JP4076085B2 - Paper conveying apparatus and image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to a sheet conveying apparatus and an image forming apparatus that convey a sheet using a conveying belt.
[0002]
[Patent Document 1]
Japanese Patent No. 2897960
[Patent Document 2]
JP-A-7-53081
[Patent Document 3]
JP 2000-190473 A
[0003]
[Prior art]
As an image forming apparatus (or image recording apparatus) such as a printer, a facsimile machine, and a copying apparatus, for example, an ink jet recording apparatus is known. Inkjet recording apparatus means paper (not limited to paper, but also OHP, etc.) from an ink recording head, meaning that ink droplets, developer, other liquids, etc. can adhere to the recording medium or recording medium, It is also called recording paper etc.). It records by ejecting ink on it, can record high-definition images at high speed, has low running cost, low noise, and multicolor ink. It has the advantage that it is easy to record a color image using
[0004]
As an inkjet head, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that uses a phase change due to liquid film boiling using an electrothermal transducer such as a heating resistor, a shape memory alloy actuator that uses a metal phase change due to a temperature change, 2. Description of the Related Art An electrostatic actuator using an electrostatic force or the like is known as an energy generating unit for ejecting ink.
[0005]
By the way, in the ink jet recording method, when an image is formed in order to make ink adhere to the paper, there is a phenomenon that the paper is stretched by moisture contained in the ink. This phenomenon is called cockling. The cockling causes the paper to wave, and the position of the nozzle of the head and the surface of the paper changes from place to place. If the degree of cockling deteriorates, in the worst case, the paper will come into contact with the nozzle surface of the head, and the nozzle surface of the head may become dirty, or the paper itself may become dirty, resulting in a decrease in image quality. The impact position of the ink droplet may be shifted due to the influence.
[0006]
Therefore, in an ink jet recording apparatus, printing is performed on a platen provided with a recess that absorbs paper cockling, and a spur having a protrusion on the circumference is provided as a presser for the paper. What happens is also a problem.
[0007]
Further, in the conventional ink jet recording apparatus, paper is fed by rollers, and two sets of rollers (one is a combination of a spur and a roller as described above) are arranged across a printing area. However, with this configuration, the sheet feeding accuracy can be guaranteed only when the sheet is engaged with the two sets of rollers.
[0008]
However, in recent years, since it is desired to increase the image printing area, it is impossible to guarantee the sheet feeding accuracy in order to secure the printing area, that is, one of the two pairs of rollers. However, there is also an ink jet recording apparatus that performs printing in a state where the paper is not bitten. However, in the state where the paper bites only one of the roller pairs, if the paper floats, it is impossible to cope with it, and because the paper conveyance force cannot be secured, the feeding accuracy cannot be guaranteed, so the image quality is also deteriorated. Problem arises.
[0009]
Pursuing high image quality in an inkjet recording device requires accuracy of the landing position of ink droplets on the paper, and it is necessary to improve the flatness of the paper, but as described above, when printing on plain paper In other words, the moisture contained in the ink causes the paper fibers to swell and deform into a wave shape, resulting in a shift in the dot landing position. So far, it has been found that it takes about 3 seconds or more after the ink adheres to the paper to cause a large deformation of the paper.
[0010]
Therefore, as described in [Patent Document 1] and [Patent Document 2], in order to maintain the flatness of the paper, an endless charging belt is provided, and the surface of the charging belt is charged to electrostatically charge the paper. An ink jet recording apparatus has been proposed in which a sheet is conveyed by adsorbing and rotating the charging belt in this state, thereby preventing the sheet from lifting from the charging belt and maintaining high flatness.
[0011]
Here, Patent Document 1 discloses a paper transport device and an image recording apparatus in which a voltage applying means is brought into contact with the surface of the charging belt and an alternating charge pattern is formed on the surface of the charging belt, for example, in a belt shape. . [Patent Document 2] discloses a printing apparatus in which the potential on the charging belt is neutralized with a neutralizing brush in order to obtain a stable potential on the charging belt at all times.
[0012]
However, when the sheet is electrostatically adsorbed and conveyed by using the conveyance belt in this way, if charging on the conveyance belt leaks, the adsorption force is reduced and normal conveyance is performed. Disappear.
[0013]
Therefore, conventionally, as described in [Patent Document 3], at least a part of the deployment site of the power feeding unit for applying a voltage to the static electricity generating unit provided on the transport belt is disposed on the sheet placement surface of the transport belt. There is a displacement means for displacing upward to prevent an unintended flow of ink to the power supply unit and to avoid occurrence of a short circuit or the like.
[0014]
[Problems to be solved by the invention]
However, as in the device described in the above-mentioned [Patent Document 3], it is not possible to cope with the case where a leak occurs only by adopting a structure that prevents the leakage of the conveyor belt, and the adsorption force is reduced and stable. There is a problem that it becomes impossible to carry out the transfer.
[0015]
The present invention has been made in view of the above problems, and an object of the present invention is to provide a sheet conveying apparatus and an image forming apparatus capable of performing stable conveyance.
[0016]
[Means for Solving the Problems]
  In order to solve the above-described problems, a paper transport device according to the present invention isThe transport belt has a surface layer formed of a resin material, and a back surface serving as a ground layer that suppresses resistance with the same material as the surface layer.Conveyor beltApplying voltage to the front and back of the conveyor beltsurfaceTheElectrificationCurrent between the front and back of the conveyor beltWith means to detect leaksIt was set as the structure.
[0017]
  Here, the liquid adheres to the surface of the conveyor belt.CurrentDetecting as a leak, damage to the conveyor belt surfaceCurrentIt is preferable to detect it as a leak, and each polarity when applying an alternating voltage to the conveyor beltCurrent inIt is preferable to detect leaks. further,CurrentDepending on the amount of leakUntil it is recognized as a current leaktimeCan be configured to adjust.Furthermore,CurrentIt is preferable that high voltage output for charging the conveyor belt is stopped when a leak is detected.
[0018]
The image forming apparatus according to the present invention includes the paper conveying device according to the present invention.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. A first embodiment of an image forming apparatus according to the present invention provided with a paper conveying apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram for explaining the overall configuration of the apparatus, FIG. 2 is a plan view for explaining a main part of the apparatus, and FIG. 3 is a front view of the main part of the apparatus.
[0020]
An ink jet recording apparatus, which is an image forming apparatus, holds a carriage 3 slidably in a main scanning direction with a main guide rod 1 and a sub guide rod 2 which are guide members horizontally mounted on left and right side plates (not shown). The scanning motor 4 (FIG. 2) moves and scans in the direction of the arrow in FIG. 2 via the timing belt.
[0021]
The carriage 3 is provided with a recording head 4 composed of four ink jet heads that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk), and a plurality of ink ejection openings. They are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.
[0022]
As the ink jet head constituting the recording head 4, 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. A shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like as an energy generating means for discharging ink can be used.
[0023]
In addition, the carriage 3 is mounted with replaceable sub tanks 5 for each color for supplying ink of each color to the recording head 4. Ink is supplied to the sub tank 5 from a main tank (ink cartridge) (not shown) via an ink supply tube 6.
[0024]
On the other hand, as a paper feeding unit for feeding the paper 12 stacked on the paper feeding unit 11, a half-moon roller (paper feeding roller) 13 and a paper feeding roller 13 that separate and feed the paper 12 from the paper stacking unit 11 one by one. Is provided with a separation pad 14 made of a material having a large friction coefficient, and this separation pad 14 is urged toward the sheet feeding roller 13.
[0025]
A conveyance belt 21 for electrostatically adsorbing and conveying the paper 12 as a conveyance unit for conveying the paper 12 fed from the paper supply unit 11 below the recording head 4, and a paper supply unit 11, a sheet pressing roller 22 for conveying the sheet 12 fed through the guide 15 between the conveying belt 21 and a sheet pressing roller 22 that is conveyed substantially vertically upward, and the conveyance belt 21 A conveyance guide 23 for following the upper side and a tip roller 25 urged toward the conveyance belt 21 by a pressing member (not shown) are provided.
[0026]
The conveyor belt 21 is an endless or connected belt (these are referred to as “endless”), and is stretched between the conveyor roller 27 and a tension roller 28 to which tension is applied, and the conveyor roller 27 is sub-scanned. The motor 31 (FIG. 2) is configured to rotate around the belt conveyance direction by being driven to rotate. A charging roller 26 as a charging means for charging the surface of the transport belt 21 is disposed at a position facing the transport roller 27.
[0027]
As shown in FIG. 4, the transport belt 21 has a surface layer 21a that forms a sheet adsorbing surface made of a resin material having a pure thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material, and the surface layer 21a. It has a back layer (medium resistance layer, earth layer) 21b in which the resistance is controlled by carbon.
[0028]
The thickness of the insulating layer (surface layer) 21a of the transport belt 21 affects the electrostatic capacity. When the thickness increases, the electrostatic capacity decreases and the amount of charge on the belt decreases when charged. According to the experiment, a desired electrostatic attraction force was obtained by setting the thickness of the surface layer 21a to 60 μm or less. However, in consideration of the range of film thickness that varies in manufacturing, scratches generated on the belt in the actual machine However, the electrostatic attraction force can be further improved by making the layer thickness as thin as possible within the range where the layer thickness does not become zero.
[0029]
Further, the thickness of the back layer (medium resistance layer, earth layer) 21b of the conveyor belt 21 does not directly affect the electrostatic action. However, as the total thickness of the belt increases, the rigidity increases and the belt is stretched on the actual machine. Sometimes it is difficult to ensure the flatness of the belt, while it cannot be made too thin to ensure the required strength. According to experiments, the thickness of the back layer 21b is preferably about 40 to 200 μm.
[0030]
In this way, by providing the resistance control layer 21b on the entire back side of the transport belt 21 as a two-layer structure, after the charge is formed on the surface layer 21a that is an insulating layer in advance, the charge is further increased when the sheet adsorbed to the belt comes into contact The electrostatic attraction force between the paper and the conveyor belt 21 can be increased. For example, in the case of a single insulating layer, the adsorption force is halved compared to the case of two layers, and in the case of a single layer, the position where the paper starts to contact the belt faces the ground roller located inside the belt. However, by using two layers, such a restriction is eliminated.
[0031]
In this case, a surface resistance of 1E + 10Ω / □ or more was used as the surface layer 21a, and a surface resistance of 1E + 08Ω / □ or less was used as the back layer 21b, whereby a desired electrostatic adsorption force was obtained.
[0032]
The charging roller 26 is disposed so as to contact the surface layer of the conveyor belt 21 and rotate following the rotation of the conveyor belt 21, and applies 2.5N to both ends of the shaft as a pressing force. The transport roller 27 also serves as an earth roller, is placed in contact with the middle resistance layer of the transport belt 21 and is grounded via a ground line.
[0033]
Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 4, a separation unit 41 for separating the paper 12 from the conveyance belt 22 and a paper discharge tray for stocking the paper 12 to be discharged. 42.
[0034]
Next, a means for detecting a leak when charging the conveyor belt 21 will be described with reference to FIG.
In this apparatus, a high voltage power supply 50 for charging the conveyor belt 21 is provided. The high voltage power supply 50 includes an AC high voltage output unit 51 that applies an AC high voltage to the shaft 26a of the charging roller 26, and the AC high voltage output unit. When a high voltage is applied from 51 to the charging roller 26, a current flows from the AC high voltage output unit 51 through the charging roller 26, the conveyance belt 21, the conveyance roller 27, and a closed circuit represented by the AC high voltage output unit 51. And a current monitor circuit 52 for monitoring the current.
[0035]
When a current flows from the AC high voltage output unit 51 through the charging roller 26, the conveyance belt 21, the conveyance roller 27, and the closed circuit represented by the AC high voltage output unit 51, if a leak occurs, the current value increases. Therefore, the current monitor circuit 52 outputs a leak detection signal when the current value increases. For example, when ink adheres to the conveyance belt 21, the impedance decreases in the ink adhesion portion and the current flowing in the closed circuit increases, and when the surface of the conveyance belt 21 is damaged, the impedance of the damaged belt decreases. As a result, the current flowing in the closed circuit increases. Furthermore, the current flowing in the closed circuit may increase due to adhesion of paper dust or the like.
[0036]
In this case, the current monitor circuit 52 is configured to be able to detect both positive and negative currents for an AC high voltage using an electronic circuit such as a transistor, resistor, and PWMIC. That is, as will be described later, an AC voltage (or a bipolar pulse voltage) is applied to the transport belt via the charging roller, and positive and negative charges are applied to the transport belt in the moving direction of the transport belt. By applying them alternately, a stable adsorption force can be obtained.
[0037]
Therefore, when detecting a leak by applying an AC high voltage to the conveyor belt, if the leak can be detected only with one polarity of positive polarity or negative polarity, the leak will be missed. By making detection possible in both positive and negative polarities, leak detection is ensured.
[0038]
Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit includes a printer controller 70, a motor driver 81 for driving the main scanning motor 4 and the sub-scanning motor 31, and a head driver (head driving circuit, driver IC for driving the recording head 4 (inkjet head)). 82) and the like.
[0039]
The printer controller 70 is an interface (hereinafter referred to as “I”) that receives print data and the like from a host side 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. 72), a main control unit 73 comprising a CPU, ROM, RAM, I / F, etc., a RAM 74 used as various buffers and work memory, etc., and a ROM 75 storing various data processing routines, etc. A drive signal generation circuit 77 for generating a drive waveform for the recording head 7 and I / Fs 78 and 79 are provided.
[0040]
Further, the main control unit 73 has various outputs such as an output of an encoder 34 composed of a slit plate 32 fixed to a shaft 27a of a conveyance roller 27 rotated by a sub-scanning motor 31 and a photosensor 33 as shown in FIG. Signals from sensors and switches are also input.
[0041]
Here, the main control unit 73 instructs the AC high voltage output unit 51 of the high voltage power supply 50 to output the AC high voltage to the charging roller 26 via the I / F 79 when the paper 12 is conveyed. At this time, the leak detection signal from the current monitor circuit 52 of the high voltage power supply 50 is monitored.
[0042]
Further, the main control unit 73 reads and analyzes the print data in the reception buffer included in the I / F 72, stores the analysis result (intermediate code data) in a predetermined area of the RAM 74, and reads the ROM 75 from the stored analysis result. Is used to generate dot pattern data for outputting an image, and is stored again in a different predetermined area of the RAM 74. Note that when image data is expanded into bitmap data and transferred to the recording apparatus by the printer driver on the host side, the received bitmap image data is simply stored in the RAM 74.
[0043]
When the main control unit 73 obtains dot pattern data corresponding to one row of the recording head 4, the main control unit 73 synchronizes the dot pattern data for one row with the clock signal CLK from the oscillation circuit. Serial data is sent to the head driver 82 via F78, and a latch signal is sent to the head driver 82 at a predetermined timing.
[0044]
The drive signal generation circuit 77 is a ROM (can also be configured by the ROM 75) storing pattern data of a drive waveform (drive signal), and a D / A for D / A converting the drive waveform data read from the ROM. It consists of a waveform generation circuit including a converter, an amplifier, and the like.
[0045]
The head driver 82 is a shift register that receives a clock signal from the main control unit 73 and serial data that is a print signal, a latch circuit that latches a register value of the shift register using a latch signal from the main control unit 73, and a latch circuit A level conversion circuit (level shifter) that changes the output value of the signal and an analog switch array (switch means) whose on / off is controlled by this level shifter, and driving waveform by controlling on / off of the analog switch array Is selectively applied to the head 4.
[0046]
In the ink jet recording apparatus configured as described above, the paper 12 is separated and fed one by one from the paper feeding unit 11, and the fed paper 12 is guided by the transport guide 15, and the transport belt 21 and the paper pressing roller 22. , The direction is changed by the guide 23, and the paper is further sequentially fed between the leading end roller 25 and the conveying belt 21 and fed.
[0047]
At this time, the main controller 73 applies a positive output and a negative output to the charging roller 26 from the high voltage circuit (high voltage power source) 50 alternately, that is, an alternating voltage (here, AC voltage) is applied. . As a result, as shown in FIG. 7, the surface of the conveyor belt 21 (insulating layer 21 a) is charged with a strip-shaped voltage pattern (this is referred to as “charging voltage pattern”) 91 with alternating polarity. That is, the conveyance belt 21 is alternately charged in a band shape with a predetermined width (referred to as a charging width or a charging pitch) between plus and minus in the sub-scanning direction that is the circumferential direction.
[0048]
In this way, the paper 12 is fed onto the conveying belt 21 that is alternately charged positively and negatively, so that the paper 12 is attracted to the conveying belt 21 by electrostatic force. Therefore, the paper 12 is transported by a predetermined amount by the circular movement of the transport belt 21 and stopped, and the recording head 4 is driven in accordance with the image signal while the carriage 3 is moved. To record one line. When recording for one line is completed, the conveying belt 21 is driven to convey the paper 12 by a predetermined amount, and then the next line is recorded. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished, and the paper 12 is discharged onto the paper discharge tray 42.
[0049]
Note that a recovery device for recovering defective ejection of the recording head 4 is disposed at a position outside the recording area on one end side in the moving direction of the carriage 3 and moved to the recovery device side during standby to perform capping. The recording head 4 is capped by the means, and the nozzle portion is kept in a wet state to prevent ejection failure due to ink drying. In addition, by ejecting ink droplets not related to recording even during recording, all the ejection ports The ink viscosity is kept constant and stable ejection performance is maintained.
[0050]
Further, when a discharge failure occurs, the nozzle of the recording head 4 is sealed with a capping unit, bubbles and the like are sucked out of the nozzle together with ink through a tube, and the ink and dust adhering to the nozzle surface are cleaned with a cleaning unit. A process for recovering the ejection failure by removing by the above is performed.
[0051]
Accordingly, a first embodiment of the leak detection operation in this ink jet recording apparatus will be described with reference to FIG.
First, the main controller 73 controls the high voltage power supply 50 to apply an AC high voltage to the charging roller 26 to apply (charge) the conveying belt 21 with a high voltage. At this time, the current monitor circuit 52 monitors whether the current flowing in the closed circuit represented by the charging roller 26, the conveyance belt 21, the conveyance roller 27, and the AC high voltage output unit 51 has increased as described above. When the signal increases, a leak detection signal is output.
[0052]
The main control unit 73 polls the output of the current monitor circuit 52 for at least 5 μsec, determines whether or not a leak detection signal is output from the current monitor circuit 52, and continuously monitors the current monitor circuit at least three times. When a leak detection signal is output from 52, it is recognized that a leak has occurred.
[0053]
The main control unit 73 counts the leak detection signal every polling when the current monitor circuit 52 outputs a leak detection signal at the time of polling, and counts the leak detection signal 10 times in total. Recognize that has occurred.
[0054]
When the leakage is recognized, a signal for stopping the output of the AC high voltage is output to the AC high voltage output unit 51 of the high voltage power supply 50. That is, when a leak occurs, the output of the AC high voltage output unit 51 may be in a state close to a short-circuit state. Therefore, when the leak is recognized, the AC high-voltage output is stopped and the output of the high-voltage power supply is short-circuited. It prevents the situation from becoming close to the state.
[0055]
In this way, by making it possible to detect a leak when charging the conveyance belt, it is possible to reduce paper conveyance failure due to a decrease in the adsorption force of the conveyance belt.
[0056]
Here, by setting the current value for outputting the leak detection signal from the current monitor circuit as the current value when the ink adheres on the transport belt 21, it is possible to detect the ink adhesion to the transport belt as a leak.
[0057]
In other words, if ink adheres to the surface of the transport belt, a discharge occurs on the ink from the charging roller when performing the charging operation, the output of the high voltage power supply becomes close to a short circuit, and the charge on the transport belt. Will be neutralized by the ink, causing a reduction in the attractive force and inducing jamming. Furthermore, the ink is transferred to the paper to be conveyed and becomes dirty. Therefore, it is possible to carry out stable paper conveyance by detecting ink adhesion to the conveyance belt as a leak, and it is possible to quickly cope when the output of the high-voltage power supply is close to a short circuit. it can.
[0058]
Further, by setting the current value for outputting the leak detection signal from the current monitor circuit as the current value when the surface of the transport belt 21 is damaged, it is possible to detect the damage of the transport belt as a leak.
[0059]
In other words, if there is damage on the surface of the conveyor belt, when charging operation is performed, the output of the high-voltage power supply is close to a short circuit at the damaged part, and the damaged part is not fully charged, resulting in a decrease in adsorption power. This makes it impossible to carry the paper stably. Therefore, by detecting the damage of the conveying belt as a leak, it is possible to carry out stable paper conveyance, and it is possible to quickly cope when the output of the high voltage power supply is in a state close to a short circuit.
[0060]
Also, by performing polling processing of the leak detection signal as in this embodiment, it is not always necessary to monitor the leak detection signal, and the burden on the control unit side is reduced.
[0061]
Next, a second embodiment of the leak detection operation will be described with reference to FIG.
First, as described above, the main control unit 73 controls the high voltage power supply 50 to apply an AC high voltage to the charging roller 26 to apply (charge) the conveying belt 21 with a high voltage. At this time, the current monitor circuit 52 monitors whether the current flowing in the closed circuit represented by the charging roller 26, the conveyance belt 21, the conveyance roller 27, and the AC high voltage output unit 51 has increased as described above. When the signal increases, a leak detection signal is output.
[0062]
The main control unit 73 checks the output of the current monitor circuit 52. When a leak detection signal is output from the current monitor circuit 52, the main control unit 73 increments the count value (+1) at the rise (or fall) of the leak detection signal. And the time from the rise to the fall of the leak detection signal (the output time of the leak detection signal) is measured.
[0063]
Then, the main control unit 73 recognizes that a leak has occurred when the total count value of the leak detection signal is 10 times or more, or when the output time of the leak detection signal is 15 msec or more.
[0064]
Thus, by counting the rise or fall of the leak detection signal, the burden on the control unit is relatively reduced compared to the next third embodiment, but by monitoring the output time of the leak detection signal The burden on the control unit is greater than in the first embodiment.
[0065]
Next, a third embodiment of the leak detection operation will be described with reference to FIG.
Here, as described above, the high voltage power supply 50 is controlled by the main control unit 73 and an AC high voltage is applied to the charging roller 26 to apply (charge) the conveying belt 21 with a high voltage. At this time, the current monitor circuit 52 monitors whether the current flowing in the closed circuit represented by the charging roller 26, the conveyance belt 21, the conveyance roller 27, and the AC high voltage output unit 51 has increased as described above. When the signal increases, a leak detection signal is output.
[0066]
The main control unit 73 checks the output of the current monitor circuit 52. When a leak detection signal is output from the current monitor circuit 52, the main control unit 73 measures and integrates the output time of the leak detection signal, and integrates the leak. When the output time of the detection signal becomes 50 msec or more, or when the output time of the leak detection signal is continuously 15 msec or more, it is recognized that a leak has occurred.
[0067]
As described above, by constantly monitoring the leak detection signal, it is possible to prevent a leak from being missed, but the burden on the control unit for constant monitoring increases.
[0068]
Next, a fourth embodiment of the leak detection operation will be described with reference to FIG.
Here, as described above, the high voltage power supply 50 is controlled by the main control unit 73 and an AC high voltage is applied to the charging roller 26 to apply (charge) the conveying belt 21 with a high voltage. In this embodiment, the current monitor circuit 52 monitors the current flowing through the closed circuit represented by the charging roller 26, the conveyor belt 21, the conveyor roller 27, and the AC high voltage output unit 51 as described above. A signal corresponding to the current flowing through the circuit is output.
[0069]
The main control unit 73 checks the output signal of the current monitor circuit 52. Based on the output signal from the current monitor circuit 52, the current flowing in the closed circuit is 100 μA or more in absolute value and continues for 50 msec or more. Or when an absolute value of 200 μA flows, it is immediately recognized that a leak has occurred.
[0070]
As described above, by quantitatively measuring the amount of leak based on the value of the current flowing in the closed circuit, a slight leak can be ignored according to the amount of leak, and a large leak can be immediately recognized as a leak. However, since the current value is quantitatively monitored, there is a possibility that the current value becomes weak against noise.
[0071]
That is, when a leak occurs in the transport belt, the leak may occur due to the adhesion of a small ink droplet on the transport belt or paper dust. In this case, since the leak may be recovered by natural drying, paper dust scattering, or the like, it is advantageous not to immediately recognize that the leak has occurred even if the leak is detected. In addition, when a large amount of leak occurs due to a laceration of the conveyor belt or adhesion of ink, it is necessary to quickly recognize that the leak has occurred.
[0072]
Therefore, as described above, by changing the time until recognizing that there is a leak according to the leak amount (recognizing at a different time according to the leak amount), a slight leak is ignored, and a large leak A leak can be immediately recognized as a leak.
[0073]
In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to a serial (shuttle type) ink jet recording apparatus that is scanned by a carriage. However, the present invention is similarly applied to a line type ink jet recording apparatus having a line type head. be able to.
[0074]
The image forming apparatus according to the present invention can be applied to a facsimile apparatus, a copying apparatus, a printer / fax / copier multifunction machine, etc., in addition to an ink jet printer. Furthermore, the present invention can also be applied to an image forming apparatus that discharges a liquid other than ink, such as a resist or a DNA sample in the medical field.
[0075]
【The invention's effect】
  As described above, according to the paper transport device of the present invention,The transport belt has a surface layer formed of a resin material, and a back surface serving as a ground layer that suppresses resistance with the same material as the surface layer.Conveyor beltApplying voltage to the front and back of the conveyor beltsurfaceTheElectrificationCurrent between the front and back of the conveyor beltWith means to detect leaksConfiguration andTherefore, it is possible to prevent the conveyance from becoming unstable due to a decrease in the suction force of the conveyance belt.
[0076]
According to the image recording apparatus of the present invention, since the sheet conveying apparatus according to the present invention is provided, the sheet conveyance stability is improved and the image quality is improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus including a paper conveying device according to the present invention.
FIG. 2 is an explanatory plan view of a main part of the image forming apparatus.
FIG. 3 is an explanatory front view of a main part of the image forming apparatus.
FIG. 4 is a schematic diagram illustrating a configuration of a conveyance belt of the image forming apparatus.
FIG. 5 is an explanatory diagram for explaining leak detection means;
FIG. 6 is a block diagram illustrating an overview of a control unit of the image forming apparatus.
FIG. 7 is an explanatory diagram of a charging voltage pattern by the image forming apparatus.
FIG. 8 is a flowchart for explaining a first embodiment of a leak detection operation in the image forming apparatus;
FIG. 9 is a flowchart for explaining the second embodiment of the leak detection operation in the same manner.
FIG. 10 is a flowchart for explaining the third embodiment of the leak detection operation in the same manner.
FIG. 11 is a flowchart for explaining the fourth embodiment of the leak detection operation in the same manner.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 3 ... Carriage, 4 ... Recording head, 12 ... Paper, 21 ... Conveyance belt, 26 ... Charging roller, 27 ... Conveyance roller, 50 ... High voltage power supply, 51 ... AC high voltage output part, 52 ... Current monitor circuit.

Claims (7)

In a paper transport device that transports paper by charging the surface of an endless transport belt,
The transport belt has a surface layer formed of a resin material, and a back surface serving as a ground layer that suppresses resistance with the same material as the surface layer.
A paper conveying apparatus comprising: means for detecting a current leak between the front and back of the conveying belt when a voltage is applied to the front and back of the conveying belt to charge the surface of the conveying belt . 2. The paper transport apparatus according to claim 1, wherein adhesion of liquid to the surface of the transport belt is detected as a current leak. 2. The paper conveying apparatus according to claim 1, wherein damage on the surface of the conveying belt is detected as a current leak. 2. The paper conveying apparatus according to claim 1, wherein a current leak in each polarity is detected when an alternating voltage is applied to the conveying belt. 2. The paper conveying apparatus according to claim 1, wherein a time until the current leakage is recognized is adjusted according to a current leakage amount. 6. The paper conveying apparatus according to claim 1, wherein a high voltage output for charging the conveying belt is stopped when a current leak is detected.   7. The image forming apparatus according to claim 1, further comprising: a paper transport device that charges a surface of an endless transport belt and transports the paper, and forms an image by ejecting liquid droplets onto the paper from a liquid droplet ejection head. An image forming apparatus comprising the sheet conveying device according to claim 1.

Images