Patent Grant
8045875
The present application is based on and claims priority to Japanese Patent Application Nos. 2007-295110, filed on Nov. 14, 2007, and 2008-125090, filed on May 12, 2008 in the Japan Patent Office, the entire contents of each of which are hereby incorporated herein by reference.
1. Field of the Invention
Exemplary aspects of the present invention relate to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method using the image forming apparatus for controlling a voltage of an electric field to transfer a toner image.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form a color image on a recording medium (e.g., a transfer sheet) based on image data using electrophotography. Thus, for example, chargers uniformly charge surfaces of image carriers. An optical writer emits light beams onto the charged surfaces of the image carriers to form electrostatic latent images on the image carriers according to the image data, respectively. Development devices supply yellow, cyan, magenta, and black toner particles to the electrostatic latent images formed on the image carriers to make the electrostatic latent images visible as yellow, cyan, magenta, and black toner images, respectively. A transfer member transfers the toner images directly from the image carriers and superimposes the toner images onto a transfer sheet conveyed on a conveyance belt in a direct transfer method to form a color toner image on the transfer sheet. Alternatively, a first transfer member transfers the toner images from the image carriers and superimposes the toner images onto an intermediate transfer member in an indirect transfer method to form a color toner image on the intermediate transfer member, and a second transfer member transfers the color toner image from the intermediate transfer member onto a transfer sheet. Cleaners clean the surfaces of the image carriers after the toner images are transferred from the image carriers. Finally, a fixing device applies heat and pressure to the transfer sheet bearing the color toner image to fix the color toner image on the transfer sheet, thus forming the color image on the transfer sheet.
In each of the direct transfer method and the indirect transfer method, the transfer member, including the first transfer member and the second transfer member, applies a transfer bias having a polarity either identical to or opposite to a polarity of the toner image to a transfer electric field generator, that is, the conveyance belt in the direct transfer method and the intermediate transfer member and the transfer sheet in the indirect transfer method, so as to generate a transfer electric field. An electrostatic attractive force or an electrostatic repulsive force generated by the transfer electric field transfers the toner image onto the intermediate transfer member or the transfer sheet.
The transfer member and the transfer electric field generator generally include a semi-conductive material whose resistance fluctuates with environmental conditions such as temperature and humidity. The resistance also changes gradually over time due to deterioration of the semi-conductive material. Accordingly, the transfer bias applied by the transfer member to the transfer electric field generator changes, resulting in decreased transfer efficiency and formation of a faulty toner image.
To address these problems, the transfer bias is adjusted to a predetermined constant voltage or a predetermined constant current by measuring a voltage or a current flowing in the transfer member contacting the transfer electric field generator or a surface potential of the transfer electric field generator, for example. However, such measurements may not be precise due to changes in speed of an image forming operation and measurement error caused by movement of the transfer electric field generator.
Obviously, such decreased transfer efficiency and its resulting formation of a faulty toner image are undesirable, and accordingly, there is a need for a technology to generate a stable transfer electric field regardless of change in resistance of the transfer electric field generator and the transfer member.
This specification describes below an image forming apparatus according to an exemplary embodiment of the present invention. In one exemplary embodiment of the present invention, the image forming apparatus includes an image carrier configured to carry a toner image and a transfer device including at least one transfer member, a transfer electric field generator, a toner image receiver, a voltage applier, a potential measurement device, and a controller. The at least one transfer member is configured to apply a transfer bias. The transfer electric field generator is configured to receive the transfer bias applied by the at least one transfer member to generate a transfer electric field. The toner image receiver is configured to receive the toner image transferred from the image carrier by the transfer electric field generated by the transfer electric field generator. The voltage applier is configured to apply a predetermined voltage to the transfer electric field generator. The potential measurement device is configured to measure a surface potential of the transfer electric field generator when a predetermined time period elapses after the voltage applier applies the predetermined voltage to the transfer electric field generator. The controller is configured to determine the transfer bias to be applied by the at least one transfer member to the transfer electric field generator based on the measured surface potential of the transfer electric field generator.
This specification further describes below an image forming method according to an exemplary embodiment of the present invention. In one exemplary embodiment of the present invention, the image forming method includes carrying a toner image with an image carrier, applying a voltage to a transfer electric field generator with a voltage applier, and measuring a surface potential of the transfer electric field generator with a potential measurement device when a predetermined first time period elapses after the voltage applier applies the voltage to the transfer electric field generator. The image forming method further includes determining a transfer bias to be applied by at least one transfer member to the transfer electric field generator based on the measured surface potential of the transfer electric field generator, and applying the transfer bias to the transfer electric field generator with the at least one transfer member. The image forming method further includes generating a transfer electric field by the transfer bias applied by the at least one transfer member with the transfer electric field generator, and transferring the toner image from the image carrier onto a toner image receiver with the transfer electric field.
This specification further describes below an image forming method according to an exemplary embodiment of the present invention. In one exemplary embodiment of the present invention, the image forming method includes carrying a toner image with an image carrier, applying a voltage to a transfer electric field generator with a voltage application member serving as a voltage applier and contacting the transfer electric field generator, and measuring a surface potential of the transfer electric field generator with a potential measurement device when a predetermined first time period elapses after the voltage application member applies the voltage to the transfer electric field generator. The image forming method further includes connecting a constant-voltage power source to at least one transfer member using a switch to change the voltage applier from the voltage application member to the at least one transfer member, applying a voltage to the transfer electric field generator with the at least one transfer member, and measuring the surface potential of the transfer electric field generator again with the potential measurement device when a predetermined second time period elapses after the at least one transfer member applies the voltage to the transfer electric field generator. The image forming method further includes determining a transfer bias to be applied by the at least one transfer member to the transfer electric field generator based on the measured surface potentials of the transfer electric field generator that compensates for change in resistance of the at least one transfer member, and applying the transfer bias to the transfer electric field generator with the at least one transfer member. The image forming method further includes generating a transfer electric field by the transfer bias applied by the at least one transfer member with the transfer electric field generator, and transferring the toner image from the image carrier onto a toner image receiver with the transfer electric field.
A more complete appreciation of the invention and the many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
In describing exemplary embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, in particular to
As illustrated in
The image forming apparatus 100 can be a copier, a facsimile machine, a printer, a plotter, a multifunction printer having at least one of copying, printing, scanning, plotter, and facsimile functions, or the like. According to this non-limiting exemplary embodiment of the present invention, the image forming apparatus 100 functions as a tandem-type printer for forming a color image on a transfer material by electrophotography using an indirect transfer method.
In the image forming device 1, the four image forming units A1, A2, A3, and A4 form yellow, cyan, magenta, and black toner images, respectively. Specifically, the yellow, cyan, magenta, and black toner images are formed on outer circumferential surfaces of the photoconductive drums 1A, 1B, 1C, and 1D, respectively. The transfer device B transfers the yellow, cyan, magenta, and black toner images formed on the photoconductive drums 1A, 1B, 1C, and 1D onto a transfer sheet, serving as a transfer material, using the indirect transfer method.
The image forming apparatus 100 further includes an exposure device, a sheet supplier, and a fixing device. The sheet supplier includes a paper tray, a feeding roller, a friction pad, and a registration roller pair. Specifically, the exposure device, such as an LSU (laser scanning unit), emits laser beams onto the photoconductive drums 1A, 1B, 1C, and 1D based on image data sent from a personal computer, for example, to selectively expose the outer circumferential surfaces of the photoconductive drums 1A, 1B, 1C, and 1D, so as to form electrostatic latent images on the photoconductive drums 1A, 1B, 1C, and 1D, respectively. The sheet supplier supplies a transfer sheet to the transfer device B. Specifically, the paper tray loads and stores transfer sheets having a predetermined size, including paper and a resin sheet, such as an OHP (overhead projector) transparency. The feeding roller feeds the transfer sheets loaded on the paper tray one by one toward a conveyance path. The friction pad includes an elastomer and separates each transfer sheet from other transfer sheets. The registration roller pair feeds the transfer sheet to a second transfer nip formed between the intermediate transfer belt 6 and the second transfer belt 9 at a proper time. The fixing device includes a fixing roller and a pressing roller. The fixing roller and the pressing roller apply heat and pressure to the transfer sheet bearing a toner image to fix the toner image on the transfer sheet.
The image forming units A1, A2, A3, and A4 form a tandem structure in which the image forming units A1, A2, A3, and A4 are arranged in this order from an upstream toward a downstream in a rotating direction A of the intermediate transfer belt 6. The image forming units A1, A2, A3, and A4 form yellow, cyan, magenta, and black toner images, respectively, and have a common structure. For example, in the image forming unit A1, the charging roller 3A and the development device 4A surround the photoconductive drum 1A. The photoconductive drum 1A, serving as a latent image carrier and an image carrier, has a roller shape and rotates in a rotating direction D. The charging roller 3A opposes the photoconductive drum 1A without contacting the photoconductive drum 1A. The charging roller 3A applies a charging bias onto the outer circumferential surface of the photoconductive drum 1A to uniformly charge the outer circumferential surface of the photoconductive drum 1A. The charging roller 3A also cancels an electrostatic latent image formed on the photoconductive drum 1A after a toner image formed in correspondence to the electrostatic latent image is transferred from the photoconductive drum 1A to the intermediate transfer belt 6 to initialize the photoconductive drum 1A. The development device 4A applies a development bias to an electrostatic latent image formed on the photoconductive drum 1A by the exposure device to adhere yellow toner to the electrostatic latent image, so as to make the electrostatic latent image visible as a yellow toner image.
In the transfer device B, the first transfer device B1 applies a first transfer bias to the yellow toner image formed on the photoconductive drum 1A to transfer the yellow toner image onto the intermediate transfer belt 6 having an endless belt shape. Similarly, cyan, magenta, and black toner images are formed on the photoconductive drums 1B, 1C, and 1D, respectively, transferred from the photoconductive drums 1B, 1C, and 1D, and superimposed onto the yellow toner image on the intermediate transfer belt 6 to form a color toner image on the intermediate transfer belt 6. The second transfer device B2 applies a second transfer bias to the color toner image formed on the intermediate transfer belt 6 to transfer the color toner image onto the transfer sheet fed by the registration roller pair. The intermediate transfer belt 6 is looped over the driving roller 20 connected to and driven by a driver, the driven roller 21, and the counter roller 22. The driving roller 20 rotates the intermediate transfer belt 6 in the rotating direction A.
The first transfer rollers 5A, 5B, 5C, and 5D, serving as transfer members, contact an inner circumferential surface of the intermediate transfer belt 6 to apply first transfer biases to the intermediate transfer belt 6. The first transfer rollers 5A, 5B, 5C, and 5D oppose the photoconductive drums 1A, 1B, 1C, and 1D via the intermediate transfer belt 6, respectively. A contact-separate mechanism applies pressure to the inner circumferential surface of the intermediate transfer belt 6 to press the intermediate transfer belt 6 toward the photoconductive drums 1A, 1B, 1C, and 1D, so as to form first transfer nips between the intermediate transfer belt 6 and the photoconductive drums 1A, 1B, 1C, and 1D, respectively. The first transfer rollers 5A, 5B, 5C, and 5D are electrically connected to the power sources 10A, 10B, 10C, and 10D, serving as constant-voltage power sources, respectively, via a conductive material, and grounded. The first transfer rollers 5A, 5B, 5C, and 5D apply first transfer biases onto the inner circumferential surface (e.g., a back surface) of the intermediate transfer belt 6, serving as a transfer electric field generator, to generate a transfer electric field having a polarity opposite to a polarity of the yellow, cyan, magenta, and black toner images formed on the photoconductive drums 1A, 1B, 1C, and 1D at the first transfer nips, respectively. Accordingly, an electrostatic attractive force transfers the yellow, cyan, magenta, and black toner images from the photoconductive drums 1A, 1B, 1C, and 1D onto an outer circumferential surface (e.g., a front surface) of the intermediate transfer belt 6.
In the second transfer device B2, the second transfer roller 7, serving as a driving roller, is connected to a driver. The second transfer belt 9, having an endless belt shape and serving as a conveyance belt, is looped over the second transfer roller 7 and the driven roller 8. The second transfer belt 9 contacts the intermediate transfer belt 6 at a position between the second transfer roller 7 and the counter roller 22 to form a second transfer nip. The power source 15, serving as a constant-voltage power source, is electrically connected to the counter roller 22 via a conductive material, and grounded. The counter roller 22, serving as a transfer member, applies a second transfer bias onto the inner circumferential surface of the intermediate transfer belt 6, serving as a transfer electric field generator, to generate a transfer electric field having a polarity identical to a polarity of the color toner image formed on the intermediate transfer belt 6 at the second transfer nip. Accordingly, an electrostatic repulsive force transfers the color toner image from the intermediate transfer belt 6 onto the transfer sheet conveyed to the second transfer nip. Alternatively, the second transfer roller 7, instead of the counter roller 22, may apply a second transfer bias to generate a transfer electric field having a polarity opposite to the polarity of the color toner image formed on the intermediate transfer belt 6.
In the transfer device B, the conductive brush 11, the metal plate 12, and the surface potential sensor 13, which serve as a potential measurement device, are provided between the first transfer rollers 5C and 5D. The metal plate 12 has a rectangular plate shape and is connected to the conductive brush 11, serving as a conductor, via a conductive material. The surface potential sensor 13 is provided with respect to the metal plate 12 in such a manner that a predetermined gap is provided between the surface potential sensor 13 and the metal plate 12, and measures a surface potential of the intermediate transfer belt 6 without contacting the intermediate transfer belt 6.
The timer 41 counts a time period elapsed after the power source 10C, serving as a voltage applier, starts applying a voltage. The recording member 42 includes a memory and an AD board, for example, and records the surface potential of the intermediate transfer belt 6 measured by the surface potential sensor 13 together with the time period counted by the timer 41. The controller 43 includes a CPU (central processing unit) and controls the timer 41 and the recording member 42. The power sources 10A, 10B, 10C, and 10D are connected to the controller 43. The surface potential sensor 13 is connected to the controller 43 via the recording member 42. The controller 43 recognizes the measured surface potential of the intermediate transfer belt 6 recorded by the recording member 42 together with the time period counted by the timer 41 as a function of time. Alternatively, the controller 43 recognizes the measured surface potential of the intermediate transfer belt 6 as an increasing speed of the surface potential of the intermediate transfer belt 6.
Alternatively, the conductive fiber 11B may include a resin other than the nylon resin or a metal. A conductive sponge material, such as urethane in which carbon black is dispersed, may replace the conductive brush 11. In order to prevent the intermediate transfer belt 6 from being worn by the conductive brush 11 or the conductive sponge, the conductive brush 11 or the conductive sponge may separate from the intermediate transfer belt 6 during an image forming operation.
Referring to
When the image forming device 1 starts an image forming operation, the photoconductive drums 1A, 1B, 1C, and 1D rotate in the rotating direction D. The charging rollers 3A, 3B, 3C, and 3D uniformly charge the outer circumferential surfaces of the photoconductive drums 1A, 1B, 1C, and 1D, respectively, to have a predetermined polarity. The exposure device emits laser beams onto the charged surfaces of the photoconductive drums 1A, 1B, 1C, and 1D according to yellow, cyan, magenta, and black image data to form electrostatic latent images on the outer circumferential surfaces of the photoconductive drums 1A, 1B, 1C, and 1D, serving as latent image carriers and image carriers, respectively. The development devices 4A, 4B, 4C, and 4D make the electrostatic latent images formed on the photoconductive drums 1A, 1B, 1C, and 1D visible as yellow, cyan, magenta, and black toner images, respectively. The first transfer rollers 5A, 5B, 5C, and 5D, serving as transfer members, apply first transfer biases to the intermediate transfer belt 6, serving as a transfer electric field generator, to generate a transfer electric field having a polarity opposite to a polarity of the yellow, cyan, magenta, and black toner images formed on the photoconductive drums 1A, 1B, 1C, and 1D at the first transfer nips, respectively. Accordingly, an electrostatic attractive force transfers the yellow, cyan, magenta, and black toner images formed on the photoconductive drums 1A, 1B, 1C, and 1D onto the intermediate transfer belt 6, serving as a toner image receiver, in such a manner that the yellow, cyan, magenta, and black toner images are superimposed on the intermediate transfer belt 6, respectively, to form a color toner image on the intermediate transfer belt 6, serving as an image carrier. At the second transfer nip formed between the intermediate transfer belt 6 and the second transfer belt 9, the counter roller 22, serving as a transfer member, applies a second transfer bias to the intermediate transfer belt 6, serving as a transfer electric field generator, to generate a transfer electric field having a polarity identical to a polarity of the color toner image formed on the intermediate transfer belt 6. An electrostatic repulsive force generated by the transfer electric field transfers the color toner image from the intermediate transfer belt 6 onto a transfer sheet, supplied by the sheet supplier and serving as a toner image receiver. Alternatively, when the image forming device 1 forms a monochrome image, the image forming device 1 performs an image forming operation by using only a predetermined photoconductive drum (e.g., the photoconductive drum 1D for forming a black toner image).
Referring to
In step S101, the image forming apparatus 100 is powered on. In step S102, the timer 41 is turned on to start counting a time period. In step S103, before the image forming apparatus 100 starts an image forming operation, that is, when the photoconductive drums 1A, 1B, 1C, and 1D, the first transfer rollers 5A, 5B, 5C, and 5D, and the intermediate transfer belt 6 stop rotating, the power sources 10C and 10D, serving as constant-voltage power sources, apply predetermined voltages, for example, 1,000 V and 0 V, to the first transfer rollers 5C and 5D, respectively. Simultaneously, the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. In step S104, the controller 43 determines whether or not the time period counted by the timer 41 reaches a predetermined time period (e.g., 1.0 second). For example, the controller 43 determines whether or not a predetermined time period elapses after the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. When the time period counted by the timer 41 reaches the predetermined time period, that is, when YES is selected in step S104, the surface potential sensor 13 measures a surface potential of the intermediate transfer belt 6 via the conductive brush 11 and the metal plate 12 in step S105. In step S106, the recording member 42 records the measured surface potential of the intermediate transfer belt 6. In step S107, the controller 43 calculates and determines a proper transfer bias to be applied by the first transfer rollers 5A, 5B, 5C, and 5D to transfer a toner image at which the image forming apparatus 100 can provide proper transfer efficiency and image quality. In step S108, the image forming apparatus 100 starts an image forming operation or other control operation.
In the flowchart shown in
As illustrated in
The surface potential of the intermediate transfer belt 6 can be measured once or a plurality of times. The surface resistivity of the intermediate transfer belt 6 can be predicted with an improved precision based on the potential increasing speed and curve of the intermediate transfer belt 6 recorded by the recording member 42.
Referring to
In step S201, the image forming apparatus 100 is powered on. In step S202, first and second timers equivalent to the timer 41 are turned on to start counting a time period. In step S203, before the image forming apparatus 100 starts an image forming operation, that is, when the photoconductive drums 1A, 1B, 1C, and 1D, the first transfer rollers 5A, 5B, 5C, and 5D, and the intermediate transfer belt 6 stop rotating, the power sources 10C and 10D, serving as constant-voltage power sources, apply predetermined voltages to the first transfer rollers 5C and 5D, respectively. Simultaneously, the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. In step S204, the controller 43 determines whether or not the time period counted by the first timer reaches a predetermined first time period. For example, the controller 43 determines whether or not a predetermined first time period elapses after the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. When the time period counted by the first timer reaches the predetermined first time period, that is, when YES is selected in step S204, the surface potential sensor 13 measures a surface potential of the intermediate transfer belt 6 via the conductive brush 11 and the metal plate 12 in step S205. In step S206, the recording member 42 records the measured surface potential of the intermediate transfer belt 6. In step S207, the controller 43 determines whether or not the time period counted by the second timer reaches a predetermined second time period. For example, the controller 43 determines whether or not a predetermined second time period elapses after the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. When the time period counted by the second timer does not reach the predetermined second time period, that is, when NO is selected in step S207, the first timer is reset in step S208. In step S209, a voltage applied to measure the potential of the intermediate transfer belt 6, that is, a voltage applied by the first transfer roller 5C, is changed in step S209. When the time period counted by the second timer reaches the predetermined second time period, that is, when YES is selected in step S207, the controller 43 calculates and determines a proper transfer bias to be applied by the first transfer rollers 5A, 5B, 5C, and 5D in step S210. In step S211, the image forming apparatus 100 starts an image forming operation or other control operation.
Determining the proper transfer bias as described above changes the potential of the intermediate transfer belt 6 transiently. Further, a material included in the intermediate transfer belt 6 causes an electric field to affect the resistance of the intermediate transfer belt 6. Considering those, the potential of the intermediate transfer belt 6 is measured by changing the voltage applied to the intermediate transfer belt 6, and the surface resistivity of the intermediate transfer belt 6 is predicted based on a potential change curve recorded by the recording member 42 with an improved precision. In other words, even when the intermediate transfer belt 6 includes an electron conduction material such as a carbon dispersion material, the controller 43 can determine the proper transfer bias with an improved precision.
The process shown in
The surface resistivity of the intermediate transfer belt 6 may be predicted based on an electric current flowing between the first transfer rollers 5C and 5D. However, in general image forming apparatuses using electrophotography, an electric current in an amount of about 1 μA flows between the first transfer rollers 5C and 5D. Therefore, a high-precision ammeter may be needed or measurement error may increase. To address this, in the image forming apparatus 100 according to this exemplary embodiment, the surface potential sensor 13, that is, a non-contact type sensor, measures the surface potential of the intermediate transfer belt 6. When the non-contact type sensor is used, an electric charge does not escape from the intermediate transfer belt 6. Further, the non-contact type sensor can measure a slight amount of electric charges as a great potential by decreasing an amount of electrostatic charges around a measurement area on the intermediate transfer belt 6.
The surface potential sensor 13 may be provided near the outer circumferential surface or the inner circumferential surface of the intermediate transfer belt 6. In this case, the surface potential sensor 13 measures a small area on the intermediate transfer belt 6. Further, variation in the surface resistivity of the intermediate transfer belt 6 or toner particles on the intermediate transfer belt 6 may degrade sensitivity of the surface potential sensor 13. To address this, according to this exemplary embodiment, the conductive brush 11 contacts the inner circumferential surface of the intermediate transfer belt 6 across substantially the full width of the intermediate transfer belt 6. The conductive brush 11 is connected to the metal plate 12 via the conductive wire, so that the surface potential sensor 13 measures the potential of the metal plate 12. Thus, the surface potential sensor 13 can measure an average potential of the intermediate transfer belt 6 properly. An experiment performed by locating the image forming apparatus 100 in an environmental condition of high temperature and humidity, an environmental condition of ambient temperature and humidity, and an environmental condition of low temperature and humidity revealed that the image forming apparatus 100 could provide high transfer efficiency and high image quality under such various environmental conditions.
According to this exemplary embodiment, the first transfer rollers 5C and 5D serve as voltage appliers for applying a voltage to the intermediate transfer belt 6. Alternatively, the first transfer rollers 5A and 5B may serve as the voltage appliers. Yet alternatively, the photoconductive drums 1A, 1B, 1C, and 1D or other members may apply a voltage to the intermediate transfer belt 6.
Further, according to this exemplary embodiment, the surface potential sensor 13 is provided at a position between the first transfer rollers 5C and 5D to measure the potential of the intermediate transfer belt 6. Alternatively, the surface potential sensor 13 may be provided at a position between adjacent stations (e.g., the image forming units A1, A2, A3, and A4), a position upstream from the first transfer roller 5A in the rotating direction A of the intermediate transfer belt 6, a position downstream from the first transfer roller 5D in the rotating direction A of the intermediate transfer belt 6, or a position near the counter roller 22, so as to provide effects equivalent to the effects provided by the surface potential sensor 13 disposed between the first transfer rollers 5C and 5D.
Referring to
The conductive brushes 16 and 17, serving as voltage application members, apply a voltage to the intermediate transfer belt 6. The switch 18 turns on and off a bias supplied to the conductive brush 16 and the first transfer roller 5C. The switch 19 turns on and off a bias supplied to the conductive brush 17 and the first transfer roller 5D. The conductive brush 16 is provided upstream from the first transfer roller 5C in the rotating direction A of the intermediate transfer belt 6. Points of a conductive fiber of the conductive brush 16 contact the inner circumferential surface (e.g., the back surface) of the intermediate transfer belt 6. Similarly, the conductive brush 17 is provided upstream from the first transfer roller 5D in the rotating direction A of the intermediate transfer belt 6. The conductive brushes 16 and 17 have a structure substantially equivalent to the structure of the conductive brush 11 shown in
Referring to
In step S301, the image forming apparatus 100A is powered on. In step S302, the timer 41 is turned on to start counting a time period. In step S303, before the image forming apparatus 100A starts an image forming operation, that is, when the photoconductive drums 1A, 1B, 1C, and 1D, the first transfer rollers 5A, 5B, 5C, and 5D, and the intermediate transfer belt 6 stop rotating, the power sources 10C and 10D, serving as constant-voltage power sources, apply predetermined voltages, for example, 1,000 V and 0 V, to the conductive brushes 16 and 17, respectively. Accordingly, the conductive brushes 16 and 17 apply the voltages to the intermediate transfer belt 6, respectively. In step S304, the controller 43 determines whether or not the time period counted by the timer 41 reaches a predetermined first time period. For example, the controller 43 determines whether or not a predetermined first time period elapses after the conductive brushes 16 and 17 apply the voltages to the intermediate transfer belt 6, respectively. When the time period counted by the timer 41 reaches the predetermined first time period, that is, when YES is selected in step S304, the surface potential sensor 13 measures a surface potential of the intermediate transfer belt 6 in step S305. In step S306, the controller 43 calculates a surface resistivity of the intermediate transfer belt 6 based on the measured surface potential of the intermediate transfer belt 6 and a relation between a pre-recorded potential and the surface resistivity of the intermediate transfer belt 6, and the recording member 42 records the calculated surface resistivity of the intermediate transfer belt 6. In step S307, the switches 18 and 19 are turned on to connect the power sources 10C and 10D to the first transfer rollers 5C and 5D, respectively. In step S308, the power sources 10C and 10D apply predetermined voltages to the first transfer rollers 5C and 5D, respectively. Accordingly, the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. In step S309, the controller 43 determines whether or not the time period counted by the timer 41 after the timer 41 is turned on in step S302 reaches a predetermined third time period. Alternatively, the controller 43 determines whether or not a predetermined third time period elapses after the first transfer rollers 5C and 5D apply the voltages to the intermediate transfer belt 6, respectively. When the time period counted by the timer 41 reaches the predetermined third time period, that is, when YES is selected in step S309, the surface potential sensor 13 measures the surface potential of the intermediate transfer belt 6 again in step S310. In step S311, the recording member 42 records the measured surface potential of the intermediate transfer belt 6. In step S312, the controller 43 calculates and determines a proper transfer bias to be applied by the first transfer rollers 5A, 5B, 5C, and 5D to transfer a toner image at which the image forming apparatus 100A can provide proper transfer efficiency and image quality. In step S313, the image forming apparatus 100A starts an image forming operation or other control operation.
According to this exemplary embodiment, the surface potential of the intermediate transfer belt 6 affected by a resistance of the first transfer rollers 5C and 5D or the surface potential of the intermediate transfer belt 6 changing over time is measured and recorded. On the other hands, when the recording member 42 records in advance relations between the proper transfer bias and the potential of the intermediate transfer belt 6 with combinations of the intermediate transfer belt 6 and the first transfer rollers 5C and 5D having various resistances, the proper transfer bias that compensates for change in resistance of the intermediate transfer belt 6 and the first transfer rollers 5C and 5D due to change in an environmental condition can be determined based on the potential of the intermediate transfer belt 6 affected by the resistance of the first transfer rollers 5C and 5D, the recorded relations between the proper transfer bias and the potential of the intermediate transfer belt 6, or the relation between the proper transfer bias and the predicted surface resistivity of the intermediate transfer belt 6. Thus, the image forming apparatus 100A can determine the proper transfer bias with an improved precision that compensates for the change in resistance of the first transfer rollers 5C and 5D due to the change in the environmental condition affecting measurement of the potential of the intermediate transfer belt 6, providing improved image quality.
Referring to
The surface potential sensor 13 of the image forming apparatus 100B is identical with the surface potential sensor 13 of the image forming apparatus 100. The driving roller 20 serves as a conductor including metal. The driving roller 20 contacts the inner circumferential surface of the intermediate transfer belt 6 across the full width of the intermediate transfer belt 6. Accordingly, the surface potential sensor 13 can measure an average potential of the intermediate transfer belt 6. Consequently, the conductive brush 11 and the metal plate 12 can be omitted in the image forming apparatus 100B, reducing manufacturing costs. The driving roller 20 is grounded via a switch during an image forming operation, and electrically floated when the potential of the intermediate transfer belt 6 is measured. An image forming operation and a process for determining a proper transfer bias performed in the image forming apparatus 100B are equivalent to the image forming operation and the process for determining the proper transfer bias performed in the image forming apparatus 100, and thereby descriptions about the image forming operation and the process for determining the proper transfer bias performed in the image forming apparatus 100B are omitted.
Referring to
In the image forming apparatus 100, the first transfer rollers 5C and 5D serve as voltage appliers. However, in the image forming apparatus 100C, one of the conveyance roller pairs 32 and 33 serves as a voltage applier. The conveyance roller pairs 32 and 33 are provided on the conveyance path 36 connecting the paper tray 30 to the second transfer nip formed between the intermediate transfer belt 6 and the second transfer belt 9 to convey a transfer sheet S from the paper tray 30 to the second transfer nip. Further, in the image forming apparatus 100, the conductive brush 11, the metal plate 12, and the surface potential sensor 13, serving as a potential measurement device, measure the surface potential of the intermediate transfer belt 6. However, in the image forming apparatus 100C, the metal plate 12 and the surface potential sensor 13, serving as a potential measurement device, measure a surface potential of a transfer sheet S.
In the sheet supplier C, the paper tray 30 contains transfer sheets S serving as a transfer material and having a predetermined size (e.g., A4 size). The feeding roller 31 feeds the transfer sheets S loaded on the paper tray 30 one by one toward the registration roller pair 34 through the conveyance path 36 illustrated in a broken line in
The power source 35, serving as a constant-voltage power source and a voltage applier, is electrically connected to the roller 32A, that is, one of rollers forming the conveyance roller pair 32 provided closer to the paper tray 30 than the conveyance roller pair 33 is. The power source 35 and the roller 32A serve as a voltage applier. The metal plate 12 and the surface potential sensor 13, serving as a potential measurement device, are connected to the roller 33A, that is, one of rollers forming the conveyance roller pair 33.
The potential measurement device includes the metal plate 12 and the surface potential sensor 13. The metal plate 12 has a rectangular plate shape and is connected to the roller 33A via a conductive material. A predetermined gap is provided between the metal plate 12 and the surface potential sensor 13, that is, a non-contact type sensor. When the transfer sheet S contacts both the conveyance roller pairs 32 and 33, the power source 35 applies a voltage to the transfer sheet S via the roller 32A and the surface potential sensor 13 measures a potential of the transfer sheet S via the roller 33A and the metal plate 12.
The conveyance roller pair 32 includes the rollers 32A and 32B opposing each other. The roller 32A serves as a conductive roller and the roller 32B serves as a non-conductive roller. The roller bases 32D of the conductive roller 32A include a conductive rubber containing conductive carbon black. For example, at least an outer circumferential surface of the roller bases 32D, which contacts the transfer sheet S, includes the conductive rubber. A resistance of the conductive rubber is sufficiently lower than a resistance of the transfer sheet S. Preferably, the conductive rubber has a volume resistivity not greater than 106 Ω·cm. On the contrary, the roller 32B may not be conductive, and thereby the roller bases 32D of the roller 32B may include either a conductive material or an insulative material. However, when an outer circumferential surface of the roller 32B has an electric resistance lower than an electric resistance of the transfer sheet S, an electric charge injected by the power source 35 depicted in
Like the conveyance roller pairs 32 and 33 depicted in
Referring to
In step S401, the image forming apparatus 100C receives scanner data or print data. In step S402, the feeding roller 31 and the conveyance roller pairs 32 and 33 start rotating, and thereby the feeding roller 31 feeds transfer sheets S loaded on the paper tray 30 one by one toward the registration roller pair 34 via the conveyance roller pairs 32 and 33, so that the transfer sheet S is contacted and stopped by the registration roller pair 34. In step S403, the controller 43 determines whether or not the transfer sheet S reaches the registration roller pair 34. If the transfer sheet S reaches the registration roller pair 34 (e.g., if YES is selected in step S403), the feeding roller 31 and the conveyance roller pairs 32 and 33 stop rotating in step S404. In step S405, the timer 41 is turned on. In step S406, the power source 35 applies a predetermined voltage (e.g., 100 V) to the transfer sheet S via the conductive roller 32A. Simultaneously, the timer 41 starts counting a time period. The conductive roller 33A is grounded. Therefore, an electric charge injected by the conductive roller 32A into the transfer sheet S moves to the conductive roller 33A to increase a surface potential of the transfer sheet S. Consequently, a potential of the conductive roller 33A also increases. In step S407, the controller 43 determines whether or not the time period counted after the power source 35 applies the predetermined voltage reaches a predetermined fourth time period (e.g., 1.0 second). If the counted time period reaches the predetermined fourth time period (e.g., if YES is selected in step S407), the surface potential sensor 13 measures the surface potential of the transfer sheet S via the metal plate 12 in step S408. In step S409, the recording member 42 records the measured surface potential of the transfer sheet S. Prior examinations, such as experiments, may measure surface potentials of transfer sheets S having different surface resistivities, respectively, when the predetermined fourth time period elapses, so as to store the measured surface potentials into a database. In step S410, the surface resistivity of the transfer sheet S is predicted based on the measured surface potential of the transfer sheet S and the surface potentials stored in the database. In step S411, the controller 43 calculates and determines a proper transfer bias (e.g., a second transfer bias) to be applied by the counter roller 22 to transfer a toner image from the intermediate transfer belt 6 onto the transfer sheet S based on the predicted surface resistivity of the transfer sheet S. In step S412, the feeding roller 31 and the conveyance roller pairs 32 and 33 resume rotating. In step S413, the image forming apparatus 100C starts an image forming operation and other control operation.
In the flowchart shown in
An increasing speed of the potential of the transfer sheet S varies depending on the surface resistivity of the transfer sheet S. The lower the surface resistivity is, the faster the increasing speed of the potential of the transfer sheet S is. Namely, the surface resistivity of the transfer sheet S can be predicted by measuring the increasing speed of the potential of the transfer sheet S or the potential of the transfer sheet S when a predetermined time period elapses after a voltage is applied. The proper transfer bias for forming an image is determined based on such relation and the measured potential or the surface resistivity of the transfer sheet S. Thus, the image forming apparatus 100C can provide an improved robustness against the resistance of the transfer sheet S varying depending on type of the transfer sheet S or an environmental condition of the image forming apparatus 100C.
The potential measurement device (e.g., the metal plate 12 and the surface potential sensor 13) measured the surface potential of the three types of a transfer sheet S having the three different volume resistivities, respectively, over time according to Japanese Industrial Standards JIS K6911. As illustrated in
Further, as illustrated in
Alternatively, the surface resistivity of the transfer sheet S may be predicted by measuring an electric current flowing between the conductive roller 32A and the metal roller 34A when a voltage is applied to the conductive roller 32A. However, under a condition that the transfer sheet S has a surface resistivity of 1011 Ω·cm, a distance between the conductive roller 32A and the metal roller 34A is 10 cm, the conductive roller 32A has a width of 10 cm, and a voltage of 100 V is applied to the conductive roller 32A, the electric current flowing between the conductive roller 32A and the metal roller 34A shows a relation of I=V/R=100/(1E9×0.1/0.1)=1E−7=0.1 μA. Accordingly, a high-precision ammeter capable of measuring a microelectric current is needed. The microelectric current may be affected by noise, generating increased measurement error. To address this, in the image forming apparatus 100C, the non-contact type surface potential sensor 13 measures the surface potential of the transfer sheet S and recognizes a slight difference in an amount of electric charge as an enlarged electric signal corresponding to the difference between the surface resistivities of the transfer sheet S. Especially, when elements provided around the surface potential sensor 13 include a resin to have a small electrostatic capacity, that is, when the elements are electrically floated, the surface potential sensor 13 can provide improved measurement sensitivity.
According to this exemplary embodiment, the surface potential sensor 13 is a non-contact type sensor. Alternatively, the surface potential sensor 13 may be replaced by a contact-type sensor or a contact-type high-voltage probe. When the surface potential sensor 13 is replaced by the contact-type sensor or probe, an amount of electric charge flowing into the sensor or the probe increases with respect to an amount of electric charge flowing inside a transfer sheet S, unless the sensor or the probe has a sufficiently high input impedance. Accordingly, the input impedance of the sensor or the probe may affect the measurement. When an A4 size sheet having a thickness of 100 μm and a volume resistivity of 1011 Ω·cm is used as a transfer sheet S, both edges of the transfer sheet S in a long direction of the transfer sheet S have a resistance represented by 1E9×0.293/100E−6/0.21=1.4E13Ω. Therefore, the contact-type sensor or probe may preferably have an input impedance having a resistance greater by about double-digit than the above resistance of the both edges of the transfer sheet S, that is, a resistance not smaller than 1015Ω.
Alternatively, the surface potential sensor 13 may be provided near a front surface or a back surface of a transfer sheet S. However, in this case, the transfer sheet S may be jammed. Moreover, the surface potential sensor 13 may measure a limited area on the transfer sheet S. Varied resistances of the transfer sheet S may also affect measurement of the surface potential sensor 13 and paper dust generated by the transfer sheet S may degrade sensitivity of the surface potential sensor 13. To address those, according to this exemplary embodiment, the conductive roller 33A is connected to the metal plate 12 via a conductive wire so that the surface potential sensor 13 measures a surface potential of the metal plate 12.
Alternatively, any member, having an arbitrary shape, other than the conductive rollers 32A and 33A may apply a voltage to a transfer sheet S and may contact the transfer sheet S to measure a potential of the transfer sheet S, as long as such member is a conductive member which can stably contact the transfer sheet S. However, change in position at which the conductive member applies a voltage to the transfer sheet S or change in contact area in which the conductive member contacts the transfer sheet S may cause variation in measurement of the surface potential sensor 13 and may cause the transfer sheet S to be jammed while the transfer sheet S is conveyed. To address those, according to this exemplary embodiment, the conductive rollers 32A and 33A are used to stably apply a voltage to the transfer sheet S, to stably measure the voltage of the transfer sheet S, and to prevent the transfer sheet S from being jammed. Further, the metal roller 34A is grounded to provide a path for stably supplying an electric current inside the transfer sheet S, resulting in measurement of the potential of the transfer sheet S with an improved reproduction. Thus, the image forming apparatus 100C can determine and apply a proper transfer bias under any temperature and humidity with any type of transfer sheet S, providing improved transfer efficiency and output of a high-quality image.
According to the above-described exemplary embodiments, each of the image forming apparatus 100 depicted in
The conveyance belt 6D is looped over the driving roller 20 and the driven roller 21 and conveys a transfer sheet S in a direction E to transfer nips at which toner images are transferred from the photoconductive drums 1A, 1B, 1C, and 1D onto the transfer sheet S conveyed by the conveyance belt 6D. Specifically, the first transfer rollers 5A, 5B, 5C, and 5D, serving as transfer members, apply transfer biases onto the conveyance belt 6D, serving as a transfer electric field generator, to generate a transfer electric field to transfer the toner images from photoconductive drums 1A, 1B, 1C, and 1D, serving as image carriers, and superimpose the toner images onto the transfer sheet S, serving as a toner image receiver. Thus, a color toner image is formed on the transfer sheet S.
The conductive brush 11, the metal plate 12, and the surface potential sensor 13, serving as a potential measurement device, measure a surface potential of the conveyance belt 6D.
Alternatively, the image forming apparatus 100D may further include the conductive brushes 16 and 17 and the switches 18 and 19 depicted in
Namely, the above-described exemplary embodiments may be applied to any image forming apparatus including a transfer device in which one or more transfer members apply a transfer bias to an intermediate transfer belt, a conveyance belt, or a transfer sheet serving as a transfer electric field generator to transfer a toner image formed on an image carrier onto the intermediate transfer belt or the transfer sheet using the direct or indirect transfer method.
The exposure device, the image forming device 1, the sheet supplier C, the fixing device, the controller 43, the recording member 42, and the like according to the above-described exemplary embodiments are examples and may have other known structures and shapes to provide the above-described effects.
In an image forming apparatus (e.g., the image forming apparatus 100 depicted in
The potential measurement device measures the surface potential of the transfer electric field generator while the transfer electric field generator stops moving or moves at a speed slower than a speed at which the transfer electric field generator moves during an image forming operation. Therefore, measurement error may not occur due to vibration of the transfer electric field generator. Accordingly, the potential measurement device can provide an improved measurement precision. Further, a surface resistivity of the transfer electric field generator can be predicted with an improved precision. Consequently, the image forming apparatus can determine a proper transfer bias.
The image forming apparatus further includes a recording member (e.g., the recording member 42 in
The potential measurement device includes a conductor (e.g., the conductive brush 11 depicted in
A general surface potential sensor measures a potential of the transfer electric field generator in a small area and is vulnerable to local variation in resistance of the transfer electric field generator including a non-uniform material. To address this, according to the above-described exemplary embodiments, the conductor contacts the transfer electric field generator across substantially a full width of the transfer electric field generator. Thus, the surface potential sensor can stably measure an average surface potential of the transfer electric field generator with an improved precision.
When a time period elapsed after the voltage applier applies a voltage reaches a predetermined second time period, the controller changes the voltage to be applied by the voltage applier to the transfer electric field generator. Namely, the potential of the transfer electric field generator changes transiently. Further, an electric field may affect a resistance of the transfer electric field generator when the transfer electric field generator includes some material. Considering those, the potential of the transfer electric field generator is measured while the applied voltage is changed, so as to predict the surface resistivity of the transfer electric field generator based on a curve plotted by the changed surface potentials of the transfer electric field generator. Accordingly, the surface resistivity of the transfer electric field generator can be predicted with an improved precision.
The voltage applier applies a voltage to the transfer electric field generator via an image carrier (e.g., the photoconductive drums 1A, 1B, 1C, and 1D depicted in
The voltage applier includes the voltage application member, which is neither the image carrier nor the transfer member, for contacting the transfer electric field generator to apply a voltage to the transfer electric field generator. In other words, the voltage application member, other than the image carrier and the transfer member, applies a voltage to the transfer electric field generator. Therefore, a resistance of the image carrier or the transfer member may not affect measurement of the surface potential of the transfer electric field generator. Accordingly, a proper transfer bias can be determined more precisely.
The voltage applier includes a constant-voltage power source. A switch (e.g., the switches 18 and 19 depicted in
As illustrated in
As illustrated in
The voltage applier applies a voltage to the transfer electric field generator. When a predetermined time period elapses, the potential measurement device measures a surface potential of the transfer electric field generator. Based on the measured surface potential of the transfer electric field generator, the image forming apparatus determines a proper transfer bias to be applied by the transfer member to the transfer electric field generator to transfer a toner image. Even when a resistance of the intermediate transfer belt or the transfer material, serving as the transfer electric field generator, changes substantially under an environmental condition of high temperature and humidity or an environmental condition of low temperature and humidity, the proper transfer bias can be selected to transfer the toner image, providing an improved robust control against change in the environmental condition and formation of a high-quality image.
The voltage applier applies a voltage to the transfer electric field generator. When a predetermined time period elapses, the potential measurement device measures a surface potential of the transfer electric field generator. When another predetermined time period elapses, the voltage applied by the voltage applier is changed and the voltage applier applies the changed voltage to the transfer electric field generator. When yet another predetermined time period elapses, the potential measurement device measures the surface potential of the transfer electric field generator. A surface resistivity of the transfer electric field generator is predicted based on a curve plotted by the measured surface potentials of the transfer electric field generator. Accordingly, in addition to the above-described effects, even when the toner image receiver, serving as the transfer electric field generator, is affected by an electric field, the surface resistivity of the transfer electric field generator can be predicted with an improved precision. Further, a proper transfer bias can be selected to form a high-quality image.
One of the transfer members is used as the voltage applier to apply a voltage to the transfer electric field generator. When a predetermined time period elapses, the potential measurement device measures a surface potential of the transfer electric field generator. Then, the voltage application member is used as the voltage applier to apply a voltage to the transfer electric field generator. When a predetermined time period elapses, the potential measurement device measures the surface potential of the transfer electric field generator again. A proper transfer bias to be applied by the transfer member to the transfer electric field generator to transfer a toner image is determined to compensate for change in resistance of the transfer member based on the measured surface potentials of the transfer electric field generator. Namely, the proper transfer bias can be determined and applied with an improved precision to compensate for change in resistance of the transfer member, such as a first transfer roller (e.g., the first transfer rollers 5A, 5B, 5C, and 5D depicted in
The conveyance roller applies a voltage to the transfer material. When a predetermined time period elapses, the potential measurement device measures a surface potential of the transfer material. A surface resistivity of the transfer material is predicted based on the measured surface potential of the transfer material. Based on the predicted surface resistivity of the transfer material, a proper transfer bias to be applied by the transfer member to the transfer material to transfer a toner image is determined. Thus, change in surface resistivity of the transfer material due to change in an environmental condition can be predicted with an improved precision. Accordingly, a robust control can be provided against change in the environmental condition, resulting in formation of a high-quality image.
The present invention has been described above with reference to specific exemplary embodiments. Note that the present invention is not limited to the details of the embodiments described above, but various modifications and enhancements are possible without departing from the spirit and scope of the invention. It is therefore to be understood that the present invention may be practiced otherwise than as specifically described herein. For example, elements and/or features of different illustrative exemplary embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.
| Number | Date | Country | Kind |
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| 2007-295110 | Nov 2007 | JP | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20090123168 A1 | May 2009 | US |
