JP2009098175A - Image reading apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reading apparatus with a cold cathode tube as a light source and capable of efficiently starting operation of the cold cathode tube by a simple configuration without using a temperature sensor or the like, thereby shortening the time required until image reading becomes possible. <P>SOLUTION: In a method of controlling the image reading apparatus with the cold cathode tube lamp as the light source to start operation of the cold cathode tube lamp by applying the initial voltage being higher than the voltage when reading images and detect quantity of light of the cold cathode tube lamp by a photoelectric transfer element, the time for switching to the voltage when reading images is decided based on a value indicating quantity of light immediately after lighting the lamp, and the time for switching is set in such a way that the larger the value indicating the quantity of light is, the shorter the time for switching is. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image reading apparatus such as a copying machine, a scanner, and a facsimile, and more particularly to an image reading apparatus provided with a cold cathode tube lamp as a light source.

  In general, in an image reading apparatus, light from a light source is irradiated onto a document, and the reflected light is imaged on an image reading sensor via a mirror and a lens. The post-image reading sensor performs photoelectric conversion, and is read as image data. In recent years, a cold cathode tube which is relatively inexpensive and easily obtains a sufficient amount of light is often used as the illumination light source.

  However, the light quantity characteristics of a cold cathode tube are greatly affected by temperature, and the rise time until reaching a stable quantity of light becomes longer as the temperature is lower. Therefore, when using a cold cathode tube as a light source, it is required to make some contrivance in order to shorten the waiting time associated with the rise of the cold cathode tube as much as possible.

Conventional approaches to this have been to keep the cold cathode tube lit at all times or to guide the heat of the fixing device of the image forming apparatus to the cold cathode tube to increase the tube wall temperature and shorten the lighting rise time. It was. (For example, see Patent Document 1)
Another idea is to apply a voltage higher than the voltage applied during the image reading operation at the start of lighting of the cold cathode tube to shorten the start-up time. (For example, see Patent Document 2)
JP 2002-99194 A JP-A-1-267630

  However, lighting the cold cathode tube at all times consumes electric power and causes a decrease in the life of the cold cathode tube. In addition, using the heat of the fixing device complicates the apparatus configuration, and when the image forming apparatus is in a standby state for a long time, the heater of the fixing device is also turned off, so that heat flows into the cold cathode tube. As a result, the tube wall temperature of the cold cathode tube is lowered.

  Moreover, in patent document 2, since environmental temperature is not considered, even if the same time passes, depending on environmental temperature, tube wall temperature may be too high or too low.

  In addition, providing a temperature sensor to measure the environment leads to an increase in cost.

  The present invention has been made to solve the above problems, and in an image reading apparatus provided with a cold cathode tube as a light source, the cold cathode tube can be started up with a simple configuration without using a temperature sensor or the like. It is an object to reduce the time until the image can be read efficiently.

  In order to solve the above problems, an image reading apparatus of the present invention includes a light source that exposes a document, a lighting circuit that applies a voltage to the light source to light it, a detection unit that detects a light amount of the light source, Control means for controlling the lighting circuit so that the light source is turned on at a first voltage and then switched on to a second voltage lower than the first voltage, and the control means includes the light source. A switching time until switching from the first voltage to the second voltage is set based on the output of the detection means after a predetermined time from the start of lighting.

  According to the present invention, it is possible to realize an appropriate start-up of a cold cathode tube with an inexpensive configuration without using a temperature sensor or the like, and to improve the life of the cold cathode tube.

[First Embodiment]
An example of the best mode of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view of an image reading apparatus according to an embodiment of the present invention. 3 is a cold cathode tube as a light source, 14, 15 and 16 are mirrors, 5 is a lens, and 6 is a photoelectric conversion element such as a CCD as document reading means. Reference numeral 17 denotes a platen glass, 18 denotes an automatic document feeder, and 19 denotes a standard white plate.

  When the original is read, the cold cathode tube 3 moves below the standard white plate, and the cold cathode tube 3 is turned on. The standard white plate 19 is a member that serves as a reference when reading the amount of light when the cold cathode fluorescent lamp 3 is turned on. It is also used when correcting sensitivity unevenness of the photoelectric conversion element 6. After the light quantity of the cold cathode tube 3 is stabilized, the automatic document feeder 18 feeds a plurality of documents set on the document tray one by one to the document table 17. The document conveyed to the document table 17 is irradiated with light by the cold cathode tube 3 and the mirrors 14, 15, 16 moving in the left direction (sub-scanning direction) in the figure, and the reflected light is reflected from the mirror 14. , 15, 16 and the lens 5, an image is formed on the photoelectric conversion element 6. The photoelectric conversion element 6 converts the reflected light from the document into an electrical signal and obtains image information. After the image reading operation is completed, the cold cathode tube 3 and the mirrors 14, 15 and 16 are moved to the initial positions, and the cold cathode tube 3 is turned off.

  The document reading method may be a so-called flow reading method in which the document is exposed at a fixed position while the document is conveyed and the reflected light is read.

  FIG. 2 is a block diagram showing the configuration of the image reading apparatus according to the embodiment of the present invention. The CPU circuit unit 2 controls the entire apparatus by a control program stored in the ROM 11. The RAM 9 temporarily stores control data and is used as a work area for arithmetic processing of the CPU 9 accompanying control. The timer 10 is used for measuring a switching time or the like for switching the voltage applied to the cold cathode tube from the initial voltage to the voltage at the time of image reading. The lighting circuit unit 8 is based on a command from the CPU circuit unit 2. 3 controls the voltage applied to 3 and the lighting / extinguishing control. The photoelectric conversion element 6 converts reflected light from the document into an analog signal. An analog signal that is an output of the photoelectric conversion element 6 is converted into a digital signal by the A / D conversion unit 7. This digital signal is sent to the image forming unit 12 after the image processing unit 13 corrects the sensitivity unevenness of the photoelectric conversion element 6 and the like. The photoelectric conversion element 6 also functions as a detection means for detecting the light quantity of the cold cathode tube 3. The image forming unit 12 forms an image on a sheet or the like based on the image signal from the image processing unit. Reference numeral 20 denotes an operation unit for inputting or displaying an instruction related to image formation.

  FIG. 3 is a flowchart showing lighting control of the cold cathode tube 3 of the image reading apparatus. The processing of this flowchart is executed by the CPU circuit unit 2 in accordance with a control program stored in the ROM 11.

  First, the CPU circuit unit 2 determines whether there is a reading instruction by pressing the start key of the operation unit 20 (S1). When there is a reading instruction, the CPU circuit unit 2 moves the optical system including the cold cathode tube 3 below the standard white plate 19, and the lighting signal at the initial voltage V <b> 1 (first voltage) is sent to the lighting circuit unit 8. And time measurement by the timer 10 is started (S2). The initial voltage V1 is higher than the lighting voltage V2 (second voltage) at the time of actual image reading. The lighting circuit unit 8 applies an initial voltage V1 to the cold cathode tube 3 based on a lighting signal from the CPU circuit unit 2. Lighting with the initial voltage V1 corresponds to the first lighting step. The CPU circuit unit 2 waits for a time during which the cold cathode tube 3 is reliably turned on and the difference in tube wall temperature appears in the light quantity of the cold cathode tube 3 (S3). The standby time may be any time, but it is necessary to be at least equal to or less than the time when the light quantity of the cold cathode tube 3 is saturated. It is desirable that it is substantially about 0.5 to 2 seconds.

  After a predetermined time from the start of lighting, the CPU circuit unit 2 detects the reflected light from the standard white plate 19 via the photoelectric conversion element 6 and the A / D conversion unit 7, and stores it as the light amount X (S4). Here, the light quantity X is detected by the photoelectric conversion element 6 for image reading. However, using a dedicated photoelectric conversion element, the light quantity of the cold cathode tube 3 is directly read instead of the reflected light from the standard white plate 19. Also good. The CPU circuit unit 2 compares the light amount A preset in the RAM 9 with the detected light amount X (S5).

  The amount of light A, which is comparison data preset in the RAM 9, will be described. The numbers in parentheses are examples. In the RAM 9, switching times T1, T2, and T3 from the voltage V1 to the voltage V2 corresponding to the light amount X immediately after lighting are set in advance. The amount of light immediately after the cold cathode tube 3 is lit increases as the environmental temperature increases as shown in FIG. In this embodiment, the amount of light 2 seconds after the start of lighting when the ambient temperature is 15 degrees and 30 degrees is used as a reference value for comparison, and the amount of light at 15 degrees is A (0.18), 30 degrees. Is set to B (0.30). The unit is indicated by voltage.

  Next, the switching times T1, T2, and T3 will be described. FIG. 6 shows the light quantity change characteristics when the quiet temperature is 15 degrees and the voltage switching time is 6 seconds in this embodiment. In this case, the time to reach a stable light amount is 21 seconds. FIG. 7 shows the light quantity change characteristic when the voltage switching time is 7 seconds at an environmental temperature of 15 degrees. In this case, the time for reaching the stable light amount is 19 seconds. FIG. 8 shows the light quantity change characteristic when the voltage switching time is 8 seconds at the environmental temperature of 15 degrees. In this case, the time to reach the stable light amount is 12 seconds. FIG. 9 shows the light quantity change characteristics when the voltage switching time is 9 seconds at an environmental temperature of 15 degrees. In this case, the time to reach a stable light amount is 13 seconds. FIG. 10 shows the light quantity change characteristics when the voltage switching time is 10 seconds at an environmental temperature of 15 degrees. In this case, the time to reach the stable light amount is 14 seconds.

  As shown in FIGS. 6 and 7, when the application time of the initial voltage V <b> 1 is short, no overshoot of the light amount occurs, so the time to reach the stable light amount becomes long. On the contrary, as shown in FIGS. 9 and 10, even if the application time of the initial voltage V1 is too long, the amount of overshooting of the light amount becomes large, and the time for reaching the stable light amount becomes long. Therefore, in this embodiment, the switching time T2 is set to 8 seconds shown in FIG. 10 so that the time to reach the stable light amount is as short as possible. Similarly, T1 is set to 10 seconds and T3 is set to 6 seconds so that the switching times T1 and T3 are each as short as possible to reach the stable light amount. The higher the environmental temperature, the larger the light quantity value X immediately after lighting, and the shorter the rise time. Therefore, the switching time T is set shorter as the light quantity value X is larger.

  Returning to FIG. 2, the startup operation of the cold cathode tube will be described. As a result of comparing the light amount X and the light amount A, the CPU circuit unit 2 proceeds to S6 if the light amount A ≧ the light amount X, and proceeds to S7 if the light amount A <the light amount X. In S6, the CPU circuit unit 2 compares the light quantity B set in the RAM 9 in advance. If the light quantity B> the light quantity X, the process proceeds to S8. If the light quantity B ≦ the light quantity X, the process proceeds to S9. To do. In S7, the CPU circuit unit 2 sets a switching time T1 corresponding to the case where the light amount A <light amount X set in the RAM 9 in advance, and proceeds to S10. In S8, the CPU circuit unit 2 sets a switching time T2 corresponding to the case where the light amount A ≦ the light amount X <the light amount B set in the RAM 9 in advance, and proceeds to S11. In S9, the CPU circuit unit 2 sets a switching time T3 corresponding to the case where the light amount X ≧ the light amount B preset in the RAM 9 and proceeds to S11. In S10, the CPU circuit unit 2 waits until the timer 10 reaches T1, and proceeds to S13. In S11, the CPU circuit unit 2 waits until the timer 10 reaches T2, and proceeds to S13. In S12, the CPU circuit unit 2 waits until the timer 10 reaches T3, and proceeds to S13. In S <b> 13, the CPU circuit unit 2 outputs a voltage switching signal to the lighting circuit unit 8. The lighting circuit unit 8 switches the voltage applied to the cold cathode tube 3 from the initial voltage V1 to the voltage V2 at the time of image reading lower than V1. Lighting with the voltage V2 corresponds to the second lighting step. In S15, the CPU circuit unit 2 waits for a time for the light amount to stabilize after switching to the voltage V2, ends the time measurement by the timer 10, and proceeds to S16. In S16, the CPU circuit unit 2 starts an image reading operation.

  In the present embodiment, the comparison determination is performed in three steps based on the light amount immediately after lighting, but the step may be determined in more detail or in two steps, and the initial voltage application time may be controlled accordingly.

Cross section of image reader Block diagram showing the configuration of the image reading apparatus Flow chart showing cold cathode tube lighting control Data table showing the relationship between light intensity and voltage switching time Light intensity characteristics of cold cathode tubes Light intensity characteristics of cold cathode tubes Light intensity characteristics of cold cathode tubes Light intensity characteristics of cold cathode tubes Light intensity characteristics of cold cathode tubes Light intensity characteristics of cold cathode tubes

Explanation of symbols

2 CPU circuit section 3 Cold cathode tube 6 Photoelectric conversion element 8 Lighting circuit section 9 RAM
10 Timer 11 ROM
19 Standard white plate

Claims (6)

A light source for exposing the document;
A lighting circuit for applying a voltage to the light source to light it;
Detecting means for detecting the light quantity of the light source;
Control means for controlling the lighting circuit so that the light source is lit at a first voltage and then switched to a second voltage lower than the first voltage.
And the control means sets a switching time until switching from the first voltage to the second voltage based on the output of the detection means.   The image reading apparatus according to claim 1, wherein the control unit shortens the switching time as the output of the detection unit after a predetermined time from the start of lighting of the light source increases.   The image reading apparatus according to claim 1, wherein the detection unit also serves as a reading unit that reads an image of a document.   2. The image reading apparatus according to claim 1, wherein the light source is a cold cathode tube. In a control method of an image reading apparatus having a light source that exposes a document and a lighting circuit that applies a voltage to the light source to turn it on,
A first lighting step of lighting the light source at a first voltage;
A detection step of detecting the light quantity of the light source;
A setting step for setting a switching time until switching to a second voltage lower than the first voltage, based on the amount of light detected in the detection step;
A second lighting step of lighting the light source at the second voltage based on the switching time set in the setting step;
An image reading apparatus control method comprising:   6. The method of controlling an image reading apparatus according to claim 5, wherein, in the setting step, the switching time is shortened as the light amount of the light source after a predetermined time from the start of lighting of the light source increases.

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