JP2015194609A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a reduction in throughput and enable imaging of a recording medium in a device that controls acceleration and deceleration of a recording medium.SOLUTION: There is provided an image forming apparatus that includes an image forming part that forms an image on a recording medium, an LED 41 that irradiates the recording medium with light, a line sensor 43 that is irradiated by the LED 41 and photographs the light transmitted through the recording medium as an image, and a control part 10 that controls image formation conditions for the image forming part, and further includes a conveyance roller 5 that conveys the recording medium. In a period during which the conveyance roller 5 increases or decreases the conveyance speed of the recording medium to be supplied to the image forming part from a first speed, and conveys the recording medium while maintaining a second speed that is different from the first speed, the line sensor 43 photographs the recording medium, and the control part 10 controls the image formation conditions for the image forming part on the basis of the image of the recording medium photographed by the line sensor 43.

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a laser beam printer, and a facsimile, and more particularly, to an image forming apparatus including a recording medium imaging apparatus that images a recording medium.

  2. Description of the Related Art Conventionally, an image forming apparatus provided with a recording medium imaging device that images the surface of a recording medium in order to determine the type of recording medium used for image formation (for example, plain paper or glossy paper). There is. For example, Patent Document 1 and Patent Document 2 propose a video reading apparatus that images the surface of a recording medium with a CMOS sensor and detects the surface smoothness from the captured image to determine the type of the recording medium. Then, based on the determination result of the type of the recording medium, the image forming apparatus determines conditions such as image formation and fixing temperature. In such a recording medium imaging device, in order to easily and accurately capture a surface image of a recording medium, imaging is conventionally performed while the recording medium is being transported at a steady speed.

JP 2002-182518 A JP 2004-038879 A

  However, in recent image forming apparatuses, control is performed to appropriately maintain the distance from the preceding recording medium during continuous printing by accelerating or decelerating the conveyance speed of the recording medium. Also in an image forming apparatus having an intermediate transfer body to which a toner image on a photosensitive drum is transferred, an image formed on the photosensitive drum is transferred to the intermediate transfer body, and a recording medium is matched with the image on the intermediate transfer body In order to adjust the position of the recording medium, acceleration / deceleration control of the recording medium conveyance speed is performed. In the state where acceleration / deceleration control is performed, the conveyance speed of the recording medium changes, so that the conveyance speed of the recording medium changes during imaging, and it is difficult to image with high accuracy. Therefore, conventionally, imaging of the recording medium by the imaging apparatus has been performed at the timing when the acceleration / deceleration control is finished and the recording medium is conveyed at a constant speed. However, as the equipment is downsized and the printing speed is increased, after the acceleration / deceleration control of the recording medium conveyance speed is completed, if the recording medium is imaged by the imaging device after waiting for a constant speed, the conditions for image formation Changes, changes in fixing temperature, etc. will not be in time for the conveyance timing of the recording medium. For this reason, the image forming operation has to be temporarily stopped, and there is a problem that throughput is lowered.

  The present invention has been made under such circumstances, and an object of the present invention is to enable imaging of a recording medium while reducing a decrease in throughput in an apparatus that performs acceleration / deceleration control of the recording medium.

  In order to solve the above-described problems, the present invention is configured as follows.

  (1) An image forming unit that forms an image on a recording medium, an irradiating unit that irradiates the recording medium with light, an imaging unit that is irradiated by the irradiating unit and captures light through the recording medium as an image, And a control unit that controls image forming conditions of the image forming unit. The image forming apparatus includes a transport unit that transports a recording medium, and the transport unit supplies the recording to the image forming unit. The image pickup unit images the recording medium during a period in which the medium is conveyed while the medium conveyance speed is accelerated or decelerated from the first speed and the second speed different from the first speed is maintained. And an image forming apparatus configured to control the image forming condition by the image forming unit based on an image of the recording medium captured by the imaging unit.

  According to the present invention, in a device that performs acceleration / deceleration control of a recording medium, it is possible to image the recording medium while reducing a decrease in throughput.

1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. FIG. 3 is a perspective view, a cross-sectional view, and a top view illustrating the configuration of the recording medium imaging apparatus according to the first embodiment. Control block diagram showing control of recording medium imaging apparatus of embodiment 1 The figure explaining the change of the brightness when the shading correction of Example 1 is performed The figure explaining the recording medium discrimination | determination timing of Example 1, The figure which shows the brightness data of the recording medium according to conveyance speed The figure which shows the control operation timing from the printing start of Example 1 and a prior art example to completion of printing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Outline of image forming apparatus]
The recording medium imaging apparatus according to the first embodiment can be used in an image forming apparatus such as a copying machine or a printer. FIG. 1 is a schematic cross-sectional view of an image forming apparatus in which an intermediate transfer belt is employed and a plurality of image forming units are arranged in parallel as an electrophotographic image forming apparatus 1 equipped with a recording medium imaging device. It is.

  In FIG. 1, the recording medium P is stored in the paper feed cassette 2, and the recording medium P is loaded on the paper feed tray 3. The paper feed roller 4 feeds the recording medium P from the paper feed cassette 2 to the transport path, and the paper feed roller 4 ′ feeds the recording medium P from the paper feed tray 3 to the transport path. Conveying rollers 5 and 5 ′ serving as conveying means convey the recording medium P fed from the paper feeding cassette 2 or the paper feeding tray 3 and supply it to the image forming unit, and conveying counter rollers 6 and 6 ′ are conveying rollers, respectively. It is a roller which opposes 5 and 5 '. The photosensitive drums 11Y, 11M, 11C, and 11K that are photosensitive members respectively carry developers (toners) of yellow (Y), magenta (M), cyan (C), and black (K). Hereinafter, symbols Y, M, C, and K representing the color of the developer are omitted unless necessary. A charging roller 12 as a primary charging unit charges the photosensitive drum 11 to a predetermined potential. The optical unit 13 irradiates the photosensitive drum 11 charged by the charging roller 12 with laser light corresponding to the image data of each color transmitted from the control unit 10 based on the print image signal. An electrostatic latent image is formed.

  The developing device 14 visualizes the electrostatic latent image formed on the photosensitive drum 11 with toner (developer). The developer transport roller 15 sends the developer (toner) in the developing device 14 to a portion facing the photosensitive drum 11. The primary transfer roller 16 receives an image (toner image) formed on the photosensitive drum 11 </ b> K that rotates in the direction of the arrow (counterclockwise direction) in FIG. Transfer to belt 17. The intermediate transfer belt 17 carrying the transferred image is driven by a driving roller 18 in the direction of the arrow in the figure. The secondary transfer roller 19 is a transfer roller for transferring an image formed on the intermediate transfer belt 17 to the recording medium P, and the secondary transfer counter roller 20 is a roller facing the secondary transfer roller 19. . The fixing unit 21 melts and fixes the toner image on the recording medium P by heating and pressurizing the toner image transferred to the recording medium P while conveying the recording medium P. The paper discharge roller 22 discharges the recording medium P on which the toner image is fixed by the fixing unit 21 to the outside of the apparatus.

  The photosensitive drum 11, the charging roller 12, the developing device 14, and the developer conveying roller 15 are integrated for each color. As described above, a unit in which the photosensitive drum 11, the charging roller 12, the developing device 14, and the like are integrated is referred to as a process cartridge. The process cartridges for each color are configured to be easily removable from the image forming apparatus 1. .

  The control unit 10 controls the photosensitive drum 11, the charging roller 12, the optical unit 13, the developing device 14, and the like that constitute the image forming unit, and forms an image on the recording medium P, controls the conveyance of the recording medium P, and the like. . Further, the control unit 10 has a timer function for measuring time. The control unit 10 includes a ROM and a RAM (not shown). The ROM stores a program and data for controlling the image forming apparatus 1. The RAM stores information stored temporarily by the control program executed by the control unit 10. Is the memory used to store

  Next, the image forming process will be described. The charging roller 12 charges the photosensitive drum 11 to a predetermined potential. Subsequently, the optical unit 13 emits a light beam for exposing the photosensitive drum 11 charged by the charging roller 12. An electrostatic latent image is formed on the photosensitive drum 11 by exposure with the light beam.

  The developing device 14Y develops the electrostatic latent image formed on the photosensitive drum 11Y with yellow toner. The developing device 14M develops the electrostatic latent image formed on the photosensitive drum 11M with magenta toner. The developing device 14C develops the electrostatic latent image formed on the photosensitive drum 11C with cyan toner. The developing device 14K develops the electrostatic latent image formed on the photosensitive drum 11K with black toner.

  The yellow toner image formed on the photosensitive drum 11Y is transferred to the intermediate transfer belt 17 by the primary transfer roller 16Y. The magenta toner image formed on the photosensitive drum 11M is transferred to the intermediate transfer belt 17 by the primary transfer roller 16M. The cyan toner image formed on the photosensitive drum 11C is transferred to the intermediate transfer belt 17 by the primary transfer roller 16C. The black toner image formed on the photosensitive drum 11K is transferred to the intermediate transfer belt 17 by the primary transfer roller 16K.

  The toner image of each image forming unit is transferred onto the intermediate transfer belt 17 so as to form a full-color toner image. The toner image transferred onto the intermediate transfer belt 17 is transferred to the recording medium P conveyed from the paper feed cassette 2 or the paper feed tray 3 by the secondary transfer roller 19 and the secondary transfer counter roller 20. The toner image transferred to the recording medium P is fixed by the fixing unit 21 and discharged by the discharge roller 22 after the fixing process.

  In the image forming apparatus 1 of FIG. 1, a recording medium imaging device 40 serving as a detection unit is disposed on the upstream side in the conveyance direction of the recording medium P with respect to the conveyance roller 5 and the conveyance counter roller 6, and is conveyed from the paper feed cassette 2 or the like. The surface smoothness of the recorded recording medium P is detected. In this embodiment, the recording medium P is discriminated by the recording medium imaging device 40 which is a media sensor. The recording medium P is sent out from the paper feed cassette 2 or the like into the image forming apparatus 1, and the recording medium P is recorded in the recording medium imaging device 40. This is done when passing through. In the recording medium imaging device 40 of this embodiment, a line sensor described later is used for imaging the recording medium P.

[Outline of recording medium imaging device]
Next, the recording medium imaging device 40 will be described with reference to FIG. 2A is a perspective view showing a configuration of a recording medium imaging device 40 for obtaining a surface image reflecting the surface smoothness, and FIG. 2B is an imaging of the recording medium shown in FIG. 4 is a cross-sectional view of the apparatus 40 cut in parallel with the conveyance direction of the recording medium P. FIG. 2A and 2B are upside down from FIG. 1 for convenience of explanation. Further, FIG. 2C is a top view of the recording medium imaging device 40 shown in FIG. 2A as viewed from above in FIG.

  As shown in FIG. 2, the recording medium imaging device 40 includes an LED 41, an imaging lens 42, a CMOS line sensor 43 (hereinafter referred to as a line sensor 43), reference plates 46a and 46b, a protective member 47, and a discrimination processing unit 45 described later. (FIG. 3). The LED 41 that is an irradiation unit is a light emitting diode that irradiates the surface of the recording medium P with a light beam. The imaging lens 42 that is an imaging unit strikes the surface of the recording medium P with the light beam emitted from the LED 41 and forms an image of the reflected light reflected. The line sensor 43 serving as an imaging unit images the light beam imaged by the imaging lens 42. As shown in FIG. 2A, the longitudinal direction of the line sensor 43 is orthogonal to the conveyance direction of the recording medium P. A portion where the light beam emitted from the LED 41 strikes the recording medium P and the light beam is reflected is a reflecting portion, and the reflected light reflected by the reflecting portion is captured by the line sensor 43 as a surface image. The protection member 47 is provided to protect the imaging lens 42 and the LED 41. Inner surface reference plates 46a and 46b (hereinafter also referred to as reference plates 46a and 46b) are arranged at the ends of regions in the direction perpendicular to the conveyance direction of the recording medium P, which can be irradiated with the light beam of the LED 41. The reference plates 46 a and 46 b are installed on the surface of the recording member P on the line sensor 43 side (imaging means side), that is, on the surface of the protective member 47 on the imaging lens 42 side. The transport mechanism for transporting the recording medium P includes transport rollers 5 and 5 ′ for transporting the recording medium P, transport opposing rollers 6 and 6 ′ provided opposite to the transport rollers 5 and 6 ′, and a transport path for the recording medium P. The illustrated conveyance guide is provided.

  2B, the light beam emitted from the LED 41 hits the reflection portion of the recording medium P via the reference plate 46a and the protection member 47, and the light beam reflected by the reflection portion is the protection member 47, the reference plate 46a, It is a figure which shows a mode that it injects into the line sensor 43 through the imaging lens. In FIG. 2B, the trapezoidal wall provided between the LED 41 and the imaging lens 42 is a light shielding wall (not shown in FIG. 2A), and the light beam emitted from the LED 41 is directly connected to the line. It is provided to prevent the light from entering the sensor 43. As shown in FIG. 2B, the imaging lens 42 and the line sensor 43 are arranged so as to be orthogonal to the conveyance direction of the recording medium P. Thus, the line sensor 43 can simultaneously capture the reflected light reflected by the surface of the recording medium P and the reflected light reflected by the surfaces of the reference plates 46a and 46b by the light emitted from the LED 41. it can. The LED 41 is arranged to emit light at an angle of 10 degrees with respect to the surface of the recording medium P. When the LED 41 is irradiated, the reference plates 46a and 46b are simultaneously irradiated together with the recording medium P. Note that the irradiation angle of the LED 41 is an example, and is not necessarily limited to an angle of 10 degrees as long as an image sufficient for determining the recording medium P can be obtained.

  FIG. 2C is a view of the recording medium imaging device 40 as viewed from above. The positional relationship among the LED 41, the imaging lens 42, the line sensor 43, the reference plates 46a and 46b, and the protection member 47, and the irradiation from the LED 41 are illustrated. The irradiation range of the light beam is shown. In FIG. 2C, the LED 41 is preferably disposed and mounted as an ideal mounting position so that the center of the optical axis of the irradiated light beam is orthogonal to the central portion of the line sensor 43. However, in consideration of the mounting accuracy of the LED 41 during assembly, the center of the optical axis of the LED 41 does not necessarily have to be orthogonal to the line sensor 43, and the light beam from the LED 41 is applied to the reference plates 46a and 46b. It ’s fine. That is, when the optical axis of the irradiation light from the LED 41 is not orthogonal to the line sensor 43 and is largely inclined, the irradiation light is biased and the irradiation light does not hit one of the reference plates 46a and 46b. Therefore, correction by a reference plate described later cannot be performed. Therefore, even if the optical axis of the irradiation light from the LED 41 is not orthogonal to the line sensor 43, both the reference plates 46a and 46b are irradiated with the irradiation light so that the correction by the reference plates 46a and 46b is possible. I shall do it.

  As shown in FIG. 2C, the irradiation angle of the light beam emitted from the LED 41 includes an inner surface reference plate irradiation angle range a, a recording medium irradiation angle range, and an inner surface reference plate irradiation angle range b. In each irradiation angle range, an inner surface reference plate effective image range a, a recording medium effective image range, and an inner surface reference plate effective image range b are provided. The “recording medium irradiation angle range” represents an area where the surface information of the recording medium P is acquired, and the “recording medium effective image range” represents the type of the recording medium P based on the lightness distribution of the light emitted from the LED 41. The range of the surface image to be used for discrimination is shown. The “inner surface reference plate irradiation angle range a, b” in the reference plates 46a, 46b represents a region for acquiring the surface information of the respective inner surface reference plates 46a, 46b. The “inner surface reference plate effective image range a, b” indicates a range of an area used for calculating the amount of reflected light from the respective inner surface reference plates 46a, 46b.

[Outline of operation of recording medium imaging device]
FIG. 3 is a diagram illustrating a configuration of a control function of the recording medium imaging device 40 and a relationship with a control function related to the recording medium imaging device 40 in the control unit 10. The recording medium imaging device 40 includes an LED 41, an imaging lens 42, a line sensor 43, and a determination processing unit 45 that performs paper type determination based on the acquired surface image data of the recording medium P. A light beam is emitted from the LED 41 to the surface of the recording medium P conveyed through the conveyance path. The irradiated light beam hits the recording medium P, and the reflected light from the recording medium P is captured as a surface image of the recording medium P by the line sensor 43 through the imaging lens 42. Then, the surface image data of the recording medium P imaged by the line sensor 43 is output to the discrimination processing unit 45.

  The discrimination processing unit 45 includes functional blocks of an A / D conversion unit 451, an image extraction unit 452, a feature amount calculation unit 453, a paper type discrimination unit 454, a storage area 455, and a light amount correction amount calculation unit 456. The A-D conversion unit 451 performs AD conversion (analog / digital conversion) on the surface image data of the recording medium P output from the line sensor 43, and converts the surface image data on the same straight line perpendicular to the conveyance direction of the recording medium P. obtain. Regarding AD conversion, for example, in this embodiment, an 8-bit A / D conversion IC (integrated circuit) is used, and the A / D conversion unit 451 outputs a value of 0 to 255 as a digital value.

  Subsequently, the image extraction unit 452 joins the surface image data of the recording medium P digitized by the A-D conversion unit 451 along the conveyance direction of the recording medium P to generate two-dimensional surface image data, It memorize | stores in the memory area 455 which is a memory | storage means. In this embodiment, the conveyance speed of the recording medium P when the conveyance rollers 5 and 5 ′ are rotated at a steady speed is 80 mm / second, and the resolution of the line sensor 43 is 600 dpi of one line. 600 dpi (dot per inch) means that the number of pixels (number of dots) per inch (= 2.54 cm) is 600. Therefore, the size of one dot is about 42 μm (= 2.54 cm / 600). In this embodiment, an area corresponding to 5 mm × 5 mm of the recording medium P is imaged by the line sensor 43 in order to determine the paper type of the recording medium P. Therefore, the necessary image size of the surface image of the recording medium P can be calculated as 118 dots × 118 dots by dividing 5 mm by 42 μm. As a result, when the recording medium P is transported at a transport speed of 80 mm / second, the imaging by the line sensor 43 is performed every time the recording medium P is transported by 42 μm, that is, about 530 μsec (= 42 μm ÷ 80 mm / second). Done at intervals. Thereby, it is possible to capture images without overlapping the imaging areas on the recording medium P. The storage area 455 stores information on the effective image range of the recording medium P described with reference to FIG. 2C, the optical axis center position of the irradiation light from the LED 41, and the like. Based on these information, the image extraction unit In 452, the surface image used for discrimination of the paper type of the recording medium P is extracted. At this time, in order to determine the paper type of the recording medium P, the surface image of the recording medium P is subjected to shading correction. Details of the shading correction will be described later.

  The feature amount calculation unit 453 calculates the feature amount from the surface image data extracted by the image extraction unit 452. The paper type determination unit 454 determines the paper type of the recording medium P based on the calculation result of the feature amount calculation unit 453, and outputs the determination result to the image forming condition control unit 101 of the control unit 10.

  The image forming condition control unit 101 of the control unit 10 controls the image forming conditions in the image forming unit based on the determination result of the paper type determining unit 454. The “image forming condition” refers to conditions such as a transfer voltage applied to the primary transfer roller 16 and the like, a conveyance speed of the recording medium P, and a fixing temperature of the recording medium P in the fixing unit 21. For example, rough paper is less fixable than plain paper. For this reason, when the paper type determination unit 454 determines that the paper type of the recording medium P is rough paper, the image forming condition control unit 101 reduces the conveyance speed of the recording medium P by the fixing unit 21. Control such as extending the fixing time or increasing the fixing temperature is performed. Further, the image forming condition control unit 101 of the control unit 10 may control the image forming conditions of the image forming apparatus 1 directly from the information of the captured image instead of the determination result of the paper type determining unit 454.

  In the storage area 455, the current value for controlling the light emission of the LED 41, the light amount target value necessary for adjusting the light amount, which will be described later, the dark current data when the LED 41 is turned off and the light amount when the LED 41 is turned on are used to correct the light amount unevenness. Uneven data is stored. The light amount unevenness data when the LED 41 is lit stores the effective image range and the light amount value on the inner surface reference plates 46a and 46b described with reference to FIG. Further, in the light amount unevenness data when the LED 41 is turned on, information on the pixel range corresponding to the optical axis center position in the recording medium effective image range of the irradiation light from the LED 41, the light amount value thereof, and the like is also stored.

  In order to acquire an appropriate surface image of the recording medium P, it is necessary to adjust the light amount of the LED 41 and acquire light amount unevenness data. The light quantity adjustment of the LED 41 is performed, for example, when the light quantity of the irradiation light from the LED 41 is excessive, the light quantity of the reflected light from the recording medium P increases, and the acquired surface image becomes too bright, and the characteristics of the image This is because the amount may not be obtained correctly. On the other hand, if the amount of light emitted from the LED 41 is insufficient, the acquired surface image becomes too dark, and the feature amount of the image may not be obtained correctly. Further, the amount of light emitted from the LED 41 decreases with time. For this reason, before taking a surface image, light quantity adjustment is performed so that LED41 may be made to light-emit with the light quantity suitable for imaging.

  When adjusting the light amount of the LED 41, the image extraction unit 452 outputs the acquired surface information of the reference plates 46 a and 46 b to the light amount correction amount calculation unit 456. Then, the light amount correction amount calculation unit 456 calculates the light amount correction amount of the LED 41 based on the information output from the image extraction unit 452 and outputs it to the irradiation control unit 102 of the control unit 10. The irradiation control unit 102 performs light emission control of the LED 41 based on the light amount correction amount calculated by the light amount correction amount calculation unit 456.

  In order to finely control the light emission amount of the LED 41, it is ideal to perform light amount correction every time one image of the recording medium P is captured. In the present embodiment, the reference plates 46a and 46b are disposed between the recording medium P and the line sensor 43, and the surface images of the reference plates 46a and 46b are also captured within the period during which the surface image of the recording medium P is captured. Can be done simultaneously. Therefore, even when the recording medium P is continuously printed and the interval between sheets is short, the light amount can be corrected based on the surface images (surface information) of the inner surface reference plates 46a and 46b. Can be prevented.

  Further, the acquisition of the light amount unevenness data and the shading correction are performed even if the light emission amount of the LED 41 is appropriately adjusted, and the effective image range of the recording medium P shown in FIG. Because it is difficult to do. That is, the brightness of the pixel near the center of the optical axis is high, and the brightness of the pixel decreases as the distance from the center of the optical axis increases. As a result, a light amount difference occurs within the effective image range, and the brightness of the surface image for each portion within the effective image range varies due to the light amount difference. Therefore, shading correction is performed to reduce the influence of lightness on the surface image. In this embodiment, the initial data for shading correction is acquired by a reference recording medium or a reference reference plate at the time of factory shipment, and the acquired initial data is written in the storage area 455 as reference data. It is.

[Overview of shading correction]
FIG. 4 is a diagram for explaining the change in brightness of the surface image of the recording medium P when the shading correction of the present embodiment is performed. In FIG. 4, the vertical axis indicates the brightness, and the horizontal axis indicates the imaging position (pixel position) of the recording medium P having a predetermined pixel width from the optical axis center of the light beam emitted from the LED 41. FIG. 4I is a diagram showing the lightness distribution of the above-described reference data, and the reference data is correction data for unevenness in the amount of light stored in the storage area 455 in advance. 4 (ii) is a diagram showing the brightness distribution of the surface image captured by the line sensor 43 of the recording medium P before shading correction, and FIG. 4 (iii) is the recording medium data of FIG. 4 (ii). It is the figure which showed the brightness distribution after performing shading correction | amendment. In the image extraction unit 452, the brightness value of each pixel in the recording medium effective image range is close to a predetermined digital value, for example, 192, based on the reference data shown in FIG. 4 (i) and the brightness distribution shown in FIG. 4 (ii). Thus, the ratio of the output values of each pixel is calculated. Then, the shading correction is performed by multiplying the calculated ratio of each pixel to each pixel of the surface image of the recording medium P. Then, in FIG. 4 (iii) after the shading correction, the light amount unevenness in the surface image data of the recording medium P is reduced compared to FIG. 4 (ii) before the shading correction. Since the shading correction method can be performed by a conventionally known method, detailed description thereof is omitted.

  Next, the feature amount calculation unit 453 calculates the feature amount of the unevenness on the surface of the recording medium P from the surface image data subjected to the shading correction by the image extraction unit 452. The feature amount calculation unit 453 obtains the standard deviation of the brightness distribution of each pixel of the surface image of the recording medium P, and uses the value as the feature amount of the unevenness on the surface of the recording medium P. Since the surface image data D of the recording medium P is composed of 118 dots (lines) × 118 dots (pixels), the surface image data D of the i-th pixel in the j line is Dj [i], and the average of all data Let the value be DA. The standard deviation is the square root of (the sum of ((Dj [i] −DA) squared) ÷ number), that is, the value obtained by squaring the difference between the individual surface image data and the average value is summed over all data. It can be obtained by calculating the square root of the value obtained by dividing the obtained total value by the number of data.

  Next, the paper type determination unit 454 determines the type of the recording medium P based on the obtained feature amount, and outputs the determination result to the image forming condition control unit 101 of the control unit 10. The paper type discrimination unit 454 compares the feature amount of the recording medium P obtained by the feature amount calculation unit 453 with the feature amount for specifying the type of the recording medium P stored in the storage area 455 in advance. The paper type of the recording medium P is determined. Then, the image forming condition control unit 101 controls the image forming conditions such as the conveyance speed of the recording medium P and the fixing temperature adjustment of the fixing unit 21 based on the paper type of the recording medium P output from the paper type determining unit 454. To do.

  The recording medium discrimination method using the recording medium imaging device 40 has been described above. The recording medium imaging device 40 has been described with respect to a general configuration. For example, the installation position and presence / absence of the reference plates 46a and 46b, the number of LEDs 41 serving as a light source, and the like are not limited to the above-described configuration. Absent.

[Detection of recording medium during acceleration / deceleration of recording medium]
Next, detection of the recording medium P at the time of acceleration / deceleration of the recording medium conveyance speed will be described. FIG. 5A is a diagram for explaining the recording medium discrimination timing in this embodiment. In FIG. 5A, the horizontal axis indicates the position of the recording medium P on the transport path, the left side of the figure indicates the upstream side in the transport direction, and the right side indicates the downstream side in the transport direction. The vertical axis indicates the conveyance speed of the recording medium P. In the image forming apparatus 1 of the present embodiment, after the recording medium P is fed from the paper feed cassette 2 or the paper feed tray 3, a distance (hereinafter referred to as recording) from the preceding recording medium P is detected by a sensor (not shown). (Also referred to as inter-medium distance). Here, the distance between the recording media refers to the trailing edge of the recording medium P (preceding recording medium P) that is fed before the recording medium P and conveyed in advance, and the recording medium P (subsequent recording). This is the distance (between sheets) between the front end of the medium P). When the measured distance between the recording media P is larger (wider) than the predetermined distance, the control unit 10 performs control to accelerate the conveyance speed of the subsequent recording media P. Conversely, when the distance between the recording media P is smaller (narrower) than the predetermined distance, the control unit 10 performs control to reduce the conveyance speed of the subsequent recording media P. In this way, by performing acceleration / deceleration control of the conveyance speed of the subsequent recording medium P, the distance between the recording media P is maintained at an appropriate distance. Further, when an image is formed on the intermediate transfer body prior to the recording medium P as in the image forming apparatus 1 using the intermediate transfer body as in the present embodiment, on the conveyance path of the recording medium P. In order to adjust the position to the image transfer timing, the conveyance speed of the recording medium P is accelerated or decelerated.

  In the image forming apparatus 1 of the present embodiment, as shown in FIG. 5A, the conveyance speed Vt in a steady state (hereinafter also referred to as a steady speed Vt) that is the speed at the time of image formation (in this embodiment, 80 mm / Second), two types of high-speed conveyance speeds and one type of low-speed conveyance speed are provided. There are two types of high-speed conveyance speeds: high-speed Vh1 (for example, 100 mm / second) with a higher conveyance speed and high-speed Vh2 (for example, 90 mm / second), which is slower than the high-speed Vh1. On the other hand, the low conveyance speed is a low speed Vl1 (for example, 65 mm / second), which is slower than the steady speed Vt. As described above, when the distance between the recording media P is large, the distance between the recording media P is reduced by conveying the subsequent recording media P at a high speed. That is, when the distance between the recording media P is significantly wide, the conveyance speed is greatly accelerated like the high speed Vh1, and the distance between the recording media P is narrowed, and when the distance is slightly wide, it is a little like the high speed Vh2. Acceleration / deceleration control of the conveyance speed, such as acceleration of the conveyance speed, is performed. As a result, the distance is adjusted so as to be an appropriate distance regardless of the distance between the recording media.

  As shown in FIG. 5A, the actual adjustment of the conveyance speed of the recording medium P is performed by accelerating / decelerating the conveyance speed from the steady speed Vt to the target conveyance speed. Then, after reaching the target transport speed, the transport mechanism is operated at the target transport speed for a predetermined period, and then the transport speed is again accelerated or decelerated to the steady speed Vt. When the transport speed reaches the steady speed Vt, the transport speed is maintained at the steady speed Vt until the image formation on the recording medium P is completed.

  In FIG. 5A, timing 51 indicates the timing for discriminating the conventional recording medium P, and recording is performed after the acceleration / deceleration control of the conveyance speed of the recording medium P ends and the conveyance speed reaches the steady speed Vt. It can be seen that imaging by the medium imaging device 40 is performed. On the other hand, the timing 50 indicates the recording medium discrimination timing in the present embodiment, and the image is captured during a period (section) in which the conveyance speed of the recording medium P, which is earlier than the timing 51, is accelerated / decelerated. I understand.

[Adjustment of imaging time interval and LED light intensity]
Next, description will be given regarding imaging when acceleration / deceleration control is performed. As described above, in this embodiment, imaging at the steady speed Vt (conveyance speed 80 mm / second) is performed every 42 μm per dot, that is, at intervals of about 530 μsec (= 42 μm ÷ 80 mm / second). On the other hand, in the case of high speed Vh1 (conveying speed 100 mm / second), imaging is performed at intervals of about 420 μsec (= 42 μm ÷ 100 mm / second). As a result, the image size is 118 dots × 118 dots as in the steady speed, and an area corresponding to 5 mm × 5 mm of the recording medium P can be imaged. Recording at high speed or low speed, where Vhl is the transport speed at high speed or low speed of the recording medium, Vt is the transport speed of the recording medium at steady state, and Tt is the imaging time (imaging time interval) of the recording medium at steady state. The imaging time T of the medium can be calculated by the following equation (1).
T = Vt / Vhl × Tt (1)

  When performing acceleration / deceleration control of the conveyance speed of the recording medium P, if the speed difference between the steady speed Vt and the high / low speed Vhl is small, the detection result by the line sensor 43 without changing the light quantity of the LED 41 Since there is almost no effect on the recording medium, no erroneous detection of the paper type of the recording medium occurs. However, when the speed difference between the transport speeds is large, the light quantity of the LED 41 adjusted to the steady speed Vt is insufficient when the transport speed is high, or is low when the speed is low. It becomes excessive.

  FIG. 5B is a graph showing lightness data when the recording medium P is imaged for each conveyance speed of the recording medium P. 5 (b) (i) shows an image of the recording medium P being conveyed at a steady speed Vt, and FIG. 5 (b) (ii) shows an image of the recording medium P being conveyed at a high speed Vh1 or Vh2. FIGS. 5B and 5I show lightness data when the recording medium P being conveyed is imaged at a low speed Vl1. In FIG. 5B, the vertical axis indicates the brightness, the horizontal axis indicates the imaging position of the recording medium P, the left end of each figure indicates the leading end in the recording medium conveyance direction, and the right end indicates the trailing end. As shown in FIGS. 5B and 5I, the brightness data of the recording medium P imaged at the steady speed Vt has an average value of about 192, and has a predetermined amplitude according to the surface state of the recording medium P. Is obtained. On the other hand, as shown in FIGS. 5B and 5I, when imaging is performed when the conveyance speed is the high speed Vh1 or Vh2, the value of the brightness data is the steady speed Vt due to the insufficient amount of light emitted from the LED 41. It becomes lower overall. As a result, the average value of the brightness data also decreases, and the amplitude also decreases (becomes smaller) than in the case of the steady speed Vt. Further, as shown in FIG. 5 (b) (iii), when imaging is performed when the conveyance speed is the low speed V11, the lightness data is generally higher than the case of the steady speed Vt due to excessive light quantity. As a result, the average value of the brightness data is also increased, and the amplitude is increased (increased) as compared with the case of the steady speed Vt. For this reason, when the difference between the conveyance speed at the steady speed and the high / low speed is large, the standard deviation value of the brightness data, which is the feature amount calculated even on the same recording medium, is different. There is a possibility of being detected.

Therefore, in order to solve this problem, the amount of light emitted from the LED 41 is adjusted in accordance with the state of the conveyance speed control of the recording medium. That is, assuming that the light emission amount of the LED 41 when the conveyance speed of the recording medium P is the steady speed Vt is LVt, the light emission amount LVhl of the LED 41 when the conveyance speed Vhl of the recording medium P is high or low is It can be calculated by equation (2).
LVhl = Vhl / Vt × LVt (2)

[Timing relationship between image formation control and recording medium discrimination operation]
FIG. 6 is a diagram illustrating the timing relationship between the conveyance control of the recording medium P, the image formation control, and the paper type discrimination operation of the recording medium P by the recording medium imaging device 40 in the present example and the conventional example. (A) shows a conventional example, and FIG. 6 (b) shows a timing relationship in this embodiment. In FIGS. 6A and 6B, the recording medium control is a process that is sequentially performed from the start of printing to the completion of printing in order to form an image on the recording medium. The “pickup” process refers to feeding the recording medium P from the paper feed cassette 2 or the paper feed tray 3. In the “acceleration / deceleration control” step, a sensor (not shown) measures the distance between the fed recording medium P and the preceding recording medium P, and the conveyance speed is adjusted according to the measured distance. . In the “steady speed conveyance” step, the recording medium P is conveyed to the secondary transfer roller 19 at a steady speed. In the “image transfer” step, the toner image on the intermediate transfer belt 17 is transferred to the recording medium P to be conveyed. In the “image fixing” step, the toner image on the recording medium P is heated and fixed by the fixing unit 21, and the toner image is fixed on the recording medium P. In the “recording medium discharge” step, the recording medium P is discharged outside the apparatus.

  In the recording medium imaging device 40, as shown in the recording medium imaging device control in FIGS. 6A and 6B, the emitted light amount adjustment of the LED 41 is performed in the “light amount adjustment” step. In the “recording medium discrimination” step, the recording medium P conveyed through the conveying path is imaged, and the paper type of the recording medium P is determined based on the brightness data of the surface image. Further, as shown in the image formation control in FIGS. 6A and 6B, the control unit 10 performs the “image formation” process based on the determination result of the paper type of the recording medium P by the recording medium imaging device 40. After changing the image forming conditions, image formation is performed in each process cartridge. Further, the control unit 10 controls the fixing unit 21 according to the recording medium P in the “fixing temperature adjustment” step.

  As shown in FIG. 6A, conventionally, when the acceleration / deceleration control of the recording medium P is finished and the conveyance speed reaches a steady speed, the paper type of the recording medium is determined. After that, the control unit 10 performs change setting of the image forming condition and adjustment of the fixing temperature based on the determination result of the paper type. As soon as the setting of the image forming condition is completed, the image transfer is performed and the adjustment of the fixing temperature is completed. Then, image fixing is performed and printing is completed. In addition, since the recording medium P is not used for the light amount adjustment of the LED 41 described above, it can be performed regardless of the conveyance state of the recording medium, and as shown in the figure, at an arbitrary timing before the recording medium determination. It can be carried out. In FIG. 6A, immediately after the steady-speed conveyance process is completed, the image forming condition change setting is not completed, and the process cannot proceed to the image transfer process. For this reason, a “standby” process is provided in which the conveyance of the recording medium P is temporarily stopped until the change setting of the image forming conditions is completed.

  On the other hand, in the present embodiment shown in FIG. 6B, since the paper type of the recording medium P can be determined during the acceleration / deceleration control of the conveyance speed of the recording medium P, the conventional method shown in FIG. It can be seen that the paper type of the recording medium is determined earlier than in the example. As a result, in this embodiment shown in FIG. 6B, the setting change of the image forming conditions can be performed in parallel with the steady-speed conveyance process, and can be completed. Printing can be completed earlier than the example. As a result, in FIG. 6B of the present embodiment, it is possible to shorten the printing time and to prevent a decrease in throughput as compared with FIG. 6A of the conventional example.

  As described above, according to the present embodiment, it is possible to image a recording medium while reducing a decrease in throughput in an apparatus that performs acceleration / deceleration control of the recording medium. In this embodiment, by adjusting the recording medium imaging time (imaging time interval) according to the recording medium conveyance speed, the recording medium can be imaged even at the timing when the acceleration / deceleration control of the recording medium conveyance speed is performed. This enables recording medium discrimination at an earlier timing. As a result, it is possible to change the image forming conditions and the fixing temperature more quickly, and it is possible to shorten the printing operation and the printing time in the image forming apparatus, thereby preventing a decrease in throughput.

  As described above, in this embodiment, imaging is performed during a period in which the recording medium P is conveyed while maintaining the target conveyance speed after acceleration or deceleration from the steady speed Vt. Since the speed is constant during this period, for example, an image of the surface of the recording medium can be captured with higher accuracy than when imaging is performed while the conveyance speed is being accelerated or decelerated. Further, when imaging is performed while the conveyance speed is being accelerated or decelerated, control is complicated because it is necessary to dynamically change the imaging time and the amount of light according to the conveyance speed. According to the present embodiment, the optimal imaging time and light amount may be calculated once from the above-described equations (1) and (2) in accordance with the target conveyance speed. In the above-described embodiments, an example of a laser beam printer has been described. However, the image forming apparatus to which the present invention is applied is not limited to this, and other printing methods such as an ink jet printer or a copying machine. But you can.

5 Conveying roller 10 Control unit 41 LED
43 Line sensor

Claims (8)

Image forming means for forming an image on a recording medium;
Irradiating means for irradiating the recording medium with light;
An imaging unit configured to capture an image of light irradiated by the irradiation unit and transmitted through the recording medium;
Control means for controlling image forming conditions of the image forming means;
An image forming apparatus comprising:
Comprising a conveying means for conveying the recording medium,
The recording is performed in a state in which the transport unit accelerates or decelerates the transport speed of the recording medium supplied toward the image forming unit from the first speed and maintains a second speed different from the first speed. The image pickup unit picks up an image of the recording medium while the medium is transported, and the control unit controls the image forming condition by the image forming unit based on the image of the recording medium picked up by the image pickup unit. An image forming apparatus.   The image forming apparatus according to claim 1, wherein the imaging unit adjusts an imaging time of the recording medium according to the second conveyance speed.   The image forming apparatus according to claim 1, wherein the irradiation unit adjusts the amount of light to be irradiated according to the second transport speed.   4. The image forming apparatus according to claim 1, wherein the control unit determines the type of the recording medium based on an image of the recording medium captured by the imaging unit. 5. .   The image forming apparatus according to claim 4, wherein the control unit controls the image forming conditions of the image forming unit based on the type of the recording medium determined by the control unit. A light reflecting portion from which the light from the irradiation means hits the recording medium, and the light hitting the recording medium is reflected to the imaging means;
A reference plate that is arranged closer to the imaging unit than the reflecting unit and adjusts the amount of light emitted from the irradiation unit;
Have
6. The image forming apparatus according to claim 1, wherein the imaging unit simultaneously images reflected light from the reflecting portion of the recording medium and reflected light from the reference plate.   The image forming apparatus according to claim 6, wherein when the image of the recording medium is picked up, the light amount is controlled based on the image of the reference plate and light is emitted from the irradiation unit. Storage means for storing correction data corresponding to the light amount;
8. The image forming apparatus according to claim 6, wherein brightness of an image of a recording medium captured by the imaging unit is corrected based on the correction data stored in the storage unit. 9.

Images