JP2005231814A - Paper carrying device and image forming device therewith - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To safely continue paper carrying operation even when a leak occurs on a conveyer belt. <P>SOLUTION: A paper carrying device 10 carries paper by making the paper attached to an electrified surface thereof, while electrifying a surface of the endless conveyer belt 21 by applying high voltage thereto by an AC high-voltage output part 51, and is provided with a current monitor circuit 52 for detecting the leak of the surface of the conveyer belt 21, and a main control part 73 for detecting the leak position on the conveyer belt 21 of the leak detected by the current monitor circuit 52. The main control part 73 stops application of the high voltage by the AC high-voltage output part 51 to the leak position where the leak is detected when the current monitor circuit 52 detects the leak, and also controls so as to continue electrification of a portion other than the leak position. Thus, paper carrying can be continued by making the paper attached to the conveyer belt 21. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet adsorbed on the surface of a charged conveying belt, and an image forming apparatus including the sheet conveying apparatus.

As described above, for example, Japanese Patent Application Laid-Open No. 2004-133620 discloses a paper transport device that transports the paper adsorbed on the charged transport belt surface.
In this paper transport device, a transport belt composed of a dielectric endless belt is rotatably supported between a support roller and a drive roller, and the outer surface of the transport belt is wound around the support roller. An electrode roller for forming a charge pattern is brought into rolling contact, and an AC voltage is applied to the electrode roller from an AC power source to form a charge density pattern in which charge densities −σ and + σ are alternately arranged in the belt moving direction on the belt outer surface. The sheet is conveyed in an electrostatically attracted state to the outer surface of the conveying belt by an unequal electric field formed by the charge density pattern.
Japanese Patent No. 2897960 (page 4)

However, as described in Patent Document 1, in the case of a paper conveyance device that applies a high voltage to a conveyance belt and charges the conveyance belt, a high voltage is applied to a portion where a leak occurs on the conveyance belt. Is applied, it is very dangerous because the high-voltage output is in a state close to a short circuit in that portion.
Therefore, in order to avoid danger in such a case, it is necessary to perform maintenance work to stop the paper transport operation and recover the transport belt from the leak state. Since the paper transport operation cannot be performed, inconvenience may occur in the case of paper transport that requires urgent.
The present invention has been made in view of the above problems, and can respond to a urgent user's paper transport request by allowing a paper transport operation to continue safely even when a leak occurs on the transport belt. The purpose is to be able to.

In order to achieve the above object, the present invention comprises a high voltage applying means for applying a high voltage to the endless conveying belt surface to charge the conveying belt, and the conveying belt surface charged by the high voltage applying means is provided on the surface of the conveying belt. In the paper transport device that sucks the paper and transports the paper,
A leak detecting means for detecting a leak on the surface of the conveyor belt; a leak position detecting means for detecting a leak position of the leak detected by the leak detecting means on the conveyor belt; and when the leak detecting means detects a leak, the leak High voltage application stopping means for stopping application of high voltage by the high voltage applying means to the leak position detected by the position detecting means is provided.

The high voltage applying means may be a means capable of independently applying and stopping a high voltage to at least two or more non-overlapping charged regions on the surface of the conveyor belt.
In any one of the above-described paper transport apparatuses, when the area of the leak portion where the leak detected by the leak position detection unit exceeds a preset allowable area, the application of the high voltage by the high voltage application unit is completely stopped. It is preferable to provide a high voltage application complete stopping means.
Also provided is an image forming apparatus provided with any one of the above-mentioned paper transport devices, which forms an image by discharging liquid droplets from a liquid droplet discharge head onto the paper transported by the paper transport device. .

  According to the present invention, when a leak occurs on the surface of the conveyor belt, the application of a high voltage to the leak position where the leak is detected is stopped, so that the leak occurs in a state close to a short circuit. Can prevent danger. Then, since the high voltage is applied to the portions other than the portion where the leakage on the surface of the conveyance belt is charged, the sheet conveyance operation can be safely continued by adsorbing the sheet to the belt surface.

The best mode for carrying out the present invention will be described below with reference to the drawings.
[Example 1]
FIG. 1 is a schematic configuration diagram showing the configuration of Embodiment 1 of a paper transport apparatus according to the present invention, and FIG. 2 is a schematic configuration diagram showing an ink jet recording apparatus which is an image forming apparatus equipped with the paper transport apparatus.
A sheet conveying apparatus 10 shown in FIG. 1 includes an AC high voltage output unit 51 that is a high voltage applying unit that applies a high voltage to the surface (outer surface) of an endless conveying belt 21 to charge the conveying belt 21. The AC high voltage output unit 51 is a device that transports the paper by attracting the paper to the surface of the transport belt 21 charged by application of a high voltage.

In addition, the paper transport device 10 detects a leak position on the transport belt 21 of a current monitor circuit 52 that functions as a leak detection unit that detects a leak on the surface of the transport belt 21, and the current monitor circuit 52. And a main control unit 73 (also see FIG. 7) functioning as leak position detecting means. In the first embodiment, when the current control circuit 52 detects a leak, the main controller 73 stops the application of a high voltage by the AC high voltage output unit 51 to the leak position detected by the leak position detection means. It also functions as a voltage application stop means.
A detailed description of the high voltage application control performed by the main control unit 73 will be given later. The AC high voltage output unit 51 and the current monitor circuit 52 constitute a high voltage power supply 50.

The sheet conveying apparatus 10 is provided in, for example, an ink jet recording apparatus that is an image forming apparatus shown in FIG.
This inkjet recording apparatus is a recording apparatus that forms an image by ejecting droplets from a recording head 5 that is a droplet ejection head onto a sheet P fed from a sheet feeding unit 11 and conveyed by a sheet conveying apparatus 10. The carriage 3 is held movably in the main scanning direction (front and back in FIG. 2) by the main guide rod 1 and the secondary guide rod 2 which are guide members horizontally mounted on left and right side plates (not shown). 3 is moved and scanned in the direction of arrow A via the timing belt by the main scanning motor 4 shown in FIG.

The carriage 3 includes the above-described recording head 5 including four inkjet heads 5a to 5d that eject ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk). A plurality of ink ejection openings are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.
As the ink-jet head constituting the recording head 5, for example, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that utilizes a phase change caused by liquid film boiling using an electrothermal transducer such as a heating resistor, a metal phase change caused by a temperature change It is possible to use a shape memory alloy actuator that uses an electrostatic force, an electrostatic actuator that uses an electrostatic force, or the like as an energy generating means for ejecting ink.

Further, as shown in FIG. 2, the carriage 3 is mounted with replaceable sub tanks 7 for each color for supplying ink of each color to the recording head 5. Ink is supplied to the sub tank 7 from a main tank (ink cartridge) (not shown) via an ink supply tube 6.
The paper feeding unit 11 includes a half-moon-shaped paper feeding roller 13 that separates and feeds the paper P stacked thereon one by one, and a separation pad 14 made of a material having a large friction coefficient and disposed opposite to the paper feeding roller 13. The separation pad 14 is urged by a spring 9 toward the sheet feeding roller 13 side.

The paper P fed from the paper feeding unit 11 is transported to the lower part of the recording head 5 by the paper transport device 10 described above. The conveyance of the paper P by the paper conveyance device 10 is performed by rotating the paper P in the direction indicated by the arrow B in FIG.
When the paper P fed from the paper feeding unit 11 is transported to the paper transport device 10, the paper P is guided by the guide 15 and transported between the paper pressing roller 22 and the transport belt 21. It is transported substantially vertically upward by the transport force of the sheet pressing roller 22 and the transport belt 21, is turned approximately 90 ° by the transport guide 23, and is sent onto the transport belt 21.
A leading end roller 25 is provided on the entrance side of the conveyor belt 21 in a state of being pressed against the outer surface of the conveyor belt 21.

The conveyor belt 21 is an endless or joined belt (these are referred to as “endless shape”), and is stretched between the conveyor roller 27 and a tension roller 28 to which tension is applied. 3), the conveying roller 27 is rotationally driven to move around in the direction indicated by the arrow B in FIG.
The surface of the conveyor belt 21 is charged by the high voltage power supply 50 as described above. The charging is applied to the charging roller 26 disposed opposite the conveyor roller 27 with the conveyor belt 21 interposed therebetween. To apply a high voltage.

  The charging roller 26 contacts the surface layer of the conveyor belt 21 and rotates following the rotation of the conveyor belt 21 in the direction indicated by the arrow B. The charging roller 26 applies, for example, 2.5 N to each end of the roller shaft as a pressing force. Further, the conveying roller 27 also serves as an earth roller, and is disposed in contact with the middle resistance layer constituting the inner layer of the conveying belt 21 and is grounded via a ground line (FIG. 1).

As shown in FIG. 5, the transport belt 21 has a surface layer 21a that forms a sheet adsorbing surface formed of a pure resin material having a thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material. It has a back layer (medium resistance layer, earth layer) 21b in which the resistance is controlled by carbon.
The thickness of the surface layer (insulating layer) 21a of the conveyor belt 21 affects the dielectric constant. As the thickness increases, the capacitance decreases, and the amount of charge on the belt when charged is reduced. 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, it is generated on the belt by an actual machine. The electrostatic attraction force can be further improved by reducing the layer thickness as much as possible within a range in which the layer thickness does not become zero even by scratches.

The thickness of the back layer (medium resistance layer, ground 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. It becomes 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.
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.
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.
The ink jet recording apparatus shown in FIG. 2 further includes a separation unit 41 for separating the paper from the conveyor belt 21 as a paper discharge unit for discharging the paper recorded by the recording head 5, and a paper to be discharged. And a paper discharge tray 42 for stocking.

  By the way, as described with reference to FIG. 1, the sheet conveying apparatus 10 included in the ink jet recording apparatus includes a current monitoring circuit 52 that detects a leak on the surface of the conveying belt 21, and a conveying belt that leaks detected by the current monitoring circuit 52. The AC high voltage output unit 51 applies a high voltage to the leak position detected by the leak position detecting means when the current monitor circuit 52 detects a leak. And a main controller 73 that also functions as a leak position detecting means for stopping the operation.

The AC high voltage output unit 51 of the high voltage power supply 50 applies an AC high voltage to the roller shaft 26 a of the charging roller 26 to charge the transport belt 21.
The current monitor circuit 52 is a means for detecting a leak when the AC high voltage output unit 51 charges the conveying belt 21. When a high voltage is applied from the AC high voltage output unit 51 to the charging roller 26, the AC monitor voltage 52 This is a circuit for monitoring the current flowing from the high voltage output unit 51 through the closed circuit represented by the charging roller 26, the conveyance belt 21, the conveyance roller 27, and the current monitor circuit 52.
The current monitor circuit 52 outputs a leak detection signal when the current value increases because a current value increases when a leak occurs when a current flows through the closed circuit.

  For example, when ink adheres to the conveyor belt 21, the impedance decreases at the ink adhering portion, and the current flowing through the closed circuit increases. Further, even when the surface of the conveyor belt 21 is damaged, the current flowing through the closed circuit increases due to a decrease in the impedance of the damaged belt. Further, the current flowing in the closed circuit may be increased by paper dust or the like adhering to the surface of the conveyor belt 21.

Therefore, the current monitor circuit 52 is configured to detect both positive and negative currents for the AC high voltage using an electronic circuit such as a transistor, a resistor, and PWMIC.
As will be described in detail later, the AC high voltage output unit 51 applies an AC voltage (or a bipolar pulse voltage) to the transport belt 21 via the charging roller 26, and has positive polarity on the transport belt 21. By applying negative charge alternately with respect to the moving direction of the belt, a stable attracting force can be obtained by electrostatic force (FIG. 6).
Therefore, when the AC high voltage is applied to the conveyor belt 21 to detect the leak, the leak can be overlooked in the configuration in which the leak can be detected only with either the positive polarity or the negative polarity. According to the first embodiment, positive and negative leaks can be reliably detected.

Next, a control system of the ink jet recording apparatus will be described with reference to FIG.
This ink jet recording apparatus 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 for driving the recording head 5 (ink jet head)). IC) 82) and the like.
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 5 and I / Fs 78 and 79 are provided.

The main control unit 73 includes an output from an encoder 34 composed of a slit plate 32 and a photosensor 33 fixed to a shaft 27a of a conveying roller 27 that is rotationally driven by a sub-scanning motor 31 shown in FIG. Inputs signals from sensors and switches.
In this ink jet recording apparatus, since the ROM 75 stores in advance how many counts the encoder 34 counts when the conveyor belt 21 makes one revolution (one rotation), the main controller 73 counts the count value of the encoder 34. The position of the transport belt 21 in the rotational direction can always be known.

Therefore, 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 interface (I / F) 79 when conveying the paper. A signal is transmitted, and at that time, a leak detection signal from the current monitor circuit 52 of the high-voltage power supply 50 is monitored.
When the main control unit 73 detects a leak detection signal, the encoder pulse count value when the leak detection signal is detected is associated with the main control unit 73 at the same time. Thereby, the position in the belt rotation direction of the leak portion generated on the transport belt 21 can be determined. Then, information on the position of the leak occurrence position in the belt rotation direction is stored in the RAM 74.

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 from the stored analysis result Using the font data stored in the ROM 75, dot pattern data for outputting an image is generated and 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.
Then, when the dot pattern data corresponding to one row of the recording head 5 is obtained, 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.

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. A waveform generation circuit including a converter, an amplifier, and the like are included.
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 Are selectively applied to the recording head 5.

The ink jet recording apparatus shown in FIG. 2 separates and feeds the paper P one by one from the paper feeding unit 11, and the paper P is guided by the guide 15 and conveyed between the conveying belt 21 and the paper pressing roller 22. The direction is changed by the conveyance guide 23 and fed between the leading end roller 25 and the conveyance belt 21.
At this time, the main controller 73 applies a positive output and a negative output to the charging roller 26 from the high-voltage power supply 50 alternately, that is, an alternating voltage (here, AC voltage) is applied. As a result, as shown in FIG. 6, the surface of the transport belt 21 (insulating layer 21 a described with reference to FIG. 5) is charged to a strip-shaped voltage pattern (this is referred to as “charging voltage pattern”) 91 with alternating polarity. The

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.
In this way, the sheet is fed onto the conveying belt 21 that is alternately charged positively and negatively, so that the sheet is attracted to the conveying belt 21 by an electrostatic force. Accordingly, the paper is stopped by conveying a predetermined amount of paper by the circular movement of the conveyor belt 21 and driving the recording head 5 according to the image signal while moving the carriage 3 shown in FIG. Ink droplets are ejected to record one line.
When the recording for one line is completed, the conveyance belt 21 is driven to convey a predetermined amount of paper on the belt, and then the next line is recorded. When a recording end signal or a signal that the trailing edge of the paper reaches the recording area is received, the recording operation is finished and the paper is discharged onto the paper discharge tray 42.

In this ink jet recording apparatus, a recovery device for recovering the ejection failure of the recording head 5 is disposed at a position outside the recording area on one end side in the moving direction of the carriage 3, and this recovery device is in a standby state. The recording head 5 is capped by the capping means, and the nozzle portion is kept in a wet state, thereby preventing ejection failure due to ink drying.
Further, by ejecting ink droplets that are not related to recording even during recording or the like, the ink viscosity of all the ejection ports is made constant and stable ejection performance is maintained.

  Further, in the case where an ejection failure occurs, this ink jet recording apparatus seals the nozzle of the recording head 5 with a capping unit, sucks out bubbles and the like from the nozzle with a suction unit through a tube, and adheres to the nozzle surface. The dust and the like are removed by the cleaning means, and processing for recovering the ejection failure is performed.

By the way, the main control unit 73 functioning as the high voltage application stopping unit shown in FIG. 1 is a leak position detection unit (also serving as the main control unit 73) when the current monitor circuit 52 detects a leak as described above. The control for stopping the application of the high voltage by the AC high voltage output unit 51 to the leak position detected by (1) is explained.
Therefore, the high voltage application stop control to the leak position on the conveyor belt 21 performed by the main control unit 73 will be described in detail.

  As described above, when the conveyor belt 21 rotates, the encoder 34 shown in FIG. 3 and the like counts encoder pulses, and when the leak position on the conveyor belt 21 is detected by the current monitor circuit 52 at that time, The main control unit 73 in FIG. 1 recognizes the encoder pulse value corresponding to the leak position. Then, control is performed so as to stop application of high voltage to the charging roller 26 by the AC high voltage output unit 51 of the high voltage power supply 50.

For example, when a leak is detected at the leak position Lp on the transport belt 21 shown in FIG. 6, the entire range of the length L in the moving direction of the transport belt 21 in the region where the leak has occurred is defined as the non-charge region NC. Application of a high voltage to the non-charged area NC is stopped. Then, a high voltage is applied to the area other than the non-charged area NC to make the area charged normally as shown in FIG.
In order to stop the application of the high voltage, for example, in the first embodiment, the main control unit 73 performs control so as to cut off the current supply to the transformer inside the high-voltage power supply 50. You may make it carry out by interrupting | blocking the output high voltage using relays, such as a mechanical relay.

As described above, in this ink jet recording apparatus, the region where the leak occurs on the conveyance belt 21 is the non-charged region NC to which a high voltage is not applied, and a high voltage is applied to the other regions to form a normal charged region. Therefore, even if a leak occurs on the conveyor belt 21, it is possible to prevent the danger that the high voltage output becomes close to a short-circuit state at that portion.
Since the non-charged area NC becomes an uncharged area, the paper cannot be adsorbed on the transport belt 21 due to static electricity in that portion, but there are few areas where the electrostatic force does not work. It is possible to continue the conveyance by sucking the sheet onto the conveyance belt 21 without hindering the conveyance.

Although depending on the size of the area in which the leak has occurred, the area in which the leak has occurred becomes an area where the sheet cannot be sucked as described above, so that the suction force of the sheet onto the transport belt 21 is reduced. It is inevitable to do. Therefore, it is not preferable to continue the paper transporting operation in a state where the non-charged area NC is detected because the jam rate increases. Therefore, the continuation of the paper transporting operation is a paper that requires the user's urgency. It is better to make it within the range to answer the transport request.
Then, in order to inform the user that the sheet conveyance operation is continued in a state where the non-charged area NC is detected, for example, the main controller 73 shown in FIG. The processing apparatus may be configured to display a warning for prompting maintenance of the conveyor belt 21.

[Example 2]
FIG. 8 is a schematic structural view similar to FIG. 1 showing Embodiment 2 of the sheet conveying apparatus included in the image forming apparatus according to the present invention, and portions corresponding to those in FIG.
The sheet conveying apparatus according to the second embodiment is higher than the sheet conveying apparatus according to the first embodiment by a high voltage from the AC high voltage output unit 51 of the high-voltage power supply 50 earlier by a preset encoder pulse count value (safe stop count value). The only difference is that the main control unit 73 'controls the output to be stopped.
The main control unit 73 ′ has the same configuration as that of the main control unit 73 described with reference to FIGS. Further, as described above, the ink jet recording apparatus which is the image forming apparatus according to the second embodiment is different from the sheet conveying apparatus according to the first embodiment only in the control contents performed by the main control unit 73 '. Since the configuration of is the same as that described in FIG.

In the case of the sheet conveying apparatus of the first embodiment described above, the main control unit 73 described with reference to FIGS. 1 and 7 commands to stop the high voltage output (application) to the charging roller 26 by the AC high voltage output unit 51. It takes several m to several tens of msec until the high voltage that has already been output falls to a safe voltage value.
Therefore, even if a command for stopping the high voltage application at the pinpoint is issued from the main control unit 73 to the leak occurrence position of the conveyor belt 21, the high voltage is continuously applied to the leak occurrence position for several m to several tens of msec. End up.

In view of this, the sheet conveying apparatus according to the second embodiment has a preset encoder pulse count value as described above (a safe stop count value corresponding to several m to several tens of msec that is required until the high voltage drops to a safe voltage value). 8), the main control unit 73 'shown in FIG. 8 performs control so that the high voltage output from the AC high voltage output unit 51 of the high voltage power supply 50 is stopped.
The safe stop count value is, for example, 3 msec until the conveyor belt 21 moves by 10 μm by one encoder pulse output from the encoder 34 and the high voltage applied to the conveyor belt 21 decreases to a safe level. If the maximum moving speed of the conveyor belt 21 is 300 mm / sec,
3 m (sec) × 300 m (m) / 10 μ (m) = 90, and the safe stop count value is 90 counts.

FIG. 9 is a flowchart showing a charging operation process performed by the control system (main control unit) of the sheet conveying apparatus according to the second embodiment.
The main control unit 73 ′ of the paper transport device starts the charging operation process shown in FIG. 9 at a predetermined timing.
In the first step, it is determined whether or not a leak has occurred based on a leak detection signal sent from the current monitor circuit 52. Therefore, if no leak occurs, monitoring is continued until the leak occurs, and if it is determined that the leak has occurred, the process proceeds to the next step.
In this case, information indicating the position in the belt rotation direction is stored in a RAM (similar to the RAM 74 described in FIG. 7) by associating the leak occurrence position on the conveyor belt 21 with the encoder pulse count value.

In the next step, the output of the high voltage from the high voltage output unit 51 is stopped at the timing of the encoder pulse count value corresponding to the leak occurrence position + the preset encoder pulse count value (the above-described safe stop count value). .
That is, the output of the high voltage from the AC high voltage output unit 51 is stopped at a timing that is advanced by a preset encoder pulse count value (safety stop count value) with respect to the leak occurrence location, and other than the leak occurrence position Continues the charging operation and ends the processing of this routine.

As described above, according to this paper transport device, the application of the high voltage is stopped earlier than the leak occurrence position on the transport belt 21 by the safe stop count value, so that the high voltage is close to a short circuit at the leak occurrence position. It can be prevented from becoming a state.
On the other hand, when the application stop timing of the high voltage is advanced by the safe stop count value as described above, the safe stop count value is a predetermined count value. May change, the high voltage may not be applied to the region of the chargeable belt surface that is not leaking. Therefore, in this case, the uncharged area that is not charged is unnecessarily widened, and the suction force of the sheet to the transport belt 21 is reduced. Therefore, it is necessary to pay attention to this point in the second embodiment.

Example 3
FIG. 10 is a bottom view of the sheet conveying apparatus included in the image forming apparatus according to the third embodiment of the present invention. FIG. 11 is a plan view of the sheet conveying apparatus. Parts corresponding to those in FIGS. Is attached.
The sheet conveying apparatus of the third embodiment is independent of the three charged areas that do not overlap each other on the surface of the conveying belt 21 (the number can be changed if it is two or more), compared to the sheet conveying apparatus of the first embodiment. The difference is that a high voltage can be applied and stopped.

That is, the paper transport device includes a high-voltage power supply 50 ′ having an AC high-voltage output unit 51 and a high-voltage blocking unit 60 that blocks application of a high voltage from the AC high-voltage output unit 51. In the third embodiment, the high voltage power supply 50 ′ and the high voltage cut-off unit 60 constitute a high voltage applying unit.
In addition, the ink jet recording apparatus which is an image forming apparatus according to the third embodiment is configured such that a high voltage can be applied and stopped independently to each of the above-described three non-overlapping charged regions, and the high voltage applying unit is a high voltage power source. Since only the point constituted by 50 'and the high voltage cut-off section 60 is different from the first embodiment, the entire inkjet recording apparatus is not shown.

  As shown in FIG. 10, the sheet conveying device includes three charging rollers 26 </ b> A at a position facing the conveying roller 27 on the lower surface of the conveying belt 21 that is rotatably laid between the conveying roller 27 and the tension roller 28. , 26B, and 26C are provided in contact with each other. As a result, the charging roller 26A is charged with a high voltage from the AC high voltage output unit 51 via the output current monitor circuit 52A, thereby charging the region 21A of the transport belt 21.

The charging roller 26B also charges a region 21B of the conveyor belt 21 when a high voltage is applied thereto from the AC high voltage output unit 51 via the output current monitor circuit 52B. Further, the charging roller 26 </ b> C also charges the region 21 </ b> C portion of the transport belt 21 by applying a high voltage to the charging roller 26 </ b> C via the output current monitor circuit 52 </ b> C.
In this way, the three regions 21A to 21C are charged by applying a high voltage to each of the three regions 21A to 21C, and the application of the high voltage is also stopped independently. In this way, each charging area on the surface of the conveyor belt 21 is divided into three.

  The high voltage cut-off unit 60 selectively cuts off and connects the high voltage charging rollers 26A, 26B, and 26C output from the transformer of the AC high voltage output unit 51 by relays 61A, 61B, and 61C such as mechanical relays. Is. It should be noted that even if a relay other than this relay is used, any means may be used as long as it can selectively block and connect the charging rollers 26A, 26B, and 26C. .

Further, the arrangement intervals of the charging rollers 26A, 26B, and 26C are set so that unintended discharge between adjacent charging rollers does not occur, so that the rubber portions and the rubber portions of the adjacent charging rollers 26A and 26B are adjacent to each other. The rubber portions and the rubber portions of the matching charging rollers 26B and 26C are preferably separated by at least 2 mm.
Further, it is preferable that the charging rollers 26A and 26B adjacent to each other and the rubber portions and the shaft portions of the charging rollers 26B and 26C be separated by at least 2 mm.

Also in this embodiment, the current monitor circuit 52 detects the leak on the conveyor belt 21. Thereby, it is detected where the leak occurs in the paper conveyance direction (the arrow direction in FIG. 10). The detected leak occurrence position in the sheet conveyance direction is stored in the control unit in association with the encoder pulse.
At that time, the current is also monitored by the three output current monitor circuits 52A, 52B and 52C which monitor the high voltage output current. Therefore, if a leak occurs in any of the charging areas created by the charging rollers 26A, 26B, and 26C, the current increases correspondingly in any of the three output current monitoring circuits 52A, 52B, and 52C. It can be determined where the leak occurred in the three charged regions. That is, it can be seen whether a leak has occurred in any of the three regions 21A to 21C.
For example, when the current monitor circuit 52 detects a leak and at that time the output current monitor circuit 52C detects an increase in the output current, the relay 61C is set in accordance with the length of the leak during the next rotation of the conveyor belt 21. And cut off. In this way, the high voltage application stop control at the pinpoint as shown in FIG. 11 can be performed.

As described above, according to this paper transport apparatus, for example, as shown in FIG. 11, when a leaked portion is formed at the illustrated leak position Lp in the region 21 </ b> C among the three regions on the transport belt 21. The voltage cut-off unit 60 (FIG. 10) cuts off the application of a high voltage to the charging roller 26C at a timing when the portion having the leak position Lp is set as the non-charged region NC.
Accordingly, the non-charged area NC can be limited only to the range of the width W in the main scanning direction, so that the non-charged area can be made smaller than that in the first embodiment described with reference to FIG. 1/3). As a result, even if a part of the conveyor belt has a leak, it is possible to reduce the decrease in the adsorption force (electrostatic force) of the entire conveyance belt to the paper. It is possible to reduce the occurrence rate and perform a more stable paper transport operation.
10 and 11 show an example in which there is one conveyance belt, the conveyance belts may be provided in three portions corresponding to the regions 21A, 21B, and 21C, respectively.

Example 4
FIG. 12 is a flowchart showing a high voltage application process performed by the control system of the sheet conveying apparatus included in the image forming apparatus according to the fourth embodiment of the present invention.
The paper conveying apparatus of the fourth embodiment is different from the paper conveying apparatus of the first embodiment only in the high voltage application process performed by the control system, and the configuration of the mechanical part of each unit is the same as that of the first embodiment. Therefore, illustration of the configuration is omitted, and description will be made using the reference numerals used in the first embodiment as necessary.
Further, the structure of the mechanical part of the ink jet recording apparatus, which is an image forming apparatus having the paper transport apparatus, is the same as that described with reference to FIG.

In this paper conveying apparatus, when the area of the leaked portion on the conveying belt 21 where the leakage detected by the current monitor circuit (leak position detecting means) 52 exceeds a preset allowable area, an AC high voltage output unit (high The high voltage application complete stop means for completely stopping the application of the high voltage by the voltage application means) 51 is provided. In the fourth embodiment, as the high voltage application complete stop means, the main control unit (configuration is the main control section of FIG. 7). The same as the control unit 73) functions.
Hereinafter, the high voltage application process performed by the main control unit will be described with reference to FIG.
When the high voltage application process of FIG. 12 is started, it is first determined whether or not there is a leaking portion on the conveyor belt 21, and if no leak has occurred, the occurrence of the leak is detected as it is. If monitoring is continued and it is determined that a leak has occurred (YES), the process proceeds to the next step.

In this case, the leak occurrence position on the conveyor belt 21 is stored in the RAM, and the encoder pulse described in FIG. 9 is also stored in the RAM as information corresponding to the area of the leak portion. Then, in the next step, the application of the high voltage to the portion where the leak has occurred is stopped, and the charging operation is continued by applying the high voltage except for the leak occurrence position.
In the next step, it is determined again whether or not there is a leak occurring on the conveyor belt 21, and if no new leak is detected there, the process returns to the previous step. The application of the high voltage by the AC high voltage output unit 51 to the portion where the leak that has been stored so far has been stopped is repeated each time the conveyor belt 21 rotates.

Then, when it is determined that a leak has occurred at a new location on the conveyor belt 21, in the next step, an encoder pulse that becomes information corresponding to the area of the leak portion described above (the application of a high voltage due to the occurrence of the leak) is performed. (Corresponding to the area where the current is stopped) is integrated, and it is determined whether or not the total area of the integrated leak portion has become an integrated value of encoder pulses having a value exceeding a preset allowable value (allowable area).
The permissible value corresponding to the preset permissible area is set to a value at which, for example, the rate of occurrence of jam when the paper is transported by the transport belt 21 is 1% or more. The encoder pulse integrated value of the non-charged area corresponding to the allowable area at that time is obtained by experiment.

  If the total area of the accumulated leak portion does not exceed a permissible area (allowable value), the suction force of the transport belt 21 is in a range in which the jam occurrence rate is permissible. Repeatedly stop the application of high voltage to the part where the leak occurred. Further, if it is determined that the total area of the accumulated leak portion is greater than or equal to the allowable area (YES determination), the process proceeds to the next step from the AC high voltage output unit 51 of the high-voltage power supply 50 to the conveyor belt (accurately). In this case, control is performed to completely stop the application of a high voltage to the device (via a charging roller), and this processing is terminated.

As described above, the sheet conveying apparatus according to the fourth exemplary embodiment applies the high voltage from the AC high voltage output unit 51 when the area of the leaked portion on the conveying belt 21 where the leakage occurs exceeds a preset allowable area. Stop completely.
As a result, when the area of the leaked portion generated on the transport belt 21 is gradually increased, the suction performance of the transport belt 21 to the paper is correspondingly reduced, so that the paper transport performance is lowered and jammed. However, when the area of the leaked portion exceeds the preset allowable area, the application of the high voltage to the conveyor belt 21 is completely stopped, so that jamming can be suppressed within an allowable range. it can. Therefore, the jam does not occur so much that the user exceeds the allowable limit, and the user can be prevented from feeling unpleasant.

The high voltage application stop control may be performed by cutting off the current supply to the transformer provided in the high voltage power supply 50, or the high voltage output from the transformer may be a mechanical relay. Alternatively, it may be performed by blocking with a relay such as.
As described above, in the case of the sheet conveying apparatus according to the fourth embodiment, since the application of the high voltage to the conveying belt 21 is completely stopped when the area of the leaked portion exceeds the preset allowable area, It is possible to quickly enter the previous stage where maintenance of the conveyor belt 21 is performed.

  The present invention can be widely applied to a sheet conveying apparatus that adsorbs and conveys paper onto the surface of the conveying belt by electrostatic force, and is particularly useful when used in an image forming apparatus such as an ink jet recording apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram illustrating a configuration of a first embodiment of a paper conveying apparatus according to the present invention. FIG. 2 is a schematic configuration diagram illustrating an ink jet recording apparatus that is an image forming apparatus that similarly includes the sheet conveying device. It is a top view which shows the inkjet recording device partially similarly. FIG. 3 is a right side view partially showing the inkjet recording apparatus. It is the schematic which showed the belt part in the cross section in order to demonstrate the conveyance belt of 2 layer structure. It is a top view which shows the state electrically charged by the strip | belt-shaped voltage pattern of the polarity which the surface of the conveyance belt alternates similarly.

FIG. 3 is a block diagram showing a control system of the ink jet recording apparatus of FIG. 2 and its related configuration. FIG. 3 is a schematic configuration diagram similar to FIG. 1 illustrating a second embodiment of a sheet conveying device included in the image forming apparatus according to the present invention. FIG. 10 is a flowchart illustrating a charging operation process performed by a control system of the sheet conveying apparatus according to the second exemplary embodiment. FIG. 6 is a bottom view of a sheet conveying device included in an image forming apparatus according to Embodiment 3 of the present invention. FIG. 9 is a plan view of the sheet conveying apparatus according to the third embodiment. It is a flowchart which shows the high voltage application process which the control system of the paper conveying apparatus which the image forming apparatus of Example 4 of this invention has has.

Explanation of symbols

10: paper transport device, 21: transport belt, 50, 50 ': high voltage power supply, 51: AC high voltage output unit (high voltage application unit), 52: current monitor circuit (leak detection unit), 73: main control unit

Claims (4)

A sheet having high voltage applying means for applying a high voltage to the endless conveying belt surface to charge the conveying belt, and conveying the sheet by adsorbing the sheet to the conveying belt surface charged by the high voltage applying means In the transport device,
Leak detection means for detecting a leak on the conveyor belt surface, a leak position detection means for detecting a leak position on the conveyor belt of the leak detected by the leak detection means, and when the leak detection means detects a leak, A sheet conveying apparatus, comprising: a high voltage application stopping unit that stops application of a high voltage by the high voltage applying unit at a leak position detected by the leak position detecting unit.   2. The sheet transport according to claim 1, wherein the high voltage applying unit is a unit capable of applying and stopping a high voltage independently to at least two or more non-overlapping charged regions on the surface of the transport belt. apparatus.   3. The paper conveying apparatus according to claim 1, wherein when the area of the leak portion where the leak is detected detected by the leak position detection unit exceeds a preset allowable area, a high voltage is applied by the high voltage application unit. A sheet conveying apparatus comprising high voltage application complete stopping means for completely stopping the operation. An image forming apparatus comprising the paper transport device according to claim 1, wherein an image is formed by ejecting liquid droplets from a liquid droplet ejection head onto the paper transported by the paper transport device. An image forming apparatus.

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