIYUKI C/O SEIKOSHA CO. LTD, KAKUTA, MITSUHIRO C/O SEIKOSHA CO.LTD CHIBA OFFICE, Miyata, Shinji, c/o Seikosha Co.,Ltd. Chiba Office, Nakamura, Tomoki, c/o Seikosha Co.,Ltd.
Applicants: SEIKO PRECISION KK, SEIKO PRECISION INC.
Application year: 1992
Main classification: G03B7
IPC codes: G03B7, G03B9