JP2004163249A - Method for measuring quantity of light of led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring the quantity of light of LEDs of an LED print head for exposing a photosensitive body mounted to an image forming device and capable of reducing exposure variations in the surface of the photosensitive body even when a set current value of each LED is regulated directly according to a measured value of the acquired quantity of light of each LED. <P>SOLUTION: Light from an LED 7 is received by a sensor 14 having constant sensitivity via a filter 15 matched with the specific spectral sensitivity characteristics of the material of the photosensitive body, and its quantity of light is outputted as a measured value. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for measuring the light amount of an LED used for exposing a photosensitive member mounted on an electrophotographic image forming apparatus such as a copying machine, a facsimile, and a printer. The present invention relates to a method for measuring the amount of light for each LED in an LED print head.
[0002]
[Prior art]
Generally, an image forming apparatus is equipped with a drum-shaped photoreceptor rotatable about an axis, and an LED print head that is opposed to the surface of the photoreceptor at a predetermined interval and extends in the axial direction. A large amount of light corresponding to the gradation of each pixel is irradiated from each of a large number of LEDs regularly arranged on the LED print head toward the photoconductor, thereby exposing the photoconductor surface to a desired bright potential. Thus, an electrostatic latent image corresponding to the input image is formed. As each LED, for example, an Al-Ga-As-based LED is generally used, which has high luminous efficiency, but has a main luminous band (at a wavelength of about 780 nm) where a main luminous peak exists, and a sub-luminous peak separately from this. Sub-emission band (wavelength around 870 nm).
[0003]
By the way, in the manufacturing stage of the image forming apparatus, it is usual to finely adjust the set current value for each LED in order to equalize the amount of light per unit time between the LEDs in the attached LED print head. Therefore, it is necessary to grasp the light amount of each LED in advance, and in grasping the light amount, the method of measuring the light amount for each LED is extremely important.
[0004]
In the conventional light quantity measuring method, a sensor such as a PIN photodiode having a constant sensitivity regardless of the wavelength range receives light from the LED and outputs the light quantity, and the output light quantity (measured value) Includes not only the main light emission band described above but also the sub light emission band. However, since the amount of light in the sub-emission band varies not only between the LEDs but also hardly contributes to the exposure of the photoconductor, if the amount of light is included in the measured value, the LED will reach an appropriate set current value. Cannot be adjusted, and the measured value cannot be used. For such inconvenience, in order to positively exclude the light amount in the sub-emission band from the measured value, a band-pass filter that blocks light in the sub-emission band and transmits light in the main emission band with high efficiency is used. Thus, a method of receiving light with a sensor has been proposed (for example, see Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-158129 A (Page 4-5, FIG. 1-4)
[0006]
[Problems to be solved by the invention]
However, although an LED (LED print head) substantially forms a pair with a photoconductor in an image forming apparatus, unlike a semiconductor laser, the half-width shows a wide wavelength distribution of about 40 nm. Depending on the spectral sensitivity characteristics of the photoreceptor, that is, the difference in the material of the photoreceptor, even if the set current value of each LED is adjusted in accordance with the measurement value of each LED light amount obtained by the above light amount measurement method, There is a problem that the exposure amount on the surface, that is, the light potential varies, and the quality of image formation is hindered. The reason will be described below with reference to FIG.
[0007]
FIG. 2 is a diagram showing the spectral sensitivity characteristics of the photoconductor for each material. Here, as the material of the photoconductor, OPC (organic photoconductor), a-Si (amorphous silicon), and Se (Se) -based Se-Te (selenium-tellurium) are representatively mentioned. The hatched portions in the drawing are the main light emission bands in an Al-Ga-As-based LED as an example. Conventionally, in the case of OPC, which is the most common, the sensitivity is almost constant over a wide wavelength range, as shown by the broken line in the figure, and particularly the sensitivity is constant in the main light emission band. On the other hand, in the case of a-Si, as shown by the solid line in the figure, the sensitivity is high over a wide range of wavelengths, but the change in sensitivity is remarkable according to the wavelength, especially in the main emission band. In the case of Se-Te, the sensitivity in the main emission band is the lowest and the change is large, as indicated by the dashed line in the figure.
[0008]
Therefore, when the photoreceptor is a-Si or Se-Te, the change in the photoreceptor sensitivity in the main emission band is large. With the light from the LED whose set current value is adjusted as it is, the exposure amount on the surface of the photoreceptor varies, and the above problem occurs. On the other hand, when the photoconductor is OPC, since the photoconductor sensitivity in the main light emission band is constant, the exposure amount on the photoconductor surface does not vary, and the above problem does not occur.
[0009]
In view of the above, the present invention has been made in view of the above-described problem, and the LED of a LED print head for exposing a photosensitive member mounted on an image forming apparatus is directly used in accordance with the measured value of each obtained LED light amount. It is another object of the present invention to provide a light amount measuring method capable of reducing the variation in the exposure amount on the photoreceptor surface even when the set current value of each LED is adjusted.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for measuring the light amount of an LED according to the present invention is a method for measuring the light amount of an LED in an LED print head in which a large number of LEDs for exposing a photoreceptor are arranged, Light from the LED is received by a sensor having a constant sensitivity via a filter adapted to the spectral sensitivity characteristic of the photoconductor, and the amount of light is output. As a result, the measured value of the amount of light of each LED obtained corresponds to the spectral sensitivity characteristic of the photoconductor. Therefore, even if the set current value of each LED is adjusted in accordance with these measured values, Variations in surface exposure can be suppressed.
[0011]
For example, the filter preferably has a different transmittance for each predetermined wavelength. Further, it is suitable for a photoreceptor having high sensitivity in the main light emission band of the LED but having a large change in sensitivity. In particular, the photoreceptor is preferably amorphous-silicon.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a main part of a light quantity measuring device adopting the LED light quantity measuring method of the present invention. In the figure, reference numeral 1 denotes an LED print head, which includes a large number of LEDs 2 regularly arranged on a straight line, and terminals (not shown) for supplying a current to each of the LEDs 2. Actually, each LED 2 is housed in a chip-shaped LED head 3 at a predetermined number.
[0013]
Such a light quantity measuring device for measuring the light quantity of each of the LEDs 2 of the LED print head 1 is roughly composed of a light emission signal transmission unit 11 connected to a terminal of the LED print head 1 and giving a light emission signal to each LED 2, and an LED print head 1 And a light-collecting unit 13 such as a lens that collects light emitted by the LEDs 2, and a light from the light-collecting unit 13. , A sensor 15 for detecting the amount of light and converting it into an electric signal, a filter 15 disposed on the light receiving surface of the sensor 14, and a detection signal processing unit 16 for receiving the electric signal from the sensor 14 and performing predetermined processing. Be composed. Note that the entire measurement operation is controlled by a control unit (not shown) such as a CPU based on an input operation.
[0014]
Here, the sensor 14 has a constant sensitivity regardless of the wavelength range, and for example, a PIN photodiode is preferable. Further, the filter 15 is characteristic of the present embodiment, and has a light transmittance matching the spectral sensitivity characteristic specific to the material of the photoconductor paired with the LED print head 1 in the image forming apparatus. Specifically, when the photosensitive member is made of a material having a spectral sensitivity characteristic in which the sensitivity changes in the main light emission band of the LED 2 in accordance with the wavelength, for example, a-Si, the filter 15 is configured such that the transmittance is different for each predetermined wavelength. Has become.
[0015]
A method for measuring the light amount by the light amount measuring device having such a configuration will be described below. The holding unit 12 is driven by an instruction from the control unit, and one LED 2 is positioned on the optical axis of the light collecting unit 13, the filter 15, and the sensor 14. Next, a light emission signal is given to the LED 2 from the light emission signal transmission unit 11 to cause the LED 2 to emit light. Light from the LED 2 is condensed through the light condensing unit 13, and is received by the sensor 14 via the filter 15. The sensor 14 detects the amount of light received, converts it into an analog electric signal, and outputs the electric signal to the detection signal processing unit 16. Then, the detection signal processing unit 16 displays the amount of light based on the electric signal as a measured value on a screen, prints it on paper, or converts the electric signal into a digital signal by an AD converter and stores the measured value in a memory. Or memorize it. Subsequently, the above operation is repeated for all the LEDs 2, and the light quantity measurement is completed.
[0016]
Since the measured value of the light amount of each LED 2 obtained in this way is detected through the filter 15, it depends on the spectral sensitivity characteristic of the photoconductor. Then, even if the set current value of each LED 2 is adjusted directly according to these measured values, the variation in the exposure amount on the surface of the photoreceptor is effectively suppressed, and the quality of image formation is improved.
[0017]
In the present embodiment, as a material of the photoconductor, a-Si, which is excellent in terms of high sensitivity, has been described as an example. It is also applicable to Se type. Of course, OPC may be used.
[0018]
In addition, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0019]
【The invention's effect】
As described above, according to the method for measuring the light amount of the LED of the present invention, the obtained measured value of the light amount of each LED corresponds to the spectral sensitivity characteristic of the photoreceptor. Even if the set current value of the LED is adjusted, the variation in the exposure amount on the surface of the photoconductor is suppressed, and the quality of image formation is improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a main configuration of a light quantity measuring device employing a method for measuring the light quantity of an LED according to the present invention.
FIG. 2 is a diagram illustrating spectral sensitivity characteristics of a photoconductor for each material.
[Explanation of symbols]
1 LED print head 2 LED
3 LED Head 11 Light Emitting Signal Transmitting Unit 12 Holding Unit 13 Condensing Unit 14 Sensor 15 Filter 16 Detection Signal Processing Unit

Claims (3)

In an LED light quantity measuring method for measuring the light quantity of each LED in an LED print head in which a large number of LEDs for exposing a photoconductor are arranged,
A light quantity measuring method for an LED, comprising: receiving light from the LED by a sensor having a constant sensitivity via a filter adapted to a spectral sensitivity characteristic of the photoconductor; and outputting the light quantity. The method according to claim 1, wherein the filter has a different transmittance for each predetermined wavelength. The method according to claim 2, wherein the photoconductor is made of amorphous silicon.

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