JP5459603B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device used in a digital copying machine, a page printer, and the like and constituting a raster writing optical system using a light beam such as a laser beam. The present invention relates to an optical scanning device and an image forming apparatus using such an optical scanning device.

Conventionally, in order to achieve high-speed printing and high image quality in color copiers such as digital copiers and page printers that form images by scanning light beams such as laser beams, laser beam scanning is performed by rotating a polygon mirror. It is necessary to rotate the polygon scanner to be performed at a high speed of 25,000 rpm or more and with high accuracy. On the other hand, in order to improve the image quality by reducing the diameter of the laser beam, the inscribed circle radius and the length in the main scanning direction of the polygon mirror used in the polygon scanner described above are relatively large, and the trend of increasing the load as a polygon scanner is increasing. is there.
Due to this high load, the power consumption of the polygon scanner increases, and the heat generation adversely affects the optical elements such as the scanning lens. Specifically, for example, the temperature rise of the scanning lens closest to the polygon scanner. The heat generated in the polygon scanner increases the temperature of the scanning lens by indirect heat conduction or direct heat radiation by the optical housing. In addition, in practice, the temperature of the scanning lens is not raised uniformly, but the main scanning direction, which is the longitudinal direction in particular, depends on the distance from the polygon scanner that is the heat source, the difference in the thermal expansion coefficient of each material, and the influence of airflow. Has a temperature distribution (temperature deviation).

When the scanning lens has a temperature distribution in the main scanning direction, in particular, the shape accuracy and refractive index of the scanning lens change, the spot position of the laser beam fluctuates, and the image quality deteriorates. This problem is particularly noticeable when a plastic having a high coefficient of thermal expansion is used as the lens material.
In particular, in a color machine, for example, laser beams corresponding to each color such as yellow, magenta, cyan, and black are scanned, so that in addition to the above-described problems, there is a temperature deviation between optical scanning systems corresponding to each color. It becomes a problem. Such a temperature deviation causes a deviation in the relative positional relationship between the beam spots corresponding to the respective colors, resulting in an image color deviation.
Further, the temperature rise due to heat generation of the high-load polygon mirror induces a fine movement of the rotating body components, particularly the polygon mirror having a large mass ratio, changes the rotating body balance, and generates unnecessary vibration. In addition, if the thermal expansion coefficient of the parts that make up the rotating body, that is, the flange and shaft to which the polygon mirror or rotor magnet is fixed, is different, or even if the thermal expansion coefficients match, the component tolerance and fixing method In the case where the control and the like are not strictly controlled and inspected, fine movement due to the balance change of the rotating body occurs during high-temperature and high-speed rotation, and as a result, unnecessary vibration is increased. Such vibration is transmitted and amplified to an optical element such as a folding mirror in the optical scanning device, causing banding, which causes image deterioration and noise.

In order to deal with such a problem, instead of the rotating polygon mirror deflector described above, the deflection mirror is oscillated using a resonance phenomenon as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-208460. An oscillating mirror deflector using a moving system has been studied.
That is, in Patent Document 1 (Japanese Patent Laid-Open No. 2005-208460), as the resonance frequency increases, the drive frequency of the deflection mirror surface is increased and the oscillation amplitude of the deflection mirror surface is decreased (Θ1). → Θ2) The time that the light beam scans from the light beam detection position A to the light beam detection position B is PT, which is substantially equal to the scanning time PT before the resonance frequency is increased. Thus, energy can be saved by efficiently controlling the drive signal for driving the deflecting mirror surface, and the surface to be scanned can be stably scanned with the light beam. However, even if the scanning time is made equal as described above, the scanning characteristics within the scanning time change, so a linearity error regarding the magnification of the image remains, and the entire image is distorted in the main scanning direction. There is a problem that the image deteriorates.

As described above, the scanning method using the oscillating mirror deflector consumes less power and reduces the temperature rise of the scanning lens used in the optical scanning device or the temperature deviation and vibration of each color optical scanning system of the color machine. There is a merit. However, scanning characteristics such as jitter or amplitude are affected by the relationship between the resonance frequency and the driving frequency.
Therefore, the present invention has been made in view of the above-described circumstances, and has low power consumption, temperature rise of a scanning lens used for optical scanning, and temperature deviation and vibration for each color optical scanning system in a color machine. It is an object of the present invention to provide an optical scanning device and an image forming apparatus that can reduce, in particular, obtain good scanning characteristics with little jitter and ensure the temporal stability of an image.
That is, it is an object of the present invention to provide an optical scanning device that can obtain good scanning characteristics with little jitter.
A second object of the present invention is to provide an optical scanning device that can always detect the difference between the resonance frequency fr and the drive frequency fd and can effectively prevent the device from stopping. is there.

The object of the third aspect of the present invention is to adjust the driving frequency fd according to the difference between the resonance frequency fr and the driving frequency fd, and to obtain good scanning characteristics with little jitter even in a situation where the temperature environment changes. An object of the present invention is to provide an optical scanning device that can be obtained.
The object of claim 4 of the present invention is to provide an optical scanning device that can detect the difference between the resonance frequency fr and the drive frequency fd at all times and prevent the device from stopping more effectively. It is in .
The purpose of claim 5 of the present invention, in particular, low power consumption in the optical scanning apparatus, the temperature rise of the scanning lens used in the optical scanning, as well as by reducing the temperature deviation and vibration per optical scanning system, an image of An object of the present invention is to provide an image forming apparatus capable of ensuring stability over time .
The object of claim 6 of the present invention is to provide an image forming apparatus capable of ensuring the temporal stability of an image by reducing temperature deviation and vibration for each color optical scanning system in a color machine. There is.

In order to achieve the above-described object, an optical scanning device according to the present invention described in claim 1 is provided.
An optical scanning device comprising scanning imaging means for deflecting and scanning a laser beam emitted from a light source device in a main scanning direction by a single oscillating mirror deflector and condensing images on a plurality of scanned surfaces. ,
The vibration mirror includes an amplitude control loop that controls the amplitude of the vibration mirror, an offset control loop that controls a difference between the amplitude center of the ideal amplitude waveform of the vibration mirror and the amplitude center of the actual amplitude waveform, a reference clock, and the vibration Drive-controlled by a control means composed of a phase control loop that controls the relationship with the deflection angle of the mirror,
In a state where the amplitude of the oscillating mirror is controlled to be constant, the relationship between the resonance frequency fr of the oscillating mirror and the drive frequency fd is as follows:
fd <fr
fr−fd ≦ (fr × 0.002)
The drive frequency fd of the oscillating mirror is set so as to satisfy the above.
An optical scanning device according to the present invention described in claim 2 is the optical scanning device according to claim 1,
A laser beam detector that detects a scanning beam that is arranged in the main scanning region and is deflected and scanned, and the relationship between the resonance frequency fr and the driving frequency fd of the vibrating mirror is based on the voltage waveform of the driving frequency; The calculation is based on the phase difference with the output signal from the laser beam detector.

Optical scanning device according to the present invention described in 請 Motomeko 3 is an optical scanning apparatus according to claim 1 or 2,
It has a control means for detecting a difference between the resonance frequency fr and the drive frequency fd of the vibrating mirror and adjusting the drive frequency fd according to the detection result.
The optical scanning device according to the present invention described in claim 4 is the optical scanning device according to claim 3 ,
During deflection scanning by the vibrating mirror, the difference between the resonance frequency fr and the drive frequency fd is always detected .

An image forming apparatus according to the present invention described in claim 5
An image forming apparatus that forms a latent image on a latent image carrier by optical scanning and visualizes the latent image to obtain a desired recorded image,
The optical scanning device according to any one of claims 1 to 4 is used for optical scanning of the latent image carrier .
The image forming apparatus according to the present invention described in 請 Motomeko 6 is an image forming apparatus according to claim 5,
The image forming apparatus is a color image forming apparatus that forms a color image for each of a plurality of colors.

According to the present invention, the power consumption is low, and the temperature rise of the scanning lens used for optical scanning and the temperature deviation and vibration of each color optical scanning system in the color machine are reduced, thereby ensuring the temporal stability of the image. It is possible to provide an optical scanning device and an image forming apparatus that can perform the above.
That is, according to the optical scanning device of claim 1 of the present invention,
An optical scanning device comprising scanning imaging means for deflecting and scanning a laser beam emitted from a light source device in a main scanning direction by a single oscillating mirror deflector and condensing images on a plurality of scanned surfaces. ,
The vibration mirror includes an amplitude control loop that controls the amplitude of the vibration mirror, an offset control loop that controls a difference between the amplitude center of the ideal amplitude waveform of the vibration mirror and the amplitude center of the actual amplitude waveform, a reference clock, and the vibration Drive-controlled by a control means composed of a phase control loop that controls the relationship with the deflection angle of the mirror,
In a state where the amplitude of the oscillating mirror is controlled to be constant, the relationship between the resonance frequency fr of the oscillating mirror and the drive frequency fd is as follows:
fd <fr
fr−fd ≦ (fr × 0.002)
By setting the drive frequency fd of the vibrating mirror so as to satisfy
It is possible to obtain good scanning characteristics with less jitter.

According to the optical scanning device of claim 2 of the present invention, in the optical scanning device of claim 1,
A laser beam detector that detects a scanning beam that is arranged in the main scanning region and is deflected and scanned, and the relationship between the resonance frequency fr and the driving frequency fd of the vibrating mirror is based on the voltage waveform of the driving frequency; By calculating based on the phase difference with the output signal from the laser beam detector,
In particular, the difference between the resonance frequency fr and the drive frequency fd can always be detected, and the apparatus can be effectively prevented from stopping .

According to the optical scanning device of claim 3 of the present invention, in the optical scanning device of claim 1 or 2 ,
By having a control means for detecting the difference between the resonance frequency fr and the drive frequency fd of the vibrating mirror and adjusting the drive frequency fd according to the detection result,
In particular, by adjusting the drive frequency fd according to the difference between the resonance frequency fr and the drive frequency fd, it is possible to obtain good scanning characteristics with little jitter even in a situation where the temperature environment changes.
According to the optical scanning device of claim 4 of the present invention, in the optical scanning device of claim 3 ,
During deflection scanning by the vibrating mirror, by always detecting the difference between the resonance frequency fr and the drive frequency fd,
In particular, the difference between the resonance frequency fr and the drive frequency fd can be always detected to prevent the apparatus from being stopped more effectively .
Also, according to the image forming apparatus according to claim 5 of the present invention,
In an image forming apparatus that forms a latent image on a latent image carrier by optical scanning and visualizes the latent image to obtain a desired recorded image.
By using the optical scanning device according to any one of claims 1 to 4 for optical scanning of the latent image carrier,
In particular, the power consumption of the optical scanning device is small, and the temperature rise of the scanning lens used for optical scanning and the temperature deviation and vibration for each optical scanning system can be reduced to ensure the temporal stability of the image. Become .
According to the image forming apparatus of claim 6 of the present invention, in the image forming apparatus of claim 5 ,
The image forming apparatus is a color image forming apparatus that forms a color image for each of a plurality of colors.
In particular, it is possible to reduce the temperature deviation and vibration of each color light scanning system in the color machine, and to ensure the temporal stability of the image.

1 is a perspective view schematically showing a configuration of a main part of an optical scanning device according to a first embodiment of the present invention. It is a front view which shows the structure seen from the front of the vibration mirror part used for the optical scanning device of FIG. 2A and 2B are detailed views of a vibrating mirror unit used in the optical scanning device of FIG. 1, in which FIG. 1A is a rear view showing a configuration viewed from the back side, and FIG. It is a disassembled perspective view which shows the structure of the vibration mirror part used for the optical scanning device of FIG. It is a perspective view which shows the attachment structure of the vibration mirror part used for the optical scanning device of FIG. FIG. 2 is a schematic diagram for explaining a beam scanning range of main scanning in the optical scanning device of FIG. 1. 2 is a timing chart showing waveforms of respective portions related to resonance and drive control of a vibrating mirror in the optical scanning device of FIG. 1. FIG. 2 is a waveform diagram for schematically explaining the principle of amplitude control of a vibrating mirror in the optical scanning device of FIG. 1. FIG. 2 is a waveform diagram for schematically explaining the principle of offset control in the case of having an offset within an allowable range of a vibrating mirror in the optical scanning device of FIG. 1. FIG. 5 is a waveform diagram for schematically explaining the principle of offset control when the offset exceeding the allowable range of the vibrating mirror is provided in the optical scanning device of FIG. 1. FIG. 2 is a waveform diagram for schematically explaining the principle of phase control of a vibrating mirror in the optical scanning device of FIG. 1. FIG. 2 is a waveform diagram for schematically explaining a driving frequency and a resonance frequency of a vibrating mirror in the optical scanning device of FIG. 1. FIG. 2 is a schematic block diagram of a control system that performs amplitude control, offset control, phase control, and frequency control related to resonance drive control of a vibrating mirror in the optical scanning device of FIG. 1. It is a figure which shows the relationship between the frequency difference of a resonant frequency and a drive frequency, and a jitter. It is a figure which shows the phase characteristic which is a phase difference which is the phase difference of the resonant frequency characteristic in case the resonant frequency in the amplitude gain of a vibrating mirror falls, and the drive voltage waveform which drives a vibrating mirror. It is a figure which shows the phase characteristic which is a phase difference which is the phase difference of the resonant frequency characteristic in case the resonant frequency in the amplitude gain of a vibrating mirror rises, and the drive voltage waveform which drives a vibrating mirror. It is a figure for demonstrating the relationship between a light receiving element and a laser beam scanning, and the signal waveform of a light receiving element. It is sectional drawing which shows typically the structure of the principal part of the image forming apparatus which concerns on the 2nd Embodiment of this invention.

Hereinafter, based on an embodiment of the present invention, an optical scanning device of the present invention will be described in detail with reference to the drawings.
1 to 4 show the configuration of the main part of the optical scanning device according to the first embodiment of the present invention. FIG. 1 is a perspective view schematically showing the configuration of the main part of the optical scanning device, FIG. 2 is a front view schematically showing the configuration of a vibrating mirror substrate having a vibrating mirror that deflects and swings a laser beam, and FIG. FIG. 4 shows in detail the vibration mirror portion of the vibration mirror substrate, (a) is a rear view seen from the back side, (b) is a cross-sectional view thereof, and FIG. 4 is for explaining the vibration mirror portion in more detail. FIG.
In this case, for example, the optical scanning device shown in FIG. 1 includes four photosensitive drums 3Y that are arranged in contact with the intermediate transfer belt 2 of the image forming unit of the image forming apparatus (see FIG. 5) to form the image forming unit. 3M, 3C, and 3K (any one or all of these are referred to as “photosensitive drum 3”) are configured as an optical scanning device 5 that scans with a laser beam, and includes a light source unit 10 (light source units 10Y and 10M). 10C and 10K), vibrating mirror 11, cylindrical lens 12, folding mirror 13, first lens 14 constituting the scanning lens group in the scanning imaging optical system, imaging lens 15 (15-1, 15-2), Mirror 16 (16Y, 16M, 16C and 16K), second lens 17 (17Y, 17M, 17C and 17K) constituting the scanning lens group in the scanning imaging optical system, Over 18 (18Y, 18M and 18C) are provided with and a light receiving element PD (PD1 and PD2). The photoreceptor drums 3Y, 3M, 3C, and 3K correspond to yellow (Y), magenta (M), cyan (C), and black (K) colors, respectively (hereinafter, subscripts Y, M, and C are added to symbols). And K indicate the portions corresponding to the respective colors of Y: yellow, M: magenta, C: cyan, and K: black).

As described above, in this case, the optical scanning device 5 is located above the image forming unit in which the four photosensitive drums 3Y, 3M, 3C, and 3K of yellow, magenta, cyan, and black are arranged in parallel in the image forming apparatus. Has been placed. The optical scanning device 5 includes a light source unit 10 including four light sources 10Y, 10M, 10C, and 10K that generates laser beams corresponding to the respective colors, and deflection that deflects and scans the laser beams from the light sources 10Y, 10M, 10C, and 10K. A scanning lens of a scanning imaging optical system that guides the vibrating mirror 11 serving as scanning means and the laser beam reflected and deflected by the vibrating mirror 11 onto the scanned surfaces on the outer circumferences of the four photosensitive drums 3Y, 3M, 3C, and 3K, respectively. The first lens 14 constituting the group and the second lenses 17Y, 17M, 17C and 17K corresponding to the respective colors are provided, and these constituent members are accommodated in an optical housing (not shown). Yes.
The light source unit 10 shown in FIG. 1 has four light source units 10Y, 10M, 10C, and 10K corresponding to each color, and each of the light source units 10Y, 10M, 10C, and 10K includes a semiconductor laser and a coupling lens. It is comprised by. The four semiconductor lasers in the light source unit 10 emit laser beams as light beams for writing color component images of yellow, magenta, cyan, and black, respectively.

The laser beam emitted from each semiconductor laser is converted by a coupling lens into a light beam form suitable for the subsequent optical system, that is, a parallel light beam, or a light beam form such as a weak divergent or convergent light beam, and is turned back. The beam is focused in the sub-scanning direction by the cylindrical lens 12 through the mirror 13 and formed as a long line image in the main scanning direction in the vicinity of the deflection reflection surface of the vibration mirror 11 serving as the deflection scanning means.
Although not clearly shown on the incident side of the oscillating mirror 11, a laser transmitting member is disposed, and each light beam emitted from each light source unit 10Y, 10M, 10C, and 10K on the light source unit 10 side. Enters the oscillating mirror 11 via the laser transmitting member and is reflected and deflected in the same direction. The deflected light beams for four colors deflected by the oscillating mirror 11 and whose emission directions are oscillated by the oscillation of the oscillating mirror 11 are transmitted through the first lens 14 constituting the scanning lens group of the scanning imaging optical system. For example, a light beam for writing a black (K) component image passing through the position of the upper end of the first lens 14 in the scanning lens group is reflected by the mirror 16K and transmitted through the second lens 17K constituting the scanning lens group. Thus, the light spot is condensed as a light spot on the cylindrical outer peripheral surface of the photosensitive drum 3K which is a drum-shaped photoconductive photosensitive member serving as a scanning surface, and the outer peripheral surface of the photosensitive drum 3K is illustrated by this light spot. Scan in the direction of the arrow.

As the material of the first lens 14 and the second lens 17 (here 17K) constituting the scanning lens group, a plastic material that can be easily formed at a low cost is used. Specifically, polycarbonate having excellent low water absorption, high transmittance and moldability, and a synthetic resin material mainly composed of polycarbonate are preferable.
Light beams for writing images of color components of yellow (Y), magenta (M), and cyan (C) other than black (K) are reflected by mirrors 16Y, 16M, and 16C, respectively. The light spots are transmitted through 17M and 17C, and further reflected by mirrors 18Y, 18M, and 18C to form light spots on the outer peripheral surfaces of the photosensitive drums 3Y, 3M, and 3C, and the respective colors are scanned in the same arrow direction.
By these optical scans, electrostatic latent images of color component images corresponding to the respective photosensitive drums 3Y, 3M, 3C and 3K are formed. These electrostatic latent images are visualized with a corresponding color toner by the developing device (6), and transferred onto the intermediate transfer belt 2. At the time of transfer, the toner images of the respective colors are superimposed on each other to form a color image. This color image is transferred and fixed onto a sheet-like recording medium such as recording paper. The intermediate transfer belt 2 after the color image is transferred is cleaned by a cleaning device (not shown).

As described above, the optical scanning device shown in FIG. 1 is a vibrating mirror that repeatedly swings the light beams emitted from a plurality of light source devices respectively corresponding to a plurality of color component images constituting a color image. 11, a first lens 14 that deflects and scans in the same direction and transmits a deflected light beam corresponding to each color in common, and a second lens 17 (17Y, 17M, 17C) provided for each color individually. And 17K), the optical scanning is performed by individually condensing the photosensitive drums 3Y, 3M, 3C, and 3K corresponding to the image of each color component on the scanned surface on the outer periphery. The scanning imaging optical system has a scanning lens group including a first lens 14 and a second lens 17 (17Y, 17M, 17C, and 17K), and includes four scanning imaging units corresponding to the respective color components. Configure.
Laser beams corresponding to the respective colors are incident on the reflection surface of the above-described vibrating mirror 11 at a predetermined angle in the sub-scanning direction, thereby forming a so-called oblique incidence optical system. Specifically, the laser beam corresponding to the color having the maximum incident angle is set to be 5 ° or less. When the incident angle is 5 ° or more, the scanning line is greatly bent on the surface to be scanned, and the diameter of the laser beam is increased. As a result, the image is deteriorated.

On the other hand, if the laser beam corresponding to each color does not enter obliquely and enters perpendicularly at an oblique incident angle of 0 ° with respect to the sub-scanning direction, a large width of the reflecting surface in the sub-scanning direction is required. There is a problem in that the size of the mirror 11 itself increases, the driving load of the vibrating mirror 11 increases, and the vibration frequency cannot be increased.
Details of the vibrating mirror 11 are shown in FIGS. FIG. 2 is a front view of the entire vibrating mirror 11 as seen from the reflecting surface side. 3A and 3B show the main part of the oscillating mirror 11, in which FIG. 3A is a rear view and FIG. 3B is a cross-sectional view. FIG. 4 is an exploded perspective view of the entire vibrating mirror 11 shown in FIG.
2 to 4 includes a mounting substrate 40, a movable mirror 41, a torsion beam 42 (42A, 42B), a vibration plate 43, a reinforcing beam 44 (44A, 44B), a frame 46, a frame 47, and a yoke. 49, permanent magnet 50 (50A, 50B), connection electrode 52, planar pattern coil 53, terminal 54 (54A, 54B), trimming patch 55 and pedestal 56. The oscillating mirror 11 includes a movable mirror part 41 that forms a mirror surface on its surface to form a vibrator, a torsion beam 42 (42A, 42B) that forms a shaft that rotatably supports the movable mirror part 41 by torsional deformation, and these Frames 46 and 47 as support portions for supporting the substrate are formed, and each of these portions is basically formed by cutting an Si (silicon) substrate by etching.

These are configured on the mounting substrate 40, and specifically, for example, manufactured using a wafer in which two Si layers of 60 μm and 140 μm called SOI substrates are bonded in advance with an oxide film interposed therebetween. To do. Incidentally, the SOI (silicon on insulator) substrate is a substrate with a structure in which SiO ₂ is inserted between the Si substrate and the surface Si layer, and can reduce the parasitic capacitance of the transistor, which is effective in improving the operation speed and reducing power consumption. It is said that there is. Compared with the case of using a normal Si substrate, the operating speed can be improved by 20% to 30%, and the power consumption can be expected to be reduced by 50% or more.
That is, an example in which an SOI substrate composed of a 140 μm first substrate 61 constituting the first Si layer and a 60 μm second substrate 62 constituting the second Si layer is used will be described. First, the torsion beams 42A and 42B, the vibration plate 43 on which the planar pattern coil 53 is formed, and the reinforcing beam forming the skeleton of the movable mirror unit 41 are formed from the surface of the 140 μm first substrate 61 on the back side by a dry process by plasma etching. 44A and 44B and the frame 46 are left, and the other portions are removed by penetrating to the oxide film. Next, by performing anisotropic etching using KOH (potassium hydroxide) or the like from the surface of the 60 μm substrate (first substrate) 62 on the front surface side, the movable mirror portion 41 and the frame 47 are left, and the other portions are removed. The oxide film is penetrated and removed. Finally, the oxide film around the movable mirror portion 41 is removed and separated to form the structure of the vibrating mirror 11.

Here, the width of each of the torsion beams 42A and 42B and the reinforcing beams 44A and 44B is 40 to 60 μm. The moment of inertia I of the vibrator is preferably small in order to increase the deflection angle, but on the other hand, the mirror surface is deformed by the inertial force. It is said.
Further, an aluminum thin film is vapor-deposited on the surface side of the second substrate 62 having a thickness of 60 μm to form a reflection surface, and the surface pattern on the back side of the first substrate 61 having a thickness of 140 μm is made of a copper thin film and the planar pattern coil 53. Terminals 54A and 54B wired to 53 via torsion beams 42A and 42B and trimming patches 55 are formed. Naturally, conversely, a configuration in which a thin-film permanent magnet is provided on the diaphragm 43 side and a planar coil is formed on the frame 47 side may be employed. In this way, the movable mirror portion 41 that is the main body portion of the vibrating mirror 11 and the surrounding related portions are configured.
On the mounting substrate 40, a frame-like base 56 for mounting the above-described main body portion of the vibration mirror 11 and a yoke 49 formed so as to surround the main body portion of the vibration mirror 11 are provided. A pair that generates a magnetic field in a direction orthogonal to the rotation axis of the diaphragm 43 formed by the torsion beams 42A and 42B, with the S and N poles facing each other substantially corresponding to both ends of the movable mirror portion 41. Permanent magnets 50A and 50B are coupled.

The movable mirror portion 41 of the oscillating mirror 11 is mounted on the pedestal 56 with the mirror surface facing the front side at the frame 46 and 47 portions, and a current is passed between the terminal 54A and the terminal 54B to allow the planar pattern coil 53 to When a Lorentz force is generated on each side parallel to the rotation axis (by the torsion beams 42A and 42B), a torsional deformation is generated by rotating the torsion beams 42A and 42B to rotate the movable mirror portion 41, and the current is cut off. It returns horizontally due to the return deformation force of the torsion beams 42A and 42B.
Therefore, by alternately switching the direction of the current flowing in the planar pattern coil 53 by the AC signal, the movable mirror unit 41 can be vibrated by reciprocating rocking. Then, when the current switching period is made close to the natural frequency of the primary vibration mode having the torsion beams 42A and 42B of the structure constituting the oscillating mirror 11 as the rotation axis, the so-called resonance frequency f0, resonance is excited. A swing angle with a large amplitude can be obtained.
On the other hand, by applying a direct current component to the current flowing through the planar pattern coil 53, the swing rotation angle of the movable mirror portion 41 can be changed statically, and the amplitude center of vibration can be changed. However, since the resonance phenomenon is used, the change according to the current is within ± 1 ° in angle. By superimposing the DC component on the AC signal described above, it is possible to change the amplitude center of oscillation while deflecting and vibrating the oscillating mirror 11.

The vibrating mirror 11 is mounted on an optical housing (not shown) of the optical scanning device in the form of a vibrating mirror unit 70 as shown in FIG. The oscillating mirror unit 70 shown in FIG. 5 includes the oscillating mirror 11, a bracket 71, a substrate 72, an electrode portion 73, an electrical connector 74, and the like. The vibration mirror 11 is fixed to the bracket 71 provided on the substrate 72 by being fitted and fixed at the edge of the mounting substrate 40, and the connection electrode 52 is in contact with the electrode portion 73 provided on the bracket 71. 72 is electrically connected. The substrate 72 is installed in an optical housing (not shown) and is connected via an electrical connector 74.
The above-described oscillating mirror 11 has a movable part having a mass and inertia (inertia) that are very small compared to a conventional polygon mirror, so the drive part is also miniaturized, and the efficiency of the magnetic circuit is increased. It can be suppressed to 1/10 or less of the mirror. As a result, heat generation is reduced and the temperature rise of the optical element and housing of the writing optical system can be substantially eliminated. For this reason, in particular, the resin scanning lens does not have a local temperature distribution, the laser beam scanning position is not changed, and the occurrence of color misregistration during color image formation can be suppressed. It becomes.

Furthermore, since the mass and inertia of the movable part of the oscillating mirror 11 are small, the vibration generated by mass imbalance when the movable part is swung and transmitted to the outside is reduced to 1/100 or less of the polygon mirror. Accordingly, since vibration transmitted to the optical element of the writing optical system is substantially eliminated, occurrence of banding, which is a density variation in the sub-scanning direction during image formation due to vibration of the folding mirror, is also eliminated.
In order to make use of the advantages of the vibrating mirror 11 described above, it is necessary to perform control as described below.
FIG. 6 schematically shows a main part corresponding to one photosensitive drum 3 in the optical scanning device for color image formation shown in FIG. The laser beam LB deflected and scanned by the oscillating mirror 11 is distinguished by the range of the scanning position, and the laser beam corresponding to the scanning position range of the maximum deflection angle is received by the light receiving element PD1 disposed within the range of the maximum deflection angle LBa. The laser beam corresponding to the scanning position range between the positions where the laser beam is incident on the element PD2 and the output signal is generated is LBb, and the laser beam corresponding to the scanning position range between the ends of the image area on the photosensitive drum 3 Was LBc. The actual laser beam LB is scanned between the timings when it enters the light receiving element PD1 and the light receiving element PD2 disposed within the maximum deflection angle range and an output signal is generated.

FIG. 7 shows the amplitude of the vibrating mirror 11 with respect to time in this case. Since the oscillating mirror 11 generates a large amplitude using a resonance phenomenon, the amplitude of the oscillating mirror draws a sinusoidal locus with respect to time as shown in the figure, and when there is no scanning lens, deflection scanning is performed. The scanning speed of the laser beam is not constant and varies depending on the scanning position. The first and second lenses 14 and 17 of the scanning lens group have f · arcsin characteristics so that the scanning speed is constant even at such a scanning speed. FIG. 7 shows a drive voltage waveform, a drive reference signal, an output of the light receiving element PD1, an output of the light receiving element PD2, and a reference phase clock waveform in addition to the vibration mirror amplitude at that time.
Even if the scanning lens having the above-described characteristics is used, fluctuation variation of the oscillation mirror 11 as shown in FIGS. 8 to 11 occurs. Therefore, the amplitude control (see FIG. 8) Each control of offset control (FIGS. 9 and 10) and phase control (FIG. 11) is performed. Even if the resonance frequency of the oscillating mirror 11 is constant, phenomena such as the amplitude waveforms AW1 to AW4 shown in FIGS. 8 to 11 occur, and all of these change in the scanning position of the laser beam with respect to the ideal amplitude waveform AW0 formed of a sine waveform. This will degrade the image.

That is, FIG. 8 shows amplitude fluctuations, and when the amplitude of the amplitude waveform AW1 is larger than the target ideal amplitude waveform AW0 (almost the same when small), it is indicated by an arrow in order to obtain the ideal amplitude. Perform such control. In this case, as shown in FIG. 7, control is performed so that the calculated values of the time interval A (A1, A2,...) Of the output of the light receiving element PD1 and the time interval B (B1...) Of the output of the light receiving element PD2 are constant. . Specifically, for example, averaging is performed a plurality of times as (A1 + B1) / 2, (A2 + B2) / 2, and so on, and control is performed so that the control target value is uniquely determined from the resonance frequency.
Here, the drive frequency fd of the vibrating mirror 11 will be described in detail with reference to FIG. The drive frequency fd is a frequency for realizing the number of image formations such as the number of prints, and the fact that it matches the resonance frequency can increase the amplitude Y1 (shown by a solid line in FIG. 12) necessary for optical scanning. In practice, however, there may be cases where the resonance frequency does not match due to fluctuations in the resonance frequency of the oscillating mirror 11 (including initial variations). In such a case, as shown in FIG. 12, in order to obtain the amplitude Y1 necessary for the optical scanning, the input energy (voltage, current, etc.) to the oscillating mirror 11 is increased, and the amplitude is Y2 at the drive frequency fd. The amplitude control of the oscillating mirror 11 is performed by increasing the amplitude of the only oscillating mirror 11 and amplifying it to the amplitude Y1 as shown by the broken line in FIG.

FIGS. 9 and 10 show the positional relationship between the amplitude center of the oscillating mirror 11 and the scanning center, and are offset (vibrated) into the amplitude waveforms AW2 and AW3 with respect to the scanning center which is the center of the optical scanning waveform AW0. This shows a state in which there is a difference between the center of the amplitude waveform AW2 or AW3 of the mirror 11 and the center of the optical scanning waveform AW0. 9 and 10 are different in the offset amount. FIG. 9 is an example in the case where the offset amount is within the allowable level, and FIG. 10 is a case in which the offset amount exceeds the allowable level. It is an example. The offset amount affects the linearity in the optical scanning characteristic and the beam diameter, but the offset amount does not necessarily have to be zero in consideration of the influence on the image. Specifically, for the linearity error, linearity is corrected by controlling the lighting timing of the laser beam based on the image information to suppress the influence, and the beam diameter in the photoconductor to suppress the influence. By controlling the light amount, that is, the integrated light amount so that the electrostatic latent images are equal, the influence of the offset is reduced.
In the first place, if the offset amount is within the allowable offset, it can be allowed as it is. Therefore, the above-described control may not be performed when the offset amount is within the allowable offset. For example, by setting the allowable offset amount so that the deviation from the design value in linearity is 1% or less and the deviation from the design value in beam diameter is 10% or less, the influence on the image is suppressed as much as possible. As described above, there is no problem even if the control for reducing the influence of the offset is not performed.

FIG. 10 shows a state where the offset amount exceeds the allowable offset. In such a case, as described above, it is necessary to perform control adjustment to correct within the allowable range, that is, within the allowable offset. . In the adjustment control method, a direct current component corresponding to the offset amount is superimposed on an alternating current component that is a substantial driving voltage of the oscillating mirror 11 to change the posture in the main scanning direction so that the amplitude center is within an allowable offset. Adjust so that In another embodiment, the adjustment can be made by a driving mechanism that changes the posture of the vibrating mirror 11.
For example, a stepping motor (not shown) is disposed on the lower surface of the substrate 72, and the drive mechanism is disposed such that the rotation axis of the motor and the vibration center axis of the vibration mirror 11 coincide. This drive mechanism adjusts the oscillating mirror unit 70 to be within the allowable offset range by rotating the oscillating mirror unit 70 about the oscillating center axis to change the posture. In this case, the rotation step resolution of the stepping motor needs to be an amount corresponding to at least half of the allowable offset amount.
This type of offset adjustment itself has been conventionally performed, but conventionally, the control adjustment is performed so that the offset amount is ideally zero instead of the concept of the allowable offset as described above.

In this case, the DC component superimposing circuit required for offset adjustment must have a performance having an output voltage capable of adjusting all the offset amounts shown in FIG. 10, the circuit becomes large, and the heat generation amount is large. As a result, the temperature in the optical scanning device rises and the optical scanning characteristics are deteriorated. Further, in this case, there is a problem that the cost increases as the circuit size increases. Further, since the drive control current or voltage at the time of offset adjustment is also limited by the upper limit of the current rating of the vibrating mirror 11, it cannot be driven indefinitely according to the offset amount. That is, when the drive control current exceeds the current rating, the element is destroyed. In particular, in the case of the electromagnetic drive type described above, the power consumption of the direct current component becomes the power consumption of the coil (that is, copper loss), so there is a concern that when the offset adjustment amount increases, heat is generated and the temperature rises. Come.
In FIG. 10, in order to control and adjust the offset within the allowable offset range, as shown in the arrow direction of FIG. 10, the output time interval A (A1, A2) of the light receiving element PD1 as described in FIG. ..) And the output time interval B (B1,...) Of the light receiving element PD2 are controlled to be constant. Specifically, A1-B1, A2-B2,... Are averaged several times to determine whether they are within the allowable offset (the comparison unit 107 in FIG. 13 described later in detail). If the allowable offset is exceeded without performing control, offset control is performed so that the offset is within the allowable range.

FIG. 11 shows the phase fluctuation of the amplitude waveform of the oscillating mirror 11, and the amplitude waveform AW4 in which the phase fluctuation occurs with respect to the reference phase clock (see FIG. 7 for the waveform) of the reference phase waveform AW0 as shown in FIG. It has become. In such a case, in order to adjust the phase of the amplitude waveform AW4 as indicated by an arrow in FIG. 11, as shown in FIG. 7, a reference phase clock and light receiving signal for driving the vibrating mirror 11 are received. Control is performed such that the phase of the output time interval C (C1, C2,...) Of the element PD1 is constant. Specifically, averaging is performed a plurality of times at time intervals C1, C2,..., And control is performed so that the target value becomes zero. The output of the light receiving element PD1 for counting the time interval C is preferably an output corresponding to the timing immediately before the image forming area (the rear end side of the time interval A). This is because the phase is adjusted because the accuracy is higher immediately before the start of writing of the scanning line of the image (that is, the rear end side of the time interval A) than immediately after the end of writing of the scanning line of the image ( Immediately after the end of writing of the scanning line, that is, in the case of the front end side of the time interval A, the phase accuracy at the time of image formation decreases due to the phase fluctuation within the time interval A).
In the case of the excessive amplitude waveform AW1 in FIG. 8 and the amplitude waveform AW3 having an excessive offset exceeding the allowable offset in FIG. 10, the scanning speed shift in the main scanning direction is different from the ideal scanning speed and scanning timing. It becomes. For example, image degradation such as an error in main scanning magnification and jitter (vertical line fluctuation) in the main scanning direction is caused, which is a common defect not only in color images but also in monochrome (monochrome) images.

On the other hand, the phase fluctuation of the amplitude waveform AW4 in FIG. 11 with respect to the reference phase clock causes a particularly serious problem when forming a color image. As shown in FIG. 1, a single oscillating mirror 11 scans the photosensitive drum 3 for each color with a laser beam emitted from a light source of each color according to an image signal. Since the deflection scanning position of the laser beam for each color changes, the sub-scanning position fluctuates on the image on the intermediate transfer belt 2, and color misregistration and color unevenness occur.
FIG. 13 shows a block diagram of the drive control system of the oscillating mirror 11 that realizes the above-described amplitude, offset, and phase control. The vibrating mirror control system shown in FIG. 13 includes counters 101, 102, 103, and 104, an average calculation / difference calculation unit 105, comparison units 106, 107, and 108, a controller 109, a multiplication unit 110, an addition unit 111, a drive circuit 112, Phase comparators 113 and 114, a low-pass filter (LPF) 115, an integrator 116, a sine wave signal generation unit 117, and a difference calculation unit 118 are provided.

The signals output from the respective light receiving elements PD1 and PD2 are measured by the counter 101 and the counter 102, respectively, by the laser beam that is deflected and scanned to scan the photosensitive drum 3 and the light receiving element PD, and are shown in FIG. Time interval A and time interval B are obtained. The average calculation / difference calculation unit 105 calculates an average of (A + B) / 2 from these time intervals A and B, and the comparison unit 106 compares the average with the target amplitude. Similarly, the average calculation / difference calculation unit 105 obtains the average of the values corresponding to the difference of A−B, that is, the offset amount, and the comparison unit 107 compares and determines whether the value is within the allowable offset. If the offset amount is within the allowable range, it is output without correction to the controller 109 as it is, and if it is outside the allowable range, the offset correction amount is output to adjust the difference from the allowable range, and the adder 111 Is supplied to the drive circuit 112 via Therefore, the adjustment residual is suppressed so that the offset amount does not become zero after the adjustment but is within the allowable range at the maximum.
Note that the amplitude and the offset amount based on the time interval A and the time interval B are averaged. The reason why the averaging process is performed in this manner is to prevent the control from being performed by incorrect information when sudden electrical noise is mixed. In addition, the frequency | count of averaging is performed in the range of 2-10 times. This is because if it is 10 times or more, the correction timing is delayed and the control deviation is increased.

The controller 109 calculates amplitude and offset correction amounts based on the comparison results described above, and the amplitude correction amount is multiplied by the multiplication unit 110 with respect to the sine wave generated by the sine wave signal generation unit 117. The offset correction amount is added to the sine wave output from the multiplier 110, and the sine wave drive signal corrected in this way is amplified by the drive circuit 112, which is an amplifier. The vibration mirror 11 is driven and controlled.
The control system loop described above is an amplitude and offset control loop. The offset control is performed in a state where the amplitude control is performed.
As for the phase control loop, the amplitude control and the offset control described above work normally, and the phase control loop is executed in the control state where each of the target values falls within the required range, and the reference phase clock signal and the vibration mirror shake. The angles are set to have a predetermined phase relationship. Phase control is more accurate than amplitude control and offset control. Therefore, if all controls are executed simultaneously, they will interfere with each other and drive signal fluctuation will increase, and all controls will be within the control target value range. It takes a lot of time to converge. Therefore, by performing amplitude control as the highest priority, performing offset control next, and then performing phase control as fine adjustment, it is possible to shorten the time until convergence within the control range. .

In FIG. 13, the phase deviation (time interval C in FIG. 7) between the output signal from the light receiving element PD 1 and the reference phase clock signal is detected by the phase comparator 113 and measured by the counter 103. A so-called phase-locked loop (PLL) in which the measurement result is converted into a voltage corresponding to the phase deviation by a low-pass filter (LPF: Low Pass Filter) 115 and an integrator 116 and the phase is changed according to the voltage amount. ) Control. When generating a sine wave signal corresponding to a phase change, a sine wave signal for obtaining an optimum phase is generated in accordance with a preset phase change amount step, that is, resolution.
In this way, control is performed such that the drive signal for driving the oscillating mirror 11 and the deflection angle of the oscillating mirror 11 have a certain phase relationship. It should be noted that the generation resolution of the sine wave signal corresponding to the phase control needs to be highly accurate beyond the allowable range of control, but the higher the accuracy, the higher the cost because a memory is required. Therefore, the generation resolution of the sine wave signal is set to be 50 μm or less which is visually recognized as a color shift in the sub-scanning direction.

FIG. 14 shows the relationship between the frequency difference between the resonant frequency fr and the drive frequency fd and the jitter. The frequency difference between the resonance frequency fr and the drive frequency fd is expressed as a percentage (%) of (fr−fd).
(Fr−fd) / fr × 100
It is calculated by the following formula. Jitter is a characteristic indicating scanning stability in the main scanning direction, that is, variation in scanning. Since jitter is recognized as image fluctuation, it is an important item of image characteristics.
A state in which the drive frequency fd is matched with the resonance frequency fr is a jitter ratio of 1.0, which indicates that the jitter changes due to a difference in frequency difference between the resonance frequency fr and the drive frequency fd. For example, a jitter ratio of 1.2 means that the jitter is increased by 20% compared to when the drive frequency fd is matched with the resonance frequency fr, and a jitter ratio of 0.9 is reduced by 10%.
In this case, different characteristics are shown depending on whether the frequency difference between the resonance frequency fr and the drive frequency fd is positive or negative, and when the frequency difference is positive (fr) compared to when there is no frequency difference (fr = fd). > Fd), the jitter is improved. On the other hand, when the frequency difference is negative (fr <fd), the jitter is deteriorated. However, even in the positive case, the jitter is improved only in the range of the relationship of fr−fd ≦ (fr × 0.002) when the frequency difference takes into account the measurement variation.

For example, in the case of the oscillating mirror 11 with the resonance frequency fr = 3000 Hz, the drive frequency fd at which the jitter is improved is
fd <3000Hz
And
3000 Hz-fd ≦ (3000 Hz × 0.002)
That is,
→ fd ≧ 2994Hz
Range.
Thus, the preferred frequency range is
2994 Hz ≦ fd <3000 Hz
It becomes.
In order to maintain the above-described preferable frequency difference, the difference between the resonance frequency fr and the drive frequency fd is always detected (this point will be described in detail later). Control means for adjusting the drive frequency fd to a suitable frequency difference range according to the difference detection result is provided, and a suitable frequency difference is always maintained.

Note that in the above-described frequency difference setting, a state in which the amplitude (the range of the swing angle) of the vibrating mirror 11 is controlled to be constant is essential. If the amplitude is not constant, the scanning characteristic (scanning linearity) of the image region varies (for example, the slope of the amplitude waveform in FIG. 8 changes), and the magnification of the main scanning image is distorted. In order to control the amplitude to be constant, the control system shown in FIG. 13 is constructed as described above, and the control shown in FIG. 8 is performed.
Also, as shown in FIG. 14, the influence on the jitter varies due to the difference in frequency difference between the resonance frequency fr and the drive frequency fd. As shown in FIG. 13, the control system controls the amplitude control, offset control and phase control. This is because the phase lag on the transfer characteristic of the oscillating mirror 11 changes due to the frequency difference. In particular, the phase delay is small and the control system is stable when drive frequency fd <resonance frequency fr. Note that if the difference between the drive frequency fd <resonance frequency fr becomes too large, a large amount of drive power is required, so that the feedback (FB to feedback) gain increases and the jitter deteriorates due to the influence of the oscillation phenomenon.

In the embodiment described above, the adjustment of the drive frequency fd according to the detection result of the frequency difference between the resonance frequency fr and the drive frequency fd has been described. However, as another preferred embodiment, the vibrating mirror 11 is used. A drive frequency fd that satisfies the relationship of fd <fr at the upper temperature limit of the temperature range in which is used may be set, and the drive frequency fd may be a fixed value within the use temperature range.
When the operating temperature range is 0 to 50 ° C. (plus the temperature rise in the apparatus added to the environmental temperature to which the optical scanning device according to this embodiment and the image forming apparatus incorporating the same are exposed), the vibrating mirror 11 The spring constant varies depending on the temperature. For example, in the case of a silicon material, the spring constant decreases with increasing temperature, and the resonance frequency fr tends to decrease (−0.1 Hz / ° C.).
2 to 4, the torsion beam 42 (42A, 42B) connects the movable part such as the movable mirror part 41 of the oscillating mirror 11 and the fixed part such as the frames 46 and 47. In such a structure, the resonance frequency tends to decrease with increasing temperature regardless of the material. This is because the rigidity (Young's modulus) of the torsion beam 42 (42A, 42B) decreases with increasing temperature.

Specifically, for example, when the resonance frequency fr is measured in advance in an environment of 25 ° C. and a result of 3000 Hz is obtained, 3002.5 Hz (= 3000 × (−0.1 × −25)) at 0 ° C. When the temperature is 50 ° C., the frequency is 2997.5 Hz (= 3000 × (−0.1 × 25)). Therefore, in order to maintain the relationship of drive frequency fd <resonance frequency fr at 50 ° C., it is desirable to set the drive frequency fd as a fixed value below 2997.5 Hz.
Next, detection of the difference between the resonance frequency fr of the oscillating mirror 11 and the drive frequency fd will be described in detail.
FIG. 15 and FIG. 16 show a phase characteristic that is a phase difference between the resonance frequency characteristic in the amplitude gain of the oscillating mirror 11 and the drive voltage waveform for driving the oscillating mirror 11. The thick solid line is the initial resonance frequency characteristic and phase characteristic. In this case, the amplitude gain characteristic Gain and the phase characteristic Phase can be expressed by the following equations.

Here, Q is a Q value representing a resonance state, and is 200 in this embodiment.
ω ₀ (= 2πf ₀ ) [rad / s] corresponds to the resonance frequency (fr), and in this embodiment, f ₀ = 3000 [Hz].
From these expressions (1) and (2), the amplitude gain characteristic Gain and the phase characteristic Phase when driving at a frequency of ω (= 2πf) are obtained.
15 and 16, since the rigidity of the torsion beam 42 (42A, 42B) of the oscillating mirror 11 changes due to the change of the environmental temperature, the resonance frequency fr (= ω ₀ ) becomes the direction indicated by the arrows (D1 and D2). To change. FIG. 15 shows the fluctuation direction D1 of the resonance frequency fr when the environmental temperature increases, and FIG. 16 shows the fluctuation direction D2 of the resonance frequency fr when the environmental temperature decreases. Here, the environmental temperature is the environmental temperature to which the optical scanning device (vibrating mirror 11) is exposed. The unit including the optical scanning device provided in the image forming apparatus and the image forming apparatus are installed. Contains ambient temperature to be burned.

Here, the example of FIG. 15 will be described with reference to FIGS. 7 and 13. When the frequency of the drive voltage is also 3000 Hz with respect to the vibration mirror 11 having the resonance frequency of 3000 Hz, the phase difference between the drive voltage signal and the vibration of the vibration mirror 11 is −90 °. The frequency of the driving voltage is constant, and when the resonance frequency fr changes in the direction of arrow D1 in FIG. 15 as the environmental temperature rises, the phase characteristics also change in conjunction with it, so the phase difference is It changes in the direction of arrow E1.
In the example of FIG. 16, when the frequency of the drive voltage is 3000 Hz with respect to the vibration mirror 11 having the resonance frequency of 3000 Hz, the phase difference between the drive voltage signal and the vibration of the vibration mirror 11 is −90 °. The frequency of the drive voltage is constant, and when the resonance frequency fr rises and fluctuates in the direction of arrow D2 in FIG. 16 as the environmental temperature decreases, the phase characteristics also fluctuate in conjunction with this, and the phase difference increases in the direction of arrow E2. Change. By detecting such a change amount of the phase difference, the fluctuation of the resonance frequency fr can be grasped.

As shown in FIG. 15, when the resonance frequency fr decreases by 10 Hz, the phase difference becomes −90 ° to −144 ° (the phase difference is obtained from the equation (2)). In order to detect -54 ° for the phase difference fluctuation, a plurality of averaging processes of the time intervals P (P1, P2,...) Of the drive voltage signal (drive reference signal) and the output of the light receiving element PD1 in FIG. Can be achieved by measuring (preferably). Since the position where the light receiving element PD1 is arranged is not the center of the scanning range, it cannot directly detect −90 ° or −144 ° as described above, but δ is assumed to be a phase shift from the center of scanning. For example, since the time interval P = (− 90 ° −δ °), the variation in the phase difference can be detected by measuring the variation in the time interval P.
In the block diagram of FIG. 13, the phase difference between the drive voltage signal output from the adding unit 111 and the detection signal of the light receiving element PD1 is measured by the phase comparator 114 and the counter 104, and the difference calculating unit 118 A difference from the resonance frequency fr is calculated. If the difference is compared with an allowable value by the comparison unit 108 and is outside the allowable value range, the drive frequency fd is changed by controlling the sine wave signal generation unit 117 to match the resonance frequency fr. adjust. The allowable set value is set from a limit value that can correct a decrease in amplitude caused by a change in the resonance frequency fr. In order to correct the amplitude drop and control the amplitude to be constant, the drive voltage is increased. Therefore, the tolerance of the difference is set so that either the breakdown voltage of the drive circuit 112 or the allowable breakdown voltage of the vibrating mirror 11 is lower. The value is decided. In this embodiment, the allowable breakdown voltage of the oscillating mirror 11 is given priority and is set within ± 10 Hz.

The difference between the resonance frequency fr and the drive frequency fd of the oscillating mirror 11 is detected in a state where the amplitude of the oscillating mirror 11 is controlled to be constant. This is because if the amplitude is not constant, the timing of the output signal of the light receiving element PD1 changes and affects the time interval P.
The frequency adjustment timing of the driving voltage needs to be in a required condition because the scanning characteristic of the deflected scanning beam changes. That is, in a preferred embodiment, the determination is performed using a determination unit that determines whether image information is input to the light source of the optical scanning device, that is, whether the laser beam is scanned over the scanned surface area. This is performed at a timing during non-image formation without image information indicating no (the scanning beam to the light receiving elements PD1 and PD2 is deflected also at this time). “Non-image forming” means the interval between print sheets at the time of image printing and the interval between print jobs (print jobs).
On the other hand, in the other preferred embodiments, the adjustment is performed at any time (at any time when the drive frequency is out of the allowable value) regardless of whether or not the scanning surface area is scanned with the laser beam as described above. In order to make it possible, the frequency fluctuation at the time of adjustment is changed stepwise. For example, when the difference exceeds 10 Hz and becomes 11 Hz, the drive frequency is not changed immediately by 11 Hz, but 110 steps are changed stepwise in units of 0.1 Hz, for example. The change time is preferably the time from the start to the completion of the adjustment timing so that an image can be formed on one print sheet (the side effect of image deterioration is reduced by slowly changing the frequency).

Conventionally, the resonance frequency is measured by measuring the amplitude when the drive frequency is swept (swept) by temporarily stopping the image formation of the optical scanning device in order to measure the amplitude gain characteristic Gain. Since the resonance frequency is increased, the optical scanning device, that is, the image forming apparatus in which the optical scanning device is incorporated cannot be used. In the embodiment of the present invention, during normal deflection scanning by the oscillating mirror 11 (at least when output signals are generated from the light receiving element PD1 and the light receiving element PD2-at this time, the laser beam is not deflected and scanned in the image area. However, since the difference between the resonance frequency fr and the drive frequency fd can be detected by scanning the light receiving element PD1 and the light receiving element PD2), it is not necessary to temporarily stop the operation of the apparatus even during image formation.
If a difference between the resonance frequency fr of the vibrating mirror 11 and the drive frequency fd is detected and the drive frequency is adjusted in accordance with the difference, the sub-scan magnification at the time of image formation changes accordingly. Therefore, a suitable predetermined value is set in advance for the adjustment of the drive frequency fd. The image magnification in the sub-scanning direction is adjusted when the fluctuation amount due to the adjustment of the drive frequency fd becomes a predetermined value or more. The predetermined value here is set to 1%, at which the image magnification is visually acceptable. Depending on the target of the output image, even 1% may cause a problem. In consideration of such a situation, a predetermined value setting changing unit is provided so that the user can change the setting of the predetermined value as appropriate.

Correction of the sub-scanning position magnification requires complicated magnification correction by image processing and speed adjustment in the sub-scanning direction (adjustment of each unit of the photosensitive unit, intermediate transfer belt unit, paper feed unit, and fixing unit), which is complicated. In addition, there is a need to consider a time lag and the like, and there is a time when image formation must be stopped. It is preferable as the image quality of the image forming apparatus that the drive frequency is not changed as much as possible.
FIG. 17 illustrates in detail the relationship with laser beam scanning, taking the light receiving element PD1 as an example. As shown in FIG. 1, the light receiving element PD1 is optically equivalent to the beam diameter and the scanning speed of the laser beam that scans the outer peripheral surface of the photosensitive drum 3 (that is, the scanning laser beam spot passes). Has been placed. The arrangement of the light receiving element PD1 is preferably on the scanning extension of the outer peripheral surface of the photosensitive drum 3. However, depending on the convenience of the layout, the light receiving element PD1 may be scanned with a laser beam via a folding mirror. The light receiving element PD1 includes a light receiving unit 91 basically composed of a PIN photodiode, an amplifier circuit that amplifies an output signal from the light receiving unit 91, and a circuit unit 92 having a comparator circuit that shapes the output signal. An IC (integrated circuit) is encapsulated in a laser beam transmitting member made of a resin to form a single package. An IC lead terminal 93 for electrically connecting the light receiving unit 91 and the circuit unit 92 from the outside is led out of the package. When the scanning beam spot passes on the light receiving portion 91, a light receiving element output signal shown in FIG. 17 is generated, and the light receiving element output signal is compared with a threshold voltage to generate a comparator output signal.

  In a region indicated by a broken line in FIG. 17, the laser beam light source is turned off, or the flare light is received by the light receiving elements PD1 and PD2, or the light quantity is at a level that forms a latent image on the outer peripheral surface of the photosensitive drum 3. It is assumed that it has been dimmed to the extent that it does not become. When the laser beam light source emits light in a region between the maximum deflection angle of the oscillating mirror 11 and the vicinity of the light receiving element PD1, ghost light is generated due to irregular reflection of the optical components arranged in the optical scanning device, and the light receiving element Since noise is mixed in the light reception signals of PD1 and light receiving element PD2, the time intervals A, B, and C described above are disturbed, resulting in control malfunction or instability. In order not to cause such a problem, the light is turned off in advance at the above-mentioned timing, or the ghost light is received by the light receiving elements PD1 and PD2, or the latent image is formed on the outer peripheral surface of the photosensitive drum 3. It is set to be dimmed to such an extent that it does not become a light amount. This extinction or dimming also has the effect of extending the life of the laser light source composed of a semiconductor laser and the effect of suppressing the temperature rise of the laser light source. The above-described vicinity of the light receiving element intends a scanning position at which the above-described time intervals A, B, and C are light emission timings that can be normally measured without affecting the output of the comparator circuit of the circuit unit 92. .

In addition, if the amount of light decreases due to a decrease in reflectance or transmittance due to deterioration of the optical element over time, the rising direction to the threshold voltage that determines the comparator output becomes loose, and the time required for rising becomes longer, so erroneous detection Will go. Therefore, when the light receiving elements PD1 and PD2 are scanned, the above-described problem is solved by controlling the laser light source so that the light quantity is always constant.
FIG. 18 shows a configuration of a main part of an image forming apparatus according to the second embodiment of the present invention in which the above-described optical scanning device is incorporated. The image forming apparatus shown in FIG. 18 is a color image forming apparatus, and includes a paper feed cassette 1, an intermediate transfer belt 2, a photosensitive drum 3 (3Y, 3M, 3C, 3K), the above-described optical scanning device 5, and a developing device 6. (6Y, 6M, 6C, 6K) and the fixing device 7.
The color image forming apparatus is configured as a tandem type color image forming apparatus in which a plurality of photosensitive drums 3 (3Y, 3M, 3C, 3K) of four colors of yellow, magenta, cyan, and black are arranged in parallel. Yes. In order from the top of the apparatus, the optical scanning device 5, the developing device 6 (6Y, 6M, 6C, 6K), the photosensitive drum 3 (3Y, 3M, 3C, 3K), the intermediate transfer belt 2, the fixing device 7, and the paper feed cassette 1 is laid out. On the intermediate transfer belt 2, photosensitive drums 3Y, 3M, 3C and 3K corresponding to the respective colors are arranged in parallel at equal intervals in parallel.

The photosensitive drums 3Y, 3M, 3C, and 3K are formed to have the same diameter, and members for performing an electrophotographic process are sequentially disposed around each of the photosensitive drums 3Y, 3M, 3C, and 3K. The photoconductor 3Y will be described as an example. A charging charger (not shown), a laser beam L1 based on an image signal emitted from the optical scanning device 5, a developing device 6Y, a transfer charger (not shown), and a cleaning device (not shown). Etc.) are sequentially arranged. The same applies to the other photosensitive drums 3M, 3C and 3K. That is, in this embodiment, the photosensitive drums 3Y, 3M, 3C, and 3K are scanned surfaces set for the respective colors, and the laser beams L1, L2, L3, and L4 from the optical scanning device 5 are provided for each color. Are fired to correspond to each.
The photosensitive drum 3Y that is uniformly charged by the charging charger rotates in the direction of the arrow A in the figure, thereby sub-scanning the laser beam L1, and an electrostatic latent image is formed on the photosensitive drum 3Y. Further, a developing device 6Y that supplies toner to the photosensitive drum 3Y is disposed downstream of the irradiation position of the laser beam L1 by the optical scanning device 5 in the rotation direction of the photosensitive drum 3, and yellow toner is supplied. The The toner supplied from the developing device 6Y adheres to the portion where the electrostatic latent image is formed, and a toner image is formed. Similarly, single-color toner images of magenta M, yellow Y, and black K are formed on the photoreceptors 3M, 3C, and 3K, respectively.

  The intermediate transfer belt 2 is disposed further downstream in the rotational direction than the position where the developing unit 6Y of the photosensitive drum 3Y is disposed. The intermediate transfer belt 2 is wound around a plurality of rollers 2a, 2b, and 2c and is stretched, and is driven by a motor (not shown) to be moved and conveyed in the direction of arrow B. By this conveyance, the intermediate transfer belt 2 is sequentially moved to the photoreceptors 3Y, 3M, 3C, and 3K. The intermediate transfer belt 2 sequentially superimposes and transfers the monochrome images developed by the photoreceptors 3Y, 3M, 3C, and 3K, and forms a color image on the intermediate transfer belt 2. Thereafter, the transfer paper is conveyed from the paper feed tray 1 in the direction of the arrow C in the figure, and the color image is transferred. The transfer paper on which the color image is formed is discharged as a color image after being fixed by the fixing device 7.

DESCRIPTION OF SYMBOLS 1 Paper feed cassette 2 Intermediate transfer belt 3 (3Y, 3M, 3C, 3K) Photosensitive drum 5 Optical scanning device 6, (6Y, 6M, 6C, 6K) Developing device 7 Fixing device 10 Light source unit 10Y, 10M, 10C, 10K light source unit 11 vibrating mirror 12 cylindrical lens 13 folding mirror 14 first lens constituting scanning lens group 15, (15-1, 15-2) imaging lens 16, (16Y, 16M, 16C, 16K) mirror 17 , (17Y, 17M, 17C, 17K) Second lens constituting scanning lens group 18, (18Y, 18M, 18C) Mirror 40 Mounting substrate 41 Movable mirror part 42 (42A, 42B) Torsion beam,
43 Diaphragm 44, (44A, 44B) Reinforcement beam 46, 47 Frame 49 Yoke 50, (50A, 50B) Permanent magnet 52 Connection electrode 53 Planar pattern coil 54 (54A, 54B) Terminal 55 Trimming patch 56 Base 91 Light receiving portion 92 Circuit section 93 IC lead terminal 101, 102, 103, 104 Counter 105 Average calculation / difference calculation section 106, 107, 108 Comparison section 109 Controller 110 Multiplication section 111 Addition section 112 Drive circuit 113, 114 Phase comparator 115 Low-pass filter ( LPF)
116 integrator 117 sine wave signal generation unit 118 difference calculation unit PD, (PD1, PD2) light receiving element

JP-A-2005-208460

Claims (6)

In an optical scanning device including a scanning imaging unit that deflects and scans a laser beam emitted from a light source device in a main scanning direction by a single oscillating mirror deflector and focuses and forms an image on a plurality of scanned surfaces.
The vibration mirror includes an amplitude control loop that controls the amplitude of the vibration mirror, an offset control loop that controls a difference between the amplitude center of the ideal amplitude waveform of the vibration mirror and the amplitude center of the actual amplitude waveform, a reference clock, and the vibration Drive-controlled by a control means composed of a phase control loop that controls the relationship with the deflection angle of the mirror,
In a state where the amplitude of the oscillating mirror is controlled to be constant, the relationship between the resonance frequency fr of the oscillating mirror and the drive frequency fd is as follows:
fd <fr
fr−fd ≦ (fr × 0.002)
The drive frequency fd of the oscillating mirror is set so as to satisfy the above. A laser beam detector that detects a scanning beam that is arranged in the main scanning region and is deflected and scanned, and the relationship between the resonance frequency fr and the driving frequency fd of the vibrating mirror is based on the voltage waveform of the driving frequency; The optical scanning device according to claim 1, wherein calculation is performed based on a phase difference with an output signal from the laser beam detector. Wherein, light as claimed in claim 1 or 2, wherein detecting the difference in the resonance frequency fr and drive frequency fd of the vibrating mirror, and wherein the benzalkonium adjust the drive frequency fd depending on the detection result Scanning device. 4. The optical scanning device according to claim 3 , wherein a difference between the resonance frequency fr and the drive frequency fd is always detected during deflection scanning by the vibrating mirror. In an image forming apparatus that forms a latent image on a latent image carrier by optical scanning and visualizes the latent image to obtain a desired recorded image.
An image forming apparatus using the optical scanning device according to any one of claims 1 to 4 for optical scanning of the latent image carrier. The image forming apparatus according to claim 5 , wherein the image forming apparatus is a color image forming apparatus.

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