JPH07214819A - Exposure system using LED array - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an exposure apparatus using an LED array capable of correcting a change in light amount due to temperature. [Configuration] An L having a power source (4) according to image data
LE for exposing the image carrier by causing the ED array (1) to emit light
An exposure apparatus using a D array, which is a temperature detecting means (2) for detecting the temperature of the LED array (1), and a supply voltage of the power source (4) according to the detection result by the temperature detecting means (2). And voltage control means (3) for changing

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array of an electrophotographic image forming apparatus using an LED array as an exposing means for exposing an image bearing member.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an LED array has been used as an exposure device that exposes an image carrier according to image data. This LED array is made up of thousands of LEDs arranged side by side.
Each light emission variation in manufacturing is corrected by 2-bit image data. Incidentally, various gradation expression methods have been proposed for an exposure apparatus using this LED array. For example, according to "Study of LED head pulse width modulation gradation method" announced by Oki Electric at the 1991 Spring National Convention of the Institute of Electronics, Information and Communication Engineers, by changing the emission time of each LED according to the image data, By expressing the tones, variations in light emission due to LED manufacturing are also corrected by changing the light emission time (lines 3 to 5, lines 20 to 26, etc.).

[0003]

However, in the above-mentioned conventional exposure apparatus using the LED array, the light emission output thereof changes depending on the ambient temperature or heat generated when the LED is turned on, and decreases when the temperature rises. For example, the light emission output at 50 ° C. is about half that at 25 ° C. Therefore, it is necessary to correct the change in the light amount due to temperature in order to perform accurate gradation expression, but there is a problem that this is not done at present. Therefore, it is an object of the present invention to solve the above-mentioned conventional problems and to provide an exposure apparatus using an LED array capable of correcting a change in light amount due to temperature.

[0004]

The gist of the present invention resides in that, in claim 1, an LE that exposes an image carrier by causing an LED array having a power source to emit light in accordance with image data.
The exposure apparatus using the D array includes temperature detection means for detecting the temperature of the LED array, and voltage control means for changing the supply voltage of the power source according to the detection result by the temperature detection means. According to claim 2, in the exposure apparatus using the LED array, the LED
The light emitting dot shape of the single LED of the array has a size of 1 dot in the main scanning direction and a size in which the lighting time is controlled in a range smaller than 1 dot in the sub scanning direction according to the number of gradations. Item 3, in an exposure apparatus using the LED array, a light emission time control unit that determines a light emission time of the LED array according to the image data to express a gradation, and a temperature that detects the temperature of the LED array. L according to the detection means and the detection result by this temperature detection means
And a correction means for correcting the light emission time of the ED array.

[0005]

Therefore, in the present invention, the temperature detecting means detects the temperature of the LED array, and the detection result is input to the voltage control means. Then, the voltage control means changes the supply voltage of the power source according to the detection result.
As a result, the light emission output of each LED alone is maintained at a predetermined value according to the image information data, regardless of the temperature. Also,
According to a second aspect of the present invention, the light emitting dot shape of the single LED of the LED array has a size of 1 dot in the main scanning direction, and lights up in the sub scanning direction in a range smaller than 1 dot depending on the number of gradations. Control the time. In this way, by controlling the lighting time of each LED alone, gradation expression in 1-dot units is performed. Further, in the third aspect, gradation is expressed by determining the light emission time of the LED array according to the image data by the light emission time control means. At this time, the temperature of the LED array is detected by the temperature detection means. The detection result is input to the correction means, the correction means corrects the light emission time according to the detection result, and the correction signal is input to the light emission time control means, so that the image data is not affected by the temperature. Accurately express gradation according to.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. First, an embodiment based on claim 1 will be described with reference to FIG. In the figure, a thermistor 2 (temperature detecting means) is attached to a heat dissipation plate (not shown) of the LED array 1. An LED voltage control circuit 3 (voltage control means) is connected to the LED array 1 (collection of individual LEDs 1 ₁ ... 1n), and an LED supply power source is supplied to the LED array 1 and the LED voltage control circuit 3. 4 is connected. In this configuration, the thermistor 2 detects the temperature, and the detection signal is input to the LED voltage control circuit 3. In the LED voltage control circuit 3, the output voltage of the LED supply power source 4 is changed within the range of 2 to 10 V according to the input temperature. That is, the output voltage of the LED array 1 is kept constant by raising the output voltage as the temperature rises.

Next, an embodiment based on claim 2 will be shown from FIG. 2 and FIG. In FIG. 2, the shaded area is the LED array 1
The light emission shape of a single body 1 ₁ (1 ₁ ... 1 n) is shown. The amount of emitted light is as shown in FIG. 4A, the characteristic line is concave, or as shown in FIG. It may be convex. Then, as shown in FIG. 3, the size of the single LED 1 _{1 in} the main scanning direction is 1 dot (dot), and by controlling the lighting time in the sub scanning direction according to the gradation,
Gradation is expressed in 1-dot units. The lighting time at this time is
As shown in the figure, the area is set so as not to exceed the size of one dot in the sub-scanning direction. In addition, this single LED 1 ₁ (1 ₁ ...
1n) light emission shape depends on how many gradations are expressed,
The light emitting shape is elongated as the number of gradations is increased.

Next, an embodiment based on claim 3 will be described with reference to FIG. In the figure, the shift register 5 (5
₁ · · · 5n) counter 6 (6 ₁ ··· 6n) each is connected, the counter 6 ₁ · · · 6n via the LED light emission circuit 7 L
Each LED unit 1 ₁ ... 1n of the ED array 1 is connected to each LED. This shift register 5, counter 6, and LE
The D light emission circuit 7 constitutes a light emission time control means. In this configuration, the feed to the shift register 5 ₁ 1 dot in 8-bit image data, the shift register 5 ₁ ...
Image data corresponding to each single LED ₁ 1 · · · 1n at 5n is determined by the clock 1, it is set in the counter 6 ₁ · · · 6n, from the clock 2 of each single LED 1 ₂ · · · 1n The light emission time is counted. That is, each LE from the image data
By determining the light emission time of the single D 1 ₂ ... 1n and causing the LED light emission circuit 7 to emit each single LED 1 ₂ ... 1n for the time counted by the counter 6 ₁ ... 6n. , Gradation expression is performed.

At this time, some of the 8 bits of the image data are used as the temperature correction bits. That is, a temperature detection result obtained by a thermistor or the like (not shown) (similar to the embodiment of claim 1) which is a temperature detecting means is inputted to a correction circuit which is a correction means (not shown), and each LED unit 1 ₂ to be corrected in this correction circuit ... The light emission time of 1n is determined, the information is expressed by the temperature correction bit, and the shift register 5
Input to ₁ ... 5n, and correct the light emission time of each LED 1 ₂ ... 1n. As a result, the light emission time is corrected according to the temperature, and gradation expression that is not affected by the temperature change is performed.

[0010]

As described above, according to the first aspect, the temperature detecting means for detecting the temperature of the LED array and the voltage for changing the supply voltage of the power source according to the detection result by the temperature detecting means. With the control means,
The light emission output of each LED alone can be maintained at a predetermined value according to the image information data regardless of the temperature change of the environment, and accurate gradation expression can be performed.

According to a second aspect of the present invention, the shape of a light emitting dot of a single LED of the LED array is 1 in the main scanning direction.
Since the dot size and the sub-scanning direction are the sizes in which the lighting time is controlled in a range smaller than 1 dot according to the number of gradations, it is possible to control the lighting time of each LED by 1
It is possible to perform gradation expression in dot units and obtain a fine-grained image.

According to a third aspect of the invention, a light emission time control means for determining a light emission time of the LED array according to the image data to express a gradation, and a temperature detection means for detecting a temperature of the LED array. And the correction means for correcting the light emission time of the LED array according to the detection result of the temperature detection means, the temperature correction can be performed with a simple configuration, and the same effect as that of claim 1 can be obtained. Obtainable.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an exposure apparatus according to an embodiment of the present invention (claim 1).

FIG. 2 is an explanatory diagram showing a light emitting shape of a single LED array of claim 2;

FIG. 3 is an explanatory diagram showing a light emitting shape of an LED array according to an embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of an exposure apparatus of an embodiment according to claim 3;

[Explanation of symbols]

 1 LED array 2 Temperature detecting means 3 Voltage control means 4 Power supply 5, 6, 7 Light emission time control means

Claims (3)

[Claims] 1. An exposure apparatus using an LED array, which exposes an image carrier by causing an LED array to emit light in accordance with image data, and a temperature detecting means for detecting the temperature of the LED array, and the temperature detecting means. An exposure apparatus using an LED array, comprising: a voltage control unit that changes a supply voltage of the LED power supply according to a detection result. 2. An exposure apparatus using an LED array that exposes an image carrier by emitting light from the LED array according to image data, wherein each LED light emitting portion of the LED array is 1 in the main scanning direction. An exposure apparatus using an LED array, which is formed to have a dot size and has a size capable of controlling a lighting time in a range smaller than 1 dot in the sub-scanning direction according to the number of gradations. 3. An LED having a power source according to image data.
In an exposure apparatus using an LED array that exposes an image carrier by causing an array to emit light, a light emission time control unit that determines a light emission time of the LED array according to the image data and expresses gradation, and the LE.
A temperature detecting means for detecting the temperature of the D array, and a correcting means for correcting the light emitting time of the LED array according to the detection result of the temperature detecting means.
An exposure apparatus using an ED array.