Patent Grant
8412076
1. Field of the Invention
The present invention relates to an image forming apparatus having image bearing members and development units for developing latent images formed on the image bearing members.
2. Description of the Related Art
With some of conventional image forming apparatuses based on the electrophotographic process, an image formed on each of a plurality of image-forming photosensitive drums is transferred onto an intermediate transfer belt facing them, or onto a conveyed transfer material, in succession and layered on top of one another. This process is referred to as an in-line method. A contact development method can be employed by such image forming apparatuses. This contact development method performs development with development rollers, as developer bearing members, in rotational contact with the photosensitive drums.
When development is performed by using the contact development method, since the development rollers and photosensitive drums are rotationally driven while they are in contact with each other, the photosensitive drums and development rollers are worn out by friction therebetween. Therefore, leaving contact between a photosensitive drum and a development roller for a longer duration than necessary shortens their lifetime. To address this situation, a configuration for enabling contact and separation between the development roller and the photosensitive drum is discussed in Japanese Patent Application Laid-Open No. 2006-292868.
However, contact and separation between the photosensitive drum and the development roller in the development process involve member attachment error, driving source (motor) control timing, and other variation factors. In consideration of such variation factors, therefore, conventional techniques provide a predetermined amount of margin before and after the contact duration for performing image formation, thus causing the development rollers to securely contact the photosensitive drums during the image forming duration.
Since this margin causes a contact state between the development roller and the photosensitive drum even while image formation is not performed, the lifetime of the development rollers and photosensitive drums may be shortened.
The present invention is directed to an image forming apparatus capable of reducing the shortening of the lifetime of photosensitive drums and development rollers due to unnecessary contact therebetween.
According to an aspect of the present invention, an image forming apparatus includes a first image bearing member, a second image bearing member, a first development unit configured to contact the first image bearing member having a latent image formed thereon to develop the latent image, a second development unit configured to contact the second image bearing member having a latent image formed thereon to develop the latent image, wherein the image forming apparatus is capable of changing over between a state where the first image bearing member is separated from the first development unit and a state where the first image bearing member is in contact with the first development unit to enable developing the latent image, and is capable of changing over between a state where the second image bearing member is separated from the second development unit and a state where the second image bearing member is in contact with the second development unit to enable developing the latent image, a detection unit configured to detect a first contact duration during which the first image bearing member is in contact with the first development unit and a second contact duration during which the second image bearing member is in contact with the second development unit, and a control unit configured to control contact or separation timing between the first image bearing member and the first development unit according to the first contact duration detected by the detection unit, wherein, after performing timing control for the first image bearing member and the first development unit, the control unit controls contact or separation timing between the second image bearing member and the second development unit according to the first and second contact durations detected by the detection unit.
Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention.
Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings.
The photosensitive drums 1Y, 1M, 1C, and 1K are charged to a predetermined negative potential by the charging rollers 2Y, 2M, 2C, and 2K, respectively. Then, electrostatic latent images are formed on the photosensitive drums 1Y, 1M, 1C, and 1K by laser units 7Y, 7M, 7C, and 7K, respectively. The electrostatic latent images on the photosensitive drums are developed, and negatively charged toner is applied thereto by the development rollers 3Y, 3M, 3C, and 3K, respectively. Then, toner images Y, M, C, and K are formed on the photosensitive drums 1Y, 1M, 1C, and 1K, respectively.
The intermediate transfer belt unit includes an intermediate transfer belt 8, a drive roller 9, and a driven roller 10. Primary transfer rollers 6Y, 6M, 6C, and 6K are disposed inside the intermediate transfer belt 8, respectively facing the photosensitive drums 1Y, 1M, 1C, and 1K, to apply transfer bias thereto by a bias application unit (not illustrated). A color misregistration detection sensor 27 (optical sensor) is disposed in the vicinity of the drive roller 9 to detect a toner pattern for color misregistration detection formed on the intermediate transfer belt 8.
The color misregistration detection sensor 27 includes an infrared light emitting element such as a light-emitting diode (LED), a light-sensitive element such as a photo-diode, an IC for processing light-sensitive data, and a holder for storing these components. The principle of toner pattern detection is that infrared light emitted by the light-emitting element is reflected by the toner pattern, and the intensity of the reflected light is detected by the light-sensitive element to detect presence or absence of the toner pattern of each color. Either regular or diffuse reflected light may be detected as the reflected light.
While the photosensitive drums 1Y, 1M, 1C, and 1K are rotating in the direction of respective arrows, and the intermediate transfer belt 8 is moving in the direction of arrow A, positive bias is applied to the primary transfer rollers 6Y, 6M, 6C, and 6K to transfer toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K onto the intermediate transfer belt 8 in this order, thus forming a four-color (Y, M, C, and K) toner image thereon. The four-color toner image is conveyed to a secondary transfer roller 11.
A sheet conveyance unit 12 includes a feed roller 14 which feeds a transfer material T from a feed cassette 13 containing transfer materials T, and a conveyance roller pair 15 which conveys the fed transfer material T. The transfer material T conveyed by the sheet conveyance unit 12 is further conveyed to the secondary transfer roller 11 by a registration roller pair 16. By applying positive bias to the secondary transfer roller 11, the image formed on the intermediate transfer belt 8 is secondarily transferred onto the conveyed transfer material T. The transfer material T having the secondarily transferred image thereon is further conveyed to a fixing unit 17, in which it is heated and pressurized by a fixing film 18 and a pressurization roller 19 for fixing. The fixed transfer material T is discharged by a discharge roller pair 20.
Meanwhile, toner remaining on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K after primary transfer is removed by cleaning blades 4Y, 4M, 4C, and 4K, respectively. Toner remaining on the intermediate transfer belt 8 after secondary transfer to the transfer material T is removed by the transfer belt cleaning blade 21, and the removed toner is collected into a waste toner container 22.
A control substrate 25 in
The pattern formation control unit 55 includes an exposure control unit 51, an exposure timing control unit 52, a high-voltage control unit 53, and a drive control unit 54. The exposure control unit 51 controls a scanner drive unit 60, which rotatably drives a polygon mirror (not illustrated) in a laser unit 7, and a laser emitting unit 61, which emits laser light. The laser unit 7 includes a synchronous sensor 62, which detects laser light reflected by the polygon mirror. The synchronous sensor 62 sends a detection signal to the exposure timing control unit 52 in the pattern formation control unit 55. The exposure timing control unit 52 generates a timing with reference to the detection signal input from the synchronous sensor 62. The exposure control unit 51 drives the laser emitting unit 61 based on the generated timing. Electrostatic latent images are formed on the photosensitive drums 1 by the laser light from the laser emitting unit 61. The formed electrostatic latent images are developed by the development rollers 3 to form respective toner patterns. Controlling laser emission timing with reference to the synchronous sensor 62 enables forming a toner pattern within a range detected by the color misregistration detection sensor 27 as illustrated in
The high-voltage control unit 53 controls a charging bias generator 63, a development bias generator 64, and a transfer bias generator 65, which generate necessary voltages for image formation. The drive control unit 54 controls a photosensitive drum drive unit 66, an intermediate transfer belt drive unit 67, and a primary transfer mechanism drive unit 68 as drive control for image formation.
The contact/separation timing control unit 59 includes a contact/separation control unit 56, a drive timing control unit 57, and a pattern detector 58. The contact/separation control unit 56 controls a pulse generator 69 for driving the contact/separation motor 31. The pulse generator 69 generates a pulse signal and sends it to a motor drive unit (motor drive IC) 36. The drive timing control unit 57 receives a signal from a photo interrupter 42 (position detection sensor) and uses it for contact/separation control. The pattern detector 58 receives the result of toner pattern detection from the color misregistration detection sensor 27 and then reflects the result to contact/separation control for image formation.
A mechanism for providing contact and separation between the development roller 3 and the photosensitive drum 1 will be described below with reference to
A state transition from the standby state in
Due to this phase shift, when the cams 35Y, 35M, 35C, and 35K rotate clockwise, the cam 35Y releases pressing to the side face of the process cartridge PY first. Subsequently, the cams 35M, 35C, and 35K release pressing to the side faces of the process cartridges PM, PC, and PK, respectively, in this order according to the degree of phase shift. Thus, when the contact/separation motor 31 is forwardly rotated from the standby state in
In the standby state in
This control can be attained by a rib 41 partially provided on a cam gear 34 for yellow (Y) as illustrated in
In an ordinary printing operation, contact and separation between the development roller 3 and the photosensitive drum 1 are changed, specifically, from the standby state to the full-color contact state or from the standby state to the monochrome contact state according to a timing to start image formation.
Firstly, contact/separation state changeover control for full-color printing will be described below. A combination of the development roller 3 and photosensitive drum 1 forms each image forming station. Specifically, an image forming station that performs image formation with yellow toner is referred to as a first image forming station (also simply referred to as first station or 1st). Likewise, image forming stations that perform image formation with magenta, cyan, and black toners are referred to as second, third, and fourth image forming stations (also simply referred to as second, third, and fourth stations, or 2st, 3st, and 4st), respectively.
When performing full-color printing, the contact/separation motor 31 is forwardly rotated by a predetermined number of steps according to a timing to start image formation. When the contact/separation motor 31 starts being forwardly rotated, each station undergoes an indefinite duration during which the respective development roller 3 and photosensitive drum 1 may or may not be in contact with each other. Then, contact between the development roller 3 and the photosensitive drum 1 is established in order of the first station (yellow), second station (magenta), third station (cyan), and fourth station (black), as illustrated in
Secondly, contact/separation state changeover control for monochrome printing will be described below. When performing monochrome printing, the contact/separation motor 31 is reversely rotated by a predetermined number of steps according to a timing to start image formation. When the contact/separation motor 31 starts being reversely rotated, the fourth image forming apparatus (black) undergoes an indefinite duration. Then, contact between the development roller 3K and the photosensitive drum 1K of the fourth station (black) is established, and the fourth station (black) starts image formation. The number of driving steps of the contact/separation motor 31 is such that the contact/separation motor 31 stops when only the fourth station (black) completes contact. Upon completion of image formation, the contact/separation motor 31 is forwardly rotated by a predetermined number of driving steps. When the contact/separation motor 31 starts being forwardly rotated, separation between the development roller 3K and the photosensitive drum 1K of the fourth station (black) is established, and the fourth image forming apparatus (black) completes printing. The number of driving steps of the contact/separation motor 31 is such that the contact/separation motor 31 stops when all of the stations complete separation.
A method for detecting a contact margin will be described below with reference to the timing chart of
At timing <1>, the contact/separation motor 31 is started to change the first station (Y) from the separation state to the contact state. At timing <2>, before the first station (Y) enters the indefinite duration in the contact/separation changeover process, formation of an electrostatic latent image of yellow toner pattern (Y) on the surface of the photosensitive drum 1Y is started by exposure from the laser unit 7Y. Formation of the electrostatic latent image is continued until the contact state is achieved. At timing <3>, the first station (Y) enters the indefinite duration during which the state between the development roller 3Y and the photosensitive drum 1Y is indefinite. At timing <4>, the development roller 3Y contacts the photosensitive drum 1Y by driving the contact/separation motor 31, and a toner pattern 28 is formed on the photosensitive drum 1Y. The formed toner pattern 28 is transferred onto the intermediate transfer belt 8.
At timing <5>, the color misregistration detection sensor 27 starts detecting the toner pattern on the intermediate transfer belt 8. At timing <6>, contact between the development roller 3Y and the photosensitive drum 1Y is completed, and toner pattern formation is completed. At timing <7>, the color misregistration detection sensor 27 detects the toner pattern 28 on the intermediate transfer belt 8. At timing <8>, it ends toner pattern detection.
The contact margin refers to a time duration between timing <7> at which the color misregistration detection sensor 27 starts detecting the toner pattern 28 transferred onto the intermediate transfer belt 8 and timing <8> at which it ends toner pattern detection.
A method for detecting a separation margin will be described below with reference to the timing chart of
At timing <1>, the contact/separation motor 31 is started to change the first station (Y) from the contact state to the separation state. At timing <2>, the first station (Y) starts toner pattern formation. At timing <3>, the first station (Y) enters the indefinite duration during which the state between the development roller 3Y and the photosensitive drum 1Y is indefinite. At timing <4>, the development rollers 3 and the photosensitive drums 1 are separated, and toner pattern development onto the photosensitive drum 1Y is ended. The toner pattern formed on the photosensitive drum 1Y is transferred onto the intermediate transfer belt 8.
At timing <5>, the color misregistration detection sensor 27 starts detecting the toner pattern on the intermediate transfer belt 8. At timing <6>, separation between the development roller 3Y and the photosensitive drum 1Y is completed, and formation of electrostatic latent image onto the photosensitive drum 1Y is ended. At timing <7>, the color misregistration detection sensor 27 can no longer detect the toner pattern formed on the intermediate transfer belt 8. At timing <8>, it ends toner pattern detection.
The contact margin refers to a time duration between timing <5> at which the color misregistration detection sensor 27 starts detecting the toner pattern transferred onto the intermediate transfer belt 8 and timing <7> at which it can no longer detect the toner pattern.
A method for detecting contact and separation timings, and a method for controlling these timings according to detected contact/separation timings will be described below.
In step S1, the program checks whether or not a process cartridge is replaced. When the process cartridge is not replaced (NO in step S1), the program terminates processing. When the process cartridge is replaced (YES in step S1), the program proceeds to step S2 to start driving the driving source (the contact/separation motor 31) to detect contact timing. In step S3, the program forms a toner pattern used to detect the contact/separation state.
In step S4, the program starts establishing contact between the development roller 3 and the photosensitive drum 1. In step S5, the color misregistration detection sensor 27 detects the toner pattern formed on the intermediate transfer belt 8. In step S6, the program stops the driving source with a contact state between the development roller 3 and the photosensitive drum 1. In step S7, the program calculates a contact margin, that is, a duration between the time when contact between the development roller 3 and the photosensitive drum 1 is started and the time when the color misregistration detection sensor 27 detects the toner pattern, and stores it in memory.
In step S8, the program starts driving the driving source (the contact/separation motor 31) from the contact state between the development roller 3 and the photosensitive drum 1 to detect separation timing. In step S9, the color misregistration detection sensor 27 detects a timing at which a toner pattern is no longer formed on the intermediate transfer belt 8 by the separation between the development roller 3 and the photosensitive drum 1. In step S10, the program stops driving the driving source with a separation state between the development roller 3 and the photosensitive drum 1. In step S11, the program calculates a separation margin, that is, a duration between the time when separation between the development roller 3 and the photosensitive drum 1 is started and the time when the color misregistration detection sensor 27 can no longer detect the toner pattern, and stores it in memory.
In step S12, the program determines whether contact/separation timing detection is completed at all of the stations. When contact/separation timing detection is not completed at any station (NO in step S12), the program returns to step S3 to repeat contact/separation duration detection. When contact/separation timing detection is completed at all of the stations (YES in step S12), the program proceeds to step S13 to control the driving speed of the contact/separation motor 31 based on the detected contact/separation margin stored in memory to optimize the contact duration at each station. A method for determining the driving speed of the contact/separation motor 31 from the detection result will be described below in detail.
A method for detecting contact timing will be described below with reference to the timing chart of
A duration between timing 81 at which the contact/separation motor 31 is started and timing 83 at which the color misregistration detection sensor 27 starts detecting the toner pattern is referred to as a detection duration 1 which serves as the above-mentioned contact margin. The driving speed of the contact/separation motor 31 is controlled according to the detection duration 1. A method for controlling the driving speed of the contact/separation motor 31 from the detection duration 1 will be described below in detail.
A duration between timing 83 at which the color misregistration detection sensor 27 starts detecting the toner pattern and timing 84 at which it can no longer detect the toner pattern is referred to as a detection duration 2. During the detection duration 2, contact between the development roller 3 and the photosensitive drum 1 is established, and an image is formed on the intermediate transfer belt 8. The detection duration 2 serves as a guaranteed image region where image formation is guaranteed.
A method for controlling the driving speed of the contact/separation motor 31 to attain a contact duration suitable for each station based on the detected contact duration will be described below with reference to
When a contact duration is detected at each station as illustrated by the dotted line in
A method for correcting the contact duration at each station will be described below with reference to
A method for controlling the contact duration at each station will be described below with reference to the above-mentioned relations and the graphs of
Firstly, the contact duration of the first station will be corrected with reference to
The contact duration of the second station will be corrected with reference to
The contact duration of the third station will be corrected with reference to
The contact duration of the fourth station will be corrected with reference to
y=−1.1365*x+1195.6 (1)
With the second, third, and fourth stations, the driving frequency of the contact/separation motor 31 can be obtained by assigning a correction amount for each station to formula (2) (for calculating the driving frequencies of the second, third, and fourth stations):
y=−3*x+1200 (2)
With the second station, the correction amount of contact duration is 70 ms, and the driving frequency is 990 pps. With the third station, the correction amount of contact duration is −70 ms, and the driving frequency is 1410 pps. With the fourth station, the correction amount of contact duration is 120 ms, and the driving frequency is 840 pps.
The contact duration can be controlled by accelerating or decelerating the contact/separation motor 31 at each station in this way. This control enables shortening unnecessary durations of contact between the development roller 3 and the photosensitive drum 1, thus alleviating the shortening of the lifetime of the development rollers 3 and photosensitive drums 1.
A method for detecting separation timing will be described below with reference to
At timing 121, a signal for starting driving the contact/separation motor 31 is output, an electrostatic latent image of toner pattern starts being formed on the photosensitive drum 1, and separation between the development roller 3 and the photosensitive drum 1 is started. At timing 122, the toner pattern formed on the photosensitive drums 1 is transferred onto the intermediate transfer belt 8, and detected by the color misregistration detection sensor 27. At timing 123, separation between the development roller 3 and the photosensitive drum 1 is established, the toner pattern is made visible, and the color misregistration detection sensor 27 completes detection of the toner pattern on the intermediate transfer belt 8. At timing 124, separation between the development roller 3 and the photosensitive drum 1 is completed, and formation of an electrostatic latent image of toner pattern is ended. Formation of an electrostatic latent image is performed during the duration B in
A duration between timing 121 at which the contact/separation motor 31 is started and timing 123 at which the color misregistration detection sensor 27 can no longer detect the toner pattern is referred to as a detection duration 3. The driving speed of the contact/separation motor 31 is controlled according to the detection duration 3. A method for controlling the driving speed of the contact/separation motor 31 from the detection duration 3 will be described below in detail.
A duration between timing 122 at which the color misregistration detection sensor 27 starts detecting the toner pattern and timing 123 at which it can no longer detect the toner pattern is referred to as a detection duration 4. During the detection duration 4, contact between the development roller 3 and the photosensitive drum 1 is established, and an image is formed on the intermediate transfer belt 8. The detection duration 4 serves as a guaranteed image region where image formation is guaranteed.
A method for controlling the driving speed of the contact/separation motor 31 to attain a separation duration suitable for each station based on the detected separation duration will be described below with reference to
When a separation duration is detected at each station as illustrated by the dotted line in
A method for correcting the separation duration at each station will be described below with reference to
A method for controlling the separation duration at each station will be described below with reference to the above-mentioned relations and the graphs of
The separation duration of the second station will be corrected with reference to
The separation duration of the third station will be corrected with reference to
The separation duration of the fourth station will be corrected with reference to
With the second, third, and fourth stations, the driving frequency of the contact/separation motor 31 can be obtained by assigning a correction amount for each station to x in formula (2) (for calculating the driving frequencies of the second, third, and fourth stations). With the second station, the correction amount of separation duration is −40 ms, and the driving frequency is 1080 pps. With the third station, the correction amount of separation duration is 60 ms, and the driving frequency is 1380 pps. With the fourth station, the correction amount of separation duration is −100 ms, and the driving frequency is 900 pps.
The present exemplary embodiment has specifically been described based on a case where durations of contact between the photosensitive drum 1 and the development roller 3 are controlled according to the guaranteed image domain. However, contact duration control is not limited to the guaranteed image domain. For example, when an image size for respective colors is received from a controller, contact durations can also be optimally controlled according to the image size for respective colors. Controlling contact durations according to the image size for respective colors enables reducing wear of the photosensitive drums 1 and the development rollers 3. In addition, similar to contact durations, separation durations can also been controlled according to the image size.
The separation duration can be controlled by accelerating or decelerating the contact/separation motor 31 at each station in this way. This control enables shortening unnecessary durations of contact between the development roller 3 and the photosensitive drum 1, thus alleviating the shortening of their lifetime.
The first exemplary embodiment has specifically been described based on acceleration/deceleration control for the contact/separation motor 31 in association with the result of contact/separation timing detection. A second exemplary embodiment of the present invention will be described below based on a method for decelerating the contact/separation motor 31, after contact/separation timing detection, to control contact and separation durations. The first exemplary embodiment has specifically been described based on a case where the contact/separation motor 31 is accelerated. In other words, a costly motor needs to be used as the contact/separation motor 31 in the first exemplary embodiment. However, since the output torque of a motor decreases with increasing driving speed, required motor specifications (which guarantee the output torque at high speeds) will become severer. Therefore, as an example of optimization without raising the specifications of the contact/separation motor 31, the present exemplary embodiment will be described below based on a method for controlling contact and separation operations by using a low-cost motor. Descriptions on the same configuration as the first exemplary embodiment will be omitted.
A method for controlling the driving speed of the contact/separation motor 31 to attain a contact duration suitable for each station based on the detected contact duration will be described below with reference to
When a contact duration is detected at each station as illustrated by the dotted line in
With the third station, since the contact duration is shorter than that of the second station, the contact/separation motor 31 is accelerated during a time between the time when contact is completed at the second station and the time when contact is completed at the third station as denoted by the solid line III in
A method for setting the driving speed of the contact/separation motor 31 at each station will be described below with reference to
A method for controlling the contact duration at each station will be described below with reference to the above-mentioned relations and
The contact duration of the second station will be corrected. With the second station, since contact is established 80 ms longer than the guaranteed contact duration (X) due to contact duration correction at the first station, the contact/separation motor 31 is decelerated so that contact is established 40 ms longer than the guaranteed contact duration (X). The above-mentioned control is performed because of the following reason. Since the contact/separation motor 31 drives all of the stations as a single driving source, correcting the contact duration up to the guaranteed contact duration (X) at the second station will disable suitably correcting the third and fourth stations on the downstream side of the second station. Therefore, contact durations are controlled so that the contact duration of a preceding (upstream-side) station having the shortest one does not fall below a predetermined value, i.e., the guaranteed contact duration (X). In this case, since the contact duration of the second station is corrected by 40 ms so that the contact duration of the third station coincides with the guaranteed contact duration (X), the contact durations of the third and fourth stations are also corrected by 40 ms.
The contact duration of the third station will be corrected. With the third station, since contact is established for the guaranteed contact duration (X) due to contact duration correction at the first and the second stations, the contact/separation motor 31 is driven at the setup speed and therefore contact duration correction is not performed.
The contact duration of the fourth station will be corrected. With the fourth station, since contact is established 80 ms longer than the guaranteed contact duration (X) due to contact duration correction at the first, second, and third stations, the contact/separation motor 31 is decelerated to match the contact duration of the fourth station with the guaranteed contact duration (X).
When the maximum driving speed of the contact/separation motor 31 is predetermined in specifications and hence its driving speed cannot be accelerated more than the setup speed, contact durations of the four stations are compared and suitably controlled so that the contact durations do not fall below the guaranteed setup duration (X).
Referring to
In step S1103, the CPU 26 determines whether the contact duration Tm1 is minimum. If the contact duration Tm1 is minimum, the processing proceeds to step S1104. If the contact duration Tm1 is not minimum, the processing proceeds to step S1105. In step S1104, the CPU 26 determines whether the contact duration Tk1 is greater than the contact duration Tc1. If the contact duration Tk1 is greater than the contact duration Tc1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Tm1, Tm2=0, Tc2=Tc1−Tm1, and Tk2=Tk1−Tc1. If the contact duration Tk1 is not greater than the contact duration Tc1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Tm1, Tm2=0, Tc2=Tk1−Tm1, and Tk2=0.
In step S1105, the CPU 26 determines whether the contact duration Tc1 is greater than the contact duration Tm1. If the contact duration Tc1 is greater than the contact duration Tm1, the processing proceeds to step S1106. If the contact duration Tc1 is not greater than the contact duration Tm1, the processing proceeds to step S1108. In step S1106, the CPU 26 determines whether the contact duration Tk1 is greater than the contact duration Tc1. If the contact duration Tk1 is greater than the contact duration Tc1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Ty1, Tm2=Tm1−Ty1, Tc2=Tc1−Tm1, and Tk2=Tk1−Tc1. If the contact duration Tk1 is not greater than the contact duration Tc1, the processing proceeds to step S1107. In step S1107, the CPU 26 determines whether the contact duration Tk1 is greater than the contact duration Tm1. If the contact duration Tk1 is greater than the contact duration Tm1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Ty1, Tm2=Tm1−Ty1, Tc2=Tk1−Tm1, and Tk2=0. If the contact duration Tk1 is not greater than the contact duration Tm1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Ty1, Tm2=Tk1−Ty1, Tc2=0, and Tk2=0.
In step S1108, the CPU 26 determines whether the contact duration Tk1 is greater than the contact duration Tc1. If the contact duration Tk1 is greater than the contact duration Tc1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Ty1, Tm2=Tc1−Ty1, Tc2=0, and Tk2=Tk1−Tc1. If the contact duration Tk1 is not greater than the contact duration Tc1, the CPU 26 sets the correction amounts of contact duration at the respective image forming stations as Ty2=Ty1, Tm2=Tk1−Ty1, Tc2=0, and Tk2=0.
With the second, third, and fourth stations, the driving frequency of the contact/separation motor 31 can be obtained by assigning a correction amount for each station to x in formula (2) (for calculating the driving frequencies of the second, third, and fourth stations) described in the first exemplary embodiment. With the second station, the correction amount of contact duration is 40 ms, and the driving frequency is 1080 pps. With the third station, the correction amount of contact duration is 0 ms, and the driving frequency is 1200 pps. With the fourth station, the correction amount of contact duration is 80 ms, and the driving frequency is 960 pps.
The drive of contact/separation motor 31 in the present exemplary embodiment is controlled based on a driving frequency table (based on the two-phase excitation method) illustrated in
As operations of the image forming apparatus according to the present exemplary embodiment, processing flow from the step of detecting contact durations to the step of determining the driving frequency profile of the contact/separation motor 31 will be described below with reference to the flow chart of
Since the duration of contact between the development roller 3 and the photosensitive drum 1 depends on the combination of image forming apparatus and process cartridges, the program, in step S2001, checks whether any process cartridge is replaced. When no process cartridge is replaced (NO in step S2001), the program terminates the processing. When a process cartridge is replaced (YES in step S2001), the program, in step S2002, initializes the correction amount of contact duration for the relevant station. In step S2003, the program detects a contact duration of the station where the process cartridge is replaced. The driving frequency of the contact/separation motor 31 at the time of contact duration detection is 1200 pps, which is the maximum driving speed as mentioned above.
In step S2004, the program clears the information about the replacement of process cartridge at the station that completed contact duration detection. In step S2005, the program checks whether a process cartridge is replaced at any other station. When a process cartridge is replaced at other stations (YES in step S2005), the program returns to step S2002. Otherwise (NO in step S2005), the program proceeds to step S2006 to determine a driving speed (driving frequency) profile of the contact/separation motor 31. Then, the program terminates the processing.
When contact duration detection is performed at the maximum driving speed of the contact/separation motor 31, the image forming apparatus is able to control the guaranteed contact duration to a suitable duration within the driving speed range by comparing contact durations of the four stations and decelerating the contact/separation motor 31. This control can optimize contact durations and hence reduce unnecessary contact durations without using a high-speed motor as the contact/separation motor 31. Accordingly, the image forming apparatus becomes able to alleviate the shortening of the lifetime of the development rollers 3 and photosensitive drums 1 without raising cost and specifications.
A method for controlling the driving speed of the contact/separation motor 31 to attain a separation duration suitable for each station based on the detected separation duration with reference to
Since the maximum driving speed of the contact/separation motor 31 cannot be accelerated more than the setup speed at the time of separation duration detection, separation durations cannot be made suitable through acceleration control. To suitably control separation durations by driving the contact/separation motor 31 at driving frequencies not exceeding the maximum driving frequency, the timing to start driving the contact/separation motor 31 is brought forward to attain a suitable separation duration of the first station as illustrated in
Referring to
A method for setting the driving speed of the contact/separation motor 31 at each station will be described below with reference to
A method for controlling the separation duration at each station will be described below with reference to the above-mentioned relations and
The separation duration of the second station will be corrected. With the second station, contact is established 30 ms longer than the guaranteed separation duration (Y). However, since the separation duration of the second station cannot be matched with the guaranteed separation duration (Y) by accelerating the contact/separation motor 31, it is driven at the setup speed and, therefore, separation duration correction is not performed.
The separation duration of the third station will be corrected. With the third station, since contact is established −30 ms shorter than the guaranteed separation duration (Y), the contact/separation motor 31 is decelerated to match the separation duration of the third station with the guaranteed separation duration (Y).
The separation duration of the fourth station will be corrected. With the fourth station, since contact is established −50 ms shorter than the guaranteed contact duration (X) due to separation duration correction at the third station, the contact/separation motor 31 is decelerated to match the separation duration of the fourth station separation with the guaranteed separation duration (Y).
When the maximum driving speed of the contact/separation motor 31 is predetermined and the motor cannot be accelerated more than the setup speed in this way, separation durations of the four stations are compared and, separation durations are suitably controlled so that they do not become smaller than the guaranteed separation duration (Y).
Referring to
In step S1805, the CPU 26 determines whether the duration Tc4 is less than 0. If the duration Tc4 is less than t0, the processing proceeds to step S1806. If the duration Tc4 is not less than 0, the processing proceeds to step S1807. In step S1806, the CPU 26 determines whether the duration Tk4 is less than the duration Tc4. If the duration Tk4 is less than the duration Tc4, the CPU 26 sets the correction amounts of separation duration at the respective stations as Tm5=0, Tc5=−Tc4, and Tk5=−(Tk4−Tc4). If the duration Tk4 is not less than the duration Tc4, the CPU 26 sets the correction amounts of separation duration at the respective stations as Tm5=0, Tc5=−Tc4, and Tk5=0. In step S1807, the CPU 26 determines whether the duration Tk4 is less than 0. If the duration Tk4 is less than 0, the CPU 26 sets the correction amounts of separation duration at the respective stations as Tm5=0, Tc5=0, and Tk5=−Tk4. If the duration Tk4 is not less than 0, the CPU 26 sets the correction amounts of separation duration at the respective stations as Tm5=0, Tc5=0, and Tk5=0.
With the second, third, and fourth stations, the driving frequency of the contact/separation motor 31 can be obtained by assigning a correction amount for each station to x in formula (2) (for calculating the driving frequencies of the second, third, and fourth stations). With the second station, the correction amount of separation duration is 0 ms, and the driving frequency is 1200 pps. With the third station, the correction amount of separation duration is −30 ms, and the driving frequency is 1110 pps. With the fourth station, the correction amount of separation duration is −50 ms, and the driving frequency is 1050 pps.
When separation duration detection is performed at the specified maximum driving speed of the contact/separation motor 31, the image forming apparatus is able to control the guaranteed separation duration to a suitable duration within the driving speed range by comparing separation durations of the four stations and decelerating the contact/separation motor 31 by changing its driving timing. This control can optimize separation durations and hence reduce unnecessary separation durations without using a high-speed motor as the contact/separation motor 31. Accordingly, the image forming apparatus becomes able to alleviate the shortening of the lifetime of the development rollers 3 and photosensitive drums 1 without raising cost and specifications.
Although the present exemplary embodiment has specifically been described on the premise that the driving speed of the contact/separation motor 31 at the time of contact duration detection is the maximum driving speed, a correction method illustrated in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions.
This application claims priority from Japanese Patent Applications No. 2009-141391 filed Jun. 12, 2009 and No. 2010-024604 filed Feb. 5, 2010, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-141391 | Jun 2009 | JP | national |
| 2010-024604 | Feb 2010 | JP | national |
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