JP5568460B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus and an image forming apparatus that suppress heat generation of a light source used when reading an image.

  In recent years, image reading is performed by irradiating a document with light, and receiving reflected light from an image sensor such as a CCD (Charge Coupled Device) and converting it into image data, thereby converting the image drawn on the document into data. The device has been put into practical use. An LED (Light Emitting Diode) light source has come to be frequently used as a light source for irradiating a document with light.

  When an LED is used as a light source, a large number of LEDs are used to obtain a sufficient amount of light, or a high-brightness LED is used. Furthermore, the temperature of the LED also increases when the continuous irradiation time of the LED takes a long time due to continuous reading of a large number of sheets. Thus, when the temperature of the LED exceeds the use upper limit temperature, characteristics such as light amount and chromaticity change, and there is a problem that high-quality image data cannot be obtained.

  Therefore, Patent Document 1 describes an image reading apparatus that adjusts the temperature of a light source using a cooling fan.

JP 2002-237927 A

  However, when the light source is cooled by the cooling fan, there is a possibility that dust, dust or the like may adhere to the optical system in the apparatus. If dust or dirt adheres to the optical system, there is a problem that an image from which the dust or dirt is read appears as a streak image.

  If the reading of the original is stopped for cooling down when the light source exceeds a predetermined temperature, the productivity of the apparatus is deteriorated, and the user is inconvenienced.

  SUMMARY An advantage of some aspects of the invention is that it provides an image reading apparatus and an image forming apparatus that prevent an increase in the temperature of a light source and reduce deterioration of a read image. .

According to one aspect of the present invention, it converts an image reading apparatus, a light source for illuminating a document that will be transported in the sub-scanning direction, into an electric signal by receiving reflected light of light irradiated to the document An image data generating means for outputting image data, a temperature detecting means for detecting the temperature of the light source, and a predetermined time for reading the original for one line in the main scanning direction perpendicular to the sub-scanning direction at normal times. By turning on the light source from the beginning of the reading period, an original reading unit that repeats an operation of reading the original by one line in the main scanning direction, and after the start of reading of the original by the original reading unit, the temperature detection unit when the temperature is above the set temperature predetermined to but was detected by adjusting the duty ratio of the driving voltage applied to the light source by the PWM control, before in each of said reading period And adjusting means for adjusting the lighting time of the light source shorter than during the normal, the integrating filter by weighted addition with respect to the surrounding of the pixel data of each pixel data and the pixel data constituting the image data by the image data generating means has an output Processing means for performing processing, and the processing means performs integral filter processing on the image data output by the image data generation means when the adjustment means adjusts the lighting time of the light source to be short. is there.

  In the present invention, since heat generation of the light source can be suppressed, characteristic changes such as chromaticity due to temperature rise of the light source can be prevented, and power consumption can be suppressed. Further, when the light source is turned off until the temperature of the light source decreases, the reading of the document is interrupted, which causes inconvenience to the user. However, in the present invention, continuous reading for a long time is possible, and the user can wait. Absent. Furthermore, by applying integral filter processing to the read image data, it is possible to reduce image noise caused by a decrease in the amount of light caused by adjusting the lighting time of the light emitting element to be short, and to minimize image quality degradation. it can.

A second aspect of the present invention is the image reading apparatus according to the first aspect, wherein the adjusting means adjusts the lighting time of the light source and the temperature detected by the temperature detecting means and the set temperature. The lighting time of the light source is adjusted to be shorter as the temperature difference between is larger.
A third aspect of the present invention is the image reading apparatus according to the first or second aspect, wherein the processing unit is configured to store the image data even when the adjustment unit does not adjust the lighting time of the light source. When performing integral filter processing on the image data output from the generating means, when the adjusting means adjusts the lighting time of the light source to be short, the processing means sets a larger coefficient than when performing the integral filter processing in the normal time. The integral filter processing is executed on the image data output from the image data generation means by performing weighted addition using the image data.

  According to the present invention, it is possible to reduce image noise caused by a decrease in the amount of light caused by adjusting the lighting time of the light emitting element to be short with respect to the read image data, and it is possible to minimize image quality deterioration.

According to a fourth aspect of the present invention, there is provided the image reading apparatus according to any one of the first to third aspects and an image forming unit that forms an image on a sheet based on the image data acquired by the image reading apparatus. An image forming apparatus provided.

  In this invention, there exists an effect similar to Claim 1 or 2.

  In the present invention, since heat generation of the light source can be suppressed, characteristic changes such as chromaticity due to temperature rise of the light source can be prevented, and power consumption can be suppressed. Further, when the light source is turned off until the temperature of the light source decreases, the reading of the document is interrupted, which causes inconvenience to the user. However, in the present invention, continuous reading for a long time is possible, and the user can wait. Absent. Furthermore, by applying integral filter processing to the read image data, it is possible to reduce image noise caused by a decrease in the amount of light caused by adjusting the lighting time of the light emitting element to be short, and to minimize image quality degradation. it can.

FIG. 2 is a side view schematically showing an internal configuration of the image forming apparatus. FIG. 3 is a schematic diagram when a document reading unit is viewed from above. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus. The flowchart for demonstrating the lighting process of a light source. The timing diagram which shows the lighting timing of a light source. The figure for demonstrating original reading. The figure for demonstrating an example of an integral filter process.

  Hereinafter, an embodiment of an image forming apparatus 1 according to the present invention will be described with reference to the drawings. FIG. 1 is a side view schematically showing an internal configuration of an image forming apparatus 1 according to an embodiment of the present disclosure. The image forming apparatus 1 has functions such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes a main body 2, a stack tray 3 disposed on the left side of the main body 2, and a main body. 2 has a document reading unit 4 disposed above the document reading unit 4 and a document conveying unit 5 disposed above the document reading unit 4. In the present embodiment, the present invention will be described using the image forming apparatus 1. However, the present invention may be applied to an image reading apparatus including only the document reading unit 4. That is, the image forming apparatus 1 only needs to have at least a function of acquiring image data using a scanner function or the like. For example, the image forming apparatus 1 may have only a facsimile function.

  The document feeder 5 includes an ADF (Automatic Document Feeder), and includes a document tray 51, a pickup roller 52, and a paper discharge tray 59. A document to be read is placed on the document tray 51. The documents placed on the document tray 51 are taken one by one by the pickup roller 52 and sequentially conveyed to the conveyance path through the gap. Documents that have passed through the conveyance path are sequentially discharged to a discharge tray 59.

  The document reading unit 4 optically reads an image of a document and generates image data. The document reading unit 4 includes a contact glass 41, a light source 42, a first mirror 43, a second mirror 44, a third mirror 45, a first carriage 46, a second carriage 47, and a lens unit 400. The contact glass 41 is a place on which a document is placed by a user's hand when the document is not read by the document conveying unit 5. The light source 42 includes a plurality of LEDs arranged in the main scanning direction, and is lit by a driving voltage applied from a light source driving circuit described later. A thermistor 421 is disposed in the vicinity of the light source 42. The thermistor 421 is for measuring the temperature of the light source 42, and outputs the detection result to a control unit described later.

  The lens unit 400 includes a lens 48 and a CCD 49. FIG. 2 is a schematic view of the document reading unit 4 as viewed from above. The light emitted from the light source 42 is reflected by the original image placed on the contact glass 41, and the reflected light is guided to the CCD 49 by the first mirror 43, the second mirror 44, the third mirror 45 and the lens 48. The CCD 49 photoelectrically converts the received light and outputs image data.

  As a document reading method, there are a flatbed reading mode in which the CCD 49 reads a document placed on the contact glass 41, and an ADF reading mode in which the document is taken in by the document transport unit 5 (ADF) and is read during the transport. . In the flat bed reading mode, the light source 42 irradiates a document placed on the contact glass 41, and the reflected light for one line in the main scanning direction is reflected in the order of the first mirror 43, the second mirror 44, and the third mirror 45. Then, the light passes through the lens 48 and enters the CCD 49. The CCD 49 is a one-dimensional image sensor, and simultaneously processes image data of one line extending in the main scanning direction. The first carriage 46 and the second carriage 47 are configured to be movable in a direction orthogonal to the main scanning direction (sub-scanning direction, arrow Y direction). When reading of one line is completed, the first carriage 46 and the second carriage 47 are moved in the sub-scanning direction. The first carriage 46 and the second carriage 47 move, and the next line is read.

  In the ADF reading mode, the document conveying unit 5 takes in the documents placed on the document tray 51 one by one by the pickup roller 52. At this time, the first carriage 46 and the second carriage 47 are disposed below the document reading window 53 made of a transparent material such as a glass member. When the original passes through the original reading window 53 in the original conveyance by the original conveyance section 5, the light source 42 irradiates the original, and the reflected light for one main scanning line is reflected in the first mirror 43, the second mirror 44, and the third. The light is reflected in the order of the mirror 45, passes through the lens 48, and enters the CCD 49. Subsequently, the original is conveyed by the original conveying section 5 and the next line is read.

  An input operation unit 6 is provided on the front surface of the document reading unit 4. The input operation unit 6 displays a start key 61 for a user to input an execution instruction, a numeric keypad 62 for inputting the number of copies to be printed, operation guide information for various operations, etc., and a touch panel for inputting these various settings. Display unit 63 having a liquid crystal display or the like having a function, a reset key 64 for resetting setting contents set in the display unit 63, a stop key 65 for stopping an operation being executed, a copy function, a printer function, a scanner function And a function switching key 66 for switching the facsimile function.

  The main body 2 includes a plurality of paper feed cassettes 19, a paper feed roller 20 that feeds the paper from the paper feed cassette 19 one by one and transports it to the image forming unit 21, and an image on the paper transported from the paper feed cassette 19. And the stack tray 3 and the discharge tray 29 on which sheets to be discharged are stacked.

  The image forming unit 21 outputs a laser beam or the like based on the image data acquired by the document reading unit 4 to expose the photosensitive drum 22 to form an electrostatic latent image on the surface of the photosensitive drum 22. A developing unit 24 that forms a toner image by attaching toner to the surface of the photosensitive drum 22 on which the electrostatic latent image is formed, and a transfer unit 25 that transfers the toner image on the photosensitive drum 22 to a sheet. A fixing device 28 provided with a fixing roller 26 and a pressure roller 27 for heating the paper on which the toner image is transferred to fix the toner image on the paper, and a paper conveying path in the image forming unit 21; Are provided with a pair of conveying rollers 30 and 31 and the like.

  When images are formed on both sides of a sheet, the image forming unit 21 forms an image on one side of the sheet, and then the sheet is nipped between the pair of conveying rollers 30 on the discharge tray 29 side. In this state, the conveyance roller pair 30 is reversed to switch back the sheet, and the sheet is sent to the sheet conveyance path 32 to be conveyed again to the upstream area of the image forming unit 21. The image forming unit 21 forms an image on the other surface. After that, the paper is discharged to the stack tray 3 or the discharge tray 29.

  FIG. 3 is a block diagram illustrating an electrical configuration of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 71, a storage unit 72, a document transport unit 5, a document reading unit 4, an image memory 73, an image processing unit 74, an image forming unit 21, an input operation unit 6, and a network I / F unit 75. It is prepared for. In addition, the same code | symbol is attached | subjected to the same component as demonstrated using FIG. 1, and description is abbreviate | omitted.

  The storage unit 72 stores programs, data, and the like for realizing various functions provided in the image forming apparatus 1. The image memory 73 temporarily stores an image read by the document reading unit 4 and an image transmitted from an external device via the network I / F unit 75. The image processing unit 74 performs image processing such as correction and enlargement / reduction on the image read by the document reading unit 4, and includes a filter unit 741. The filter unit 741 performs integral filter processing on the image, and details will be described later. The network I / F unit 75 is a communication interface circuit that communicates with an external device via a network such as a LAN (Local Area Network) or a WAN (Wide Area Network).

  The control unit 71 is configured by a CPU (Central Processing Unit) or the like, reads a program stored in the storage unit 72 and executes processing, and outputs an instruction signal to each functional unit, data transfer, and the like. The image forming apparatus 1 is comprehensively controlled and has a temperature detection unit 711.

  The temperature detection unit 711 takes in the detection signal of the thermistor 421 and calculates the temperature of the light source 42. When the calculated temperature is equal to or higher than a predetermined set temperature, an instruction signal for shortening the lighting time of the light source 42 is output to the light source driving circuit 422. The set temperature can be arbitrarily set according to the characteristics of the LED used for the light source 42, and is set in advance by a designer at the design stage of the apparatus and stored in advance in a storage unit in the control unit 71.

  When the light source driving circuit 422 receives an instruction signal for shortening the lighting time from the temperature detection unit 711, the light source driving circuit 422 adjusts the pulse width of the driving voltage applied to the light source 42 by PWM (Pulse Width Modulation) control. As an adjustment method, for example, when a drive voltage is applied to the light source 42 with a duty ratio of 100% in normal times (the temperature of the light source 42 is lower than the set temperature), when an instruction signal is received from the temperature detection unit 711, the light source drive circuit 422 Decreases the lighting time of the light source 42 by setting the duty ratio of the pulse width of the driving voltage to a predetermined ratio (for example, 70%) smaller than the normal time.

  Since the LED used as the light source 42 is a highly efficient light source, the need for forced cooling is low. However, if a large number of LEDs are used to obtain a sufficient amount of light, or if a high-brightness LED is used, May exceed the upper limit of use temperature. In addition, when the lighting time of the light source 42 is long, such as when a plurality of originals are continuously read, the use upper limit temperature may be exceeded. Generally, the upper limit temperature for use of the LED is about 70 ° C. to 100 ° C. If this temperature is exceeded, characteristics such as chromaticity change, and further problems such as deterioration of the package and the fluorescent agent occur.

  Therefore, when the temperature of the light source 42 becomes equal to or higher than the set temperature, the pulse width of the driving voltage applied to the light source 42 by the light source driving circuit 422 is adjusted to be short in response to an instruction from the temperature detection unit 711. Thereby, the lighting time of the light source 42 becomes short, and a temperature rise can be prevented.

  This will be specifically described below. FIG. 4 is a flowchart for explaining the lighting process of the light source 42. When the user presses the start key 61 to instruct the start of document reading (step S11), the temperature detection unit 711 takes in the detection signal of the thermistor 421 and calculates the temperature of the light source 42 (step S12). When the calculated temperature of the light source 42 is equal to or higher than the set temperature (step S13; YES), the temperature detection unit 711 outputs an instruction signal for shortening the lighting time of the light source 42 to the light source driving circuit 422. The light source drive circuit 422 receives this instruction signal and adjusts the pulse width of the drive voltage applied to the light source 42 to be short by PWM control (step S14).

  When the temperature of the light source 42 is lower than the set temperature (step S13; NO), the control unit 71 causes the light source drive circuit 422 to normally light the light source 42 (step S15). When the reading of one original is completed (step S16; YES) and then the next original is read (step S17; NO), the control unit 71 shifts the processing to step S12. When all the originals have been read (step S17; YES), the control unit 71 causes the light source driving circuit 422 to turn off the light source 42.

  The above processing may be performed for each original document (or for each predetermined number of one or more documents), or the temperature of the light source 42 is detected at predetermined time intervals during reading of the original document. When the temperature exceeds the set temperature, the lighting time of the light source 42 may be adjusted to be short even during reading. However, if the lighting time of the light source 42 changes during the reading of the original, the image quality changes in one original image acquired by the CCD 49. Therefore, when reading a plurality of documents, it is desirable to detect the temperature of the light source 42 for every predetermined number of sheets and adjust the lighting time. Alternatively, the lighting time of the light source 42 may be adjusted by detecting the temperature of the light source 42 only when the number of documents is a predetermined number or more (for example, 100 or more).

  Next, the adjustment method of the lighting time of the light source 42 performed in step S14 of FIG. 4 will be described in detail. 5A and 5B are timing charts showing the lighting timing of the light source 42. FIG. 5A shows a timing chart when the lighting time of the light source 42 is adjusted to be short, and FIG. . The signal S1 is a signal indicating that reading of one line in the main scanning direction is started. At the time of reading the first line, the light source driving circuit 422 applies a driving voltage to the light source 42 in synchronization with the signal S1, The light source 42 is turned on at the rising edge of this signal (ON = lighting and OFF = light-off in the figure). Further, when the CCD charge accumulation time is at the H level, it indicates that the CCD 49 is accumulating charges.

  During this time, in the flatbed reading mode, the light source 42 moves at a constant speed in the sub-scanning direction (the arrow Y direction in FIG. 1), and in the ADF reading mode, the position of the light source 42 is fixed and the document is moved in the sub-scanning direction. Since the document is conveyed, the relative positional relationship between the document and the light source 42 moves at a constant speed in the sub-scanning direction. Normally, the light source 42 is continuously turned on until the reading of the original is completed.

  However, when the temperature of the light source 42 becomes equal to or higher than the set temperature, the temperature detection unit 711 outputs an instruction signal, and the light source driving circuit 422 receives this signal and the pulse width of the driving voltage by PWM control based on the falling timing of the signal S1. Adjust briefly. The duty ratio of drive voltage (ratio of times Ta and Tb) may be set in advance, or the duty ratio is adjusted in proportion to the difference between the set temperature and the detected temperature (the larger the temperature difference, the longer the lighting time Ta). It may be shortened).

  In this way, when the light source 42 is turned off during reading for one line, the amount of light is reduced in the pixels on the downstream side in the sub-scanning direction in one line, and pixels that cannot be read sufficiently are generated. This point will be described with reference to FIGS. For example, one pixel in the sub-scanning direction read when scanning one line is divided into four. The quartered pixels A, B, C, and D shown in FIG. 5B are pixels arranged in the sub-scanning direction. Then, as shown in FIG. 5B, when a driving voltage is applied to the light source 42 at a duty ratio of 50%, for example, the light source 42 is turned on when reading A and B, but C and D are changed. When reading, the light source 42 is turned off. Actually, since there is afterglow after turning off, ambient light other than the light source 42, etc., there is a slight amount of light when reading C and D, but the amount of light is lower than when reading A and B.

  That is, as shown in FIG. 6, the A and B lines can be read with a sufficient amount of light, but the C and D lines are read in a state where the amount of light is insufficient. Therefore, when compared with an image read with the light source 42 continuously turned on (normal time), noise in the read image increases (S / N deteriorates).

  Therefore, when the filter unit 741 performs the integral filter process on the image read when the lighting time of the light source 42 is shortened, the filter process is performed using a larger coefficient than in the normal case. By doing so, noise can be reduced. However, since the integral filter is a filter that works in a direction that eliminates edges, if the filter process is performed using a larger coefficient than in the normal case, the image after the filter process becomes an image in which the shading is smoothed.

  However, if the lighting time of the light source 42 is shortened, an effect of relatively increasing the resolution can be obtained, so that the disadvantages due to the filter processing using the large coefficient described above can be offset. This point will be described in detail with reference to FIG. As described above, when the drive voltage supplied to the light source 42 is 100% duty ratio (normally lit), all four lines A, B, C and D can be irradiated and read normally, and the duty ratio is 50%. If the lighting time is shortened, only the A and B lines are irradiated.

  Here, since the light receiving portion of the CCD 449 has a predetermined light receiving width in the sub-scanning direction, for example, the A, B, and C lines are read simultaneously. Therefore, when reading with a duty ratio of 100% while scanning in the sub-scanning direction with the light receiving width, when the Nth A line is used as a starting point, A to G are read. Then, when scanning shifts to the (N + 1) th line, E to K are read.

  Next, considering a case where the duty ratio is 50%, A to E are read. When the scan shifts to the (N + 1) th line, E to I are read. Compared to when the duty ratio is 100%, when the duty ratio is 50%, when reading the F and G lines, the light source 42 is not lit, so this line is not read. In other words, since reading is always performed across a plurality of lines when the duty ratio is 100%, the image acquired by the CCD 449 is blurred in the sub-scanning direction. When the duty ratio is 50%, the overlapped reading amount (ratio) of the adjacent line is lowered, and this blurred state is reduced. Therefore, when the lighting time of the light source 42 is shortened, an effect of relatively increasing the resolution can be obtained.

FIG. 7 is a diagram for explaining an example of the integral filter processing. In the integral filter process, the filter unit 741 develops the image data sent from the document reading unit 4 into a 3 × 3 pixel matrix. Here, assuming that the pixel G3 is a pixel of interest, the filter unit 741 calculates a weighted average indicated by a coefficient 91 for each pixel data of the pixels G1, G2, G4, and G5 in contact with the pixel G3, Data after the integral filter processing of the pixel G3 is obtained. Data P3 after the integration filter processing of the target pixel G3 is calculated according to the following equation (1).
P3 = (a * G1 + b * G2 + c * G3 + b * G4 + a * G5) / 256 (1)
Here, when integral filter processing is performed on an image read when the light source 42 is in a normal lighting time, a normal coefficient is used, and an image read when the light source 42 is in a short lighting time is used. When performing integral filter processing, a coefficient larger than a normal coefficient is used. By doing so, it is possible to reduce noise generated due to insufficient light quantity of the light source 42.

  As described above, when the temperature of the light source 42 becomes equal to or higher than the set temperature, the temperature detection unit 711 outputs an instruction signal to the light source driving circuit 422, and the light source driving circuit 422 receives the signal and applies it to the light source 42. The pulse width of the driving voltage to be reduced is shortened by PWM control. Thereby, the temperature rise of the light source 42 can be prevented. Then, when the filter unit 741 performs integral filter processing on the image read when the lighting time of the light source 42 is shortened, the coefficient used when the integral filter processing is performed on the image read at the normal lighting time. Perform filtering using large coefficients. By doing so, it is possible to reduce the influence of image noise caused by a decrease in the amount of light, and to minimize image quality degradation.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Main-body part 3 Stack tray 4 Original reading part (image reading apparatus)
41 Contact glass 42 Light source 421 Thermistor (temperature detection means)
422 Light source drive circuit (adjustment means)
48 Lens 49 CCD (Image data generating means)
5 Document Feeding Unit 6 Input Operation Unit 71 Control Unit 711 Temperature Detection Unit (Temperature Detection Unit)
72 Storage Unit 73 Image Memory 74 Image Processing Unit 741 Filter Unit (Processing Means)
75 Network I / F section

Claims (4)

A light source for irradiating light to the document that will be transported in the sub-scanning direction,
Image data generating means for receiving reflected light of the light irradiated on the original, converting it into an electrical signal, and outputting image data;
Temperature detecting means for detecting the temperature of the light source;
Normally, by turning on the light source from the beginning of a predetermined reading period for reading the original for one line in the main scanning direction orthogonal to the sub-scanning direction, the original is scanned for one line in the main scanning direction. Document reading means for repeating the reading operation;
After the reading of the original by the original reading means, when the temperature detected by the temperature detecting means is equal to or higher than a preset temperature, by adjusting the duty ratio of the drive voltage applied to the light source by PWM control, Adjusting means for adjusting the lighting time of the light source in each of the reading periods to be shorter than the normal time ;
Processing means for performing integral filter processing by weighted addition on each pixel data constituting the image data output by the image data generating means and pixel data around the pixel data;
And the processing means performs integral filter processing on the image data output from the image data generation means when the adjustment means adjusts the lighting time of the light source to be short. The adjustment means adjusts the lighting time of the light source to be shorter as the temperature difference between the temperature detected by the temperature detection means and the set temperature is larger when adjusting the lighting time of the light source. The image reading apparatus according to 1. Even when the adjusting means does not adjust the lighting time of the light source, when the processing means performs integral filter processing on the image data output from the image data generating means, the adjusting means When the lighting time is adjusted to be short, the processing means performs integral filter processing on the image data output by the image data generating means by performing weighted addition using a larger coefficient than when performing the integral filter processing in the normal time. the image reading apparatus according to claim 1 or 2 is to run. An image reading apparatus according to any one of claims 1 to 3, and an image forming unit that forms an image on a sheet based on image data acquired by the image reading apparatus;
An image forming apparatus.