JP2007111986A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of improving a printing speed by accurately detecting a top of a paper sheet even when reducing an interval between the paper sheets. <P>SOLUTION: A first paper sensor 81 having a reflection type photosensor for detecting a top of a paper sheet 12 to be conveyed is provided to a carriage 3. A second paper sensor 82 for detecting the top of the paper sheet 12 is disposed to a position opposing a conveyance roller 27 at the upstream side of the first paper sensor 81 in the paper conveyance direction in the vicinity of a pressing roller 25 at the upstream side thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus in which a recording head is mounted on a carriage.

  As various image forming apparatuses such as printers, facsimiles, copying machines, plotters, printer / fax / copier multifunction machines, etc., recording heads (printing heads) constituted by droplet discharging heads that discharge recording liquid (for example, ink) droplets are used. ) Is mounted on a carriage, and the carriage is also referred to as a recording medium (hereinafter referred to as “paper”, but the material is not limited to paper, and the recording medium, recording paper, transfer material, printing material, printing medium, etc.) In addition, serial scanning is performed in a direction orthogonal to the conveyance direction), and the recording medium is intermittently conveyed according to the recording width, and the image is recorded on the recording medium by alternately repeating conveyance and recording. There is a serial type image forming apparatus that forms (recording, printing, printing, and printing are also used synonymously).

In such an image forming apparatus, when a deviation occurs in the paper edge detection, the liquid droplets are ejected to the outside of the paper, so that the image quality deteriorates or the liquid droplets land on a conveyance means such as a conveyance belt. And has the disadvantage of getting dirty. Therefore, as described in Patent Document 1, for example, a sheet detection unit that detects a sheet is provided on a carriage that scans in the sheet width direction, and the edge detection of the sheet is accurately performed on a flat surface near the image forming unit. I try to do it.
JP 2004-237893 A

  Incidentally, the image forming apparatus is required to improve the printing speed. For this purpose, the distance between the preceding sheet and the succeeding sheet (hereinafter referred to as “inter-sheet space”) is as narrow as possible during continuous printing. It will be necessary to make it smaller.

  However, in the configuration in which the detection means for detecting the leading edge of the paper is provided on the carriage as described above, when performing printing of a plurality of pages by continuous printing, the paper that follows after the last scan of the preceding paper is performed. Since the carriage moves to a predetermined position for detecting the leading edge of the paper and starts the leading edge detection operation of the following paper, a time loss occurs until the leading edge of the trailing paper is detected. As a result, the gap between the sheets cannot be kept below a certain level. As a result, there arises a problem that the limit in relation to the detection of the leading edge of the paper also arises in improving the printing speed.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of improving the printing speed by accurately detecting the leading edge of a sheet even when the interval between the sheets is reduced.

  In order to solve the above-described problems, an image forming apparatus according to the present invention is arranged with a first detection unit that detects a recording medium mounted on a carriage, and upstream of the first detection unit in the recording medium conveyance direction. And a second detection means for detecting the recording medium.

  Here, the leading end of the recording medium can be detected by either the first detection unit or the second detection unit in accordance with the conveyance speed of the recording medium. Further, the leading end of the recording medium can be detected by either the first detection unit or the second detection unit according to the print mode. Further, based on the detection result of the second detection means, the recording medium reaches the detection position by the first detection means before reaching the predetermined detection position where the first detection means detects the leading edge of the recording medium. If detected, the conveyance speed of the recording medium can be reduced. Further, based on the detection result of the second detection means, the recording medium reaches the detection position by the first detection means before reaching the predetermined detection position where the first detection means detects the leading edge of the recording medium. In this case, the leading end of the recording medium can be detected by using the second detection means.

  The recording medium detection position by the first detection unit and the recording medium detection position by the second detection unit are preferably different in the scanning direction of the carriage.

  In this case, it is preferable to detect the skew amount of the recording medium based on the detection results of the first detection means and the second detection means, and the recording medium is formed on the recording medium based on the detection result of the skew amount of the recording medium. The image data can be rotated, the recording medium can be discharged and then re-feeded, and an error display can be performed.

  Furthermore, it is preferable that the second detection means is disposed at a position facing a conveyance roller for conveying the recording medium toward a recording area by the recording head. In this case, the conveyance roller can be configured to drive a conveyance belt that adsorbs and conveys the recording medium with an electrostatic force.

  According to the image forming apparatus of the present invention, the first detection unit that detects the recording medium mounted on the carriage, and the recording medium that is disposed upstream of the first detection unit in the recording medium conveyance direction is detected. Therefore, by detecting the leading edge with at least one of the first and second detecting means, the leading edge of the recording medium can be accurately detected even if the paper interval is reduced during continuous printing. It becomes possible to detect it, and it is possible to improve the printing speed.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory side view for explaining the overall structure of the mechanism unit of the image forming apparatus, and FIG. 2 is an explanatory plan view of the main part of the apparatus.

  In this image forming apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2 which are guide members horizontally mounted on left and right side plates (not shown), and a driving pulley 6 a is driven by a main scanning motor 4. 2 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 5 spanned between the driven pulley 6b. Note that guide bushes (bearings) 3a and 3a are interposed between the carriage 3 and the guide rod 1, respectively.

  The carriage 3 includes, for example, four recording heads 7 each including a droplet discharge head that discharges yellow (Y), cyan (C), magenta (M), and black (Bk) ink droplets. The ejection ports are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.

  As a droplet discharge head constituting the recording head 7, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses film boiling of a liquid using an electrothermal transducer such as a heating resistor, or a metal phase change due to a temperature change is used. For example, a shape memory alloy actuator, an electrostatic actuator using an electrostatic force, or the like provided as energy generating means for discharging ink (recording liquid) can be used. Note that the recording head can also be configured by one or a plurality of liquid droplet ejection heads provided with a plurality of nozzle rows that eject different colors.

  The carriage 3 is equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) (not shown) via an ink supply tube 9. In addition to the recording head 7 that discharges ink droplets, a recording head that discharges a fixing treatment liquid (fixing ink) that reacts with the recording liquid (ink) to improve the fixing property of the ink can be provided.

  On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feeding cassette 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.

  As a transport unit for transporting the recording medium (paper) 12 fed from the paper feed unit on the lower side of the recording head 7, a transport belt 21 for sucking and transporting the paper 12 with electrostatic force. A counter roller 22 for transporting the paper 12 fed from the paper feed section via the guide 15 between the transport belt 21 and the paper 12 fed substantially vertically upward by turning about 90 °. A conveyance guide 23 for following the conveyance belt 21 and a tip pressurizing roller 25 urged toward the conveyance belt 21 by a pressing member 24 are provided. In addition, a charging roller 26 constituting a charging means for charging the surface of the transport belt 21 is provided.

  Here, the conveyance belt 21 is an endless belt (either an endless belt in molding or a belt made endless by connecting both ends), and a tension as a conveyance roller 27 as a driving roller and a tension as a driven roller. The roller 28 is wound around the roller 28 and rotated from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33 to rotate around the belt conveying direction (sub-scanning direction) in FIG. It is configured as follows. A guide member 29 is disposed on the back side of the conveying belt 21 corresponding to the image forming area by the recording head 7.

  The transport belt 21 may be a single-layer belt as shown in FIG. 3, or may be a multilayer (two or more layers) belt as shown in FIG. In the case of the transport belt 21 having a one-layer structure, the entire layer is formed of an insulating material because it contacts the paper 12 and the charging roller 28. In the case of the transport belt 21 having a multilayer structure, the side that contacts the paper 12 and the charging roller 26 is formed of an insulating layer 21A, and the side that does not contact the paper 12 and the charging roller 26 is formed of a conductive layer 21B. Is preferred.

Examples of the insulating material for forming the single-layered conveyance belt 21 and the insulating material for forming the insulating layer 21A of the multilayered conveying belt 21 include resins such as PET, PEI, PVDF, PC, ETFE, and PTFE, and elastomers. It is preferable that the material does not contain a conductivity control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. In addition, as a material for forming the conductive layer conductive layer 21B of the transport belt 21 having a multilayer structure, the resin or elastomer may be made to contain carbon so that the volume resistivity is 10 ⁵ to 10 ⁷ Ωcm. preferable.

The charging roller 26 is disposed so as to come into contact with the insulating layer 21A (in the case of a multilayer belt) forming the surface layer of the conveyor belt 21, and to rotate following the rotation of the conveyor belt 21, and is applied to both ends of the shaft. Pressure is applied. The charging roller 26 is formed of a conductive member having a volume resistivity of 10 ⁶ to 10 ⁹ Ω / □. As will be described later, for example, a 2 kV positive / negative AC bias is applied to the charging roller 26 from the AC bias supply unit 114. The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  Further, as shown in FIG. 2, an encoder wheel 34 is attached to the shaft of the conveying roller 27, and an encoder sensor 35 including a transmission type photosensor that detects a slit of the encoder wheel 34 is provided. A rotary encoder 36 is constituted by the encoder sensor 35.

  As shown in FIG. 1, an encoder scale 42 having slits is provided on the front side of the carriage 3, and an encoder sensor comprising a transmissive photosensor that detects the slits of the encoder scale 42 on the front side of the carriage 3. The linear encoder 44 for detecting the position of the carriage 3 in the main scanning direction is formed.

  Further, the carriage 3 is provided with a first sheet sensor (first sheet sensor) 81 which is a first detection means including a reflection type photosensor for detecting the leading end of the sheet 12 being conveyed. Further, a reflection type photosensor for detecting the leading edge of the paper 12 at a position facing the conveyance roller 27 on the upstream side of the presser roller (pressing roller) 25 that is upstream of the first paper sensor 81 in the paper conveyance direction. A second sheet sensor (second sheet sensor) 82 as second detecting means is arranged. Note that the first and second paper sensors 81 and 82 are not limited to reflective sensors, and transmissive sensors, physical switches, and the like can also be used.

  The second sheet sensor 82 is preferably as close as possible to the first sheet sensor 81 in terms of detection accuracy. However, in consideration of the fact that the movement of the carriage 3 should not be hindered and the installation space, this image forming apparatus is used. Then, although it has arrange | positioned in the upstream vicinity of the presser roller 25, it is not restricted to this. However, in order to perform detection in a state where the sheet 12 is stably conveyed, the position facing the conveying roller 27 is preferable. It is also possible to use a conveying means that does not use a conveying belt (for example, a conveying means using a conveying roller).

  Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation claw 51 for separating the paper 12 from the transport belt 21, a paper discharge roller 52 and a paper discharge roller 53, and a discharge And a paper discharge tray 54 for stocking the paper 12 to be printed.

  A double-sided paper feeding unit 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport belt 21.

  Further, an extension tray 70 can be attached to the bottom of the image forming apparatus. The extension tray 70 includes a pressure plate (paper placement plate) 71 on which the paper 12 is placed, a paper feed roller 73, and a separation pad 74 in the same manner as the paper feed tray 10. A sheet is separated and fed one by one by a roller 73 and a separation pad 74, and the sheet is fed between the counter roller 22 and the conveyor belt 21 from below the apparatus main body by conveyance rollers 75 and 76. .

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
The control unit 100 includes a CPU 101 that controls the entire apparatus, a ROM 102 that stores programs executed by the CPU 101 and other fixed data, a RAM 103 that temporarily stores image data, and the power supply of the apparatus. A rewritable non-volatile memory 104 for holding data and an ASIC 105 for processing input / output signals for controlling various types of signal processing and rearrangement of image data and for controlling the entire apparatus. ing.

  The control unit 100 also includes an I / F 106 for transmitting / receiving data and signals to / from the host 90 which is a data processing device such as a personal computer, a print control unit 107 for driving and controlling the recording head 7, and the like. A head driver 108, a main scanning motor driving unit 111 for driving the main scanning motor 4, a sub scanning motor driving unit 113 for driving the sub scanning motor 31, a first paper sensor 81, and a second paper sensor 81. In addition, an I / O 116 and the like are provided to input detection and detection signals from the linear encoder 44 and the rotary encoder 34.

  The control unit 100 is connected to an operation panel 117 for inputting and displaying information necessary for the apparatus. Further, the control unit 100 controls on / off of an output of an AC bias supply unit (high voltage power source) 114 that applies an AC bias to the charging roller 26.

  Here, the control unit 100 receives print data including image data from the host 90 side such as a data processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera via a cable or a network. Received by the I / F 106. It should be noted that the print data generation output for the control unit 100 is performed by the printer driver 91 on the host 90 side.

  Then, the CPU 101 reads and analyzes the print data in the reception buffer included in the I / F 106, performs data rearrangement processing by the ASIC 105, and transfers the image data to the head drive control unit 107. Note that the conversion of print data for image output into bitmap data is performed by developing the image data into bitmap data by the printer driver 91 on the host 90 side and transferring it to this apparatus as described above. For example, font data may be stored in the ROM 102.

  When the print control unit 107 receives image data (dot pattern data) corresponding to one row of the recording head 7, the dot pattern data for one row is serially transmitted to the head driver 108 in synchronization with the clock signal. And a latch signal is sent to the head driver 108 at a predetermined timing.

  Further, the print control unit 107 performs D / A conversion on the ROM (which can be configured by the ROM 102) storing pattern data of the drive waveform (drive signal) and the drive waveform data read from the ROM. A waveform generation circuit including a D / A converter and a drive waveform generation circuit including an amplifier and the like are included.

  The head driver 108 also includes a shift register that inputs a clock signal from the print control unit 107 and serial data that is image data, a latch circuit that latches a register value of the shift register using a latch signal from the print control unit 107, It includes a level conversion circuit (level shifter) that changes the output value of the latch circuit, an analog switch array (switch means) that is controlled to be turned on / off by the level shifter, and the like, and controls the on / off of the analog switch array. A required drive waveform included in the drive waveform is selectively applied to the actuator means of the recording head 7 to drive the head.

  The main scanning motor driving unit 111 calculates a control value based on a target value given from the CPU 101 side and a speed detection value obtained by sampling a detection pulse from the encoder 44, and passes the main scanning motor via an internal motor driver. 4 is driven.

  Similarly, the sub-scanning motor drive control unit 113 calculates a control value based on the target value given from the CPU 101 side and the speed detection value obtained by sampling the detection pulse from the encoder 36, and passes through the internal motor driver. Then, the sub-scanning motor 31 is driven.

An operation during printing in this image forming apparatus will be described with reference to FIGS.
First, a portion related to charging control for the conveyor belt 21 will be described with reference to FIG. As described above, the amount of rotation is detected by the encoder 36 provided at the end of the conveying roller 27 that drives the conveying belt 21, and the sub-scanning motor driving unit 113 of the control unit 100 performs sub-scanning according to the detected amount of rotation. The motor 31 is driven and controlled, and the output of an AC bias supply unit (high voltage power source) 114 that applies a high voltage (AC bias) to the charging roller 26 is controlled.

  The AC bias supply unit 114 controls the period (application time) of the positive and negative voltages applied to the charging roller 26, and at the same time, the control unit 100 controls the driving of the conveyance belt 21. The positive and negative charges can be applied to the electrode with a predetermined charging cycle length. Here, the “charging cycle length” is a width (distance) in the transport direction per cycle of the applied voltage of the positive and negative electrodes as shown in FIG.

  When printing is started, the conveyance roller 27 is driven to rotate by the sub-scanning motor 31 to rotate the conveyance belt 21 clockwise in FIG. Apply a square wave. As a result, the charging roller 26 is in contact with the insulating layer 21A of the conveyor belt 21, so that positive and negative charges are transferred to the insulating belt 21A of the conveyor belt 21 as shown in FIG. Are applied alternately in the conveying direction (band-shaped positive charging areas 201 and negative charging areas 202 are alternately formed), and an unequal electric field is generated on the conveying belt 21 as shown in FIG. The

  As described above, the insulating layer 21a of the conveyor belt 21 to which the positive and negative charges are applied has a volume resistance of 1E12 Ωcm or more, preferably 1E15 Ωcm. Therefore, positive and negative charges charged on the insulating layer 21a. However, movement at the boundary can be prevented, and positive and negative charges applied to the insulating layer 21a can be held.

  On the other hand, the paper 12 is separated and fed by the paper feed roller 13 and the separation pad 14, and is fed into the conveyor belt 21 in which an unequal electric field is generated by forming positive and negative charges on the insulating layer 21a. It is. Then, as shown in FIG. 8, the sheet 12 sent on the unequal electric field on the conveyor belt 21 is instantaneously polarized along the direction of the electric field. Due to the unequal electric field, the charge that forms an attractive force with the conveyance belt 21 on the conveyance belt surface side of the sheet 12 becomes dense, and the charge that forms a repulsive force with the conveyance belt 21 that appears on the opposite sheet surface becomes sparse. Due to this charge difference, the sheet 12 is instantaneously adsorbed to the transport belt 21. Further, since the sheet 12 has a finite resistance, at the same time, a true charge is induced on the adsorption surface of the sheet 12 and the opposite side.

  The positive and negative true charges induced on the suction surface side are attracted stably by attracting the charges applied on the conveyor belt 21, but the positive and negative true charges induced on the opposite side are unstable. It is. The true charge induced on the surface of the paper opposite to the suction surface can move because the paper resistance has a finite resistance value ranging from 1E7Ω / □ to 1E13Ω / □. The electric charge of each of them attracts and moves and decreases while being neutralized. As a result, the charge on the conveyor belt balances with the true charge induced on the sheet adsorption surface side, the electric field is closed, and the true charge induced on the opposite side of the sheet adsorption surface is neutralized as described above. The electric field is closed. That is, the electric field toward the recording head decreases. In addition, since the charge applied to the surface of the transport belt 21 and the charge of the transport belt 21 and the charge forming a weak force decrease from the surface of the paper 12, the adsorption force of the paper 12 to the transport belt 21 increases with time.

  In this way, the paper 12 adsorbed on the transport belt 21 is detected by the second paper sensor 82 at the leading edge of the paper. At this time, the main control unit 100 stores the timing (number of pulses) when the second sheet sensor 82 detects the leading edge or the distance obtained from the number of pulses and the conveyance speed in a predetermined area of the RAM 103.

  The paper 12 whose leading edge has been detected is conveyed to the bottom of the recording head 7 provided in the carriage 3 while being pressed against the conveying belt 21 by the pressing roller 25. Then, the leading edge of the sheet is detected by the first sheet sensor 81 provided on the carriage 3 that has moved to the predetermined leading edge detection position. The main control unit 100 stores the number of pulses when the first sheet sensor 81 detects the leading edge or the distance obtained from the number of pulses and the conveyance speed in a predetermined area of the RAM 103.

  On the other hand, the print data in the reception buffer included in the I / F 106 is read and analyzed by the CPU 101, and the data is rearranged by the ASIC 105 and sent to the print control unit 107. Then, the conveyance of the sheet 12 is stopped at the timing when the sheet 12 is conveyed to the writing start position (first scan position) of the image data sent to the print control unit 107, and the carriage 3 is reciprocated in the main scanning direction. At the same time, ink droplets are ejected from the recording head 7 according to the data sent by the print control unit 107, so that one reciprocation of the recording head on the paper 12 (or two or more reciprocations and one or more reciprocation directions) In the following, an explanation will be given for one round trip).

  When an image for one reciprocation is thus formed, the paper 12 is sent to the next printing position by the conveyor belt 21, and image formation for one reciprocation is performed again. The paper on which image formation has been completed is transported as it is, separated from the transport belt 21 by the separation claw 51, and stacked on the paper discharge tray 54. The above is the printing operation for one page of paper.

  Here, in this image forming apparatus, when the print data extends over a plurality of pages, that is, when printing is continuously performed on a plurality of pages, the next page is processed while the image is formed on the preceding page. It is determined whether or not image formation is necessary. When image formation on the next page is necessary, the image formation operation for the next page starts while image formation on the preceding page (current page) is being performed. Will do. That is, the sheet feeding operation of the sheet 12 is started by the sheet feeding roller 13 at a timing at which the distance between the preceding page and the next page is a predetermined distance (between sheets). An image will be formed.

A first embodiment according to the present invention will be described with reference to FIGS.
First, the operation during continuous printing will be described with reference to FIG. FIG. 9 is an explanatory diagram schematically illustrating a state in which print data is a plurality of pages, image formation on the preceding page is completed, and a paper edge detection (leading edge detection) operation is performed on the next page.
As shown in FIG. 9A, at the timing when the final scan image formation of the preceding page (preceding paper) 12a is completed, the next page (following paper) 12b is placed with a predetermined interval as described above. Is being transported.

  At this time, the carriage 3 moves to a predetermined sheet leading edge detection position (a predetermined position for detecting the leading edge of the sheet 3) in the direction of the arrow as shown in FIG. 9B in order to detect the leading edge of the next page 12b. However, in order to increase productivity (increase the printing speed), the sheet 12b is conveyed by the conveying belt 21 while the carriage 3 is moved to the predetermined sheet leading edge detection position. Therefore, depending on the transport speed, as shown in FIG. 5B, before the carriage 3 arrives at the paper leading edge detection position, the leading edge of the next page 12b passes under the carriage 3, and the carriage 3 Depending on the one-sheet sensor 81, the leading edge of the next page 12b may not be detected.

  Here, in this image forming apparatus, the sheet end (tip) detection position by the first sheet sensor 81 is a position 5 mm from the left end (left end in the sheet transport direction) of the smallest usable sheet. In this case, assuming that the interval between the sheets is 60 mm, the leading edge of the succeeding sheet 12b is the first after the last scanning of the preceding sheet 12b when the sheet conveyance speed is 240 mm / sec or less from the scanning speed of the carriage 3. The carriage 3 can move to the paper leading edge detection position before reaching the leading edge detection position by the one paper sensor 81.

  Therefore, in the printing process shown in FIG. 10, after the paper 12 is fed, it is determined whether or not the paper conveyance speed is 240 mm / sec or less. At this time, if the sheet conveyance speed is 240 mm / sec or less, the first sheet sensor 81 of the carriage 3 is set to detect the leading edge of the sheet, and the sheet conveyance speed exceeds 240 mm / sec. For example, the second paper sensor 82 on the upstream side of the first paper sensor 81 is used to detect the leading edge of the paper.

  Then, the conveyance belt 21 conveys the sheet, detects the leading edge of the sheet 12 conveyed using the set first sheet sensor 81 or the second sheet sensor 82, and further starts writing the image data (first scan position). ), The paper 12 is conveyed, and it is determined whether or not the timing for feeding the next paper 12 is reached. When the timing for feeding the next paper 12 is reached, feeding of the paper 12 for the next page is started. If the timing of feeding the next sheet 12 is not reached, a printing process for forming an image on the sheet 12 of the current page is performed, and the conveyance and printing of the sheet 12 are repeated until printing for the sheet 12 of the current page is completed.

  Then, it is checked whether it is the last page or not, and it is determined whether or not printing for all the pages is completed. Printing for each page is repeated until the last page is reached, and when the last page is reached, the last page is discharged and this page is discharged. The printing process ends.

  As described above, the first paper sensor or the second paper sensor detects (detects) the leading edge of the paper in accordance with the paper conveyance speed, so that when the plurality of pages are continuously printed, the gap between the papers becomes narrow and the first is detected. Even when the leading edge detection by the sheet sensor is not in time, the leading edge detection can be performed by the second sheet sensor, so that the printing speed can be improved and stable image formation can be performed while accurately detecting the leading edge of the sheet. .

Next, a second embodiment of the present invention will be described with reference to FIGS.
Here, whether to detect the paper end (front end) by the first paper sensor 81 or to detect the paper end (front end) by the second paper sensor 82 is selected according to the print mode. That is, in the present embodiment, the gap between the sheets is changed as shown in FIG. 12 according to the print mode (here, the sheet type). This is because the gap between plain papers for which higher speed printing is required is reduced (here, 40 mm), but on the other hand, reducing the gap between the papers increases the risk of double feeding and continuous feeding. This is because other paper types such as OHP have a space between the sheets (here, 60 mm).

  When the conveyance speed is constant, the time between the end of the preceding sheet passing the sheet leading edge detection position by the first sheet sensor 81 after the last scanning of the preceding sheet is completed when the sheet interval becomes short (decreases). Becomes shorter. For this reason, when the sheet interval is less than or equal to a predetermined value, the leading edge of the next page may pass under the carriage 3 before the carriage 3 arrives at the leading edge detection position.

  Therefore, in the printing process shown in FIG. 11, it is determined whether or not the printing mode is to print on a sheet having a sheet interval larger than 50 mm after feeding the sheet 12. At this time, if the paper gap is larger than 50 mm, the first paper sensor 81 of the carriage 3 is set to detect the leading edge of the paper. If the paper gap is 50 mm or less, the first paper sensor 81 is upstream. The second paper sensor 82 on the side is used to detect the leading edge of the paper.

  Then, the conveyance belt 21 conveys the sheet, detects the leading edge of the sheet 12 conveyed using the set first sheet sensor 81 or the second sheet sensor 82, and further starts writing the image data (first scan position). ), The paper 12 is conveyed, and it is determined whether or not the timing for feeding the next paper 12 is reached. When the timing for feeding the next paper 12 is reached, feeding of the paper 12 for the next page is started. If the timing of feeding the next sheet 12 is not reached, a printing process for forming an image on the sheet 12 of the current page is performed, and the conveyance and printing of the sheet 12 are repeated until printing for the sheet 12 of the current page is completed.

  Then, it is checked whether it is the last page or not, and it is determined whether or not printing for all the pages is completed. Printing for each page is repeated until the last page is reached, and when the last page is reached, the last page is discharged and this page is discharged. The printing process ends.

  As described above, when a plurality of pages are continuously printed by detecting (detecting) the leading edge of the sheet by the first sheet sensor or the second sheet sensor according to the interval between the sheets (according to the type of sheet to be printed). Even when the gap between the sheets is narrow and the leading edge detection by the first sheet sensor is not in time, the leading edge detection can be performed by the second sheet sensor. Image formation can be performed.

  Depending on the printing conditions, the paper interval may be smaller than the paper interval determined in the print mode due to paper feed. For this reason, it is also effective to measure the interval between sheets by the second sheet sensor or other separately provided detection means and switch the sheet sensor to be used using the measured data.

  In the present embodiment, the sheet interval is used as the print mode condition for switching between the first sheet sensor and the second sheet sensor as the detection means for detecting the leading edge of the sheet, but the type of sheet to be used, the sheet thickness, the resistance value, The first paper sensor 81 and the second paper 82 can be switched and used as a paper sensor for detecting the leading edge using conditions such as the presence / absence of printing / double-sided printing and paper size.

  In each of the above embodiments, the first paper sensor or the second paper sensor is used from the detection of the leading edge of the paper on the first page. However, the first paper sensor may be used only on the first page. it can.

Next, a third embodiment according to the present invention will be described with reference to FIGS.
Here, the first paper sensor 81 and the second paper sensor 82 are jointly used. That is, in the printing process shown in FIG. 13, first, the second paper sensor 82 detects the leading edge of the paper 12 fed by the paper feed roller 13 and conveyed by the conveyor belt 21. The timing at which the second paper sensor 82 detects the leading edge of the paper 12 (number of pulses) or the distance obtained from the number of pulses and the conveyance speed is stored in a predetermined area of the RAM 103.

  Next, at this stage, the CPU 101 that controls the entire system compares various data in the ROM 102, the RAM 103, and the nonvolatile memory 104 with the sheet detection timing stored in the RAM 103, and the leading end of the detected sheet 12 is moved to the carriage 3. It is determined whether or not detection can be performed by the first paper sensor 81 provided in the above. The various data referred to here are conveyance speed, image data, scanning speed of the carriage 3, paper interval, paper type, presence / absence of single-sided / double-sided printing, idle ejection timing, and the like.

  At this time, if the leading edge detection by the first sheet sensor 81 is not possible, that is, if the movement of the carriage 3 to the leading edge detection position is not in time, the conveyance speed of the paper 12 is reduced until the time is reached.

  Then, after setting the leading edge detection by the first sheet sensor 81, the sheet 12 is conveyed, and when the leading edge is detected by the first sheet sensor 81, the sheet is further up to the image data writing start position (first scan position). 12 is determined, and it is determined whether or not the timing for feeding the next sheet 12 is reached. When the timing for feeding the next sheet 12 is reached, feeding of the sheet 12 for the next page is started and the next sheet is fed. If the paper feed timing is not 12, print processing for forming an image on the paper 12 is performed, and then the second paper sensor 82 detects the leading edge of the next page.

  Thereafter, the conveyance and printing of the paper 12 are repeated until the printing on the paper 12 of the current page is completed. Next, it is checked whether or not printing has been completed for all pages by checking whether it is the last page, and printing for each page is repeated until the last page is reached. The printing process ends.

This process will be described with reference to FIGS. 14 and 15 are schematic views of the carriage 3 and the transport unit as viewed from above.
First, FIG. 14A shows an image formed up to the last end of the current page paper, and FIG. 15A shows that one scan is not performed up to the last edge of the current page paper. The image has been formed to the front. From here, the state in which the carriage 3 has moved to the paper leading edge detection position and the paper on the next page has been conveyed in order to detect the leading edge of the next page is shown in FIGS. 14B and 15B, respectively. It is.

  In this case, in FIG. 15B in which image formation is not performed up to the trailing edge of the sheet, the leading edge of the next page can be detected by the first sheet sensor 81 mounted on the carriage 3, whereas up to the trailing edge of the sheet. In FIG. 14B in which image formation is performed, the sheet on the next page has already passed, so the first sheet sensor 81 cannot detect the leading edge of the sheet. For this reason, in this embodiment, when image formation is performed up to the trailing edge of the sheet as shown in FIG. 14A, the carriage 3 is moved in time to the sheet leading edge detection position when the next page is conveyed. In addition, the conveyance speed of the paper 3 is reduced. Thus, after the carriage 3 is moved to the paper leading edge detection position, the leading edge of the paper on the next page can be detected.

Next, a fourth embodiment according to the present invention will be described with reference to FIG.
Again, the first paper sensor 81 and the second paper sensor 82 are used jointly. That is, as in the third embodiment, the second paper sensor 82 detects the leading edge of the paper 12 fed by the paper feed roller 13 and transported by the transport belt 21. Then, the timing (number of pulses) at which the second sheet sensor 82 detects the sheet 12 or the distance obtained from the number of pulses and the conveyance speed is stored in a predetermined area of the RAM 103.

  Next, at this stage, the CPU 101 that controls the entire system compares various data in the ROM 102, the RAM 103, and the nonvolatile memory 104 with the paper detection timing stored in the RAM 103, and detects the paper detected by the second paper sensor 82. It is determined whether or not the tip of 12 can be detected by the first paper sensor 81 provided in the carriage 3.

  At this time, if the first paper sensor 81 can detect the leading edge of the paper, the first paper sensor 81 is set to be used for detecting the leading edge of the paper. If the first paper sensor 81 cannot detect the leading edge of the paper, Processing is performed using the detection result (data) of the second paper sensor 82 as the leading edge of the paper. Since the subsequent processing is the same as that of the third embodiment, description thereof is omitted.

Next, a fifth embodiment according to the present invention will be described with reference to FIGS.
As described above, the paper leading edge detection position by the first paper sensor 81 and the paper leading edge detection position by the second paper sensor 82 are different in the main scanning direction (paper width direction). , 82 is detected based on the detection result, and the ASIC 105 performs image data rotation processing or the like at the time of image formation in accordance with the detected skew amount, thereby making it possible to correct the skew. Become.

  17 will be described. First, the paper 12 is fed and transported, the leading end of the sheet is detected by the second sheet sensor 82, and the leading end of the sheet is further detected by the first sheet sensor 81. Then, the skew amount is calculated based on the detection results of the second and first paper sensors 82 and 81, and after performing correction such as image rotation processing based on the calculated skew amount, the print processing and the discharge processing are performed. Do.

  For example, as shown in FIG. 18, when the paper detection positions by the first paper sensor 81 and the second paper sensor 82 are defined, the positions (or the number of pulses) of the first paper sensor 81 and the second paper sensor 82 in the paper conveyance direction. Since the distance Xc is a known value, the first paper sensor 81 is earlier than the normal timing (the timing when there is no skew) when the paper is tilted to the right, and the paper is tilted to the left. When it is, the paper is detected later than the normal timing.

That is, the skew amount per unit distance of the paper is Yc when the distance in the paper conveyance direction of the first and second paper sensors 81 and 82 is Yc.
Skew amount = {paper front edge position detected by first paper sensor 81− (paper front edge position detected by second paper sensor 82 + Yc)} / Xc
Is required. Thereby, the skew amount of the paper can be calculated from the paper position detected by the first paper sensor 81 and the paper position detected by the second paper sensor 82.

  Here, the skew amount is detected and calculated using the distance, but the same result can be obtained by using the timing (number of pulses of the encoder) for the position of both sensors and the distance of paper detection.

  Further, as the distance in the width direction between the paper detection position by the first paper sensor 81 and the paper detection position by the second paper sensor 82 increases, the skew amount of the paper can be obtained more accurately. Therefore, if the sheet detection position in the width direction by the first sheet sensor 81 is changed for each sheet size specified by the printer driver, for example, the sheet is detected at a position 5 mm from the end of the sheet, more accurately. The skew amount of the paper can be measured.

  Further, when the skew amount is equal to or larger than a predetermined value, a warning may be simply displayed (through the display means of the operation panel or the printer driver on the host side) together with the image rotation process or instead of the image rotation process. Alternatively, it is also possible to forcibly eject a sheet having a large skew and refeed the next sheet for printing.

Next, registration adjustment using the first paper sensor 81 and the second paper sensor 82 will be described with reference to FIGS.
The registration adjustment process shown in FIG. 19 is started at the time of shipment or in response to a user instruction. First, as shown in FIG. 20, the carriage 3 is moved so that the first paper sensor 81 is orthogonal to the transport direction of the second paper sensor 82. Align so that it is the same position in the direction of As described above, the first paper sensor 81 and the second paper sensor 82 are aligned, so that even if the paper is skewed, the skew can be ignored, and more accurate registration adjustment can be performed. It can be carried out.

  Next, the paper 12 is fed, and the paper 12 is transported by the transport belt 21. Then, the number of pulses is counted from the rotary encoder 36 from the time when the second paper sensor 82 detects the leading edge of the paper 12 to the time when the first paper sensor 81 detects the leading edge of the paper 12, and the number of pulses (or the number of pulses) is counted. The distance X between the second paper sensor 82 and the first paper sensor 81 shown in FIG. 21 is stored in a predetermined area of the RAM 103.

  Thereafter, the paper 12 is transported based on the leading edge detection result of the first paper sensor 81, and the first nozzle 7n1 (referred to as the nozzle on the most downstream side in the transport direction) of the recording head 7 is used as shown in FIG. Print the adjustment chart and eject it.

  Then, the adjustment value input from the operation panel 117 or the like is captured by visually checking the adjustment chart printed by the user, and the distance N1 between the first paper sensor 81 and the first nozzle 7n1 is corrected. Further, the distance N2 between the second paper sensor 82 and the first nozzle 7n1 is corrected using the corrected distance N1.

  For example, as shown in FIG. 22, a pattern P1 is printed on a paper 12 of a predetermined size at a position where the paper 12 is conveyed by a predetermined distance (theoretical value N1a + a1 of the distance N1) after detecting the leading edge by the first paper sensor 81. Further, when the pattern P2 is printed by transporting the sheet 12 by a predetermined feed amount such that the distance a2 is equal to the distance a1 from the rear end of the sheet 12, the patterns P1 and P2 are theoretically printed on the sheet. It will overlap when folded in half.

  However, the distance a1 and the distance a2 are not the same due to variations in the mounting position of the first paper sensor 81, and if the first paper sensor 81 is shifted upstream in the paper transport direction, the distance a1 is shortened and the paper transport is performed. If it is shifted to the downstream side in the direction, the distance a1 becomes longer. Therefore, the user or the like visually confirms the amount of deviation, and inputs an adjustment value (with positive or negative) from the operation panel 117, so that, as described above, between the first paper sensor 81 and the first nozzle 7n1. The distance is corrected, and the distance N2 from the second paper sensor 82 to the first nozzle 7n1 is calculated using the corrected distance N1 and the measured distance X between the first paper sensor 81 and the second paper sensor 82. Correct.

  Thus, by providing a means for storing the distance (X) between the first detection means and the second detection means, the alignment between one detection means and the nozzles of the recording head is corrected, and the correction result is obtained. By using this, it is possible to correct the alignment between the other detection means and the nozzles of the recording head, which facilitates resist adjustment.

  In the case of using a transport unit that transports a sheet on the peripheral surface corresponding to the transport roller as in this image forming apparatus, the distance (diameter) between the rotation center of the transport roller and the sheet surface varies depending on the thickness of the sheet. Therefore, the movement amount of the sheet surface slightly changes with respect to the rotation amount of the same conveying roller.

  Therefore, a means for storing a plurality of distances between the first detection means and the second detection means is provided (for example, by assigning a plurality of addresses to the address of the non-volatile memory 104), and the type of paper, for example, the type of plain paper or thick paper Accordingly, the distance between the first detection means and the second detection means is stored separately, and registration adjustment is also performed according to the paper type, and the paper type to be used (for example, input from the operation panel 117 or The image is formed using a correction value (registration value) according to the printer driver on the host side), so that registration with higher accuracy can be performed.

1 is an explanatory side view illustrating an overall configuration of a mechanism unit of an image forming apparatus according to the present invention. It is a plane explanatory view of the mechanism part. It is typical explanatory drawing explaining an example of the conveyance belt of the apparatus. It is typical explanatory drawing explaining the other example of the conveyance belt of the apparatus. It is a block explanatory drawing explaining the outline | summary of the control part in the apparatus. It is explanatory drawing of the part in connection with the charge control with which it uses for description of printing operation in the same apparatus. It is explanatory drawing with which it uses for description when the conveyance belt is charged. FIG. 6 is an explanatory diagram for explaining when a sheet comes into contact with the conveyance belt. It is explanatory drawing with which it uses for description of the paper front-end | tip detection operation | movement in 1st Embodiment which concerns on this invention. It is a flowchart with which it uses for description of the printing process of the embodiment. It is a flowchart with which it uses for description of the printing process of 2nd Embodiment which concerns on this invention. It is explanatory drawing explaining an example of the paper gap setting used for description of the embodiment. It is a flowchart with which it uses for description of the printing process of 3rd Embodiment which concerns on this invention. It is explanatory drawing with which description of the embodiment is provided. FIG. 15 is also an explanatory diagram for explaining an example in which the final image forming position is different from that in FIG. 14. It is a flowchart with which it uses for description of the printing process of 4th Embodiment which concerns on this invention. FIG. 6 is a flowchart for explaining skew correction processing in the image forming apparatus. It is explanatory drawing with which it uses for description of a skew correction process similarly. 3 is a flowchart for explaining registration adjustment in the image forming apparatus. FIG. It is explanatory drawing similarly used for description of a resist adjustment. It is explanatory drawing regarding the distance similarly provided for description of a resist adjustment. It is explanatory drawing with which it uses for description of the chart for adjustment similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 3 ... Carriage 7 ... Recording head 21 ... Conveyance belt 81 ... 1st paper sensor 82 ... 2nd paper sensor

Claims (12)

In an image forming apparatus in which a recording head is mounted on a carriage and a recording medium is conveyed in a direction perpendicular to the scanning direction of the carriage to form an image on the recording medium.
First detection means for detecting the recording medium mounted on the carriage, and second detection means for detecting the recording medium disposed upstream of the first detection means in the recording medium conveyance direction. An image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the leading end of the recording medium is detected by one of the first detection unit and the second detection unit in accordance with a conveyance speed of the recording medium. Forming equipment.   The image forming apparatus according to claim 1, wherein the leading end of the recording medium is detected by one of the first detection unit and the second detection unit according to a printing mode.   2. The image forming apparatus according to claim 1, wherein the recording medium reaches a detection position by the first detection means before the first detection means reaches a predetermined detection position for detecting a leading edge of the recording medium. An image forming apparatus characterized in that when the detection is made based on the detection result of the second detection means, the conveyance speed of the recording medium is reduced.   2. The image forming apparatus according to claim 1, wherein the recording medium reaches a detection position by the first detection means before the first detection means reaches a predetermined detection position for detecting a leading edge of the recording medium. An image forming apparatus comprising: detecting the leading edge of the recording medium using the second detection unit when the detection is performed based on a detection result of the second detection unit.   2. The image forming apparatus according to claim 1, wherein a recording medium detection position by the first detection unit and a recording medium detection position by the second detection unit are different in a scanning direction of the carriage. .   7. The image forming apparatus according to claim 6, wherein a skew amount of the recording medium is detected based on detection results of the first detection unit and the second detection unit.   8. The image forming apparatus according to claim 7, wherein the image data to be formed on the recording medium is rotated based on a detection result of the skew amount of the recording medium.   8. The image forming apparatus according to claim 7, wherein the recording medium is discharged after being discharged based on a detection result of a skew amount of the recording medium.   8. The image forming apparatus according to claim 7, wherein an error display is performed based on a detection result of a skew amount of the recording medium.   11. The image forming apparatus according to claim 1, wherein the second detection unit is arranged at a position facing a conveyance roller for conveying the recording medium toward a recording area by the recording head. An image forming apparatus. 12. The image forming apparatus according to claim 11, wherein the conveyance roller is a roller for driving a conveyance belt that adsorbs and conveys the recording medium with electrostatic force.

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