JP2002258182A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device where an image of high quality can be formed by preventing deviation in image forming position in a multiple images formation. SOLUTION: In the device, correction time A for picture elements writing (=T+(tp-tp')) is calculated as a correction value for picture elements writing time T which is initially set by utilizing a difference value between a phase difference value tp in normal times and a phase difference value tp' when a phase misalignment is generated between the two signals in the whole signal and the SOS signal, by taking into account any deviation in phase difference between a whole signal and an SOS signal generated by influence of temperature, etc., inside and outside the device when an image forming job is started.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a light source and a plurality of image carriers, and sequentially scans light beams modulated and emitted from the light source based on a plurality of different image signals, so that each of the light beams is sequentially scanned. The present invention relates to an image forming apparatus that forms different original images on the respective image carriers corresponding to image signals, and transfers the original images to the same recording medium by multiplex transfer to form an image.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus such as a color copying machine and a color printer, a laser beam emitted from a laser light source is bidirectionally scanned by a single rotating polygon mirror to obtain cyan, magenta, and yellow. , And an image is formed on a photosensitive drum as an image carrier corresponding to each color of cyan, magenta, yellow, and black by a scanning line passing through an fθ lens corresponding to each color of black, and multiplexed on a transfer material. A device that forms a multiplex image by transferring the image is known.

[0003] However, in such an image forming apparatus, there is a relative inclination or positional deviation between a scanning line scanned on the surface of the photosensitive drum and the rotation axis of the photosensitive drum, so that the position of the image to be transferred may be reduced. A gap may occur.

[0004] As a technique for solving this problem, a technique described in Japanese Patent Application Laid-Open No. 3-142412 is known. In this technique, as shown in FIG. 17, a register mark 76 is previously transferred onto a transfer material conveying belt 78, and the register mark 76 is transferred to each color of cyan (C), magenta (M), yellow (Y), and black (BK). The corresponding register mark 76 is read by the CCD sensor 74 having the optical systems 70 and 72, and the relative inclination and positional deviation of the scanning line for scanning on the photosensitive drum 1C (1M, 1Y, 1BK) are grasped. The inclination of the mirrors 6 and 7 that fold the scanning lines is adjusted so that the inclination of the image formed by the reference photosensitive drum 1C among the plurality of photosensitive drums matches the inclination of the image formed by the other photosensitive drums 1M, 1Y, and 1BK. By adjusting the top margin and the left margin (margin in the main scanning direction) electrically, and correcting the amount of deviation, the inclination and positional deviation at the time of forming a multiple image are eliminated. Thereby enabling the door.

[0005]

However, in the above-mentioned prior art, the CCD sensor 74 for reading the register mark 76 transferred onto the transfer material conveying belt 78, the optical systems 70 and 72 associated therewith, and the scanning line are folded back. The actuator 84 for adjusting the inclination of the mirrors 6 and 7 is required, which may complicate the configuration of the entire device and increase the manufacturing cost.

Another factor relating to the positional deviation of an image is a housing (usually made of resin) of an optical scanning device including the light source and the rotary polygon mirror 3 due to the effect of temperature rise inside and outside the device. ) Thermally expands, and a synchronous detector (not shown) attached to the housing for synchronizing the start of main scanning, and a position change such as a tilt of a mirror for guiding scanning light to the synchronous detector. Can be Also,
Another factor is the positional deviation of the scanning light caused by the fluctuation of the refractive index of the scanning light in the fθ lens due to the wavelength fluctuation of the laser diode as the light source. Due to these factors, a positional shift in the main scanning direction occurs, resulting in a positional shift in a formed image, which may degrade image quality.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an image forming apparatus capable of preventing a shift of an image forming position at the time of forming a multiple image and forming a high quality image. The purpose is to do.

[0008]

According to a first aspect of the present invention, there is provided a light source and a plurality of image carriers, wherein a light beam modulated based on a plurality of different image signals and emitted from the light source is used. Deflected by a rotating polygonal mirror that rotates at a high speed, by sequentially scanning in a predetermined main scanning direction in each of the image carriers corresponding to each of the image signals, on each of the image carriers corresponding to each of the image signals. In an image forming apparatus that forms different original images and multiplex-transfers the respective original images onto the same recording medium to form an image, a rotation position of the rotating polygon mirror is detected and a rotation position detection signal is output. Rotation position detection means, and scan start position detection means provided near the scan start position in the main scanning direction and outputting a scan start signal by detecting a light beam deflected by the rotating polygon mirror; From the time of detection of the scanning start detection signal, after the elapse of a predetermined scan waiting time,
Control means for controlling to start scanning on the image carrier by the light beam deflected by the rotating polygon mirror; and the scanning standby based on a phase difference between the rotation position detection signal and the scanning start signal. Correction means for correcting time.

According to the first aspect of the present invention, the rotational position detecting means detects the rotational position of the rotary polygon mirror and outputs a rotational position detection signal. Further, a scanning start position detecting means provided near the scanning start position in the main scanning direction outputs a scanning start signal by detecting the light beam deflected by the rotary polygon mirror. The control means controls to start scanning on the image carrier by the light beam deflected by the rotary polygon mirror after a predetermined scanning standby time has elapsed from the time when the scanning start detection signal is detected. . The correction means corrects the scanning standby time based on the phase difference between the rotation position detection signal and the scanning start signal so that the scanning standby time becomes substantially constant. This makes it possible to make the scan start standby time from the point when the scan start detection signal is detected substantially constant, and to match the pixel positions of the plurality of image carriers in the main scanning direction.

According to a second aspect of the present invention, in the first aspect of the present invention, there is further provided a storage means for storing a plurality of phase difference values between the rotational position detection signal and the scan start signal, and the correction means. Is characterized in that the scanning standby time is corrected based on an average value of each phase difference value stored in the storage means.

According to the present invention, the storage means stores a plurality of phase difference values between the rotational position detection signal and the scan start signal. The correction unit corrects the scan standby time based on the average value of each phase difference value stored in the storage unit. As a result, it is possible to perform appropriate correction that is less affected by noise of each signal and variation in the phase difference value.

[0012] The invention according to claim 3 is the invention according to claim 1 or 2.
In the invention described in the above, the rotational position detecting means has a magnet having a plurality of poles which are concentrically connected to the rotary polygon mirror and rotate integrally, and detects the rotational position of the magnet to detect the rotational position. It is characterized in that the rotational position of the rotary polygon mirror is detected.

According to the third aspect of the present invention, the rotational position detecting means includes a magnet having a plurality of poles which are concentrically connected to the rotary polygon mirror and rotate integrally, and the rotational position of the magnet is determined. Is detected, the rotational position of the rotary polygon mirror is detected. Here, as the magnet, for example, it is preferable to employ a magnet provided in a motor having a general configuration that is a rotation driving source of a rotary polygon mirror. In this case, the rotation position of the rotary polygon mirror can be detected by detecting the rotation position of the motor. That is, the rotation position of the rotary polygon mirror can be detected by a simple configuration using a configuration provided in a general motor.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the number of poles of the magnet and the number of surfaces of the rotary polygon mirror are the same, or the number of poles of the magnet is the same as that of the rotary polygon mirror. It is characterized in that it is an even multiple of the number of surfaces.

According to the fourth aspect of the invention, the number of poles of the magnet is equal to the number of faces of the rotary polygon mirror, or the number of poles of the magnet is an even multiple of the number of faces of the rotary polygon mirror. Therefore, the correspondence between the rotation position detection signal, the scan start detection signal, and the timing of the pulse edge can be simplified, and, for example, the phase difference between the two signals can be easily calculated and detected.

According to a fifth aspect of the present invention, in accordance with any one of the second to fourth aspects of the present invention, there is further provided a temperature detecting means for detecting a temperature in the apparatus, and the storage means comprises: The temperature value detected by the temperature detecting means is stored in association with the phase difference value between the rotation position detection signal and the scanning start signal at the time when the temperature value is detected.

According to the fifth aspect of the present invention, the temperature detecting means detects the temperature inside the device. In addition, the storage means,
The temperature value detected by the temperature detecting means is stored in association with the phase difference value between the rotation position detection signal and the scanning start signal at the time when the temperature value is detected. This allows
When the temperature inside and outside the image forming apparatus fluctuates, an appropriate phase difference value corresponding to the temperature value detected by the temperature detecting means can be read from the storage means, so that the temperature inside and outside the image forming apparatus fluctuates. Each time, for example, it is not necessary to perform predetermined arithmetic processing for calculating an appropriate phase value corresponding to the temperature value, and as a result, the overall image forming time can be reduced.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 schematically shows an image forming apparatus 10 to which the present invention is applied. This image forming apparatus 10
Has four developing units (cyan developing unit C, magenta developing unit M, yellow developing unit Y, and black developing unit K) corresponding to each color signal forming a color image signal, and each developing unit has the same configuration. And includes a photosensitive drum 12 as an image carrier.

Further, the image forming apparatus 10 includes a laser scanning device 11 for irradiating the photosensitive drum 12 included in each of the developing units with a laser beam.

FIG. 2 schematically shows the laser scanning device 11 viewed from the direction of arrow A in FIG. The laser scanning device 11 includes a plano-convex lens and a plano-concave lens centered on a rotating polygon mirror (polygon mirror) 22 provided in an optical deflector 42 (see FIG. 4) described later and rotating at a constant speed in the direction of the arrow in FIG. The configured fθ lens 36 is arranged in each of the vertical directions in FIG. Further, the laser scanning device 11 is provided with a laser diode 30 (see FIG. 3) for emitting laser light modulated based on each color signal constituting a color image signal sent from an image data input unit (not shown). The laser light emitted from the laser diode 30 passes through the fθ lens 36 and passes from the scanning start position P1 in the direction of the arrow in FIG. 2 and from the scanning start position P2 in the direction of the arrow in FIG. The light beams are deflected in directions opposite to each other and are incident on the corresponding mirrors 28, respectively. In addition, near the scanning start positions P1 and P2, a laser light synchronization detecting section 4 for synchronizing the scanning start timing of the laser light is provided.
1 (details will be described later).

The laser light incident on the mirror 28 is reflected by the mirror 28 and is applied to the photosensitive drum 12 of each developing unit.
(Hereinafter referred to as the drum surface) at the exposure scanning position 13. Therefore, the laser light scans the drum surface at a constant speed by the action of the fθ lens 36. Each optical path of the laser light is indicated by a dotted line 15.

In each developing unit, the photosensitive drum 12 is rotated at a predetermined angular speed in the direction of the arrow in FIG. 1 by a motor (not shown). Thereby, the laser light deflected by the polygon mirror 22 is
Position the drum surface in the axial direction of the photosensitive drum 12 (main scanning direction)
Are repeatedly scanned along.

In each developing unit, a charger 14 is provided slightly upstream of the exposure scanning position 13 along the drum rotation direction indicated by the arrow in FIG. 1 so that the drum surface is uniformly charged. ing. Thereby, the charger 1
Exposure scanning with laser light is performed on the drum surface uniformly charged by 4 to remove charged charges other than the image portion and form an electrostatic latent image with the charge left on the image portion. It has become.

The developing device 1 is located slightly downstream of the exposure scanning position 13 along the drum rotation direction indicated by the arrow in FIG.
6 are provided. The developing device 16 is filled with toner charged to a polarity opposite to that of the electrostatic latent image, and the electrostatic latent image formed on the drum surface is colored in respective colors (cyan, magenta, yellow, and black). The visible toner (toner image) is formed by electrostatically adhering the toner, which is the charged fine particles.

A transfer unit 18 is provided below the photosensitive drum 12 in FIG. 1, and an intermediate transfer member 18A for transferring the toner image is sandwiched between the transfer unit 18 and the photosensitive drum 12. I have. This intermediate transfer member 18A is
The developing rollers Y, M, C, and K are sequentially transported in the direction of the arrow in FIG. 1 by the driving roller. In the transfer unit 18 in each developing unit, a charge is applied to the intermediate transfer member 18A, and the toner image of each color is sequentially transferred to the intermediate transfer member 18A by the electrostatic force.

Further, a fixing device 24 is disposed downstream of the intermediate transfer member 18A on which the toner image of each color is transferred in the direction of the arrow in FIG. The fixing device 24 applies heat or pressure to the intermediate transfer body 1 while nipping and transporting a recording medium 26 for recording an image in the direction of the arrow in FIG.
The toner image transferred to 8A is fused to the recording medium 26.

The photosensitive drum 12 of each developing unit
A cleaner 20 for removing toner and the like remaining on the photosensitive drum 12 after transfer is provided at the rearmost end in the rotation direction (the direction of the arrow in FIG. 1).

FIG. 3 shows a schematic configuration of the laser scanning device 11 as viewed from the direction of arrow A in FIG.

The laser scanning device 11 is provided with the laser diode 30 as a light source. A lens part 32 is arranged on the optical axis X of the laser light emitted from the laser diode 30. This lens part 32
Is to collimate the laser light from the laser diode 30 into a parallel beam and to condense it to a predetermined beam diameter. The laser beam passes through as a converged light beam.

A beam diameter for adjusting the beam diameter of the laser light emitted from the laser diode 30 is provided on the optical axis X between the lens unit 32 and the polygon mirror 22 provided in the optical deflector 42. A regulator 34 is arranged.

Further, the laser light synchronization detecting section 41 described above
It comprises a reflection mirror 38 that reflects the laser light, and a synchronization detector 40 that detects the laser light in order to synchronize the timing of the start of main scanning (SOS) by the laser light. The synchronization detector 40 is provided with a sensor unit for sensing laser light, and outputs a high-level signal (hereinafter, referred to as an H signal) when the laser light is not sensed, and outputs a low-level signal when the laser light is sensed. A level signal (hereinafter, referred to as an L signal) is output.

The laser scanning device 11 includes an exposure scanning control unit (not shown) for monitoring each unit and controlling the entire exposure scanning operation. The optical deflector 42 is connected. The exposure scanning control unit is constituted by a CPU that plays a central role in exposure scanning control, a memory that stores various control data such as a RAM and a ROM, and an input / output controller that sends and receives various control signals. For example, various control signals are output to the laser diode 30 and the optical deflector 42, and an output signal (hereinafter, referred to as an SOS signal) from the above-described synchronization detector 40 is received.

Thus, the laser beam emitted from the laser diode 30 is scanned on the photosensitive drum 12 via the polygon mirror 22, the fθ lens 36, and the mirror 28, and is arranged at the head of the scanning line. When the light is reflected by the reflecting mirror 38 and enters the synchronous detector 40, an L signal is output from the synchronous detector 40 to the exposure scanning controller. In addition, the exposure scanning control section starts to write an image by scanning the photosensitive drum 12 with a laser beam after a lapse of a predetermined time T after receiving the L signal (low-level SOS signal). (Hereinafter, this predetermined time T is referred to as a pixel writing time T.) Note that the pixel writing time T corresponds to the scanning standby time of the present invention.

FIG. 4 schematically shows a cross section of the optical deflector 42 taken along the direction of arrows AA in FIG.

The optical deflector 42 includes a rotating body (rotor) 48 penetrating an iron control board 44 serving as a base thereof, and a drive control IC 46 installed on the control board 44. It is configured.

The rotor 48 has a cylindrical cover member 4 having an open bottom surface and a flange at the periphery.
8A, and a ring-shaped drive magnet 48B in which N-poles and S-poles are alternately connected is provided on the inner side surface facing the hollow portion of the cover member 48A (FIG. 5). reference). Also, the cover member 48A of the rotor 48
Has the polygon mirror 22 having six reflecting surfaces,
The connecting members 48C are connected so as to share the rotation shaft 50. As a result, the polygon mirror 22 and the rotor 48 can rotate integrally about the rotation shaft 50. The rotating shaft 50 is supported in a vertical direction by a bearing 50A provided on a resin housing 52 of the laser scanning device 11 on which the control board 44 is installed.

Further, on the control board 44, a stator coil group 54 is fixed at a position facing the inner peripheral portion of the drive magnet 48B in the circumferential direction, and a position facing the drive magnet 48B vertically downward. Has a rotor 48
Are provided with three Hall elements 56 as rotational position detectors.

That is, in the optical deflector 42, a brushless motor (hereinafter, referred to as a motor) 58 is constituted by the rotor 48 including the rotating shaft 50, the stator coil group 54, and the Hall element 56. In this case, the stator coil Group 54 is preferably of three phases (U-phase, V-phase, and W-phase). Here, the following table shows the structural relationship between the total number of slots (Slot) of the stator coil group 54 of the three-phase brushless motor and the number of poles (Pole) of the drive magnet 48B.

[0040]

[Table 1]

As shown in FIG. 6, each Hall element 5
6A, 56B, and 56C are installed at an interval of a predetermined angle θ in a counterclockwise direction from the reference line A, and the predetermined angle θ can be set to an optimum value by the following equation (1).

(Predetermined angle θ) = (360 degrees) ÷ (total number of slots) (1) Similarly, the drive control IC 46 provided on the control board 44 controls the drive of the motor 58. As shown in FIG. 7A, the phase comparator 4
6A, a loop filter 46B, and a drive circuit 46C are connected in this order to form an integrated circuit. Note that the phase comparator 4
The Hall element 56 is connected to the drive circuit 6A and the drive circuit 46C, and START / S for inputting a control signal for instructing drive / stop of the motor 58 is input to the drive circuit 46C.
The TOP signal input unit 62 is connected.

The phase comparator 46A compares the phase of the output signal from the Hall element 56 (hereinafter referred to as the Hall signal) with the reference signal output from the reference signal generator 60 and corresponding to the laser scanning speed. , And outputs a signal (phase difference signal) corresponding to the phase difference. The loop filter 46B converts a phase difference signal output from the phase comparator 46A into an integrated voltage. The drive circuit 46C is connected to the START / STOP signal input unit 62
Filter 46B by the drive signal inputted from the
An exciting current proportional to the input signal voltage from the
Are supplied to the stator coil group 54 of FIG. In addition,
For example, each signal having the waveform shown in FIG. 7B is transmitted between the blocks.

As a result, the motor 58 is controlled so that its rotation speed is appropriately increased / decreased and rotated at a constant speed. Thus, by rotating the polygon mirror 22 at a constant speed and continuously changing the incident angle of the laser light on each reflection surface, the laser light is deflected and sent to the mirror 28 side while being deflected along the main scanning direction. The photosensitive drum 12 in each developing unit.

In this embodiment, an example is shown in which the constant speed control of the motor 58 is performed based on the Hall signal. In addition, the motor 58 is controlled by a control signal (FG signal) by a general frequency generator. May be performed.

Here, the Hall signal by the Hall element 56 provided in the optical deflector 42 and the SOS signal from the synchronization detector 40 provided in the laser scanning device 11 will be described with reference to FIG. explain.

The number of pulses of the Hall signal is determined by the number of poles of the driving magnet 48B provided on the rotor 48 of the motor 58, and the number of pulses of the Hall signal per rotation of the rotor 48 is half of the number of poles of the driving magnet 48B. .

The number of pulses of the SOS signal is
The number of pulses of the SOS signal per rotation of the rotor 48 is equal to the number of reflection surfaces of the polygon mirror 22.

From this, when the number of poles of the drive magnet 48B is an even multiple of the number of reflection surfaces of the polygon mirror 22, either the rising edge or the falling edge of the Hall signal corresponds to the edge of the SOS signal. Will be. For example, when the number of drive magnets 48B is 12 poles and the number of reflection surfaces of the polygon mirror 22 is 6, as shown in FIG. 8A, the rising edge of the Hall signal H1 and the SOS signal S1 ( S2, S3) correspond to the edges.

When the number of poles of the drive magnet 48B and the number of reflection surfaces of the polygon mirror 22 match, the rising edge and the falling edge of the Hall signal
The edges of the SOS signal will correspond. For example, if the number of drive magnets 48B is 12 poles and the polygon mirror 2
In the case where the number of the reflection surfaces of No. 2 is 12, as shown in FIG. 8B, the edge of the SOS signal S1 (S2, S3) includes both the rising edge and the falling edge of the Hall signal H1. It corresponds to.

Therefore, as for the relationship between the number of poles of the driving magnet 48B and the number of reflecting surfaces of the polygon mirror 22, the number of poles of the driving magnet 48B and the number of reflecting surfaces of the polygon mirror 22 match (same number), or It is preferable that the number of poles of the drive magnet 48B be an even multiple of the number of reflection surfaces. Thus, the above-described phase comparator 46A can easily detect the phase difference between the Hall signal and the SOS signal by simply reading the edge of the Hall signal.

As is apparent from FIG. 8, the timing of the edge of the Hall signal and the timing of the edge of the SOS signal do not always coincide with each other, and a certain phase difference may occur (the Hall signal H1 and the SOS signal). S2, S
3). This is because the phase difference between the Hall signal and the SOS signal is determined by the assembly accuracy in the manufacturing process of the rotor 48 provided with the drive magnet 48B of the optical deflector 42 and the polygon mirror 22 fixed concentrically to the rotor 48. , And from this,
An individual difference occurs in the value of the phase difference.

Therefore, in the image forming apparatus 10 according to the present embodiment, the time (tp + T) obtained by adding the initial phase difference tp and the pixel writing time T from the timing of the edge of the hole signal by the exposure scanning control unit. After the lapse of time, the laser beam from the laser scanning device 11 is scanned over the photosensitive drum 12, and writing of pixels is started. Hereinafter, the phase difference between the Hall signal and the SOS signal, which is generated depending on the assembling accuracy in the manufacturing process as described above, is referred to as an initial phase difference tp. It should be noted that the phase difference between the Hall signal and the SOS signal can be maintained at zero (the same phase) or constant by accurately positioning the rotor 48 and the polygon mirror 22 at a predetermined rotation angle. The production cost is high and is not generally done.

Further, the phase difference (shift) between the Hall signal and the SOS signal may fluctuate depending on the use environment of the apparatus, and this also causes the position shift of the output image at the time of image output. For example, as shown in FIG. 9A, a resin housing 52 of the laser scanning device 11 thermally expands due to an influence of a use environment such as an increase in an environmental temperature inside and outside the image forming apparatus, and is mounted on the housing 52. The installation positions of the synchronization detector 40 and the reflection mirror 38 fluctuate, causing a shift in the optical path of the laser light. As a result, the synchronization detector 40
Will be shifted in the timing of the edge of the SOS signal. Also, as shown in FIG. 9B, the wavelength of the laser diode 30 as a light source fluctuates, the refractive index of the laser light in the fθ lens 36 fluctuates, and similarly, a shift occurs in the optical path of the laser light. As a result, the timing of the edge of the SOS signal from the synchronization detector 40 is shifted.

In particular, when the laser beam is bidirectionally scanned around the optical deflector 42 as in the laser scanning device 11 according to the present embodiment (see FIG. 2), the laser beam is scanned on the photosensitive drum 12. The directions of the laser scanning lines are opposite to each other (see FIG. 2).
(Arrow direction and arrow direction), as a result, the above-described positional shift of the output image may appear as a shift in the opposite direction in the main scanning direction. In this case, the positional deviation on the output image is doubled as compared with the case of a scanning device that scans only in one direction. That is,
As shown in FIG. 10, a shift (Δt) occurs in the timing of the edge of the SOS signal from the synchronization detector 40, so that the scanning start positions P1 and P2 fluctuate in the main scanning direction in opposite directions. become.

Therefore, in the image forming apparatus 10 according to the present embodiment, the phase difference between the Hall signal and the SOS signal, which causes the position shift in the output image (that is, the position shift in the main scanning direction of the laser beam), occurs. In response to the fluctuation, the pixel start time is corrected to be constant based on the phase difference between the Hall signal and the SOS signal during the laser scanning by the image signal corresponding to each color by a job start process described later. By doing so, it is possible to prevent positional deviation of an image that is finally multiply transferred and output.

Next, the operation of the present embodiment will be described in detail.

In the image forming apparatus 10 according to the present embodiment, a processing routine shown in FIG. 11 is executed as an initial process for performing a preparatory stage operation before image formation at startup.

First, in step 100, the phase difference between the Hall signal and the SOS signal is counted. The counted phase difference value tp is stored in the memory.

In the next step 102, it is determined whether or not the count has been performed N times (N is a natural number). If the determination is negative, the process returns to step 100, and if the determination is affirmative, the process proceeds to the next step 104.

In the next step 104, the average value tp _ave of the phase difference values is calculated and stored in the memory, and the processing routine is terminated.

By the above-described initial processing, the phase difference value tp between the Hall signal and the SOS signal, which is an individual difference depending on the assembling accuracy in the manufacturing process, in the optical deflector 11 can be properly grasped. Hereinafter, the average value tp _ave of the phase difference value between the Hall signal and the SOS signal will be referred to as an individual average phase difference value tp _ave .

Subsequently, when an instruction to start image formation is given, the processing routine shown in FIG.

First, in step 200, the phase difference value tp 'between the Hall signal and the SOS signal is counted and stored in the memory.

In the next step 202, it is determined whether or not the count has been performed N times (N is a natural number). If the determination is negative, the process returns to step 200, and if the determination is affirmative, the process proceeds to the next step 204.

[0066] In the next step 204, it calculates an average value tp _'ave of the retardation value, stored in the memory. Here, by obtaining the average of the phase difference values of the Hall signal and the SOS signal, the Hall signal and the SOS signal are less affected by noise in each of the signals and the variation in the phase difference value due to the rotation fluctuation of the optical deflector 42. A phase difference value between the signal and the SOS signal can be obtained. In the following, the average value tp ′ _ave of the phase difference between the Hall signal and the SOS signal will be described.
_Is referred to as an average phase difference value tp ′ _ave .

In the next step 206, the preset pixel writing time T and the individual average phase difference value tp _ave calculated in the above initial processing are read from the memory.

In the next step 208, a pixel writing time A (hereinafter referred to as a pixel writing correction time A) as a correction value is calculated. Here, the following (2) As shown in equation a mean phase difference value tp _'ave of the Hall signal and the SOS signal of the image formation start immediately before the above-mentioned individual mean phase difference value t
the difference between the _{p ave (tp ave -tp 'ave} ), adds the pixel writing time T set in advance.

A = T + (tp _ave −tp ′ _ave ) (2) In the next step 210, the calculated pixel writing correction time A is set, and the process proceeds to the next step 212, where the set pixel writing is set. The image forming job is started with the correction time A as the pixel writing start time, and the processing routine ends.

By the above-described job start processing, FIG.
As shown in (A) and (B), even when the phase difference value between the Hall signal and the SOS signal is shifted, the writing start time of the pixel can be kept substantially constant.
It is possible to prevent the recording position of the output image from being shifted.

Next, a modification of this embodiment will be described. In this modification, a temperature sensor (not shown) for detecting the temperature inside the image forming apparatus 10 is added to the image forming apparatus 10 described above. The other configuration is the same as that of the image forming apparatus 10 described above.

Next, the operation of the present modification will be described. In this modification, at the time of starting the first job after the apparatus is started, FIG.
Is executed.

First, in step 300, the phase difference value tp 'between the Hall signal and the SOS signal is counted and stored in the memory.

In the next step 302, the temperature value X in the apparatus detected by the temperature sensor is read and stored in the memory.

In the next step 304, the Hall signal and S
The phase difference value tp ′ with the OS signal and the temperature value X are changed N times (N
It is determined whether or not it has been read. If the determination is negative, the process returns to step 300, and if the determination is affirmative, the process proceeds to the next step 306.

In the next step 306, the average phase difference value t
Calculate _p'ave , store it in the memory, and execute the next step 3
08, the average temperature value X _ave (hereinafter, the average temperature value X
called _ave . ) Is calculated and stored in the memory. As a result, the memory holds the table data indicating the correspondence between the average temperature value X _ave and the average phase difference value tp ' _{ave at} that time.

Here, the timing for storing the temperature value and the phase difference value may be a fine step that changes every moment, but a large-capacity memory is required for that, so that the actual image may be affected. It is also possible to confirm in advance an experiment or the like a temperature limit value that may cause a phase difference deviation such that a phase difference occurs, and store the phase difference corresponding to a stepwise changing temperature value. . For example, if an image is affected by a temperature change of 7 ° C. or more, a phase difference value in increments of 7 ° C. is stored as an item of table data, and, for example, the detected temperature value of the temperature sensor during image formation is 20 to 27. If it is within the range of ° C., the corresponding phase difference value in the table data is read. If it exceeds the range, the subsequent phase difference value in the table data is read. Further, when a predetermined period has elapsed since the construction of the table data, the latest phase difference is obtained and rewritten with the data in the table, so that the components constituting the apparatus change over time and fall / fall.
You may make it possible to respond to the tendency change of each measured value by the influence by an impact.

In the next step 310, the preset pixel writing time T and the individual average phase difference value tp _ave calculated in the above-mentioned initial processing (see FIG. 11) are read from the memory.

In the next step 312, the pixel writing correction time A is calculated by the above equation (2).

In the next step 314, the calculated pixel writing correction time A is set, and the flow advances to the next step 316 to start an image forming job with the set pixel writing correction time A as the pixel writing start time. This processing routine ends.

At the start of the job after the first time,
The processing routine shown in FIG.

First, at step 400, the temperature value X in the apparatus detected by the temperature sensor is read and stored in the memory.

In the next step 402, the temperature value X is set to N
It is determined whether or not the reading has been performed a number of times (N is a natural number). If the determination is negative, the process returns to the above-described step 400, and if the determination is affirmative, the process proceeds to the next step 404.

In the next step 404, the average temperature value X
_ave is calculated and stored in the memory.

In the next step 406, the correspondence relationship between the average temperature value X _ave and the average phase difference value tp ' _{ave at} that time, which is constructed in the memory by the above-described first job start processing steps 306 and 308, is shown. Referring to the table data, the average temperature value X calculated in step 404 above
_The average phase difference value tp'ave corresponding to _ave is read.

In the next step 408, the preset pixel writing time T and the individual average phase difference value tp _ave calculated in the above-described initial processing (see FIG. 11) are read from the memory.

In the next step 410, the pixel writing correction time A is calculated by the above equation (2).

In the next step 412, the calculated pixel writing correction time A is set, and the flow advances to the next step 414, where the set pixel writing correction time A is used as the pixel writing start time to start an image forming job. This processing routine ends.

According to the above-described processing, after the apparatus is started, in the job start processing except the first time, the correspondence between the average temperature value X _ave stored in the memory and the average phase difference value tp ' _ave of the Hall signal and the SOS signal is obtained. by referring to the table data indicating a relationship, by reading an average retardation value tp _'ave corresponding to the temperature value at temperature variations of the internal changes and device environmental temperature at the start of a job (or the average temperature value), the image Each time a forming job is started, the pixel writing correction time A as a correction value can be calculated and set without calculating the average value of the phase difference values of the Hall signal and the SOS signal at that time. As a result, the overall image forming time can be reduced.

In particular, in image forming apparatus 10 according to the present embodiment, as shown in FIG. 16, for example, the arrangement position of Hall element 56 may be provided at the center of the scanning area. That is, the Hall element 56 is arranged at a concentric position with respect to the rotation axis 50 of the optical deflector 42,
2 is fixed to the laser scanning device 11 with the rotation axis 50 as the center, so that the position is set while rotating the optical deflector 42 about the rotation axis 50, so that the pixel writing position (entire image) Can be maintained at a position determined from the center position of the scanning area (center registration).

[0091]

As described above, according to the present invention,
Based on the phase difference between the rotation position detection signal of the rotary polygon mirror and the scanning start signal, the scanning standby time until the scanning with the light beam corresponding to each of the plurality of image signals is started is set as the scanning start time between the image signals. Since the timing is corrected so as not to cause a shift, there is an excellent effect that a shift of an image forming position at the time of forming a multiple image can be prevented and an image forming apparatus capable of forming a high quality image can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a laser scanning device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of main components of the laser scanning device according to the embodiment of the present invention, as viewed from the direction of arrows AA in FIG. 2;

FIG. 4 shows the optical deflector according to the embodiment of the present invention;
FIG. 3 is a schematic cross-sectional view along the arrow AA direction of FIG.

FIG. 5 is a diagram for explaining an arrangement position of a drive magnet provided on the rotor according to the embodiment of the present invention.

FIG. 6 is a diagram for explaining an arrangement position of a Hall element provided in the optical deflector according to the embodiment of the present invention.

FIG. 7A is a block diagram illustrating a schematic configuration of an optical deflector according to an embodiment of the present invention, and FIG. 7B is a timing chart illustrating waveforms of various signals between blocks.

FIG. 8A is a diagram showing a driving magnet having 12 poles;
6 is a timing chart showing waveforms of a Hall signal and an SOS signal when the polygon mirror has six reflecting surfaces, and FIG.
When the polygon mirror has 12 reflecting surfaces,
5 is a timing chart showing waveforms of a Hall signal and an SOS signal.

FIG. 9A is a diagram for explaining a state of deviation of a laser light path due to a change in the installation position of a synchronization detector and a reflection mirror, and FIG. 9B is a diagram illustrating a refractive index of a laser beam in an fθ lens; FIG. 9 is a diagram for explaining a state of a deviation of a laser light path due to a change.

FIG. 10 is a timing chart of an SOS signal corresponding to each direction for explaining a deviation between write-out positions P1 and P2 of pixels in each direction during bidirectional scanning.

FIG. 11 is a flowchart showing a flow of an initial process according to the embodiment of the present invention.

FIG. 12 is a flowchart illustrating a flow of a job start process according to the embodiment of the present invention.

FIGS. 13A and 13B are timing charts for explaining an SOS signal when a phase shift (leading direction and lagging direction) occurs with respect to a normal SOS signal.

FIG. 14 is a flowchart showing a flow of a first job start process according to the embodiment of the present invention.

FIG. 15 is a flowchart illustrating a flow of a next job start process according to the embodiment of the present invention.

FIG. 16 is a schematic diagram for explaining a state of center registration in which an arrangement position of a Hall element of the optical deflector according to the embodiment of the present invention is set at the center of a scanning area.

FIGS. 17A, 17B, and 17C are schematic configuration diagrams of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 image forming device 11 laser scanning device 12 photoreceptor drum 18 transfer device 18A intermediate transfer member 22 polygon mirror 26 recording medium 30 laser diode 36 fθ lens 38 reflection mirror 40 synchronization detector 42 optical deflector 44 control board 46 drive control IC 46A Phase comparator 48 Rotor 48B Drive magnet 50 Rotary axis 54 Stator coil group 56 Hall element 58 Motor 60 Reference signal generator

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 BA31 BA32 BA50 BA51 BA52 BA69 BA70 BB32 BB37 BB39 CA22 CA39 2H030 AB02 AD17 BB02 BB16 BB23 BB42 BB63 2H045 AA53 BA22 BA34 CA88 CA98 CB65 5C072 AA11 H15 BA20 HAB

Claims (5)

[The claims] A light source that includes a light source and a plurality of image carriers, and that deflects a light beam that is modulated based on a plurality of different image signals and emitted from the light source by a rotating polygonal mirror that rotates at a constant speed. By sequentially scanning in a predetermined main scanning direction in each of the image carriers corresponding to image signals,
An image forming apparatus, wherein different original images are formed on the respective image carriers corresponding to the respective image signals, and the original images are multiplex-transferred onto the same recording medium to form an image. A rotation position detection means for detecting a rotation position of the rotation position detection signal and outputting a rotation position detection signal; and a light beam deflected by the rotary polygon mirror provided near the scanning start position in the main scanning direction. Scanning start position detecting means for outputting a start signal, and after a predetermined scanning standby time has elapsed since the time when the scan start detection signal was detected, the light beam deflected by the rotating polygon mirror is used to scan the image carrier. Control means for controlling to start scanning, and correction means for correcting the scanning standby time based on a phase difference between the rotational position detection signal and the scanning start signal, An image forming apparatus having. 2. A storage unit for storing a plurality of phase difference values between the rotational position detection signal and the scanning start signal, wherein the correction unit is configured to calculate an average value for each phase difference value stored in the storage unit. 2. The image forming apparatus according to claim 1, wherein the scanning standby time is corrected based on the following. 3. The rotating position detecting means includes a magnet having a plurality of poles which are concentrically connected to the rotating polygon mirror and rotate integrally, and detect the rotating position of the magnet to detect the rotational position. The image forming apparatus according to claim 1, wherein a rotation position of the polygon mirror is detected. 4. The number of poles of the magnet and the number of faces of the rotary polygon mirror are the same, or the number of poles of the magnet is an even multiple of the number of faces of the rotary polygon mirror.
The image forming apparatus as described in the above. 5. The apparatus according to claim 1, further comprising a temperature detection unit configured to detect a temperature inside the apparatus, wherein the storage unit stores the temperature value detected by the temperature detection unit at the time when the temperature value is detected. 5. The method according to claim 2, wherein the data is stored in correspondence with a phase difference value between the scan start signal and the scan start signal.
Item 10. The image forming apparatus according to item 1.