JP2005181810A - Illumination control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination control unit which, when photographing is carried out using an illuminating device, drives the illuminating device with a signal that has a waveform including no high frequency of a rectangular wave signal, which reduces an influence of various noises. <P>SOLUTION: The illumination control unit for an imaging device includes: an illuminating means for emitting light to a subject by receiving a sawtooth wave signal that has a fixed length of off-period between a fall time and rise time for the subsequent waveform during exposure; and a signal supply means for supplying the sawtooth wave signal to the illuminating means. The signal supply means includes: a rectangular wave signal output means for outputting the rectangular wave signal with a constant pulse amplitude and a constant pulse cycle; a waveform conversion means for converting a rectangular wave signal into the sawtooth wave signal that has a constant amplitude and a constant cycle and indicates the peak when the rectangular wave signal falls, and then outputting the thus converted signal; and a lighting means for supplying the sawtooth wave signal to the illuminating means via the transistor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an illumination control device in an imaging apparatus, and more particularly to improvement of a signal waveform for driving 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 driving, an energization off period is provided, so that it is possible to suppress an increase in LED temperature due to heat generated by light emission. FIG. 2 shows time on the horizontal axis, LED temperature rise in the case of DC drive (line (1) in FIG. 2), and LED temperature rise in the case of rectangular wave pulse drive ((2) in FIG. 2). It is a figure which shows the difference of a line. 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, in the rectangular wave pulse drive of the apparatus of Patent Document 1, the influence of the power line noise due to a sudden on / off signal change, the noise on the peripheral circuit due to the high frequency component contained in the rectangular wave, and the influence of the inrush current Occurs.

  Therefore, an object of the present invention is to provide an illumination control device that drives an illumination device with a signal having a waveform obtained by removing high-frequency components of a rectangular wave signal that reduces the influence of various noises when imaging is performed using the illumination device. That is.

  The illumination control device of the imaging device according to the present invention has a sawtooth wave signal having an off period of a certain time between the falling edge within the exposure time and the rising edge of the next waveform, or the rising edge of the next waveform instantly after the falling edge. Illuminating means for lighting the subject by receiving supply of a starting triangular wave signal, and signal supplying means for supplying a sawtooth wave signal or a triangular wave signal to the illuminating means. As a result, the waveform has an energization-off period like the rectangular wave signal, so that the temperature rise of the illumination means of the exposure apparatus can be suppressed, and the waveform is less affected by high-frequency components than when driven by the rectangular wave signal. The illumination means can be turned on by a sawtooth wave signal or a triangular wave signal.

  Preferably, the signal supply means includes a rectangular wave signal output means for outputting a rectangular wave signal with a constant pulse amplitude and a constant pulse period, and a waveform converting means for converting the rectangular wave signal into a sawtooth wave signal or a triangular wave signal and outputting the same. And a lighting means for supplying a sawtooth wave signal or a triangular wave signal to the lighting means via an amplifier. This makes it possible to convert the rectangular wave signal and supply a sawtooth wave signal or a triangular wave signal to the illumination means.

  More preferably, the amplitude and period of the sawtooth wave signal and the triangular wave signal are the same as the pulse amplitude and pulse period of the rectangular wave signal.

  Preferably, the waveforms of the sawtooth wave signal and the triangular wave signal show a peak when the waveform of the rectangular wave signal falls.

  More preferably, the waveform converting means includes an inverting amplifier circuit that converts a rectangular wave signal into an antiphase, and an integrating circuit that converts the antiphase rectangular wave signal into a sawtooth wave signal or a triangular wave signal. Thereby, it becomes possible to supply a sawtooth wave signal or a triangular wave signal having a peak timing in accordance with the ON state timing of the rectangular wave signal to the illumination means.

  More preferably, the output terminal of the first operational amplifier included in the inverting amplifier circuit is connected to the inverting input terminal of the second operational amplifier included in the integrating circuit, and the non-inverting input terminal of the first operational amplifier included in the inverting amplifier circuit includes the integrating circuit. It is connected to the non-inverting input terminal of the second operational amplifier.

  Preferably, the period of the sawtooth wave signal and the triangular wave signal is 1/50 second or less. Thereby, it becomes possible to suppress flickering of the illumination means.

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

  Preferably, the amplifying unit includes a transistor.

  As described above, according to the present invention, when imaging is performed using a lighting device, the lighting control device drives the lighting device with a signal having a waveform obtained by removing high-frequency components of a rectangular wave signal that reduces the influence of various noises. Can be provided.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a perspective view from the back of the imaging apparatus 1 including the illumination control apparatus according to the first embodiment. FIG. 4 is a front view of the imaging apparatus 1. FIG. 5 is a circuit configuration diagram of the imaging apparatus 1. 6 shows a circuit configuration diagram of the waveform conversion circuit of FIG. FIG. 7 shows a change in waveform in each part of the waveform conversion circuit. The imaging device 1 will be described as a digital camera.

  In the present embodiment, the definition of the pulse amplitude and the amplitude will be described by referring to the difference between the maximum value and the minimum value, that is, the width of vibration in any of a rectangular wave, a sawtooth wave, and a triangular wave signal. The pulse amplitude and pulse period are used for a rectangular wave signal, and the amplitude and period are used for other signals.

  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 sawtooth wave signal or a triangular wave signal. The sawtooth signal has an amplitude Vcc and a period C1, and an off period a1 is provided between the falling edge and the rising edge of the next waveform. The triangular wave signal has an amplitude Vcc and a period C1, and an off period is not provided between the falling time and the rising time of the next waveform, and the rising of the next waveform starts at the moment when the voltage is turned off due to the falling. The period C1 of the sawtooth wave signal and the triangular wave signal is preferably 1/50 second or less at which the lighting LED 31 does not flicker.

  The sawtooth wave signal or the triangular wave signal supplied to the illumination LED 31 is obtained by converting the rectangular wave signal output from the port P20 of the CPU 21 described later by the waveform conversion circuit 34. The ratio of the time length of the on state in one cycle of the rectangular wave signal is represented by a duty ratio D. When the illumination LED 31 is used, during the exposure time in which the imaging operation is performed, the CPU 21 has the same pulse amplitude Vcc as the amplitude Vcc of the sawtooth wave signal, the same pulse cycle C1 as the cycle C1 of the sawtooth wave signal, and the duty ratio. A rectangular wave signal is output at D (0% <D <100%), and no rectangular wave signal is output outside the exposure time. Here, the reciprocal number of the pulse period C1 of the rectangular wave signal is defined as a duty frequency f. The duty frequency f is set in the CPU 21 in advance, but may be changed by the user. The duty ratio D is set in a PWM timer function in the CPU 21 in accordance with a desired light amount to be irradiated on the subject. Therefore, the CPU 21 has a rectangular wave signal generation function.

  In the present embodiment, a mode in which the illumination LED 31 is forcibly turned on when the user turns on the LED on switch 12a will be described. However, the illumination LED 31 is automatically selected based on the magnitude of the exposure value obtained by photometry. It may be a form of lighting up.

  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.

  At the port P20, a waveform conversion circuit 34 that supplies a sawtooth wave signal or a triangular wave signal for turning on the illumination LED 31 is connected. The CPU 21 inputs a rectangular wave signal having a duty ratio D to the waveform conversion circuit 34 via the port P20.

  The waveform conversion circuit 34 includes an inverting amplification circuit 341 and an integration circuit 342. The inverting amplifier circuit 341 converts a rectangular wave signal (waveform at the time of in in FIG. 7) having a pulse amplitude Vcc and a pulse period C1 into a rectangular wave signal having an opposite phase (a waveform in FIG. 7A). The integration circuit 342 converts the rectangular wave signal having an opposite phase into a sawtooth wave signal or a triangular wave signal having an amplitude Vcc and a period C1 (waveform at the time of out in FIG. 7).

  The inverting amplifier circuit 341 includes resistors R11 and R12 and a first operational amplifier 3410, and the output rectangular wave signal has a pulse amplitude Vcc and a pulse with respect to the pulse amplitude Vcc and pulse period C1 of the input rectangular wave signal. It is comprised so that it may become a period C1 and an antiphase. A power supply voltage Vcc is applied to the first operational amplifier 3410. A rectangular wave signal as an input signal is input to the inverting input terminal of the first operational amplifier 3410 via the resistor R11. The non-inverting input terminal of the first operational amplifier 3410 is connected to a 1/2 Vcc power source. Further, it is connected to a non-inverting input terminal of a second operational amplifier 3420 of an integration circuit 342 described later. From the output terminal of the first operational amplifier 3410, a rectangular wave signal having the same amplitude, the same period, and an opposite phase as the rectangular wave signal at the time of input is output. The output terminal of the first operational amplifier 3410 is connected to the inverting input terminal of the first operational amplifier 3410 via the resistor R12.

  The integrating circuit 342 includes resistors R2 and R3, a capacitor C, a diode D1, and a second operational amplifier 3420, and is output with respect to a pulse amplitude Vcc and a pulse period C1 of an input anti-phase rectangular wave signal. The wave signal or the triangular wave signal is configured to have an amplitude Vcc and a period C1. Vcc is applied to the second operational amplifier 3420 as a power supply voltage. An inverted input rectangular wave signal, which is an input signal, is input to the inverting input terminal of the second operational amplifier 3420 via the resistor R3, and a resistor R2 and a diode D1 are connected in parallel with the resistor R3. The non-inverting input terminal of the second operational amplifier 3420 is connected to the non-inverting input terminal of the first operational amplifier 3410 of the inverting amplifier circuit 341. A sawtooth wave signal or a triangular wave signal is output from the output terminal of the second operational amplifier 3420. The output terminal of the second operational amplifier 3420 is connected to the inverting input terminal of the second operational amplifier 3420 through the capacitor C.

  When the resistor R2 connected in series and the diode D1 are connected in parallel to the resistor R3 between the output terminal of the first operational amplifier 3410 and the inverting input terminal of the second operational amplifier 3410, The output waveform is a sawtooth wave, and when there is no diode D1 and only the resistor R2 is connected in parallel with the resistor R3, the output waveform from the second operational amplifier 3420 is a triangular wave.

  The sawtooth wave signal or the triangular wave signal is supplied to the illumination LED 31 via the current limiting resistor 33, the transistor Tr1, and the limiting resistor 32 corresponding to the lighting means. The transistor Tr1 is an NPN transistor connected to amplify a sawtooth wave signal or a triangular wave signal supplied to the lighting LED 31, and has a base connected to the CPU 21 via the current limiting resistor 33 and the waveform conversion circuit 34. The emitter of the transistor Tr1 is grounded, and the collector is connected to the cathode of the illumination LED 31 via the limiting resistor 32. Moreover, the anode of the LED 31 for illumination is connected to the power supply Vcc. Therefore, the CPU 21, the waveform conversion circuit 34, the current limiting resistor 33, the transistor Tr1, and the limiting resistor 32 have a signal supply function of supplying a sawtooth wave signal or a triangular wave signal to the illumination LED 31.

  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 outputs a rectangular wave signal in accordance with the exposure timing of the imaging block 22. The sawtooth wave signal or the triangular wave signal that is output and converted by the waveform conversion circuit 34 lights the LED 31 for illumination.

  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 on and the LED on switch 12a and the continuous shooting switch 15a are both on, a rectangular wave signal is output from the CPU 21 for each exposure time.

  In accordance with the exposure time, the CPU 21 outputs a rectangular wave signal having a pulse period C1, a duty ratio D, and a pulse amplitude Vcc. The waveform conversion circuit 34 converts and outputs a rectangular wave signal into a sawtooth wave signal or a triangular wave signal having a period C1 and an amplitude Vcc. The sawtooth wave signal or the triangular wave signal is supplied to the illumination LED 31 through the current limiting resistor 33, the transistor Tr1, and the limiting resistor 32.

  A sawtooth wave signal or a triangular wave signal is a signal obtained by removing a high frequency component from a rectangular wave signal. Accordingly, while the illumination LED 31 is turned on by the sawtooth wave signal or the triangular wave signal from which the high frequency component has been removed, the peripheral circuit due to the noise and the high frequency component of the power supply line is compared with the case where the illumination LED 31 is turned on by the rectangular wave signal. It becomes possible to reduce the influence of noise on and the inrush current.

  Further, by repeating the continuous blinking operation with the sawtooth wave signal or the triangular wave signal during the exposure time, the effect of suppressing the temperature rise of the illumination LED 31 can be obtained in the same manner as the driving of the illumination LED 31 by the rectangular wave signal. . Furthermore, the sawtooth wave signal or triangular wave signal supplied during the exposure time has a constant amplitude Vcc, so that the amplitude is increased with time during the exposure time, such as stable light emission, instantaneous light quantity supply, and circuit simplification. There is a merit compared to the case of supplying a triangular wave signal or the like by changing.

  Next, the lighting control of the LED 31 for illumination 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 f of the rectangular wave signal is set in the CPU 21 in step S12. However, the duty frequency f may be set in advance.

  In step S13, it is determined whether or not the photometric switch 13 is 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 has not been turned on, it is determined in step S17 whether or not the photometry switch 13a has been 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 illumination 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. CCD charge accumulation, that is, exposure is performed. If it is in the ON state, a rectangular wave signal is output at the set duty ratio D (0% <D <100%) during the exposure time corresponding to the release switch 14a of step S16 in step S19. The rectangular wave signal is converted into a sawtooth wave signal or a triangular wave signal by the waveform conversion circuit 34, and the sawtooth wave signal or the triangular wave signal is supplied to the illumination LED 31 via the current limiting resistor 33, the transistor Tr1, and the limiting resistor 32, and the step. In S20, charge accumulation of the CCD, that is, exposure, is performed with the illumination LED 31 turned on.

  After the exposure time ends, in step S21, the illumination LED 31 lit in step S19 is turned off. That is, the duty ratio D of the rectangular wave signal output from the CPU 21 is set to 0%. 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 of FIG. 8 can be replaced not only with continuous shooting but also with lighting control of the illumination LED 31 at the time of moving image capturing (the moving image switch 16a is in an on state).

  In the present embodiment, the form in which the pulse amplitude and the pulse period of the rectangular wave signal are the same as the amplitude and period of the sawtooth wave signal and the triangular wave signal has been described, but a different form may be used. This is because the same effect can be obtained by performing the circuit configuration with the pulse amplitude and pulse period of the rectangular wave signal in accordance with the amplitude and period of the desired sawtooth wave signal and triangular wave signal.

  In addition, the illumination device has been described as being based on the light emission of the LED, but it is illuminated within the exposure time by rectangular wave drive through a transistor circuit, and the temperature of the light emitting member rises by continuous use, and the light quantity decreases by the temperature rise. Such other light emitting members 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 a rectangular wave 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 of the imaging device of embodiment. It is a circuit block diagram of a waveform conversion circuit. The change of the waveform of the signal in each part of a waveform conversion circuit is shown. It is a flowchart which performs lighting control of LED for illumination 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
34 Waveform conversion circuit

Claims (9)

The subject is supplied with a sawtooth wave signal having a fixed off period between the falling edge and the rising edge of the next waveform within the exposure time, or a triangular wave signal that immediately starts rising of the next waveform after the falling edge. Lighting means for turning on,
An illumination control apparatus for an imaging apparatus, comprising: a signal supply unit that supplies the sawtooth wave signal or the triangular wave signal to the illumination unit.   The signal supply means includes a rectangular wave signal output means for outputting a rectangular wave signal with a constant pulse amplitude and a constant pulse period, and a waveform conversion for converting the rectangular wave signal into the sawtooth wave signal or the triangular wave signal and outputting it. The lighting control apparatus according to claim 1, further comprising: a lighting unit that supplies the sawtooth wave signal or the triangular wave signal to the lighting unit via an amplification unit.   The illumination control device according to claim 2, wherein the sawtooth wave signal and the triangular wave signal have the same amplitude and cycle as the pulse amplitude and pulse cycle of the rectangular wave signal.   The lighting control device according to claim 2, wherein the waveforms of the sawtooth wave signal and the triangular wave signal show a peak when the waveform of the rectangular wave signal falls.   The waveform converting means includes an inverting amplifier circuit for converting the rectangular wave signal into an antiphase, and an integrating circuit for converting the antiphase rectangular wave signal into the sawtooth wave signal or the triangular wave signal. Item 3. The lighting control device according to Item 2.   The output terminal of the first operational amplifier included in the inverting amplifier circuit is connected to the inverting input terminal of the second operational amplifier included in the integrating circuit, and the non-inverting input terminal of the first operational amplifier included in the inverting amplifier circuit includes the integrating circuit. The lighting control device according to claim 5, wherein the lighting control device is connected to a non-inverting input terminal of the second operational amplifier.   The lighting control device according to claim 1, wherein a period of the sawtooth wave signal and the triangular wave signal is 1/50 second or less.   The illumination control apparatus according to claim 1, wherein the illumination unit includes an LED as a light source. The lighting control device according to claim 2, wherein the amplification unit includes a transistor.

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