JP5139245B2 - Image reading apparatus and control method thereof - Google Patents

Description

  The present invention generally relates to an image reading apparatus, and more particularly to a power saving technique of an image reading apparatus.

  It is desirable to reduce power consumption also in the image reading apparatus. According to Patent Document 1, it is proposed to reduce power consumption by stopping a clock signal to an image pickup unit in a standby state in which a document can be read in a standby state.

  According to Patent Document 2, the control means determines the first drive signal frequency sent via the connection cable during reading standby and the second drive frequency sent via the connection cable during the document image information reading operation. There has been proposed an image reading apparatus that suppresses power consumption during standby operation by switching and sending out without requiring a rise time of the apparatus.

According to Patent Literature 3, in a power consumption control apparatus that controls power consumption according to any of a plurality of power consumption modes, a time measurement that measures a predetermined elapsed time from an external signal input or a preset timing as a starting point. Means, a power mode switching means for switching to another power consumption mode for a predetermined time after the elapsed time has passed, and an operating frequency switching means for switching the operating frequency according to the switched power consumption mode. It has been proposed to perform power saving control by finely switching the operation speed.
International Publication WO02 / 019693 JP 2004-72602 A JP 2004-242217 A

  According to Patent Document 1, it has only been proposed to reduce power consumption in a standby state in which a document can be read and is not considered to reduce power consumption during a reading operation. . Similarly, Patent Document 2 merely describes suppressing power consumption during a standby operation, and does not consider reducing power consumption during a reading operation. Further, according to Patent Document 3, the operation frequency is switched for each power consumption mode, but there is no specific proposal on how to reduce the power consumption during the reading operation.

  Note that, as in Patent Document 1, if the clock is stopped every time one line is read, various adverse effects also occur. Generally, a CDS (correlated double sampling) circuit or the like for suppressing noise is mounted on an image reading apparatus. In order to operate such a circuit stably, it is necessary to always supply a clock so that the capacitive element is not completely discharged. Therefore, the image reading apparatus discards the first few lines of data as invalid at the initial stage of image reading, and outputs the data as a valid image after the CDS circuit or the like can stably output a normal image. ing. Therefore, if the clock is stopped for each line, there is a possibility that a normal image cannot be output.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to reduce power consumption during a reading operation. Other issues can be understood throughout the specification.

The image reading apparatus of the present invention includes:
Reading means for outputting an image of a document as an electrical signal;
Line synchronization signal output means for outputting a line synchronization signal for ensuring synchronization for each line of the image;
An image effective area signal output means for outputting an image effective area signal indicating an effective area of the image of the document;
Clock generation means for generating a clock to be supplied to the reading means;
The frequency of the clock applied during a period from the timing when the effective area of the image of the original indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal is determined as the effective area of the image. Clock adjusting means for adjusting the frequency to be lower than the frequency of the clock applied in
With
The clock adjusting means includes a period from a timing when an effective area of the original image indicated by the image effective area signal ends to a synchronization timing of a next line indicated by the line synchronization signal, and the image effective area signal indicates Clock frequency determining means for determining the frequency of the clock applied in the period based on the time from the timing when the effective area of the image of the document ends to the timing when the sensor effective area of the reading means ends. ,
The clock frequency determining means is a source for generating an original from which the clock generating means generates a time from a timing when the effective area of the image of the document indicated by the image effective area signal ends to a timing when the sensor effective area of the reading means ends. By dividing by the period of the clock, and further by dividing by the period from the timing when the effective area of the original image indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal, A calculating means for calculating the frequency of the clock applied during the period is provided .

  According to the present invention, power consumption during a reading operation can be reduced.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[Embodiment 1]
FIG. 1 is a block diagram illustrating an image reading apparatus according to an embodiment. The image reading apparatus 100 is sometimes called an image reader or an image scanner. In addition, the image reading apparatus 100 may be commercialized as a single unit, or may be commercialized as a part of an image forming apparatus such as a facsimile, a copier, or a multifunction peripheral.

  The CPU 1 is a unit that comprehensively controls the entire image reading apparatus. The RAM 2 is a storage unit that functions as a work memory for the CPU 1. The ROM 3 is a storage unit for storing the computer program of the CPU 1 and necessary data. The ASIC 4 is a control circuit unit in which circuits relating to image reading processing are integrated. The reading sensor 5 is an optical sensor as image reading means. The reading sensor 5 is a line sensor such as a CIS (contact sensor) method or a CCD (charge coupled device) method. The reading sensor 5 is an example of a reading unit that outputs an image of a document as an electric signal.

  The AD converter 6 is a unit that converts an analog image signal output from the reading sensor 5 into a digital image signal. The image output unit 7 is an interface for outputting the image signal output from the ASIC 4 to a PC (personal computer) or the like. The image output unit 7 is, for example, a USB interface, a SCSI interface, a LAN interface, or the like.

  The ASIC 4 includes the following functional units. The PAGE signal output unit 10 outputs a PAGE signal indicating an effective period in the sub-scanning direction at the time of image reading. The sub-scanning direction is generally the direction in which the reading sensor 5 moves relative to the document. Note that the scanning direction of the line sensor orthogonal to the sub-scanning direction is a so-called main scanning direction.

  The HSYNC signal output unit 11 outputs an HSYNC signal indicating the synchronization timing in the main scanning direction during image reading. Generally, in an image reading apparatus that reads an image of a document line by line, an HSYNC signal is output line by line.

  The SP signal output unit 12 outputs an SP signal for indicating the start of reading to the reading sensor 5. When the falling edge of the HSYNC signal is detected, the SP signal falls after one clock and rises again after a half clock. Thus, the SP signal is synchronized with the HSYNC signal. Therefore, the SP signal output unit 12 is an example of a line synchronization signal output unit that outputs a line synchronization signal for ensuring synchronization for each line of an image.

  The variable clock generator 13 generates a clock signal C_CLK for operating the reading sensor 5 and outputs the clock signal C_CLK to the reading sensor 5. The LED signal output unit 14 generates and outputs an LED signal for turning on the LED that is the light source of the reading sensor 5.

  The ADCLK signal output unit 16 outputs an ADCLK signal indicating the sampling timing of the AD converter 6 to the AD converter 6. The MCLK signal output unit 17 outputs an MCLK signal, which is a clock signal serving as a reference for the output timing of image data, to the AD converter 6 and the data capturing unit 19.

  The HAVA signal output unit 18 outputs a HAVA signal indicating the effective width of the image in the main scanning direction to the data capturing unit 19. The HAVA signal output unit 18 is an example of an image effective area signal output unit that outputs an image effective area signal indicating an effective area of an original image.

  The data capturing unit 19 captures digital data from the AD converter 6 according to the MCLK signal and the HAVA signal. The image processing unit 20 performs various types of image processing (eg, γ correction) on the captured image. The register unit 21 holds various parameters set by the CPU 1.

  The operation panel 8 includes a display device and an input device, and is used, for example, to input information such as a document size. Therefore, the operation panel 8 is an example of a designation unit that designates an effective area of an original image.

  FIG. 2 is a diagram showing the relationship between various signals and the effective area of an image. The size of the effective area of the image in the main scanning direction is indicated as a period TH from the falling edge to the rising edge of the HAVA signal. The size in the sub-scanning direction of the effective area of the image is indicated as a period TV from the falling edge to the rising edge of the PAGE signal.

  FIG. 3 is a block diagram illustrating the variable clock generation unit 13 according to the embodiment. FIG. 4 is an exemplary timing chart of the image reading process according to the embodiment.

  The register 30 holds a value of T0 that is the SP interval. The register 31 holds T2, which is the time HAVA2 from the fall of the SP signal to the fall of the HAVA signal. The register 32 holds T3 which is the effective width HAVA3 of the HAVA signal. The register 33 holds T1, which is the time (sensor effective width) required for reading the effective portion of the reading sensor 5. These registers are included in the register unit 21. Each value is set by the CPU 1. When the sensor effective width includes a dummy region that needs to perform a reading operation in order to maintain a normal operation, a period for the dummy region is included.

  The clock frequency calculation unit 34 calculates a frequency division ratio according to the parameter supplied from the register unit 21 and sets it in the clock frequency divider 35. The clock divider 35 divides the original clock signal C_CLK0 (cycle Ta) transmitted from the original clock unit 36 according to the set division ratio, and outputs the divided clock signal C_CLK to the reading sensor 5. To do. The original clock unit 36 is an example of a clock generation unit that generates a clock to be supplied to the reading unit.

According to FIG. 4, the period from the fall of the SP signal to the next fall is called the SP interval and is indicated by T0. The period from the falling edge to the rising edge of the sensor effective width signal is called the sensor effective width, and is indicated by T1. The period from the fall of the SP signal to the fall of the HAVA signal is called HAVA2 and is indicated by T2. The period from the fall of the HAVA signal to the rise is called HAVA and is indicated by T3. T3 is the same as TH in FIG.

  T4 indicates the time from the timing when the effective area of the original image indicated by the HAVA signal (image effective area signal) ends to the timing when the sensor effective area of the reading sensor 5 ends. T5 indicates a period corresponding to the invalid area of the reading sensor 5. T6 indicates a period from the timing when the effective area of the original image indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal.

  Using these parameters, the clock frequency calculation unit 34 adjusts the clock frequency applied in the period T6 to be lower than the clock frequency applied in the effective region of the image. For example, the clock frequency calculation unit 34 determines the frequency of the clock applied to the period T6 from the length of the period T6, the length of the period T4, and the period Ta of the original clock signal C_CLK0. As described above, the clock frequency calculation unit 34 applies the frequency of the clock applied in the period from the timing when the effective area of the original image indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal. Is an example of a clock adjustment unit that adjusts the frequency to be lower than the frequency of the clock applied in the effective area of the image. The clock frequency calculation unit 34 also includes a period from the timing when the effective area of the document image indicated by the image effective area signal ends to the synchronization timing of the next line indicated by the line synchronization signal, and the original indicated by the image effective area signal. The frequency of the clock applied to the period is determined based on the time from the end of the effective area of the image to the timing of the end of the sensor effective area of the reading means and the period of the original clock generated by the clock generation means It is an example of the clock frequency determination means to perform.

  The length of the period T6 from the rising edge of the HAVA signal to the falling edge of the next SP signal can be calculated by the following equation.

T6 = T0− (T2 + T3)
A period T4 from the rise of the HAVA signal to the end of the sensor effective width can be calculated by the following equation.

T4 = T1- (T2 + T3)
The clock number CNT1 from the rise of the HAVA signal to the end of the sensor effective width can be calculated by the following equation.

CNT1 = T4 / Ta
Therefore, the clock frequency f required as the lower limit value can be calculated by the following equation.

      f = CNT1 / T6 [Hz].

  As apparent from FIG. 4, the frequency f of the adjusted clock signal C_CLK is lower than the frequency f0 of the original clock signal C_CLK0. Therefore, in the period T6, power saving can be achieved without stopping the clock. Further, by doing so, the necessary clock can be supplied to the reading sensor 5 until the reading sensor 5 completes the output of the reading information within the sensor effective width, so that the operation of the reading sensor 5 is not hindered. . As described above, the clock frequency calculation unit 34 generates the time from the timing at which the effective area of the document image indicated by the image effective area signal is completed to the timing at which the sensor effective area of the reading unit is completed. By dividing by the period of the clock, and by dividing by the period from the timing when the effective area of the original image indicated by the image effective area signal ends to the synchronization timing of the next line indicated by the line synchronization signal, the period T6 is reached. It is an example of the calculation means which calculates the frequency (lower limit) of the clock which reduced the applied frequency.

  FIG. 5 is a diagram showing a table for obtaining a frequency division ratio to be set corresponding to a necessary clock frequency. The clock frequency calculation unit 34 determines the frequency division ratio from the table according to the required value of the clock frequency f and sets it in the clock frequency divider 35. This table is set in advance so that, for example, a clock signal having a MAX value f2 that is a target value of a necessary clock frequency can be obtained by using the division ratio of R1. This table is stored in the ROM 3. The clock frequency calculation unit 34 sends a necessary clock frequency (lower limit value) f value to the CPU 1 and inquires and acquires the corresponding frequency division ratio.

  The timing at which the clock frequency calculation unit 34 sets the frequency division ratio in the clock frequency divider 35 can be obtained from the register setting value. For example, in the periods T2 and T3, the clock frequency calculation unit 34 outputs a frequency division ratio that can output a clock having a frequency that provides a steady reading speed. After the periods T2 and T3 have elapsed (that is, when the period T6 is entered), the clock frequency calculation unit 34 sets the determined frequency dividing ratio in the clock frequency divider 35.

  As described above, according to the present embodiment, the clock frequency is reduced in the period T6 during the reading operation of the image reading apparatus 100. In particular, conventionally, since the operation was performed with a stationary clock during the period T5, power was wasted. However, according to the present embodiment, only a necessary clock can be supplied to the reading sensor 5 in the period T5. Therefore, in this embodiment, power consumption can be reduced even during the reading operation. Note that since the clock is not stopped, it is possible to suppress deterioration in image quality due to the operation of the noise reduction circuit being stopped.

  For example, the clock frequency calculation unit 34 determines the frequency (lower limit value) f of the clock applied to the period T6 from the period T6, the period T4, and the period Ta of the original clock signal C_CLK0, thereby reading the sensor 5. The operating frequency can be made close to the lower limit value. For example, the influence of electromagnetic radiation noise (EMI) may be reduced. Further, when the reading sensor 5 operates at a clock frequency lower than normal, heat generation is reduced, dark current of the charge coupled device is reduced, and image quality is improved.

In the first embodiment, a method of dividing the original clock by providing the clock divider 35 as the variable clock generator 13 has been described. However, instead of the clock divider 35, the original clock is thinned out. You may build logic. Further, the to produce a clock of low frequency performed by the clock frequency calculator 34 and the clock divider 35 may be replaced by a variable frequency oscillator such as a possible PLL frequency synthesizer generates a clock of a frequency a target .

[Embodiment 2]
In the image reading apparatus according to the present embodiment, which is a modification of the first embodiment, the image effective area can be changed by the operator specifying the document size. In particular, any document size narrower than the sensor effective width of the reading sensor 5 can be freely specified. Therefore, in the present embodiment, an image reading operation when the operator specifies a document size narrower than the sensor effective width will be described.

  FIG. 6 is an exemplary timing chart of the image reading process according to the second embodiment. The description will be simplified by giving the same reference numerals to the parts already described.

  When the document size is designated by the operator through the operation panel 8, the CPU 1 changes the value of HAVA3 from the initial value T3 to T3 'in accordance with the size of the document, and stores T3' in the register 32. The HAVA signal output unit 18 outputs a HAVA signal corresponding to the effective area of the document image designated by the CPU 1.

  Note that the periods T0, T1, T2, and T5 are parameters that do not depend on the size of the document, but the period T4 is changed depending on the document and becomes T4 '. Similarly, the period T6 is also changed to T6 '.

  If the size of the document in the main scanning direction becomes smaller, the period T4 'becomes longer than the period T4. Therefore, the number of clocks CNT2 that needs to be given to the reading sensor 5 after the rise of the HAVA signal increases.

  The clock frequency calculation unit 34 calculates a period T6 'from the rising edge of the HAVA signal to the falling edge of the next SP signal by the following equation.

T6 ′ = T0− (T2 + T3 ′)
The clock frequency calculation unit 34 calculates a period T4 ′ from the rise of the HAVA signal to the end of the sensor effective width by the following equation.

T4 '= T1- (T2 + T3')
The clock frequency calculation unit 34 calculates the clock number CNT2 from the rising edge of the HAVA signal to the end of the sensor effective width by the following equation.

CNT2 = T4 '/ Ta
Finally, the clock frequency calculation unit 34 calculates the lower limit value f of the required clock frequency by the following equation.

f = CNT2 / T6 ′ [Hz]
Note that the frequency division ratio may be determined from the necessary clock frequency (lower limit value) f using a table as in the first embodiment.

  As described above, according to the present embodiment, the clock frequency is adjusted according to the size of the document in the main scanning direction designated by the operator. Therefore, in addition to the same effects as in the first embodiment, the reading sensor 5 can be operated at a clock frequency suitable for the size of the document. That is, if the original size can be specified, the power saving effect during the reading operation can be increased as compared with the case where the reading size is fixed regardless of the size of the original.

[Embodiment 3]
In the image reading apparatus 100 according to the present embodiment, which is a modification of the first embodiment, the operator can change the image reading speed through the operation panel 8. For example, when the reading speed is lowered, the SP interval becomes wider. If the SP interval becomes wide, it is necessary to lengthen the length of the period T6 during which the clock is reduced during the reading operation. Therefore, in the third embodiment, an image reading operation when the image reading speed is changed will be described.

  FIG. 7 is an exemplary timing chart of the image reading process according to the third embodiment. The description will be simplified by giving the same reference numerals to the parts already described.

  When the image reading speed is designated by the operator through the operation panel 8, the CPU 1 sets the designated image reading speed in the ASIC 4. Therefore, the CPU 1 is an example of a setting unit that sets the image reading speed of the reading unit. The HSYNC signal output unit 11 changes the HSYNC interval according to the set image reading speed and outputs an HSYNC signal. Therefore, the SP signal output unit 12 changes the SP interval according to the set image reading speed and outputs an SP signal. Therefore, the period T0 is changed to T0 ″.

  Note that the periods T1, T2, T3, and T4 are parameters that do not depend on the image reading speed, but the period T5 is changed depending on the T5 ″. Similarly, the period T6 is also changed to T6 ″.

  According to FIG. 7, the period T5 ″ is longer than the period T5 by T7 (T7 = T0 ″ −T0). After the HAVA signal rises, the number of clocks CNT3 that need to be given to the reading sensor 5 is the same as CNT1.

  The clock frequency calculation unit 34 calculates a period T6 ″ from the rising edge of the HAVA signal to the falling edge of the next SP signal by the following equation.

T6 "= T0"-(T2 + T3)
Note that the period T4 and the number of clocks are the same as in the first embodiment (CNT3 = CNT1). Therefore, the necessary clock frequency (lower limit value) f is as follows.

f = CNT3 / T6 "[Hz]
Note that the frequency division ratio may be determined from the lower limit value f using a table as in the first embodiment.

  As described above, according to the present embodiment, the clock frequency is adjusted according to the set image reading speed. Therefore, in addition to the same effects as those of the first embodiment, the reading sensor 5 can be operated at a suitable clock frequency according to the image reading speed. That is, if the clock frequency is adjusted according to the image reading speed, the power saving effect during the reading operation can be increased.

[Other Embodiments]
It is obvious that the second embodiment and the third embodiment may be combined. That is, the present invention can be suitably applied even if the size of the document is specified and the image reading speed is changed. In this case, the clock frequency is determined according to the following equation.

T6a = T0 ″ − (T2 + T3 ′)
T4a = T1- (T2 + T3 ′)
CNTa = T4a / Ta
f = CNTa / T6a
Therefore, even in an image reading apparatus in which the document size and the image reading speed can be changed, it is possible to reduce power consumption during the reading operation. T6a corresponds to T6, and T4a corresponds to T4. In each of the embodiments described above, it is preferable that the clock frequency of the portion for reducing the clock is set slightly higher than the above-described calculated value (lower limit value f). This is to reduce power consumption while preventing noise degradation. When the frequency division ratio is determined using a table, it may be set slightly higher than the lower limit f, and is included in the present invention. Even when the actual frequency is determined by a method other than the table, it may be set slightly higher than the lower limit value f, and is included in the present invention.

1 is a block diagram illustrating an image reading apparatus according to an embodiment. It is the figure which showed the relationship between various signals and the effective area | region of an image. It is a block diagram which shows the variable clock generation part 13 which concerns on embodiment. 3 is an exemplary timing chart of image reading processing according to the first embodiment. It is the figure which showed the table for obtaining the frequency division ratio which should be set corresponding to a required clock frequency. 6 is an exemplary timing chart of image reading processing according to the second embodiment. 10 is an exemplary timing chart of image reading processing according to the third embodiment.

Explanation of symbols

1 CPU
2 RAM
3 ROM
4 ASIC
5 Reading Sensor 6 AD Converter 7 Image Output Unit 8 Operation Panel 12 SP Signal Output Unit 13 Variable Clock Generation Unit 18 HAVA Signal Output Unit 34 Clock Frequency Calculation Unit 35 Clock Divider

Claims (5)

Reading means for outputting an image of a document as an electrical signal;
Line synchronization signal output means for outputting a line synchronization signal for ensuring synchronization for each line of the image;
An image effective area signal output means for outputting an image effective area signal indicating an effective area of the image of the document;
Clock generation means for generating a clock to be supplied to the reading means;
The frequency of the clock applied during a period from the timing when the effective area of the image of the original indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal is determined as the effective area of the image. Clock adjusting means for adjusting the frequency to be lower than the frequency of the clock applied in
Equipped with a,
The clock adjusting means includes a period from a timing when an effective area of the original image indicated by the image effective area signal ends to a synchronization timing of a next line indicated by the line synchronization signal, and the image effective area signal indicates Clock frequency determining means for determining the frequency of the clock applied in the period based on the time from the timing when the effective area of the image of the document ends to the timing when the sensor effective area of the reading means ends. ,
The clock frequency determining means is a source for generating an original from which the clock generating means generates a time from a timing when the effective area of the image of the document indicated by the image effective area signal ends to a timing when the sensor effective area of the reading means ends. By dividing by the period of the clock, and further by dividing by the period from the timing when the effective area of the original image indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal, An image reading apparatus comprising: a calculating unit that calculates the frequency of the clock applied during the period . Further comprising designation means for designating an effective area of the image of the document;
The image reading apparatus according to claim 1, wherein the clock adjusting unit adjusts a frequency of the clock according to an effective area specified by the specifying unit. Setting means for setting an image reading speed of the reading means;
Said clock adjustment means includes an image reading apparatus according to claim 1 or 2, characterized in that to adjust the frequency of said clock in accordance with an image reading speed set by said setting means.   The said clock adjustment means adjusts the frequency of the said clock higher than the lower limit of the frequency of the said clock calculated by the said calculation means, when adjusting the frequency of the said clock. Image reading device. A method for controlling an image reading apparatus including reading means for outputting an image of a document as an electrical signal,
Generating a clock for supplying to the reading means;
Outputting an image effective area signal indicating an effective area of the image of the document;
Outputting a line synchronization signal for ensuring synchronization for each line of the image;
The frequency of the clock applied during a period from the timing when the effective area of the image of the original indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal is determined as the effective area of the image. Adjusting the frequency to be lower than the frequency of the clock applied in
Only including,
In the step of adjusting the frequency of the clock,
The period from the end of the effective area of the original image indicated by the image effective area signal to the synchronization timing of the next line indicated by the line synchronization signal, and the validity of the original image indicated by the image effective area signal In determining the frequency of the clock applied in the period based on the time from the timing when the region ends to the timing when the sensor effective region of the reading unit ends.
Dividing the time from the end of the effective area of the original image indicated by the image effective area signal to the end of the sensor effective area of the reading unit by the period of the original clock generated by the clock generation unit; Further, by dividing by a period from the timing when the effective area of the original image indicated by the image effective area signal ends to the timing of synchronization of the next line indicated by the line synchronization signal, the division is applied to the period. A method for controlling an image reading apparatus, comprising calculating a frequency of a clock .

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