Patent Grant
9341976
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, printer, or facsimile of, for example, an electrophotography system or electrostatic recording system.
2. Description of the Related Art
Conventionally, a color image forming apparatus, which forms an image for one color by an image forming unit including a pair of laser scanners and an image bearing member, and includes image forming units as many as the number of colors, is known. In this arrangement, laser light beams, which are deflected and scanned by rotary polygon mirrors arranged for respective colors, are detected by laser detectors (to be referred to as Beam Detection (BD) sensors hereinafter) for respective colors, so as to generate horizontal sync signals (to be referred to as BD signals hereinafter) required to detect image write start timings of respective colors. Then, rotation cycles (to be referred to as BD cycles hereinafter) of scanner motors of respective colors are detected based on the BD signals. Also, emission (to be referred to as force emission hereinafter) of a semiconductor laser is performed until the BD cycles reach a predetermined value, and respective image bearing members are irradiated with laser light beams of respective colors reflected by the rotary polygon mirrors using a plurality of reflection surfaces.
Also, as a more inexpensive arrangement, a color image forming apparatus including one laser scanner and a plurality of image bearing members is known. In this arrangement, a single rotary polygon mirror, which is driven by a single scanner motor, is irradiated with laser light beams of respective colors, and the respective image bearing members are irradiated with the laser light beams using a plurality of reflection surfaces.
For example, Japanese Patent Application Laid-Open No. H04-313776 has proposed an arrangement in which a plurality of light sources is simultaneously scanned on a photosensitive member by different surfaces of a polygon mirror. Then, it proposes a unit which determines BD signals of respective colors of remaining light sources besides a light source provided with a BD sensor from a BD signal of the light source provided with the BD sensor and the rotation phase differences of the surfaces of the polygon mirror. For example, Japanese Patent Application Laid-Open No. 2004-345171 has proposed the following arrangement so as to solve color misregistration at transfer timings of respective colors caused by surface-division precisions of respective mirror surfaces of a rotary polygon mirror, which do not completely match. That is, this arrangement includes one BD sensor, which receives reflected laser light from the rotary polygon mirror, a BD signal output unit, which outputs a BD signal at a reception timing of the reflected laser light, and a pseudo BD sensor signal generation unit, which generates a pseudo BD sensor signal as a pseudo signal after an elapse of a predetermined period of time from the BD sensor. Then, a reference signal of a write start position in a main scanning direction of laser light with which a surface different from that irradiated with laser light, with which the BD sensor is irradiated, is irradiated with and reflected is defined by the pseudo BD sensor signal generation unit. Since Japanese Patent Application Laid-Open No. 2004-345171 includes such arrangement, misregistration at transfer timings of respective colors can be reduced even by one BD sensor.
In Japanese Patent Application Laid-Open No. H04-313776, the following control is executed. That is, during a period until a scanner motor is rotated at a stable speed (to be referred to as a scanner start-up period hereinafter), semiconductor lasers of respective colors emit laser light beams so as to detect a BD cycle and to calculate a rotation number of the scanner motor. Then, the semiconductor lasers of respective colors emit laser light beams, and light amount adjustment of the semiconductor lasers of respective colors is also executed at that timing. At this time, in a station in which force emission is performed, a photosensitive member surface is irradiated with laser light to change a potential of the photosensitive member surface. For this reason, control for determining a voltage required to supply a predetermined current to a transfer unit at an image formation timing (to be referred to as Active Transfer Voltage Control (ATVC) control hereinafter) cannot be executed during the scanner start-up period. As a result, a first print-out time (FPOT) from a print instruction until printing of the first page is completed cannot be shortened.
The present invention has been made in consideration of the above situation, and enables to shorten the FPOT.
In this context, the purpose of the present invention is to provide an image forming apparatus including a first image bearing member and a second image bearing member, on each of which an electrostatic latent image is formed by laser light, a first developing device and a second developing device, each configured to develop the electrostatic latent image formed on the corresponding image bearing member to form a toner image, a first transfer device and a second transfer device, each configured to transfer the toner image on the corresponding image bearing member onto a recording medium, an application unit configured to apply a voltage to the second transfer device; a current detection unit configured to detect a current flowing when the application unit applies the voltage to the second transfer device, a first light source and a second light source, each configured to emit laser light to the corresponding image bearing member, a rotary polygon mirror configured to deflect the laser light beams emitted from the first light source and the second light source, a motor configured to drive the rotary polygon mirror, a detection unit configured to detect the laser light deflected by the rotary polygon mirror, and a control unit configured to execute, based on a detection result of the detection unit, start-up control for controlling driving of the motor so that a rotation number of the motor reaches a predetermined rotation number, and determination control for determining a voltage to be applied from the application unit to the second transfer device upon execution of image formation, wherein the detection unit is arranged at a position where the detection unit detects the laser light deflected by the rotary polygon mirror toward the first image bearing member, and the control unit executes the start-up control and the determination control in parallel.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.
With the arrangement of the first embodiment, when a BD station and image forming station are different upon execution of a monochrome mode, ATVC control of the image forming station is executed without waiting until a scanner motor is stably rotated at a target speed. That is, when the BD station is different from the image forming station which executes the mode, force emission of the image forming station is skipped at a scanner start-up timing, and ATVC control is executed in the image forming station parallel to the scanner start-up. Note that the BD station is an image forming station of a color including a BD sensor as a laser detector. Also, the ATVC control is determination control for determining a voltage required to supply an appropriate current to a transfer unit at an image formation timing.
Configuration of Image Forming Apparatus
As an exposure unit which exposes each photosensitive drum 100, a scanner unit 156 is arranged. The scanner unit 156 includes semiconductor lasers 107 as light sources, and a rotary polygon mirror 109 connected to a scanner motor 108. In this manner, this embodiment adopts an arrangement in which laser light beams emitted from the four semiconductor lasers 107a, 107b, 107c, and 107d are deflected by one rotary polygon mirror 109. Laser light emitted from each semiconductor laser 107 is reflected and deflected by the rotary polygon mirror 109 rotated by the scanner motor 108, and a surface of the corresponding photosensitive drum 100 is irradiated with that laser light by a corresponding reflection mirror 106. Note that the scanner unit 156 includes the semiconductor lasers 107, scanner motor 108, rotary polygon mirror 109, reflection mirrors 106, and a BD sensor 110 as a laser detector.
The charging roller 101 uniformly charges the surface of each photosensitive drum 100. When the surface of the photosensitive drum 100, which is uniformly charged by the charging roller 101, is irradiated with laser light reflected by the reflection mirror 106, an electrostatic latent image is formed on the photosensitive drum 100. The BD sensor 110 as a laser detector receives laser light, and generates a BD signal. The BD sensor 110 is arranged on a scanning line of the laser beam. The BD sensor 110 is arranged on an optical path of laser light which is reflected by the rotary polygon mirror 109 and with which the reflection mirror 106a is irradiated. In this embodiment, since a yellow image forming station (to be referred to as an image forming station Y hereinafter; the same applies to the remaining colors) includes the BD sensor 110, the image forming station Y will also be referred to as a BD station Y hereinafter. A rotation number of the scanner motor 108 is calculated from a cycle of the BD signal generated by the BD sensor 110.
The developing unit 105 applies toner (developing agent) of each color on the surface of the photosensitive drum 100 on which an electrostatic latent image is formed by a developing roller 104, thereby visualizing the electrostatic latent image as a toner image. The cleaning device 102 removes residual toner on the surface of the photosensitive drum 100 after transfer. At a position opposing the photosensitive drums 100, an intermediate transfer belt 112 as an intermediate transfer member is extended between a driving roller 113, tension roller 114, and driven roller 115. The intermediate transfer belt 112 pivots in a clockwise direction, as indicated by an arrow in
At a position opposing the driving roller 113 behind the intermediate transfer belt 112, a driven secondary transfer roller 124 is arranged. Toner images formed on the photosensitive drums 100 are primarily transferred onto the intermediate transfer belt 112 upon operations of the primary transfer units 103. The primary transfer unit 103d includes a transfer current detection circuit 111, which measures a current value according to a voltage applied to each primary transfer unit 103. Note that the image forming station Y, image forming station M, image forming station C, and image forming station K are arranged in turn from the upstream side toward the downstream side of a conveyance direction (pivot direction) of the intermediate transfer belt 112. The transfer current detection circuit 111 is required for the ATVC control as control for determining a transfer voltage, as will be described later. In this embodiment, the transfer current detection circuit 111 is arranged in the image forming station K as a most-downstream side image forming station.
On the other hand, a recording material 119 picked up by a pickup roller 120 from a paper cassette is separated and fed one by one by a separation unit (not shown). Next, the recording material 119 fed from a conveyance roller pair 121 turns on a registration sensor 122, and is conveyed to a position between the driving roller 113 and secondary transfer roller 124 at a predetermined timing by a registration roller pair 123. Toner images on the intermediate transfer belt 112 are transferred onto the recording material 119 by the secondary transfer roller 124, and are fixed by a fixing unit 125. The fixing unit 125 includes a fixing roller 127, a surface layer of which is covered by a fixing film 126, and a pressure roller 128, and the fixing roller 127 and pressure roller 128 are in contact with each other. After the toner images are fixed, a paper width of the recording material 119 is detected by paper width sensors 129 (on the left side in the conveyance direction of the recording material 119) and 130 (on the right side). After that, the recording material 119 turns on a fixing/exhaust sensor 131, is conveyed by an exhaust roller pair 132, and is then exhausted onto an exhaust tray 133 arranged on an upper portion of the image forming apparatus main body.
System Configuration of Image Forming Apparatus
Configuration of Engine Control Unit and Respective Controllers
To the transfer voltage output circuit 253, the transfer current detection circuit 111 is connected. The transfer current detection circuit 111 detects a current flowing through the primary transfer unit 103, and inputs an analog signal corresponding to the current value to the CPU 211. Note that “4th station” in
The CPU 211 can set a light-on method of the semiconductor laser 107 in the ASIC 212. Note that the light-on method of the semiconductor laser 107 which can be set by the CPU 211 in the ASIC 212 includes, for example, light-off, force emission, and unblanking emission. Note that unblanking emission is a light-on method of turning on laser light only in the vicinity of the BD sensor 110, that is, in only a non-image area of the photosensitive drum 100. When the BD sensor 110 receives laser light of the semiconductor laser 107, it outputs a BD signal to the engine control unit 202. The engine control unit 202 outputs the BD signal to the controller 201, which outputs a video signal to the engine control unit 202 in synchronism with the BD signal.
The CPU 211 sets a target rotation number (indicated by a solid line in
As described above, in the comparative example, during the interval emission zone 401, the rotation number of the scanner motor 108 is detected by the interval emission of the semiconductor laser 107a, and the light amount adjustment of the semiconductor laser 107d is executed by the interval emission of the semiconductor laser 107d.
The CPU 211 repetitively executes the interval emission of the semiconductor laser 107a during the zone 401 to judge whether or not the rotation number of the scanner motor 108 has reached a predetermined rotation number. If the CPU 211 detects that the rotation number of the scanner motor 108 has reached the predetermined rotation number, and the rotation speed has reached a predetermined rotation speed, it controls the semiconductor lasers 107a and 107d to always emit light via the ASIC 212 (zone 402). The ASIC 212 accelerates or decelerates the scanner motor 108 so as to control the rotation number of the scanner motor 108 to reach the target rotation number set by the CPU 211. If the CPU 211 judges that the rotation number of the scanner motor 108, that is, the rotary polygon mirror 109 has reached the target rotation number, it controls the ASIC 212 to execute unblanking emission, in which the semiconductor laser is turned on only in the vicinity of the BD sensor 110 (zone 403). In this embodiment, since the BD sensor 110 is arranged in the image forming station Y, the semiconductor laser 107a executes unblanking emission. Then, the CPU 211 executes the ATVC control required to determine a transfer voltage of the image forming station K (described as “Kst” in
If the CPU 211 judges in S502 that the emission timing of the semiconductor laser 107a is reached, it controls the semiconductor laser 107a to emit light for a certain period in S503, and the process advances to S504. In S504, the CPU 211 controls the semiconductor laser 107d (described as “semiconductor K” in
The CPU 211 judges in S505 whether or not start-up of the scanner motor 108 is completed. If the CPU 211 judges in S505 that start-up of the scanner motor 108 is not completed, the process returns to S502. If the CPU 211 judges in S505 that start-up of the scanner motor 108 is completed, it controls the semiconductor lasers 107a and 107d (described as “semiconductor laser Y/K” in
Upon completion of the processing of the ATVC control of the image forming station K, the CPU 211 outputs a /TOP signal to the controller 201 in S508, thus starting a printing operation in S509. Note that the process of S508 corresponds to the timing 405 described in
ATVC Control
As described above, the CPU 211 controls the semiconductor laser 107 to make unblanking emission to start execution of the ATVC control. Simultaneously with the beginning of execution of the ATVC control, the CPU 211 controls the transfer voltage output circuit 253 to apply a predetermined start-up voltage Va to the primary transfer unit 103, and controls the transfer current detection circuit 111 to measure a current value I flowing through the primary transfer unit 103 (zone 601). At this time, the CPU 211 judges whether or not the current value (to be referred to as a measured current value hereinafter) I measured by the transfer current detection circuit 111 falls within a range of a coarse adjustment threshold value ΔIr with reference to a target current value Im (to check if Im−ΔIr≦I≦Im+ΔIr is satisfied). Then, if the CPU 211 judges that the measured current value I falls outside the range of the coarse adjustment threshold value ΔIr, it adds a coarse adjustment gain ΔVr to a voltage Vn currently applied to the primary transfer unit 103. Note that an initial value of Vn is a predetermined start-up voltage Va (=V1 (n=1)).
V=Vn+ΔVr (1)
The CPU 211 controls the transfer voltage output circuit 253 to apply the voltage V given by equation (1) to the primary transfer unit 103, controls the transfer current detection circuit 111 to measure the current value I, and judges whether or not the measured current value I falls within the range of the coarse adjustment threshold value ΔIr with reference to the target current value Im. The CPU 211 repeats this control (to be referred to as coarse adjustment control hereinafter) until the measured current value I falls within the range of the coarse adjustment threshold value ΔIr of the target current value Im (zone 602).
After the aforementioned coarse adjustment control is repeated, when the CPU 211 judges that the measured current value I measured by the transfer current detection circuit 111 falls within the range of the coarse adjustment threshold value ΔIr of the target current value Im, it adjusts the current value I using a fine adjustment gain ΔVf which satisfies ΔVr>ΔVf. When the CPU 211 judges that the measured current value I measured by the transfer current detection circuit 111 is smaller than the target current value Im, it adds the fine adjustment gain ΔVf to the voltage Vn currently applied to the primary transfer unit 103.
V=Vn+ΔVf (2)
On the other hand, when the CPU 211 judges that the measured current value I measured by the transfer current detection circuit 111 is larger than the target current value Im, it subtracts the fine adjustment gain ΔVf from the voltage Vn currently applied to the primary transfer unit 103.
V=Vn−ΔVf (3)
After that, the CPU 211 repeats the control of equation (2) or (3) (to be referred to as fine adjustment control hereinafter) until it judges that the measured current value I measured by the transfer current detection circuit 111 falls (converges) within a range of a fine adjustment threshold value ΔIf of the target current value Im (zone 603). Note that the CPU 211 judges that the measured current value I converges within the range of the fine adjustment threshold value ΔIf when it satisfies Im−ΔIf/2≦I≦Im+ΔIf/2.
When the CPU 211 judges that the measured current value I measured by the transfer current detection circuit 111 falls within the range of the fine adjustment threshold value ΔIf of the target current value Im, it detects an impedance (zone 604). The CPU 211 determines a voltage required to supply the target current value Im to the primary transfer unit 103 during an image forming operation based on the detected impedance. During the image forming operation, constant voltage control is executed so that the voltage determined by the ATVC control is a constant voltage. Alternatively, constant current control for changing a voltage value by the CPU 211 based on the measured current value I so as to maintain the target current value Im even during the image forming operation may be executed.
Note that the ATVC control detects a current flowing through the primary transfer unit 103 by the transfer current detection circuit 111 so as to detect impedance. When the semiconductor laser 107 is controlled to emit light to irradiate the photosensitive drum 100 with laser light while the transfer current detection circuit 111 detects a current, the surface potential of the photosensitive drum 100 changes, and a correct current value cannot be detected. For this reason, in the control of the comparative example, the ATVC control is not executed during the interval emission zone 401 for executing the light amount adjustment of the semiconductor laser 107d or the always-emission zone 402, but is executed during the unblanking emission zone 403 (see
After the ATVC control of the image forming station K is completed, and start-up of the scanner motor 108 is completed, the CPU 211 controls the semiconductor lasers 107a and 107d to make always-emission until the rotation number of the scanner motor 108 is stabilized (zone 703). Then, the CPU 211 executes the light amount adjustment of the semiconductor laser 107d during the always-emission zone 703 of the semiconductor laser 107d (zone 704). This point is different from the control of the comparative example of the zone 402 described using
As described above, in this embodiment, the ATVC control for the image forming station K ends during the zone 701, and the light amount adjustment of the semiconductor laser 107d ends during the zone 703. For this reason, the control of this embodiment shown in
The CPU 211 judges in S803 whether or not an emission timing of the semiconductor laser 107a is reached. If the CPU 211 judges that the emission timing is not reached, the process returns to S803. If the CPU 211 judges in S803 that the emission timing of the semiconductor laser 107a is reached, it controls the semiconductor laser 107a to emit light for a constant period in S804. The CPU 211 judges in S805 whether or not start-up of the scanner motor 108 is completed. If the CPU 211 judges that start-up is not completed, the process returns to S803. Note that the processes of S801 to S805 correspond to the interval emission zone 701 described using
If the CPU 211 judges in S805 that start-up of the scanner motor 108 is completed, it judges in S806 whether or not the ATVC control of the image forming station K is completed. If the CPU 211 judges in S806 that the ATVC control of the image forming station K is not completed, the process returns to S806. Note that
If the CPU 211 judges in S806 that the ATVC control of the image forming station K is completed, it controls the semiconductor lasers 107a and 107d to make always-emission in S807, thus starting light amount adjustment of the semiconductor laser 107d. Note that the process of S806 corresponds to the zone 702 included in the interval emission zone 701 in
As described above, the ATVC control of the image forming station K can be executed at the start-up timing of the scanner motor 108. For this reason, in this embodiment, the /TOP signal is output to start image formation immediately after the semiconductor laser starts unblanking emission. Thus, this embodiment can shorten the FPOT (first print-out time). Note that this embodiment has explained the case in which the image forming station Y is the BD station. However, the same applies to a case in which the monochrome mode is executed when the image forming station M or C is a BD station.
The second embodiment relates to control when a BD station is a black image forming station K in a color printing mode. This embodiment executes ATVC control of the image forming station without waiting until a scanner motor 108 is stably rotated at a target speed. Note that since the arrangement of an image forming apparatus of this embodiment is the same as the first embodiment except for the arrangement of a scanner unit 156 and the number of transfer current detection circuits 111 to be arranged (to be described later), the same reference numerals denote the same components, and a description thereof will not be repeated.
Arrangement of Scanner Unit
On the other hand, the CPU 211 does not execute light amount adjustment of semiconductor lasers 107a, 107b, and 107c in association with image forming stations Y, M, and C (described as “Y/M/Cst” in
After the ATVC control of the image forming stations Y, M, and C is completed, and start-up of the scanner motor 108 is completed, the CPU 211 executes the following processing. That is, the CPU 211 controls the semiconductor lasers 107a, 107b, 107c, and 107d to make always-emission until the rotation number of the scanner motor 108 is stabilized (zone 1003). The CPU 211 executes the light amount adjustment of the semiconductor lasers 107a, 107b, and 107c during a zone 1004 included in the always-emission zone 1003. Note that the semiconductor laser 107d is controlled to make always-emission so as to monitor the rotation number of the scanner motor 108 by the BD sensor 110 during the zone 1003. When the CPU 211 judges that the rotation number of the scanner motor 108 has reached the target rotation number, it controls the ASIC 212 to transition to an unblanking emission zone (zone 1005). In this embodiment, since the BD sensor 110 is included in the image forming station K, the semiconductor laser 107d makes unblanking emission. The CPU 211 permits the ASIC 212 to output a /TOP signal, and the /TOP signal is output to a controller 201, thus starting image formation (timing 1006). Note that in the color printing mode of this embodiment, black is formed by mixing three color toners Y, M, and C.
The CPU 211 judges in S1103 whether or not an emission timing of the semiconductor laser 107d is reached. If the CPU 211 judges that the emission timing is not reached, the process returns to S1103. If the CPU 211 judges in S1103 that the emission timing of the semiconductor laser 107d is reached, it controls the semiconductor laser 107d to emit light for a certain period in S1104. The CPU 211 judges in S1105 whether or not start-up of the scanner motor 108 is completed. If the CPU 211 judges that start-up is not completed, the process returns to S1103. Note that the processes of S1101 to S1105 correspond to the interval emission zone 1001 of the semiconductor laser 107d described using
If the CPU 211 judges in S1105 that start-up of the scanner motor 108 is completed, it judges in S1106 whether or not the ATVC control of the image forming stations Y, M, and C is completed. If the CPU 211 judges in S1106 that the ATVC control of the image forming stations Y, M, and C is not completed, the process returns to S1106. If the CPU 211 judges in S1106 that the ATVC control of the image forming stations Y, M, and C is completed, it controls the semiconductor lasers 107a, 107b, 107c, and 107d to make always-emission via the ASIC 212 in S1107. Then, the CPU 211 starts light amount adjustment of the semiconductor lasers 107a, 107b, and 107c. Also, the CPU 211 monitors the rotation number of the scanner motor 108 by detecting laser light emitted from the semiconductor laser 107d by the BD sensor 110. Note that the process of S1106 corresponds to the zone 1002 included in the interval emission zone 1001 shown in
After the rotation number of the scanner motor 108 is stabilized, the CPU 211 controls the semiconductor laser 107d to make unblanking emission via the ASIC 212 in S1108. Note the processes after S1008 and subsequent steps correspond to the unblanking emission zone 1005 described using
As described above, according to this embodiment, when the image forming station K is the BD station, and a color printing instruction is input, the following arrangement is adopted. That is, the arrangement in which the ATVC control of the image forming stations Y, M, and C is executed without waiting until the scanner motor 108 is stably rotated at a target speed is adopted. Therefore, the /TOP signal is output to the controller 201 to start image formation immediately after the unblanking emission of the scanner, thus shortening the FPOT. As described above, according to this embodiment, the first print-out time can be shortened.
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 such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-272402, filed Dec. 13, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-272402 | Dec 2012 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 20090135243 | Yamazaki | May 2009 | A1 |
| 20090214239 | Horiuchi | Aug 2009 | A1 |
| 20110025811 | Lee | Feb 2011 | A1 |
| 20120099880 | Inoue et al. | Apr 2012 | A1 |
| Number | Date | Country |
|---|---|---|
| 04-313776 | Nov 1992 | JP |
| 2004-345171 | Dec 2004 | JP |
| 2009-210986 | Sep 2009 | JP |
| 2012-088553 | May 2012 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20140169816 A1 | Jun 2014 | US |
