JP2004345171A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an image forming apparatus equipped with only one laser scanner unit for a plurality of image carriers in which deterioration of image quality is eliminated with a small circuit scale even when the image forming apparatus is equipped with only one sensor (BD sensor) for detecting the image writing position in main scanning. <P>SOLUTION: The image forming apparatus comprises a rotary polygon mirror being driven to rotate by a laser scanner motor and reflecting modulated laser lights from a plurality of laser light sources on a plurality of reflective surfaces, a BD sensor for receiving reflected light from the rotary polygon mirror and outputting the reference signal of writing start position in the main scanning direction on an image carrier, and a means for generating a pseudo BD sensor signal upon elapsing a predetermined time after the reference signal is outputted from the BD sensor wherein the reference signal of writing start position in the main scanning direction on the image carrier of a laser light impinging and reflecting on a surface different from that of a laser light impinging on the BD sensor is generated from the pseudo BD sensor signal generating means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic apparatus such as a copying machine, a printer, and a facsimile that performs image exposure using a plurality of laser beams.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus including a plurality of lasers and an image carrier has two main configurations. The first type is provided with one laser scanner unit per image carrier (see FIGS. 9 and 10). In this type of image forming apparatus, since each laser scanner unit is independent, the configuration of the laser scanner unit can be simplified and the number of mirrors can be reduced. However, since each laser scanner unit must be equipped with a polygon motor, a mirror, a BD sensor, and the like, the cost increases. Further, synchronous control of four scanner motors is required, and the control becomes complicated (see Patent Document 1).
[0003]
The second type is provided with only one laser scanner unit for a plurality of image carriers (see FIG. 1). In the case of this type of image forming apparatus, a plurality of lasers are irradiated to one polygon mirror and each image carrier is irradiated using a folding mirror or the like, so that the configuration of the laser scanner unit is complicated. However, it suffices to provide one polygon motor and one mirror, and the cost can be reduced compared to the above type. However, a BD sensor signal for detecting the writing start position in the main scanning direction is provided on the image carrier or in the laser scanner unit, one for each image carrier (see Patent Document 2). . However, in recent years, the cost has been further reduced, and an image forming apparatus including a scanner unit that includes one BD sensor signal has been considered.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 08-146827 [Patent Document 2]
Japanese Patent Application Laid-Open No. 05-019586
[Problems to be solved by the invention]
However, if the number of BD sensors is reduced to one and the operations of all the scanner units are controlled in synchronization therewith, the accuracy of the mirror is affected, which causes image deterioration. In addition, in the case of performing image formation with a certain time delay after detection of the BD sensor for each laser, it is necessary to have a configuration capable of counting independently for several cycles, and the circuit configuration becomes large, and complicated control is required. turn into.
[0006]
Accordingly, an object of the present invention is to provide only one sensor (BD sensor) for detecting a main scanning image writing position in an image forming apparatus of a type in which only one laser scanner unit is provided for a plurality of image carriers. An object of the present invention is to provide an image forming apparatus in which the circuit scale is reduced even when the operation is not performed, and the image quality does not deteriorate.
[0007]
[Means for Solving the Problems]
In order to achieve such an object, the invention according to claim 1 rotates by driving a laser scanner motor and reflects modulated laser light from a plurality of laser light sources on a plurality of reflection surfaces. Rotating polygon mirror, a BD sensor that receives reflected light from the rotating polygon mirror, and outputs a reference signal of a writing start position in the main scanning direction on the image carrier, and a pseudo BD sensor after a predetermined time from the BD sensor A pseudo BD sensor signal generating means for generating a signal, wherein a reference signal of a writing start position in the main scanning direction on the image carrier of a laser beam to be irradiated and reflected on a surface different from the laser to be irradiated on the BD sensor is used for the pseudo BD sensor. It is characterized by using a signal generated from a BD sensor signal generating means.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
FIG. 1 is a sectional view of an image forming apparatus embodying the present invention. The image forming apparatus of the present embodiment is of the electrophotographic type, and will be described as a color image output apparatus in which a plurality of image forming units considered to be particularly effective for the present invention are arranged in parallel.
[0010]
The image output unit 1P is roughly composed of an image forming unit 10, a paper feed unit 20, an intermediate transfer unit 30, a fixing unit 40, and a control unit (not shown).
[0011]
Further, individual units will be described in detail. The image forming section 10 has the following configuration. Photosensitive drums 11a, 11b, 11c and 11d as image carriers are pivotally supported at their centers and are driven to rotate in the direction of the arrow. The primary chargers 12a, 12b, 12c, 12d, the laser scanner unit 13, and the developing devices 14a, 14b, 14c, 14d are arranged in the rotation direction opposite to the outer peripheral surfaces of the photosensitive drums 11a to 11d. In the primary chargers 12a to 12d, charges of a uniform charge amount are given to the surfaces of the photosensitive drums 11a to 11d. Next, the laser scanner unit 13 exposes the photosensitive drums 11a to 11d to a light beam such as a laser beam modulated in accordance with a recording image signal, thereby forming an electrostatic latent image thereon. Details of the operation of the laser scanner unit will be described later. Further, the electrostatic latent images are visualized by developing devices 14a to 14d each storing a developer of four colors of yellow, cyan, magenta, and black (hereinafter, referred to as toner). On the downstream side of the image transfer areas Ta, Tb, Tc, Td for transferring the visualized visible image to the intermediate transfer member, the photosensitive drums 11a to 11d are not transferred to the transfer material by the cleaning devices 15a, 15b, 15c, 15d. The toner remaining on 11d is scraped off to clean the drum surface. According to the process described above, image formation using each toner is sequentially performed.
[0012]
The paper feeding unit 20 includes cassettes 21 a and 21 b for storing the recording material P and a manual tray 27, pickup rollers 22 a and 22 b for sending out the recording material P one by one from the cassette or from the manual tray, and each pickup roller. Roller pair 23 and a paper feed guide 24 for conveying the recording material P sent from the printer to the registration roller, and for sending the recording material P to the secondary transfer area Te in accordance with the image forming timing of the image forming unit. It consists of registration rollers 25a and 25b.
[0013]
The intermediate transfer unit 30 will be described in detail. The intermediate transfer belt 31 (for example, PET (polyethylene terephthalate), PVdF [polyvinylidene fluoride], or the like is used as the material) includes a drive roller 32 that transmits drive to the intermediate transfer belt 31, and biasing of a spring (not shown). Thus, the intermediate transfer belt 31 is wound around a tension roller 33 that applies an appropriate tension to the intermediate transfer belt 31 and a driven roller 34 that faces the secondary transfer area Te with the belt interposed therebetween. Among these, a primary transfer plane A is formed between the drive roller 32 and the tension roller 33. The drive roller 32 has a surface of a metal roller coated with rubber (urethane or chloroprene) having a thickness of several mm to prevent slippage with the belt. The drive roller 32 is driven to rotate by a pulse motor (not shown). In primary transfer areas Ta to Td where the respective photosensitive drums 11a to 11d and the intermediate transfer belt 31 face each other, primary transfer chargers 35a to 35d are arranged behind the intermediate transfer belt 31. A secondary transfer roller 36 is arranged to face the driven roller 34, and forms a secondary transfer area Te by nip with the intermediate transfer belt 31. The secondary transfer roller 36 is pressed with an appropriate pressure on the intermediate transfer member. A brush roller (not shown) for cleaning the image forming surface of the intermediate transfer belt 31 and a waste toner box (not shown) for storing waste toner are provided on the intermediate transfer belt and downstream of the secondary transfer area Te. Is provided.
[0014]
The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a roller 41b pressed by the roller (the roller may also be provided with a heat source), and a transfer material to a nip portion of the roller pair. A guide 43 for guiding P, an inner discharge roller 44 and an outer discharge roller 45 for further guiding the transfer material P discharged from the roller pair to the outside of the apparatus.
[0015]
The control unit includes a control board and a motor drive board (not shown) for controlling the operation of the mechanism in each unit.
[0016]
Next, the configuration and operation of the laser scanner unit will be described below with reference to FIG.
[0017]
First, the laser scanner unit 13 is configured as shown in FIG. This unit is a rotating polygon mirror 201 and a laser scanner motor 202 for rotating and driving the rotating polygon mirror. The number of surfaces of the rotary polygon mirror 201 is determined by parameters such as print speed and resolution, but this patent assumes the case of four surfaces. Reference numeral 203 denotes a laser driver on which a laser diode serving as a recording light source is mounted. This is necessary for each color, so four are mounted. The laser diode is turned on or off by a drive circuit (not shown) according to an image signal or a control signal, and the light-modulated laser light emitted from the laser diode is emitted toward the rotary polygon mirror 201. The rotating polygon mirror 201 is rotating in the direction of the arrow, and the laser light emitted from the laser diode is reflected as a changed beam whose angle continuously changes on its reflecting surface with the rotation of the rotating polygon mirror 201. The reflected light undergoes correction of distortion by a lens group (not shown), and is applied to photosensitive drums 208, 209, 210, and 211 via reflecting mirrors 204, 205, 206, and 207. One surface of the rotary polygon mirror 201 corresponds to scanning of one line, and the laser light emitted from the laser diode by the rotation of the rotary polygon mirror 201 scans the photosensitive drums 11a to 11d line by line in the main scanning direction. The positions of the reflecting mirrors 204, 205, 206, and 207 on the scanning optical system are driven by the pulse motors M1 to M8, so that the deviation of the registration magnification and the inclination can be mechanically corrected.
[0018]
Further, a BD sensor 212 is arranged to generate a scanning start position reference signal in the main scanning direction. Actually, it is ideal to install the sensor near the scanning start position (near the photosensitive drum 208). However, the BD sensor 212 is arranged in the laser scanner unit by using a folding mirror (not shown) or the like. That is, the laser light reflected by each reflecting surface of the rotary polygon mirror 201 is detected by the BD sensor 212 prior to scanning one line. The detected BD sensor signal is used as a scanning start reference signal in the main scanning direction, and based on this signal, the writing start position of each line in the main scanning direction is synchronized. Details of this operation will be described later. Further, using the BD sensor signal 212, the rotation speed control and the phase control of the laser scanner motor are performed.
[0019]
The order of arrangement of the drum colors shown in this figure is merely an example, and is not particularly limited. In this patent, the position of the BD sensor is also set to Bk, but is not limited thereto.
[0020]
Next, the rotation speed control and phase control of the laser scanner motor will be described with reference to the block diagram of FIG.
[0021]
A brushless motor is used as the laser scanner motor 202, and the inside of a broken line indicates an equivalent circuit thereof. The inductance 305 is star-connected and excited by the bridge circuit 300 to generate a rotating magnetic field. A magnetic pattern is magnetized on the rotor 304, and the rotor 304 is rotated by the rotating magnetic field of the inductance 305 to drive the rotating polygon mirror 201 to rotate. The Hall elements 301 to 303 detect a magnetic field magnetized on the rotor 304, and the detected magnetic field is input to the rotating magnetic field control circuit 306. The rotating magnetic field control circuit 306 detects the rotational position of the rotor 304 based on the output signals of the Hall elements 301 to 303, and controls the bridge circuit 300 so as to always generate a magnetic field in which the rotor 304 rotates. Further, the acceleration signal and the deceleration signal from the acceleration / deceleration control unit 307 are input to the rotating magnetic field control circuit 306, and the speed control and the phase control are performed by controlling the rotation of the motor based on the signals.
[0022]
The acceleration / deceleration control unit 307 includes a first acceleration / deceleration control unit (speed control unit) 308, a second acceleration / deceleration control unit (phase control unit) 309, and an acceleration / deceleration signal synthesis unit that synthesizes signals from the control units. It comprises a signal generator 311.
[0023]
First, the control of the first acceleration / deceleration control unit 308 will be described with reference to the timing chart of FIG. FIG. 4A shows the timing when the deceleration signal is output. The signal interval of the BD sensor 212 is alternately counted using two counters. When the counter reaches the set value X, the counter stops counting. If the next BD sensor signal is not input at the time when the counter stops, that is, if the motor speed has not reached the set value, a deceleration signal is output until the next BD sensor signal is input. FIG. 4B shows the timing when the acceleration signal is output. This is when the BD sensor signal is input before the set value X is reached, that is, when the motor speed exceeds the set value. After the BD sensor signal is input, the acceleration signal is output until the set value X is reached. Is done. These controls are performed each time a BD sensor signal is input, and the speed is controlled so as to rotate at the target speed X.
[0024]
Next, the control of the second acceleration / deceleration control unit 309 will be described with reference to the timing chart of FIG. FIG. 5A shows the timing when the deceleration signal is output. When the phase ON signal is input to the second acceleration / deceleration control unit, the counter 1 that counts the BD sensor signal and the counter 2 that counts the reference signal generated by the reference signal generation unit start counting. A difference when the count value reaches a value set by the CPU or the like is detected. FIG. 5A shows a case where the set value is 3. When the BD signal reaches the set count value earlier, it outputs a deceleration signal calculated from the difference. For example, as shown in the figure, a pulse width that is 1/4 of the difference is output. Actually, the ratio of the output pulse width to the detected difference is determined by the characteristics of the motor and the like (FIG. 5-a is merely an example). FIG. 5B shows a case where the acceleration signal is output. In this case, if the counter value for counting the reference signal exceeds the BD signal before reaching the set count value, the acceleration signal calculated from the difference is output. FIG. 5B shows a case where the set value is set to 3 and a pulse width of １ ／ of the difference is output as in the case of deceleration. This is merely an example, and the ratio of the pulse width is determined by the characteristics of the motor and the like as in the case of deceleration. In the above example, the case where the count value for the difference comparison is set to 3 has been described. However, if this value is determined in consideration of the characteristics of the motor and the signal output from the first acceleration / deceleration control unit, more accurate control can be performed. it can.
[0025]
The acceleration / deceleration signals generated by the first and second acceleration / deceleration control units are combined by an acceleration / deceleration signal combining unit 310 and output to the control circuit 306 to control the rotation of the motor.
[0026]
In particular, although the output timing of the acceleration signal and the deceleration signal is not particularly specified this time, the image quality is not deteriorated by performing acceleration and deceleration in the non-image area. In the case of using the above-described configuration, since the input timing of the BD sensor is known, it is naturally possible to know the image area. Therefore, it is desired to detect a non-image area and output a signal in other areas.
[0027]
Next, a phase control and speed control sequence will be described with reference to the flowchart of FIG. First, it waits until the laser scanner motor is turned on at f1. When the motor is turned on, the process proceeds to f2 to determine whether the phase control (second acceleration / deceleration control) is turned on. In the case of the single color mode, it is not necessary to turn on the phase control, and the phase control is turned on only in the full color mode. That is, when the phase control is not turned on (monochrome mode), only the first acceleration / deceleration control (speed control) operates. In this case, the process proceeds to f4, and the control as described in FIG. 4 (first acceleration / deceleration control), that is, the acceleration or deceleration signal is generated so that the interval between the BD sensor signals is constant. Proceeding to f6, these signals are given to the control circuit 306 to control the rotation of the motor. If the phase control is turned on at f2 (second acceleration / deceleration control) (full color mode), the process proceeds to f3, where not only the rotation control (first acceleration / deceleration control) but also the second acceleration / deceleration control (phase Control) also works. This generates a control signal for adjusting the phase of the BD sensor signal to the reference signal under the control described with reference to FIG. Proceeding to f5, the signals generated by the first and second acceleration / deceleration control are combined and given to the control circuit 306 to control the rotation speed and phase of the motor. Next, the process proceeds to f7, and if the motor is not turned off, the process returns to f2 again to determine whether or not the phase control is on, and the control is repeatedly performed. If the motor is turned off at f7, the control is terminated.
[0028]
Next, the generation of the main scanning write start timing signal to each drum by one BD signal will be described with reference to the block diagram of FIG. 7 and the timing signal diagram of FIG.
[0029]
The signal input from the BD sensor 212 is connected to a BD synchronous IC (701, 704) for generating an image write timing signal for Bk and Cyan, and to a pseudo BD signal generation unit 717. The signal of the BD sensor 212 and the image CLK are input to the BD synchronization IC (701) of Bk, and a synchronization signal delayed by a certain time (a) after the input of the BD sensor signal and an image CLK signal synchronized with the signal are output. The data is input to the data output unit 702. When Bk is used as a reference color, the delay time is determined at a position irradiated to the drum and is a fixed value. The image data output from the image data output unit 702 is transferred to a laser driver 703 using, for example, an LVDS signal or the like, and drives the laser. The signal of the BD sensor 212 and the image CLK are also input to the BD synchronization IC (704) of Cyan, and a synchronization signal delayed by a certain time (b) after the input of the BD sensor signal and an image CLK signal synchronized with the signal are output. The data is input to the data output unit 705. The delay time (b) is determined by a color shift correction amount between Bk and Cyan when Bk is used as a reference color. The image data output from the image data output unit 705 is transferred to a laser driver 706 using, for example, an LVDS signal or the like, and drives the laser. FIG. 8A shows the timing from the input of the BD sensor signal to the output of the Bk and Cyan image data.
[0030]
Next, the pseudo BD signal generation unit 717 will be described. The BD sensor signal is input to one of the BD synchronous ICs (708, 709, 710) connected to the stage subsequent to the selector 707. Here, three BD synchronous ICs are prepared because the number of surfaces of the polygon mirror is four, and the surface where the BD signal of Bk is detected is irradiated with the laser of Yellow and Mazenta by the 180 ° mirror. This is because it is necessary to count for three cycles since it is rotated. When the BD sensor signal is input to the selector 707, it is repeatedly output to the BD synchronization IC (708, 709, 710) in order. Upon receiving the BD sensor signal, each BD synchronization IC inputs a synchronization signal and CLK (output from the CLK generation unit 722) to the counters (711 to 713). This is composed of a counter that counts a constant value, and counts a constant count value (b) as shown in FIG. 8B to output a signal. That is, a pulse signal is generated at a position b (a position assumed to be output when the 180 ° mirror rotates) about two cycles later. By ORing the signals generated by the respective pseudo BD signal generation circuits (711 to 713) by the OR circuit 714, a pseudo BD sensor signal delayed by a certain time from the BD sensor signal is generated, and the BD synchronous IC (Yellow, Mazenta) 715, 718). FIG. 8B shows the timing until the pseudo BD signal is generated from the BD sensor signal.
[0031]
The BD synchronization IC (715) of Yellow receives the pseudo BD sensor signal and the image CLK, and outputs a synchronization signal delayed by a certain time (c) after the pseudo BD sensor signal is input and an image CLK signal synchronized with the synchronization signal. The data is input to the data output unit 716. The delay time is determined by a color shift correction amount of Bk and Yellow when Bk is used as a reference color. The image data output from the image data output unit 716 is transferred to a laser driver 717 by, for example, an LVDS signal or the like, and drives the laser. Similar to Yellow, the BD synchronous IC (718) of Mazenta also receives the pseudo BD sensor signal and the image CLK, and outputs a synchronous signal delayed by a certain time (d) after the pseudo BD sensor signal is input and an image CLK signal synchronized with the synchronous signal. The data is input to the image data output unit 719. The delay time is determined by a color shift correction amount of Bk and Magenta when Bk is used as a reference color. The image data output from the image data output unit 719 is transferred to a laser driver 720 using, for example, an LVDS signal to drive the laser. FIG. 8C shows the timing from the input of the pseudo BD sensor signal to the output of the Yellow and Magenta image data.
[0032]
The control circuit assumes that the polygon mirror has four surfaces and the irradiation is on the opposite surface. However, the number of BD synchronous ICs and counters in the generation circuit must be changed due to the difference in the number of surfaces and the difference in the laser irradiation position. There is.
[0033]
In addition, the circuit can be controlled by one chip by adopting AISC.
[0034]
Next, the operation of the apparatus will be described.
[0035]
When the image forming operation start signal is issued, the sheet feeding operation is started from the sheet feeding stage selected according to the selected sheet size or the like. For example, a case where paper is fed from the upper paper feed stage will be described. First, the transfer material P is fed out one by one from the cassette 21a by the pickup roller 22a. Then, the transfer material P is guided between the paper feed guides 24 by the paper feed roller pair 23, and is conveyed to the registration rollers 25a and 25b. At that time, the registration roller is stopped, and the leading end of the paper strikes the nip. Thereafter, the registration roller starts rotating based on a timing signal at which the image forming unit starts forming an image. The rotation timing is set so that the transfer material P and the toner image primarily transferred from the image forming unit onto the intermediate transfer belt just coincide with each other in the secondary transfer area Te.
[0036]
On the other hand, in the image forming section, when an image forming operation start signal is issued, an electrostatic latent image is formed on the drum of each color. The formation timing in the sub-scanning direction is determined and controlled in order from the photosensitive drum (M in the case of the present invention) which is the most upstream in the rotation direction of the intermediate transfer belt 31 according to the distance between the image forming units. In addition, for the writing start timing of each drum in the main scanning direction, a pseudo BD sensor signal is generated and controlled using one BD sensor signal (located at BK in this patent) by the above-described circuit operation. The formed electrostatic latent image is developed by the above-described process. Then, the toner image formed on the uppermost photosensitive drum 11d is primarily transferred to the intermediate transfer belt 31 in the primary transfer area Td by the primary transfer charger 35d to which a high voltage is applied. The primary-transferred toner image is transported to the next primary transfer area Tc. In this case, the image formation is performed by the timing signal described above with a delay of the time for transferring the toner image between the respective image forming units, and the next toner image is transferred by registering the registration on the previous image. It will be. Hereinafter, the same steps are repeated, and the toner images of four colors are primarily transferred on the intermediate transfer belt 31 after all.
[0037]
Thereafter, when the recording material P enters the secondary transfer area Te and comes into contact with the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 36 in accordance with the passage timing of the recording material P. Then, the four color toner images formed on the intermediate transfer belt by the above-described process are transferred onto the surface of the recording material P. Thereafter, the recording material P is accurately guided to the fixing roller nip by the conveyance guide 43. Then, the toner image is fixed on the paper surface by the heat of the roller pair 41A and 41B and the pressure of the nip. Thereafter, the paper is conveyed by the inner and outer paper discharge rollers 44 and 45, and the paper is discharged outside the machine.
[0038]
【The invention's effect】
Even if the image forming apparatus is equipped with only one laser scanner unit for a plurality of image carriers, and is equipped with only one sensor (BD sensor) for detecting the image writing position for main scanning, An image forming apparatus without image quality degradation can be realized with a small circuit scale.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a color image forming apparatus according to the present invention. FIG. 2 is a configuration diagram of a laser scanner unit of the present invention. FIG. 3 is a control block diagram of a laser scanner motor of the present invention. FIG. 5 is a timing chart for phase control (second acceleration / deceleration control unit). FIG. 6 is a flowchart illustrating a phase control and speed control sequence. FIG. 7 is a BD of the present invention. FIG. 8 is a control block diagram based on a sensor signal and a pseudo BD sensor signal. FIG. 8 is a timing chart based on a BD sensor signal and a pseudo BD sensor signal of the present invention. FIG. 9 is a schematic cross-sectional view of a conventional color image forming apparatus. Optical unit layout of image forming apparatus
11a to 11d Photosensitive drum 13 Optical unit 31 Intermediate transfer belt 40 Fixing unit 212 BD sensor 203 Laser driver 201 Rotating polygon mirror 202 Laser scanner motor 204 to 207 Reflecting mirror 306 Control circuit 307 Acceleration / deceleration control unit

Claims (1)

A rotating polygon mirror that rotates by driving a laser scanner motor and reflects modulated laser light from a plurality of laser light sources on a plurality of reflecting surfaces,
A BD sensor that receives reflected light from the rotating polygon mirror and outputs a reference signal of a writing start position in the main scanning direction on the image carrier;
A pseudo BD sensor signal generating unit that generates a pseudo BD sensor signal after a predetermined time from the BD sensor;
A signal generated from the pseudo BD sensor signal generation unit is used as a reference signal of a writing start position in the main scanning direction on the image carrier of a laser beam to be irradiated and reflected on a surface different from the laser irradiated on the BD sensor. An image forming apparatus comprising:

Images