JP2003143343A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that suppresses fluctuations in power supplied to an IC logic such as an A/D converter so as to enhance the image quality. SOLUTION: The image forming device is provided with: an illumination means 32 that illuminates a read object; a photoelectric conversion means 31 that receives light reflected from the read object and converts the received light into a voltage depending on the received light; an A/D conversion means 312 that converts an analog image signal converted by the photoelectric conversion means into a digital image signal; and a power supply means 310 that supplies power to each means. The power supply means supplies at least the power to the illumination means and the A/D conversion means through separate power lines 20, 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus including an image reading device such as a scanner or a digital copying machine.

[0002]

2. Description of the Related Art Conventionally, image forming apparatuses such as scanners, digital copying machines, and digital facsimiles use image reading apparatuses that illuminate an original with an image sensor and convert the reflected light into electric signals by photoelectric conversion. I have it. In such an image reading apparatus, an A / D conversion element is used as a means for converting an analog image signal from an image sensor into a digital image signal.

FIG. 3 is a diagram showing an example of an output signal of the image sensor. In the waveform shown in the figure, the data of a plurality of pixels are serially output, and one cycle is output data of one pixel. The High level portion of the signal is the dark output level of the sensor which is the reference of the image signal, and the Low level portion is the reading level of the reflected light, which is the image signal obtained by converting the reflected light from the document into an electric signal. This level difference (Δd) between High and Low is A
The D / D converted signal becomes a digital image signal, and the reflected light becomes stronger as the level difference is larger, and the strongest reflected light is the white image. The image forming apparatus performs various kinds of image processing on such image data as necessary to form a monochrome or color image.

By the way, the light source (illuminating means) uses an LED formed in the image sensor, and the amount of light is controlled by ON / OFF controlling this LED.

FIG. 4 is a schematic block diagram of an image reading apparatus of a conventional image forming apparatus. In FIG. 4, the control line is omitted and only the power supply line is shown. As shown in the figure, as a power supply line configuration, an 8 V power supply line from the power supply source 50 is supplied to the substrate 10 on which the A / D conversion element 52 and the like are mounted by one line. . A /
The power supply for the D conversion element 52 and other IC logic 53 uses the voltage conversion element 51 on the substrate to set the voltage level to 5
Converted to V and supplied, the power supply for the image sensor is 8V
This substrate is relayed and supplied as it is. As described above, in the conventional image forming apparatus, the power is supplied from the power supply source 50 to the substrate 10 by one power line, and the A /
It is used by branching to a power supply for an IC logic including a D conversion element and a power supply for an image sensor.

[0006]

However, as in the conventional device, the image sensor 54 that projects light onto the original document.
When the power source for the illumination means and the power source for the IC logic such as the A / D conversion element 52 are supplied through the same power source line, the power supply to the illumination means is turned on within the time for reading one line.
When / OFF is switched, the voltage level (8V) of the power supply fluctuates by turning off and lighting the lighting means, and the A / D conversion element 5
The reference voltage of 2 is also affected, and the result of A / D conversion fluctuates.

Generally, the dynamic range of the output signal from the image sensor 54 is about 1 to 1.5 V, and 10 bits (resolution is 10) used in a general image forming apparatus.
In the case of the A / D conversion element 52 of 24 steps), it becomes about 1 to 1.5 mV per 1 bit, and when the power supply voltage (A / D conversion reference voltage) fluctuates more than this voltage, the density of the formed image becomes And the image quality was deteriorated.

The present invention has been made based on the above circumstances, and provides an image forming apparatus capable of improving the image quality by suppressing the fluctuation of the power supply to the IC logic such as the A / D conversion element. The purpose is to provide.

[0009]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an illumination means for illuminating an object to be read and a light received by the reflected light from the object to be read. A photoelectric conversion means for converting the voltage into a voltage according to the above, an A / D conversion means for converting the analog image signal converted by the photoelectric conversion means into a digital image signal, and a power supply means for supplying power to the respective means. It is characterized in that at least the power supplies to the illumination means and the A / D conversion means are supplied from separate power supply lines from the power supply means.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image reading apparatus of an image forming apparatus according to an embodiment of the present invention. The image reading apparatus shown in FIG. 1 includes an image sensor 301 that converts an optical signal into an electric signal, and an image sensor 301.
A scanner motor 302 for scanning in the sub-scanning direction and a document table glass 303 on which a document is placed are provided.

FIG. 2 is a schematic block diagram of the image reading apparatus of the image forming apparatus of this embodiment. Since the control line of the present embodiment is the same as the conventional one, the control line is omitted in FIG. 2 and only the power supply line is shown. The image forming apparatus according to the present exemplary embodiment has two power supply lines 20, 21.
And a voltage conversion element 31 for reducing the power supply voltage supplied from the power supply source from 8V to 5V.
1 and an A / D conversion element 312 for converting an analog image signal from the image sensor 301 into a digital image signal,
An IC logic 313 other than the A / D conversion element, a power control unit 314 that controls the power supplied to the image sensor,
An A / D board 10 on which a voltage conversion element, an A / D conversion element 312 and the like are mounted, and a control board 11 on which a power control unit 314 and the like are mounted are provided. Although not shown, the control board 11 of the image forming apparatus according to the present embodiment includes a CPU that controls the entire apparatus such as an operation unit and individual parts, a ROM that stores a control program and various data in a nonvolatile manner, And RA used as a work area used for CPU processing and a temporary storage area for data
M etc. are placed.

The image sensor 301 of this embodiment comprises a CCD chip 31 as a photoelectric conversion element and an LED 32 as an illumination means. In addition, the power control unit 314
Is P that controls the power supplied to the image sensor 301.
WM control (pulse width modulation control) is performed.

A document is placed on the platen glass 303,
When a start key (not shown) is pressed, the scanner motor 302 scans the image sensor 301 in the sub-scanning direction. Reading in the main scanning direction is performed line by line, and by scanning this in the sub scanning direction,
Read the image information of the original. The CCD chip 31, which is a photoelectric conversion element, reads the reflected light from the document illuminated by the LED 32, which is the illumination means installed in the image sensor 301, and converts it into an electrical signal. The electrically converted image information is output as an analog image signal as shown in FIG. 3, and this analog image signal is A / D.
It is converted into a digital image signal by the conversion element 312.
Although not shown, the image forming apparatus according to the present embodiment includes a reference density storage unit that stores reference density data obtained by reading a reference density member that gives a reference density by a photoelectric conversion element, and a reference density storage unit. A shading correction unit that corrects the read image data based on the above data. In addition, it goes without saying that the image forming apparatus according to the present embodiment includes an input masking circuit, a magnification varying circuit, and the like that perform various kinds of processing necessary for image formation, as in the known image forming apparatus.

In the image forming apparatus of the present embodiment, the A / D converter is connected from the power supply source 310 to the power supply line 20 (lead wire).
Power is supplied to the IC logic such as the conversion element 312, and the power supply line 21 supplies power for the image sensor. Further, in the apparatus of the present embodiment, in order to improve the accuracy of A / D conversion, the power supply 5V for IC logic is not directly supplied from the power supply source, but the A / D substrate 1 is supplied from the power supply source.
It is supplied with an 8V power supply up to 0, and is used by stepping it down from 8V to 5V by a voltage conversion element 311 mounted on the same substrate 10 as the A / D conversion element 312. By using the voltage conversion element in this way, the A /
It is possible to suppress variations in voltage drop to the D conversion element.

In the image forming apparatus of this embodiment, A
Power supply 8V for IC logic such as / D conversion element 312,
The power supply 8V for the LED of the image sensor is supplied by separate power supply lines, and the power supply for the LED is separated from the power supply for the IC logic.

As a result, the current capacity of each power supply line can be made to have a margin, and the state of the LED (lighting / extinguishing)
Regardless of this, the power supply to the IC logic such as the A / D conversion element 312 is stable, and the A / D conversion can be performed accurately.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the present invention. For example, in the above-described embodiment, a case has been described in which the power control unit that controls the power supplied to the image sensor performs PWM control. However, the power control unit may simply perform ON / OFF or continuous control. May be performed. Further, the voltage conversion element may be omitted, and the power supply source may supply power of 8V and 5V. Further, in the above-described embodiment, not only the A / D conversion element but also the power supplied to the other IC logic is supplied through the power supply line separate from the power supply for the illumination means. Only the power source for the conversion element may be supplied by a power line separate from the lighting means.

[0018]

As described above, according to the image forming apparatus of the present invention, the power supply for the illumination means and the power supply for the IC logic such as the A / D conversion means are supplied by separate power supply lines. By doing so, a stable power can be supplied to the IC logic regardless of the operation or non-operation of the illumination means, so that the result of A / D conversion is stable and the quality of the formed image can be improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image reading apparatus of an image forming apparatus that is an embodiment of the present invention.

FIG. 2 is a schematic block diagram of an image reading apparatus of an image forming apparatus according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of an output signal of an image sensor.

FIG. 4 is a schematic block diagram of an image reading apparatus of a conventional image forming apparatus.

[Explanation of Codes] 301: Image Sensor, 302: Scanner Motor,
303: Platen glass, 310: Power supply source, 31
1: voltage conversion element, 312: A / D conversion element, 31
3: Other IC logic, 314: Power control unit, 1
0: A / D board, 11: control board, 20, 2
1: Power line, 31: CCD, 32: LED

Claims (3)

[Claims] 1. Illumination means for illuminating an object to be read,
A photoelectric conversion unit that receives the reflected light from the object to be read and converts it into a voltage according to the received light, and an A / D conversion unit that converts the analog image signal converted by the photoelectric conversion unit into a digital image signal. And power supply means for supplying power to each of the means, and at least the power supplied to the lighting means and the A / D conversion means is supplied from the power supply means through separate power lines. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the power supplied to the lighting means is controlled by pulse width modulation. 3. The image forming apparatus according to claim 1, wherein the power supplied from the power supply means to the A / D conversion means is one whose voltage is stepped down by the voltage conversion means. apparatus.