JP2007062238A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an image may be disturbed or a recording medium may be contaminated by contact of a recording head to a printed face when a recording medium having an image on its front face is flipped, and then the printing is carried out on the rear face. <P>SOLUTION: After an image is formed on a front face of a paper sheet 22, a carriage 31 is moved to move a recording head 11 to shelter it to an operation start position (a next printing operation start position) for performing the printing on the rear face of the paper sheet 22. When the sheltering of the recording head 11 is completed, a conveyance belt 31 is moved in the reverse direction to convey the paper sheet 22 in the direction opposite to that in the printing operation to input it in a perfecting unit 51 to make it to be flipped. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that includes a recording head that discharges droplets of recording liquid and is capable of duplex printing.

  As a variety of image forming apparatuses such as printers, facsimiles, copying apparatuses, plotters, printer / fax / copier multifunction machines, etc., a recording head composed of a liquid discharging head for discharging recording liquid droplets is mounted on the carriage. Are serially scanned in a direction orthogonal to the transport direction of the recording medium (also referred to as paper, recording medium, recording paper, etc.), and the recording medium is intermittently transported according to the recording width, and transported. And a serial type that forms an image on a recording medium by alternately repeating recording and recording (recording, printing, printing, and printing are also used synonymously).

In such an image forming apparatus, as described in Patent Document 1, for example, as described in Japanese Patent Application Laid-Open No. 2004-133867, double-sided printing (double-sided recording) for performing printing on both sides of a recording medium is performed. A sheet material reversing unit, and after the recording unit records on the first surface of the recording sheet material, the sheet material conveying unit conveys the recording sheet material to the sheet material reversing unit, and the sheet material reversing unit Double-sided recording can be performed in which the recording sheet material is reversed, the reversed recording sheet material is conveyed again by the sheet material conveyance unit to the recording unit, and recording is performed on the second surface of the recording sheet material. Things are known.
Japanese Patent Laying-Open No. 2005-074746

Further, as described in Patent Document 2, as an image forming apparatus that can perform double-sided printing and includes a detection unit that detects a conveyed sheet, the sheet is detected on a member on which a recording head is mounted. There is a detecting means for detecting the sheet on the upstream side in the sheet conveying direction from the recording start position by the recording head.
JP 2004-237893 A

  By the way, in an image forming apparatus capable of double-sided printing, recording is finished on the front side surface (first surface) of the recording medium, and the recording medium is placed in a direction opposite to the conveying direction at the time of printing. It is necessary to transport to a recording medium reversing unit (also referred to as a duplex unit). For this reason, the recording medium having the ink attached passes under the recording head. At this time, cockling, warpage, or the like occurs on the recording medium due to the influence of ink or the like. When the recording medium is transported in the reverse direction in this state, there is a problem that an image formed on the recording medium is disturbed or smeared due to contact between the recording medium and the recording head.

  In this case, as described in Patent Document 1, it is possible to prevent the contact between the recording head and the recording medium by widening the interval between the recording head and the recording medium when the recording medium is conveyed in the reverse direction. However, since the recording head is not at the next recording start position, extra time is required at the start of printing, which causes a new problem of reducing the throughput.

  Further, in the apparatus described in Patent Document 2, even if the recording head is retracted and the recording medium is reversed, the medium attached to the recording head side in order to specify the printing start position of the recording medium Since the detection sensor detects the leading edge position of the recording medium, it is necessary to move the recording head again on the recording medium conveyance path, and the time required for reversing the recording medium becomes long and it takes time to print on both sides. There is.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an image forming apparatus with improved double-sided printing.

  In order to solve the above problems, the image forming apparatus according to the present invention moves the recording head to an operation start position for recording on the back side of the recording medium after recording on the recording medium surface is completed. It was set as the structure provided with the means to make.

  Here, the recording medium is transported in the same direction as during recording to a predetermined position after the recording on the surface is finished, and the movement of the recording head to the operation start position is started. It is preferable that all or part of the movement operation of the recording head to the operation start position is performed in parallel.

  Further, it is preferable that the recording head is moved to the operation start position when conveyance of the recording medium is stopped for a predetermined time after the recording on the surface is completed.

  The image forming apparatus according to the present invention includes means for moving the recording head to an operation start position for recording on the back side of the recording medium after the recording on the recording medium surface is completed. Therefore, after the reversal of the recording medium is completed, the time required to start printing on the back side of the recording medium can be reduced, the printing speed of double-sided printing is improved, and the throughput is improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an example of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a side view for explaining the overall configuration of the image forming apparatus, and FIG. 2 is a schematic plan view for explaining the same.

  In this image forming apparatus, a carriage 4 is slidably held in a main scanning direction by a guide rod 2 and a stay 3 which are guide members horizontally mounted on left and right side plates 1A and 1B constituting a frame 1, and a main scanning motor. 5 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG. 2 via the timing belt 7 spanned between the driving pulley 6A and the driven pulley 6B.

  The carriage 4 includes, for example, a recording head 11 composed of four droplet ejection heads that eject ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). The nozzle rows on the nozzle surface 11a on which the ejection ports (nozzles) are formed are arranged in a direction (sub-scanning direction) orthogonal to the main scanning direction, and the ink ejection direction is directed downward. Although an independent droplet discharge head is used here, a configuration in which one or a plurality of heads having a plurality of nozzle rows that discharge droplets of recording liquid of each color can be used. Further, the number of colors and the arrangement order are not limited to this.

  As an inkjet head constituting the recording head 11, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. It is possible to use a shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like provided as pressure generating means for generating a pressure for discharging a droplet.

  A driver IC is mounted on the recording head 11 and connected to a control unit (not shown) via a harness (flexible print cable) 12.

  In addition, the carriage 4 is equipped with a sub tank 15 for each color for supplying ink of each color to the recording head 11. Each color sub-tank 15 is supplementarily supplied with ink of each color from the ink cartridge 10 of each color mounted in the cartridge loading unit 9 via the ink supply tube 16 of each color. The cartridge loading section 9 is provided with a supply pump unit 17 for feeding the ink in the ink cartridge 10, and the ink supply tube 16 is attached to the rear plate 1C constituting the frame 1 in the middle of turning. It is held by the locking member 18.

  On the other hand, as a paper feed unit for feeding the paper 22 stacked on the paper stacking unit (pressure plate) 21 of the paper feed tray 20, a half-moon roller (feed) that separates and feeds the paper 22 one by one from the paper stacking unit 21. A separation pad 24 made of a material having a large friction coefficient is provided opposite to the sheet roller 23 and the sheet feeding roller 23, and the separation pad 24 is biased toward the sheet feeding roller 23 side.

  In order to feed the paper 22 fed from the paper feeding unit to the lower side of the recording head 11, a guide member 25 for guiding the paper 22, a counter roller 26, a conveyance guide member 27, and a tip pressure roller. And a holding belt 28 as a conveying means for electrostatically attracting the fed paper 22 and conveying it at a position facing the recording head 11.

  The conveyance belt 31 is an endless belt, is configured to wrap around the conveyance roller 32 and the tension roller 33 and circulate in the belt conveyance direction (sub-scanning direction). 34 is charged (charged).

  The transport belt 31 may be a single-layer belt or a multi-layer (two or more layers) belt. In the case of the conveyance belt 31 having a one-layer structure, the entire layer is formed of an insulating material because it contacts the paper 32 and the charging row 34. In the case of the transport belt 31 having a multi-layer structure, the side that contacts the paper 22 and the charging roller 34 is preferably formed of an insulating layer, and the side that does not contact the paper 22 and the charging roller 34 is preferably formed of a conductive layer. .

As an insulating material for forming the transport belt 31 having a single-layer structure or an insulating material for forming the insulating layer of the transport belt 31 having a multi-layer structure, for example, a conductive material such as PET, PEI, PVDF, PC, ETFE, or PTFE is used. It is preferable that the material does not contain a control material, and the volume resistivity is 10 ¹² Ωcm or more, preferably 10 ¹⁵ Ωcm. Further, as a material for forming the conductive layer of the transport belt 31 having a multi-layer structure, it is preferable that carbon is contained in the resin or elastomer so that the volume resistivity is 10 ⁵ to 10 ⁷ Ωcm.

The charging roller 34 is disposed so as to come into contact with an insulating layer (in the case of a multilayer belt) that forms the surface layer of the transport belt 31 and to rotate following the rotation of the transport belt 31. It is over. The charging roller 34 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 (high voltage) is applied to the charging roller 34 from an AC bias supply unit (high voltage power supply). The AC bias may be a sine wave or a triangular wave, but a square wave is more preferable.

  In addition, a guide member 35 is disposed on the back side of the conveyance belt 31 so as to correspond to a printing area by the recording head 11. The guide member 35 has an upper surface that protrudes toward the recording head 11 from the tangent line of the two rollers (the conveyance roller 32 and the tension roller 33) that support the conveyance belt 31, thereby maintaining high-precision flatness of the conveyance belt 31. Like to do.

  The transport belt 31 rotates in the belt transport direction of FIG. 2 when the transport roller 32 is rotationally driven by the sub-scanning motor 36 via the drive belt 37 and the timing roller 38. Although not shown, an encoder wheel having a slit is attached to the shaft of the conveying roller 32, and a transmission type photosensor for detecting the slit of the encoder wheel is provided, and the wheel encoder is configured by the encoder wheel and the photosensor. It is composed.

  Further, as a paper discharge unit for discharging the paper 22 recorded by the recording head 11 to the paper discharge tray 40, a separation claw 41 for separating the paper 22 from the transport belt 31, a paper discharge roller 42, and paper discharge The roller 43 is provided.

  In addition, a double-sided unit 51, which is a means for inverting the paper 22 when performing double-sided printing, is detachably mounted on the back surface of the apparatus main body 1. The duplex unit 51 takes in the paper 22 returned by the reverse rotation of the transport belt 31, reverses it, and feeds it again between the counter roller 26 and the transport belt 31. The upper surface of the duplex unit 51 is a manual feed tray 52.

  Further, a maintenance / recovery mechanism 61 for maintaining and recovering the state of the nozzles of the recording head 11 is disposed in a non-printing area on one side in the scanning direction of the carriage 4. The maintenance / recovery mechanism 61 includes cap members (hereinafter referred to as “caps”) 62 a to 62 d (hereinafter referred to as “caps 62” when not distinguished) and nozzles for capping the nozzle surfaces 11 a of the recording head 11. A wiper blade 63 that is a blade member for wiping the surface 11a, an empty discharge receiver 64 that receives liquid droplets when performing an empty discharge for discharging liquid droplets that do not contribute to recording in order to discharge the thickened recording liquid, and the like It has. Here, the cap 62a is a suction and moisture retention cap, and the other caps 62b to 62d are moisture retention caps.

  Further, in the non-printing area on the other side of the scanning direction of the carriage 4, there is an empty space for receiving a liquid droplet when performing an empty discharge for discharging a liquid droplet that does not contribute to recording in order to discharge the recording liquid thickened during recording or the like. A discharge receiver 68 is disposed, and the idle discharge receiver 68 is provided with an opening 69 along the nozzle row direction of the recording head 11.

  As shown in FIG. 1, an encoder scale 72 having slits is provided along the main scanning direction on the front side of the carriage 4, and a transmission type that detects the slits of the encoder scale 72 on the front side of the carriage 4. An encoder sensor 73 composed of a photosensor is provided, and these constitute a linear encoder 74 for detecting the position of the carriage 4 in the main scanning direction.

  Further, a sheet sensor 75 for detecting the presence or absence of the sheet 22 conveyed by the conveying belt 31 is provided on the side surface portion of the carriage 4 on the print area side. In addition, a paper leading edge detection sensor 76 serving as a detecting means for detecting the leading edge of the paper 22 conveyed by the conveying belt 31 is provided at a position upstream of the recording head 11 in the paper conveying direction. The sheet leading edge detection sensor 76 is fixedly provided on the apparatus main body side.

  In the image forming apparatus configured as described above, the paper 22 is separated and fed one by one from the paper feeding unit, and the paper 22 fed substantially vertically upward is guided by the guide 25, and the conveyance belt 31 and the counter roller 26. The leading end is guided by the conveying guide 27 and pressed against the conveying belt 31 by the leading end pressure roller 29, and the conveying direction is changed by approximately 90 °.

  At this time, a positive output and a negative output are alternately and repeatedly applied to the charging roller 34 from an AC bias supply unit, which will be described later, that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 31 alternates, that is, a loop In the sub-scanning direction, which is the direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 32 is fed onto the conveying belt 31 that is alternately charged with plus and minus, the paper 22 is attracted to the conveying belt 31 by electrostatic force, and the paper 22 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 31. Is done.

  Therefore, by driving the recording head 11 according to the image signal while moving the carriage 4, ink droplets are ejected onto the stopped paper 22 to record one line, and after the paper 22 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 22 has reached the recording area, the recording operation is finished and the paper 22 is discharged onto the paper discharge tray 40.

  In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 32 is fed into the double-sided paper feeding unit 51 by rotating the conveyor belt 31 in reverse. The paper 22 is reversed (with the back surface being the printing surface), fed again between the counter roller 26 and the conveyor belt 31, controlled in timing, and conveyed by the conveyor bell 31 as described above. After recording on the back surface, the paper is discharged onto the paper discharge tray 40.

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 controls the entire apparatus, and includes a CPU 101 that also serves as a unit that controls the conveyance operation of the paper 22 and the movement operation of the recording head 11 during duplex printing according to the present invention, and a program executed by the CPU 101 ROM 102 for storing other fixed data, RAM 103 for temporarily storing image data and the like, rewritable nonvolatile memory 104 for retaining data even while the apparatus is powered off, and various kinds of image data An ASIC 105 that processes image processing for signal processing, rearrangement, and other input / output signals for controlling the entire apparatus is provided.

  Further, the control unit 100 generates an I / F 106 for transmitting and receiving data and signals to and from the host side, and a drive waveform for driving the recording head 11, and selects a pressure generating means for the recording head 11. A head control unit 107 that outputs image data to be driven and various data associated therewith to the head driver 108, a main scanning motor driving unit 110 for driving the main scanning motor 5, and sub-scanning for driving the sub-scanning motor 36. Motor drive unit 111, AC bias supply unit 112 for supplying AC bias to charging roller 34, detection pulse from linear encoder 74 and wheel encoder 136, detection signal from paper sensor 75, detection from paper leading edge detection sensor 76 I / O 113 for inputting signals and detection signals from various other sensors That. The control unit 100 is connected to an operation panel 114 for inputting and displaying information necessary for the apparatus.

  Here, the control unit 100 transmits print data generated by the printer driver 201 of the host 200 such as an information 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.

  Then, the CPU 101 of the control unit 100 reads and analyzes the print data in the reception buffer included in the I / F 106, performs necessary image processing, data rearrangement processing, and the like in the ASIC 105 and transfers them to the head control unit 107. Then, image data and drive waveforms are output from the head controller 107 to the head driver 108 at a required timing. The generation of dot pattern data for outputting an image may be performed by storing font data in the ROM 102, for example, or the image data is developed into bitmap data by the printer driver 201 on the host 200 side. You may make it forward. In this case, the printer driver 201 is used.

  The drive waveform generation unit of the head control unit 107 includes a D / A converter and an amplifier that perform D / A conversion on the drive pulse pattern data stored in the ROM 102 and read by the CPU 101, and includes one drive pulse or a plurality of drive pulses. A drive waveform composed of drive pulses is output to the head driver 108.

  The head driver 108 generates drive pulses constituting a drive waveform provided from the drive waveform generation unit of the head control unit 107 based on image data (dot pattern data) corresponding to one row of the recording head 11 input serially. The recording head 11 is driven by selectively applying to the pressure generating means of the recording head 11. The head driver 108 shifts the level of the output value of the shift register that receives, for example, a shift register that receives clock data and serial data that is image data, a latch circuit that latches the register value of the shift register using a latch signal, and the like. A level conversion circuit (level shifter) and an analog switch array (switch means) whose on / off is controlled by this level shifter, etc., and the required drive pulse included in the drive waveform by controlling the on / off of the analog switch array Is selectively applied to the pressure generating means of the recording head 11.

  The main scanning motor driving unit 110 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 linear encoder 74, and performs main scanning via an internal motor driver. The motor 5 is driven.

  Similarly, the sub-scanning motor drive control 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 wheel encoder 136 to calculate an internal motor driver. And the sub-scanning motor 36 is driven.

Next, a first embodiment of the present invention in this image forming apparatus will be described with reference to the flowchart of FIG.
When a printing command is received from the host 200 side, the paper 22 is fed, and after the feeding is finished, the recording droplets are ejected from the recording head 11 while performing the main scanning of the carriage 4, and one line is formed on the front side of the paper 22. Recording is performed (printing), and when the printing for one line is completed, the conveying belt 31 is moved to feed the sheet 22 by one line, and this operation is completed until the image formation on the front side of the sheet 22 is completed. Repeat.

  Then, after the image formation (front surface printing) on the front side of the paper 22 is completed, the carriage 31 is moved to move the recording head 11 to the operation start position (next printing operation start position) for printing on the back side of the paper 22. Evacuate to).

  When the retreat of the recording head 11 is completed, the transport belt 31 is moved in the reverse direction, so that the paper 22 is transported in the reverse direction to that during the printing operation and transported into the duplex unit 51. As the sheet 22 passes through the duplex unit 51, the recording surface is reversed from the front side to the back side.

  As a result, the sheet 22 is sent again between the counter roller 26 and the conveying roller 32 with the back side as the printing surface. At this timing, the conveying roller 32 rotates again in the direction of the printing operation, and is conveyed by the conveying belt 31. The paper 22 is conveyed for back side printing.

  Then, the leading edge of the paper 22 is detected by the paper leading edge detection sensor 76. Thereby, the print start position in the paper transport direction can be specified. After detecting the leading edge of the paper, the paper 22 is conveyed to a predetermined printing start position. Similarly to the above, the printing operation for one line by main scanning and the intermittent feeding of the paper 22 are repeated to form an image on the back side of the paper 22, and the paper 22 is discharged after the image formation is completed. .

  As described above, by providing a sheet detection unit (detection unit such as the above-mentioned sheet leading edge detection sensor 76) for detecting the sheet on the apparatus main body side, after the printing on the front side of the sheet is finished, By retreating the recording head to the next printing start position (printing start position on the back side), it is possible to start the printing operation on the back side of the paper after the paper reversal is completed, thereby improving the printing speed. Can do.

Next, a second embodiment of the present invention will be described with reference to the flowchart of FIG.
In this embodiment, after the printing on the front side of the paper 22 is completed, the paper 22 is transported in the same direction as when printing a predetermined amount (predetermined amount), and recording is performed in parallel with the transport operation of the paper 22. The head 11 is moved to the next printing start position (printing start position on the back side).

  That is, when the actual image forming area on the front surface side of the sheet 22 is small, a portion that becomes a non-recording area occurs until the end (rear end) of the sheet 22. At this time, if the end of the paper 22 does not reach the paper feed port of the duplex unit 51, the paper 22 cannot be fed into the duplex unit 51 and reversed. Therefore, the paper 22 is conveyed in the same direction as in the printing operation to a position where the paper 22 can be fed into the duplex unit 51.

  When the paper 22 is transported in the same direction as the printing operation in order to allow the paper 22 to be fed into the duplex unit 51, printing on the front side of the paper 22 has been completed. The recording head 11 is retracted to the next printing operation start position. That is, all or part of the retreating movement operation of the recording head and the conveyance operation of the paper 22 are performed in parallel.

  As described above, by performing part or all of the operation of moving the recording head to the retracted position and the paper transporting operation in the printing direction at the same time, it becomes possible to reduce the time delay due to the head retracting operation, and printing. Speed can be improved.

Next, a third embodiment of the present invention will be described with reference to the flowchart of FIG.
In this embodiment, after the printing on the front side of the paper 22 is finished, the conveyance of the paper 22 is stopped, and the recording head 11 is moved to the next printing start position (printing on the back side in parallel with the conveyance stop operation of the paper 22). The operation of retracting to the start position is performed.

  That is, depending on the type of paper 22, it may take time to dry the ink after image formation. In this case, if the paper 22 is sent to the duplex unit 51 in a state where the ink is not dried, the image formed on the front side of the paper 22 is disturbed or the paper 22 is soiled. Therefore, after the printing on the front side of the sheet 22 is finished, the conveyance of the sheet 22 is stopped for a predetermined time before the reverse conveyance of the sheet 22 is started, so that the ink attached to the sheet 22 is dried. At this time, since the printing of the recording head 11 has been completed, the recording head 11 is retracted to the next printing start position simultaneously with the stop of the sheet conveyance or while the conveyance of the sheet is stopped.

  As described above, by moving the recording head while the conveyance of the paper is stopped, a time delay due to the head retracting operation can be reduced, and the printing speed can be improved.

1 is an explanatory side view illustrating an overall configuration of an example of an image forming apparatus according to the present invention. It is a schematic plane explanatory drawing similarly. FIG. 2 is a block explanatory diagram illustrating an overview of a control unit in the image forming apparatus. FIG. 2 is a flowchart for explaining the first embodiment of the present invention in the image forming apparatus. It is a flowchart with which it uses for description of 2nd Embodiment of this invention in the image forming apparatus. It is a flowchart with which it uses for description of 3rd Embodiment of this invention in the image forming apparatus.

Explanation of symbols

4 ... Carriage 5 ... Main scanning motor 11 ... Recording head 20 ... Paper feed tray 22 ... Recording medium (paper)
DESCRIPTION OF SYMBOLS 31 ... Conveyance belt 32 ... Conveyance roller 36 ... Sub-scanning motor 51 ... Duplex unit 76 ... Paper front-end | tip detection sensor (detection means)

Claims (3)

  After transporting the recording medium, a recording liquid droplet is ejected from the recording head to form an image on the front surface side of the recording medium, and then the recording medium is transported in the reverse direction to be reversed to the back side. In the image forming apparatus that performs double-sided printing by transporting the recording medium again for recording, the recording head records on the back side of the recording medium after the recording on the recording medium surface is completed. An image forming apparatus comprising means for moving to an operation start position for   The image forming apparatus according to claim 1, wherein the recording medium is transported in the same direction as during recording to a predetermined position after the recording on the surface is completed, and the movement of the recording head to the operation start position is started. An image forming apparatus, wherein the recording medium conveying operation and the recording head moving operation to the operation start position are all or partly performed in parallel. 2. The image forming apparatus according to claim 1, wherein the recording head is moved to the operation start position when conveyance of the recording medium is stopped for a predetermined time after completion of recording on the surface. Forming equipment.

Images