JP4819456B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that conveys a recording medium by a conveying belt.

  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 referred to as a recording medium (hereinafter referred to as “paper”, but the material is not limited to paper, and is also referred to as recording medium, recording paper, recording paper, transfer material, etc.) )) Is serially scanned in a direction orthogonal to the conveyance direction, and the recording medium is intermittently conveyed according to the recording width, and an image is formed (recorded) by alternately repeating conveyance and recording. Printing, printing, and printing are also used interchangeably.) A serial type image forming apparatus or a line type recording head equipped with a line type recording head to form an image while feeding paper. There is emission type image forming apparatus.

In such an ink jet recording type image forming apparatus, it is necessary to increase the landing position accuracy of the ink droplets on the paper in order to improve the image quality. For example, the transport belt that transports the paper is positively charged, By adsorbing the paper with an electrostatic force, the distance between the recording head and the paper is kept constant, and the paper feed is accurately controlled to prevent paper misalignment and to prevent paper lift. There are known ones that prevent jamming and smearing due to the contact between the paper and the recording head.
JP-A-4-201469 JP-A-9-254460

  As described above, when the paper is transported by uniformly and positively charging the transport belt and attracting the paper with an electrostatic force, the droplets ejected from the recording head are affected by the generated electric field and the flight direction thereof is affected. The image formation position shifts due to bending, etc., and the mist of the ejected droplets flows backward and adheres to the vicinity of the ejection part of the recording head, resulting in ejection failure and reducing the quality of the formed image. There is a problem of inviting.

Therefore, Patent Document 3 describes that an electrode having the same polarity as that of the recording paper is provided on the print head so that the mist that is scattered does not contaminate the head surface.
Japanese Patent No. 3224528

Patent Document 4 describes that the surface potential of the recording paper is measured and the voltage applied on the belt is controlled in order to minimize the influence of the electric field on the print head.
Japanese Patent No. 3014815

In addition, as described in Patent Document 5, as a charging method for the conveyor belt, an adsorbing force is generated between the recording medium and the conveyor belt by applying positive and negative AC charges on the conveyor belt. It has been known.
JP 2003-103857 A

In addition, as described in Patent Document 4, as a charging method for the conveyor belt, an adsorption force is generated between the recording medium and the conveyor belt by applying positive and negative AC charges on the conveyor belt. It has been known.
JP 2003-103857 A

In addition, the one described in Patent Document 5 uses a conveyor belt in the electrophotographic method, and the one described in Patent Document 6 relates to the height position adjustment of the carriage related to this case.
Japanese Patent No. 2905544 Japanese Patent Application Laid-Open No. 8-118761

  However, as described in Patent Document 3, a configuration in which an electrode having the same polarity as the recording paper is provided on the print head can be used when the print head uses thermal energy such as a thermal head. However, in the case of a recording head that involves capacitance such as a piezoelectric head or an electrostatic head that uses a piezoelectric actuator or an electrostatic actuator as a pressure generating means, the behavior of the actuator becomes unstable. Therefore, there is a problem that it cannot be used. Further, it is necessary to perform fine precision processing on the head surface, and there remains a problem in terms of cost.

  Further, as described in Patent Document 4, in order to control the voltage applied to the conveying belt by measuring the surface potential of the recording paper, the charging voltage to the conveying belt must be changed, and static electricity is generated. There is a problem that the structure of the high-voltage power supply for making the power supply complicated.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus in which head contamination due to mist backflow is reduced with a simple configuration.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A carriage equipped with a recording head for discharging droplets;
A conveying belt arranged to be capable of circular movement for conveying a recording medium facing the recording head;
Means for alternately applying positive and negative charges along the moving direction on the conveyor belt in a strip shape;
Gap adjusting means for changing a relative distance between the recording head and the conveying belt;
A surface potential sensor that is mounted in the vicinity of the recording head of the carriage and measures electrostatic force on the conveyor belt;
Means for comparing the measurement result of the surface potential sensor with a predetermined set value and determining whether or not adjustment of the relative distance between the recording head and the transport belt is necessary;
Means for controlling the relative distance between the recording head and the transport belt by driving the gap adjusting means when the determining means determines that adjustment of the relative distance is necessary. ,
The means for controlling the relative distance is configured to move the recording head in a direction away from the conveying belt to widen the relative distance, and the relative distance is affected by an electric field due to the electrostatic force. It was set as the structure which performs the control which adjusts to the distance which is not reached.

Here, when the relative distance between the recording head and the conveying belt is adjusted, the droplet landing position is predicted from the height information of the recording head, and the ejection control is performed so that the landing position is the same as before the adjustment. Can be configured. Further, the relative distance from the conveying belt can be changed by moving the carriage on which the recording head is mounted up and down .

According to the image forming apparatus of the present invention, it is necessary to measure the electrostatic force on the conveyance belt, compare the measurement result with a predetermined set value, and adjust the relative distance between the recording head and the conveyance belt. When discriminated, the recording head is moved away from the conveyor belt to increase the relative distance, and the relative distance is adjusted to a distance that does not affect the recording head due to the electrostatic field. When the force is strong, the recording head can escape to a range where the electrostatic force is weak, and it is possible to reduce the contamination of the head due to mist adhesion and improve the image quality.

Embodiments of the present invention will be described below with reference to the accompanying drawings. An example of an image forming apparatus according to the present invention will be described with reference to FIG. 1 is a schematic side view for explaining the overall configuration of the image forming apparatus, and FIG. 2 is an enlarged explanatory view of an engine portion of the mechanism portion.
In this image forming apparatus, although not shown, a carriage 1 is held by a guide rod and a guide rail so as to be slidable in the main scanning direction (in the direction perpendicular to the paper surface of FIG. 1). ), Cyan (C), magenta (M), and black (K) ink droplets are arranged in a direction crossing the main scanning direction with a plurality of recording heads 3 to eject ink droplets. Wearing the direction downward.

  As a liquid discharge head constituting the recording head 2, a piezoelectric actuator such as a piezoelectric element, a thermal actuator using film boiling of a recording liquid using an electrothermal transducer such as a heating resistor, and a metal phase change due to temperature change are used. A shape memory alloy actuator, an electrostatic actuator using an electrostatic force, or the like provided as energy generating means (pressure generating means) for discharging ink (liquid) can be used.

  Below the carriage 1, an endless transport belt 11 is arranged around a driving roller 12 and a driven roller 13 to electrostatically attract and transport the paper 3. The conveyor belt 11 rotates around when the driving roller 12 is rotationally driven by the sub-scanning motor 14. Further, a charging roller 16 which is a charging unit for charging the surface of the conveyance belt 11 is disposed in contact with each other, and a guide member 17 for providing the flatness of the conveyance belt 31 corresponding to the image forming region is provided. 11 on the back side.

  Further, an inlet pressure roller 18 facing the driven roller 13 and a tip pressure roller 19 facing the inlet side of the guide member 17 are respectively attached to a pressing member 20 that is pressed and urged. Further, a neutralizing brush 21 that neutralizes the surface of the conveyor belt 31 and a removing member 22 that removes paper dust and the like are disposed on the surface of the conveyor belt 31.

  Further, an encoder wheel 25 is attached to the driven roller 13, and an encoder sensor 26 for detecting a slit of the encoder wheel 25 is disposed, thereby providing a rotary encoder for detecting the moving amount and moving speed of the transport belt 11. It is composed.

  On the other hand, the sheets 3 stacked and accommodated in a sheet accommodating portion such as a sheet cassette 30 are separated and fed one by one by a sheet feeding roller 31 and a separation pad 32 made of a material having a large friction coefficient, and the registration rollers 33 register the sheets. After that, the sheet 3 is fed between the conveyance belt 31 and the inlet pressure roller 18 (nip portion).

  Further, in order to discharge the paper on which the image is formed, a separation claw 41 for separating the paper from the transport belt 11, a paper discharge transport roller pair 42, and a transport roller pair (one side) for transporting the paper to be discharged Is a roller or roller, and the other is a spur) 44, 45, a pair of conveyance rollers (both rollers or rollers) 46 to 48, and a pair of paper discharge rollers 49. The paper is discharged from the paper discharge roller 49 onto the paper discharge tray 50. Make paper.

  In this image forming apparatus, a surface potential sensor 61 for measuring the electrostatic force on the conveyor belt 11 is disposed in the vicinity of the recording head 2 of the carriage 1. In addition, by arranging a height adjustment mechanism that moves the carriage 1 up and down with respect to the conveyance belt 11, the relative distance between the carriage 1 and the conveyance belt 11 is variable. As the carriage height adjustment mechanism, for example, a mechanism described in Japanese Patent Application Laid-Open Nos. 09-099603 and 08-118761 can be used.

  In this image forming apparatus, the sheets 3 are separated and fed one by one from the sheet feeding cassette 30, and the sheets 3 fed substantially vertically upward are fed from the registration roller pair 33 to the conveying belt 11 and the inlet pressure roller 18. Sent in between. The registration roller 33 sends out the paper 3 in synchronization with image formation based on the detection signal of the registration sensor 71.

  At this time, by applying an alternating voltage to the charging roller 16, positive and negative charges are alternately applied in a strip shape with a predetermined width in the sub-scanning direction, which is the circumferential direction, on the conveyor belt 11. 11 is charged. By feeding the sheet 3 onto the conveyance belt 11 charged alternately with positive and negative electrodes, the sheet 3 is attracted to the conveyance belt 11 by electrostatic force, and the sheet 3 is conveyed in the sub-scanning direction by the circular movement of the conveyance belt 11. Is done.

  Therefore, by driving the recording head 2 in accordance with the image signal while moving the carriage 1 in the forward and backward directions, ink droplets are ejected onto the stopped paper 3 to record one line, and the paper 3 is After transporting a predetermined amount, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the sheet 3 has reached the recording area, the recording operation is terminated, and the sheet 3 is discharged and conveyed to the discharge tray 50.

Next, an outline of the control unit of the image forming apparatus will be described with reference to the block diagram of FIG.
The main control unit 101 in the control unit is cut off from the CPU that controls the entire apparatus, the ROM that stores programs and other fixed data, the RAM that temporarily stores image data, and the power supply of the apparatus. A rewritable non-volatile memory for holding data in between, image processing for performing various signal processing and rearrangement on image data, and an ASIC for processing input / output signals for controlling the entire apparatus, etc. ing.

  The main control unit 101 processes image data received from the host (not shown) and transfers it to the print control unit 102. The print control unit 102 drives and controls each actuator of the recording head 2 based on the received image data. Then, droplets are ejected from the recording head 2.

  Further, the main control unit 101 drives and controls the main scanning motor 104 via the motor driving circuit 103 to move the carriage 1 in the main scanning direction, and passes through the motor driving circuit 103 based on the detection signal from the encoder sensor 26. Then, the sub-scanning motor 14 is driven and driven, and the driving roller 12 is rotated to drive the conveying belt 11 intermittently as described above.

  Further, the main control unit 101 controls the AC bias supply unit 105 to apply an AC bias to the charging roller 16, thereby performing charging control on the conveyance belt 11.

  Further, the main control unit 101 inputs a detection signal from the surface potential sensor 61 to measure the electrostatic force on the conveyor belt 11 and, based on the measurement result, the carriage height (head height) via the drive circuit 106. ) The driving means of the adjusting mechanism 107 is driven to adjust the height of the carriage 1 (the height of the recording head 2) with respect to the transport belt 11. As a driving unit for the carriage height adjusting mechanism 107, a motor, a solenoid, an electromagnetic clutch, or the like can be used.

Here, the driving of the conveyor belt 11 will be described with reference to FIG.
As shown in FIG. 4A, the conveyance belt 11 is rotated by driving the sub-scanning motor 14. At this time, by applying the AC bias shown in FIG. 4B to the charging roller 16, the conveying belt 11 is charged with a predetermined width with the positive and negative electrodes as described above. Further, while the conveyor belt 11 is moving around, detection signals shown in FIGS. 4C and 4D are output from the encoder sensor 26. Then, the electrostatic force on the conveyor belt 11 is detected from the surface potential sensor 61 and a detection signal as shown in FIG. 4D is output, and this detection signal is input to the main control unit 101.

The head height adjustment process performed by the main control unit 101 will be described with reference to FIG.
The main control unit 101 acquires a detection signal (one of sensor information) from the surface potential sensor 61, measures the electrostatic force on the conveyor belt 11, and based on the measurement result and a preset set value, Determine whether a height change is required. The measurement by the surface potential sensor 61 is performed in synchronization with the main scanning of the carriage 1.

  At this time, as sensor information, in addition to the detection signal of the surface potential sensor 61, information such as the adsorption force and temperature / humidity environment of the transport belt 11 and the number of sheets passing over time, the thickness of the sheet, and the contamination of the head due to ink scattering It is preferable to acquire various kinds of information such as a threshold value for and to determine the necessity of changing the head height based on each piece of information.

  If the head height needs to be adjusted, the drive means (for example, a motor) of the carriage height adjusting mechanism 107 is driven and controlled to change the height of the recording head 2 so that the relative distance from the transport belt 11 is increased. Change.

  Thereafter, a detection signal (sensor information) from the surface potential sensor 61 is acquired again, the electrostatic force on the conveyor belt 11 is measured, and the head height needs to be adjusted based on the measurement result and a predetermined set value. If the head height needs to be adjusted, the process of adjusting the height of the recording head 2 by repeatedly controlling the driving means of the carriage height adjusting mechanism 107 is repeated, and readjustment is unnecessary. If this is the case, the process ends.

  As an actual operation, as shown in FIG. 6, when a printing operation is performed in a state where the carriage 3 is under the influence of an electric field due to the electric lines of force generated on the paper 3 in a steady state, the mist is generated. It will be charged by the electric field and adsorbed according to the direction of the lines of electric force. Therefore, as shown in FIG. 7, the distance (gap) between the recording head 2 and the conveying belt 11 is adjusted (in this case, the direction indicated by the arrow is displaced upward), and the influence of the electric field is effected. The carriage 1 is moved in the height direction so as not to reach.

  In this case, since the gap (distance) between the recording head 2 and the paper 3 fluctuates, the landing position is predicted based on the set height information of the recording head 2, and the ejection control is performed to adjust the height. It is preferable to prevent landing position deviation.

  As described above, since the relative distance between the recording head and the conveying belt is changed based on the strength of the electrostatic force on the conveying belt, it is possible to suppress head contamination due to scattering of the recording liquid with a simple structure. .

  At this time, by detecting the electrostatic force generated on the sheet caused by charging of the conveyance belt, the influence of the thickness of the recording sheet can be taken into consideration. Further, the electrostatic force closer to the recording head can be measured by arranging the means for measuring the electrostatic force in the vicinity of the recording head.

  Note that the relative distance from the recording head can be adjusted by displacing the conveying belt side. Although the present invention has been described with a serial image forming apparatus having a printer configuration, the present invention is not limited to this, but a serial image forming apparatus having a printer / facsimile / copier multifunction peripheral (MFP) configuration, and other line type image forming apparatuses. It can also be applied to.

1 is a schematic configuration diagram of a mechanism unit of an image forming apparatus according to the present invention. It is principal part expansion explanatory drawing of the mechanism part. It is a block explanatory view explaining the outline of a control part similarly. It is explanatory drawing with which it uses for the description regarding the drive of a conveyance belt similarly. It is a flowchart with which it uses for description of head height adjustment which a control part performs. It is explanatory drawing with which it uses for description of the same height adjustment. It is explanatory drawing with which it uses for description of the state which changed head height similarly.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Carriage 2 ... Recording head 11 ... Sub-scanning motor (drive motor)
DESCRIPTION OF SYMBOLS 16 ... Charging roller 61 ... Surface potential sensor 101 ... Main control part 107 ... Carriage height adjustment mechanism

Claims (3)

A carriage equipped with a recording head for discharging droplets;
A conveying belt arranged to be capable of circular movement for conveying a recording medium facing the recording head;
Means for alternately applying positive and negative charges along the moving direction on the conveyor belt in a strip shape;
Gap adjusting means for changing a relative distance between the recording head and the conveying belt;
A surface potential sensor that is mounted in the vicinity of the recording head of the carriage and measures electrostatic force on the conveyor belt;
Means for comparing the measurement result of the surface potential sensor with a predetermined set value and determining whether or not adjustment of the relative distance between the recording head and the transport belt is necessary;
Means for controlling the relative distance between the recording head and the transport belt by driving the gap adjusting means when the determining means determines that adjustment of the relative distance is necessary. ,
The means for controlling the relative distance is configured to move the recording head in a direction away from the conveying belt to widen the relative distance, and the relative distance is affected by an electric field due to the electrostatic force. An image forming apparatus characterized by performing control to adjust the distance to less than .   When the relative distance between the recording head and the transport belt is adjusted, the droplet landing position is predicted from the height information of the recording head, and discharge control is performed so that the landing position is the same as before the adjustment. The image forming apparatus according to claim 1.   3. The image forming apparatus according to claim 1, wherein a relative distance from the conveying belt is changed by moving a carriage on which the recording head is mounted up and down.

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