Patent Grant
10466633
The present disclosure generally relates to image forming apparatuses, such as copying machines, printers, and facsimile apparatuses, and more specifically to those that use an electrophotographic method or electrostatic recording method.
In an electrophotographic image forming apparatus, a transfer voltage is applied to a transfer member disposed to face an image bearing member, such as a drum-shaped photosensitive member or intermediate transfer member, to electrostatically transfer a toner image borne on the image bearing member onto a transfer medium, such as a sheet or overhead projector (OHP) sheet. Thereafter, the transfer medium onto which the toner image is transferred at a transfer portion formed by the image bearing member and the transfer member is conveyed to a fixing unit and then heated and pressed by the fixing unit so that the toner image is fixed to the transfer medium.
Japanese Patent Application Laid-Open No. 11-219042 discusses an arrangement in which a conductive member disposed upstream from a transfer portion with respect to the conveyance direction for a transfer medium is provided with a current detection unit and a transfer voltage is set based on a result of detection by the current detection unit.
According to the arrangement discussed in Japanese Patent Application Laid-Open No. 11-219042, however, it is difficult to control the transfer voltage as appropriate, since the current leakage is undetectable if a current leakage occurs from a conductive member that is provided with no detection unit.
The present disclosure is generally directed to an image forming apparatus capable of controlling a transfer voltage as appropriate regardless of the current leakage path from a transfer portion via a transfer medium.
According to an aspect of the present disclosure, an image forming apparatus includes an image bearing member configured to bear a toner image, a transfer member configured to form a transfer portion where the transfer member is brought into contact with the image bearing member, a transfer power source configured to apply a voltage to the transfer member, a detection unit configured to detect a current flowing in the transfer member when the voltage is applied from the transfer power source to the transfer member, a control unit configured to control the transfer power source to transfer the toner image from the image bearing member onto a transfer medium by applying a first voltage from the power source to the transfer member, wherein the control unit sets the first voltage based on a value of the voltage applied from the transfer power source to the transfer member during a value of the current detected by the detection unit is a predetermined value while the transfer medium is not held in the transfer portion, and a fixing unit disposed downstream from the transfer member in a conveyance direction of the transfer medium, the fixing unit including a heating member configured to heat the transfer medium and a pressing member configured to form a fixing portion where the pressing member is brought into contact with the heating member, wherein while the transfer medium is held in the transfer portion, a predetermined voltage is applied from the transfer power source to the transfer member to transfer a toner image from the image bearing member onto the transfer medium, wherein the control unit sets a second voltage to be applied from the transfer power source to the transfer member, based on a simple average value of a current value detected by the detection unit during a predetermined time period, after a leading edge of the transfer medium in the conveyance direction for the transfer medium is held in the transfer portion and while the first voltage is applied from the transfer power source to the transfer member.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Various exemplary embodiments of the present disclosure will be described below with reference to the attached drawings. It should be noted that the dimensions, materials, shapes, relative locations, etc. of components described below are to be changed as needed according to various conditions and the structure of an apparatus to which an exemplary embodiment of the present disclosure is applied. Thus, unless otherwise specified, the description below is not intended to limit the scope of the disclosure.
[Structure of Image Forming Apparatus]
As illustrated in
A charging roller 2, an exposure unit 4, a development unit 5, and a cleaning unit 6 are disposed around the photosensitive drum 1. The development unit 5 includes a development roller 5a which is a development member. The cleaning unit 6 includes a cleaning blade 6a. Toner is stored in the development unit 5, and a development power source (not illustrated) applies a voltage having polarity opposite to the normal charging polarity of the toner so that the development roller 5a can bear the toner stored in the development unit 5.
Further, a transfer roller 8 is disposed to face the photosensitive drum 1. The transfer roller 8 is a transfer member which is abutted against the photosensitive drum 1 to form a transfer portion Nt. The transfer roller 8 includes a metal core and an elastic member, such as rubber, which is conductive and formed on the surface of the metal core. In the present exemplary embodiment, the metal core has an outside diameter of 5 mm, the elastic member has a thickness of 3.75 mm, and the electric resistance value of the transfer roller 8 is adjusted to 107Ω to 109Ω. Further, the transfer roller 8 is connected to a transfer power source 18. Between the transfer roller 8 and the transfer power source 18, a detection unit 19 which detects a current flowing toward the transfer roller 8 is provided.
A fixing unit 14 including a pressing member 30 and a heating member 31 is provided downstream from the transfer portion Nt in the conveyance direction for a transfer medium P. Further, the image forming apparatus 100 includes a sheet feeding cassette 15 and a sheet discharge tray 27. The sheet feeding cassette 15 is a storage unit which stores the transfer mediums P such as sheets and overhead projector (OHP) sheets. The sheet discharge tray 27 is a stacking unit for stacking the transfer mediums P on which an image is formed and which are discharged from the image forming apparatus 100.
A pre-transfer guide 17, a top sensor 10, a sheet conveyance roller 9 which is a conveyance unit, a sheet feeding roller 7 which is a sheet feeding unit, and the sheet feeding cassette 15 are disposed upstream from the transfer portion Nt in the conveyance direction for the transfer medium P. The pre-transfer guide 17 is a guide member for guiding the transfer medium P conveyed by the sheet conveyance roller 9 to the transfer portion Nt. In the present exemplary embodiment, a pre-transfer guide made of an insulative polycarbonate-acrylonitrile butadiene styrene polymer (PC-ABS) resin is used as the pre-transfer guide 17. The top sensor 10 is capable of detecting the leading edge of the transfer medium P fed from the sheet feeding cassette 15 by the sheet feeding roller 7 in the conveyance direction for the transfer medium P, and detection results detected by the top sensor 10 are input to the controller circuit 23, as illustrated in
An image forming operation is started in response to the receipt of an image signal by the controller circuit 23 (illustrated in
A voltage having polarity (which is positive in the present exemplary embodiment) opposite to the normal charging polarity of the toner is applied from the transfer power source 18 to the transfer roller 8 and the toner image formed on the photosensitive drum 1 is transferred in the transfer portion Nt onto the transfer medium P fed from the sheet feeding cassette 15. After the leading edge of the transfer medium P conveyed to the transfer portion Nt is detected by the top sensor 10 provided upstream from the transfer portion Nt in the conveyance direction for the transfer medium P, the transfer medium P is held in the transfer portion Nt, and the toner image is transferred from the photosensitive drum 1 onto the transfer medium P. The transfer roller 8 is biased toward the photosensitive drum 1 by a biasing unit (not illustrated), and when the toner image is transferred from the photosensitive drum 1 onto the transfer medium P, the transfer roller 8 is rotated by the rotation of the photosensitive drum 1.
The electric resistance value of the transfer roller 8 changes based on the temperature and humidity of the surrounding environment, durability of the transfer roller 8, etc. Thus, when the toner image is transferred from the photosensitive drum 1 onto the transfer medium P, the voltage (hereinafter, “transfer voltage Vt”) to be applied from the transfer power source 18 to the transfer roller 8 is set based on the change in the electric resistance value of the transfer roller 8. More specifically, the transfer voltage Vt is set by control referred to as “active transfer voltage control” (ATVC). The following describes ATVC.
First, constant current control is performed in such a manner that a current of a predetermined value flows in the transfer roller 8 before the transfer medium P reaches the transfer portion Nt, and the electric resistance value of the transfer roller 8 is calculated from the value of voltage V0 that is applied from the transfer power source 18 to the transfer roller 8 during the constant current control. The current flowing in the transfer roller 8 is detected by the detection unit 19, and the controller circuit 23 controls the transfer power source 18 based on the detection result input from the detection unit 19. In this way, the constant current control is performed.
Next, the controller circuit 23 refers to a look-up table (LUT) recorded in advance in a built-in memory to set the transfer voltage Vt (first voltage) based on the calculated electric resistance value of the transfer roller 8 and the value of the voltage V0. The controller circuit 23 thereafter feeds back the set transfer voltage Vt to the transfer power source 18, and the transfer power source 18 applies the transfer voltage Vt to the transfer roller 8 to transfer the toner image onto the transfer medium P in the transfer portion Nt. According to the present exemplary embodiment, when the toner image is transferred from the photosensitive drum 1 onto the transfer medium P, constant voltage control is performed based on the transfer voltage Vt set by the above-described method.
The transfer medium P onto which the toner image is transferred in the transfer portion Nt is conveyed to the fixing unit 14 after charges accumulated on the surface of the transfer medium P are neutralized by a neutralizing member 20. Then, the transfer medium P is heated by the heating member 31 and pressed by the pressing member 30 in the fixing unit 14 so that the toner image is fixed to the transfer medium P. The toner (residual toner) that remains on the surface of the photosensitive drum 1 after the toner image is transferred onto the transfer medium P is cleaned and removed by the cleaning blade 6a and collected into the cleaning unit 6. The transfer medium P to which the toner image is fixed in the fixing unit 14 is discharged to the sheet discharge tray 27 by a pair of sheet discharge rollers 16. The image forming apparatus 100 in the present exemplary embodiment performs the above-described operations to form an image on the transfer medium P.
[Fixing Unit]
The present exemplary embodiment employs a fixing unit using a film fixing method.
The pressing member 30 is a roller having an outside diameter of 14 mm and including a metal core 30a, an elastic layer 30b, and a release layer 30c. The elastic layer 30b is formed on the outer periphery of the metal core 30a. The release layer 30c is formed on the outer periphery of the elastic layer 30b. Silicone rubber, fluoro-rubber, etc. can be used as the elastic layer 30b, and a fluoro-resin, such as a tetrafluoroethylene-perfluoro alkyl vinyl ether copolymer (PFA), etc. can be used as the release layer 30c. The pressing member 30 is rotatably supported at respective ends of the metal core 30a in the lengthwise direction.
The heating member 31 includes a film 31a, a heater 31b, a support portion 31c, and a pressing stay 31d. The heater 31b is in the shape of a plate and disposed to face the pressing member 30 via the film 31a and be in contact with the inner periphery of the film 31a. The support portion 31c supports the heater 31b. The pressing stay 31d reinforces the support portion 31c. The heater 31b which is a heating unit is disposed in the fixing portion Nf, and an alternating-current voltage is applied to the heater 31b from a commercial power source (alternating-current power source) through a bidirectional thyristor 51 (triode for alternating current (TRIAC)). The controller circuit 23 controls the current flowing to a gate of the bidirectional thyristor 51 to turn on/off the bidirectional thyristor 51, and the alternating-current voltage to be applied to the heater 31b is controlled to adjust the temperature of the heater 31b.
The film 31a is a roll-shaped flexible member including a substrate layer (not illustrated), an elastic layer (not illustrated), and a release layer (not illustrated). The elastic layer is formed on the outer periphery of the substrate layer. The release layer is formed on the outer periphery of the elastic layer. The substrate layer of the film 31a needs to be resistant to heat to receive heat from the heater 31b and needs to have durability to rub against the heater 31b, so a metal, such as stainless steel or nickel, or a heat-resistant resin, such as polyimide, is desirably used as the substrate layer of the film 31a. Further, a fluoro-resin, such as perfluoroalcoxy resin (PFA) or polytetrafluoroethylene resin (PTFE), is desirably used as the release layer of the film 31a. The film 31a in the present exemplary embodiment has an outside diameter of 18 mm. Polyimide with a thickness of about 60 μm is used as the substrate layer of the film 31a. Silicon rubber with a thickness of about 150 μm is used as the elastic layer of the film 31a. Further, PFA which is excellent in releasability and heat-resistance among fluoro-resins is used as the release layer, and the thickness of the release layer is set to 10 μm.
As illustrated in
The support portion 31c is made of a liquid crystal polymer and has rigidity, heat resistance, and heat insulation properties. The support portion 31c has the role of supporting the inner periphery of the film 31a being in contact with the support portion 31c and the role of supporting the heater 31b. The pressing stay 31d has a U-shaped cross section when viewed from the lengthwise direction in order to increase the flexural rigidity of the heating member 31. The pressing stay 31d is formed by bending a stainless-steel plate having a thickness of 1.6 mm.
When the fixing unit 14 fixes a toner image to the transfer medium P, a rotation force from the driving source M is transmitted to the pressing member 30, and the pressing member 30 is driven and rotated in the direction of an arrow R2 specified in
The transfer medium P is guided into the fixing portion Nf while the film 31a and the pressing member 30 are rotated, a current is applied to the heater 31b, and the temperature detected by the thermistor 31e for the heater 31b reaches a target temperature. The toner image transferred onto the transfer medium P in the transfer portion Nt is heated and pressed while the transfer medium P is conveyed through the fixing portion Nf, whereby the toner image is melted and fixed to the transfer medium P. The transfer medium P conveyed through the fixing portion Nf is separated from the film 31a due to the curvature of the film 31a and discharged to the sheet discharge tray 27 by the pair of sheet discharge rollers 16.
The distance from the transfer portion Nt to the fixing portion Nf in the image forming apparatus 100 according to the present exemplary embodiment is 40 mm. More specifically, in the cases of forming an image on a normal A4-size or letter-size transfer medium P, a toner image is fixed to the transfer medium P in the fixing unit 14 concurrently with transfer of the toner image from the photosensitive drum 1 onto the transfer medium P in the transfer portion Nt.
[Transfer Control]
In the present exemplary embodiment, the transfer voltage Vt is controlled based on the current IL. The following describes details of the control according to the present exemplary embodiment in a case of forming an entirely black solid image on a transfer medium P, Red Label A4-size sheet (grammage 80 g/m2) manufactured by Océ, under a high-temperature, high-humidity environment with a room temperature of 32.5 degrees and a humidity of 80%. Two types of the transfer medium P were prepared, a moisture-absorbed sheet having been left under a high-temperature, high-humidity environment for 48 hours and thus having absorbed moisture and an immediately-unwrapped sheet immediately unwrapped, and the image forming was performed on the respective sheets. Further, the value of the voltage V0 in the case in which ATVC was performed to cause a current of 3 μA to flow was 500 V. From this result, the controller circuit 23 set the transfer voltage Vt to be applied from the transfer power source 18 to the transfer roller 8 in the case of transferring a toner image from the photosensitive drum 1 onto the transfer medium P to 750 V and started image forming.
A current signal that is actually detected by the detection unit 19 contains noise, etc. on the circuit. Thus, according to the present exemplary embodiment, the simple moving average of a current signal detected by the detection unit 19 is calculated twice to obtain a waveform, and the simple average of the obtained waveform is calculated, and the calculated value of the simple average is determined as the current Itr. More specifically, the current Itr is obtained in a predetermined time period corresponding to a section of about 10 mm in the conveyance direction for the transfer medium P from the application timing for the transfer voltage Vt from the transfer power source 18 to the transfer roller 8 excluding the waiting period for a circuit response. Then, a change width ΔV in the transfer voltage Vt is determined using the current Itr and formula 1 below.
While the waiting period for a circuit response depends on the circuit configuration, it is suitable to delay the calculation of the current Itr during the predetermined period until the output from the transfer power source 18 and the signal detected by the detection unit 19 are stabilized to control the transfer voltage Vt with greater accuracy. According to the present exemplary embodiment, the waiting period was set to 100 millisecond (ms) from the timing when the transfer voltage Vt has been applied from the transfer power source 18 to the transfer roller 8, and the current Itr was calculated after the period of 100 ms had passed.
In formula (1), the current IM is a current at the time when the electric resistance value of the transfer medium P is low and the current flowing from the transfer portion Nt to the ground via the transfer medium P and the metal plate 15a becomes the maximum value. Further, the voltage VM is a voltage that needs to be applied from the transfer power source 18 to the transfer roller 8 in order to transfer a toner image from the photosensitive drum 1 onto the transfer medium P in the case in which the current IM flows from the transfer portion Nt to the ground, and is a voltage different from the transfer voltage Vt determined by ATVC. Further, formula 1 is convertible into formula (2) below.
The current Itr1 is a transfer current that is used for transferring a toner image from the photosensitive drum 1 to the transfer medium P in the transfer portion Nt in the case in which the electric resistance of the transfer medium P is high and no current flows from the transfer portion Nt to the ground via the transfer medium P and the metal plate 15a. Specifically, the current IL is calculated by subtracting the current Itr1 from the current Itr detected by the detection unit 19. Further, the current Itr2 is a transfer current that is used for transferring a toner image from the photosensitive drum 1 to the transfer medium P in the transfer portion Nt in the case in which the electric resistance value of the transfer medium P is low and the amount of the current flowing from the transfer portion Nt to the ground via the transfer medium P and the metal plate 15a reaches the maximum amount. Specifically, the current IM is calculated by subtracting the current Itr1 from the current Itr2.
In the present exemplary embodiment, the current Itr1, the current Itr2, the current IM, and the voltage VM are each stored in advance in the controller circuit 23. The lower the electric resistance of the transfer roller 8 is, the greater the amount of the current Itr flowing to the transfer roller 8 becomes and the greater the amount of escape current to the metal plate 15a becomes. Thus, the current Itr1 and the current Itr2 are set based on the voltage V0 obtained by ATVC.
For example, according to the case of performing image forming on the moisture-absorbed sheet in the present exemplary embodiment, the voltage V0 was 500 V, the current Itr1 was 10.5 μA, the current IM was 1.5 μA, the voltage VM was 800 V, and the current Itr detected by the detection unit 19 was 11.1 μA. From the foregoing values and formula (1), the current IL is 0.6 μA and the change width ΔV=320 V. Thus, in the case of performing image forming on the moisture-absorbed sheet, after the detection unit 19 detects the current Itr, the voltage to be applied from the transfer power source 18 to the transfer roller 8 is changed from 750 V to 1070 V.
The longer the transfer medium P is left under a high-temperature, high-humidity environment, the lower the electric resistance of the transfer medium P becomes and the more the amount of current leaking in the transfer portion Nt becomes. Further, the contact state between the metal plate 15a and the transfer medium P is not constant, and the contact resistance between the transfer medium P and the metal plate 15a changes depending on the thickness, orientation, etc. of the transfer mediums P stored in the sheet feeding cassette 15. For example, in the case which the sheet feeding cassette 15 stores a large amount of transfer mediums P, the level of contact between the transfer medium P and the metal plate 15a is high, and a more amount of current leaks to the ground. Further, if the level of contact between the transfer medium P and the metal plate 15a is changed due to the orientation of the transfer medium P, the amount of current leaking to the ground also changes.
<Image Evaluation Result>
An entirely black solid image was formed on a moisture-absorbed sheet and an immediately-unwrapped sheet in the present exemplary embodiment and the first and second comparative examples, and the following results were obtained.
First, in the first comparative example, when the image forming was performed on the moisture-absorbed sheet, a current leakage occurred from the transfer portion Nt to the ground via the transfer medium P and the metal plate 15a and thus the current flowing from the transfer roller 8 toward the photosensitive drum 1 in the transfer portion Nt became insufficient. This causes a transfer defect. Meanwhile, when the image forming was formed on the immediately-unwrapped sheet, no transfer defect occurred.
Further, in the second comparative example, no transfer defect occurred when the image forming was performed on the moisture-absorbed sheet. However, when the image forming was performed on the immediately-unwrapped sheet, an excessive current flowed from the transfer roller 8 to the photosensitive drum 1. This causes a transfer defect. This is because the voltage to be applied from the transfer power source 18 to the transfer roller 8 is set also with respect to the immediately-unwrapped sheets which have a high electric resistance and via which less current thus leaks from the transfer portion Nt to the ground, based on the assumption that a current leakage to the ground via the transfer medium P and the metal plate 15a is likely to occur.
On the contrary, according to the present exemplary embodiment, the voltage to be applied from the transfer power source 18 to the transfer roller 8 was controlled as appropriate regardless of the type of the transfer medium P and thus a transfer defect resulting from a current leakage from the transfer portion Nt to the ground via the transfer medium P and the metal plate 15a was prevented.
As described above, in the present exemplary embodiment, the voltage change width ΔV in the transfer portion Nt and the voltage to be applied to the transfer roller 8 are set based on the current detected by the detection unit 19 while the transfer voltage Vt set by ATVC is applied to the transfer roller 8. In this way, the voltage to be applied to the transfer roller 8 at the time of transferring a toner image onto the transfer medium P is controlled as appropriate.
While the arrangement in which the voltage change width ΔV in the transfer portion Nt and the voltage to be applied to the transfer roller 8 are set with respect to a single transfer medium P is described in the present exemplary embodiment, the arrangement is not limited to the above-described arrangement. For example, in the case of continuously performing image forming on a plurality of transfer mediums P (hereinafter, this image forming will be referred to as “continuous printing”), the transfer mediums P which are continuously conveyed are considered to have substantially the same electric resistance. Thus, the value of the change width ΔV that is set with respect to the first transfer medium P can be reflected in the voltage to be applied from the transfer power source 18 to the transfer roller 8 in the case of forming an image on the second transfer medium P.
More specifically, in the case of executing a continuous printing job, the voltage (transfer voltage Vt+change width ΔV) that is set at the time of forming an image on the first transfer medium P is applied from the transfer power source 18 to the transfer roller 8 and constant voltage control is performed from the leading edge to the trailing edge of the second transfer medium P. In this way, the waiting period for a response and the detection of the current Itr in
Further, while the metal plate 15a provided to the sheet feeding cassette 15 is described as the conductive member connected to the ground according to the present exemplary embodiment, the conductive member is not limited to the metal plate 15a. For example, an image forming apparatus including a guide member which is a conductive member disposed upstream from the transfer portion Nt in the conveyance direction for the transfer medium P and connected to the ground and is configured to guide the transfer medium P to the transfer portion Nt can perform control similar to the control in the present exemplary embodiment and produce a similar advantage.
Further, while the metal plate 15a is grounded without an electric resistor according to the present exemplary embodiment, the structure is not limited to the above-described structure, and the metal plate 15a can be grounded via an electric resistor having a predetermined resistance value. In this case, an advantage similar to that of the present exemplary embodiment is produced by storing the electric resistance value of the electric resistor in advance in the controller circuit 23 and calculating the change width ΔV based on the electric resistance value.
According to the first exemplary embodiment, the arrangement in which the voltage change width ΔV is set based on the current Itr detected by the detection unit 19 while the transfer medium P is held in the transfer portion Nt and the transfer voltage Vt is applied from the transfer power source 18 to the transfer roller 8, and the change width ΔV is fed back to the transfer control is described. According to a second exemplary embodiment, the voltage change width ΔV is set using a method similar to the method in the first exemplary embodiment, but the second exemplary embodiment is different from the first exemplary embodiment in that the change width ΔV is fed back to the transfer control at or after the point at which the transfer medium P reaches the fixing portion Nf. In the following description, components that are similar to those in the first exemplary embodiment are given the same reference numerals, and description of the similar components is omitted.
In the case in which the resistance of the transfer medium P is low, an image defect as illustrated in
As illustrated in
Under the condition that a current leakage occurs from the transfer portion Nt to the ground via the transfer medium P as described in the first exemplary embodiment, since the electric resistance of the transfer medium P is low, an AC banding image is likely to occur. Furthermore, in such a state, the current flowing from the transfer roller 8 to the photosensitive drum 1 in the transfer portion Nt is likely to decrease due to the current leakage. Specifically, in the case in which AC banding occurs, the toner image transferability in the transfer portion Nt differs between the position at which the current is insufficient and the position at which the current is not insufficient and the transfer is performed, and consequently an AC banding image is formed. Thus, in the case in which AC banding occurs, the occurrence of AC banding is reducible by increasing the absolute value of the voltage to be applied from the transfer power source 18 to the transfer roller 8.
According to the present exemplary embodiment, in the case in which the alternating-current voltage from the commercial power source 52 is superimposed on the transfer voltage Vt via the transfer medium P and the waveform during the frequency period of the alternating-current voltage is thus detected by the detection unit 19, the controller circuit 23 performs control to change the transfer voltage Vt. According to the present exemplary embodiment, the controller circuit 23 changes the voltage to be applied from the transfer power source 18 to the transfer roller 8 from the transfer voltage Vt (first voltage) to a voltage (first voltage) that is the sum of the voltage change width ΔV and the transfer voltage Vt which are set by a method similar to the method according to the first exemplary embodiment.
As described above, the value of the voltage change width ΔV that is set before the transfer medium P is held in the fixing portion Nf is reflected in the transfer control performed after AC banding is detected. This enables more appropriate control of the voltage to be applied from the transfer power source 18 to the transfer roller 8.
More specifically, for example, even in the case in which the electric resistance of the transfer medium P is high and thus the amount of current flowing from the transfer portion Nt to the ground is small, if the image printing ratio is low, i.e., if the amount of toner in the transfer portion Nt is small, the electric resistance in the transfer portion Nt becomes low. In other words, the amount of current flowing from the transfer roller 8 to the photosensitive drum 1 becomes relatively large, and thus the value of the current Itr detected by the detection unit 19 increases, whereby the voltage change width ΔV also increases. As a result, the voltage to be applied from the transfer power source 18 to the transfer roller 8 may be set to an excessively large value.
Meanwhile, the waveform during the frequency period of the alternating-current voltage from the commercial power source 52 is transmitted from the fixing portion Nf to the transfer portion Nt depending on the electric resistance of the transfer medium P regardless of the image printing ratio. Thus, in the case in which the electric resistance of the transfer medium P is high, AC banding is not detected in the transfer portion Nt. Accordingly, the value of the change in the voltage ΔV that is set before the transfer medium P is held in the fixing portion Nf is reflected in the transfer control performed after AC banding is detected so that more appropriate control of the voltage to be applied from the transfer power source 18 to the transfer roller 8 becomes possible.
[Occurrence Detection of AC Banding]
The following describes details of the control according to the present exemplary embodiment which is performed when an entirely black solid image was formed under a high-temperature, high-humidity environment with a room temperature of 32.5 degrees and a humidity of 80% on a transfer medium P, A4-size sheet (grammage 80 g/m2) manufactured by Océ Red Label, that had been left under the same high-temperature, high-humidity environment for 48 hours or longer. According to the present exemplary embodiment, the circumferential speed of the photosensitive drum 1 is 118 mm/seconds, the voltage from the commercial power source 52 is 220 V, and the power source frequency is 50 Hz. Further, the value of the voltage V0 when ATVC control was performed to pass a current of 3 μA was 500 V. Based on this result, the controller circuit 23 set the transfer voltage to be applied from the transfer power source 18 to the transfer roller 8 in the toner image transfer from the photosensitive drum 1 onto the transfer medium P to 750 V and started image forming.
The current flowing in the transfer roller 8 is detected by the detection unit 19, and if AC banding occurs when the image forming is started and the transfer medium P reaches the fixing portion Nf, the detection unit 19 detects a signal containing noise as illustrated in
The simple moving average may also be considered as a low-pass filter, and a gain G suitable for use in calculating the simple moving average to obtain a waveform that the amplitudes of frequencies higher than a signal frequency f are attenuated is expressed by formula (3) as shown below. According to the present exemplary embodiment, the power source frequency from the commercial power source 52 is 50 Hz, and the waveforms C and D are obtained using formula (3) to remove, as noise, the amplitudes frequencies higher than 60 Hz from the detection result in
where G is gain, τ is M (moving average score)×Δt (sampling interval of 1 ms), and f is signal frequency of 60 Hz. From formula (3), the obtained score of the simple moving average (moving average score) is seven.
The waveform C illustrated in
As illustrated in
Alternatively, it can be determined that AC banding occurs if the value of the frequency ½ΔT is within the predetermined frequency range of 40 Hz<½ΔT<70 Hz. In this way of setting, the predetermined frequency range includes both the power source frequencies of 50 Hz and 60 Hz so that AC banding is detectable regardless of whether the power source frequency of the commercial power source is 50 Hz or 60 Hz.
Further, in the present exemplary embodiment, the difference (difference ΔI) between the current values of adjacent peaks is calculated, and the frequency ½ΔT at which the value of the difference ΔI is not less than a predetermined value is compared with the frequency of the alternating-current voltage, as illustrated in
The current that flows in the transfer roller 8 can be deflected at the moment when the transfer medium P enters the fixing portion Nf or due to a change in the amount of toner transferred onto the transfer medium P. In order to remove such noise, it is desirable to compare the difference ΔI and the frequency ½ΔT for at least three consecutive peaks (1.5 periods). This prevents detection of such a noise that the current flowing in the transfer roller 8 is deflected due to a cause other than AC banding, and thus AC banding is detectable with great accuracy.
According to the present exemplary embodiment, the difference ΔI and the frequency ½ΔT for five consecutive peaks (2.5 periods) are compared to prevent an occurrence of an image defect, while the accuracy of AC banding detection can further be improved by comparing more peaks. From the foregoing detection result, if the controller circuit 23 determines that AC banding occurs, the controller circuit 23 controls the transfer power source 18 to change the voltage to be applied to the transfer roller 8 from the transfer voltage Vt to a voltage that is the sum of the transfer voltage Vt and the voltage change width ΔV.
The method of calculating the voltage change width ΔV is as described above in the first exemplary embodiment. Further, the image forming conditions according to the present exemplary embodiment are similar to those in the first exemplary embodiment. Specifically, as illustrated in
Further, in the arrangement according to the present exemplary embodiment, in the case in which the controller circuit 23 determines that no AC banding occurs, the voltage to be applied to the transfer roller 8 is not changed from the transfer voltage Vt even if the value of the current Itr measured before the transfer medium P reaches the fixing portion Nf is large. This enables more appropriate control of the voltage to be applied from the transfer power source 18 to the transfer roller 8.
In the arrangement according to the present exemplary embodiment, in the case of continuous image forming on a plurality of transfer mediums P, the AC banding occurrence detection can be performed on each sheet or on each continuous printing job. For example, in the case in which the detection unit 19 detects an occurrence of AC banding during image forming on a first transfer medium P1 while there remains a job for forming an image on a second transfer medium P2 following the first transfer medium P1, the AC banding detection does not have to be performed on the second transfer medium P2. The transfer mediums P stored in the sheet feeding cassette 15 are under the same environment, and it is thus considered that the type and state of the transfer mediums P are substantially similar. Thus, the voltage to be applied to the transfer roller 8 may be changed based on the same setting as the setting for the first transfer medium P1 at the timing at which the second transfer medium P2 is held in the fixing portion Nf, without performing AC banding detection on the second transfer medium P. In this way, an occurrence of an image defect is prevented while the number of times of AC banding detection is reduced.
While applications to a monochrome image forming apparatus are described in the above-described exemplary embodiments, the present disclosure is not limited to the above-described exemplary embodiments. An exemplary embodiment of the present disclosure is also applicable to any apparatus including a fixing unit and a transfer member configured to transfer a toner image from an image bearing member onto a transfer medium P. Specifically, as illustrated in
In the image forming apparatus 300 according to the present exemplary embodiment, an image signal transmitted from an information device, such as a personal computer (not illustrated), is received and analyzed in the image forming apparatus 300 and the analyzed image signal is transmitted to a control unit 323. Then, the control unit 323 controls various units to start an image forming operation in the image forming apparatus 300.
The image forming unit SK includes a photosensitive drum 301K which is a drum-shaped photosensitive member, a charging roller 302K which is a charging unit, a development roller 305K which is a development unit, and a cleaning unit 306K. When the image forming operation is started, the photosensitive drum 301K is driven and rotated in the direction indicated by an arrow R31 at a predetermined circumferential speed, and during the rotation process, the photosensitive drum 301K is uniformly charged with a predetermined polarity (which is negative according to the present exemplary embodiment) to a predetermined potential by the charging roller 302K. The photosensitive drum 301K is then exposed by an exposure unit 304K based on the image signal and an electrostatic latent image is formed on the surface of the photosensitive drum 301K. The electrostatic latent image formed on the surface of the photosensitive drum 301K is developed with toner supplied from the development roller 305K and a toner image is formed on the photosensitive drum 301K.
An endless intermediate transfer belt 307 which is an image bearing member stretched around stretching rollers 327a to 327c which are a stretching member is disposed to face the photosensitive drum 301K, and the intermediate transfer belt 307 is driven and rotated in the direction of an arrow R32 in
A secondary transfer roller 328 which is a transfer member is disposed to face the stretching roller 327a via the intermediate transfer belt 307 which is an image bearing member, and a secondary transfer portion Nt3 which is a transfer portion is formed at the position at which the intermediate transfer belt 307 is in contact with the secondary transfer roller 328. The secondary transfer roller 328 is connected to a transfer power source 318, and the control unit 323 controls the transfer power source 318 to apply a voltage to the secondary transfer roller 328. The toner images of the plurality of colors are thus secondarily transferred from the intermediate transfer belt 307 onto the transfer medium P.
The transfer medium P stacked in the sheet feeding cassette 309 is fed from the sheet feeding cassette 309 by a sheet feeding roller 311 and conveyed to the secondary transfer portion Nt3 in synchronization with the timing at which the toner images of the plurality of colors formed on the intermediate transfer belt 307 reach the secondary transfer portion Nt3. The transfer medium P onto which the toner images of the plurality of colors are secondarily transferred in the secondary transfer portion Nt3 is conveyed to a fixing unit 314 and heated by a heating unit 331 and pressed by a pressing unit 330 and the toners of the respective colors are melted and fixed to the transfer medium P. The transfer medium P is then discharged by a sheet discharge roller 316 to a sheet discharge tray 327 which is a sheet stacking unit.
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of priority from Japanese Patent Application No. 2017-252537, filed Dec. 27, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-252537 | Dec 2017 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20040184828 | Bannai | Sep 2004 | A1 |
| 20080063418 | Kyung | Mar 2008 | A1 |
| 20150338813 | Deno | Nov 2015 | A1 |
| Number | Date | Country |
|---|---|---|
| 11-219042 | Aug 1999 | JP |
| 2003-149959 | May 2003 | JP |
| 2011-215538 | Oct 2011 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20190196377 A1 | Jun 2019 | US |
