JP2005128403A - Illumination controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination controller capable of securing sufficient driving energy to be outputted without increasing burden imposed on an illuminator in the case of performing image pickup by using the illuminator. <P>SOLUTION: The illumination controller of an imaging apparatus is equipped with an illumination means to perform lighting to a subject by receiving a supplied pulse signal of fixed frequency in an exposure time, and a pulse signal output means to supply the 1st pulse signal having the fixed frequency, a 1st duty ratio and 1st pulse amplitude and the 2nd pulse signal having the fixed frequency, a 2nd duty ratio smaller than the 1st duty ratio and 2nd pulse amplitude and including the starting time and the finishing time of an on-state while the 1st pulse signal is in the on-state to the illumination means. The pulse signal output means has a CPU to output 1st and 2nd control signals for outputting the 1st and the 2nd pulse signals, and 1st and 2nd lighting means to supply the 1st and the 2nd control signals as the 1st and the 2nd pulse signals to the illumination means through 1st and 2nd transistors. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an illumination control device in an imaging apparatus, and more particularly to an improvement in illumination operation by a combination of two pulse signals that drive an illumination LED.

  Conventionally, an illuminating device using an LED that can be driven at a low voltage and has a simple circuit configuration has been proposed in place of an illuminating device using strobe light emission such as a xenon tube that has been widely used in imaging devices such as cameras.

  By causing the LED to continuously emit light, the temperature of the LED increases. This increase in temperature causes the light amount of the LED to decrease. FIG. 1 is a diagram showing the relationship between the temperature rise and the light quantity of the LED, and it can be seen that the light quantity, that is, the luminance of the LED decreases with the temperature rise.

Patent Document 1 discloses an LED illumination device that performs LED light emission by pulse driving of a rectangular wave and enables continuous shooting of light-emission shooting of a still image. When pulse driving is used as compared with DC (current) driving, an energization off period is provided, so that it is possible to suppress the temperature rise of the LED due to heat generated by light emission. FIG. 2 takes time on the horizontal axis, and shows the rise in LED temperature in the case of DC drive (line (1) in FIG. 2) and the rise in LED temperature in the case of pulse drive (line (2) in FIG. 2). It is a figure which shows a difference. In any case, when the signal is in the on state, the illumination LED is lit. In the case of DC driving, since the steady current flows during the period in which the LED is to be lit (T0 to T5), the temperature of the LED continues to rise. The temperature decreases from the time point of turning off (T5). On the other hand, in the case of pulse driving, there is a period (T1-T2, T3-T4) in which the signal is turned off during the period in which the LED is to be turned on, and the temperature of the LED decreases during this period. Therefore, the LED temperature repeatedly rises and falls during the LED lighting period (T0 to T5), and as a result, heat accumulation is less than that in the case of DC driving.
JP 2003-101836 A

  However, when the pulse drive of the apparatus of Patent Document 1 is adopted, the drive energy itself decreases and the amount of light decreases when the ratio (duty ratio) in which the pulse signal is turned on is reduced. On the other hand, if the ON state of the pulse signal is lengthened (large duty ratio), the amount of light increases but the burden on the LED also increases. In particular, when the amplitude is close to the peak current value for driving the LED, the LED can emit light to the maximum extent, but increasing the peak state (large duty ratio) may shorten the life of the LED. is there.

  Therefore, an object of the present invention is to provide an illumination control device that ensures sufficient driving energy to be output without increasing the burden on the illumination device when imaging is performed using the illumination device.

  An illumination control device of an imaging apparatus according to the present invention includes an illumination unit that performs lighting toward a subject by receiving a pulse signal having a constant frequency within an exposure time, a constant frequency, a first duty ratio, and a first pulse amplitude. The on-state start and end times while the first pulse signal has the first pulse signal having a constant frequency and the second duty ratio smaller than the first duty ratio and the second pulse amplitude and the first pulse signal is in the on-state. And a pulse signal output means for supplying the second pulse signal including the light to the illumination means. As a result, by shortening the peak time of the pulse signal required for output, it becomes possible to ensure the driving energy of the illumination device without increasing the burden on the illumination means.

  Preferably, the pulse signal output means outputs the first and second control signals to output the first and second pulse signals, and the first and second control signals through the first and second transistors. 1. It has the 1st, 2nd lighting means supplied to an illumination means as a 2nd pulse signal.

  Preferably, the constant frequency is 50 Hz or more. It is possible to suppress flickering when the lighting means is turned on.

  Preferably, the illumination unit includes an LED as a light source.

  More preferably, the first and second transistors of the first and second transistors are arranged so that the sum of the first and second pulse amplitudes of the amplified first and second pulse signals does not exceed the peak current value of the illumination means. The collectors are both connected to the cathode side of the LED through first and second constant current diodes that allow a current of a certain amount or less to flow.

  More preferably, the first and second transistors of the first and second transistors are arranged so that the sum of the first and second pulse amplitudes of the amplified first and second pulse signals does not exceed the peak current value of the illumination means. The collectors are both connected to the cathode side of the LED via first and second resistors that allow a current of a certain amount or less to flow.

  As described above, according to the present invention, it is possible to provide an illumination control device that ensures sufficient driving energy to be output without increasing the burden on the illumination device when imaging is performed using the illumination device. it can.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a perspective view from the back of the imaging device 1 including the illumination control device of the present embodiment. FIG. 4 is a front view of the imaging apparatus 1. 5 and 6 are circuit configuration diagrams of the imaging apparatus 1. The imaging device 1 will be described as a digital camera. FIG. 7 shows the waveform of the pulse signal output from each part.

  The part related to imaging of the imaging apparatus 1 includes an optical viewfinder 11, an LED on button 12, a release button 14, a continuous shooting button 15, a moving image button 16, an LCD monitor 17, and an illumination LED 31. The optical viewfinder 11 is a device that can optically observe a subject image. The subject image can also be displayed on the LCD monitor 17 as an image picked up by the image pickup block 22 composed of an image pickup device such as a CCD (not shown).

  When the LED on button 12 is pressed, the LED on switch 12a is turned on, and the illumination LED 31 is turned on at the time of exposure or the like. When the release button 14 is half-pressed, the photometry switch 13a is turned on to perform photometry, distance measurement, and focusing operation. When the release button 14 is fully pressed, the release switch 14a is turned on to perform imaging. When the continuous shooting button 15 is pressed, the continuous shooting switch 15a is turned on, and while the release switch 14a is turned on, a plurality of subjects such as three frames per second are imaged in succession. The The moving image button 16 captures an image of a subject at a recording frame interval while the release switch 14a is on.

  The illumination LED 31 is an illumination device that is lit during an exposure time in accordance with the exposure timing and supplies an appropriate amount of light to the subject when the surroundings are dark. The illumination LED 31 is driven by a pulse signal. The pulse signal is a rectangular wave signal that is repeatedly turned on and off at a constant period (reciprocal of the duty frequency). This duty frequency is preset in the CPU 21, but may be changed by the user. . The pulse signal supplied to the illumination LED 31 will be described later.

  The ratio of the time length of the ON state in one cycle of the pulse signal is represented by the duty ratio. When the illumination LED 31 is used, the CPU 21 outputs two types of signals during the exposure time during which the imaging operation is performed. The first is a first control signal for outputting a first pulse signal having a first pulse amplitude I1, a first pulse width τ1, and a first duty ratio D1 (0% <D1 <100%) from a first lighting circuit 33a described later. The second control is to output a second pulse signal having a second pulse amplitude I2, a second pulse width τ2, and a second duty ratio (0% <D2 <100%) from a second lighting circuit 33b described later. Signal. It is desirable that the duty frequency f1 of the first and second pulse signals is the same, and that the lighting LED 31 does not flicker at 50 Hz or more, that is, the period C1 (reciprocal of the duty frequency f1) is 1/50 second or less. The first duty ratio D1 is larger than the second duty ratio D2 (D1> D2). No pulse signal is output outside the exposure time (duty ratio: 0%). Therefore, the CPU 21, the first and second lighting circuits 33a and 33b have a pulse signal output function for outputting a pulse signal with the first and second duty ratios D1 and D2.

  In the present embodiment, a mode is described in which the illumination LED 31 is forcibly turned on when the user turns on the LED on switch 12a. However, the illumination LED 31 is automatically turned on from the exposure value obtained by photometry. It may be a form to be made.

  Various outputs corresponding to the input signals of these switches are controlled by the CPU 21. The input / output signals of the CPU 21 will be described with reference to the circuit configuration diagram of FIG. On / off information of the LED on switch 12a, photometry switch 13a, release switch 14a, continuous shooting switch 15a, and moving image switch 16a is input to the ports P12, P13, P14, P15, and P16 of the CPU 21 as 1-bit digital signals, respectively. The The imaging block 22, the subject photometric operation is performed to calculate the exposure value, the AE unit 23 that calculates the aperture value and the exposure time necessary for photographing based on the exposure value, and the distance measurement is performed based on the distance measurement result. The AF unit 24 that performs a focusing operation necessary for photographing inputs and outputs signals at ports P3, P4, and P5, respectively.

  In the port P20, a first lighting circuit 33a that supplies a first pulse signal for lighting the illumination LED 31 is connected. The CPU 21 outputs the first control signal via the port P20 and outputs the first pulse signal having the cycle C1, the first pulse amplitude I1, the first pulse width τ1, and the first duty ratio D1 (= τ1 / C1) as the first. It is generated by the lighting circuit 33a.

  In the port P21, a second lighting circuit 33b that supplies a second pulse signal for lighting the illumination LED 31 is connected. The CPU 21 outputs the second control signal via the port P20 and outputs the second pulse signal having the cycle C1, the second pulse amplitude I2, the second pulse width τ2, and the second duty ratio D2 (= τ2 / C1) to the second. It is generated by the lighting circuit 33b.

  Two pulse signals (first and second pulse signals) are supplied to the illumination LED 31. The first control signal output from the port P20 of the CPU 21 is supplied to the illumination LED 31 as the first pulse signal through the first lighting circuit 33a and the first constant current diode 36a. The second control signal output from the port P21 of the CPU 21 is supplied to the illumination LED 31 as a second pulse signal through the second lighting circuit 33b and the second constant current diode 36b. The illumination LED 31 to which the first and second pulse signals are supplied is turned on with the same effect as when a pulse signal obtained by adding two pulse signals is supplied.

  The first and second pulse amplitudes I1 and I2 indicating the maximum current values of the first and second pulse signals are such that the combined third pulse amplitude I3 (I1 + I2) does not exceed the peak drive current value of the LED 31 for illumination. As restricted respectively. That is, the current value is limited by the first and second constant current diodes 36a and 36b connected to flow a current of a certain amount or less. However, the circuit configuration of the first and second constant current diodes 36a and 36b may be a circuit configuration using first and second resistors 37a and 37b serving the same purpose as shown in FIG.

  The first lighting circuit 33a includes a first transistor Tr1 and first and second bias resistors 34a and 35a. The first transistor Tr1 is an NPN transistor connected to generate the first pulse signal supplied to the lighting LED 31 by switching, and the base is connected to the port P20 via the first resistor 34a. The second resistor 35a is connected between the base and the emitter.

  The second lighting circuit 33b has the same configuration as that of the first lighting circuit 33a, and includes a second transistor Tr2 and third and fourth bias resistors 34b and 35b. The second transistor Tr2 is an NPN transistor connected to generate a second pulse signal supplied to the lighting LED 31 by switching, and has a base connected to the port P21 via the third resistor 34b. The fourth resistor 35b is connected between the base and the emitter.

  In the present embodiment, the collectors of the first and second transistors Tr1 and Tr2 are connected to the cathode side of the illumination LED 31 via the first and second constant current diodes 36a and 36b.

  When the ON signal is input to the port P13 by turning on the photometric switch 13a (pressing the release button 14 halfway), the CPU 21 drives an AE sensor (not shown) of the AE unit 23 to A photometric operation is performed to calculate an exposure value, and based on this exposure value, an aperture value and an exposure time necessary for photographing are calculated. Further, the CPU 21 drives an AF sensor (not shown) of the AF unit 24 to perform distance measurement. Based on the distance measurement result, a lens control circuit (not shown) of the AF unit 24 is driven to displace the lens position in the optical axis direction and adjust the focal length.

  When the release switch 14a is turned on (the release button 14 is fully pressed) and an on signal is input to the port P14, the CPU 21 performs an imaging operation. That is, an aperture mechanism (not shown) is driven according to the above-described aperture value, a shutter mechanism (not shown) is released at a predetermined shutter speed, and an imaging block 22 such as a CCD is driven to perform exposure.

  When the release switch 14a is in the on state, the LED on switch 12a is in the on state, and an on signal is input to the ports P12 and P14, the CPU 21 adjusts the first and first timings in accordance with the exposure timing of the imaging block 22. 2 control signals are output, and the first and second pulse signals light the illumination LED 31 via the first and second lighting circuits 33a and 33b and the first and second constant current diodes 36a and 36b.

  When the release switch 14a is in an on state, the continuous shooting switch 15a is in an on state, and an on signal is input to the ports P14 and P15, the CPU 21 continues while the release switch 14a is on. Imaging is performed at regular intervals, that is, the shutter mechanism is released, the imaging block 22 is driven, and exposure is performed. Therefore, the CPU 21 has a continuous shooting control function for performing imaging of a subject twice or more continuously in time. When the moving image switch 16a, not the continuous shooting switch 15a, is turned on and an on signal is input to the ports P14 and P16, the CPU 21 records the frame interval for recording while the release switch 14a is kept on. Thus, the imaging block 22 is driven and exposed.

  When the release switch 14a is in the on state and both the LED on switch 12a and the continuous shooting switch 15a are in the on state, the CPU 21 first and within the exposure time that matches the exposure timing of the imaging block 22. The second control signal is output, and the first and second pulse signals light the lighting LED 31 via the first and second lighting circuits 33a and 33b and the first and second constant current diodes 36a and 36b.

  In accordance with the exposure time, the port P20 of the CPU 21 outputs a first pulse signal having a cycle C1, a first pulse amplitude I1, a first pulse width τ1, and a first duty ratio D1 via the first lighting circuit 33a. The port P21 of the CPU 21 outputs a second pulse signal having a cycle C1, a second pulse amplitude I2, a second pulse width τ2, and a second duty ratio D2 via the second lighting circuit 33b. The first and second pulse signals are output to the illumination LED 31 via the first and second constant current diodes 36a and 36b, respectively.

  The first and second pulse signals are simultaneously turned on. However, the second pulse signal may have a waveform timing at which the on-state starts and ends while the first pulse signal is on even if the on-state is not simultaneously turned on as in the present embodiment.

  The first and second pulse signals are pulse signals having first and second pulse widths τ1 and τ2, which are different in the same cycle C1, that is, first and second duty ratios D1 and D2. Therefore, the LED 31 for illumination to which both the first and second pulse signals are supplied receives a pulse signal equivalent to the pulse signal obtained by adding the two pulses of the first and second duty ratios D1 and D2 in the cycle C1. Will be.

  This will be described with reference to the timing chart of FIG. The timing chart of FIG. 7 shows waveforms that the first and second control signals output from the CPU 21 are output via the first and second lighting circuits 33a and 33b when the illumination LED 31 is lit during the exposure time. . (1) indicates the first pulse signal, (2) indicates the second pulse signal, and (3) indicates the pulse signal obtained by adding the first and second pulse signals. (4) shows a pulse signal equivalent to (3) in terms of drive energy. Between t11 and t12, a pulse signal obtained by adding the first and second pulse signals is input to the illumination LED 31. That is, an ON signal of the third pulse amplitude I3 obtained by adding the first pulse amplitude I1 and the second pulse amplitude I2 is supplied to the illumination LED 31. Accordingly, since a relatively large drive current (I3) is supplied to the illumination LED 31 during this period, the light emission level is relatively high. During the period from t12 to t13, the first pulse signal is supplied to the illumination LED 31. That is, the ON signal having the first pulse amplitude I1 is supplied to the illumination LED 31. Accordingly, since a relatively small drive current (I1) is supplied to the illumination LED 31 during this period, the light emission level is lower than that between t11 and t12.

  Between t13 and t14, since the pulse signal is turned off, the illumination LED 31 does not emit light. Similarly, during t14 to t17, t17 to t20, and t20 to t23, light emission with a relatively large amount of light, light emission with a relatively small amount of light, and no light emission are repeated. That is, during the exposure time, the illumination LED 31 repeats light emission with a relatively large amount of light, light emission with a relatively small amount of light, and no light emission.

  The driving energy M3 of the illumination LED 31 generated during one cycle C1 (t11 to t14) in the pulse signal (3) is generated during one cycle C1 (t11 to t14) in the first pulse signal (1). It is equal to the sum of the drive energy M1 of the illumination LED 31 and the drive energy M2 of the illumination LED 31 generated during one cycle C1 (t11 to t14) in the second pulse signal of (2). Accordingly, the pulse signal of (4) with the third pulse width τ3 and the third duty ratio D3 (= τ3 / C1) that is equal to the drive energy M3 with the period C1 (t11 to t14) and the third pulse amplitude I3. , (3) The drive energy of the pulse signal is equivalent. That is, the pulse signal (3) and the pulse signal (4) can cause the illumination LED 31 to emit an equivalent amount of light. The third pulse width τ3 is obtained as τ3 = τ2 + (τ1−τ2) × I1 / I3 from the first and second pulse widths τ1 and τ2 and the first and third pulse amplitudes I1 and I3.

  The longer the time for which the illumination LED 31 is driven with a large current, the more time it takes for the illumination LED 31 to be loaded, so the life of the illumination LED 31 may be shortened. The time (t11 to t12) for driving the illumination LED 31 with a relatively large drive current (I3) is compared with the illumination LED 31 in the equivalent pulse signal of (4). It is shorter than the time (t11 to t12 ′) for driving with a relatively large drive current (I3). Therefore, while realizing the same amount of light emission as when the illumination LED 31 is driven with the equivalent pulse signal of (4), the burden on the illumination LED 31 is not increased more than in the case of (4), that is, the life of the illumination LED 31 is increased. It becomes possible to use without shortening.

  Moreover, the temperature change of LED 31 for illumination in the case of pulse signals (3) and (4) is shown in FIG. When the rate of temperature rise per unit time of the LED 31 for illumination when the first and second pulse signals are both on (t11 to t12) is larger than the heat dissipation characteristics per unit time (rate of temperature drop) As shown in FIG. 8, the pulse signal obtained by adding the first and second pulse signals as in the present embodiment ((3) in FIG. 8) is equivalent to the equivalent pulse as shown in (4) in FIG. The temperature rise of the LED 31 for illumination can also be suppressed compared to the signal.

  When the release switch 14a is in the on state and both the LED on switch 12a and the moving image switch 16a are in the on state, the release switch 14a is in the on state and the LED on switch 12a and the continuous shooting switch are in the on state. As in the case where 15a is turned on, the first and second pulse signals are output within the exposure time.

  Next, the lighting control of the illumination LED 31 during continuous shooting (when the continuous shooting switch 15a is on) will be described with reference to the flowchart of FIG.

  When the power of the imaging device 1 is turned on in step S11, the duty frequency f1 of the first and second pulse signals is set in the CPU 21 in step S12. However, the duty frequency f1 may be set in advance. The continuous shooting switch 15a is turned on in advance.

  In step S13, it is determined whether or not the photometric switch 13a has been turned on. If the photometric switch 13a is not turned on, step S13 is repeated. If the photometric switch 13a is on, photometry is performed by driving the AE sensor of the AE unit 23 in step S14, and the aperture value and exposure time are calculated. Next, in step S15, the AF sensor of the AF unit 24 is driven to perform distance measurement, and the focusing operation is performed by driving the lens control circuit of the AF unit 24.

  In step S16, it is determined whether or not the release switch 14a is turned on. If the release switch 14a is not turned on, it is determined in step S17 whether or not the photometric switch 13a is turned on. If it is determined in step S17 that the photometric switch 13a is on, the process returns to step S16. If it is determined in step S17 that the photometric switch 13a has not been turned on, the process returns to step S13. If it is determined in step S16 that the release switch 14a is turned on, it is determined in step S18 whether the LED on switch 12a is turned on.

  If it is determined in step S18 that the LED on switch 12a is not turned on, the LED 31 is not driven during the exposure time corresponding to the release switch 14a, and the illumination LED 31 is turned off in step S20. Charge accumulation or exposure is performed. If it is in the ON state, the first and second pulses are output at the set first and second duty ratios D1 and D2 during the exposure time corresponding to the release switch 14a in step S16 in step S19. Then, the first and second pulse signals are supplied to the illumination LED 31 via the first and second constant current diodes 36a and 36b. In step S20, the charge accumulation of the CCD, that is, the exposure is performed with the illumination LED 31 turned on. Done.

  After the exposure time ends, in step S21, the illumination LED 31 lit in step S19 is turned off. That is, the duty ratios D1 and D2 of the output first and second pulse signals are set to zero. In step S22, the CCD input, that is, the charge accumulated in the CCD within the exposure time is moved, and in step S23, the moved charge is used as an image signal captured by the imaging block 22 as a video memory in the imaging apparatus 1. Is remembered. In step S24, the stored image signal is displayed on the LCD monitor 17.

  In step S25, it is determined whether or not the continuous shooting switch 15a is turned on. If the continuous shooting switch 15a is on, the process returns to step S16, and the next exposure is performed. If the continuous shooting switch 15a is not turned on, in step S26, the lighting control of the LED 31 for illumination during a series of continuous shooting ends.

  The flowchart in FIG. 9 can be replaced not only with continuous shooting but also with lighting control of the illumination LED 31 during moving image capturing (the moving image switch 16a is in an on state).

  Although the illumination device has been described as being based on light emission from an LED, it is possible to illuminate within the exposure time by pulse driving through a transistor circuit, and the temperature of the light emitting member increases due to continuous use, and the amount of light decreases due to temperature increase. The light emitting member may be used.

  As an embodiment of the present invention, the image pickup apparatus 1 has been described as a digital camera that picks up a subject with an image pickup device. However, the same effect can be obtained even with a silver salt camera.

It is a figure which shows the relationship between the temperature rise of LED, and light quantity reduction | decrease. It is a figure which shows the temperature change of LED by a time change in the case of DC drive and pulse drive. It is the perspective view seen from the back which shows the appearance of the imaging device of this embodiment. It is a front view of an imaging device. It is a circuit block diagram using the constant current diode of an imaging device. It is a circuit block diagram using resistance of an imaging device. It is a timing chart which shows waveforms, such as a signal which added the 1st and 2nd pulse signal and these signals. It is a chart which shows the temperature change of LED for illumination. It is a flowchart which makes LED light within the exposure time at the time of continuous shooting.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 11 Optical finder 12 LED on button 14 Release button 15 Continuous shooting button 16 Movie button 17 LCD monitor 22 Imaging block 23 AE part 24 AF part 31 LED for illumination
33a First lighting circuit 33b Second lighting circuit 36a First constant current diode 36b Second constant current diode

Claims (6)

Illumination means for lighting the subject by receiving a pulse signal having a constant frequency within the exposure time;
A first pulse signal having the constant frequency, a first duty ratio, and a first pulse amplitude; and a second duty ratio and a second pulse amplitude that are smaller than the first duty ratio at the constant frequency. An illumination control device for an imaging apparatus, comprising: a pulse signal output unit that supplies a second pulse signal including an on-state start and end point to the illumination unit while the pulse signal is in an on-state.   The pulse signal output means includes a CPU for outputting first and second control signals for outputting the first and second pulse signals, and the first and second control signals via the first and second transistors. The lighting control apparatus according to claim 1, further comprising first and second lighting units that supply the lighting unit as first and second pulse signals.   The lighting control apparatus according to claim 1, wherein the constant frequency is 50 Hz or more.   The illumination control apparatus according to claim 2, wherein the illumination unit includes an LED as a light source.   The first and second collectors of the first and second transistors are both set so that the sum of the first and second pulse amplitudes of the first and second pulse signals does not exceed the peak current value of the illumination means. The lighting control device according to claim 4, wherein the lighting control device is connected to the cathode side of the LED through first and second constant current diodes for supplying a predetermined amount of current or less. The first and second collectors of the first and second transistors are both set so that the sum of the first and second pulse amplitudes of the first and second pulse signals does not exceed the peak current value of the illumination means. The lighting control device according to claim 4, wherein the lighting control device is connected to the cathode side of the LED through first and second resistors that cause a certain amount of current to flow.

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