JP7010101B2 - Fixing device and image forming device - Google Patents

Description

The present invention relates to a fixing device for fixing a toner image on paper and an image forming device provided with the fixing device.

The image forming apparatus includes a fixing device for fixing the toner image formed on the paper. The fixing device includes a heating member that heats the toner image and a pressurizing member that pressurizes the toner image against the paper.

The image forming apparatus uses the charged toner to form an image, but the heating member of the fixing apparatus may be charged with the opposite polarity to the toner due to friction with the pressurizing member or the paper. In this case, an electric suction force is generated between the toner and the heating member, and the toner adheres to the heating member. Therefore, defects such as fixing defects and image defects, so-called offset phenomena, may occur due to the adhesion of the toner to the heating member.

In order to suppress such an offset phenomenon, for example, the fixing device of Patent Document 1 has a rotating body (heating member) having a heating source and a pressurizing member forming a pressure contact portion with the surface of the rotating body. The recording material (paper) is narrowly held and conveyed to the pressure contact portion, and the toner image electrostatically adhered and formed on the surface of the recording material is thermally fixed on the recording material. Furthermore, the surface of the rotating body has the same polarity as the toner. A charging means for charging is provided.

Japanese Unexamined Patent Publication No. 2000-305388

As described above, in order to suppress the offset phenomenon, the fixing device is charged by applying a charge having the same polarity as the toner to the surface of the heating member by a charging device such as a charging means. The charger has a discharge electrode that discharges the charge. By the way, in the fixing device, when the heating member heats the toner image, the resin component contained in the toner may be vaporized, and the resin component may contaminate the discharge electrode of the charger as the heating member rotates. When the discharge electrode is contaminated, the discharge capacity (discharge charge amount) of the charger decreases. Therefore, the charger deteriorates over time due to the use of the fixing device over time.

The degree of deterioration of the charger (degree of contamination of the discharge electrode) depends on the amount of resin component, that is, the amount of toner to be heated. Since it depends on the number of printed sheets and the like, it varies depending on various situations. Therefore, the charger applies a relatively high charging current to the discharge electrode so as to be able to exert a predetermined discharge capacity (discharge charge amount) regardless of the situation. However, when the degree of deterioration of the discharge electrode is light, if an unnecessarily high charging current is applied to the discharge electrode, the discharge electrode is damaged and the durability of the charger is lowered.

Therefore, in consideration of the above circumstances, it is an object of the present invention to suppress a decrease in the discharge capacity of the charger while suppressing an offset phenomenon in the heating member.

The fixing device of the present invention pressurizes a rotatable heating member that heats a toner image formed on a paper, and the paper that is arranged facing the heating member and passes between the heating member. It has a member, a discharge electrode that discharges a charge having the same polarity as the toner constituting the toner image, and a ground electrode provided on at least one side of the discharge electrode in the circumferential direction of the heating member, and has a predetermined charging current. A charger for charging the surface of the heating member with the electric charge discharged by the discharge electrode and a current detection unit for detecting the inflow current from the ground electrode are provided, and the rotation of the heating member is stopped. It is characterized in that the charging current applied to the discharge electrode during the fixing process increases as the saturation time until the inflow current generated when the charging current is applied to the discharge electrode becomes longer. ..

The fixing device has a first saturation time, which is the saturation time of the charger in an initial state, and a second saturation time, which is the saturation time of the charger that has been used and has reached a predetermined correction condition. If the second saturation time is longer than the first saturation time, the charging current may be increased.

In the fixing device, when the second saturation time is longer than the first saturation time, the inflow current generated when the charging current is applied to the discharge electrode while the rotation of the heating member is stopped. The charging current may be increased so that the saturation time until the is saturated is the same as the first saturation time.

In the above fixing device, the correction condition may be set for each fixing process of a predetermined number of sheets of paper.

The image forming apparatus of the present invention is characterized by including the fixing apparatus described above.

According to the present invention, it is possible to suppress a decrease in the discharge capacity of the charger while suppressing an offset phenomenon in the heating member.

It is sectional drawing which shows the printer which concerns on one Embodiment of this invention. It is sectional drawing which shows the fixing apparatus which concerns on one Embodiment of this invention. It is an enlarged sectional view of the fixing belt of the fixing device which concerns on one Embodiment of this invention. It is a graph which shows the relationship between the rotation state of the fixing belt, and the inflow current from the ground electrode of a charging device in the fixing device which concerns on one Embodiment of this invention. It is a circuit diagram which shows the current detection part of the fixing device which concerns on one Embodiment of this invention. It is a block diagram which shows the electric structure of the fixing device which concerns on one Embodiment of this invention. It is a flowchart which shows the precondition process of the correction process of the charging current in the fixing device which concerns on one Embodiment of this invention. It is a flowchart which shows the correction process of the charging current in the fixing apparatus which concerns on one Embodiment of this invention.

First, the overall configuration of the printer 1 (image forming apparatus) according to the embodiment of the present invention will be described with reference to FIG. Hereinafter, for convenience of explanation, the front side of the paper in FIG. 1 will be referred to as the front side of the printer 1. Arrows L, R, U, and Lo appropriately attached to each figure indicate the left side, right side, upper side, and lower side of the printer 1, respectively.

The printer 1 includes a substantially box-shaped printer main body 2, a paper feed cassette 3 for storing paper (recording medium) is provided in the lower part of the printer main body 2, and a paper ejection tray 4 is provided in the upper part of the printer main body 2. It will be provided.

An exposure apparatus 5 composed of a laser scanning unit (LSU) is arranged on the left side of the printer main body 2, and an image forming unit 6 is provided on the right part of the printer main body 2. A photoconductor drum 7, which is an image carrier, is rotatably provided in the image forming unit 6. A charging device, a developing device connected to a toner container, a transfer roller, and a cleaning device are arranged around the photoconductor drum 7 along the rotation direction of the photoconductor drum 7.

Further, a paper transport path 10 is provided on the right side of the printer main body 2 from the lower side to the upper side. A paper feed unit 11 is provided in the vicinity of the paper feed cassette 3 at the upstream end of the transfer path 10, and a transfer unit 12 composed of a photoconductor drum 7 and a transfer roller is provided at the middle flow portion of the transfer path 10. A fixing device 13 is provided in the downstream portion of the transport path 10, and a paper discharge section 14 is provided in the vicinity of the paper discharge tray 4 at the downstream end of the transport path 10. Further, a control device 15 for controlling the fixing device 13 is provided in the printer main body 2.

Next, the image forming operation of the printer 1 will be described. The printer 1 starts an image forming operation when image data is input from an external computer or the like and an instruction to start printing is given. First, the surface of the photoconductor drum 7 is charged by the charging device of the image forming unit 6, and then the photoconductor drum 7 is exposed to the photoconductor drum 7 by the laser beam from the exposure device 5, and the photoconductor drum 7 is exposed to the image data. An electrostatic latent image is formed on the surface of 7. Next, the developer of the image forming unit 6 develops the electrostatic latent image into a toner image using toner.

On the other hand, the paper stored in the paper feed cassette 3 is taken out by the paper feed unit 11 and conveyed on the transfer path 10. The paper on the transport path 10 is transported to the transfer unit 12 at a predetermined timing, and the toner image on the photoconductor drum 7 is transferred to the paper by the transfer unit 12. The paper on which the toner image is transferred is conveyed to the fixing device 13, and the toner image is fixed on the paper by heating and pressurizing by the fixing device 13. The paper on which the toner image is fixed is discharged from the paper ejection unit 14 to the output tray 4.

Next, the fixing device 13 will be described with reference to FIG. As shown in FIG. 2, the fixing device 13 includes a fixing belt 20 (heating member), a pressure roller 21 (pressurization member), a heat source 22, a pre-entry guide 23, a charger 24, and a voltage application unit. 25 and a current detection unit 26 are provided.

Each part of the fixing device 13 is attached to a substantially box-shaped fixing frame (not shown), and the fixing frame is a printer main body so that the transport path 10 penetrates the fixing frame in the paper transport direction (vertical direction). Attached to 2. In the fixing frame, the fixing belt 20 and the pressure roller 21 are arranged on the left side and the right side, respectively, with the transport path 10 interposed therebetween, and are arranged so as to face each other and are in contact with each other. In the transport path 10, a pressure region N is formed between the fixing belt 20 and the pressure roller 21.

The pressure region N is a region where the fixing belt 20 and the pressure roller 21 are in contact with each other, and the pressure on the paper by the fixing belt 20 and the pressure roller 21 is 0 Pa on the upstream side in the transport direction. The region from the position to the position on the downstream side in the transport direction where the pressure becomes 0 Pa again via the position in the transport direction where the pressure becomes maximum is shown.

The fixing belt 20 is a flexible material and is formed in a substantially cylindrical shape long in the width direction (front-back direction) of the paper intersecting the transport direction. As shown in FIG. 3, the fixing belt 20 is composed of, for example, a heating layer 20a (core metal), an elastic layer 20b provided around the heating layer 20a, and a release layer 20c covering the elastic layer 20b. To. For example, the heating layer 20a is formed of a metal material such as nickel electrocasting, the elastic layer 20b is formed of an elastic material such as silicon rubber, and the release layer 20c is fluorine such as a PFA (perfluoroalkoxy alkane) tube. It is made of a based resin material. The heating layer 20a is grounded. The fixing belt 20 is heated by the heat source 22, for example, the heating layer 20a of the fixing belt 20 is induced and heated by the magnetic flux generated by the heat source 22 to come into contact with the paper on which the toner image is formed to heat the toner image. ..

The fixing belt 20 is rotatably attached around a rotation axis extending in the front-rear direction, that is, the rotation axis direction of the fixing belt 20 is the front-rear direction. The fixing belt 20 comes into contact with the pressure roller 21 and rotates in accordance with the rotation of the pressure roller 21. A support member for supporting the fixing belt 20 is provided inside the fixing belt 20, and the supporting member is attached to the fixing frame. Further, inside the fixing belt 20, a pressing member 27 that presses the fixing belt 20 from the inside toward the pressure roller 21 side and a belt guide 28 that supports the cylindrical shape of the fixing belt 20 from the inside are attached to the support member. .. Grease or oil that improves the slidability of the fixing belt 20 may be applied between the pressing member 27 and the inner peripheral surface of the fixing belt 20.

The pressure roller 21 is formed in a substantially columnar shape long in the width direction. The pressure roller 21 is composed of, for example, a columnar core material, an elastic layer provided around the core material, and a release layer covering the elastic layer. For example, the core material is formed of a metal material, the elastic layer is formed of an elastic material such as silicon rubber, and the release layer is formed of a fluororesin material such as PFA.

The pressure roller 21 is rotatably attached to the fixing frame around a rotation axis extending in the front-rear direction, that is, the rotation axis direction of the pressure roller 21 is the front-rear direction. For example, the pressurizing roller 21 is rotated by a rotational driving force transmitted from a drive source 40 (see FIG. 6) such as a motor. The pressurizing roller 21 pressurizes the fixing belt 20 together with the fixing belt 20 to pressurize the paper passing through the pressurizing region N.

The heat source 22 has an outer capsule shape that covers the fixing belt 20, and is arranged on the outside (left side) of the fixing belt 20. In other words, the heat source 22 is arranged on the side opposite to the pressurizing roller 21 with the fixing belt 20 interposed therebetween, at a predetermined distance from the fixing belt 20.

The heat source 22 is composed of, for example, an IH (Induction Heating) fixing unit including an exciting coil 22a connected to a heat source power supply 41 (see FIG. 6). The heat source 22 applies a heating voltage controlled by the control device 15 and supplied from the heat source power supply 41 to the exciting coil 22a. In the exciting coil 22a, when a heating current flows according to the heating voltage, a magnetic flux penetrating the exciting coil 22a is generated. The exciting coil 22a induces and heats the fixing belt 20 (heating layer 20a) by applying a magnetic flux to the fixing belt 20. The exciting coil 22a is an outer capsule coil that is wound so as to reciprocate along the rotation axis direction of the fixing belt 20 and is formed so as to follow the curved surface (outer peripheral surface) shape of the fixing belt 20.

The pre-entry guide 23 is provided on the upstream side of the fixing belt 20 and the pressure roller 21 in the transport direction, and guides the paper transported on the transport path 10 to the pressurization region N. The fixing device 13 is a separation claw (not shown) or a separation plate that separates the paper after the fixing process from the fixing belt 20 and the pressure roller 21 on the downstream side of the fixing belt 20 and the pressure roller 21 in the transport direction. (Not shown) may be provided. Further, the fixing device 13 is provided with a discharge roller (not shown) that discharges the paper after the fixing process to the outside of the fixing device 13 along the transport path 10 on the downstream side of the separation claw or the separation plate in the transport direction. good.

The charger 24 is a charge applying device that applies a charge to the surface of the fixing belt 20. The charger 24 charges the surface of the fixing belt 20 to the positive electrode by applying a positive charge (plus) to the fixing belt 20 having a negative electrode (minus) charging row, for example. As a result, the positively charged toner on the paper passing through the fixing belt 20 repels the fixing belt 20 having the same electrode, and adhesion to the fixing belt 20 is suppressed. Then, defects such as fixing defects and image defects caused by adhesion of the toner to the fixing belt 20, so-called offset phenomenon, are suppressed.

The charger 24 is provided on the upstream side of the pressurizing region N in the rotation direction of the fixing belt 20 and in the vicinity of the peripheral surface of the fixing belt 20. FIG. 2 shows an example in which the charger 24 is arranged on the upstream side of the pressurizing region N in the transport direction, but the charger 24 is arranged on the downstream side of the pressurizing region N in the transport direction. It may be attached to the heat source 22. The charger 24 is composed of, for example, a discharge electrode 30 and a pair of ground electrodes 31.

The discharge electrode 30 is a so-called needle electrode formed of a thin metal plate long and thin in the axial direction of the fixing belt 20, for example, a SUS plate having a thickness of 0.1 mm, and having a tip formed in a serrated shape in the longitudinal direction. Has good directivity. The tip of the discharge electrode 30 faces the surface of the fixing belt 20, and the tip of the discharge electrode 30 is arranged at a predetermined distance from the surface of the fixing belt 20. The base end of the discharge electrode 30 is connected to the voltage application unit 25, and the discharge electrode 30 is discharged at the tip (for example, corona discharge) according to the charging voltage (potential difference from each ground electrode 31) applied from the voltage application unit 25. To generate.

Each ground electrode 31 is formed of a conductive material such as a SUS plate into a plate shape long in the axial direction of the fixing belt 20. The pair of ground electrodes 31 are arranged in parallel with the discharge electrodes 30 on both sides of the discharge electrodes 30 in the circumferential direction of the fixing belt 20. The ends of the ground electrodes 31 on the tip side of the discharge electrode 30 are arranged at predetermined intervals from the surface of the fixing belt 20. The base end side of each ground electrode 31 is grounded via the current detection unit 26. The pair of ground electrodes 31 stabilize the corona discharge by the discharge electrode 30, for example, the electric field generated by the discharge generated at the tip of the discharge electrode 30 does not concentrate only on the needle tip, but extends in the width direction of the fixing belt 20. It acts so that it occurs uniformly.

In the charger 24, when the electric charge applied from the discharge electrode 30 overflows on the surface of the fixing belt 20, the overflowed electric charge (current) flows into the ground electrode 31, and the inflow current flows to the ground (current) via the current detection unit 26. Output to ground). Overflow occurs, for example, when the discharge electrode 30 continues to discharge regardless of the rotation of the fixing belt 20.

Specifically, while the fixing belt 20 is normally driven and rotated by the pressure roller 21, the surface of the fixing belt 20 moves, and the position facing the discharge electrode 30 on the surface of the fixing belt 20 changes. ing. Therefore, when a certain amount of electric charge is discharged from the discharge electrode 30, the electric charge from the discharge electrode 30 is charged at the changing facing position while the fixing belt 20 is rotating normally, so that it is difficult to overflow. The inflow current to the ground electrode 31 is relatively low. In the charger 24, in order to make the charge amount of the fixing belt 20 sufficient to repel the toner, the charging is performed to such an extent that a slight overflow occurs, so that the fixing belt 20 is normally rotated. However, a small amount of inflow current is generated.

On the other hand, when the rotation of the fixing belt 20 is stopped, the movement of the surface of the fixing belt 20 is stagnant, and the position facing the discharge electrode 30 on the surface of the fixing belt 20 does not change. Therefore, when a certain amount of electric charge is discharged from the discharge electrode 30, when the rotation of the fixing belt 20 is stopped, the electric charge from the discharge electrode 30 is charged at the opposite position where it does not change, so that it easily overflows. The inflow current to the ground electrode 31 becomes relatively large, and is substantially equal to the charging current applied from the voltage application unit 25 to the discharge electrode 30.

The voltage application unit 25 is connected to the control device 15 and controlled, and applies a charging voltage (charging current) to the discharge electrode 30 of the charger 24. The voltage application unit 25 is connected to, for example, a charging power supply (not shown), and applies a charging voltage using the power supplied from the charging power supply. In this embodiment, an example in which the voltage applying unit 25 is provided in the fixing device 13 will be described, but the voltage applying unit 25 may be provided in the printer 1 outside the fixing device 13.

For example, when the charger 24 is in an initial state similar to a new one, such as immediately after the printer 1 or the fixing device 13 is shipped from the factory, or immediately after the fixing device 13 or the charging device 24 is replaced, the voltage application unit is used during the fixing process. A predetermined initial setting current (for example, 3 μA) is set as the charging current applied by the 25 to the discharge electrode 30. Further, the charging current during the fixing process is corrected by the control device 15 according to the time-dependent use of the charger 24. The correction of the charging current is performed in the charging process of the charging device 24 below.

The current detection unit 26 is connected between the ground electrode 31 of the charger 24 and the ground, and detects the inflow current generated by the ground electrode 31. The current detection unit 26 is connected to the control device 15 and outputs the detected inflow current (current value) to the control device 15.

Further, the current detection unit 26 determines whether or not the inflow current exceeds a predetermined threshold value, outputs the determination result to the control device 15, and in other words, detects the generation of the inflow current exceeding the predetermined threshold value. do. The current detection unit 26 includes, for example, a first resistance 35, a second resistance 36, a third resistance 37, and a comparator 38, as shown in FIG.

A first resistance 35 connected to the ground electrode 31 is connected to the first input 38a (non-inverting input) of the comparator 38. For example, the input voltage V1 to the first input 38a is calculated by the formula V1 = I1 × R1 using the inflow current I1 from the ground electrode 31 and the resistance value R1 of the first resistor 35.

A second resistance 36 for inputting a reference voltage Vref and a grounded third resistance 37 are connected to the second input 38b (inverting input) of the comparator 38. For example, the input voltage V2 to the second input 38b uses the reference voltage Vref, the resistance value R2 of the second resistance 36, and the resistance value R3 of the third resistance 37, and the formula V2 = Vref × (R3 / (R3 /). Calculated by R2 + R3)). That is, the input voltage V2 of the second input 38b becomes a threshold value to be compared with the input voltage V1 (voltage corresponding to the inflow current I1) of the first input 38a by the comparator 38.

The output 38c of the comparator 38 is connected to the control device 15, and when the input voltage V1 of the first input 38a exceeds the input voltage V2 of the second input 38b, the positive output voltage V3 is output to the control device 15 and flows into the control device 15. Notify the generation of current. Further, when the input voltage V1 of the first input 38a is equal to or less than the input voltage V2 of the second input 38b, the output 38c of the comparator 38 outputs a negative output voltage V3 to the control device 15 to notify that the inflow current has not occurred. do.

Next, the electrical configuration of the control device 15 that controls the fixing device 13 will be described with reference to FIG. The control device 15 is composed of a CPU or the like, and a storage device 16 such as a ROM or RAM is connected to the control device 15. As the control device 15 and the storage device 16, a main control device and a main storage device that collectively control each part of the printer 1 may be applied.

The control device 15 controls each unit connected to the control device 15 based on the control program and control data stored in the storage device 16. For example, the control device 15 is connected to the drive source 40 of the pressurizing roller 21, the heat source power supply 41 of the heat source 22, the voltage application unit 25, the current detection unit 26, and the like. The control device 15 controls various functions such as the fixing process by the fixing device 13 and the charging process of the charger 24.

In the fixing process, the control device 15 controls the heat source power supply 41 to heat the fixing belt 20 by the heat source 22 while detecting and monitoring the surface temperature of the fixing belt 20 by a temperature sensor (not shown). As a result, the control device 15 heats the fixing belt 20 until the surface temperature of the fixing belt 20 reaches a predetermined fixing temperature, and maintains the surface temperature of the fixing belt 20 at the fixing temperature.

Further, in the fixing process, the control device 15 controls the drive source 40 to rotate the pressure roller 21, and the pressure roller 21 is driven to rotate the fixing belt 20. When the paper on which the toner image is formed is supplied to the fixing device 13, it is heated by the fixing belt 20 in the pressure region N while being conveyed by the rotation of the fixing belt 20 and the pressure roller 21, and the fixing belt 20 and the pressure are applied. It is pressurized by the pressure roller 21. As a result, the toner image is fixed on the paper.

As a prerequisite process for the charging process of the charger 24, as shown in FIG. 7, the charger 24 is in the initial state as in the factory shipment of the printer 1 and the fixing device 13 and when the fixing device 13 and the charging device 24 are replaced. At this time (step S1: YES), the control device 15 measures the initial value of the saturation time of the inflow current generated in the charger 24 before the charger 24 is used in the fixing process.

Specifically, the control device 15 controls the voltage application unit 25 during the rotation stop state (step S2) in which the rotation of the pressurizing roller 21 is stopped and the rotation of the fixing belt 20 is stopped (step S2), and the initial set current is set. (See the two-dot chain line in FIG. 4) is applied to the discharge electrode 30 of the charger 24 (step S3). During this time, the control device 15 detects the inflow current (see the solid line in FIG. 4) generated from the ground electrode 31 of the charger 24 by the current detection unit 26 (step S4), and from the generation of the inflow current to the saturation. Saturation time (first saturation time) is measured (step S5).

For example, the control device 15 detects the generation of the inflow current based on the output 38c of the comparator 38 of the current detection unit 26. Alternatively, the control device 15 may monitor the amount of change in the inflow current and detect the generation of the inflow current when the amount of change exceeds a predetermined change threshold value (for example, 0.1 μA per 1 msec). Further, the control device 15 detects the saturation of the inflow current when the amount of change in the inflow current becomes less than the change threshold value. Then, after the inflow current is saturated, the control device 15 stores the measured first saturation time in the storage device 16 and stops the current application to the discharge electrode 30 by the voltage application unit 25.

The charging process of the charger 24 is performed before the paper enters between the fixing belt 20 and the pressure roller 21 (pressurized region N) in the fixing process (step S11 in FIG. 8). In the charging process, the control device 15 controls the voltage applying unit 25 to apply a charging voltage (charging current) to the discharge electrode 30 of the charger 24. At this time, as described above, when the charger 24 is in the initial state (when the charging current is not corrected through the full use of the charger 24), the charging current is set to the initial set current. Ru.

For example, when the printer 1 forms a toner image on paper using positive electrode toner, the voltage application unit 25 applies a positive electrode charging voltage to the discharge electrode 30. Then, the discharge electrode 30 discharges the positive charge to the surface of the fixing belt 20, and the surface of the fixing belt 20 is charged positively. This makes it difficult for the positive electrode toner to adhere to the surface of the fixing belt 20.

After that, as shown in FIG. 8, when the use of the charger 24 reaches a predetermined correction condition by the repeated charging process (step S12: YES), the control device 15 receives the voltage application unit 25 to the discharge electrode 30 during the fixing process. The charging current applied to the is corrected. The correction condition may be set for each fixing process of a predetermined number of sheets (for example, 50,000 sheets), or may be set for each predetermined operating time.

In the charging current correction process, first, the control device 15 measures the saturation time of the inflow current generated by the charger 24 that has reached the correction condition. Specifically, the control device 15 controls the voltage application unit 25 to apply the current charging current to the discharge electrode 30 of the charger 24 while the rotation of the fixing belt 20 is stopped (step S13) (step S13). Step S14). As described above, when the charging current is not corrected through the full use of the charging device 24, the current charging current is the initial set current. During this time, the control device 15 detects the inflow current (see the broken line in FIG. 4) generated from the ground electrode 31 of the charger 24 by the current detection unit 26 (step S15), and from the generation of the inflow current to the saturation. Saturation time (second saturation time) is measured (step S16). Then, after the inflow current is saturated, the control device 15 stops the current application to the discharge electrode 30 by the voltage application unit 25.

Further, the control device 15 corrects so that the charging current increases as the saturation time of the inflow current generated by the charger 24 becomes longer. Specifically, the control device 15 compares the measured second saturation time with the first saturation time stored in the storage device 16 and determines whether or not the second saturation time is longer than the first saturation time. Determination (step S17). For example, the control device 15 determines that the second saturation time is longer than the first saturation time when the difference obtained by subtracting the first saturation time from the second saturation time is longer than a predetermined time threshold value (for example, 100 msec). ..

Then, when the second saturation time is longer than the first saturation time (step S17: YES), the control device 15 adds a predetermined increase amount (for example, 1 μA) to the current charging current for charging. Correct the current (step S18). When the charging current corrected in this way is applied to the charger 24, the discharge capacity of the charger 24 is improved as compared with that before the correction, and the amount of charge that can be charged to the fixing belt 20 per unit time increases. do. Therefore, when the corrected charging current is applied to the charger 24 to charge the fixing belt 20 in the rotation stopped state, the saturation time of the inflow current is shorter than that before the correction. The control device 15 corrects when the second saturation time is equal to or less than the first saturation time (when the difference obtained by subtracting the first saturation time from the second saturation time is equal to or less than the time threshold value) (step S17: NO). The charging current is maintained (step S19: NO).

Further, when the charging current is corrected (step S18), the control device 15 applies the corrected charging current to the charging device 24 while the fixing belt 20 is stopped rotating (step S13) in the same manner as described above. (Step S14), the inflow current is detected (step S15), and the second saturation time is measured again (step S16). Further, the control device 15 compares the remeasured second saturation time with the first saturation time (step S17), and when the remeasured second saturation time is longer than the first saturation time (step S17:). YES), the charging current is further corrected (step S18). If the difference between the second saturation time and the first saturation time remeasured after the correction of the charging current is equal to or less than the time threshold value (step S17: NO, step S19: YES, step S20: YES), charging is performed. Maintain current. If the second saturation time remeasured after the correction of the charging current is shorter than the first saturation time (step S17: NO, step S19: YES, step S20: NO), the charging current is in the state before correction. Return to (the state at the time of the previous correction) (step S21).

The control device 15 measures the second saturation time as described above, compares the second saturation time with the first saturation time, and corrects the charging current. The second saturation time is equal to or less than the first saturation time (second saturation). Repeat until the difference obtained by subtracting the first saturation time from the time becomes equal to or less than the time threshold value).

In this way, when the second saturation time is longer than the first saturation time, the control device 15 makes the saturation time the same as the first saturation time when the corrected charging current is used. , The charging current is increased and corrected.

In the present embodiment, as described above, the fixing device 13 of the printer 1 (image forming device) faces the rotatable fixing belt 20 (heating member) for heating the toner image formed on the paper and the fixing belt 20. A pressure roller 21 (pressurizing member) that pressurizes the paper passing between the fixing belt 20 and the discharge electrode 30 and the fixing belt 20 that discharge charges having the same polarity as the toner constituting the toner image. A charger 24 having a ground electrode 31 provided on at least one side of the discharge electrode 30 in the circumferential direction of the above, and charging the surface of the fixing belt 20 with the electric charge discharged by the discharge electrode 30 according to a predetermined charging current. A current detection unit 26 for detecting the inflow current from the ground electrode 31 is provided. The control device 15 of the fixing device 13 increases the saturation time until the inflow current generated when the charging current is applied to the discharge electrode 30 while the rotation of the fixing belt 20 is stopped becomes longer during the fixing process. The charging current applied to the discharge electrode 30 is increased.

As the discharge electrode 30 of the charger 24 becomes contaminated by the use of the fixing device 13 over time, the discharge capacity of the charger 24 decreases, and the amount of electric charge that can be charged to the fixing belt 20 per unit time decreases. .. In this case, when the rotation of the fixing belt 20 is stopped, the saturation time until the inflow current is saturated becomes long. On the other hand, in the present embodiment, the charging current is increased and corrected as the saturation time becomes longer. Therefore, the discharge capacity of the charger 24 is improved as compared with that before the correction, and the amount of electric charge charged per unit time with respect to the fixing belt 20 increases.

Therefore, according to the present embodiment, the discharge capacity of the charger 24 can be improved according to the degree of deterioration of the charger 24 (the degree of contamination of the discharge electrode 30). As a result, the charger 24 charges the fixing belt 20 with an appropriate amount of charge regardless of various conditions such as the usage environment of the fixing device 13, the printing rate of the toner image to be fixed, and the number of printed sheets per day. Can be done. Therefore, the electrical suction force of the fixing belt 20 can be appropriately suppressed, the adhesion of the toner to the fixing belt 20 can be suppressed, and the offset phenomenon caused by the adhesion of the toner to the fixing belt 20 can be suppressed. Further, when the degree of deterioration of the charger 24 is light, an unnecessarily high charging current is not applied to the discharge electrode 30, damage to the discharge electrode 30 is suppressed, and the durability of the charger 24 is enhanced. Can be done. In this way, it is possible to suppress a decrease in the discharge capacity of the charger 24 while suppressing an offset phenomenon in the fixing belt 20.

For example, the control device 15 sets the first saturation time, which is the saturation time for the charger 24 in the initial state, and the second saturation time, which is the saturation time for the charger 24 which has been used and has reached a predetermined correction condition. By comparison, when the second saturation time is longer than the first saturation time, the charging current is increased. As a result, it is determined whether or not to correct the charging current when the charger 24 reaches a predetermined correction condition, so that the number of corrections of the charging current is reduced and the charging current is used according to the user's usage condition. The current can be corrected. Further, since the first saturation time in the initial state in which the charger 24 is in the optimum state is targeted for comparison, the state of the charger 24 can be appropriately determined.

Further, when the second saturation time is longer than the first saturation time, the control device 15 saturates the inflow current generated when the charging current is applied to the discharge electrode 30 while the rotation of the fixing belt 20 is stopped. The charging current is increased so that the saturation time up to is the same as the first saturation time. As a result, in order to correct the charging current based on the first saturation time in the initial state in which the charger 24 was in the optimum state, the charger 24 charges the fixing belt 20 with the optimum discharge capacity. It can be controlled to do.

Further, the correction condition of the charging current is set for each fixing process of a predetermined number of sheets of paper. As a result, the charging current can be periodically corrected according to the usage status of the user.

In the above embodiment, the case where the IH fixing unit provided with the exciting coil 22a is applied as the heat source 22 has been described, but in another different embodiment, the heat source 22 may be applied with, for example, a halogen heater or a ceramic heater. good. Further, the heat source 22 made of a halogen heater or a ceramic heater may be provided outside the fixing belt 20, but may also be provided inside the fixing belt 20.

In the above-described embodiment, the configuration in which the fixing device 13 includes a heating member as the fixing belt 20 has been described, but the heating member is not limited to this, and may be configured to include, for example, a fixing roller. Further, in the above-described embodiment, the example in which the ground electrode 31 is directly connected to the current detection unit 26 has been described in FIGS. 2 and 5, but the present invention is not limited to this, and for example, other embodiments. In the embodiment, a Zener diode may be connected between the ground electrode 31 and the current detection unit 26 to increase the discharge voltage and input to the current detection unit 26.

In the present embodiment, the case where the configuration of the present invention is applied to the monochrome printer 1 has been described, but in other different embodiments, the present invention is applied to other image forming apparatus such as a color printer, a copying machine, a facsimile, and a multifunction device. It is also possible to apply the configuration of.

1 Printer (image forming device)
2 Printer body 6 Image forming part 10 Transport path 13 Fixing device 20 Fixing belt (heating member)
21 Pressurizing roller (pressurizing member)
22 Heat source 24 Charger 25 Voltage application part 26 Current detection part 30 Discharge electrode 31 Ground electrode

Claims (5)

A rotatable heating member that heats the toner image formed on the paper,
A pressurizing member arranged to face the heating member and pressurizing the paper passing between the heating member and the paper.
It has a discharge electrode that discharges a charge of the same polarity as the toner that constitutes the toner image, and a ground electrode provided on at least one side of the discharge electrode in the circumferential direction of the heating member, and is described in accordance with a predetermined charging current. A charger that charges the surface of the heating member with the electric charge discharged by the discharge electrode, and
A current detection unit that detects the inflow current from the ground electrode is provided.
The longer the saturation time until the inflow current generated when the charging current is applied to the discharge electrode during the rotation stop state of the heating member becomes longer, the more charging is applied to the discharge electrode during the fixing process. A fixing device characterized by increasing the current. The first saturation time, which is the saturation time of the charger in the initial state, is compared with the second saturation time, which is the saturation time of the charger that has been used and reached a predetermined correction condition. 2. The fixing device according to claim 1, wherein when the saturation time is longer than the first saturation time, the charging current is increased. When the second saturation time is longer than the first saturation time, saturation until the inflow current generated when the charging current is applied to the discharge electrode while the rotation of the heating member is stopped is saturated. The fixing device according to claim 2, wherein the charging current is increased so that the time becomes the same as the first saturation time. The fixing device according to claim 2 or 3, wherein the correction condition is set for each fixing process of a predetermined number of sheets of paper. An image forming apparatus comprising the fixing apparatus according to any one of claims 1 to 4.

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