JP2009182411A - Image reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve stable image data reading by a low-cost configuration when image reading. <P>SOLUTION: A frequency of a horizontal synchronous signal H for reading out one main scanning line is used as a unit to determine a duty ratio so as not to be extremely short relative to the horizontal synchronous signal H at a frequency which is two or more times the frequency of the horizontal synchronous signal H, thereby performing PWM control by an LED control circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an image reading apparatus using an image sensor.

Conventionally, a white reference plate provided in a non-image area is irradiated with a light source, a light amount is detected from the reflected light by a photoelectric conversion element, a lighting time of the light source is determined based on the result, and a horizontal for reading one line PWM is performed at the same frequency as the frequency of the synchronization signal H. Further, the lighting time is set to be long when the light amount is small so as not to exceed the dynamic range of the AD converter, and when the light amount is strong, the lighting time is shortened to determine an appropriate time. The result of reading the image is determined by calculation from the average density of the pixel.

JP 2003-338904 A

However, in the above technique, the lighting time of the light source that performs PWM control at the same frequency as the horizontal synchronization signal H is determined for one line from the detection result of the light amount from the reference plate (white reference plate) in the non-image area. If the lighting time is extremely shorter than the horizontal synchronization signal H, the light source does not light in the second half of the one pixel in the sub-scanning direction, the data in that portion cannot be read, and the reading result of the pixel is actually There is a risk of being far from the average concentration.

This is illustrated in FIG. Original pixel data is black initially in the sub-scanning direction but white in the second half, but since the lighting time of the light source is short, the light source is lit only in the first half of the pixel, so the second half of the pixel can be read correctly. Since it is impossible to obtain a value close to black, when the data is averaged by calculation, the value of this pixel is close to black and is different from the actual average value.

In order to prevent this, there is a method of increasing the lighting time by lowering the current value of the light source. This is shown in FIG. Considering that the Y axis of the light source lighting time in the figure is reduced, the current value is reduced for convenience. To compensate for the decrease in light intensity by reducing the current value, the lighting time is extended. As a result, the latter half of the pixel in the sub-scanning direction can be read by illuminating the light source, but usually it is better to increase the amount of light. Therefore, it is necessary to control the current value of the light source in this way only when necessary. Therefore, it is necessary to add a circuit for switching the current value in order to realize this, and an increase in cost is expected.

Accordingly, an object of the present invention is to realize stable image data reading at the time of image reading with an inexpensive configuration.

An image reading apparatus according to the present invention includes a light source that irradiates a predetermined image reading surface, an image forming unit that forms an image of reflected light from the reading surface, and a plurality of light beams that receive the formed reflected light and convert them into electrical signals. In an image reading apparatus having a photoelectric conversion element, a horizontal synchronization signal H for reading out a signal from the photoelectric conversion element for one line, and a time corresponding to an accumulation time for one line based on the horizontal synchronization signal H is 1 A unit that performs PWM control at a frequency that is twice or more the frequency of the horizontal synchronization signal H within a unit time, thereby driving a light source for irradiating; a light amount detecting unit for detecting the light amount of the light source; Control means for controlling the pulse width of the PWM control based on the detection result of the light quantity detection means during the image reading operation.

Further, the driving means may drive the light source by dividing it into a plurality of substantially equal times within a unit time.

Further, the light source may be an LED.

Furthermore, the means for detecting the light amount of the light source is a photoelectric conversion element, and the light amount may be detected by reading a reference plate in a non-image area on the image reading surface.

According to the present invention, the frequency of the horizontal synchronizing signal H for reading out the signal from the photoelectric conversion element for one line is set as one unit, and the lighting time of the light source is PWMed at a frequency more than twice the frequency of the horizontal synchronizing signal H. By controlling, the drive means for driving the light source to be irradiated, the detection means for detecting the light quantity of the light source, and the PWM control pulse width based on the detection result of the light quantity detection means during the image reading operation. By providing the control means for controlling, the latter half of the image data in the sub-scanning direction of each pixel can be averaged and read reliably.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

The configuration and operation of the image reading unit in this embodiment will be described with reference to FIGS. As a typical configuration of the reading apparatus, there are a reduction optical system and an equal-magnification optical system. Here, an explanation will be given with an implementation system using a contact image sensor which is an equal-magnification optical system.

The image reading unit includes an original table glass 2-1 on which an original is placed, a pressure plate 2-2 that can be opened and closed by pressing the original table, and scanning optics that reads an original 2-3 placed on the original table. It consists of a system. As shown in FIG. 2, the optical system includes a contact image sensor (hereinafter referred to as CIS) 2-4, a carriage 2-5 for holding the CIS, and a guide function for moving the carriage in the scanning direction when reading a document. A timing belt 2-8 fixed to the carriage 2-5, pulleys 2-6, 2 arranged at both ends of the timing belt so that the timing belt 2-8 can move smoothly -7, a stepping motor 2-10 whose drive is connected to one of the pulleys, and a home position sensor 2-11 for detecting the position of the carriage 2-5 held by the CIS 2-4 in the scanning direction. Yes. In addition, a white reference plate 2-12 serving as a reference when performing light quantity adjustment control and shading correction operation is provided in a portion in contact with the document table glass 2-1.

Next, the configuration of the CIS 2-4 will be described with reference to FIG. 2-4-1 is a linear light source unit, an LED light source unit 2-4-2 disposed at the end of the light source unit, and a light guide for uniformly diffusing light emitted from the light source unit in the main scanning direction. It consists of the body 2-4-3. Irradiated light emitted from the light guide 2-4-3 is reflected by the original 2-3 on the original platen glass 2-1, and this reflected light passes through the SELFOC lens array 2-4-4 to form the substrate 2-4-. An image is formed on the light receiving element 2-4-5 fixed on the light receiving element 6. The imaged light is photoelectrically converted by the light receiving element 2-4-5 and sequentially output as an image signal.

The light quantity of the LED light source is driven by a constant current circuit that can be controlled with a constant current, and the lighting time is PWM controlled within an arbitrary number of pixels equal to or less than one line of the reading element, and the light receiving element 2-4-5 The light amount accumulation time is controlled. The light receiving element 2-4-5 is driven by a driving clock pulse that can drive the reading elements of all the pixels constituting one line within a time corresponding to one line of the reading time, and a trigger for starting reading of one line. A start pulse or the like is given, and an image signal is output for each pixel in synchronization with the timing of these pulses. 4-2 is a circuit block for controlling the light quantity of the LED light source, which is the light source of CIS2-4 (details will be described later). When the LED light source is turned on and an image signal is output, a constant light quantity is obtained. In addition, when a plurality of color light sources are lit, a control part that can be lit at a constant light quantity ratio and a part that controls the timing of lighting the LED (PWM (pulse that lights up for a certain period of time based on a predetermined timing) Width modulation) control part). The control circuit 4-3 includes a CPU 4-3-3 that controls the entire reading apparatus and a control memory 4-3-4. The offset value, gain value, and the like of the analog processing circuit 4-1 described above are included. Setting of the PWM control value of the LED of the light source control circuit 4-2, setting of each parameter of the image processing described above of the image processing circuit 4-3-1, setting of interface conditions of the interface circuit 4-3-5, etc. Various operation conditions are set for the image reading apparatus, operation is started and stopped, and interface with external devices is controlled. Further, the image data in the memory 4-3-4 in which the image data processed by the image processing circuit is stored is read out via the image processing circuit 4-3-1 by the data bus of the CPU 4-3-4. Is also possible. Further, as a control when reading an image, the CPU 4-3-3 detects the reference position of the scanning optical system 2-4 with the above-described home position sensor 2-11, and controls the scanning optical system 2-4 when reading the image. A predetermined excitation pattern is output to the stepping motor 2-10 so that it can move at a constant speed, and the stepping motor 2-10 is driven via the motor driver circuit 4-3-6. Motor drive control so that a desired image can be read. Is also going.

Next, the control and operation of the image reading apparatus will be described with reference to FIG.
When reading a document, it is first checked whether the carriage 2-5 is positioned at the home position sensor 2-11. If not, the motor 2-10 is driven, and the carriage 2-5 is moved to the home position sensor 2-11. Is detected, and the motor is stopped at the position where the predetermined pulse drive is performed, and is positioned at the home position. When the carriage 2-5 has detected the home position sensor 2-11 from the beginning, the motor is driven in the scanning direction, and once the carriage 2-5 has exited the home position sensor, the motor is then rotated in the reverse direction. The position sensor is detected again, the motor is stopped at the position where the predetermined pulse drive is performed, and the home position is set. Before starting the image reading, the PWM value of each color of the LED light source is set using the white reference plate 2-13 described above at this position. The PWM value is set by detecting the above-mentioned CIS image signal value. First, the offset value and gain value of the analog signal processing circuit are set to predetermined reference values, and the light quantity ratio of each LED color is set. The PWM value for each color is set. Next, the white reference plate 2-13 is turned on with the set light amount, and a correction value for shading correction is set. When the operation described above is completed, the motor 2-10 is driven in the scanning direction, and reading of the original image is started. When reading is started, the read image of the original is photoelectrically converted by the CIS 2-4, and the image signal of the original image is signal-processed by the image signal processing circuit. First, the signal is sampled by the analog signal processing circuit, and the offset level of the signal is corrected and the signal is amplified. When the analog signal processing is completed, the signal is converted into a digital signal by the A / D conversion circuit and output to the memory. The digitized image data is stored in the memory through shading correction, spatial filter, magnification correction, luminance signal conversion, binarization processing and the like by the image processing circuit. The above-described image processing conditions and operation parameters can be set by a CPU in the control circuit. The image data stored in the memory is output via the interface circuit while being synchronized with the control timing of the external device.

1. Description of CIS Light Source LED Control Method In FIG. 1, reference numeral 4-3 denotes a control circuit having a CPU 4-3-3 and a memory 4-3-4, and controls the entire image reading apparatus as described above. Each of the LED drive circuits 4-2-1, 4-2-2, and 4-2-3 has a constant current circuit and a switching circuit, and each of the LEDs 1 to 3 (red, green, and blue) of each color is independently It is connected. A common potential is supplied to all LEDs, and the constant current value and the switch-on time (lighting time) in the constant current circuit can be changed by a control signal based on an image signal input to the control circuit. It is. In FIG. 5, reference numeral 6-1 denotes an LED light quantity density reference plate provided at the end of the contact sensor, which is provided outside the sensor reading effective area (non-image area), and the light emitted from the LED is the LED light quantity density. It is configured to reflect on the reference plate 6-1 and reach the sensor region 2-4-5. Therefore, in order to detect the light amount of the LED, similarly to the case of reading an image, the LED is set based on the setting values of the lighting light amounts I_R, I_G, and I_B described above, the PWM is turned on, and the sensor is turned on. After the signal in the non-image area is analog-processed and A / D converted in 4-1, the monitor reads the data value held in the memory 4-3-2 in the image processing circuit of 4-3. It becomes possible.

The details of the present invention will be described.
Before starting reading an image, the white reference plate located in the non-image area is irradiated with a light source, an appropriate amount of light is detected from the reflected light, and the PWM value of the light source, that is, the duty ratio of the lighting time is determined. The frequency of the horizontal synchronizing signal H for reading one main scanning line is set as one unit, and it is not excessively short with respect to the horizontal synchronizing signal H at a frequency more than twice the frequency of the horizontal synchronizing signal H within a unit time. Thus, the duty ratio is determined and PWM control is performed by the LED control circuit described above. FIG. 8 shows a state of reading control according to the present invention. The light source lighting time in the figure shows a state in which the light source is PWM-controlled by finely dividing and driving at a frequency higher than the frequency of the horizontal synchronizing signal H so that the pixels can be read reliably. As a result, it is possible to calculate up to the second half of the pixel with a value closer to actual pixel data by turning on the light source.

The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made.

It is a LED light source drive control circuit block diagram of CIS of an embodiment according to the present invention. It is a structure figure of CIS of the embodiment concerning the present invention. 1 is a configuration diagram of an image reading apparatus according to an embodiment of the present invention. It is a control block diagram of the image reading apparatus of the embodiment according to the present invention. It is explanatory drawing of the reference | standard board which detects the LED light source light quantity of embodiment which concerns on this invention. It is a timing chart which shows the reading control of a prior art. It is a timing chart which shows the control at the time of reducing the electric current value of the light source of a prior art. It is a timing chart which shows reading control of an embodiment concerning the present invention.

Explanation of symbols

2-1 Original plate glass 2-3 Pressure plate 2-4 Contact image sensor (CIS)
2-5 Carriage

Claims (4)

A light source that irradiates a predetermined image reading surface; imaging means that forms an image of reflected light from the reading surface; and a plurality of photoelectric conversion elements that receive the imaged reflected light and convert them into electrical signals. In an image reading apparatus having
Based on the horizontal synchronization signal H for reading out the signal from the photoelectric conversion element for one line and the horizontal synchronization signal H, the time corresponding to the accumulation time for one line is defined as one unit, and the horizontal synchronization signal is within the unit time. By performing PWM control at a frequency that is at least twice the frequency of the synchronization signal H, a driving means for driving the light source to be irradiated, a light quantity detecting means for detecting the light quantity of the light source,
Control means for controlling the pulse width of PWM control based on the detection result of the light quantity detection means during the image reading operation;
An image reading apparatus comprising: The image reading apparatus according to claim 1, wherein the driving unit drives the light source by dividing the time period of irradiation by the light source substantially equally into a plurality of times within the unit time. The image reading apparatus according to claim 1, wherein the light source is an LED. 2. The image reading apparatus according to claim 1, wherein the means for detecting the light amount of the light source is the photoelectric conversion element, and the light amount is detected by reading a reference plate in a non-image area of the image reading surface.

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