JPH0395977A - Led illuminator - Google Patents

Abstract

PURPOSE:To compensate the quantity of emission of an LED so as to obtain an always stable illuminance by adjusting the supply wave to the LED based on the quantity of photodetection by a photodetector, using an LED as a light source, so as to control the quantity of emission constant. CONSTITUTION:A photodetecting circuit part 19 is a circuit consisting of a photodetector 12, an operation amplifier 20, and a resistance 21, and this converts the photodetected currents obtained by the photodetector 12 into voltage. A photodetection controllers 18 inputs the input voltage from the photodetecting circuit 19 and the reference voltage from a reference power source 22 into an operation amplifier 24 so as to differentially amplifies them, whereby it gets the voltage VA in accordance with the photodetected currents by the photodetector 12. What is more, a variable resistance 23 adjusts the quantity of photodetection of an LED 9. An emission driving part 17 adjusts the supply currents to the LED 9 according to the magnitude of voltage VA so as to control the quantity of emission constant. Monitoring the forward voltage VF of LED 9, the operation amplifier 28 controls the output according to the monitor voltage and the voltage VA. Thus, even if temperature or power source voltage changes or the light source deteriorates, the illuminance of an object 2 becomes always constant.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a lighting device suitable for illuminating an object in, for example, an image processing system. (hereinafter referred to as rLED).

For example, in an image processing system, in order to recognize the shape and position of an object, it is necessary to take an image of the object, convert it into an image, and calculate feature quantities such as area and perimeter of the binary image of the human image. Methods such as extracting the data and comparing it with standard patterns are used. When photographing this object, it is necessary to provide appropriate illumination to the object, but conventionally, as this type of illumination device,
Fluorescent lamps or halogen bulbs are commonly used as light sources.

Problems to be Solved by the Invention> However, this type of light source has a common problem of extremely short lifespan. Fluorescent lamps also have disadvantages such as the fact that the brightness takes a characteristic value, making it impossible to adjust the illuminance to the optimum value, while light bulbs deteriorate faster and shorten their lifespan when the brightness is increased to adjust the illuminance. There is.

Furthermore, if the temperature or power supply voltage fluctuates or the light source deteriorates, the brightness will fluctuate and the brightness of the input image will change, causing the shape of the binary image to fluctuate in size and its features to change as well. Put it away. For this reason, there are problems such as recognition≧s easily occurring, leading to a decrease in recognition accuracy. This invention was made focusing on the above problem, and
By constructing an illumination device using D, it is an object of the present invention to realize a long life and stabilize the illuminance, thereby enabling highly accurate image processing.

Means for Solving the Problems> The lighting device according to the present invention uses an LED as a light source for illuminating an object, a light receiving element for receiving reflected light from the object, and a light receiving element using the light receiving element. The illumination control section adjusts the current supplied to the LED based on the amount of light received to control the amount of light emitted to a constant value.

<Function> Since an LED is used as a light source, the lifespan is significantly longer than conventional examples using fluorescent lamps or halogen light bulbs.

Furthermore, even if the brightness fluctuates due to changes in temperature or power supply voltage, or changes in the light source over time, this is detected by the amount of reflected light and the amount of light emitted by the LED is corrected, so stable illuminance can always be obtained. This enables highly accurate image processing.

Embodiment> FIG. 1 shows an image processing system in which an illumination device 1 according to an embodiment of the present invention is used. and an image processing device 4 that processes the human image obtained by the imaging device 3 to recognize the shape of the object 2 and the like.

The lighting device 1 consists of a light source section 5 and a lighting control section 6, and an example of the circuit configuration of the lighting control section 6 is specifically shown in FIG. 3, which will be described later.

The light source unit 5 has a printed circuit board 8 disposed in the lower opening of the case 7, and a plurality of LEDs 9 arranged in a circular pattern around the optical axis 10 on the lower surface of the printed circuit board 8, as shown in FIG. and soldered to that pattern. Another printed circuit board l1 is arranged inside the printed circuit board 8,
A light receiving element 12 such as a photodiode is arranged on the lower surface of this printed circuit board 11 and soldered to the pattern. The printed pattern of each printed circuit board 8.11 is electrically connected to the lighting control unit 6 by a lead wire l3.

Circular through holes 15 and 16 are formed in the center of the printed circuit board 8 and the center of the upper wall 14 of the case 7, and the imaging device 3 is positioned above the through holes 16 to enable imaging of the object 'jlyJ2. . Further, the photodiode I2 is connected to the LED9.
It is located behind the through hole 15 and is configured to receive reflected light from the object 2, but not direct light from each LED 9.

FIG. 3 shows an example of a specific circuit configuration of the illumination control section 6, in which the light emission drive section 17. The light emission control unit 1B and the light receiving circuit unit 19 perform fIl.

The light-receiving circuit section 19 is a circuit including a light-receiving element 12, an operational amplifier 20, and a resistor 21, and converts the light-receiving current obtained by the light-receiving element 12 into a voltage.

The light emission control unit 18 is a circuit consisting of a reference power supply 22, a variable resistor 23, an operational amplifier 24, and two resistors 25, 26, and is configured to control the input voltage from the light receiving circuit 19 and the reference power supply 22.
is input to the operational amplifier 24 and differentially amplified, thereby obtaining a voltage vA (voltage at point A in the figure) corresponding to the light-receiving current by the light-receiving element 12. Note that the variable resistor 23 is used to adjust the amount of light emitted from the LED 9.

The light emitting drive unit 17 includes two operational amplifiers 27 and 28, a transistor 29, three resistors 3o31 and 32, and a DC power supply 3.
3, the circuit adjusts the current supplied to the LED 9 according to the magnitude of the voltage vA, thereby controlling the amount of light emitted to a constant value. Note that the operational amplifier 27 is an LED, which is a nonlinear element.
9 is monitored, and the operational amplifier 2B controls its output according to the monitored voltage and the voltage VA.

In the above precautions, the temperature and power supply voltage are fluctuating and the LE
When the amount of light emitted by D9 increases, the amount of light reflected from the object 2 also increases, and the current received by the photodiode 12 increases. Therefore, the voltage VA at point A in the light emission control section 18 decreases, and in conjunction with this, the voltage 8 at point B in the light emission drive section 17 also decreases, so the current supplied to the LED 9 is restricted and the amount of light emitted is reduced. decreases and is controlled to a constant amount of light emission (illuminance).

Further, when the amount of light emitted from the LED 9 decreases due to fluctuations in temperature and power supply voltage, the amount of light reflected from the object 2 also decreases, and the current received by the photodiode 12 decreases. For this reason, the voltage vA at point A in the light emission control unit l8 increases, and in conjunction with this, the voltage VB at point B in the light emission drive unit 17 also increases, so the current to the LED 9 increases and the amount of light emission increases. Controlled to a constant amount of light emission (illuminance).

In this way, even if the temperature or power supply voltage fluctuates or the light source deteriorates, the illuminance of the object 2 will always remain constant, so the brightness of the input image obtained by the imaging device 3 will also remain constant, and the binary image The shape does not change, nor do its features. Therefore, no recognition errors occur, and highly accurate image processing can be achieved.

Effects of the Invention> As described above, the present invention uses an LED as a light source for illuminating an object, receives reflected light from the object with a light receiving element, and adjusts the current supplied to the LED based on the amount of received light. The amount of light emitted by the LED is controlled to a constant level, resulting in a longer lifespan, and even if there are fluctuations in temperature, power supply voltage, or even changes in the light source over time, the amount of light emitted by the LED is corrected to maintain a stable state at all times. This invention achieves remarkable effects such as obtaining illumination and enabling highly accurate image processing.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an image processing system using a lighting device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing an arrangement of LEDs on a printed circuit board, and FIG. 3 is an explanatory diagram showing an arrangement of LEDs on a printed circuit board. FIG. 2 is an electric circuit diagram showing an example of a circuit configuration. 1...Lighting device 6...Lighting control section 9...
...LED 12...light receiving element? 3
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Claims (1)

[Claims] An illumination device using an LED as a light source for illuminating an object, comprising: a light receiving element for receiving reflected light from the object; A lighting device using a light emitting diode, comprising a lighting control section that controls the amount of light emitted to a constant level by adjusting the supplied current.