JP6069235B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an image reading apparatus including a contact image sensor and an image forming apparatus including the image reading apparatus.

  2. Description of the Related Art Conventionally, an image reading apparatus such as a copying machine or a scanner that reads an image of an original line by line using a line sensor such as a CCD (Charge Coupled Device) line sensor or a CIS (Contact Image Sensor) is known. It has been.

  The line sensor includes a light source that irradiates light to a document, and a solid-state imaging device that includes a plurality of light receiving elements arranged in a line in the main scanning direction. When the light receiving element receives reflected light from the document, the light receiving element outputs a charge corresponding to the amount of received light by photoelectric conversion. The solid-state imaging device amplifies and outputs the electric charge output from each light receiving element. This output voltage is used as a density voltage indicating the density of each pixel of the image of the reading target line.

  For example, a CCD line sensor uses a CCD image sensor as a solid-state imaging device. The CCD image sensor temporarily transfers the charges output from all the light receiving elements to the output unit. The CCD image sensor sequentially extracts charges from the output unit using a plurality of voltages including a high plus voltage and a minus voltage, and sequentially amplifies and outputs each charge. On the other hand, CIS uses a CMOS image sensor as a solid-state imaging device. The CMOS image sensor includes, for each light receiving element, a capacitor that accumulates the charge output from each light receiving element, and an amplifier that amplifies and outputs the charge accumulated in the capacitor using a low voltage. That is, the CMOS image sensor amplifies and outputs the charges output from each light receiving element individually.

  Such an image reading apparatus is provided with a power supply circuit that supplies a power supply voltage to a plurality of operation units such as the above-described line sensor and automatic document feeder. For this reason, while the image of the document is being read by the line sensor, the amount of current consumption varies due to the operation of other operation units. Thereby, the power supply voltage supplied to the line sensor may be different for each line to be read.

  In this case, since the power supply voltage used when the solid-state imaging device amplifies and outputs the charge differs for each line to be read, the output voltage of the solid-state imaging device is read even if the document is composed of a single color image. It will be different for each target line. As a result, the difference in output voltage for each line of the solid-state imaging device becomes a density difference between the lines, and a streak-like image extending in the main scanning direction may appear in the read image.

  Therefore, conventionally, for example, a dedicated power supply circuit for supplying power supply voltage to the line sensor is provided, and the power supply voltage supplied to the line sensor fluctuates due to the influence of the operation of other operation units. Suppression is done. However, when a dedicated power supply circuit is individually provided for the line sensor, the cost and arrangement space for providing a plurality of power supply circuits increase.

  Therefore, for example, as described in Patent Document 1 below, a drive clock signal supplied to the CCD image sensor via the driver at the start of driving of the CCD image sensor has a lower frequency than the frequency required for image reading. In other words, the current flowing through the driver is reduced to suppress fluctuations in the power supply voltage.

JP 2002-271570 A

  In an image reading apparatus, a switching power supply is generally used as a power supply circuit. However, the switching power supply outputs a power supply voltage including a ripple component that varies with the switching period. In addition, since the CMOS image sensor provided in the CIS operates at a low voltage as described above, fluctuations in the power supply voltage supplied compared to the CCD image sensor that operates at a high voltage described in Patent Document 1 above. Susceptible to. As a result of the test operation, the applicant changes the power supply voltage supplied to the CIS by 10 mV, for example, as shown in FIG. 10 when reading a document composed of a single color image by the CIS (ΔVCC = 10 mV). It has been found that the output voltage of the CMOS image sensor fluctuates by 5 mV (ΔVd = 5 mV).

  In other words, when an image of a document is read by CIS, the output voltage of the CMOS image sensor also fluctuates due to fluctuations in the power supply voltage supplied from the switching power supply in the switching period, and the read image is changed in the main scanning direction. There is a possibility that a streak-like image extending in the direction appears.

  The present invention has been made in view of the above circumstances. In an image reading apparatus including a contact image sensor that operates using a power supply voltage supplied from a switching power supply, and an image forming apparatus including the image reading apparatus. An object of the present invention is to reduce the possibility that a streak-like image extending in the main scanning direction appears in an image read by a contact image sensor.

An image reading apparatus according to the present invention includes a switching power supply that supplies a plurality of loads with a power supply voltage that fluctuates in a predetermined switching cycle, a light source that emits light, and a plurality of light receiving elements arranged in a line in the main scanning direction. A solid-state image sensor that individually outputs a light-receiving voltage indicating the amount of light received by each of the light-receiving elements using the power supply voltage, and a contact-type image sensor, wherein one of the plurality of loads is The contact-type image sensor is configured to irradiate the light source with light while moving the contact-type image sensor in the sub-scanning direction relative to the document, and to image one image of the document at a predetermined line cycle. each said is intended to be read in the solid-state imaging device, at a predetermined first timing in the line period, the first light receiving element in the image reading area outside a region facing the document , After outputting the light reception voltage when the previous line of the reading target line is read, at a predetermined second timing in the line cycle, the second light receiving element outside the image reading area is applied to the second light receiving element. A light reception voltage is output , and a differential voltage that is a value obtained by subtracting the light reception voltage output from the second light reception element from the light reception voltage output from the first light reception element is determined as a reference voltage; After determining the voltage, each of the third light receiving elements in the image reading area is caused to output the light receiving voltage, and each of the differential voltages that are values obtained by subtracting the reference voltage from each of the output light receiving voltages. A reading control unit configured to set a density voltage indicating a density of each pixel of the image of the reading target line read by the solid-state imaging device, and the switching power supply includes the first timing and the second Differential voltage of the power supply voltage supplied to timing has been grasped in advance, and the like does not match the differential voltage of the maximum value and the minimum value of the power supply voltage, the period control unit that performs periodic changing process for changing the switching period Are further provided.

  According to this configuration, the reading control unit reads the voltage immediately before the reading target line output by the first light receiving element outside the image reading area and the second light outside the image reading area. The difference voltage from the light reception voltage output by the light receiving element is determined as a reference voltage. That is, the reading control unit determines, as the reference voltage, the degree to which the light reception voltage output from the solid-state imaging device varies between lines in response to the power supply voltage supplied to the contact image sensor varies between lines. .

  Then, the reading control unit uses the difference voltage between each light reception voltage and the reference voltage output by each of the third light receiving elements in the image reading area as a density indicating the density of each pixel of the image on the reading target line. Voltage. For this reason, even if the light reception voltage output from the solid-state image sensor varies between lines due to the power supply voltage supplied to the contact image sensor varying between lines, the degree of variation in the light reception voltage between the lines Can be removed from each received light voltage output by the third light receiving element. As a result, the fluctuation of the received light voltage between the lines becomes a density difference between the lines, and the possibility that a streak image extending in the main scanning direction appears in the read image can be reduced.

  However, when the reading control unit determines the reference voltage, the difference voltage of the power supply voltage supplied to the contact image sensor at the first timing and the second timing is the maximum value and the minimum value of the power supply voltage that fluctuate in the switching cycle. May coincide with the differential voltage. In this case, since the power supply voltage used when the solid-state imaging device outputs the received light voltage to the first and second light receiving elements is greatly different, the accuracy of the reference voltage indicated by the differential voltage between the two received light voltages can be said to be good. Absent.

  However, the cycle control unit is configured so that the differential voltage of the power supply voltage supplied by the switching power supply at the first timing and the second timing does not match the differential voltage between the maximum value and the minimum value of the power supply voltage that varies in the switching cycle. Change the switching period. As a result, the voltage difference between the power supply voltages used when outputting the received light voltage to the first and second light receiving elements is reduced, so that the reading control unit can determine an accurate reference voltage. As a result, it is possible to obtain a density voltage that appropriately eliminates the difference in received light voltage between lines using the accurate reference voltage, and a streak image extending in the main scanning direction may appear in the read image. Can be reduced with high accuracy.

  The cycle control unit may lengthen or shorten the switching cycle so that the power supply voltages supplied by the switching power supply at the first timing and the second timing match in the cycle changing process. preferable.

  According to this configuration, the power supply voltages supplied by the switching power supply at the first timing and the second timing are matched. As a result, there is no voltage difference between the power supply voltages used when outputting the received light voltage to the first and second light receiving elements, so that the reading control unit can determine a highly accurate reference voltage.

  Further, it is preferable that the cycle control unit shifts the phase of the switching cycle in the cycle changing process so that the power supply voltages supplied by the switching power supply at the first timing and the second timing coincide with each other.

  According to this configuration, the power supply voltages supplied by the switching power supply at the first timing and the second timing are matched. As a result, there is no voltage difference between the power supply voltages used when outputting the received light voltage to the first and second light receiving elements, so that the reading control unit can determine a highly accurate reference voltage.

  In addition, it is preferable that the reading control unit changes the line cycle according to a resolution when the solid-state image sensor reads the image of the document.

  According to this configuration, at a predetermined first timing and second timing in the line cycle changed according to the resolution, the voltage difference between the power supply voltages used when the received light voltage is output to the first and second light receiving elements is It is reduced. Thereby, the reading control unit can determine an appropriate reference voltage according to the resolution. As a result, it is possible to accurately reduce the possibility that a streak image extending in the main scanning direction appears in the image read at each resolution.

  The light source can irradiate light of a plurality of colors, and the reading control unit can detect the line cycle according to the color of light emitted to the light source when the solid-state image sensor reads the image of the document. Is preferably changed.

  According to this configuration, when the light receiving voltage is output to the first and second light receiving elements at the predetermined first timing and second timing in the line period changed according to the color of light emitted from the light source, respectively. The voltage difference of the power supply voltage used for the is reduced. Accordingly, the reading control unit can determine an appropriate reference voltage according to the color of light irradiated on the light source. As a result, the possibility that a streak image extending in the main scanning direction appears in each read color image can be reduced with high accuracy.

  The image forming apparatus according to the present invention includes the image reading device, and an image forming unit that forms an image of the original document read by the solid-state imaging device on the sheet.

  According to this configuration, it is possible to form an image on which the streak-like image extending in the main scanning direction read by the solid-state imaging device is reduced on the sheet by the image forming unit.

  According to the present invention, in an image reading apparatus including a contact image sensor that operates using a power supply voltage supplied from a switching power supply and an image forming apparatus including the image reading apparatus, the image is read by the contact image sensor. The possibility that a streak-like image extending in the main scanning direction appears in the image can be reduced.

1 is a schematic structural diagram of a color copying machine according to an embodiment of an image forming apparatus according to the present invention. 2 is a block diagram showing an electrical configuration of the color copying machine. FIG. It is a schematic structure figure of CIS concerning one embodiment of a contact type image sensor concerning the present invention. 1 is a schematic structural diagram of a CMOS image sensor according to an embodiment of a solid-state imaging device according to the present invention. It is a figure which shows the relationship between the line period when making a CMOS image sensor read the image of a document as a monochrome image, and the output voltage of a CMOS image sensor. It is a figure which shows an example of the power supply voltage supplied to CIS before and after a switching period is changed by a period change process. It is a figure which shows an example different from FIG. 6 of the power supply voltage supplied to CIS before and after a switching period is changed by a period change process. It is a figure which shows the line period corresponding to each of three resolutions. It is a figure which shows the relationship between the color of the light irradiated with a light source, and the line period corresponding to the color of the light irradiated with a light source. It is a figure which shows the relationship between the fluctuation | variation of the power supply voltage supplied to CIS, and the fluctuation | variation of the output voltage of a CMOS image sensor.

  Embodiments according to the present invention will be described below with reference to the drawings. In this embodiment, a color copying machine will be described as an example of the image forming apparatus. However, the present invention is not limited to this, and the image forming apparatus is, for example, a monochrome copying machine, a printer, a facsimile machine, or a multifunction machine. May be.

  FIG. 1 is a schematic structural diagram of a color copying machine 1 according to an embodiment of an image forming apparatus according to the present invention. As shown in FIG. 1, the color copying machine 1 includes an operation unit 7, a document feeding unit 6, a document reading unit 5, and a main body unit 8.

  The operation unit 7 includes a start key 71, a numeric keypad 72, a display unit 73, a reset key 74, a stop key 75, and a function switching key 77.

  The start key 71 is a key for starting the operation of each function that can be executed by the color copying machine 1, such as a copy function, a printer function, a scanner function, and a facsimile function. The numeric keypad 72 is a key for inputting numbers and symbols. The display unit 73 displays a setting screen for inputting setting contents of each function, and includes a liquid crystal display having a touch panel function for these various inputs. The reset key 74 is a key for returning the setting contents of each function to the initial state. The stop key 75 is a key for stopping the operation of each function. The function switching key 77 is a key for switching the function to be executed.

  The document feeding unit 6 includes a document placement unit 61 for placing a document, a document discharge unit 62 for discharging a document whose image has been read, and a document transport mechanism 63. The document transport mechanism 63 feeds the documents placed on the document placement unit 61 one by one, transports them to a position facing a document reading slit 53 described later, and then discharges them to the document discharge unit 62.

  The document reading unit 5 includes a CIS 9 (contact image sensor), a document table 52 made of a transparent member such as glass, and a document reading slit 53.

  The CIS 9 is configured to be movable in the sub-scanning direction (Y direction in FIG. 1) by a driving unit (not shown). When reading a document placed on the document table 52, the CIS 9 moves in the sub-scanning direction along the document surface at a position facing the document table 52, and acquires image data acquired while scanning the image of the document, which will be described later. To the control unit 10 (FIG. 4). On the other hand, the CIS 9 moves to a position facing the document reading slit 53 when reading a document conveyed in the sub-scanning direction by the document feeding unit 6. The CIS 9 acquires an image of the document through the document reading slit 53 in synchronization with the document transport operation by the document feeding unit 6 and outputs the image data to the control unit 10. In this way, the CIS 9 acquires the image of the original while moving in the sub-scanning direction relative to the original, and outputs the acquired image data to the control unit 10.

  The main body 8 includes a plurality of paper feed cassettes 461 for storing paper, a plurality of paper feed rollers 462, an image forming unit 4, a stack tray 81, and a discharge tray 82. Each paper feed roller 462 feeds the paper stored in each paper feed cassette 461 one by one and conveys it to the image forming unit 4. The image forming unit 4 forms an image on the conveyed paper, and discharges the paper on which the image is formed to the stack tray 81 or the discharge tray 82.

  The image forming unit 4 includes a charge eliminating unit 421, a charging unit 422, an exposure unit 423, developing units 44K, 44Y, 44M, and 44C, a transfer drum 49, a transfer unit 41, a fixing unit 45, and a discharge roller 463. , 464.

  The neutralization unit 421 neutralizes residual charges on the surface of the photosensitive drum 43. The charging unit 422 charges the surface of the photosensitive drum 43 after charge removal. The exposure unit 423 outputs laser light based on the image data acquired by the CIS 9, and exposes the surface of the photosensitive drum 43. As a result, the exposure unit 423 forms an electrostatic latent image on the surface of the photosensitive drum 43. The developing units 44K, 44Y, 44M, and 44C apply cyan (C), magenta (M), yellow (Y), and black (K) colors to the electrostatic latent image formed on the surface of the photosensitive drum 43, respectively. Supply toner. As a result, the developing units 44K, 44Y, 44M, and 44C form toner images of the respective colors on the surface of the photosensitive drum 43. A toner image of each color formed on the surface of the photosensitive drum 43 is transferred to the transfer drum 49. The transfer unit 41 transfers the toner image transferred to the transfer drum 49 onto a sheet. The fixing unit 45 heats the sheet on which the toner image is transferred to fix the toner image on the sheet. In this way, the image forming unit 4 forms the image indicated by the image data acquired by the CIS 9 on the sheet. The discharge rollers 463 and 464 discharge the sheet on which the image is formed to the stack tray 81 or the discharge tray 48.

  FIG. 2 is a block diagram showing an electrical configuration of the color copying machine 1. As shown in FIG. 2, the color copying machine 1 further includes a switching power supply 2 and a control unit 10 inside the main body unit 8. The switching power supply 2, the document reading unit 5, and the control unit 10 constitute an example of an image reading apparatus according to the present invention.

  The switching power supply 2 generates a DC voltage by smoothing an AC voltage supplied from an external power supply (not shown). Then, the switching power supply 2 switches on and off the supply of the generated DC voltage to the smoothing circuit provided at the subsequent stage of the switching element by turning on and off the switching element at a predetermined switching cycle. Then, the switching power supply 2 outputs the voltage smoothed by the smoothing circuit. For this reason, the output voltage of the switching power supply 2 includes a ripple component that varies in the switching cycle. Hereinafter, the voltage that is output from the switching power supply 2 and fluctuates in the switching cycle is referred to as a power supply voltage.

  The power supply voltage output from the switching power supply 2 is supplied to a plurality of operation units (loads) such as the document feeding unit 6, the image forming unit 4, the document reading unit 5, and the control unit 10. For this reason, if each operation part operates using the power supply voltage supplied from the switching power supply 2 and the amount of current consumed by each operation part fluctuates, the power supply voltage output from the switching power supply 2 fluctuates accordingly. In preparation for this, the switching power supply 2 feeds back the output power supply voltage, and adjusts the period during which the switching element is turned on (off) based on the voltage value of the fed back power supply voltage. Stabilize to level.

  The control unit 10 includes, for example, a CPU (Central Processing Unit) for executing predetermined arithmetic processing, a ROM (Read Only Memory) in which a predetermined control program is stored, a RAM (Random Access Memory) in which data is temporarily stored, and the like. A storage medium such as a hard disk drive (HDD) for storing various types of data such as image data and image data, and peripheral circuits thereof. The control unit 10 is connected to the switching power supply 2, the document feeding unit 6, the image forming unit 4, the operation unit 7, and the document reading unit 5 through a control bus (not shown) so as to communicate with each other.

  The control unit 10 controls the operation of each operation unit in the color copying machine 1 by executing a control program stored in a ROM or the like by the CPU. In particular, the control unit 10 functions as an instruction receiving unit 11, a reading control unit 12, and a cycle control unit 13 for controlling the CIS 9 to read an image of a document.

  The instruction receiving unit 11 receives an instruction input by the user using the operation unit 7. The instruction includes, for example, an instruction to select whether to read an image of a document as a monochrome image or a color image, an instruction to specify a resolution for reading an image of the document, and the like.

  The reading control unit 12 irradiates a light source 91 (described later) provided in the CIS 9 with light while moving the CIS 9 in the sub-scanning direction relative to the document P, and a CMOS image sensor 93 (described later) provided in the CIS 9. In addition, reading control is performed to read the image of the document P line by line at a predetermined line cycle.

  The details of the reading control will be described below. First, the CIS 9 used for the reading control will be described in detail. As shown in FIG. 2, the CIS 9 operates using a power supply voltage supplied from the switching power supply 2 to the document reading unit 5. That is, the CIS 9 is an example of a load according to the present invention. FIG. 3 is a schematic structural diagram of the CIS 9 according to an embodiment of the contact image sensor according to the present invention. As shown in FIG. 3, the CIS 9 includes a light source 91, a condenser lens 92, and a CMOS image sensor 93 (solid-state imaging device).

  The light source 91 includes an LED light source 91R that emits R (red) light, an LED light source 91G that emits G (green) light, and an LED light source 91B that emits B (blue) light. I have. Further, the CIS 9 diffuses the light emitted from the LED light sources 91R, 91G, and 91B into light having a width corresponding to the entire region in the main scanning direction (the front and back direction in FIG. 3) orthogonal to the sub-scanning direction. A light guide member (not shown) to be irradiated is provided. However, instead of providing the light guide member, a plurality of LED light sources 91R, 91G, 91B may be provided and arranged in a line in the main scanning direction.

  When reading the image of the document P as a monochrome (monochrome) image, the reading control unit 12 turns on the LED light sources 91R, 91G, and 91B at the same time. As a result, white light is irradiated onto the document P via the document table 52 or the document reading slit 53. On the other hand, the reading control unit 12 individually lights the LED light sources 91R, 91G, and 91B when reading the image of the document P as a color image. As a result, light of each color of RGB is irradiated onto the document P individually via the document table 52 or the document reading slit 53.

  The condensing lens 92 is a rod lens array using, for example, a rod-shaped lens, and condenses the light reflected by the original P and passing through the original table 52 or the original reading slit 53 onto the CMOS image sensor 93.

  FIG. 4 is a schematic structural diagram of a CMOS image sensor 93 according to an embodiment of the solid-state imaging device according to the present invention. FIG. 4 is a plan view of the CMOS image sensor 93 viewed from above the paper surface in FIGS. 1 and 3 through the document table 52 or the document reading slit 53. As shown in FIG. 4, the CMOS image sensor 93 includes a plurality of light receiving elements 32R to 32K, 33-1 to 33-n, and 31R to 31K arranged in a line in the main scanning direction (X direction).

  Each of the light receiving elements 32R to 31K, 33-1 to 33-n, and 31R to 31K is composed of a photodiode or the like, and outputs light corresponding to the amount of light received when receiving light. Capacitors (not shown) are connected to the output ends of the light receiving elements 32R to 31K, 33-1 to 33-n, and 31R to 31K, respectively. Charges output from the light receiving elements 32R to 31K, 33-1 to 33-n, and 31R to 31K are accumulated in the capacitor. Each of the capacitors is connected to an amplifier (not shown). Each amplifier uses the power supply voltage supplied from the switching power supply 2 to amplify and output the electric charge accumulated in the capacitor connected to the amplifier. That is, the CMOS image sensor 93 individually amplifies and outputs the charges output from the light receiving elements 32R to 31K, 33-1 to 33-n, and 31R to 31K.

  In the following description, the CMOS image sensor 93 amplifies and outputs the charges accumulated in the capacitors output by the light receiving elements 32R to 31K, 33-1 to 33-n and 31R to 31K by the amplifiers. It simply indicates that the light receiving voltage is output to each of the light receiving elements 32R to 31K, 33-1 to 33-n, and 31R to 31K.

  The light receiving elements 31R to 31K outside the image reading area A, which is an area facing the document P, are collectively referred to as a first light receiving element 31. Similarly, the light receiving elements 32R to 32K outside the image reading area A are collectively referred to as the second light receiving element 32. The light receiving elements 33-1 to 33-n in the image reading area A are collectively referred to as a third light receiving element 33.

  The number of light receiving elements included in the third light receiving element 33 is equal to the maximum resolution in the main scanning direction. For example, FIG. 4 shows an example in which the maximum value of the resolution in the main scanning direction is “n”, and accordingly, the third light receiving element 33 includes n light receiving elements 33-1 to 33-n. Show.

  The light receiving element 31R and the light receiving element 32R include an optical filter that transmits only R-color light, and outputs an electric charge indicating the amount of received light of R-color only when the LED light source 91R is turned on. Similarly, the light receiving element 31G and the light receiving element 32G include an optical filter that transmits only the G color light, and outputs an electric charge indicating the amount of received light of the G color only when the LED light source 91G is turned on. In addition, the light receiving element 31B and the light receiving element 32B include an optical filter that transmits only B-color light, and outputs an electric charge indicating the amount of received light of B-color only when the LED light source 91B is turned on.

  Next, as an example of the reading control, an operation when the CMOS image sensor 93 reads an image of the document P as a monochrome image will be described. FIG. 5 is a diagram showing the relationship between the line period T0 and the output voltage Vo of the CMOS image sensor 93 when the image of the original P is read by the CMOS image sensor 93 as a monochrome image.

  When reading the document P placed on the document table 52, the reading control unit 12 moves the CIS 9 in the sub-scanning direction at a predetermined constant speed. On the other hand, when reading the document P conveyed in the sub-scanning direction by the document feeding unit 6, the reading control unit 12 moves the CIS 9 to a position facing the document reading slit 53 and then moves the document feeding unit 6 to the document feeding unit 6. The original is conveyed at the constant speed. Then, as shown in FIG. 5, the reading control unit 12 illuminates the original P with white light by simultaneously turning on the LED light sources 91R, 91G, and 91B during the line period T0.

  At time t1 (first timing) when a predetermined time has elapsed from the start time t0 of the line cycle T0, the reading control unit 12 causes the light receiving element 31K (FIG. 4) to output a light reception voltage. Thereafter, at time t2 (second timing) when a predetermined time has elapsed, the reading control unit 12 causes the light receiving element 32K (FIG. 4) to output a light reception voltage. Then, the reading control unit 12 determines the difference voltage ΔVd between the two received light voltages output at time t1 and time t2 as a reference voltage.

  Thereafter, at time t3 when a predetermined time has elapsed, the reading control unit 12 sets the number of the light receiving elements 33-1 to 33-n corresponding to the resolution in the main scanning direction received by the instruction receiving unit 11. The light receiving voltage is output to the three light receiving elements 33.

  Then, at time t4 when the output of the light reception voltage by the third light receiving element 33 is completed, the reading control unit 12 calculates the difference between each light reception voltage output by the third light receiving element 33 and the determined reference voltage. Each of the differential voltages is a density voltage indicating the density of each pixel of the image of the reading target line read by the CMOS image sensor 93. In this way, the reading control unit 12 acquires image data including values indicating the respective density voltages as image data indicating the image of the reading target line.

  Then, at the end time t5 of the line cycle T0, the reading control unit 12 leaves the charge accumulated in the capacitors connected to the output ends of the light receiving element 31K and the light receiving element 32K, and leaves the third light receiving element 33. Only the electric charge accumulated in the capacitor connected to the output terminal is erased (reset).

  In this way, the reading control unit 12 repeatedly acquires image data for one line of the document P in the line cycle T0, and acquires image data for all lines of the document P.

  That is, at time t1, the reading control unit 12 irradiates the document P with light while acquiring image data indicating an image of the line immediately before the reading target line in the previous line cycle T0. As a result, the electric charge accumulated in the capacitor connected to the light receiving element 31K is amplified and output. In this way, at time t1, the reading control unit 12 causes the light receiving element 31K to output the light receiving voltage when the line immediately before the reading target line in the line cycle T0 is read.

  Returning to FIG. The cycle control unit 13 switches the switching cycle Ts so that the differential voltage of the power supply voltage that the switching power supply 2 supplies at time t1 and time t2 does not coincide with the differential voltage between the maximum value and the minimum value of the power supply voltage that varies in the switching cycle. Cycle change processing to change

  FIG. 6 is a diagram illustrating an example of a power supply voltage supplied to the CIS 9 before and after the switching period Ts is changed by the period changing process. For example, it is assumed that the reading control unit 12 causes the CIS 9 to read an image of the document P conveyed by the document feeding unit 6. As shown in FIG. 6, the difference voltage ΔVi of the power supply voltage Vi0 supplied to the CIS 9 at time t1 and time t2 in the line cycle T0 is the difference between the maximum value and the minimum value of the power supply voltage Vi0 that fluctuates in the switching cycle Ts. Suppose that it matches the voltage. This situation can be grasped in advance by performing a test operation that causes the CIS 9 to read an image of the document P conveyed by the document feeder 6.

  In this case, the cycle control unit 13 executes the cycle changing process, and reduces the period of the switching cycle Ts to one half, for example. That is, the cycle control unit 13 outputs the power supply voltage Vi1 that fluctuates in the reduced switching cycle Ts1 (= Ts / 2) to the switching power supply 2, and the power supply voltage Vi1 supplied to the CIS 9 at time t1 and time t2. Match.

  Alternatively, the cycle control unit 13 may reduce, for example, the period of the switching cycle Ts by a quarter in the cycle changing process. That is, the cycle control unit 13 outputs the power supply voltage Vi2 that fluctuates in the reduced switching cycle Ts2 (= Ts / 4) to the switching power supply 2, and supplies the power supply voltage Vi2 supplied to the CIS 9 at time t1 and time t2. You may match.

  In this way, the cycle control unit 13 reduces the period of the switching cycle Ts to 1 / (2 × m (m is a natural number)) in the cycle changing process. Thereby, the cycle control unit 13 matches the power supply voltage Vi1 supplied to the CIS 9 at the time t1 and the time t2.

  Or the period control part 13 may expand the period of the switching period Ts by 3 times in the period change process, for example. That is, the cycle control unit 13 outputs the power supply voltage Vi3 that fluctuates in the reduced switching cycle Ts3 (= 3Ts / 2) to the switching power supply 2, and the power supply voltage Vi3 supplied to the CIS 9 at time t1 and time t2. You may match.

  According to the configuration of the above embodiment, the reading control unit 12 reads the light reception voltage output by the light receiving element 31K outside the image reading area A and the line immediately before the reading target line, and the image reading area A. A difference voltage ΔVd from the light reception voltage output by the external light receiving element 32K is determined as a reference voltage. That is, the reading control unit 12 determines, as the reference voltage, the degree to which the received light voltage output from the CMOS image sensor 93 varies between lines in response to the variation of the power supply voltage Vi0 supplied to the CIS 9 between the lines. .

  Then, the reading control unit 12 uses the difference voltage between each received light voltage and the reference voltage output by the third light receiving element 33 in the image reading area A as the density of each pixel of the image of the reading target line. The concentration voltage is as shown. For this reason, even if the light reception voltage output from the CMOS image sensor 93 varies between lines because the power supply voltage supplied to the CIS 9 varies between lines, the degree of variation in the light reception voltage between the lines is indicated. The reference voltage can be removed from each received light voltage output by the third light receiving element 33. As a result, the fluctuation of the received light voltage between the lines becomes a density difference between the lines, and the possibility that a streak image extending in the main scanning direction appears in the read image can be reduced.

  However, when the reading control unit 12 determines the reference voltage, the difference voltage ΔVi of the power supply voltage supplied to the CIS 9 at time t1 and time t2 is the difference between the maximum value and the minimum value of the power supply voltage that fluctuates in the switching cycle Ts. May match the differential voltage. In this case, since the power supply voltage used when the CMOS image sensor 93 outputs the light receiving voltage to the light receiving element 31K and the light receiving element 32K is greatly different, the accuracy of the reference voltage indicated by the difference voltage ΔVd between the two light receiving voltages is good. I can not say.

  However, the cycle control unit 13 ensures that the difference voltage ΔVi of the power supply voltage supplied by the switching power supply 2 at time t1 and time t2 does not match the difference voltage between the maximum value and the minimum value of the power supply voltage that fluctuates in the switching cycle Ts. In addition, the switching period Ts is changed. As a result, the voltage difference between the power supply voltages used when outputting the received light voltage to the light receiving element 31K and the light receiving element 32K is reduced, so that the reading control unit 12 can determine a highly accurate reference voltage. As a result, it is possible to obtain a density voltage that appropriately eliminates the difference in received light voltage between lines using the accurate reference voltage, and a streak image extending in the main scanning direction may appear in the read image. Can be reduced with high accuracy.

  Further, according to the configuration of the above-described embodiment, the cycle control unit 13 performs the cycle changing process so that the power supply voltages Vi1, Vi2, and Vi3 supplied by the switching power supply 2 at the time t1 and the time t2 coincide with each other. As a result, there is no voltage difference between the power supply voltages used when the light receiving element 31K and the light receiving element 32K output the received light voltage, so that the reading control unit 12 can determine an accurate reference voltage.

  Further, according to the configuration of the above embodiment, the image forming unit 4 can form an image in which the streak image extending in the main scanning direction read by the CMOS image sensor 93 is reduced.

  The configurations shown in FIGS. 1 to 6 are merely examples of the embodiment according to the present invention, and are not intended to limit the present invention to the embodiment.

  (1) For example, in the cycle changing process, the cycle control unit 13 may change the phase of the switching cycle Ts instead of changing the period of the switching cycle Ts as shown in FIG.

  7 is a diagram showing another example of the power supply voltage supplied to the CIS 9 before and after the switching cycle Ts is changed by the cycle changing process. For example, it is assumed that the reading control unit 12 causes the CIS 9 to read an image of the document P conveyed by the document feeding unit 6. As shown in FIG. 7, the difference voltage ΔVi of the power supply voltage Vi0 supplied to the CIS 9 at time t1 and time t2 in the line cycle T0 is the difference between the maximum value and the minimum value of the power supply voltage Vi0 that fluctuates in the switching cycle Ts. Suppose that it matches the voltage. This situation can be grasped in advance by performing a test operation that causes the CIS 9 to read an image of the document P conveyed by the document feeder 6.

  In this case, the cycle control unit 13 executes cycle change processing and delays, for example, the phase of the switching cycle Ts by 1/4 cycle (Ts / 4). That is, the cycle control unit 13 causes the switching power supply 2 to output the power supply voltage Vi4 that fluctuates in the switching cycle Ts4 after delaying the phase, and matches the power supply voltage Vi4 supplied to the CIS 9 at time t1 and time t2.

  Alternatively, the cycle control unit 13 may advance the phase of the switching cycle Ts by 1/4 cycle (Ts / 4), for example, in the cycle change process. That is, the cycle control unit 13 outputs the power supply voltage Vi5 that fluctuates in the switching cycle Ts5 after advancing the phase to the switching power supply 2, and matches the power supply voltage Vi5 supplied to the CIS 9 at time t1 and time t2. Also good.

  According to this configuration, when the cycle control unit 13 performs the cycle changing process, the power supply voltages Vi4 and Vi5 supplied by the switching power supply 2 at the time t1 and the time t2 are matched. As a result, there is no voltage difference between the power supply voltages used when the light receiving element 31K and the light receiving element 32K output the received light voltage, so that the reading control unit 12 can determine an accurate reference voltage.

  (2) Further, the reading control unit 12 changes the line cycle T0 according to the resolution when the image of the original P is read by the CMOS image sensor 93. FIG. 8 is a diagram showing line periods T0, T0u, and T0v corresponding to each of the three resolutions.

  For example, it is assumed that the instruction receiving unit 11 receives an instruction to read the image of the document P at a resolution lower than the resolution when the image of the document P is read at the above-described line cycle T0.

  In this case, the reading control unit 12 reduces the number of third light receiving elements 33 to which light reception voltages are output in order to reduce the resolution in the main scanning direction. Further, in order to reduce the resolution in the sub-scanning direction, the reading control unit 12 changes the period of the line cycle T0u corresponding to the received resolution, for example, u ( u> 1) magnification (T0u period = T0 period × u).

  In accordance with this, the reading control unit 12 also sets the intervals Δt01u to Δt45u of the predetermined times t0u to t5u in the line cycle T0u corresponding to the predetermined times t0 to t5 in the line cycle T0 to the predetermined times in the line cycle T0. The time interval t0 to t5 is enlarged to u times the intervals Δt01 to Δt45 (Δt01u = Δt01 × u, Δt12u = Δt12 × u, Δt23u = Δt23 × u, Δt34u = Δt34 × u, Δt45u = Δt45 × u).

  This increases the distance that the CIS 9 moves in the sub-scanning direction during the changed line period T0u, and reduces the number of lines to be read. As a result, the resolution of the read image in the sub-scanning direction is lowered.

  In this case, the cycle controller 13 determines that the differential voltage of the power supply voltage supplied by the switching power supply 2 at the time t1u and the time t2u in the line cycle T0u corresponding to the accepted resolution is the maximum of the power supply voltage that fluctuates in the switching cycle Ts. The switching period Ts is changed in the same manner as the period changing process described above with reference to FIG. 6 or FIG. 7 so as not to match the difference voltage between the value and the minimum value.

  On the contrary, it is assumed that the instruction receiving unit 11 receives an instruction to read the image of the document P at a resolution higher than the resolution when the image of the document P is read at the above-described line cycle T0.

  In this case, the reading control unit 12 increases the number of the third light receiving elements 33 to which the light reception voltage is output in order to increase the resolution in the main scanning direction. Furthermore, in order to increase the resolution in the sub-scanning direction, the reading control unit 12 changes the period of the line cycle T0v corresponding to the received resolution, for example, as shown in FIG. v> 1) It is reduced to 1 / (T0v period = T0 period / v).

  In accordance with this, the reading control unit 12 also sets the intervals Δt01v to Δt45v of the predetermined times t0v to t5v in the line cycle T0v corresponding to the predetermined times t0 to t5 in the line cycle T0 to the predetermined times in the line cycle T0. The interval Δt01 to Δt45 between t0 and t5 is reduced to 1 / v of the above (Δt01v = Δt01 / v, Δt12v = Δt12 / v, Δt23v = Δt23 / v, Δt34v = Δt34 / v, Δt45v = Δt45 / v) .

  This shortens the distance that the CIS 9 moves in the sub-scanning direction during the changed line cycle T0v, and increases the number of lines to be read. As a result, the resolution of the read image in the sub-scanning direction is increased.

  In this case as well, the cycle control unit 13 uses the power supply in which the differential voltage of the power supply voltage supplied by the switching power supply 2 varies at the switching cycle Ts at the time t1v and the time t2v in the line cycle T0v corresponding to the accepted resolution. The switching period Ts is changed in the same manner as the period changing process described above with reference to FIG. 6 or FIG. 7 so as not to match the differential voltage between the maximum value and the minimum value of the voltage.

  According to this configuration, the light receiving elements 31K and 32K are used to output light reception voltages at a predetermined time t1u (t1v) and time t2u (t2v) in the line cycle T0u (T0v) changed according to the resolution. The voltage difference of the power supply voltage is reduced. Thereby, the reading control unit 12 can determine an appropriate reference voltage according to the resolution. As a result, it is possible to accurately reduce the possibility that a streak image extending in the main scanning direction appears in the image read at each resolution.

  (3) In addition, the reading control unit 12 changes the line period T0 according to the color of light irradiated on the light source 91 when the image of the document P is read by the CMOS image sensor 93. FIG. 9 is a diagram showing the relationship between the color of light emitted by the light source 91 and the line periods Tr, Tg, Tb corresponding to the color of light emitted by the light source 91. In FIG.

  For example, it is assumed that the instruction receiving unit 11 receives an instruction to read the image of the document P as a color image at the same resolution as that for reading the image of the document P as a monochrome image in the line cycle T0 described above.

  In this case, the reading control unit 12 irradiates the image of the original P with light of RGB colors by the light source 91 to read the image of each color on the original P for one line, for example, as shown in FIG. The line period T0 is divided into three. Then, the reading control unit 12 obtains the line period Tr for reading the R color image for one line, the line period Tg for reading the G color image for one line, and the B color image for each of the three divided periods. A line period Tb for reading one line is set.

  In accordance with this, the reading control unit 12 sets the intervals of the predetermined times t0r to t5r in the line cycle Tr corresponding to the predetermined times t0 to t5 in the line cycle T0 to the predetermined times t0 to t5 in the line cycle T0. Is reduced to one third of each interval. Similarly, the reading control unit 12 sets intervals between predetermined times t0g to t5g in the line cycle Tg corresponding to the predetermined times t0 to t5 in the line cycle T0 as predetermined times t0 to t5 in the line cycle T0. Is reduced to one third of each interval. In addition, the reading control unit 12 determines the intervals of the predetermined times t0b to t5b in the line cycle Tb corresponding to the predetermined times t0 to t5 in the line cycle T0 as the intervals of the predetermined times t0 to t5 in the line cycle T0. It is reduced to 1/3 times.

  In this case, the reading control unit 12 irradiates the original P with light of R color by turning on only the LED light source 91R during the line period Tr.

  At a predetermined time t1r (first timing) in the line cycle Tr, the reading control unit 12 causes the light receiving element 31R (FIG. 4) to output a light reception voltage. Thereafter, at a predetermined time t2r (second timing), the light receiving element 32R (FIG. 4) outputs a light receiving voltage. Then, the reading control unit 12 uses the difference voltage between the two light reception voltages output at time t1r and time t2r as a reference voltage (hereinafter referred to as R reference voltage) when reading an R color image for one line in the line cycle Tr. To be determined).

  Thereafter, at a predetermined time t3r, the reading control unit 12 causes the number of the third light receiving elements 33 corresponding to the resolution in the main scanning direction to output the light reception voltage among the light receiving elements 33-1 to 33-n.

  Then, at time t4r when the output of the light reception voltage by the third light receiving element 33 is completed, the reading control unit 12 receives each light reception voltage output by the third light receiving element 33, the determined R reference voltage, Is a density voltage indicating the density of each pixel of the R color image of the line to be read, which is read by the CMOS image sensor 93. In this manner, the reading control unit 12 acquires image data including values indicating the respective density voltages as image data indicating an R color image of the reading target line.

  Then, at the end time t5r of the line cycle Tr, the reading control unit 12 leaves the charge accumulated in the capacitors connected to the output ends of the light receiving element 31R and the light receiving element 32R, and leaves the third light receiving element 33. Only the electric charge accumulated in the capacitor connected to the output terminal is erased (reset).

  That is, at time t1r, the reading control unit 12 applies light to the document P when acquiring image data indicating an R color image of the line immediately before the reading target line in the previous line cycle Tr. Is amplified and output from the capacitor connected to the light receiving element 31R. In this way, at time t1r, the reading control unit 12 causes the light receiving element 31R to output the light reception voltage when the R color image of the line immediately before the reading target line in the line cycle Tr is read.

  In this case, the cycle control unit 13 determines that the differential voltage of the power supply voltage supplied by the switching power supply 2 at the time t1r and the time t2r in the line cycle Tr is the maximum value and the minimum value of the power supply voltage that fluctuates in the switching cycle Ts. The switching cycle Ts is changed in the same manner as the cycle changing process described above with reference to FIG. 6 or FIG. 7 so as not to coincide with the value difference voltage.

  Next, the reading control unit 12 acquires image data for one line of G color in the line period Tg, similarly to the case of acquiring image data for one line of R color in the above-described line period Tr. Further, in this case, the cycle control unit 13 determines that the differential voltage of the power supply voltage supplied by the switching power supply 2 at the time t1g and the time t2g in the line cycle Tg is the maximum value and the minimum value of the power supply voltage that fluctuates in the switching cycle Ts. The switching cycle Ts is changed in the same manner as the cycle changing process described above with reference to FIG. 6 or FIG. 7 so as not to coincide with the differential voltage.

  Then, the reading control unit 12 acquires image data for one line of B color in the line cycle Tb, similarly to the case of acquiring image data for one line of R color in the above-described line cycle Tr. Further, in this case, the cycle control unit 13 determines that the difference voltage of the power supply voltage supplied by the switching power supply 2 at the time t1b and the time t2b in the line cycle Tb is the maximum value and the minimum value of the power supply voltage that fluctuates in the switching cycle Ts. The switching cycle Ts is changed in the same manner as the cycle changing process described above with reference to FIG. 6 or FIG. 7 so as not to coincide with the differential voltage.

  In this way, the reading control unit 12 acquires image data for one line of R color of the document P in the line cycle Tr, and acquires image data for one line of G color of the document P in the line cycle Tg. The image data for one line of RGB of the document P is acquired by acquiring the image data for one line of B color of the document P in the line cycle Tb. Then, the reading control unit 12 repeatedly obtains image data for one line of each RGB color in the document P in this way, and obtains image data for all lines of each RGB color in the document P.

  According to this configuration, the light receiving voltage is output to the light receiving element 31R and the light receiving element 32R at the predetermined time t1r and time t2r in the line cycle Tr when the color of light emitted from the light source 91 is R, respectively. The voltage difference of the power supply voltage used for the is reduced. Similarly, a power source used when the light receiving element 31G and the light receiving element 32G output light reception voltages at predetermined times t1g and t2g in the line period Tg when the color of light emitted from the light source 91 is G, respectively. The voltage difference between the voltages is reduced. The power supply voltage used when the light receiving element 31B and the light receiving element 32B output light reception voltages at predetermined times t1b and t2b in the line period Tb when the color of light emitted from the light source 91 is B, respectively. The voltage difference is reduced. Accordingly, the reading control unit 12 can determine an appropriate reference voltage according to the color of light irradiated on the light source 91. As a result, the possibility that a streak image extending in the main scanning direction appears in each read color image can be reduced with high accuracy.

1 Color copier (image forming device)
2 Switching power supply 4 Image forming unit (load)
6 Document feeder (load)
7 Operation part (load)
10 Control unit (load)
12 Reading control unit 13 Period control unit 31, 31B, 31G, 31K, 31R First light receiving element 32, 32B, 32G, 32K, 32R Second light receiving element 33, 33-1-33-n Third light receiving element 9 CIS (contact image sensor, load)
91 Light source 93 CMOS image sensor (solid-state image sensor)
A Image reading area P Document T0, T0u, T0v, Tb, Tg, Tr Line cycle t1, t1b, t1g, t1r, t1u, t1v Time (first timing)
t2, t2b, t2g, t2r, t2u, t2v time (second timing)

Claims (6)

A switching power supply that supplies a plurality of loads with a power supply voltage that fluctuates in a predetermined switching cycle;
A light source that emits light, and a solid-state imaging device that includes a plurality of light receiving elements arranged in a line in the main scanning direction and that individually outputs a light receiving voltage indicating a received light amount to each of the light receiving elements using the power supply voltage. A close contact image sensor,
With
One of the plurality of loads is the contact image sensor,
While moving the contact image sensor relative to the document in the sub-scanning direction, the light source is irradiated with light, and the solid-state image sensor reads the document image line by line at a predetermined line cycle. And
The light reception voltage when the first light receiving element outside the image reading area, which is an area facing the document, is read at the predetermined first timing in the line cycle, the line immediately before the reading target line. Is output at a predetermined second timing in the line period, the light receiving voltage is output to the second light receiving element outside the image reading area, and the light receiving element output by the first light receiving element is output. A difference voltage, which is a value obtained by subtracting the light reception voltage output from the second light receiving element from a voltage, is determined as a reference voltage;
After the determination of the reference voltage, each of the third light receiving elements in the image reading area is caused to output the light reception voltage, and a difference voltage that is a value obtained by subtracting the reference voltage from each of the output light reception voltages. A reading control unit that sets a density voltage indicating a density of each pixel of the image of the reading target line read by the solid-state imaging device;
The switching period is set such that a differential voltage between the power supply voltages supplied by the switching power supply at the first timing and the second timing does not coincide with a difference voltage between the maximum value and the minimum value of the power supply voltage , which is grasped in advance. A cycle control unit for performing cycle change processing to change
An image reading apparatus further comprising:   2. The cycle control unit according to claim 1, wherein, in the cycle change process, the cycle control unit lengthens or shortens the switching cycle so that the power supply voltages supplied by the switching power supply at the first timing and the second timing coincide with each other. The image reading apparatus described.   The cycle control unit shifts the phase of the switching cycle in the cycle changing process so that the power supply voltages supplied by the switching power supply at the first timing and the second timing coincide with each other. The image reading apparatus described.   4. The image reading apparatus according to claim 1, wherein the reading control unit changes the line cycle in accordance with a resolution when the solid-state image sensor reads an image of the document. 5. The light source can emit light of a plurality of colors,
The said reading control part changes the said line period according to the color of the light irradiated to the said light source when making the said solid-state image sensor read the image of the said document. Image reading device. An image reading apparatus according to any one of claims 1 to 5,
An image forming unit that forms an image of the original document read by the solid-state image sensor on the paper;
An image forming apparatus comprising:

Images