The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2009-008355 filed in Japan on Jan. 19, 2009.
1. Field of the Invention
The present invention relates to an image forming apparatus that transfers visible images form image carriers to a surface of an endless belt or to a recording member held on the surface of the endless bet.
2. Description of the Related Art
In a typical image forming apparatus, toner images of mutually different colors are first formed on respective image carriers and a color image is then created by transferring those toner images in a superimposed manner from the image carriers onto the surface of an endless belt. In some image forming apparatus the toner images are transferred onto a recording paper held on the surface of the belt instead of transferring them directly on the belt.
The belt is stretched over rollers so as to form a loop. One of the rollers functions as a drive roller and others function as driven rollers. A belt drive motor drives the drive roller so that the belt rotates at a constant speed. However, the diameter of the drive roller may change due to changes in the environmental temperature over time. If this happens, the belt does not rotate at the intended speed. This leads to occurrence of misregistration between the toner images of the colors (color misregistration).
Meanwhile, there has been conventionally known an image forming apparatus that endlessly moves a belt member at a predetermined target velocity by detecting a moving velocity of the belt member by a velocity detector and feeding back the result of detection to a drive speed of a belt drive motor (for example, see Japanese Patent Application Laid-open No. 2004-220006 and Japanese Patent No. 3965357). This configuration allows the endless movement of the belt member at the target speed even if the diameter of the drive roller is changed due to changes in the temperature.
The inventors of the present invention are doing research whereby it is possible to share the drive motor between one of a plurality of photosensitive elements and the belt member. This configuration leads to reduction in cost of the configuration in which the belt member is caused to endlessly move at a target speed in the above manner. More specifically, when there are four photosensitive elements corresponding to toner images of Y (yellow), C (cyan), M (magenta), and K (black), the drive motor is shared between the photosensitive element for K and the belt member. As an object for dual purpose, the photosensitive element for K is selected from among the four colors for some reasons as explained below. Namely, conventionally, in a print job in monochrome mode, it is general that wasteful energy consumption and occurrence of wear of components are reduced by driving only the photosensitive element for K and stopping the drive of the photosensitive elements for Y, C, and M. Even if the configuration is adopted, if the photosensitive element for K is selected as the photosensitive element that shares the drive motor with the belt member, the belt member can be driven irrespective of different modes.
However, if at least one of the photosensitive elements, which is not necessarily the photosensitive element for K, shares the drive motor with the belt member, a following problem arises. More specifically, for the purpose of endless movement of the belt member at the target velocity, if the drive speed of a shared drive motor is controlled based on the result of detecting the belt velocity, an angular velocity of the photosensitive element driven by the shared drive motor may differ from that of the other photosensitive elements depending on the diameter of the drive roller. Such a difference in linear velocity between the photosensitive elements causes misregistration between the toner image on the photosensitive element of the former and the toner images on the other photosensitive elements.
It is an object of the present invention to at least partially solve the problems in the conventional technology.
According to an aspect of the present invention, there is provided an image forming apparatus including a movable image carrier corresponding to each of a plurality of colors and configured to carry a visible image of a corresponding one of the colors on a surface thereof; a plurality of image-carrier drive sources configured to drive one or more of the image carriers; a belt member that is stretched and supported by a plurality of stretching and supporting members in the vicinity of the image carriers; a drive rotating body configured to support the belt member and when driven causes the belt member to endlessly move over the stretching and supporting members; a belt drive source configured to drive the drive rotating body, wherein one of the image-carrier drive sources functions as the belt drive source as a shared drive source; a velocity fluctuation detector configured to detect velocity fluctuation of the belt member when driven by the belt drive source; a drive control unit configured to control a drive speed of the belt drive source based on the velocity fluctuation detected by the velocity fluctuation detector; and a transfer unit configured to transfer the visible images from the surfaces of the image carriers onto a surface of the belt member or to a recording member held on the surface thereof. The drive control unit executes a process for controlling a drive speed of the image-carrier drive sources other than the shared drive source based on the drive speed of the shared drive source or based on the velocity of the image carrier driven by the shared drive source.
According to another aspect of the present invention, there is provided an image forming apparatus including a rotatable image carrier corresponding to each of a plurality of colors and configured to carry a visible image of a corresponding one of the colors on a surface thereof; a plurality of image-carrier drive sources configured to drive one or more of the image carriers; a belt member that is stretched and supported by a plurality of stretching and supporting members in the vicinity of the image carriers; a drive rotating body configured to support the belt member and when driven causes the belt member to endlessly move over the stretching and supporting members; a belt drive source configured to drive the drive rotating body, wherein one of the image-carrier drive sources functions as the belt drive source as a shared drive source; a velocity detector configured to detect velocity of the belt member when driven by the belt drive source; a drive control unit configured to control a drive speed of the belt drive source based on a result of detection by the velocity detector; a transfer unit configured to transfer the visible images from the surfaces of the image carriers onto a surface of the belt member or to a recording member held on the surface thereof; and a rotation detector configured to detect a parameter indicative of at least one among an angular velocity and an angular displacement of the shared drive source and an angular velocity and an angular displacement of the image carrier driven by the shared drive source. The drive control unit executes a process for controlling a drive speed of the image-carrier drive sources other than the shared drive source based on the parameter detected by the rotation detector.
According to still another aspect of the present invention, there is provided an image forming apparatus including a movable image carrier corresponding to each of a plurality of colors and configured to carry a visible image of a corresponding one of the colors on a surface thereof; a plurality of image-carrier drive sources configured to drive one or more of the image carriers; a belt member that is stretched and supported by a plurality of stretching and supporting members in the vicinity of the image carriers; a belt drive source configured to drive the belt member, wherein one of the image-carrier drive sources functions as the belt drive source as a shared drive source; a velocity detector configured to detect a velocity of the belt member when driven by the belt drive source; a drive control unit configured to control a drive speed of the belt drive source based on a result of detection by the velocity detector; and a transfer unit configured to transfer the visible images from the surfaces of the image carriers onto a surface of the belt member or to a recording member held on the surface thereof. The velocity detector detects the velocity of the belt member when driven by the shared drive source at least one detection timings selected from each time power of the image forming apparatus is turned on, each time a continuous stop time exceeds a predetermined first value, each time number of times of execution of an image forming operation exceeds a predetermined second value, and each time number of times of execution of an image forming operation in a continuous operation mode for continuously performing the image forming operation on a plurality of recording members exceeds a predetermined third value, and the drive control unit executes a process for determining a drive speed of the shared drive source and drive speeds of the image-carrier drive sources other than the shared drive source in subsequent image forming operations based on the velocity detection by the velocity detector.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
Exemplary embodiments of an image forming apparatus according to the present invention are explained below while referring to the accompanying drawings. The present invention is not limited to the embodiments explained below.
As an image forming apparatus to which the present invention is applied, a first embodiment of an electrophotographic printer (hereinafter, simply called “printer”) is explained below.
First, a basic configuration of a printer 50 according to the first embodiment is explained below.
The charging unit 4Y uniformly charges the surface of the photosensitive element 1Y caused to rotate clockwise in
The developing unit 5Y includes a developing roll 51Y provided so as to be partially exposed from an opening of a casing of the developing unit 5Y. The developing unit 5Y also includes two conveyor screws 55Y arranged in parallel to one another, a doctor blade 52Y, and a toner concentration sensor (hereinafter, called “T sensor”) 56Y.
Stored in the casing of the developing unit 5Y is the Y developer (not shown) containing the magnetic carrier and the Y toner. The Y developer is charged by friction while being stirred and conveyed by the two conveyor screws 55Y, and, thereafter, is carried on the surface of the developing roll 51Y. A layer thickness of the Y developer is controlled by the doctor blade 52Y, and the Y developer is conveyed to a developing area opposed to the y-photosensitive element 1Y for Y, where the Y toner is made to adhere to the electrostatic latent image on the photosensitive element 1Y. With this adhesion, the Y toner image is formed on the photosensitive element 1Y. In the developing unit 5Y, the Y developer in which the Y toner is consumed due to development is returned into the casing with the rotation of the developing roll 51Y.
A partition wall is provided between the two conveyor screws 55Y. The partition wall divides the casing into a first supply unit 53Y that includes the developing roll 51Y and the conveyor screw 55Y on the right side in
The T sensor 56Y formed with a permeability sensor is provided in a bottom wall of the second supply unit 54Y, and outputs a voltage of a value equivalent to a permeability of the Y developer having passed over the T sensor 56Y. The permeability of a two-component developer containing toner and magnetic carrier represents a good correlation with the toner concentration, and therefore the T sensor 56Y outputs a voltage of a value equivalent to the Y toner concentration. The value of the output voltage is sent to a controller (not shown). The controller is provided with a RAM that stores therein Vtref for Y being a target value of an output voltage output from the T sensor 56Y. Stored in the RAM are also data for Vtref for C, Vtref for M, and Vtref for K being target values of output voltages output from T sensors (not shown) mounted on the other developing units, respectively. The Vtref for Y is used for drive control of a Y-toner conveying device explained later. More specifically, the controller controls the drive of the Y-toner conveying device (not shown) to supply the Y toner into the second supply unit 54Y so that the value of the output voltage from the T sensor 56Y is brought close to the Vtref for Y. The supply allows the Y toner concentration in the Y developer inside the developing unit 5Y to be maintained within a predetermined range. In the developing units for the other process units, each toner supply control using C-, M-, and K-toner conveying devices is implemented in the above manner.
As previously shown in
Placed in the lower side, in
A registration roller pair 28 is provided near the end of the paper feeding path 70. The registration roller pair 28 is caused to rotate both rollers so as to hold the transfer paper P therebetween, however, the registration roller pair 28 is stopped once in response to the holding thereof. Then, the registration roller pair 28 feeds the transfer paper P to a secondary transfer nip explained later in appropriate timing.
Provided in the upper side, in
The drive roller 12 being a drive rotating body holds the intermediate transfer belt 8 with the secondary-transfer bias roller 19 to form the secondary transfer nip. The four-color toner image being a visible image formed on the intermediate transfer belt 8 is transferred to the transfer paper P at the secondary transfer nip. The transferred image is made a full-color toner image with a white color of the transfer paper P. Residual toner after transfer that has not been transferred to the transfer paper P adheres to the intermediate transfer belt 8 having passed through the secondary transfer nip. This is cleaned by the belt cleaning device 10. The transfer paper P to which the four-color toner image is collectively and secondarily transferred at the secondary transfer nip is sent to a fixing unit 20 through a post-transfer conveyance path 71.
The fixing unit 20 forms a fixing nip by a fixing roller 20a with a heat source such as a halogen lamp provided inside thereof and by a pressing roller 20b that rotates while being in contact with the fixing roller 20a with a predetermined pressure. The transfer paper P fed into the fixing unit 20 is held into the fixing nip so that a toner-image-carried surface of the transfer paper P not yet being fixed is brought into close contact with the fixing roller 20a. The toner in the toner image is softened under the effect of heating and pressure, and a full-color image is thereby fixed thereon.
The transfer paper P on which the full-color image is fixed in the fixing unit 20 exits the fixing unit 20, and then approaches a separation point between a paper ejection path 72 and a pre-reverse conveyance path 73. A first switching claw 75 is swingably provided at the separation point, and the course of the transfer paper P is switched by swinging of the first switching claw 75. More specifically, the tip of the claw is moved to a direction of approaching the pre-reverse conveyance path 73, to thereby change the course of the transfer paper P to a direction toward the paper ejection path 72. Furthermore, the tip of the claw is moved to a direction of being away from the pre-reverse conveyance path 73, to thereby change the course of the transfer paper P to the direction toward the pre-reverse conveyance path 73.
If the course toward the paper ejection path 72 is selected by the first switching claw 75, the transfer paper P passes from the paper ejection path 72 through a paper-ejection roller pair 100 and is ejected outside the machine, to be stacked on a stack portion 50a provided on the top face of the printer housing. On the other hand, if the course toward the pre-reverse conveyance path 73 is selected by the first switching claw 75, the transfer paper P passes through the pre-reverse conveyance path 73 and enters a nip of a reverse roller pair 21. The reverse roller pair 21 conveys the transfer paper P held between the rollers to the stack portion 50a, but reversely rotates the rollers right before the trailing edge of the transfer paper P is caused to enter the nip. The reverse rotation causes the transfer paper P to be conveyed in a direction opposite to the direction, and the trailing edge side of the transfer paper P enters a reverse conveyance path 74.
The reverse conveyance path 74 is formed into an elongating shape while being bent from the upper side toward the lower side in a vertical direction. Provided inside the path are a first reverse conveying roller pair 22, a second reverse conveying roller pair 23, and a third reverse conveying roller pair 24. The transfer paper P is conveyed while sequentially passing through nips of these roller pairs, to be thereby turned upside down. The transfer paper P after having been turned upside down is returned to the paper feeding path 70, and then reaches again the secondary transfer nip. This time a non-image carrying surface thereof is caused to enter the secondary transfer nip while being close contact with the intermediate transfer belt 8, where a second four-color toner image on the intermediate transfer belt is collectively and secondarily transferred to the non-image carrying surface thereof. Thereafter, the transfer paper P passes through the post-transfer conveyance path 71, the fixing unit 20, the paper ejection path 72, and the paper-ejection roller pair 100, to be stacked on the stack portion 50a provided outside the machine. Through the reverse conveyance, full-color images are formed on both sides of the transfer paper P.
A bottle support unit 31 is provided between the transfer unit 15 and the stack portion 50a provided in the upper side from the transfer unit 15. The bottle support unit 31 incorporates toner bottles 32Y, 32C, 32M, and 32K being toner containers for containing therein Y, C, M, and K toners respectively. The toner bottles 32Y, 32C, 32M, and 32K are arranged so as to be mutually placed at an angle slightly inclined than a horizontal line, and arranged positions are made higher in order of Y, C, M, and K. The Y, C, M, and K toners in the toner bottles 32Y, 32C, 32M, and 32K are supplied as necessary to the developing units in the process units 6Y, 6C, 6M, and 6K by toner conveying units explained later, respectively. The toner bottles 32Y, 32C, 32M, and 32K are detachably attached to the printer body, independently from the process units 6Y, 6C, 6M, and 6K respectively.
The present printer has a monochrome mode in which a mono-color image is formed and a color mode in which a color image is formed, which cause a contact state between the photosensitive element and the intermediate transfer belt to be different from each other. More specifically, among the four primary-transfer bias rollers 9Y, 9C, 9M, and 9K in the transfer unit 15, the primary-transfer bias roller 9K for K is supported by a dedicated bracket (not shown) separately from the other primary-transfer bias rollers. The three primary-transfer bias rollers 9Y, 9C, and 9M for Y, C, and M are supported by a common mobile bracket (not shown). The mobile bracket can be moved in a direction of being closer to the photosensitive elements 1Y, 1C, and 1M for Y, C, and M, and in a direction of being away from the photosensitive elements 1Y, 1C, and 1M by driving a solenoid (not shown). When the mobile bracket is moved in the direction being away from the photosensitive elements 1Y, 1C, and 1M, the stretched state of the intermediate transfer belt 8 is changed, so that the intermediate transfer belt 8 separates from the three photosensitive elements 1Y, 1C, and 1M for Y, C, and M. However, the photosensitive element 1K for K and the intermediate transfer belt 8 are kept in contact with each other. In the monochrome mode, an image forming operation is performed in the above manner in the state in which only the photosensitive element 1K for K is kept in contact with the intermediate transfer belt 8. At this time, of the four photosensitive elements, only the photosensitive element 1K for K is driven to rotate, while the photosensitive elements 1Y, 10, and 1M for Y, C, and M are stopped driving.
When the mobile bracket is moved in the direction of being closer to the three photosensitive elements 1Y, 1C, and 1M, the stretched state of the intermediate transfer belt 8 changes, and the intermediate transfer belt 8 separated so far from the three photosensitive elements 1Y, 10, and 1M comes in contact with the three photosensitive elements 1Y, 1C, and 1M. At this time, the photosensitive element 1K for K and the intermediate transfer belt 8 are kept in contact with each other. In the color mode, an image forming operation is performed in this manner in the state in which all the four photosensitive elements 1Y, 10, 1M, and 1K are in contact with the intermediate transfer belt 8. In this configuration, the mobile bracket and the solenoid or the like function as a contact/separation unit that causes the photosensitive element and the intermediate transfer belt 8 to contact each other or to separate each other.
The present printer includes a main controller (not shown) being a control unit that controls the drive of the four process units 6Y, 6C, 6M, and 6K and the optical writing unit 7. The main controller includes a CPU (central processing unit) being a computing unit, a RAM (random access memory) being a data storage unit, and a ROM (read only memory) being a data storage unit, and controls the drive of the process units and the optical writing unit based on programs stored in the ROM.
Moreover, the present printer includes a drive controller (not shown) separately from the main controller. The drive controller includes a CPU, a ROM, and a nonvolatile RAM being a data storage unit, and controls the drive of a shared drive motor and a photosensitive-element motor, explained later, based on programs stored in the ROM.
A shared drive motor 162 is fixed near the belt-drive relay gear 161 in the printer body, and a motor gear of the shared drive motor 162 is engaged with the belt-drive relay gear 161. A mechanism thereof is such that when the shared drive motor 162 is driven to rotate, the drive force is transmitted to the intermediate transfer belt 8 through the belt-drive relay gear 161, the coupling connection, and the drive roller 12.
Engaged with the belt-drive relay gear 161 is the first relay gear 152 for K in addition to the motor gear of the shared drive motor 162. Arranged near the first relay gear 152 for K is the second relay gear 153 for K in which an input gear portion 153a and an output gear portion 153b are integrally formed on the same axis. The first relay gear 152 for K is also engaged with the input gear portion 153a of the second relay gear 153 for K. The output gear portion 153b of the second relay gear 153 for K is engaged with the photosensitive-element gear 151K for K. Based on the gear arrangement as above, the rotational drive force of the shared drive motor 162 is transmitted to the photosensitive element 1K for K through the belt-drive relay gear 161, the first relay gear 152 for K, the second relay gear 153 for K, and the photosensitive-element gear 151K for K. More specifically, in the present printer, the shared drive motor 162 functions as a belt drive source being a drive source of the drive roller 12 and of the intermediate transfer belt 8, and also functions as a drive source of the photosensitive element for K being one of image-carrier drive sources.
Meanwhile, the photosensitive elements 1Y, 1C, and 1M for Y, C, and M are driven by a drive source different from the shared drive motor 162. More specifically, the motor gear of the color photosensitive-element motor 154 being the image-carrier drive source fixed in the printer body is located between the photosensitive-element gear 151C for C and the photosensitive-element gear 151M for M. The motor gear is simultaneously engaged with these gears. This configures the motor gear of the color photosensitive-element motor 154 to directly transmit the rotational drive force to the photosensitive-element gear 151C for C and also directly transmit it to the photosensitive-element gear 151M for M.
The relay gear 155 for Y rotatably supported in the printer body is located between the photosensitive-element gear 151Y for Y and the photosensitive-element gear 151C for C, and is engaged with these photosensitive-element gears. The rotational drive force of the photosensitive-element gear 151C for C is transmitted to the photosensitive-element gear 151Y for Y through itself.
It should be noted that the printer uses the roller encoder 171 that detects the angular velocity and the angular displacement of the driven roller 14, as the velocity fluctuation detector and the velocity detector, however, any other unit that detects the velocity fluctuation and the velocity using other method may be used. For example, there may be used an optical sensor in which a scale with a plurality of tick marks arranged at predetermined pitches in a belt circumferential direction is provided on the intermediate transfer belt and the velocity fluctuation of the belt and the velocity of the belt are detected based on an time interval for detecting the tick marks described in for example Japanese Patent Application Laid-open No. 2004-220006). An optical image sensor used for an optical mouse or the like being an input device of a personal computer may also be used as a unit for detecting the velocity fluctuation and the velocity of the surface of the belt. Moreover, a unit for estimating a belt velocity based on the result of detecting an in-unit temperature by a temperature sensor and based on a theoretical value of thermal expansion of the drive roller 12 may be provided as a detector.
During a continuous printing operation for continuously recording an image on a plurality of recording papers, the diameter of the drive roller 12 gradually increases with an increase in the temperature inside the printer along with the operation time. The diameter of the drive roller 12 gradually decreases with a decrease in the temperature inside the printer after the continuous printing operation is stopped. A relationship “V=rω” holds among a linear velocity V of the intermediate transfer belt 8, a radius r of the drive roller 12, and an angular velocity ω of the drive roller 12. Thus, if the angular velocity ω is set to be constant or if the drive speed of the shared drive motor 162 is made constant, the linear velocity V of the belt changes with a change in the diameter of the drive roller 12. This causes misregistration between the toner images of the colors to occur.
Therefore, the drive controller 200 performs phase locked loop (PLL) control for performing acceleration/deceleration control on the shared drive motor 162 so as to match the frequency of a pulse signal output from the roller encoder 171 with the frequency of a reference clock. This causes the driven roller 14 attached with the roller encoder 171 to be rotated at a constant angular velocity, to stabilize the velocity of the intermediate transfer belt 8 to a predetermined velocity. More specifically, by controlling the drive speed of the shared drive motor 162 based on the velocity fluctuation of and the velocity of the intermediate transfer belt 8, the intermediate transfer belt 8 is caused to endlessly move at a predetermined velocity irrespective of the change in the diameter of the drive roller 12.
In the PLL control, the velocity fluctuation in a short period of time within one cycle of the belt is detected, in addition to the velocity fluctuation in a long period caused by the change in the diameter of the drive roller 12 over time. The velocity fluctuation in the short period of time within the one cycle of the belt includes a sudden velocity fluctuation occurring when the recording paper enters the secondary transfer nip and a periodic velocity fluctuation caused by eccentricity of the drive roller 12. If the drive roller 12 is eccentric, a subtle velocity fluctuation like a one-cycle sine curve drawn per one cycle of the drive roller 12 appears in the intermediate transfer belt 8. In the PLL control, such a subtle velocity fluctuation is also detected and the result is reflected to the drive control of the shared drive motor 162, which also enables the velocity fluctuation even in the short period of time to be suppressed. In a case of suppressing only the velocity fluctuation in the long period of time caused by the change in the diameter of the drive roller 12 over time, a control method for detecting long-period velocity fluctuations may be adopted instead of the PLL control.
If the subtle velocity fluctuation caused by eccentricity of the drive roller 12 is detected and the result thereof is feedback-controlled to the drive control of the shared drive motor 162, this causes the linear velocity of the photosensitive element 1K for K to subtly fluctuate as shown in
If the setting as shown in
Incidentally, if the drive speed of the shared drive motor 162 is controlled so as to set the linear velocity of the intermediate transfer belt 8 to be constant regardless of a change in the diameter of the drive roller 12, the linear velocity of the photosensitive element 1K for K is caused to be subtly changed with the change in the diameter of the drive roller 12. Then, this causes occurrence of a linear velocity difference between the photosensitive elements 1Y, 1C, and 1M for Y, C, and M driven by the color photosensitive-element motor 154 and the photosensitive element 1K for K driven by the shared drive motor 162, which leads to occurrence of misregistration between the Y, C, and M toner images, and the K toner image.
Therefore, as previously shown in
In this state, it is configured that the flow for image processing is not started. The start flag is turned ON at Step S8, and the flow for the image processing is started. Thereafter, the flow at Steps S3 to S5 is repeatedly executed until the print job ends (Step S9) and the drive motor is tuned OFF (Step S10).
In the present printer configured in the above manner, by performing PLL-control on the shared drive motor 162 based on the result of detecting the velocity fluctuation and the velocity of the intermediate transfer belt 8, the intermediate transfer belt 8 can be endlessly moved at a target velocity regardless of any change in the diameter of the drive roller 12. In addition, by controlling the drive speed of the color photosensitive-element motor 154 based on an output, from the drum encoder 172 being a rotation detector, which reflects the velocity of the photosensitive element 1K for K driven by the shared drive motor 162, the linear velocity difference between the photosensitive element 1K for K and the photosensitive elements 1Y, 1C, and 1M for Y, C, and M is reduced. This also enables occurrence of the misregistration caused by the linear velocity difference to be suppressed.
Meanwhile, the second motor driver 202 controls the drive speed of the color photosensitive-element motor 154 based on an FG signal output from the shared drive motor 162. The shared drive motor 162 outputs the ES signal according to the angular velocity. The angular velocity of the shared drive motor 162 being the drive source of the photosensitive element 1K for K has a correlation with the linear velocity of the photosensitive element 1K. The second motor driver 202 stores therein an algorithm or a data table to determine a control target of the drive speed of the color photosensitive-element motor 154 that enables the linear velocity of the photosensitive elements 1Y, 1C, and 1M for Y, C, and M to be matched with the linear velocity of the photosensitive element 1K for K based on the FG signal. The second motor driver 202 determines a control target based on the FG signal and based on the algorithm or the data table.
This configuration allows determination of the linear velocity of the photosensitive element 1K and cost reduction without providing the roller encoder in the driven roller 14.
Next, printers according to implementation examples in which more characteristic configurations are added to the printer according to the first embodiment are explained below. The configurations of the printers according to the implementation examples are the same as that of the first embodiment unless otherwise specified.
Therefore, the drive controller of the printer according to the first implementation example is configured to use an average value, within a predetermined time such as one cycle of the photosensitive element or one cycle of the belt, as an output value of the drum encoder 172 to be referred to for correcting the control target of the drive speed of the color photosensitive-element motor 154. This configuration allows reduction of the linear velocity difference of the photosensitive elements produced caused by the velocity fluctuation of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge, as compared with a case in which the control target of the color photosensitive-element motor 154 is corrected based on only the output values of the drum encoder 172 acquired at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
It should be noted that in the printer according to the first modification, FG signals are simply averaged instead of the output value of the drum encoder 172.
This configuration allows avoidance of the linear velocity difference between the photosensitive elements produced caused by the velocity fluctuations of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge, unlike the case in which the control target of the color photosensitive-element motor 154 is corrected based on only the output values of the drum encoder 172 acquired at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
In the configuration in which the shared drive motor 162 is PLL-controlled based on the velocity of the intermediate transfer belt 8, if the diameter of the drive roller 12 deviates greatly from its standard value, then the control target of the shared drive motor 162 also deviates greatly from its standard value. Then, while the intermediate transfer belt 8 is driven at a target linear velocity, the photosensitive element 1K for K is driven at a linear velocity largely different from a standard linear velocity, and the linear velocity difference between the belt and the photosensitive element 1K is thereby comparatively increased. If the linear velocity difference is too large, then the transfer capability of the toner image from the photosensitive element 1K for K to the intermediate transfer belt 8 is significantly deteriorated, so that a target image density cannot be obtained.
Therefore, in the printer according to the third implementation example, the drive controller is configured so as to execute a process for performing PLL-control on the drive speed of the shared drive motor 162 within a range of a predetermined upper limit threshold or less. In this configuration, if the diameter of the drive roller 12 changes largely from the reference value to such an extent that the drive speed of the shared drive motor 162 is increased more than the upper limit threshold, by keeping the drive speed within the upper limit threshold, slight misregistration is allowed. However, the target image density can be obtained regardless of the change in the diameter of the drive roller 12. It should be noted that the control target of the color photosensitive-element motor 154 is determined based on the drive speed of the shared drive motor 162, and thus, similarly to the shared drive motor 162, the drive speed is controlled within the range of the predetermined upper limit threshold or less.
A printer according to a fourth implementation example is configured so as to control the drive speed of only the color photosensitive-element motor 154, of the shared drive motor 162 and the color photosensitive-element motor 154, within the upper limit threshold.
This configuration enables target image densities for Y, C, and M to be obtained regardless of the change in the diameter of the drive roller 12. Instead of determining whether the result of calculating the control target of the color photosensitive-element motor 154 exceeds the upper limit threshold, the determination may be indirectly performed depending on whether the current drive speed of the shared drive motor 162 exceeds the upper limit threshold.
Next, a printer according to a second embodiment to which the present invention is applied is explained below. The configuration of the printer according to the second embodiment is the same as that of the first embodiment unless otherwise specified.
A drive controller of the printer according to the second embodiment is configured to perform constant-speed drive at a predetermined first drive speed instead of PLL-controlling the shared drive motor 162. The color photosensitive-element motor 154 is configured to perform constant-speed drive at a second drive speed according to the first drive speed of the shared drive motor 162 so as to match the linear velocity of the photosensitive elements 1Y, 1C, and 1M for Y, C, and M with the linear velocity of the photosensitive element 1K for K. The first drive speed and the second drive speed are periodically undated in four different timings as follows. Hereinafter, arrival of any one of these timings is called “arrival of periodic timing”.
(1) Each time when power is applied to the body.
(2) Each time when a continuous stop time reaches a predetermined time or more.
(3) Each time when a printing operation (image forming operation) is performed predetermined times (each time when the printing operation is performed for a predetermined number of sheets).
(4) Each time when the printing operation in a continuous operation mode reaches predetermined times (each time when a number of continuously printed sheets reaches a predetermined number).
In the process for updating the first drive speed i.e., the drive speed of the shared drive motor 162 (Step S28), the drive speed of the shared drive motor 162 is adjusted so as to match detected velocity of the intermediate transfer belt 8 with the target linear velocity, and the result of adjustment is determined as a new first drive speed. The process is performed in the above manner, then, the second drive speed i.e., the drive speed of the color photosensitive-element motor 154 is determined based on the first drive speed and a predetermined data table (Step S29). The data table associates the first drive speed with the corresponding second drive speed (drive speed at which the linear velocity of the Y, C, and M photosensitive elements can be matched with that of the K photosensitive element). After the second drive speed is updated in this manner, the continuous printing operation is restarted, the interrupt flag is turned OFF, and the drive motor is tuned OFF (Steps S30 to S13) as necessary, and then the control flow is returned.
In the present printer configured in the above manner, by determining the first drive speed being the drive speed of the shared drive motor 162 in the subsequent printing operation in the periodic timing, based on the result of detecting the linear velocity of the intermediate transfer belt 8 driven by the shared drive motor, the belt can be endlessly moved at the target velocity regardless of the change in the diameter of the drive roller 12. In addition, in the periodic timing, by determining the second drive speed being the drive speed of the color photosensitive-element motor 154 according to the first drive speed, a linear velocity difference between the photosensitive element 1K for K and the photosensitive elements 1Y, 1C, and 1M for Y, C, and M is reduced. Thus, it is also possible to suppress occurrence of misregistration between visible images caused by the linear velocity difference.
It should be noted that the drive controller uses an average value within a predetermined time, as an output value from the roller encoder 171 being the result of detection by the velocity detector, when the first drive speed and the second drive speed are to be updated. At this time, the output value from the encoder when the recording paper is caused to enter the secondary transfer nip is not reflected to calculation of the average value. Furthermore, both the first drive speed and the second drive speed are determined within the predetermined upper limit threshold.
As explained above, the (1) to (4) different timings are adopted as the periodic timing, however, the printing operations in (3) and (4) are implemented by counting the number of operation times in the following manner. More specifically, based on A4-size paper as normal, when the printing operation is performed on the A4-size paper, the number of operation times is counted as one. On the other hand, when the printing operation is performed on a recording paper whose size in the conveying direction inside the device is one integer-th of the A4-size paper, the number of operation times is counted as one integer-th. Moreover, when the size is an integral multiple thereof, the number of printing operation times is counted as integral-multiple times.
Thus, in the printer according to the first implementation example, the transfer unit 15 being the transfer unit is configured to transfer the toner images carried on the surfaces of the photosensitive elements 1Y, 1C, 1M, and 1K to the surface of the intermediate transfer belt 8, and then transfer the toner images on the surface of the intermediate transfer belt 8 to the recording paper passing through between the intermediate transfer belt 8 and the secondary-transfer bias roller 19 being an opposed member provided opposite thereto. The drive controller 200 being the drive control unit uses the average value within the predetermined time as the output value, from the roller encoder 171, which is referred to for drive control of the color photosensitive-element motor 154 which is not the shared drive source. As already explained above, this configuration allows reduction of the linear velocity difference between the photosensitive elements produced due to the velocity fluctuations of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge, as compared with the case in which the control target of the color photosensitive-element motor 154 is corrected based on only the output values of the drum encoder 172 acquired at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
In the printer according to the second embodiment, the drive controller 200 is configured to use the average value within the predetermined time as the output value of the roller encoder 171 when the second drive speed is updated. This configuration allows reduction of the linear velocity difference between the photosensitive elements produced due to the velocity fluctuations of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge, as compared with the case in which the second drive speed is determined based on only the output values of the roller encoder 171 acquired at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
Furthermore, in the printer according to the second implementation example, the drive controller 200 is configured to execute the process for not reflecting the output value from the drum encoder 172, when the recording paper is caused to enter the secondary transfer nip, to the drive control of the color photosensitive-element motor 154. This configuration allows avoidance of the linear velocity difference between the photosensitive elements produced due to the velocity fluctuations of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
In the printer according to the second embodiment, the drive controller 200 is configured to execute the process for not reflecting the output value from the roller encoder 171, when the recording paper is caused to enter the secondary transfer nip, to these determined values of the drive speeds when the first drive speed and the second drive speed are determined respectively. This configuration allows avoidance of the linear velocity difference between the photosensitive elements produced due to the velocity fluctuations of the belt at the time of entry of the paper leading edge and at the time of ejection of the paper trailing edge.
In the printer according to the first embodiment and the printer according to the second embodiment, the drive controller is configured so as to execute the process for controlling the drive speed of at least either one of the shared drive motor 162 and the color photosensitive-element motor 154 within the predetermined upper limit threshold. This configuration allows achievement of target image density of the toner images which are transferred from the photosensitive elements driven, by controlling the drive speed within the upper limit threshold, at the controlled drive speed to the belt.
In the printer according to the second embodiment, for determining the first drive speed and the second drive speed, the printing operation for forming an image on A4-size paper is counted as one time, while the printing operation for forming an image on a recording paper whose size in the conveying direction is one integer-th or integral multiple of the A4 size is counted as one integer-th or integral multiple times. This configuration allows avoidance of improper updating time of the first drive speed and the second drive speed due to occurrence of an error between the result of counting and a practical amount of printing operation caused by the counting of the printing operation for one sheet of recording paper as one time irrespective of sizes of recording papers.
According to an aspect of the present invention, by changing the drive speed of the shared drive source according to the result of detecting the velocity fluctuation of the belt member, the belt member can be endlessly moved at the target velocity regardless of the change in the diameter of the drive rotating body. In addition, by controlling the drive speed of the image-carrier drive sources which are not the shared drive source based on the drive speed of the shared drive source or based on the velocity of the image carrier driven by the shared drive source, the linear velocity difference between the image carrier driven by the shared drive source and the image carriers respectively driven by the image-carrier drive sources which are not the shared drive source is reduced. Thus, occurrence of misregistration between the visible images caused by the linear velocity difference can also be suppressed.
According to another aspect of the present invention, by changing the drive speed of the shared drive source according to the result of detecting the velocity fluctuation of the belt member, the belt member can be endlessly moved at the target velocity regardless of the change in the diameter of the drive rotating body. In addition, by controlling the drive speed of the image-carrier drive sources which are not the shared drive source based on the angular velocity or based on the angular displacement of the image carrier driven by the shared drive source, the linear velocity difference between the image carrier driven by the shared drive source and the image carriers respectively driven by the image-carrier drive sources which are not the shared drive source is reduced. Thus, occurrence of misregistration between the visible images caused by the linear velocity difference can also be suppressed.
According to still another aspect of the present invention, by determining the drive speed of the shared drive source in the subsequent image forming operation based on the result of detecting the velocity of endless movement of the belt member driven by the shared drive source in periodic timing, the belt member can be endlessly moved at the target velocity regardless of the change in the diameter of the drive rotating body. In addition, in the periodic timing, by determining the drive speed of the image-carrier drive sources which are not the shared drive source according to the drive speed of the shared drive source, the linear velocity difference between the image carrier driven by the shared drive source and the image carriers respectively driven by the image-carrier drive sources which are not the shared drive source is reduced. Thus, occurrence of misregistration between the visible images caused by the linear velocity difference can also be suppressed.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
---|---|---|---|
2009-008355 | Jan 2009 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
20070092297 | Shimura et al. | Apr 2007 | A1 |
20080170884 | Matsuda | Jul 2008 | A1 |
Number | Date | Country |
---|---|---|
3347361 | Sep 2002 | JP |
2004-219873 | Aug 2004 | JP |
2004-220006 | Aug 2004 | JP |
2005-195679 | Jul 2005 | JP |
2006-235103 | Sep 2006 | JP |
3965357 | Jun 2007 | JP |
2008-139614 | Jun 2008 | JP |
Number | Date | Country | |
---|---|---|---|
20100183322 A1 | Jul 2010 | US |