JP6133199B2 - Image reading apparatus and image forming apparatus - Google Patents

Description

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

  2. Description of the Related Art Conventionally, a configuration in which a movable carriage is provided below a document table (contact glass) is known as an image reading apparatus such as a copying machine, a facsimile machine, a scanner, or a multifunction machine. A light source for reading a document for illuminating the document is mounted on the carriage. The light emitted from the light source is reflected by the document, and the image sensor generates a document image based on the reflected light.

  For example, a plurality of LEDs (Light Emitting Diodes) that emit light of R (red), G (green), and B (blue) are employed as light sources for reading a document. A plurality of LEDs of each color are arranged along the main scanning direction, and the amount of light necessary for image reading is generated by changing the lighting time and driving current of the LEDs of each color. In such an image reading apparatus, the light amount of the LED is changed for each image reading condition such as color, monochrome, line cycle, and resolution, and the original image is read with an optimal light amount.

  For example, Patent Document 1 does not acquire white reference data for shading correction for each image reading condition, converts white reference data acquired under a specific image reading condition according to another image reading condition, An image reading apparatus that performs shading correction using converted white reference data is disclosed. In this technique, when a document image is read at another resolution lower than the resolution included in the specific image reading condition, the light intensity and lighting time of the light source are not changed. As a result, it is possible to shorten the time until the start of reading and reduce the amount of white reference data to be stored.

JP 2010-278999 A

  In the image reading apparatus that employs a plurality of LEDs that emit each color of R, G, and B as described above, a single lighting circuit is not provided for each color LED in order to reduce the cost. In some cases, a configuration in which each color LED is turned on is employed. With such a configuration, it is not possible to light a plurality of colors of LEDs simultaneously.

  For example, when acquiring color image data, it is necessary to switch lighting of the three colors R, G, and B and to read each reflected light independently by an image sensor. In this case, there is no particular difference between a configuration in which a lighting circuit is provided for each color LED and a configuration in which each color LED is lit by a single lighting circuit.

  On the other hand, when acquiring monochrome image data, as long as only one color LED is lit as disclosed in Patent Document 1, a configuration in which a lighting circuit is provided for each color LED and a single lighting circuit are provided. Thus, there is no particular difference between the configuration in which the LEDs of the respective colors are turned on. However, in recent years, from the viewpoint of improving image quality, even when acquiring monochrome image data, image data in a state in which light of three colors is irradiated and white light is irradiated instead of any one of R, G, and B Has been done to get.

  In this case, in a configuration in which a lighting circuit is provided for each color LED, white light can be generated by simultaneously lighting each color LED. On the other hand, in the configuration in which each color LED is lit by a single lighting circuit, the lighting of each color LED of R, G, B is switched within one line cycle, and the reflected light of each color is continuously incident on the image sensor. Therefore, it is necessary to realize a state in which pseudo white light is irradiated. For this reason, in such an image reading apparatus that turns on the LEDs of each color by a single lighting circuit, conventionally, at the time of monochrome image data acquisition, the switching timing and lighting of each color LED for each image reading condition such as the line period and resolution. The time was usually fixed at a pre-specified setting. Therefore, the optimum light amount is not always obtained when obtaining monochrome image data.

  The present invention has been made in view of the above-described problems of the prior art, and in a configuration in which monochrome image data is acquired by sequentially irradiating a document with a plurality of colors of light, a more optimal amount of light than in the past. An object of the present invention is to provide an image reading apparatus and an image forming apparatus that can acquire monochrome image data.

In order to achieve the above object, the present invention employs the following technical means. That is, the image reading apparatus according to the present invention includes a light source, a light source lighting unit, an image sensor, a color lighting time holding unit, and a monochrome lighting condition determining unit. Light source is configured red for illuminating a document, a green, a blue light source. Light source lighting unit is provided in common to the color of the light source, it is turned in the forward light source for each color. The image sensor reads the image of the document by receiving light from the light source reflected on the document. The color lighting time holding unit holds the lighting time of each color of the light source when obtaining color image data of the original. The monochrome lighting condition determining unit determines the lighting time and lighting timing of each color of the light source when acquiring the monochrome image data of the document based on the lighting time held by the color lighting time holding unit. In addition, the monochrome lighting condition determining unit sets the red lighting time Tr, the green lighting time Tg, and the blue lighting time Tb of the light source to the preset necessary light amount and the color lighting time holding unit. It is expressed by the lighting time of each color, the maximum values Eb_r, Eb_g, Eb_b of all black reference light amounts of each color of red, green, and blue, and the maximum values Ew_r, Ew_g, Ew_b of all white reference light amounts of each color of red, green, and blue. The following formulas are used for calculation.
Tr = (required light amount−Eb_r) / (Ew_r−Eb_r) × (red lighting time in color)
× 0.3
Tg = (required light amount−Eb_g) / (Ew_g−Eb_g) × (green lighting time in color)
× 0.6
Tb = (required light amount−Eb_b) / (Ew_b−Eb_b) × (blue lighting time in color)
× 0.1

  According to this image reading apparatus, the light amount and lighting timing of each light source at the time of monochrome image data acquisition are determined based on the light amount of each light source determined at the time of color image data acquisition. Monochrome image data can be acquired with a more optimal light amount. As a result, the image quality of monochrome image data can be improved.

In the above-described image reading apparatus, when the monochrome lighting condition determining unit can execute the calculated lighting times Tr, Tg, and Tb within one line period, the calculated lighting times Tr, Tg, and Tb are used as the light source. In addition to determining the lighting time for each color, the lighting timing is determined based on the standby time provided at the start of one line cycle and the standby time provided during lighting of each color, and the calculated lighting times Tr, Tg, Tb are calculated. If not, carried out in a 1-line period, we adopt a configuration to reduce a feasible state in one line period by shortening the wait time provided between each color light.

  On the other hand, in another aspect, the present invention can also provide an image forming apparatus including the above-described image reading apparatus and an image forming unit that prints a document image read by the image reading apparatus on a transfer target. .

  According to the present invention, it is possible to acquire monochrome image data with a more optimal light amount than in the past.

1 is a schematic configuration diagram showing the overall configuration of a multifunction machine according to an embodiment of the present invention. The figure which shows the hardware constitutions of the multifunctional device in one Embodiment of this invention. 1 is a functional block diagram showing portions related to image reading of a multifunction peripheral according to an embodiment of the present invention. The figure which shows the structure of the lighting circuit with which the multifunctional device in one Embodiment of this invention is provided. The figure which shows an example of the lighting control signal of the light source in one Embodiment of this invention The flowchart which shows an example of the lighting condition determination procedure at the time of the monochrome which the multifunctional device in one Embodiment of this invention implements The figure which shows the parameter of the lighting conditions at the time of the monochrome of the light source in one Embodiment of this invention

  Hereinafter, an embodiment of the present invention will be described in more detail with reference to the drawings. In the following, the present invention is embodied as a digital multi-function peripheral having an image reading unit (image reading device).

  FIG. 1 is a schematic configuration diagram illustrating an example of the overall configuration of a digital multifunction peripheral according to the present embodiment. As shown in FIG. 1, the multifunction peripheral 100 includes a main body 101 including an image reading unit 120 (image reading device) and an image forming unit 140, and a platen cover 102 attached above the main body 101. An original table 103 made of a transparent plate such as contact glass is provided on the upper surface of the main body 101, and the original table 103 is opened and closed by a platen cover 102. Further, the platen cover 102 includes a document conveying device 110. An operation panel 171 is provided on the front surface of the multi-function device 100 so that the user can give a copy start or other instruction to the multi-function device 100, and can check the status and settings of the multi-function device 100.

  An image reading unit 120 is provided below the document table 103. The image reading unit 120 reads an image of a document with the scanning optical system 121 and generates digital data (image data) of the image. Here, the scanning optical system 121 is configured as a contact optical system (a so-called CIS (Contact Image Sensor) system). The document to be read can be placed on the document table 103 or the document conveying device 110.

  The scanning optical system 121 includes a carriage 122 and a guide 123. The carriage 122 includes a linear light source 131, an image sensor 132, and a 1 × optical system lens 133. Here, an LED array, a CMOS (Complementary Metal Oxide Semiconductor) line image sensor, and a gradient index lens are used as the light source 131, the image sensor 132, and the equal-magnification optical system lens 133, respectively. The light source 131 illuminates the document with a plurality of colors of light. In the present embodiment, the light source 131 illuminates the document with each color of R (red), G (green), and B (blue). The equal magnification optical system lens 133 forms an image of reflected light (light image) from the original on the light receiving surface of the image sensor 132.

  The guide 123 is arranged on the side surfaces of the main body 101 facing each other in parallel with the document table 103. The carriage 122 is provided so as to reciprocate along the guide 123. The movement of the carriage 122 is realized by driving by a driving unit (not shown). In the present embodiment, a stepping motor that is a driving unit drives the carriage 122.

  The guide 123 is provided so that the image sensor 132 mounted on the carriage 122 can be moved from one end to the other end of at least the document placement possible area (document readable area) of the document table 103. In the present embodiment, the size of the document table 103 matches the document placement area, and the image sensor 132 moves from one end to the other end of the document table 103 orthogonal to the side surface of the main body 101 provided with the guide 123. It is possible. That is, in the scanning optical system 121, the image of the document placed on the document table 103 can be read by the image sensor 132 by moving the carriage 122 along the guide 123.

  When reading an image of a document set on the document conveying device 110, the image reading unit 120 temporarily stops the carriage 122 according to the image reading position, and the image sensor 132 detects an image of the document passing through the image reading position. read. The image sensor 132 generates document image data corresponding to, for example, each color of R (red), G (green), and B (blue) from the light image incident on the light receiving surface. The generated image data can be printed on a sheet as a transfer medium in the image forming unit 140. Further, it can be transmitted to other devices (not shown) through the network 162 by the network interface 161.

  The multi-function device 100 includes a white white reference plate 135 disposed over the entire main scanning direction on the upper surface of the main body 101 adjacent to the document table 103 in the movement direction of the carriage 122. The white reference plate 135 is provided corresponding to the image reading position. That is, the reflecting surface of the white reference plate 135 is arranged in a state where the distance from the carriage 122 to the original reading position of the original placed on the original table 103 or the original conveyed by the original conveying apparatus 110 is approximately the same. Is done. The white reference plate 135 is used, for example, for shading correction for correcting light quantity variation in the main scanning direction.

  The image forming unit 140 prints image data obtained by the image reading unit 120 and image data received from another device connected to the network 162 on a sheet. The image forming unit 140 includes a photosensitive drum 141. The photosensitive drum 141 rotates in one direction at a constant speed. Around the photosensitive drum 141, a charger 142, an exposure unit 143, a developing unit 144, and an intermediate transfer belt 145 are arranged in this order from the upstream side in the rotation direction. The charger 142 uniformly charges the surface of the photosensitive drum 141. The exposure device 143 irradiates the uniformly charged surface of the photosensitive drum 141 with a light beam according to the image data to form an electrostatic latent image on the photosensitive drum 141. The developing device 144 attaches toner to the electrostatic latent image and forms a toner image on the photosensitive drum 141. The intermediate transfer belt 145 transfers the toner image on the photosensitive drum 141 onto a sheet. When the image data is color image data, the intermediate transfer belt 145 transfers each color toner image onto the same sheet. The RGB color image data is converted into C (cyan), M (magenta), Y (yellow), and K (black) image data, and the image data of each color is input to the exposure unit 143.

  The image forming unit 140 feeds paper from the manual feed tray 151, the paper feed cassettes 152, 153, and 154 to the transfer unit between the intermediate transfer belt 145 and the transfer roller 146. Various sizes of paper can be placed or stored in the manual feed tray 151 and the paper feed cassettes 152, 153, and 154. The image forming unit 140 selects a sheet specified by the user or a sheet corresponding to the automatically detected document size, and feeds the selected sheet from the manual feed tray 151 or the cassettes 152, 153, and 154 by the feeding roller 155. . The fed paper is transported to the transfer section by transport rollers 156 and registration rollers 157. The sheet on which the toner image is transferred is conveyed to the fixing device 148 by the conveyance belt 147. The fixing device 148 has a fixing roller 158 and a pressure roller 159 with a built-in heater, and fixes the toner image on the sheet by heat and pressing force. The image forming unit 140 discharges the sheet that has passed through the fixing device 148 to the discharge tray 149.

  FIG. 2 is a hardware configuration diagram of a control system in the multifunction machine. The multifunction peripheral 100 according to the present embodiment includes a CPU (Central Processing Unit) 201, a RAM (Random Access Memory) 202, a ROM (Read Only Memory) 203, an HDD (Hard Disk Drive) 204, an original conveying device 110, and an image reading unit 120. A driver 205 corresponding to each drive unit in the image forming unit 140 is connected via an internal bus 206. The ROM 203, the HDD 204, and the like store programs, and the CPU 201 controls the multifunction peripheral 100 in accordance with instructions from the control program. For example, the CPU 201 uses the RAM 202 as a work area, and controls the operation of each driving unit by exchanging data and commands with the driver 205. The HDD 204 is also used to store image data obtained by the image reading unit 120 and image data received from other devices via a network.

  An operation panel 171 and various sensors 207 are also connected to the internal bus 206. The operation panel 171 receives a user operation and supplies a signal based on the operation to the CPU 201. Further, the operation panel 171 displays an operation screen on a display provided in the operation panel 171 according to a control signal from the CPU 201. The sensor 207 includes various sensors such as an open / close detection sensor for the platen cover 102, a document detection sensor on the document table 103, a temperature sensor for the fixing device 148, and a detection sensor for the conveyed paper or document.

  The CPU 201 executes, for example, a program stored in the ROM 203 to realize the following means (functional blocks) and controls the operation of each means according to signals from these sensors.

  FIG. 3 is a functional block diagram showing portions related to image reading of the multifunction peripheral according to the present embodiment. As shown in FIG. 3, the multifunction peripheral 100 includes a light amount lighting unit 301, a color lighting time holding unit 302, and a monochrome lighting condition determination unit 303.

  The light source lighting unit 301 is provided in common for the light sources 131 of a plurality of colors, and turns on the light source 131 in order for each color. Here, the light source lighting unit 301 has a single lighting circuit, and lights the LEDs of R, G, and B colors by the lighting circuit.

  FIG. 4 is a diagram illustrating an example of a lighting circuit provided in the light source lighting unit 301. In addition, as long as it is the structure which does not light a some LED simultaneously, not only the structure illustrated in FIG. 4 but arbitrary circuit structures can be employ | adopted.

  As shown in FIG. 4, the lighting circuit 401 included in the light source lighting unit 301 of the present embodiment includes a power supply circuit 411, an input resistor Ri, drive current adjustment resistors Rr, Rg, Rb, and switch circuits Qr, Qg, Qb. The power supply circuit 411 supplies drive currents to the anodes of the red diode Dr, the green diode Dg, and the blue diode Db that constitute the light source 131 via the input resistor Ri. A red switch circuit Qr, a green switch circuit Qg, and a blue switch circuit Qb are connected to the cathode side of each of the diodes Dr, Dg, and Db. A red driving current adjustment resistor Rr, a green driving current adjustment resistor Rg, and a blue driving current adjustment resistor Rb are interposed between the diodes Dr, Dg, Db and the switch circuits Qr, Qg, Qb. By adjusting the resistance values of the drive current adjustment resistors Rr, Rg, and Rb, the drive currents that flow through the diodes Dr, Dg, and Db are adjusted.

  Each switch circuit Qr, Qg, Qb is configured by a transistor. In this embodiment, the transistor is turned on when a high level signal (for example, 3V) is applied to the gate, and the gate has a low level. When a signal (for example, 0 V) is applied, the signal is turned off. When the transistor is in an on state, a current flows through a diode connected to the switch circuit, and the diode emits light (lights up).

  A red lighting control signal PWM_r, a green lighting control signal PWM_g, and a blue lighting control signal PWM_b are input to the signal input terminals 412, 413, and 414 connected to the gates of the switch circuits Qr, Qg, and Qb, respectively. The lighting control signals PWM_r, PWM_g, and PWM_b are set so as not to be at a high level at the same time, and the light source 313 lights up in any one color of red, green, and blue. Although not particularly limited, in the present embodiment, the lighting control signals PWM_r, PWM_g, and PWM_b are generated in the signal generation unit 402 provided in the light source lighting unit 301 and input to the signal input terminals 412, 413, and 414.

  FIG. 5 is a diagram illustrating an example of the lighting control signals PWM_r, PWM_g, and PWM_b. FIG. 5A corresponds to a lighting control signal at the time of obtaining color image data with a resolution of 300 dpi. FIG. 5B corresponds to a lighting control signal when acquiring monochrome image data with a resolution of 300 dpi. FIG. 5C corresponds to a lighting control signal when acquiring monochrome image data with a resolution of 600 dpi. In FIG. 5, the horizontal axis corresponds to time, and the vertical axis corresponds to the signal level (High level and Low level). Further, in FIG. 5, a line cycle signal indicating one line cycle, a red lighting control signal PWM_r, a green lighting control signal PWM_g, and a blue lighting control signal PWM_b are shown side by side in the vertical direction.

  As shown in FIG. 5A, when acquiring color image data, one line period is assigned to lighting of each color of R, G, and B (= data reading). With this configuration, the image sensor 125 can acquire reflected light of each color of R, G, and B independently of each other. In this case, the light source 131 is lit in each color for a lighting time determined by a method described later.

  On the other hand, as shown in FIGS. 5B and 5C, when acquiring monochrome image data, each color of R, G, and B is lit within one line cycle. With this configuration, the image sensor 125 can acquire a signal in a state where reflected light of each color of R, G, and B is superimposed. In this case, the ratio of the lighting times of the respective colors within one line period is R: G: B = 3: 6: 1 in order to obtain a state in which pseudo white light is irradiated.

  As shown in FIGS. 5A and 5B, when the resolutions are the same, the lighting time of one color when acquiring color image data and the total lighting time of three colors when acquiring monochrome image data are approximately. Be the same. As shown in FIGS. 5B and 5C, in the case of monochrome image data, the lighting time of each color when the resolution is 600 dpi is approximately twice the lighting time of each color when the resolution is 300 dpi. Become.

  Conventionally, the lighting signal of each color at the time of obtaining monochrome image data as shown in FIGS. 5B and 5C is fixed to a setting designated in advance for each image reading condition such as a line period and resolution. It has become normal.

  The on-color lighting time holding unit 302 holds the lighting time of each color of the light source 131 when acquiring color image data of a document. Although not particularly limited, in this embodiment, the on-color lighting time holding unit 302 also has a function of setting the lighting time of each color of the light source 131.

  The lighting time of each color in the light source 131 is set during the above-described shading correction. That is, the color lighting time holding unit 302 includes a necessary light amount set in advance in the multifunction peripheral 100 according to an image reading condition (original reading resolution or one line cycle in original image reading) at the time of obtaining color image data, The lighting time of each color in the light source 131 is set based on the amount of light detected by the image sensor 125 at the time of shading correction. In the present embodiment, the color lighting time holding unit 302 adjusts the light amount mainly by the lighting time of the light source 131.

  At the time of shading correction, the carriage 122 is disposed at a position facing the white reference plate 135. In this state, the black reference light amount in a state where the light source 131 is turned off and the white reference light amount in each state where the light source 131 is sequentially turned on in each color are acquired. Note that the black reference light amount and the white reference light amount are acquired for each of the plurality of light receiving elements constituting the image sensor 125. When the light source 131 is lit in each color when acquiring the white reference light amount, the light source lighting unit 301 applies a drive current designated in advance to the diodes Dr, Dg, and Db of each color constituting the light source 131.

  The on-color lighting time holding unit 302 calculates an effective light amount (= white reference light amount−maximum value of all black reference light amounts) based on the black reference light amount and the white reference light amount acquired for each light receiving element. Then, the lighting times of the diodes Dr, Dg, and Db of each color are determined based on the maximum value of the effective light amount of each light receiving element and the necessary light amount preset in the above-described multifunction device 100. For example, the color lighting time holding unit 302 determines the lighting time of each of the diodes Dr, Dg, and Db by dividing the required light amount by the maximum value of the effective light amount.

  When acquiring color image data according to the image reading condition corresponding to the lighting time held in the color lighting time holding unit 302, the color lighting time holding unit 302 inputs the corresponding lighting time to the light source lighting unit 301. The signal generation unit 402 of the light source lighting unit 301 generates the above-described lighting control signals PWM_r, PWM_g, and PWM_b based on the input lighting time, and sequentially turns on the diodes Dr, Dg, and Db of each color with the input lighting time. . In this case, for example, the signal generation unit 402 generates a lighting control signal for each color that rises at a timing when a standby time specified in advance from the rising edge of the line cycle signal and maintains a high level for the input lighting time. To do. Here, the standby time is a minimum standby time provided for stable operation depending on the device structure and the like.

  When the calculated lighting time does not fall within one line cycle specified in the image reading condition, the color lighting time holding unit 302 instructs the light source lighting unit 301 to increase the driving current, and performs the above-described processing. Try again.

  The monochrome lighting condition determination unit 303 determines the lighting time and lighting timing of each color in the light source 131 when acquiring monochrome image data of the document based on the lighting time held by the color lighting time holding unit 302. In the present embodiment, the monochrome lighting condition determination unit 303 needs to be set in advance in the multifunction peripheral 100 according to the image reading conditions (original reading resolution and one line cycle in original image reading) at the time of obtaining monochrome image data. The lighting time and lighting timing of each color in the light source 131 are set based on the light amount and the light amount (black reference light amount and white reference light amount) detected by the image sensor 125 during the most recent shading correction. Although not particularly limited, the light amounts (black reference light amount and white reference light amount) detected by the image sensor 125 during the most recent shading correction are held in the color lighting time holding unit 302.

  FIG. 6 is a flowchart illustrating an example of a monochrome lighting condition determination procedure performed by the multifunction peripheral 100. The procedure starts, for example, when a monochrome image data acquisition instruction is input as a trigger. Here, the monochrome lighting condition determining unit 303 determines the lighting condition of each color of the light source 131 when acquiring monochrome image data having the same resolution as the resolution corresponding to the lighting time held by the color lighting time holding unit 302.

  When the procedure starts, the monochrome lighting condition determination unit 303 calculates the lighting time of each color according to the following equations (1) to (3) based on the black reference light amount and the white reference light amount acquired for each light receiving element. Calculate (step S601).

Red lighting time Tr = A × (Red lighting time in color) × 0.3 (1)
Green lighting time Tg = B × (color green lighting time) × 0.6 (2)
Blue lighting time Tb = C × (blue lighting time in color) × 0.1 (3)

  Here, the coefficients A, B, and C described above are determined by the maximum values Eb_r, Eb_g, and Eb_b of all black reference light amounts of R, G, and B colors, and the maximum values Ew_r, Ew_g, and Ew_b of all white reference light amounts of the respective colors. It is expressed by the following equations (4) to (6).

A = (required light amount−Eb_r) / (Ew_r−Eb_r) (4)
B = (required light amount−Eb_g) / (Ew_g−Eb_g) (5)
C = (Required light amount−Eb_b) / (Ew_b−Eb_b) (6)

  Next, the monochrome lighting condition determination unit 303 calculates the total of the calculated lighting times Tr, Tg, and Tb (step S602). Then, it is determined whether or not the total lighting time of each color is within one line cycle (step S603). In this determination, the monochrome lighting condition determination unit 303 compares the magnitudes of the time obtained by subtracting various standby times from one line period and the total lighting time.

  FIG. 7 is a diagram illustrating various standby times. As shown in FIG. 7, in addition to the above-described standby time Twst, the various standby times include the end-of-period standby time Twed, which is provided at the end of one line cycle T for stable operation depending on the device structure, etc. After the green light is turned on so that the green and blue lights do not overlap, and the waiting time Twrg between red and green provided between the rear edge of the red light and the green light turned on so that the green lights do not overlap. There is a green-blue waiting time Twgb provided between the end and the tip of blue lighting. These various waiting times are in principle the minimum waiting times provided for stable operation. Note that when the lighting of each color overlaps, the power supply circuit 411 cannot be supplied with a current sufficient to sufficiently drive the two-color diodes, so that the amount of light is greatly reduced.

  In the above determination, when the time obtained by subtracting various standby times from one line cycle is greater or equal, the monochrome lighting condition determination unit 303 determines that the total lighting time of each color is within one line cycle. (Step S603 Yes). In this case, the monochrome lighting condition determination unit 303 stores the calculated lighting times Tr, Tg, Tb, and lighting timing, and inputs them to the light source lighting unit 301 (step S605). As can be understood from FIG. 7, the red lighting timing is after the standby time Twst has elapsed from the rise of the line cycle signal, and the green lighting timing is after the red-green standby time Twrg has elapsed from the falling of the red lighting control signal. Yes, the blue lighting timing is after the green-blue standby time Twgb has elapsed since the fall of the green lighting control signal.

  The signal generation unit 402 of the light source lighting unit 301 to which the lighting time and lighting timing are input from the monochrome lighting condition determination unit 303 generates the above-described lighting control signals PWM_r, PWM_g, and PWM_b based on the input lighting time and lighting timing. Then, the diodes Dr, Dg, and Db of each color are turned on in order at the input lighting time and lighting timing. In this case, the signal generation unit 402 generates a lighting control signal for each color that rises at lighting timing and maintains a high level for the input lighting time.

  On the other hand, in the above determination, if the total lighting time of each color is longer, the monochrome lighting condition determination unit 303 determines that the total lighting time of each color is not within one line cycle (No in step S603). In this case, for example, the monochrome lighting condition determination unit 303 shortens the calculated lighting times Tr, Tg, and Tb so as to be within one line period without changing the ratio of each other. Alternatively, the lighting time or the lighting timing is adjusted by shortening the waiting time Twrg between red and green and the waiting time Twgb between green and blue (step S604). When the lighting times Tr, Tg, and Tb are shortened, the amount of light decreases. Therefore, it is preferable to shorten the waiting time Twrg between red and green and the waiting time Twgb between green and blue as much as possible.

  The monochrome lighting condition determination unit 303 that has adjusted the lighting conditions stores the adjusted lighting times Tr, Tg, Tb, and lighting timing, and inputs them to the light source lighting unit 301 (step S605).

  In the above description, the case of acquiring monochrome image data having the same resolution as that corresponding to the lighting time held by the color lighting time holding unit 302 has been described. However, the monochrome lighting condition determination unit 303 uses the light source 131 for different resolutions. It is also possible to determine the lighting conditions for each color. For example, it is assumed that the resolution corresponding to the lighting time held by the color lighting time holding unit 302 is 300 dpi. In this case, it is possible to calculate the lighting time of each color when obtaining 300 dpi monochrome image data in the above-described color lighting time calculation step S601. For example, when acquiring 600 dpi monochrome image data, as described above, twice as much light (= 600 dpi / 300 dpi) is required as compared with the case of acquiring 300 dpi monochrome image data. Therefore, by doubling the lighting time calculated in each color lighting time calculation step S601, the lighting time of each color when acquiring 600 dpi monochrome image data can be obtained. The subsequent procedure is as described above.

  In this way, by changing the lighting time and lighting timing of each color in the light source 131 based on the resolution of the acquired monochrome image data, the monochrome lighting condition determining unit 303 lights each color of the light source 131 at an arbitrary resolution. Conditions can be determined.

  In the above, when the monochrome lighting condition determining unit 303 determines that the total lighting time of each color is within one line cycle, the standby time such as the red-green standby time Twrg and the green-blue standby time Twgb is not changed. However, the waiting time such as the waiting time Twrg between red and green and the waiting time Twgb between green and blue may be extended as much as possible within the range of one line cycle. As a result, it is possible to provide a time margin when switching between the colors, and it is possible to reliably prevent the overlapping of lighting between the colors, and it is possible to realize more stable image reading.

  As described above, in the MFP 100, the light amount and lighting timing of each light source at the time of monochrome image data acquisition are determined based on the light amount of each light source determined at the time of color image data acquisition. Therefore, according to the state of the light source 131, the light quantity and lighting timing of each light source at the time of monochrome image data acquisition can be changed as appropriate. That is, in the conventional configuration in which the lighting time and the lighting timing are fixed, even when the amount of light is insufficient, the appropriate amount of light can be set by increasing the amount of light when acquiring monochrome image data. . As a result, it is possible to acquire monochrome image data with a more optimal light amount than in the past, and to improve the image quality of the monochrome image data.

  The above-described embodiments do not limit the technical scope of the present invention, and various modifications and applications other than those already described are possible within the scope of the present invention. For example, in the above-described embodiment, the configuration using the contact optical system is exemplified, but the present invention can also be applied to an image reading apparatus using a reduction optical system.

  In the flowchart shown in FIG. 6, the order of the steps can be changed as appropriate within the range where the equivalent action is achieved. For example, in the above-described embodiment, the total of the lighting times Tr, Tg, and Tb is calculated, and it is determined whether the total lighting time is within one line cycle. However, the total lighting time is within one line cycle. It may be determined whether or not the total lighting time is calculated.

  In addition, in the above-described embodiment, the present invention is embodied as a digital multi-function peripheral. It is also possible to apply the present invention.

  According to the present invention, monochrome image data can be acquired with a more optimal light amount than in the prior art, which is useful as an image reading apparatus and an image forming apparatus.

100 MFP (image forming device)
120 Image reading unit (image reading device)
125 Image sensor 131 Light source 140 Image forming unit 301 Light source lighting unit 302 Colored lighting time holding unit 303 Monochrome lighting condition determining unit

Claims (2)

Red, green and blue light sources that illuminate the document,
A light source lighting unit that is provided in common to the light sources of the respective colors, and sequentially turns on the light sources in the respective colors;
An image sensor that reads an image of the document by receiving light from the light source reflected on the document;
A color-time lighting time holding unit that holds the lighting time of each color of the light source when acquiring color image data of a document;
Based on the lighting time held by the color lighting time holding unit, when obtaining monochrome image data of a document, a monochrome lighting condition determination unit that determines the lighting time and lighting timing of each color of the light source;
With
The monochrome lighting condition determining unit includes a red lighting time Tr, a green lighting time Tg, and a blue lighting time Tb of the light source, which are stored in the preset required light amount and the color lighting time holding unit. The lighting time of each color of the light source, the maximum values Eb_r, Eb_g, Eb_b of all black reference light amounts of each color of red, green, and blue, and the maximum values Ew_r, Ew_g, Ew_b of all white reference light amounts of each color of red, green, and blue Calculated by the following formulas expressed,
When the calculated lighting times Tr, Tg, and Tb can be implemented within one line cycle, the monochrome lighting condition determination unit sets the calculated lighting times Tr, Tg, and Tb as the lighting times of the respective colors of the light source. In addition, the lighting timing is determined based on the standby time provided at the start of one line cycle and the standby time provided between lighting of each color, and the calculated lighting times Tr, Tg, and Tb are within one line cycle. in case not feasible, it is that images reader shortened feasible state in one line period by shortening the wait time provided between each color light.
Tr = (required light amount−Eb_r) / (Ew_r−Eb_r) × (red lighting time in color)
× 0.3
Tg = (required light amount−Eb_g) / (Ew_g−Eb_g) × (green lighting time in color)
× 0.6
Tb = (required light amount−Eb_b) / (Ew_b−Eb_b) × (blue lighting time in color)
× 0.1 An image reading apparatus according to claim 1 ;
An image forming unit that prints a document image read by the image reading device on a transfer medium;
An image forming apparatus comprising:

Images