JP5604287B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet or the like.

  2. Description of the Related Art Conventionally, as an image forming apparatus, an apparatus that forms an image on a sheet by ejecting ink from an inkjet head while conveying and holding the sheet on a conveying belt is known. In such an image forming apparatus, Patent Document 1 discloses a technique for imaging a conveyed sheet or conveying belt, detecting the amount of movement thereof, and forming an image on the sheet according to the detected amount of movement. Yes.

  The image forming apparatus disclosed in Patent Document 1 images a sheet or a conveyance belt by a movement amount detection sensor that captures reflected light of a laser beam irradiated on the sheet or the conveyance belt from a laser diode. Here, since the reflectance is different between the paper and the conveyor belt, it is necessary to perform light control to adjust the light emission amount of the laser diode depending on which one is imaged. This light control can be performed using an AGC (Automatic Gain Control) function of the movement amount detection sensor.

JP 2009-107310 A

  In the image forming apparatus as described above, when the object to be imaged by the movement amount detection sensor is switched between the sheet and the conveyance belt, the light is adjusted by the AGC function. A certain amount of time is required for dimming by this AGC function. For this reason, there is a case where the light control is not in time, and an area in which the image is not captured with an appropriate amount of light on the paper or the conveyor belt may occur. As a result, there is a non-detection zone in which the amount of movement of the paper or the conveyor belt is not detected, and as a result, the image quality of the image formed on the paper may deteriorate.

  The present invention has been made in view of the above, and an object of the present invention is to provide an image forming apparatus capable of suppressing deterioration in image quality.

  In order to achieve the above object, a first feature of an image forming apparatus according to the present invention is that a transport unit that holds and transports an image forming medium on a transport surface, and the image forming medium that is transported by the transport unit. An image forming unit that forms an image, a medium detection unit that is disposed upstream of the image forming unit in the transport path and detects the image forming medium that is transported, the medium detection unit and the image in the transport path An imaging unit that is disposed between the imaging unit and that has a light source, and that irradiates the image forming medium or the transport surface with light from the light source and images the image forming medium or the transport surface; Using a movement amount calculation unit that calculates a movement amount of the image forming medium or the conveyance surface based on the image obtained in step (a), generates a movement amount information, a detection output of the medium detection unit, and the movement amount information. The image forming unit In addition to controlling, the light emission amount of the light source is switched from the light emission amount for the conveyance unit to the light emission amount for the image forming medium at a timing when the leading end of the image forming medium is predicted to reach the imaging target position by the imaging unit. A control unit that performs control to switch from the light emission amount for the image forming medium to the light emission amount for the transport unit at a timing when the rear end of the image forming medium is predicted to reach the imaging target position. is there.

  A second feature of the image forming apparatus according to the present invention is that the control unit sets a light emission amount for the image forming medium in accordance with a type of the image printing medium.

  According to the first feature of the image forming apparatus of the present invention, the control unit uses the detection output of the medium detection unit and the movement amount information generated by the movement amount calculation unit to emit light from the light source of the imaging unit. Is switched from the light emission amount for the transport unit to the light emission amount for the image forming medium at a timing when the leading edge of the image forming medium is predicted to reach the imaging target position, and the trailing edge of the image forming medium reaches the imaging target position. Control is performed to switch from the light emission amount for the image forming medium to the light emission amount for the transport unit at a timing when is predicted. As a result, it is possible to prevent the occurrence of a non-detection band in which the amount of movement of the image forming medium or the conveyance surface of the conveyance unit is not detected, and as a result, it is possible to suppress the deterioration of the image quality of the image formed on the image forming medium.

  According to the second feature of the image forming apparatus according to the present invention, the light emission amount for the image forming medium is set according to the type of the image forming medium, so that even when different types of image forming media are used, the image forming apparatus is appropriately used. The amount of light emitted from the light source can be set, and deterioration in image quality formed on the image forming medium can be suppressed.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a configuration of a control system of the image forming apparatus illustrated in FIG. 1. It is a schematic block diagram of an imaging part. It is a figure for demonstrating image formation operation | movement. It is a figure for demonstrating image formation operation | movement. It is a flowchart for demonstrating the process which adjusts the light emission amount of a laser diode. An example of data obtained by converting the movement amount of the conveyance surface of the paper or the conveyance belt detected based on the captured image into the conveyance speed when the movement amount detection sensor adjusts the light emission amount of the laser diode using only the AGC function. FIG. FIG. 7 is a diagram illustrating an example of data obtained by converting a movement amount of a conveyance surface of a sheet or a conveyance belt detected based on a captured image into a conveyance speed when a light emission amount of a laser diode is set by processing of an embodiment. .

  Embodiments of the present invention will be described below with reference to the drawings. Throughout the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals. However, it should be noted that the drawings are schematic and different from the actual ones.

  Further, the embodiment described below exemplifies an apparatus or the like for embodying the technical idea of the present invention, and the technical idea of the present invention is to arrange the components and the like as follows. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of a control system of the image forming apparatus shown in FIG. As shown in FIGS. 1 and 2, the image forming apparatus 1 includes a paper feeding unit 2, a belt conveyance unit 3, an inkjet head unit 4, a paper sensor 5, a movement amount detection sensor 6, and a control unit 7. Is provided.

  In the following description, the vertical direction and the horizontal direction indicate the vertical direction and the horizontal direction shown in FIG. Further, a path indicated by a broken line in FIG. 1 is a transport path R along which the image forming medium is transported, and a direction from left to right is a transport direction. In the following description, upstream and downstream mean upstream and downstream in the transport path R, respectively.

  The paper feed unit 2 supplies paper to the belt conveyance unit 3. The paper feed unit 2 is provided on the most upstream side of the transport path R. The sheet feeding unit 2 includes a sheet feeding table 21, a sheet feeding roller 22, and a registration roller 23.

  The paper feed table 21 is for stacking paper P that is an image forming medium.

  The paper feed roller 22 takes out the paper P stacked on the paper feed tray 21 one by one and sends it out toward the registration roller 23.

  The registration roller 23 is provided on the downstream side of the paper feed roller 22. The registration roller 23 sends out the paper P sent from the paper feed roller 22 toward the belt conveyance unit 3 at a predetermined timing.

  The paper feed unit 2 includes a motor that rotationally drives the paper feed roller 22 and a motor (none of which is shown) that rotationally drives the registration roller 23.

  The belt conveyance unit 3 is provided on the downstream side of the registration roller 23. The belt conveyance unit 3 includes an annular conveyance belt 31 provided to face the inkjet head unit 4, a belt driving roller 32 that drives the conveyance belt 31 to rotate, and driven rollers 33 to 35 that are driven by the belt driving roller 32. Is provided. The belt conveyance unit 3 includes a motor (not shown) that rotationally drives the belt driving roller 32.

  The conveyor belt 31 is an endless belt having a large number of holes, and the sheet P is conveyed by negative pressure generated when air is sucked from the holes by a suction fan (not shown), and the conveyor surface 311 is the surface of the conveyor belt 31. Adsorb and hold on to transport. The conveyance belt 31 corresponds to a conveyance unit in claims. The belt conveyance unit 3 is not limited to the configuration in which the paper P is attracted and held on the conveyance surface 311 of the conveyance belt 31 by air suction as described above, and for example, the paper P is held on the conveyance surface 311 by electrostatic adsorption. It is good also as such a structure.

  The inkjet head unit 4 includes a plurality of line-type inkjet heads arranged above the belt conveyance unit 3 and having a plurality of nozzles arranged in a direction orthogonal to the conveyance direction of the paper P. The ink jet head unit 4 forms an image by ejecting ink from the ink jet head onto the paper P transported by the belt transport unit 3. The inkjet head unit 4 corresponds to the image forming unit in the claims.

  The paper sensor 5 is disposed on the upstream side of the inkjet head unit 4 and detects the paper P that is transported on the transport path R. In the present embodiment, the paper sensor 5 is composed of an optical reflective sensor disposed above the conveyor belt 31 and outputs a signal indicating “ON” when the paper P is passing.

  The movement amount detection sensor 6 is disposed above the conveyance belt 31 on the downstream side of the paper sensor 5 and upstream of the ink jet head unit 4, and detects the movement amount of the conveyance surface 311 of the conveyance belt 31 or the paper P. The movement amount detection sensor 6 irradiates the moving conveyor belt 31 or the paper P with laser light and captures images at a predetermined time interval. Based on the movement of the uneven pattern), the movement amount of the conveyance surface 311 of the conveyance belt 31 or the paper P is detected. The movement amount detection sensor 6 includes an imaging unit 61 and a movement amount calculation unit 62.

  A schematic configuration of the imaging unit 61 is shown in FIG. The imaging unit 61 includes a laser diode 611, condenser lenses 612 and 613, and an area sensor 614.

  The laser diode 611 emits laser light that irradiates the conveyance belt 31 or the paper P to be imaged. The laser diode 611 is driven by a drive circuit (not shown) and is configured to be able to adjust the light emission amount under the control of the control unit 7. The laser diode 611 corresponds to the light source of the claims.

  The condensing lens 612 condenses the laser light emitted from the laser diode 611 on the conveyance belt 31 or the paper P.

  The condensing lens 613 condenses the reflected light, which is the laser light reflected by the conveyance belt 31 or the paper P, on the area sensor 614.

  The area sensor 614 has an imaging device such as a CCD (Charge Coupled Device), receives reflected light from the transport belt 31 or the paper P, converts the received light into an electrical signal, and based on the electrical signal, an image is obtained. Is generated.

  The movement amount calculation unit 62 calculates the movement amount of the conveyance surface 311 of the conveyance belt 31 or the paper P by calculating how much the specific pattern in the image captured by the imaging unit 61 has moved by a correlation function. . The movement amount calculation unit 62 generates a pulse signal for each predetermined movement amount, and outputs this to the control unit 7. This pulse signal corresponds to the movement amount information in the claims.

  The control unit 7 includes a CPU, a memory (all not shown), and the like, and controls each unit of the image forming apparatus 1.

  The control unit 7 controls the inkjet head unit 4 using the detection output of the sheet sensor 5 and the pulse signal from the movement amount calculation unit 62 to form an image on the sheet P conveyed by the conveyance belt 31.

  Further, the control unit 7 uses the detection output of the paper sensor 5 and the pulse signal from the movement amount calculation unit 62 to predict the arrival of the leading edge and the trailing edge of the paper P at the imaging target position of the imaging unit 61. At timing, control is performed to switch the light emission amount of the laser diode 611 between the light emission amount for paper and the light emission amount for the conveyance belt. As will be described later, the control unit 7 switches the light emission amount of the laser diode 611 to the light emission amount for paper at a timing at which the leading edge of the paper P reaches the imaging target position of the imaging unit 61, and moves to the imaging target position. The light emission amount of the laser diode 611 is switched to the light emission amount for the conveyor belt at the timing when the rear end of the paper P is predicted to arrive.

  Next, the operation of the image forming apparatus 1 will be described.

  First, an image forming operation in the image forming apparatus 1 will be described. When an instruction to start image formation is given, the control unit 7 drives the paper feed roller 22 to rotate. Further, the control unit 7 rotationally drives the belt driving roller 32 of the belt conveying unit 3. As a result, the conveyor belt 31 is driven to rotate. In addition, the control unit 7 starts imaging by the movement amount detection sensor 6.

  The paper supply roller 22 takes out the paper P from the paper supply table 21 and sends it out toward the registration roller 23. When the sheet P hits the registration roller 23, the control unit 7 rotates the registration roller 23. As a result, the registration roller 23 sends the paper P toward the belt conveyance unit 3. The belt conveyance unit 3 conveys the paper P sent from the registration roller 23 while holding it on the conveyance surface 311 of the conveyance belt 31.

  The movement amount detection sensor 6 images the conveyance surface 311 of the conveyance belt 31 until the paper P reaches the imaging target position of the imaging unit 61. Then, the movement amount calculation unit 62 calculates the movement amount of the transport surface 311 and outputs a pulse signal corresponding to the movement amount.

  When the detection output of the paper sensor 5 is “ON” (the leading edge of the paper P is detected), the control unit 7 starts counting the number of pulses input from the movement amount calculation unit 62. The control unit 7 causes ink to be ejected from each nozzle of each inkjet head of the inkjet head unit 4 based on the counted number of pulses and the image data to be printed. The control unit 7 presets the number of pulses corresponding to the distance from the paper sensor 5 to each nozzle as the number of pulses indicating the timing at which ink is ejected from each nozzle.

  Here, as illustrated in FIG. 4, when the paper P has reached the imaging target position of the imaging unit 61 of the movement amount detection sensor 6, the movement amount calculation unit 62 performs a pulse corresponding to the movement amount of the paper P. Output a signal. After the conveyance of the sheet P further proceeds and the sheet P passes the imaging target position of the imaging unit 61 as shown in FIG. 5, the movement amount calculation unit 62 determines the movement amount of the conveyance surface 311 of the conveyance belt 31. The corresponding pulse signal is output. That is, the control unit 7 performs ink ejection control according to the movement amount of the paper P in the state of FIG. 4, and performs ink ejection control according to the movement amount of the transport surface 311 in the state of FIG. 5. become.

  An image is formed on the paper P by ejecting ink from the inkjet head unit 4. The paper P on which image formation has been completed is discharged and stocked on a paper discharge tray (not shown) provided on the downstream side of the belt conveyance unit 3.

  During the image forming operation as described above, the control unit 7 performs control to adjust the light emission amount of the laser diode 611. This is because the transport belt 31 and the paper P have different reflectivities, and the amount of light suitable for imaging for appropriately detecting the amount of movement is different. If the light emission amount of the laser diode 611 is not appropriate, it may be difficult to detect the pattern of the conveyance surface 311 and the surface of the paper P from the image obtained by the movement amount detection sensor 6, and the movement amount may not be detected.

  Processing for adjusting the light emission amount of the laser diode 611 will be described with reference to the flowchart of FIG.

  When the image forming operation is started and the paper feeding is started, in step S10, the control unit 7 determines whether or not the detection output of the paper sensor 5 is “ON” (the leading edge of the paper P is detected). Determine whether. When it is determined that the detection output of the paper sensor 5 is “OFF” (step S10: NO), the control unit 7 repeats the process of step S10.

  When it is determined that the detection output of the paper sensor 5 is “ON” (step S10: YES), in step S20, the control unit 7 starts counting the number of pulses input from the movement amount calculation unit 62.

  Next, in step S <b> 30, the control unit 7 determines whether or not the count value C <b> 1 of the number of pulses from the time when the detection output of the paper sensor 5 is “ON” has reached the set count value CA. The set count value CA is a pulse number indicating a movement amount corresponding to the distance from the detection target position of the paper sensor 5 to the imaging target position of the imaging unit 61. Therefore, it is predicted that the leading edge of the paper P reaches the imaging target position of the imaging unit 61 at the timing when the count value C1 becomes the set count value CA.

  When it is determined that the count value C1 is not the set count value CA (step S30: NO), the control unit 7 repeats the process of step S40. When it is determined that the count value C1 has reached the set count value CA (step S30: YES), in step S40, the control unit 7 changes the light emission amount of the laser diode 611 from the light emission amount for the conveyance belt to the light emission amount for paper. Switch to.

  Here, there are various types of paper, such as plain paper and ink jet dedicated paper. Reflectivity varies depending on the type of paper. Therefore, in step S40, the control unit 7 preferably sets the light emission amount of the laser diode 611 suitable for imaging according to the type of paper used for image formation. The type of paper is set in the control unit 7 according to a user operation or the like before the start of the image forming operation.

  Next, in step S50, the control unit 7 determines whether or not the detection output of the paper sensor 5 is “OFF” (the trailing edge of the paper P is detected). When it is determined that the detection output of the paper sensor 5 is “ON” (step S50: NO), the control unit 7 repeats the process of step S50.

  When it is determined that the detection output of the paper sensor 5 is “OFF” (step S50: YES), in step S60, the control unit 7 counts the number of pulses from when the detection output of the paper sensor 5 is “OFF”. It is determined whether the count value C2 has reached the set count value CA. It is predicted that the trailing edge of the paper P will reach the imaging target position of the imaging unit 61 at the timing when the count value C2 becomes the set count value CA.

  When it is determined that the count value C2 is not the set count value CA (step S60: NO), the control unit 7 repeats the process of step S60. When it is determined that the count value C2 has reached the set count value CA (step S60: YES), in step S70, the control unit 7 changes the light emission amount of the laser diode 611 from the light emission amount for paper to the light emission amount for the conveyance belt. Switch.

  Next, in step S80, the control unit 7 determines whether or not the paper P detected by the paper sensor 5 is the last paper on which an image is formed. When it is determined that the paper P detected by the paper sensor 5 is the last paper (step S80: YES), the control unit 7 ends the series of processes. When determining that it is not the last sheet (step S80: NO), the control unit 7 returns to step S10 and repeats the subsequent processing.

  As described above, the image forming apparatus 1 according to the present embodiment uses the detection output of the paper sensor 5 and the pulse signal from the movement amount calculation unit 62 to change the light emission amount of the laser diode 611 to the light emission amount for paper. And control to switch between the light emission amount for the conveyor belt. As a result, the image forming apparatus 1 can quickly switch the light emission amount of the laser diode 611 to an appropriate light emission amount at the boundary between the paper P and the conveyance surface 311 of the conveyance belt 31.

  Here, when the movement amount detection sensor 6 adjusts the light emission amount of the laser diode 611 using only the AGC function, the movement amount of the paper P or the conveyance surface 311 of the conveyance belt 31 detected based on the captured image is determined. An example of the data converted into the conveyance speed is shown in FIG. In the data shown in FIG. 7, there is a portion where the waveform is greatly depressed. This indicates that a non-detection zone in which the movement amount (conveyance speed) is not detected between the sheets has occurred. Such a non-detection zone occurs because the AGC function cannot adjust the light in time, and an area that cannot be imaged with an appropriate amount of light is generated.

  On the other hand, when the light emission amount of the laser diode 611 is set by the processing of the present embodiment, the movement amount of the paper P or the conveyance surface 311 of the conveyance belt 31 detected based on the captured image is converted into the conveyance speed. An example of the obtained data is shown in FIG. In FIG. 8, no non-detection zone has occurred.

  As described above, according to the present embodiment, it is possible to prevent the occurrence of a non-detection band in which the movement amount of the sheet P or the conveyance surface 311 of the conveyance belt 31 is not detected. As a result, the image quality of the image formed on the sheet P can be reduced. Reduction can be suppressed.

  Also, by setting the light emission amount of the laser diode 611 according to the type of paper used for image formation, the light emission amount of the laser diode 611 can be appropriately set even when different types of paper P are used, and formed on the paper P. Degradation of image quality can be suppressed.

  In the present embodiment, the controller 7 emits light from the laser diode 611 when the count value C2 of the number of pulses after the trailing edge of the paper P is detected by the paper sensor 5 reaches the set count value CA. The amount of light is switched to the light emission amount for the conveyor belt, but the count value C1 of the number of pulses after the leading edge of the paper P is detected by the paper sensor 5 is set to the number of pulses corresponding to the paper size in the set count value CA. When the added count value CB is reached, the light emission amount of the laser diode 611 may be switched to the light emission amount for the conveyor belt.

  In addition, after the light emission amount of the laser diode 611 is switched in steps S40 and S70 in the flowchart of FIG. 6, when the light reception amount in the area sensor 614 is out of a predetermined range, the control unit 7 emits the light emission amount of the laser diode 611. May be returned before switching. Thereby, when the light emission amount of the laser diode 611 after switching is not appropriate, it is possible to prevent the imaging from being performed as it is.

  In the present embodiment, the image forming medium is described as a sheet. However, the present invention can also be applied to the case where an image forming medium made of resin or the like is used.

  Further, the image forming apparatus 1 of the present embodiment is configured to transport the paper P by the transport belt 31, but the transport unit is not limited to this. For example, the present invention can be applied to an image forming apparatus that transports a sheet by a transport drum.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Paper feed part 3 Belt conveyance part 4 Inkjet head part 5 Paper sensor 6 Movement amount detection sensor 7 Control part 31 Conveyance belt 61 Imaging part 62 Movement amount calculation part 311 Conveyance surface 611 Laser diode 614 Area sensor

Claims (2)

A transport unit for transporting the image forming medium while being held on the transport surface;
An image forming unit that forms an image on the image forming medium conveyed by the conveying unit;
A medium detection unit that is disposed upstream of the image forming unit in a conveyance path and detects the image forming medium conveyed;
The image forming medium or the conveying surface is disposed between the medium detecting unit and the image forming unit in the conveying path, includes a light source, and irradiates the image forming medium or the conveying surface with light from the light source. An imaging unit for imaging
A movement amount calculation unit that calculates a movement amount of the image forming medium or the transport surface based on an image obtained by the imaging unit and generates movement amount information;
Using the detection output of the medium detection unit and the movement amount information, the image forming unit is controlled, and the amount of light emitted from the light source is reached by the imaging unit to the position to be imaged by the imaging unit. Is switched from the light emission amount for the conveyance unit to the light emission amount for the image forming medium at a timing at which the image forming medium is predicted, and the image forming medium for the image forming medium is predicted to arrive at the rear end of the image forming medium at the imaging target position. An image forming apparatus comprising: a control unit that performs control to switch from a light emission amount to a light emission amount for the transport unit.   The image forming apparatus according to claim 1, wherein the control unit sets a light emission amount for the image forming medium according to a type of the image printing medium.