JP2017146505A - Light source control device and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a temperature of a heated member of a light emitting device by a simple configuration.SOLUTION: Light emission of a xenon tube 12 to be provided in a flash light emitting unit 11 of a camera 10 is controlled by a flash control circuit 15. A temperature corresponding to an ambient temperature is detected by a thermometer 17, and from the detected temperature and an output upon flashing of the xenon tube 12, a temperature of a Fresnel lens 14 to be heated by the light emission of the xenon tube 12 is estimated in a camera control circuit 16. A temperature estimation is sequentially calculated from a heat generation (heating) of the Fresnel lens 14 due to the output of the xenon tube 12, and cooling due to radiation from the Fresnel lens 14. The flash control circuit 15 is configured to control a light emission interval or output of the xenon tube 12 on the basis of the estimated temperature, and prevent the Fresnel lens 14 from melting to be deformed due to overheating.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a light source control device that controls a light source that emits light, and an imaging device that includes the light emission control device.

  The flash reflects light emitted from a light source such as a flash tube with a reflector and irradiates it through a diffuser plate, an optical filter, a Fresnel lens, and the like. The diffusion plate, the optical filter, and the Fresnel lens absorb a part of heat and light energy emitted from the light source, and the temperature rises. Further, there are cases where continuous shooting is performed by a camera with continuous flash emission, but in that case, heat may accumulate in these members, which may be a problem. In particular, the Fresnel lens has significant heat accumulation, and the material of the Fresnel lens is also made of a thermoplastic resin. Therefore, there is a possibility that various performance defects may occur when the temperature rises excessively.

  In order to suppress the performance degradation due to the heat of the Fresnel panel, a configuration has been proposed in which a plurality of vents are provided in the strobe device housing to connect the space on the Fresnel panel side and the space on the outside of the housing, and cooling is performed by natural convection ventilation. (See Patent Document 1). A strobe device is also known in which a prism is arranged close to the front surface of the discharge tube instead of using a reflector. However, in this configuration, the temperature of the reflector shade in contact with the prism is measured to detect the temperature. A configuration is proposed in which strobe charging is performed when the temperature is equal to or lower than a predetermined temperature, and when the temperature is higher than the predetermined temperature, the prism is cooled by heat dissipation after waiting for a predetermined time with a heat dissipation timer (see Patent Document 2). ).

JP2012-032822A JP 2001-117148 A

  However, in the configuration of Patent Document 1, when the temperature is high or the continuous light emission continues for a long time although the heat dissipation effect is enhanced, the heat dissipation is not always sufficient, and the performance of the Fresnel panel may still deteriorate. There is. Further, in the configuration of Patent Document 2, it is necessary to newly provide a thermometer near the prism itself and the light source, which is disadvantageous in terms of cost and space, and causes overheating of the thermometer or uneven light emission.

  An object of the present invention is to obtain a light-emitting device with good performance.

  The light source control device of the present invention includes a light source control means capable of controlling a light emission amount or output of a light source, a temperature corresponding to an outside temperature, and a temperature of a member heated by a light emission operation of the light source from the light emission amount or output of the light source And a temperature estimating means for estimating.

  The light source control means controls the light emission amount or output of the light source based on the estimated temperature of the member. The temperature estimation means sequentially calculates the estimated temperature from, for example, the light emission amount or output of the light source and cooling by heat radiation from the member. For example, the light source control device records in advance the temperature information characteristic by the light emission amount and / or output of the light source with respect to the member and the cooling characteristic by heat radiation. The light source control means controls, for example, a period during which light emission of the light source is prohibited based on the estimated temperature. The light source control device may further include overheat notification means for notifying the user of overheating of the member from the estimated temperature. The member includes any one of a Fresnel lens, a diffusion plate, and an optical filter that transmits light from the light source. The light source corresponds to, for example, a flash of the imaging device. A thermometer that measures the temperature corresponding to the outside air temperature is used, for example, for measuring the temperature of the AF sensor and / or measuring the temperature of the AE sensor.

  An imaging device according to the present invention includes the light source control device.

  Further, when the light source is configured as an automatic pop-up flash, storage of the flash may be prohibited when overheating of the member is detected from the estimated temperature.

  According to the present invention, a light emitting device with good performance can be obtained.

It is a block diagram which shows the structure of the light source control apparatus which is one Embodiment of this invention. It is a graph which shows a temperature change when an object is cooled by heat radiation. It is a graph which shows the mode of the temperature change of a to-be-heated member when light is continuously light-emitted at a short time interval without considering cooling of the to-be-heated member. FIG. 4 is a graph illustrating the case where the final temperature is made lower than the melting temperature T _f by relatively increasing the light emission interval with the same output (light emission amount) as in FIG. 3. It is a graph which shows a mode that the raise of the light emission interval (light emission prohibition period) is suppressed and the raise of the temperature T of a to-be-heated member is suppressed when it becomes necessary to double light emission during continuous light emission.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a light source control apparatus according to an embodiment of the present invention.

  The light source control device of the present embodiment controls, for example, flash emission of the camera 10. The flash light emitting unit 11 transmits a xenon tube (light source) 12, a reflector 13 that reflects light from the xenon tube 12, and light from the xenon tube 12 and reflected light from the reflector 13 to irradiate the subject. A Fresnel lens 14.

  The light emission timing and the light emission amount (output) of the xenon tube 12 are controlled by the flash control circuit 15, and the flash control circuit 15 is controlled based on a command from the camera control circuit 16 that controls the entire camera. The camera 10 includes a thermometer 17 that measures a temperature substantially corresponding to the outside air temperature. The camera control circuit 16 corrects an AF sensor (not shown) and an AE sensor (not shown) based on a signal from the thermometer 17. Make corrections.

  In addition, the camera control circuit 16 of the present embodiment estimates the temperature of the Fresnel lens 14 based on the signal from the thermometer 17 and the light emission amount (output) of the xenon tube 12 as described later, and flashes based on the estimated temperature. The control circuit 15 controls the light emission and / or light emission amount (output) of the xenon tube 12 and / or the light emission inhibition period and / or the light emission interval.

  Next, the principle and method of the temperature estimation process of the present embodiment will be described with reference to FIGS. In this embodiment, the temperature estimation process of the Fresnel lens is executed by, for example, the camera control circuit 16.

  When the xenon tube 12 emits light, flash light emitted from the xenon tube 12 is reflected directly or by the reflector 13 and then passes through the Fresnel lens 14 and is irradiated to the subject toward the outside. At this time, part of the heat generated from the xenon tube 12 and the energy of the light transmitted through the Fresnel lens 14 is absorbed by the Fresnel lens 14 and the temperature of the Fresnel lens 14 rises. On the other hand, since the Fresnel lens 14 is exposed to the outside air, heat is released from the surface to the outside air and is cooled.

FIG. 2 is a graph showing a temperature change when an object is cooled by heat radiation. According to Fourier's law, the heat flux is proportional to the temperature gradient in the heat flow direction, so that the temperature of the object decreases exponentially with time and gradually approaches the surrounding temperature. In FIG. 2, the horizontal axis is time, the vertical axis is temperature, T∞ is the ambient temperature (outside temperature), T ₀ is the initial temperature of the object (Fresnel lens 14), and T is the temperature change of the object (Fresnel lens 14). Represents. In the present embodiment, the temperature change during cooling of the Fresnel lens 14 of the camera is measured in advance, the cooling characteristic of the Fresnel lens 14 by heat radiation is obtained, and the characteristic value is recorded.

FIG. 3 is a graph showing the temperature change of the Fresnel lens 14 when the xenon tube 12 emits light continuously at short time intervals without considering cooling of the Fresnel lens 14. In FIG. 3, the horizontal axis represents time, the vertical axis represents temperature, T ₀ represents the initial temperature of the Fresnel lens 14, and T represents the temperature change of the Fresnel lens 14. As shown in FIG. 3, when the xenon tube 12 emits light, the temperature T of the Fresnel lens 14 increases by a substantially constant value, and decreases along the cooling characteristic (curve) of FIG. However, if the xenon tube 12 emits light after the temperature T of the Fresnel lens 14 rises and before it is cooled, the heat accumulated in the Fresnel lens 14 cannot be dissipated, and the temperature T gradually increases every time the xenon tube 12 emits light. To rise.

  Further, as the temperature of the Fresnel lens 14 increases, the temperature difference (temperature gradient) between the surface of the Fresnel lens 14 and the outside air increases, so the amount of heat released per unit time increases and the rate of temperature increase gradually decreases. Since the temperature rise of the Fresnel lens 14 due to one light emission of the xenon tube 12 under constant output (constant light emission amount) is substantially constant, if the temperature difference between the outside air exceeds a certain value due to the balance between heat dissipation and heat storage Even if light emission of the xenon tube 12 is repeated, the temperature T of the Fresnel lens 14 remains at a substantially constant temperature as shown in FIG.

The method of increasing the temperature varies depending on the output (light emission amount) of the xenon tube 12 and the light emission interval. If the output (light emission amount) is constant, the temperature increase rate decreases as the light emission interval increases, and reaches due to repeated light emission. The final temperature is also reduced. FIG. 3 illustrates a case where the light emission interval is relatively short and the final temperature exceeds the melting temperature T _f of the Fresnel lens 14. The state of temperature rise of the Fresnel lens 14 under a constant output (light emission amount) is measured in advance, and the characteristic value is recorded.

The current temperature T _n of the Fresnel lens 14 can be estimated by, for example, sequentially calculating the following equation (1) from the initial temperature of the Fresnel lens 14.
T _n = T _n−1 −h _c (T _n−1 −T∞) Δt + h _f W (1)

Here, the second term on the right side is a cooling term (heat radiation term) proportional to the temperature gradient between the Fresnel lens 14 and the outside air, and the third term is a heat generation term proportional to the output (heat generation amount) of the xenon tube 12 ( Heating term). T _n-1 is the temperature of the Fresnel lens 14 calculated last time, and T∞ is the outside air temperature (ambient temperature). T∞ is obtained directly or indirectly from the measured value of the thermometer 17. h _c is a characteristic value of cooling including the heat transfer coefficient, obtained from a measured value measured in advance, and recorded in a memory (not shown) of the camera 10. h _f is a characteristic value of heat generation for obtaining the heat generation amount of the Fresnel lens 14 from the output (light emission amount) of the xenon tube 12, and is obtained from a measured value measured in advance and recorded in a memory (not shown) of the camera 10. Has been. W is the output (light emission amount) of the actually emitted xenon tube 12, Δt is the elapsed time between the previous and current calculations (the repetition period of this process), and is recorded in the memory (not shown) of the camera 10. Has been. The initial temperature of the Fresnel lens 14 is the temperature of the thermometer 17 when the camera 10 is turned on, and is considered to be substantially equal to the outside air temperature T∞. In the formula (1), the time required for light emission is sufficiently shorter than Δt.

In the present embodiment, the temperature T of the Fresnel lens 14 is constantly calculated by, for example, estimation processing using the equation (1), and is monitored, so that the flash control circuit 15 emits light from the xenon tube 12 during continuous light emission. Or, control the light emission interval and output (light emission amount). As a determination method, for example, it is determined whether or not the estimated latest temperature T _n is lower than the threshold T _melt (T _n <T _melt ). Here, the threshold value T _melt is a value that allows for a safety factor in the melting temperature Tf of the Fresnel lens 14, for example. Note that the calculation of the temperature T may be started from the first light emission when the camera setting is “continuous flash photography”, but may be started after the first few shots. In addition, the calculation may be paused when the continuous flash photography is stopped. Further, by storing the history of calculation results in a volatile / nonvolatile memory, even if the continuity is once paused, the previous calculation result may be diverted when restarting in a short time.

FIG. 4 exemplifies a case where the final temperature is lower than the melting temperature T _f by relatively increasing the light emission interval with the same output (light emission amount) as in FIG. 3. For example, when it is determined from the above determination that the temperature T _n is larger than the threshold T _melt (T _n > T _melt ), the light emission interval is increased and the temperature T of the Fresnel lens 14 exceeds the melting temperature T _f. To prevent. When the temperature T _n becomes smaller than the threshold value T _melt (T _n <T _melt ), the light emission interval can be restored or shortened.

FIG. 5 shows the temperature T of the Fresnel lens 14 by increasing the emission interval (emission prohibition period) and extending the cooling time, for example, when it is necessary to double the emission amount during continuous emission. The control which suppresses a rise is illustrated. That is, the temperature T is prevented from exceeding the melting temperature T _f even if the light emission interval is substantially doubled to increase the light emission amount.

  As described above, according to the present embodiment, the temperature of the members constituting the light emitting device can be estimated from the temperature corresponding to the outside air temperature and the output (light emission amount) of the light source. In addition, since the temperature corresponding to the outside air temperature can be obtained by diverting a thermometer used for AF sensor correction or the like, it is not necessary to consider mounting a new sensor, and the configuration can be simplified. it can. Further, by controlling the light emission of the flash based on the estimated temperature, overheating of members constituting the flash can be prevented.

  In the present embodiment, the temperature of the heated member is estimated using equation (1), but the temperature estimation equation is not limited to equation (1). Further, when the flash is an automatic pop-up type, the storage may be prohibited when the estimated temperature is equal to or higher than a predetermined value, and control for preventing heat accumulation may be performed. In addition to the xenon tube, a light source such as an LED can be used as the light source. In the present embodiment, the Fresnel lens is described as an example of the member to be heated whose temperature is estimated. However, the member to be heated is stored by light emission from the light source and cooled by heat radiation to the outside air. Any member may be used. For example, when the light emitting unit includes a diffusion plate or an optical filter, the light source control may be performed by estimating the temperature of a member that transmits light from these light sources.

  A thermistor, a thermocouple, etc. are used for the thermometer of this embodiment, for example. The light source control device may further include an overheat notification unit that notifies the user of overheating of the heated member from the estimated temperature. Examples of the notification method include a visual method of displaying text information or graphical information on a display or lighting a lamp, and an auditory method such as a warning sound.

  In this embodiment, the camera has been described as an example. However, the present invention can be applied to any device including a thermometer capable of measuring a temperature corresponding to the ambient environment temperature and a light source that heats a member by light emission. For example, it can also be applied to mobile phones with cameras and smart phones.

10 Camera 11 Flash light emitting unit 12 Xenon tube (light source)
13 Reflector 14 Fresnel lens (heated member)
15 Flash control circuit 16 Camera control circuit 17 Thermometer

Claims (11)

A light source control means capable of controlling the light emission amount or output of the light source;
And a temperature estimation unit configured to estimate a temperature of a member heated by a light emission operation of the light source from a temperature corresponding to an outside air temperature and a light emission amount or output of the light source.   The light source control device according to claim 1, wherein the light source control unit controls a light emission amount or an output of the light source based on an estimated temperature of the member.   3. The light source control device according to claim 1, wherein the temperature estimation unit sequentially calculates the estimated temperature from a light emission amount or output of the light source and cooling due to heat radiation from the member.   The said light source control apparatus has recorded beforehand the temperature information characteristic by the light-emission quantity and / or output of the light source with respect to the said member, and the cooling characteristic by heat dissipation. Light source control device.   The light source control device according to claim 1, wherein the light source control unit controls a period during which light emission of the light source is prohibited based on the estimated temperature.   The light source control device according to claim 1, further comprising an overheat notification unit that notifies a user of overheating of the member from the estimated temperature.   The light source control apparatus according to claim 1, wherein the member includes any one of a Fresnel lens, a diffusion plate, and an optical filter that transmit light from the light source.   The light source control device according to claim 1, wherein the light source corresponds to a flash of an imaging device.   The light source control device according to claim 8, wherein a thermometer that measures a temperature corresponding to the outside air temperature is used for temperature measurement of an AF sensor and / or temperature measurement of an AE sensor.   An imaging apparatus comprising the light source control device according to claim 1.   The imaging device according to claim 10, wherein the light source is configured as an automatic pop-up flash, and housing of the flash is prohibited when overheating of the member is detected from the estimated temperature.

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