JP4476248B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a static eliminating device for recording paper and an image forming apparatus including the same.

  A recording sheet that is fed and conveyed in the image forming apparatus and onto which the toner image is transferred is electrostatically charged when discharged from the sheet discharge unit of the image forming apparatus. The first cause of the charging of the recording paper is that the recording paper is rubbed against a plurality of rollers, paper guides and the like disposed in the paper transport path, and is charged with static electricity. Second, in the transfer step of transferring the toner onto the paper, the electric field for transfer charges the recording paper. The recording sheet discharged from the discharge unit is then dropped by its own weight and is deposited on the discharge tray.

  If the recording paper is strongly charged, the recording paper does not accumulate on the paper discharge tray due to the action of static electricity. That is, good stacking properties cannot be obtained. In order to reduce this inconvenience, the recording paper is neutralized at the paper discharge unit. Although there is a method of grounding a roller, a paper guide, or the like that contacts the recording paper, a method of more positively removing electricity by bringing a brush-like conductive member into contact with the recording paper is widely used. (For example, refer to Patent Document 1).

In recent years, an electrophotographic image forming apparatus often uses a belt transfer type transfer mechanism (see, for example, Patent Document 2). A belt transfer type transfer mechanism (belt transfer mechanism) transfers a toner image while electrostatically attracting and transporting a recording sheet onto a transfer belt having a predetermined specific resistance value. In this way, there is an advantage that “transfer deviation” hardly occurs in the transfer process. Further, it is easy to peel off the transferred paper from the photosensitive drum. The belt transfer method is particularly effective for high-resolution printing, color image printing, and high-speed printing.
JP-A-10-302993 JP 2001-22199 A

  However, the belt transfer mechanism tends to charge the discharged recording paper more strongly than other types of transfer mechanisms. This is because the recording paper is electrostatically attracted and conveyed. As described above, if the recording paper is strongly charged at the time of discharging, the recording paper deposited on the paper discharge tray is not good in stacking property. Also, if a strongly charged recording sheet is used as a copy document and fed using an automatic document reader (ADF), JAM may occur in the ADF document transport path or a feeding failure may occur.

  Therefore, in particular, in an image forming apparatus having a belt transfer mechanism, it is desired to sufficiently lower the charging potential of the recording paper before passing through the transfer process and reaching the discharge section. When the recording paper is conveyed on the transfer belt, it is charged to a potential of several hundred to several hundreds of volts. The charge amount of the recording paper discharged from the image forming apparatus varies depending on the material of the paper and environmental conditions, particularly humidity. The charging potential of the discharged recording paper and the stacking property with respect to it are as shown in Table 1 below.

  In order to deposit recording sheets discharged to the discharge tray in an orderly manner, the charging potential of the discharged recording sheets must be less than 1000V. Therefore, it is preferable to positively discharge the recording paper as early as possible before discharging. However, if the recording paper on which the unfixed toner is placed is discharged, the toner on the recording paper may scatter and cause a problem in image quality. Therefore, conventionally, it was considered that the recording paper had to be neutralized after fixing.

As the printing speed has been increased, it has been necessary to discharge the recording paper from an earlier point of time.
The present invention has been made in consideration of the above-described circumstances, and removes the charge on a recording sheet carrying an unfixed toner image without deteriorating the image quality of the toner image, so that it is good on the discharge tray. The present invention provides a method for obtaining stacking properties.

  The present invention provides a transfer unit that transfers a toner image from a photoreceptor to a recording sheet, a transfer belt that conveys the recording sheet to the transfer unit and passes through the transfer unit, and a predetermined portion between the photoreceptor and the transfer belt at the transfer unit. A transfer voltage application unit that applies a transfer voltage, a fixing unit that fixes a toner image on the recording paper that has passed through the transfer unit, and a recording unit that is disposed between the transfer unit and the fixing unit and is in contact with or close to the recording paper. There is provided an image forming apparatus comprising: a neutralizing member for neutralizing a sheet, wherein the neutralizing member is grounded via a resistor.

In the image forming apparatus of the present invention, since the neutralizing member is grounded via the resistor, the recording paper carrying the unfixed toner image is neutralized without deteriorating the image quality of the toner image, and is excellent on the discharge tray. Can be obtained.
The neutralizing member may be disposed in the vicinity of the downstream side of the region where the recording paper is separated from the transfer belt. In this way, since the recording sheet is conveyed to the fixing unit in a state where the charge is removed, there is less possibility of occurrence of problems such as a conveyance failure or a toner image disturbance due to rapid charge removal in the path to the fixing unit.

  A temperature / humidity sensor for detecting the ambient temperature and humidity level, a ground resistance storage unit for preliminarily storing a ground resistance value corresponding to the ambient temperature and humidity level, and the detected temperature and humidity level are stored. And a control unit that controls to switch the resistance value of the resistor based on the ground resistance value, and the resistor may be configured to switch the resistance value by the control unit. In this way, the resistance value of the static elimination path can be switched according to the ambient temperature and humidity, so that the toner image is distorted due to insufficient static elimination of the recording paper or conversely excessive static elimination. The trouble can be avoided.

  Alternatively, a temperature / humidity sensor that detects the stage of ambient temperature and humidity, a transfer voltage storage unit that previously stores a transfer voltage value corresponding to the stage of ambient temperature and humidity, and a grounding resistance value corresponding to each transfer voltage value Is transferred in advance based on the detected temperature and humidity level and the stored transfer voltage value, and the output transfer voltage value and the stored ground resistance value are stored. And a control unit that controls to switch the resistance value of the resistor based on the transfer voltage, the transfer voltage application unit is configured to switch the transfer voltage by the control unit, the resistor is controlled by the control unit The resistance value may be switched. In this way, the transfer voltage and the resistance value of the static elimination path can be switched according to the ambient temperature and humidity, so that a transfer failure occurs, the static elimination of the recording paper is insufficient, or conversely, It is possible to avoid a problem that the toner image is disturbed due to excessive charge removal.

  Alternatively, a paper type discriminating unit that discriminates the type of recording paper onto which the toner image is transferred, a grounding resistance storage unit that prestores a grounding resistance value corresponding to the type of recording paper, and the type of recording paper that has been discriminated. A control unit that controls to switch the resistance value further based on the stored ground resistance value may be further included, and the resistor may be configured to switch the resistance value by the control unit. In this way, the resistance value of the static elimination path can be switched according to the type of recording paper, so that the toner image is distorted due to insufficient static elimination of the recording paper or conversely excessive static elimination. Can be avoided.

  Alternatively, a paper type discriminating unit that discriminates the type of recording paper onto which the toner image is transferred, a transfer voltage storage unit that stores in advance a transfer voltage value corresponding to the type of recording paper, and a grounding resistance corresponding to each transfer voltage value A grounding resistance storage unit that stores values in advance, and switches and outputs a transfer voltage based on the determined type of recording paper and the stored transfer voltage value, and the output transfer voltage value and the stored ground resistance value And a control unit that controls the resistance value of the resistor to be switched based on the transfer voltage, the transfer voltage applying unit is configured to switch the transfer voltage by the control unit, and the resistor is controlled by the control unit. You may be comprised so that a value may be switched. In this way, the transfer voltage and the resistance value of the static elimination path can be switched according to the type of recording paper, so that a transfer failure occurs, the static elimination of the recording paper is insufficient, or conversely, the static electricity is suddenly eliminated. It is possible to avoid such a problem that the toner image is disturbed due to too much.

  In addition, a paper type selection unit that allows the user to select one type from the types of recording paper prepared in advance may be provided, and the paper type determination unit may use the selected type as the type of recording paper. In this way, the resistance value of the resistor is switched according to the type of the recording paper selected by the user, and stable neutralization of the recording paper can be realized.

  Alternatively, a paper type selection unit that allows the user to select one type from the types of recording paper prepared in advance, and a basis weight storage unit that stores in advance a basis weight that is a mass per unit area for each type of recording paper The paper type determination unit may acquire the basis weight of the recording paper based on the selected type and the stored basis weight, and the acquired basis weight may be the recording paper type. In this way, the resistance value of the resistor is switched based on the basis weight corresponding to the type of recording paper selected by the user, and stable neutralization of the recording paper can be realized.

  First, the inventors' knowledge will be described. As described above, in order to sufficiently lower the charged potential of the discharged recording paper, it is effective to neutralize the recording paper as early as possible after passing through the transfer section. However, if the recording paper on which the unfixed toner is placed is discharged, there is an adverse effect on the image such as toner scattering. This is presumed to be because the high potential recording paper is rapidly discharged. Therefore, the inventors have found that it is possible to discharge the sheet without adversely affecting the image when the discharging member is not directly grounded but grounded through some resistance. .

  However, the range of optimum conditions may be narrow in order to obtain a constant resistance for all environmental conditions and for all sheets. Therefore, the inventors also disclose a technique for changing the resistance value according to the environmental humidity and / or the type of sheet.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. The following description will provide a better understanding of the present invention. In addition, the following description is an illustration in all points, Comprising: It should be thought that it is not restrictive.

(Detailed configuration of transfer section)
Next, details of the transfer portion in the above-described image forming apparatus, particularly, the neutralizing apparatus of the present invention will be described.

  FIG. 1 is an explanatory diagram schematically showing a detailed configuration of a transfer section in the image forming apparatus according to the present invention. As shown in FIG. 1, a transfer belt driven roller 10b is disposed at the end of the transfer belt unit 10 on the registration roller 63 side. The registration roller 63 sends the sheet in the direction of the arrow D1. A predetermined voltage with respect to the ground potential is applied to the transfer belt driven roller 10b by a paper suction voltage application power source 10h. The transfer belt driven roller 10b is made of a conductive material. Accordingly, the transfer belt 10c that contacts the surface of the transfer belt driven roller 10b is also maintained at a potential corresponding to the voltage at that portion.

  Due to the potential, the sheet fed from the registration roller 63 is electrostatically attracted to the transfer belt 10c. The sheet passes through a nip portion between the elastic conductive roller 10e and the photosensitive drum 3 while being attracted to the transfer belt 10c. The photosensitive drum 3 rotates in the arrow D2 direction at substantially the same speed as the transfer belt 10c. An image of charged toner is formed on the surface of the photosensitive drum 3. A predetermined voltage (transfer voltage) is applied to the elastic conductive roller 10e with respect to the ground potential by a transfer voltage application power source 10g. On the other hand, the base of the photosensitive drum 3 is grounded. The toner image formed on the photosensitive drum 3 is transferred to the sheet by an electric field generated by a potential difference between the elastic conductive roller 10e and the substrate of the photosensitive drum 3.

  Thereafter, the sheet is conveyed on the transfer belt 10c in the arrow D3 direction. When the leading edge of the sheet reaches the vicinity of the transfer belt driving roller 10a, the sheet peels from the transfer belt 10c due to the relationship between the curvature of the transfer belt 10c and the stiffness of the sheet. The peeled sheet advances in the direction of arrow D4 while substantially maintaining its traveling direction. Thereafter, the sheet is guided by a paper guide B 62 disposed in front of the fixing unit 20 and passes through a nip portion between the heating roller 21 and the pressure roller 22.

FIG. 2 is an explanatory view showing, in an enlarged manner, a portion where the sheet peels from the transfer belt 10c in FIG.
A neutralizing member 65 is provided between the transfer belt driving roller 10a and the paper guide B62 so that the upper end of the sheet is in contact with the lower surface of the conveyed sheet. The static elimination member is grounded via a ground resistor 67. As the static eliminating member 65, a known static eliminating brush can be used. FIG. 3 is an explanatory view schematically showing the shape of the static elimination brush according to the embodiment of the present invention. The neutralizing brush 65 is formed by arranging a fibrous or thin needle-shaped conductive member (static neutralizing needle) 65a in a brush shape on a conductive sheet metal such as aluminum. The neutralizing brush is used to neutralize a sheet to be discharged by being disposed in a discharge unit of the image forming apparatus, or to neutralize a conveyed document by being disposed in a document discharge unit of an automatic document feeder. It is what. The neutralizing brush is preferably arranged in a region wider than the maximum sheet passing region in a direction orthogonal to the sheet conveying direction so that the entire region can be neutralized even when the widest sheet is conveyed.

The ground resistance 67 is preferably in a range of approximately 20 to 30 MΩ. As the resistance element, a resistor for a high voltage circuit can be used. The low power of the resistor may be about 0.25 W. As the high-voltage resistor, for example, a series of product number MHR_SA manufactured by Murata Manufacturing Co., Ltd. can be used.
In addition, a neutralization mechanism may be provided in the transfer unit, and a conventional neutralization brush may be provided in the paper discharge unit.

(Switching ground resistance)
The above-described embodiment is a case where the resistance value of the ground resistor 67 is constant. However, there are cases where it is better to change the resistance value according to the printing conditions in order to sufficiently neutralize the recording paper without adversely affecting the image quality under all use conditions. Table 2 is a table showing the static elimination results for four types of grounding resistance values when printing is performed in an ambient environment with different temperatures and humidity using the same type of recording paper. As can be seen from Table 2, if the ground resistance is too large, the recording paper is not sufficiently neutralized, and good stacking properties cannot be obtained (xx in the table). On the other hand, if the printing resistance is too small, toner scattering is conspicuous and the image quality deteriorates (x mark in the table). The range in which these conflicting elements are compatible is indicated by a circle in Table 2. As shown in Table 2, the lower the temperature and humidity, the lower the ground resistance value than the high temperature and humidity.

  Table 3 is a table showing the results of static elimination for four types of ground resistance values when papers having different masses per unit area (basis weight) are printed in an ambient environment of normal temperature and humidity. If the grounding resistance is too large, the recording paper is not sufficiently neutralized, and good stacking properties cannot be obtained (XX in the table). On the other hand, if the printing resistance is too small, toner scattering is conspicuous and the image quality deteriorates (x mark in the table). A recording paper having a small basis weight (light) preferably has a smaller ground resistance than a recording sheet having a large basis weight (heavy).

  For example, the ground resistance can be switched as follows. A plurality of high-voltage circuit metal film resistors having different resistance values are arranged on the circuit board, and the circuit is configured to switch the ground resistance using a high-voltage relay. As the high-voltage relay, for example, a series of product number S02DNA or S05LT manufactured by Kirovac can be used. In order to avoid leakage at high humidity, it is preferable to apply an insulating coating to the surface of the substrate pattern using an insulating varnish or the like.

  FIG. 5 is a block diagram showing an example of an image forming apparatus including a switchable grounding resistor according to the present invention. In the circuit of FIG. 5, the transfer belt unit 10 of the image forming apparatus 50 includes a static elimination brush 65, grounding resistors 67a to 67d, and high insulation relays 69a to 69c. The insulation relays 69a to 69c are each a make type in which relay contacts come into contact with each coil when energized. In parallel with the contacts of each relay, ground resistors 67a to 67c are connected. The ground resistors 67a to 67d are connected in series in a circuit, and their resistance values are 15 MΩ, 10 MΩ, 4.7 MΩ, and 2.7 MΩ, respectively. When the coils of the relays 69a to 69c are in a non-energized state, the static eliminating brush 65 is grounded via the ground resistors 67a to 67d. In this case, the value of the ground resistance is the largest. Hereinafter, when the coils of the relays 69a, 69b, and 69c are sequentially energized, the ground resistance becomes smaller with energization. As described above, the value of the ground resistance can be switched.

  The controller 71 controls energization of the coils of the relays 69a to 69c. In addition, the control unit 71 may control the operation of each unit of the image forming apparatus as will be described later. The control unit 71 can be composed of a microcomputer, a ROM that stores a control program executed by the microcomputer, a RAM, a nonvolatile memory, an input circuit, and an output circuit.

  A detection signal from a temperature / humidity sensor 73 that detects the ambient temperature and humidity around the image forming apparatus as a plurality of stages is input to the input circuit of the control unit 71.

  The image forming apparatus 50 also includes a display device 75a that displays the state of the image forming apparatus, and an operation panel unit 75 that includes operation keys for a user to input instructions to the image forming apparatus. For example, a dot matrix liquid crystal display panel is used as the display device 75a. Further, a tact key may be used as the operation key, or a touch panel may be provided on the upper surface of the liquid crystal display panel to function as the operation key.

  The control unit 71 controls display contents to be displayed on the display device 75a. In addition, the control unit 71 acquires a signal indicating that the operation key has been pressed through the input circuit. When the touch panel 75b is used as an operation key, the control unit 71 determines the content of the instruction according to the content displayed on the display device 75a and the pressed position of the touch panel 75b.

  Further, as will be described later, the image forming apparatus 50 includes a plurality of paper feed trays 8a to 8d, a large capacity paper feed cassette 8e, and a manual feed tray 8f that store recording paper and supply during printing. The sheet feeding trays 8a to 8d, the large-capacity sheet feeding cassette 8e, and the manual feed tray 8f are each provided with a non-volatile storage unit 77 that stores the types of recording sheets stored therein. As the nonvolatile storage unit 77, for example, a flash memory can be used. The type of each recording sheet can be selected by the user using the operation panel. Further, the basis weight corresponding to the type of each recording sheet is prepared as data in advance and stored in the ROM. The control unit 71 acquires each basis weight based on the type of the selected recording sheet and the data stored in the ROM.

As for the manual feed tray 8f, every time the user sets a recording sheet on the manual feed tray 8f, the user selects the type of the set recording sheet by using the operation panel 75. The control unit 71 acquires the basis weight of the recording paper set in the manual feed 8f based on the selected paper type and the data stored in the ROM. For example, the user who sets the recording paper in the manual feed tray selects and sets one of three types of recording paper as “plain paper”, “thick paper”, and “postcard”. When the set paper type is “plain paper”, the control unit 71 sets the basis weight of the recording paper to 85 g / m ² . If the set paper type is “thick paper”, the basis weight of the recording paper is set to 100 g / m ² . Alternatively, if the set paper type is “postcard”, the basis weight of the recording paper is set to 128 g / m ² .

  In the above description, the method in which the user selects the paper type using the operation panel unit has been described. For example, the paper type is displayed on a terminal connected to the image forming apparatus 50 via a network (not shown). May be selected. Such a method is known as designating the type of recording paper set in the paper feed unit of the printer on a host connected to the printer via a network.

  Here, based on the surrounding environmental temperature and environmental humidity, energization pattern data for turning on and off the energization of the coils of the relays 69a to 69c is prepared in advance and stored in the ROM together with the control program. The control unit 71 controls energization of the coils of the relays 69a to 69c based on the environmental temperature and the environmental humidity level detected by the temperature / humidity sensor 73 and the energization pattern stored in the ROM.

Further, energization pattern data for turning on or off energization of the coils of the relays 69a to 69c according to the type of recording paper is prepared in advance and stored in the ROM. Alternatively, energization pattern data corresponding to the basis weight may be prepared in advance. The control unit 71 controls energization of the coils of the relays 69a to 69c based on the type of recording paper acquired as described above and the energization pattern stored in the ROM. When energization pattern data corresponding to the basis weight is prepared, the control unit 71 first obtains the basis weight corresponding to the selected recording paper type. Then, an energization pattern is obtained from the calculated basis weight, and energization to the coils of the relays 69a to 69c is controlled.
Energization of the coils of the relays 69a to 69c is continuously performed from the start to the end of the printing process.

  Further, the control unit 71 may switch the ground resistance according to the transfer voltage output from the transfer voltage application power supply 10g, instead of directly switching the ground resistance based on the environmental temperature and the environmental humidity. In this case, the transfer voltage application power source 10 g is configured such that its output voltage can be switched by the control unit 71. In addition, transfer voltage data corresponding to the environmental temperature detected by the temperature / humidity sensor 73 and the stage of the environmental humidity is prepared in advance and stored in the ROM. Further, energization pattern data for turning on or off energization of the coils of the relays 69a to 69c in accordance with the transfer voltage is prepared in advance and stored in the ROM. The control unit 71 controls the transfer voltage output from the transfer voltage application power source 10g based on the environmental temperature and the environmental humidity level detected by the temperature / humidity sensor 73 and the transfer voltage stored in the ROM, and the transfer Based on the voltage and energization pattern data stored in the ROM, energization of the coils of the relays 69a to 69c is controlled.

  The optimum value of the transfer output voltage depends on the ambient temperature and humidity and the type of recording paper. Specifically, the lower the temperature and humidity, the lower the optimum voltage than the high temperature and humidity. Also, the smaller the basis weight, the lower the optimum voltage than the larger basis weight recording paper. Therefore, if the value of the ground resistance is controlled according to the transfer voltage, the value of the ground resistance is indirectly switched according to the detection result of the temperature / humidity sensor 73. In addition to the transfer voltage, the processing becomes simpler than the method of obtaining the ground resistance from the detection result of the temperature and humidity sensor 73. For example, when the transfer voltage is different between monochrome printing and color printing, this difference is also reflected in the ground resistance.

Alternatively, the controller 71 may switch the ground resistance according to the transfer voltage output from the transfer voltage application power source 10g, instead of directly switching the ground resistance depending on the type of recording paper. In this case, the transfer voltage application power source 10 g is configured such that its output voltage can be switched by the control unit 71. Further, transfer voltage data corresponding to the obtained paper type is prepared in advance and stored in the ROM. Further, energization pattern data for turning on or off energization of the coils of the relays 69a to 69c in accordance with the transfer voltage is prepared in advance and stored in the ROM. The control unit 71 controls the transfer voltage output from the transfer voltage application power source 10g based on the acquired paper type and the transfer voltage stored in the ROM, and also supplies the transfer voltage and the energization stored in the ROM. Based on the pattern data, energization of the coils of the relays 69a to 69c is controlled.
Alternatively, transfer voltage data corresponding to the basis weight of the recording paper may be stored in the ROM in advance. In this case, the control unit 71 first obtains the basis weight corresponding to the selected recording paper type. Then, an energization pattern is obtained from the determined basis weight to control the transfer voltage, and energization to the coils of the relays 69a to 69c is controlled based on the transfer voltage and the energization pattern data stored in the ROM.

(Configuration example of image forming apparatus)
Next, the overall configuration of the image forming apparatus according to the present invention will be briefly described. FIG. 4 is an explanatory diagram showing the configuration of the image forming apparatus according to the embodiment of the present invention.
The image forming apparatus 50 forms a monochrome image on a predetermined recording sheet (sheet) in accordance with image data transmitted from the outside. As shown in the figure, the exposure unit 1, the developing device 2, the photosensitive drum 3, the charger 4, the cleaner unit 5, the fixing unit (fixing device) 20, the paper transport path 7, the paper feed trays 8a to 8d, and the paper discharge tray. 9 etc.

  The charger 4 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential, and a charger-type charger 4 is used as shown in FIG. However, a contact roller type or brush type charger may be used.

  As shown in FIG. 4, the exposure unit 1 uses a laser scanning unit (LSU) including laser irradiation units 11a and 11b and reflection mirrors 12a and 12b. However, in addition to this method, there is a method using, for example, an EL or LED writing head in which light emitting elements are arranged in an array. In order to perform high-speed printing processing, this apparatus employs a technique that uses a plurality of laser beams to reduce the speed of irradiation timing, and employs a two-beam technique. The exposure unit 1 performs exposure according to the image data input to the photosensitive drum 3 uniformly charged by the charger 4, thereby forming an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 3. To form.

The developing device 2 visualizes the electrostatic latent image formed on the photosensitive drum 3 with black toner.
The cleaner unit 5 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer. The collected toner (waste toner) is stored in a waste toner container 52 through a waste toner conveyance path (not shown) on the back side of the image forming apparatus 50.

  The image forming apparatus 50 includes a control board (not shown) that functions as a control unit. The control board may correspond to the control unit 71 of FIG. The control unit includes a microcomputer, a ROM, a RAM, a nonvolatile memory, an input circuit, and an output circuit. The ROM stores a control program executed by the microcomputer. The RAM provides a work area for the microcomputer. The nonvolatile memory holds control data.

  The input circuit is a circuit to which signals from the detection means of each unit in the image forming apparatus 50 are input. An example of the detection means is a paper jam sensor that is provided in the paper transport path 7 and detects a paper jam. The output circuit is a circuit that drives a load such as an actuator or a motor for operating each unit of the image forming apparatus. The motor is, for example, a fixing driving motor (not shown) for driving the fixing unit 20. An example of the load is a heater for heating the fixing roller in the fixing unit 20.

  The electrostatic latent image formed on the photosensitive drum 3 is visualized by the developing device 2 using charged toner. That is, a toner image is formed on the photosensitive drum 3. The toner image is transferred onto a sheet by a transfer mechanism 10 (transfer belt unit in the present apparatus). The transfer mechanism 10 applies a voltage having a polarity for attracting the charged toner to the transfer belt on the back side of the sheet. As a result, the toner image on the photosensitive drum 3 is transferred onto the paper. For example, when the toner image has a (−) polarity charge, the voltage applied to the transfer belt is a (+) polarity voltage.

The transfer mechanism 10 of this apparatus is bridged by a transfer belt driving roller 10a, a transfer belt driven roller 10b, and other rollers, and has a predetermined resistance value (range of 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm). A transfer belt 10c is disposed. Further, an elastic conductive roller 10e capable of applying a transfer electric field with a conductivity different from that of the driving and driven rollers is disposed at a contact portion 10d between the photosensitive drum 3 and the transfer belt 10c. The electrostatic image (unfixed toner) transferred onto the paper by the transfer mechanism 10 is conveyed to the fixing unit 20.

  The fixing unit 20 includes a heating roller 21 and a pressure roller 22. A sheet peeling claw 35 is disposed on the outer peripheral portion of the heating roller 21. Further, although not shown, a roller surface temperature detection member (thermistor) is disposed. In addition, a heater 28 is disposed on the inner periphery thereof so that the surface of the heating roller has a predetermined temperature (fixing set temperature: approximately 160 to 200 ° C.). On the other hand, the pressure roller 22 is provided with pressure members (not shown) at both ends thereof.

  The sheet feeding trays 8a to 8d are trays for accumulating sheets used for image formation. In this apparatus, it is provided on the lower side and the side wall surface of the image forming unit. Since this apparatus is intended to perform high-speed printing processing, a large amount of sheets can be accumulated. Specifically, 1500 sheets can be stored in each of the paper feed trays 8a and 8b arranged below the image forming unit. Each of the paper feed trays 8c and 8d arranged below the paper feed trays 8a and 8b can accommodate 500 sheets. On the other hand, on the side of the apparatus, a large-capacity paper feed cassette 8e capable of storing a larger amount of sheets than the paper feed tray 8, and mainly for printing on various types of sheets and irregular-size sheets. A manual feed tray 8f to be used is arranged.

  A sheet stored in one of the paper feed trays 8a, 8b, 8c, and 8d and fed from the tray has a leading edge that hits a registration roller 63 disposed in front of the transfer belt unit 10 via the paper transport path 7. It is controlled to stop once in a state where it is in contact and slightly bent. Alternatively, the sheet accommodated in the large capacity sheet feeding cassette 8e or the manual feed tray 8f is fed from there, and temporarily stops in a state where the leading end abuts against the registration roller 63 and is slightly bent. Thereafter, the sheet is sent out from the registration roller 63 at a timing synchronized with the toner image formed on the photosensitive drum 3. The fed sheet is conveyed on the transfer belt 10c, and the toner image is transferred as described above. Further, the sheet is guided to the fixing unit 20 and receives heat and pressure when passing through the pressure contact portion between the heating roller 21 and the pressure roller 22. As a result, the transferred toner image is fixed on the surface of the sheet. Then, the sheet is discharged from the main body of the image forming apparatus 50 and is deposited on the discharge tray 9.

  The paper discharge tray 9 is disposed on the side surface opposite to the manual feed tray 8f of the apparatus. However, instead of the paper discharge tray 9, a post-processing device for paper discharge (stapling, punching, etc.) and a multi-stage paper discharge tray can be arranged as options.

  Finally, it is apparent that there can be various modifications of the present invention in addition to the above-described embodiment. Such variations are not to be construed as not belonging to the features and scope of the invention. The scope of the present invention is intended to include all modifications within the meaning and range equivalent to the scope of the claims.

FIG. 3 is an explanatory diagram schematically showing a detailed configuration of a transfer portion in the image forming apparatus according to the present invention. In FIG. 1, it is explanatory drawing which expands and shows the part from which a sheet peels from the transfer belt 10c. It is explanatory drawing which shows typically the shape of the static elimination brush of embodiment of this invention. It is explanatory drawing which shows the structure of the image forming apparatus of embodiment of this invention. FIG. 5 is a block diagram showing an example of an image forming apparatus including a switchable grounding resistor according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exposure unit 2 Developing device 3 Photoconductor, Photosensitive drum 3a Paper peeling claw 4 Charger 5 Cleaner unit 7 Paper transport path 8a, 8b, 8c, 8d Paper feed tray 8e Large capacity paper feed cassette 8f Manual feed tray 9 Paper discharge tray DESCRIPTION OF SYMBOLS 10 Transfer mechanism, transfer belt unit 10a Transfer belt drive roller 10b Transfer belt driven roller 10c Transfer belt 10d Contact portion 10e Elastic conductive roller 10f Tension roller 10g Transfer voltage application power source 10h Paper adsorption voltage application power source 11a, 11b Laser irradiation unit 12a, 12b Reflective mirror 20 Fixing device, fixing unit 21 Heating roller 22 Pressure roller 35 Paper peeling claw 50 Image forming device 52 Waste toner container 61 Paper guide A
62 Paper Guide B
63 Registration roller 65a Static elimination needle 65 Static elimination brush, Static elimination member 67, 67a-67d Ground resistance 69a-69c High insulation relay 71 Control part 73 Temperature / humidity sensor 75 Operation panel part 75a Display apparatus, Liquid crystal display panel 75b Touch panel 77 Nonvolatile memory | storage part 79a-79c driver

Claims (1)

A transfer unit for transferring a toner image from a photoconductor to a recording paper;
A transfer belt that electrostatically attracts the recording paper and transports it to the transfer unit and passes through the transfer unit;
A transfer voltage applying unit that applies a predetermined transfer voltage between the photosensitive member and the transfer belt at the transfer unit;
A fixing unit that fixes the toner image on the recording paper that has passed through the transfer unit;
A discharging member disposed between the transfer unit and the fixing unit on the downstream side of the region where the recording paper is separated from the transfer belt, and for discharging the recording paper in contact with or close to the recording paper ;
A resistor disposed in a current path for grounding the static elimination member and capable of switching a resistance value;
A temperature and humidity sensor that detects the ambient temperature and humidity level;
A ground resistance storage unit that stores in advance a ground resistance value according to the stage;
A control unit for controlling switching of the resistance value of the resistor ,
The image forming apparatus according to claim 1, wherein the control unit controls the resistance value of the resistor to switch to a ground resistance value corresponding to a detected temperature and humidity level .

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