JP4219631B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an optical scanning device used in an image forming apparatus such as a digital copying machine and a laser printer, and relates to a technique that can be applied to an optical scanning bar code reading device, a three-dimensional shape measuring device, and the like. It is.
[0002]
[Prior art]
In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector that scans a light beam. In order to achieve a higher resolution image and high-speed printing, this rotation must be further increased, and a bearing is used. Durability, heat generation due to wind damage, and noise are issues, and there is a limit to high-speed scanning.
On the other hand, research on optical deflectors using silicon micromachining has been promoted in recent years, and as disclosed in Japanese Patent No. 2924200 and Japanese Patent No. 3011144, an oscillating mirror and its axial support are supported by a Si substrate. There has been proposed a method in which torsion beams are integrally formed.
[0003]
According to this method, since reciprocal vibration is performed using resonance, there is an advantage that noise is low although high speed operation is possible. Furthermore, since the driving force for rotating the vibrating mirror can be small, the power consumption can be kept low.
[0004]
On the other hand, with the environmental temperature change, there is a problem that the material characteristics change, the resonance frequency shifts, and the deflection angle is extremely reduced, and the temperature is detected as disclosed in JP-A-7-49462. As disclosed in Japanese Patent Laid-Open No. 2001-305471, the swing angle is detected by the induced electromotive force, and the drive frequency for applying the excitation current following the resonance frequency deviation can be varied. As disclosed in Japanese Patent No. 2711158, a proposal has been made to keep the resonance frequency constant by suppressing temperature fluctuation within a predetermined range.
[0005]
[Problems to be solved by the invention]
As described above, in a method of driving a vibrating mirror using resonance, it is necessary to apply a driving voltage at a frequency that matches the resonance frequency unique to the vibrating mirror. However, the resonance frequency itself, for example, changes according to changes in self-heating or environmental temperature.When this is used instead of a polygon mirror or a galvanometer mirror, the image is recorded by changing the scanning speed. The dot interval of the pixels to be formed and the entire image width change.
[0006]
FIG. 14 is a diagram for explaining that the deflection angle changes at the same drive frequency due to a temperature change.
In the figure, the vertical axis represents the mirror deflection angle, and the horizontal axis represents the scanning frequency (drive frequency). As the drive frequency increases, the maximum value is shown when the mirror deflection angle suddenly rises from ₀ and coincides with the resonance frequency f0 of the mirror, and then suddenly decreases. It shows a gentle slope with a slight downward slope on the way, and finally it suddenly drops to zero. The existence range of this graph is called a resonance vibration band for convenience. Vibrating in this band is called resonance vibration or resonance driving.
Now, when the drive frequency fd to be given to the vibrating mirror at the reference temperature of 25 ° C. is set as shown in the figure according to the method of the present invention to be described later, the temperature of the optical scanning device is 10 ° C. Due to a temperature change of 50 ° C., the deflection angle changes to a range indicated by an arrow A in the figure.
[0007]
For example, in a tandem multicolor image forming apparatus in which a plurality of optical scanning devices and photoconductors are arranged along the moving direction of the transfer body to superimpose colors, the dot positions of the pixels of each color image do not match. Or color change. Further, as proposed in Japanese Patent Application Laid-Open No. 2001-228428, in a method in which a plurality of optical scanning devices are arranged in parallel and the images are divided into main scans and joined together, the boundary portion is required if the respective image widths do not match. However, there is a problem that the images are overlapped with each other or a gap is opened so that the joint is easily noticeable.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, in the invention according to claim 1 of the present application, the light source, light source driving means for modulating the light source according to image information, and reciprocating vibration with the torsion beam as the rotation axis, the light source In the optical scanning device having a vibrating mirror that scans a light beam from and a vibrating mirror driving unit that can change a driving frequency of the vibrating mirror according to a resonance frequency unique to the vibrating mirror, the vibrating mirror includes: The period from θS to −θS (0 <θS <θ) in the forward period from the scanning angle θ0 as a starting point until reaching −θ0, and only for the scanning period in the same direction is used for image recording according to the image information. When the scan angle θS is the search start end and the scan angle −θS is the scan end, a synchronization detection sensor that detects the synchronization of the scan start end and a scan end detection sensor that detects the beam at the scan end And comprising the synchronization By measuring the time difference between the end detection signal generated from the synchronization detection signal and the scanning end detection sensor generated from the detection sensor, comprising an amplitude detection means for detecting the amplitude of the oscillating mirror, by the amplitude detecting means Based on the detected amplitude of the oscillating mirror, the driving frequency of the oscillating mirror is changed so that the amplitude of the oscillating mirror maintains a predetermined value or more, and the light source driving means is detected by the amplitude detecting means. Based on the amplitude of the oscillating mirror, a change in the scanning speed of the oscillating mirror is detected, and a pixel clock that modulates the light-emitting source according to the detected variation in the scanning speed is set to one cycle of the reference clock of the pixel clock. Phase synchronization means for selecting from a plurality of clocks delayed by 1 / n, a new one based on the synchronization detection signal output from the synchronization detection sensor. And changes by selecting the lock.
[0011]
According to a second aspect of the present invention, in the optical scanning device according to the first aspect of the present invention, the drive frequency of the oscillating mirror is set to be shifted from the resonance frequency inherent to the oscillating mirror by a predetermined range.
[0012]
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the vibration mirror driving means has a drive frequency fd of the vibration mirror: 0 <t <1 / (4 · fd )
The drive mirror for the application time t is applied in the form of a pulse to drive the vibrating mirror.
[0013]
According to a fourth aspect of the present invention, in the optical scanning device according to the third aspect, the drive voltage is applied in a range not exceeding a period from the amplitude peak of the vibrating mirror to the amplitude of 0.
[0016]
According to a fifth aspect of the present invention, a light emitting source, light source driving means for modulating the light emitting source according to image information, and a vibrating mirror that reciprocally vibrates about a torsion beam as a rotation axis and scans a light beam from the light emitting source. And an oscillating mirror driving means for changing the driving frequency of the oscillating mirror according to the resonance frequency unique to the oscillating mirror, and a photoconductor on which an electrostatic image is formed by the optical scanning device, An image forming apparatus comprising: a developing unit that visualizes the electrostatic image with toner; and a transfer unit that transfers the visualized toner image onto a recording sheet. The vibrating mirror has a scanning angle θ0. Is the period from θS to −θS (0 <θS <θ) in the forward period until reaching −θ0, and is used for image recording according to the image information only in the scanning period in the same direction, The scanning angle θS is the search start end, the scanning angle A synchronization detection signal generated from the synchronization detection sensor, comprising a synchronization detection sensor for detecting the synchronization of the scanning start end and a scanning end detection sensor for detecting the beam at the scanning end when θS is the scanning end. and by measuring the time difference between the end detection signal generated from the scanning end detection sensor comprises amplitude detection means for detecting the amplitude of the oscillating mirror, the vibration mirror amplitude detected by said amplitude detecting means based on the so that the amplitude of the oscillating mirror to hold the predetermined value or more, change the drive frequency of the oscillating mirror, the light source drive means, a pixel clock for modulating the light emitting source, detected by the amplitude detecting means based on the vibration mirror amplitudes to detect the scanning speed changes of the oscillating mirror, in response to the detected scanning speed variations, of the pixel clock reference clock Phase synchronization means for selecting one cycle from among a plurality of clock delay for each 1 / n, and change by selecting a new clock based on the synchronization detection signal output from the synchronization detection sensor image It is characterized by recording.
[0017]
According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect of the present invention, the image forming apparatus includes a speed variable unit that changes a moving speed of the photoconductor, and the movement of the photoconductor according to the driving frequency of the vibrating mirror. The image recording is performed by changing the speed.
[0019]
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect , the image forming apparatus includes a plurality of the optical scanning devices, and performs image recording by resonance-vibrating each vibration mirror at a common drive frequency. Features.
[0020]
【Example】
FIG. 1 is an exploded perspective view showing details of a vibrating mirror module used in the optical scanning device of the present invention.
In FIG. 1, reference numeral 100 denotes a vibrating mirror module, 101 a support substrate, 102 a movable mirror, 103 a movable electrode, 104 a glass window, 105 a cover, 106 a Si substrate, 107 a Si substrate frame, and 108 a torsion beam , 109 is a fixed electrode, 110 is a fixed frame, 112 is a lead terminal, 113 is an insulating substrate, 114 is an opening, 115 and 116 are counter mirror chips, 117 and 118 are reflection surfaces, 119 is a back side of a movable mirror, and 120 is a depression Respectively.
[0021]
The oscillating mirror module 100 has a movable mirror 102 having a primary oscillation mode with a torsion beam 208 as a rotation axis, mounted on a support substrate 101 formed of sintered metal or the like, and a cover 105 formed in a cap shape. The light beam enters and exits through a glass window 104 that is sealed and disposed in the opening.
The vibration mirror substrate is configured by bonding the Si substrate 106 and the Si substrate frame via an insulating film. The Si substrate 106 is made of a Si substrate having a thickness of 60 μm, and the movable mirror 102 and a pair of torsion beams 108 that pivotally support the mirror 102 are formed by etching, leaving only the connection with the fixed frames 110 at both ends and removing the periphery. . The torsion beams 108 are arranged parallel to the sub-scanning direction.
[0022]
At both ends of the movable mirror 102 in the longitudinal direction across the torsion beam 108, the portions close to the fixed frame 110 mesh with each other through a gap of several μm, and both sides have comb-like irregularities. Is formed.
A metal coating such as Au is deposited on the surface of the movable mirror 102 and the uneven portions formed on the fixed frame 110. The metal film on the surface of the movable mirror 102 functions as a laser light reflecting surface, and the metal film near both ends functions as an electrode. The metal films 103 and 103 on the concave and convex portions at both ends of the movable mirror 102 are referred to as first and second movable electrodes, and the metal films 109 and 109 on the concave and convex portions on both sides of the opposite fixed frame 110 are referred to as first and second fixed electrodes. .
[0023]
Since the movable mirror 102 has different shapes on the front and back sides and has a slight asymmetry, the movable mirror 102 is held slightly inclined from the horizontal in a no-load state, and the movable electrode and the fixed electrode have a step of several μm. Yes. Therefore, when a voltage is applied to the fixed electrodes 109, 109, an electrostatic attractive force is generated between the movable electrodes facing each other, and the torsion beam 108 is twisted so as to return horizontally. By repetitively applying a pulse-like voltage with the same phase, the oscillation reciprocates.
The reason why the electrodes are comb-shaped is that the outer peripheral length is made as long as possible to increase the electrode length, so that a larger electrostatic torque can be obtained at a low voltage.
[0024]
Further, if the system of the torsion beam 108 and the movable mirror 102 is designed to have a natural frequency corresponding to the main scanning period necessary for the scanning device, the mass, width, length, thickness, etc. are designed to be excited. The amplitude can be enlarged. In this way, by adjusting the resonance frequency to the drive frequency, the applied current can be small and the power consumption can be reduced. However, as described above, the amplitude is reduced only by slightly deviating the drive frequency from the resonance frequency.
[0025]
As can be seen from FIG. 14, when the driving frequency fd is made to coincide with the resonance frequency f ₀ at 25 ° C. as the temperature of the optical scanning device, the mirror deflection angle becomes 0 when the temperature of the optical scanning device reaches 10 ° C. Will become unusable. Even if the temperature is controlled to be kept at 25 ° C., the resonance frequency slightly deviates due to the environmental change, and therefore the phenomenon that the mirror deflection angle becomes 0 as soon as f ₀ becomes to the right of fd. Occur.
[0026]
Therefore, as shown in FIG., The drive frequency fd is preferably set by shifting toward greater than the resonance frequency f _0. As a degree to be shifted, it is necessary that at least the mirror deflection angle does not become 0 in the use temperature range, in this example, 10 ° C. to 50 ° C. Preferably, the slope of the curve of the deflection angle graph is as gentle as possible (the absolute value is small). For example, if fd is set to the value shown in the figure, even if the drive frequency fd cannot follow the change in the temperature range, the mirror shake angle fluctuates in the range indicated by the arrow A, but the shake does not occur. There is no such thing as stopping. In the present invention, by detecting the mirror deflection angle, the drive frequency fd is changed, and correction is always performed so that the deflection angle becomes 5 degrees. Thereby, the drive frequency fd can be changed in the range of the arrow B in the figure.
[0027]
As shown in FIG. 14, the resonance vibration band shifts according to the fluctuation of the resonance frequency f ₀ due to the temperature change, and the deflection angle of the movable mirror changes.
1) The frequency of the drive voltage applied to the fixed electrode is variably controlled so as to follow the change in the resonance frequency. 2) Either the spring constant of the Si substrate is stabilized and the fluctuation range of the resonance frequency is kept small. Measures are needed.
[0028]
In the embodiment 1), the amplitude (light beam deflection angle) is measured by detecting the scanning speed of the light beam scanned by the synchronization detection sensor, and the drive frequency is periodically set so that the deflection angle is maintained. Review and reset.
FIG. 2 is a diagram showing an embodiment in which the spring constant of 2) is stabilized. By depositing and heating the thin film resistor 111 on the fixed frame 110 connected to the torsion beam 108, the spring constant is kept low even when the environmental temperature is low, and the resonance vibration band is stabilized regardless of the environmental temperature. ing.
[0029]
Here, the resonance frequency will be described in detail.
Now, assuming that the dimensions of the movable mirror are the length 2a, the width 2b, the thickness d, the length of the torsion beam is L, and the width c, the density ρ of Si and the material constant G are used.
Moment of inertia I = (4abρd / 3) × a ²
Spring constant K = {G / (2L)} × {cd (c ² + d ² ) / 12}
And the resonant frequency f is
f = {1 / (2π)} × (K / I) ^1/2
= {1 / (2π)} × {Gcd (c ² + d ² ) / (24LI)} ^1/2
It becomes.
[0030]
Since the beam length L and the deflection angle θ are in a proportional relationship, θ is a constant and θ = A / I f ²
The deflection angle θ is inversely proportional to the moment of inertia I, and the deflection angle θ is reduced unless the moment of inertia is reduced in order to increase the resonance frequency f.
Therefore, in the embodiment, the moment of inertia is reduced to about 1/5 by leaving the substrate thickness d on the movable mirror back side 119 in a lattice shape and removing the other thickness by etching to a thickness of d / 10 or less.
[0031]
On the other hand, when the dielectric constant ε of air, the electrode length H, the applied voltage V, and the inter-electrode distance δ, the electrostatic force between the electrodes F = εHV ² / (2δ)
Where B is a constant
Swing angle θ = BF / I
The deflection angle θ increases as the electrode length H increases, and a driving torque that is 2n times the number of comb teeth n can be obtained by using a comb-teeth shape.
On the other hand, if the air density is η with respect to the movable mirror speed υ and area E, C is a constant,
Viscous resistance of air P = Cηυ ² E ³
Since it works in opposition to the rotation of the movable mirror, it is preferably sealed with a cover and kept in a reduced pressure state. In the embodiment, a non-evaporable getter is included and activated by heating from the outside to be in a reduced pressure state, and the pressure is 1 torr or less.
[0032]
The Si substrate frame 107 is made of a 280 μm Si substrate, and penetrates through the center portion and is joined to the support portion of the Si substrate 106 with an insulating layer interposed therebetween, thereby forming a swinging space of the movable mirror. On the upper surface, opposing mirror chips 115 and 116 made of two Si substrates and facing the movable mirror are bonded so as to be bridged.
The counter mirror chip 116 uses a wafer inclined at a slice angle of about 9 ° from the crystal plane orientation <110> from the crystal plane orientation <111>, and the <111> plane is exposed by etching to expose from the substrate surface. An inclined surface inclined by 9 ° and 26.3 ° is formed and cut out. This surface is used as a bonding surface, and a metal film is vapor-deposited on the substrate surface continuous with the surface to form a reflecting surface. The two opposing mirror chips have a configuration in which the first reflecting surface 117 and the second reflecting surface 118 that form an angle of 144.7 ° in a roof shape with the opening 114 interposed therebetween are arranged in pairs.
[0033]
FIG. 3 is a view showing a sub-scan section layout of the vibrating mirror module. The light beam emitted from the semiconductor laser 301 passes through a coupling lens 302 and a cylinder mirror 303 as will be described later, and is approximately 20 in the sub-scanning direction with respect to the normal line in the sub-scan section including the torsion beam with respect to the movable mirror 102. The light beam is incident through the opening at an angle, the reflected light beam is incident on the first reflecting surface 117 and returned to the movable mirror, and the reflected light beam passes through the opening 114 and passes through the second reflecting surface 118. The reflection position is moved in the sub-scanning direction while reciprocating three times with the movable mirror, and the light is again emitted from the opening 114 by the reflection by the movable mirror a total of five times.
[0034]
In the embodiment, the reflection is repeated a plurality of times in this manner, so that a large scanning angle can be obtained with a small deflection angle of the movable mirror. Now, assuming that the total number of reflections N at the movable mirror is N and the deflection angle α, the scanning angle θ can be expressed by 2Nα. In this embodiment, since N = 5 and α = 5 °, the maximum scanning angle is 50 ° and the polygon mirror An equivalent scan angle is obtained.
[0035]
By using resonance, the applied voltage is very small and little heat is generated. However, as is clear from the above equation, as the recording speed, that is, the resonance frequency, increases, the spring constant of the torsion bar must be increased and the swing angle cannot be obtained. End up. Therefore, by providing the counter mirror chip as described above, the scanning angle is enlarged so that a necessary and sufficient scanning angle can be obtained regardless of the recording speed.
[0036]
In addition, a reflective surface is formed facing the roof, and the incident angle in the sub-scanning direction to the movable mirror is repeatedly distributed between positive and negative (rightward and leftward) for each reflection, so that Suppresses scanning line bending on the scanning surface, maintains linearity, and prevents the imaging performance from deteriorating by returning the light beam to its original orientation when exiting in the plane perpendicular to the optical axis. Consideration is given.
[0037]
The substrate 106 is stacked on the insulating substrate 113 and bonded thereto, and is fixed to the support substrate 101. The insulating substrate 113 includes a pad portion 113 a that penetrates the center portion to form a swinging space for the movable mirror and is electrically connected to a fixed electrode provided on the substrate 106. The lead terminal 112 is inserted through the support substrate 101 through an insulating material, and the end portion protruding upward and the pad portion are connected by wire bonding to form an internal and external electrical wiring.
[0038]
The cover 105 is fitted into a step provided on the outer periphery of the support substrate 101, and a glass window 104 is joined from the inside of the cover to the light beam emission opening. In the figure, reference numeral 120 denotes a recess for receiving the getter, and the insulating substrate 113 is bonded and blinded.
[0039]
In the above embodiment, the vibration mirror is driven by an electrostatic force. However, the same applies to a method of exciting using a piezoelectric element and a method of driving an electromagnetic force by forming a thin film coil on a movable mirror.
[0040]
4 and 5 are perspective views of the optical scanning device according to the embodiment of the present invention.
In the figure, reference numeral 400 is a light source unit, 401 is a semiconductor laser, 402 is a holder member, 403 is a through hole, 404 is a cylindrical portion, 405 is a projection, 406 is a housing, 408 is a mounting surface, 409 is an inclined surface, and 410 is a cup. Ring lens, 412 is a printed circuit board, 413 is a synchronization detection sensor, 414 is a connector, 415 is a cable, 416 is a first scanning lens, 417 is a second scanning lens, 418 is a bonding surface, 419 is a flat pressing surface, 420 Is a protrusion, 421 is a protrusion pair, 422 is a notch, 423 is a protrusion, 424 is an end, 425 is a notch, 426 is a protrusion pair, 427 is a bright aluminum plate, 428 is a mirror part, 429 is an opening part, and 430 is a vibrating mirror Module, 431 opening, 432 reference pin, 436 cylinder mirror, 438 cover, 439 opening, 600 optical scanning device It is shown, respectively.
[0041]
The semiconductor laser 401 as a light source is press-fitted into the through hole 403 of the cylindrical portion 404 from the side opposite to the contact surface of the holder member 402 to the housing 406, and is coupled to the protrusion 405 provided on the contact surface side. The lens 410 is aligned with the optical axis, positioned in the optical axis direction with respect to the light emitting point so that the emitted light beam becomes a parallel light beam, and bonded and fixed to the semi-cylindrical portion at the tip to constitute the light source unit 400. In the embodiment, three light source units are used, all having the same configuration.
[0042]
The light source unit 400 includes a cylindrical portion 404 provided coaxially with the through hole, and engages with a mating hole 407 of the housing 406 to be brought into contact with the mounting surface 408 and fixed with screws.
The light beam emitted from the light source unit is joined to the inclined surface 409 facing the mounting surface 408, is incident on the cylinder mirror 436 having a concave curvature in the sub-scanning direction, and is converged on the movable mirror surface in the sub-scanning direction. The light enters from the glass window of the vibration mirror module 430.
[0043]
The cylinder mirror 436 is abutted from the outside so that the mirror surface can be seen from the opening 431 of the inclined surface 409, and along the inclined surface 409, the rotation direction in the same surface and the sub-scanning direction are described. It is positioned and bonded and fixed so that the scanning lens is aligned with the focal line direction of the scanning lens.
[0044]
The oscillating mirror module 430 is equally spaced so that the directions of the torsion beams are parallel to each other. In the embodiment, three are mounted on the same printed circuit board 412 and abut the upper surface of the board so as to block the lower opening of the housing. Screwed. Corresponding to the three oscillating mirror modules, all three other optical elements are also prepared. Therefore, three sets of optical scanning means form one optical scanning device.
[0045]
The scanning line of each vibration mirror module 430 on the surface to be scanned has a predetermined angle (β) from the direction orthogonal to the moving direction of the surface to be scanned (photosensitive member). In the embodiment, the scanning end side is 2 to 3 from the scanning start side. It is arranged so as to be inclined, and is mounted so that the scanning lines with the adjacent optical scanning means are parallel to each other.
[0046]
The printed circuit board 412 is mounted with a drive circuit for the semiconductor laser 401, electronic components constituting the drive circuit for the movable mirror 102, and a synchronization detection sensor 413. The vibration mirror module 430 has the bottom surface of the support substrate on the printed circuit board surface. Circuit connection is made by abutting and soldering the lead terminal protruding downward through the through hole, and wiring with an external circuit is made via the connector 414. A cable 415 having one end connected to a printed circuit board is connected to a lead terminal of the semiconductor laser.
[0047]
The housing 406 is made of glass fiber reinforced resin, aluminum die cast, or the like that can secure a certain degree of rigidity. Inside the housing, a first scanning lens 416 and a second scanning lens 417 constituting an imaging means are arranged in the main scanning direction. The joint surface 418 to be joined is formed, and when the sub-scanning direction reference surface of each lens is brought into contact, the light beam emitted from the vibration mirror module 430 and the optical axis height in the sub-scanning direction are arranged so as to match. Yes.
[0048]
The first scanning lens 416 includes a protrusion 420 that projects in the center of each sub-scanning surface and performs positioning in the main scanning direction, and a flat pressing surface 419 that performs abutment in the optical axis direction at both ends of the first surface. The protrusion 420 is engaged with the notch 422 formed integrally with the surface 418, and the flat pressing surface 419 is abutted against the protrusion pair 421 so that the relative arrangement is supported.
[0049]
On the other hand, the second scanning lens 417 is connected to the main scanning, is housed in the frame body 434 and is integrally formed of resin, and the protrusion 423 at the center of the second surface side of the frame body 434 is integrally formed on the joint surface. The notch 425 is engaged, and both end portions 424 of the first surface side of the frame body 434 are abutted against the protrusion pair 426 and supported.
[0050]
The synchronization detection sensor 413 (PIN photodiode) is arranged at an intermediate position shared by adjacent vibrating mirror modules 430 and at both end positions so that a beam can be detected on the scanning start side and the scanning end side of each optical scanning module 430. It is mounted in a total of four places. On the second surface side of the second scanning lens 417, a high-luminance aluminum plate 427 in which an inverted V-shaped mirror portion 428 is formed between the scanning regions of each lens and an opening 429 is formed in the scanning region is provided. Reflecting surfaces corresponding to the adjacent scanning start side and scanning end side are arranged to face each other so that the light beam reflected by 428 is guided to each synchronization detection sensor 413.
[0051]
The cover 438 forms an opening 439 through which the light beam passes and is screwed to seal the top surface of the housing 406. The bright aluminum plate 427 is sandwiched and supported between the second scanning lens and the cover, and the reflected light beam passes again through the scanning lens 427 and is returned to the housing.
[0052]
The optical scanning apparatus configured as described above is positioned with respect to the frame of the apparatus main body by the reference pin 432 provided on the flange 433 formed at the main scanning end of the housing 406, and is attached with reference to the upper surface, and is fixed with screws. Is done.
In the embodiment, an example in which three optical scanning units are arranged is shown, but the same is true regardless of the number of arrangements.
[0053]
FIG. 6 is a diagram showing an example in which the present invention is applied to a color laser printer.
In the figure, reference numeral 601 is a transfer belt, 602 is a developing roller, 603 is a toner hopper, 604 is a photosensitive drum, 604 is a sensor, 606 is a paper feed roller, 607 is a paper feed tray, 608 is a cleaning unit, and 609 is a rotating support. , 610 denotes a registration roller, 611 denotes a secondary transfer device, 612 denotes a heat fixing roller, 613 denotes a paper discharge roller, and 614 denotes a paper discharge tray.
[0054]
The example shown in the figure shows a color laser printer in which an image is formed one color at a time by the optical scanning device 600 and the transfer belt 601 is rotated four times and the color is overlapped every rotation.
The transfer belt 601 is supported by a driving roller and two driven rollers, and a developing roller 602 and a toner hopper 603 that replenish toner corresponding to each color are provided integrally on a rotating support 609 and rotate by 1/4. The photosensitive drum 604 is opposed to the photosensitive drum 604.
[0055]
The image is recorded with the timing of writing in the sub-scanning direction triggered by a signal from a sensor 605 that detects a registration mark formed on the end of the transfer belt 601, and toner is put on the transfer belt 601 by a developing unit. Is transcribed. The residual toner after the transfer is scraped and stored by the cleaning unit 608 so as not to mix colors.
By performing these operations for each color, images are sequentially superimposed.
[0056]
The paper is supplied from the paper feed tray 607 by the paper feed roller 606, sent out by the registration roller 610 in synchronization with the image formation of the fourth color, and transferred by the transfer unit 611 from the transfer belt 601 at the same time. The transferred toner image is fixed by a fixing roller 612 and discharged to a paper discharge tray 614.
[0057]
As described above, the optical scanning device 600 connects the scanning lines of a plurality of optical scanning units to form one line.
FIG. 7 is a conceptual diagram for explaining the joining of scanning lines.
The total number of dots L per line is divided into three, and 1 to L1, L1 + 1 to L2, and L2 + 1 to L dots are assigned and printed from the beginning of the image. In this embodiment, the scanning areas overlap several mm on the photosensitive member. An overlap area is provided in the pixel area, and the pixel numbers L1 and L2 at the separation positions are not fixed, but are different for each color, so that the seams of the scan lines of the respective colors constituting the same line are not overlapped, and the boundary of the scan area is defined. It is hard to stand out.
[0058]
FIG. 8 is a block diagram showing a part of the write data processing.
In the figure, reference numeral 801 denotes a bitmap memory, 802 denotes a multiplexer, 803 to 805 denote buffer memories, and 806 to 808 denote write control units.
As described above, the image data is divided into three in the main scanning direction, stored in the bitmap memory 801 for each optical scanning unit, and the sub-scanning pitch determined by the drive frequency fd of each vibrating mirror module and the scanning line Raster expansion is performed with a template corresponding to the inclination β, and the data is stored in the buffers 803 to 805 as line data.
Therefore, even if the sub-scan recording density of each image area is slightly different, the end of each area can be matched. The stored line data is read out using each synchronization detection signal as a trigger, and image recording is performed.
[0059]
Returning to FIG. 6, the transfer belt 601 is flexibly in contact with the photosensitive drum 604 with a predetermined nip width, and even if there is a slight speed difference, in the embodiment, the speed difference is ± 0.5% or less. By transferring the image by slipping, the sub-scanning pitch shift is prevented from occurring even if the drive frequency fp of the photosensitive drum is varied.
In a stepping motor control unit (not shown) that drives the photosensitive drum 604, if the drive frequency fp is varied according to the variable information of the drive frequency fd of the movable mirror, the image width in the sub-scanning direction can also be corrected.
[0060]
FIG. 9 is a block diagram showing drive control of the semiconductor laser and the movable mirror.
In the figure, reference numeral 901 is a drive pulse generation unit, 902 is a movable mirror drive unit, 904 is a synchronization detection sensor, 905 is a termination detection sensor, 906 is an LD drive unit, 907 is a clock pulse generation unit, 908 is a phase synchronization unit, 909 Indicates a magnification calculator, and 910 indicates an amplitude calculator.
[0061]
FIG. 10 is a timing chart of the amplitude of the movable mirror and the driving pulse.
The drive pulse generator 901 divides the reference clock by a programmable frequency divider, and once in a half cycle of the movable mirror as shown in FIG. A pulse train (T <T _0/4 ) having a duty of 50% or less is generated at a frequency twice the drive frequency fd (= 1 / T ₀ ) so that a voltage pulse is applied, and a predetermined phase delay is generated by a PLL circuit δ is generated and given to the movable mirror drive unit 902 as the drive frequency fd.
[0062]
The movable mirror performs image recording only during scanning in the same direction during the period of θ _S to −θ _S (0 <θ _S <θ) in the forward period from the scanning angle θ ₀ as the starting point until reaching −θ ₀ . Image recording is not performed during the return period from the scanning angle −θ ₀ to + θ ₀ , in other words, image recording is performed every cycle of the drive frequency fd. Incidentally, θ _S / θ ₀ = 0.7 was set.
[0063]
When the power is turned on and when the system is started from the standby state, the drive frequency fd is varied from the high frequency side by continuously changing the frequency division ratio with a programmable frequency divider, and the light beam is detected with the synchronization detection sensor 904. It is determined that the resonance vibration band is obtained when the scanning angle is expanded until is detected. At the same time, the scanning angle is calculated from the time difference between the scanning start side and the scanning end side, and the drive frequency is set so that the deflection angle (amplitude) of the variable mirror becomes a predetermined value.
[0064]
At this time, since this setting is performed in each of the plurality of vibrating mirror modules, a slight difference in driving frequency occurs between the vibrating mirror modules. In the embodiment, all of the vibrating mirrors have a minimum value among them as a common driving frequency fd. This is given to the module to ensure a deflection angle greater than a predetermined value.
Note that the overlap of the image areas slightly increases with the shift of the scanning angle, but it can be corrected by setting the pixel clock described later.
In the embodiment in which the resonance vibration band of the movable mirror as shown in FIG. 2 is kept constant, the temperature may be controlled by heating the thin film resistor using the same detection method as a criterion.
[0065]
FIG. 11 is a diagram showing an output when the scanning beam passes back and forth through the synchronous detection sensor.
The synchronization detection is performed in the vicinity where the scanning angle becomes θ ₀ , but if the detection signal interval tr of the reciprocating detection signal passing through the sensor 904 is measured and the amplitude is detected by the amplitude calculation unit 910 as shown in FIG. θ ₀ can be adjusted to a predetermined value, and by performing this check at regular intervals other than at the time of startup, the stability of the deflection angle can be further improved even after long-term use.
[0066]
In the embodiment, the sensor 905 is also provided in the vicinity of the scanning angle −θ ₀ to detect the scanning end beam, and the time difference between the termination detection signal and the synchronization detection signal at the scanning start end is measured to be movable. It detects changes in the image recording width due to mirror scanning speed fluctuations and scanning lens shape errors.
As will be described later, this change in the image recording width is corrected by changing the pixel clock.
In the embodiment, since it is constituted by three optical scanning means, control is performed so that the printing operation can be performed after this setting is completed in all the vibrating mirror modules.
[0067]
FIG. 12 is a diagram showing the scanning angle of the movable mirror.
Since the movable mirror is resonantly oscillated, the scanning angle θ changes in a sin wave shape as shown in FIG.
θ = θ ₀ · sin (2πfd · t),
However, (-1/4) .fd <t <(1/4) .fd
On the other hand, it is necessary to print the main scanning dots at a uniform interval on the photosensitive drum surface that is the surface to be scanned, and the imaging characteristics of the scanning lens described above are such that the scanning distance dH / dθ per unit scanning angle is sin ⁻¹ θ. It is necessary to correct the direction of the light beam so that it is proportional to / θ ₀ , that is, as it goes slowly toward the periphery in the center of the image so as to accelerate faster, but it forms an image from the center to the periphery of the scanning lens. It is necessary to perform power distribution so as to keep the points away from each other, and there is a limit in expanding the effective scanning area θ _S with respect to the maximum amplitude θ ₀ .
[0068]
FIG. 13 is a diagram showing the image position, pulse width, and phase difference in the main scanning direction.
In order to keep the spot diameter uniform with only the scanning lens, the scanning efficiency θ _S / θ ₀ <0.5, so in the embodiment, as shown in FIG. Thus, the phase corresponding to each pixel is gradually delayed from the advanced state from the start of recording to the end of recording, and at the same time, the pulse width of each pixel is gradually increased from the long state to the center of the image. The pixel clock fm, which becomes longer in the region from the center of the image to the recording end, is applied to the LD driving unit 906 so as to be shortened, and is improved to θ _S / θ ₀ = 0.7.
[0069]
Hereinafter, a method for changing the pixel clock fm will be described.
The clock pulse generator 907 divides the reference clock f ₀ by a programmable frequency divider based on the variable data, counts the divided clock, and forms a PLL reference signal fa having a pulse length of k clocks. , pixel clock fk is generated by selecting the phase of the reference clock f ₀ based on the variable data in the PLL circuit.
By repeating this every several tens of pixels, dots can be printed at arbitrary positions along the main scan.
[0070]
For the reference clock f _0, the phase synchronization unit 908 selects a clock that is in phase with the synchronization detection signal generated by the synchronization detection sensor 904 from among the clocks delayed by 1 / n of one cycle of the reference clock f _0. , performs the phase synchronization to new reference clock f ₀ in each scan, in the embodiment, the case has to be able to select a clock having a phase different to, the timing to start the clock variable, the movable mirror Correction is performed so that the horizontal state (θ = 0) surely matches the center position of the image recording. Incidentally, if this timing is shifted, the dot interval in the main scanning direction is reduced on the one hand, and a distorted image extending on the other hand.
[0071]
Further, by changing the frequency division ratio of the reference clock f ₀ , the image width in the main scanning direction can be adjusted, and as described above, the time difference between the end detection signal and the synchronization detection signal is measured by the magnification calculator 909. If the time difference is shorter than a predetermined value, the frequency is increased, and if the time difference is longer, the frequency is corrected.
[0072]
【The invention's effect】
According to the first aspect of the present invention, even if the drive frequency is followed according to the scanning speed fluctuation, the main scanning pitch fluctuation and the image width fluctuation do not occur. This prevents the deterioration of the seam accuracy in the case, can perform high-quality image recording , and the scan speed fluctuation measurement uses the output of the synchronous detection sensor and the end detection sensor, so there is no need for special equipment and an inexpensive configuration. Scanning angle θ _S closer to the maximum amplitude with respect to the change in scanning speed by using a vibrating mirror, the characteristic that it is fast at the center of the image, slows at the periphery, and becomes _zero at the maximum amplitude θ ₀ Can maintain the uniformity of the main scanning pitch,
In addition, since the pixel clock is changed by using a phase synchronization means that selects from a plurality of clocks in which one cycle of the reference clock is delayed by 1 / n, color overlay accuracy in multicolor image formation and division scan recording are used. Therefore, even if the vibration mirror amplitude has a phase difference from the drive voltage, the variable timing of the pixel clock can be reliably matched to this amplitude even if the amplitude of the vibration mirror has a phase difference. High-quality image recording without pitch variation over a wide range can be performed, and the amplitude can be secured even when there are various environmental changes, so that stable image formation can be performed for a long period of time and reliability can be improved.
[0075]
According to the second aspect of the present invention, when configuring an image forming apparatus including a plurality of optical scanning devices, a common driving frequency can be set regardless of variations in individual resonance frequencies. Is uniform, the seam accuracy is maintained even at the image end in the sub-scanning direction, and high-quality image formation is performed.
[0076]
According to the invention of claim 3 , since it is possible to avoid the generation of rotational force at least against the progress of the oscillating mirror, it is possible to secure the deflection angle of the oscillating mirror with a smaller rotational force and to save power. it can.
According to the fourth aspect of the present invention, since the rotational force can be applied in the direction of accelerating the traveling of the vibration mirror, the deflection angle of the vibration mirror can be ensured with a smaller rotational force, and power can be saved.
[0078]
According to the fifth aspect of the present invention, even if the drive frequency is tracked according to the temporal change of the resonance frequency, the main scanning pitch fluctuation and the image width fluctuation do not occur. Further, it is possible to prevent the deterioration of the seam accuracy in the divided scanning recording and to perform high-quality image recording.
According to the invention of claim 6 , even if the drive frequency is followed according to the change with time of the resonance frequency, the sub-scanning pitch and the image width are matched, and high-quality image recording can be performed.
[0079]
According to the invention of claim 7 , by setting a common drive frequency in the plurality of optical scanning devices, the pitch of each scanning line is made uniform, and the seam accuracy is maintained even at the image end in the sub-scanning direction, High-quality image formation can be performed.
[Brief description of the drawings]
FIG. 1 is a detailed view of a vibrating mirror module used in an optical scanning device of the present invention.
FIG. 2 is a diagram showing an embodiment for stabilizing a spring constant.
FIG. 3 is a diagram showing a layout of a sub-scanning section of a vibrating mirror module.
FIG. 4 is a perspective view of an optical scanning device according to an embodiment of the present invention.
FIG. 5 is a perspective view of an optical scanning device according to an embodiment of the present invention.
FIG. 6 is a diagram illustrating an example in which the present invention is applied to a color laser printer.
FIG. 7 is a conceptual diagram for explaining joining of scanning lines.
FIG. 8 is a block diagram showing a part of write data processing;
FIG. 9 is a block diagram showing drive control of a semiconductor laser and a movable mirror.
FIG. 10 is a timing chart of movable mirror amplitude and drive pulse.
FIG. 11 is a diagram showing an output when a scanning beam passes back and forth through a synchronous detection sensor.
FIG. 12 is a diagram illustrating a scanning angle of a movable mirror.
FIG. 13 is a diagram illustrating an image position, a pulse width, and a phase difference in the main scanning direction.
FIG. 14 is a diagram for explaining that the deflection angle changes at the same drive frequency due to a temperature change.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 100 Vibrating mirror module 102 Movable mirror 103 Movable electrode 108 Torsion beam 109 Fixed electrode 117 1st reflective surface 118 2nd reflective surface 301 Semiconductor laser 400 Light source unit 401 Semiconductor laser 412 Printed circuit board 413 Synchronization detection sensor 430 Vibrating mirror module 600 Light Scanning device 601 Transfer belt 604 Photosensitive drum 901 Drive pulse generator 902 Movable mirror driver 906 LD driver 910 Amplitude calculator

Claims (7)

A light source, light source driving means for modulating the light source in accordance with image information, a vibration mirror that reciprocally vibrates about a torsion beam as a rotation axis, and scans a light beam from the light source; and a drive frequency of the vibration mirror In an optical scanning device having vibration mirror driving means that is variable according to the resonance frequency inherent to the vibration mirror,
The oscillating mirror has a period from θS to −θS (0 <θS <θ) in the forward period from the scanning angle θ0 as a starting point until it reaches −θ0, and responds to the image information only in the scanning period in the same direction. Used for recording images,
When the scan angle θS is the search start end and the scan angle −θS is the scan end, a synchronization detection sensor that detects the synchronization of the scan start end and a scan end detection sensor that detects the beam at the scan end Provided with amplitude detection means for detecting the amplitude of the vibrating mirror by measuring the time difference between the synchronization detection signal generated from the synchronization detection sensor and the termination detection signal generated from the scanning end detection sensor ,
Based on the amplitude of the oscillating mirror detected by the amplitude detecting means, the drive frequency of the oscillating mirror is changed so that the amplitude of the oscillating mirror is maintained at a predetermined value or more,
The light source driving means detects a change in scanning speed of the vibrating mirror based on the amplitude of the vibrating mirror detected by the amplitude detecting means , and modulates the light emitting source according to the detected scanning speed fluctuation. Phase synchronization means for selecting a pixel clock from a plurality of clocks obtained by delaying one cycle of the reference clock of the pixel clock every 1 / n is a new one based on the synchronization detection signal output from the synchronization detection sensor. An optical scanning device which is changed by selecting a clock . 2. The optical scanning device according to claim 1, wherein the driving frequency of the oscillating mirror is set to be shifted by a predetermined range from the resonance frequency inherent to the oscillating mirror . 3. The optical scanning device according to claim 1, wherein the oscillating mirror driving means has a driving frequency fd of the oscillating mirror.
0 <t <1 / (4 · fd)
An optical scanning device characterized in that the oscillating mirror is driven by applying a driving voltage of the applied time t in the form of pulses . 4. The optical scanning device according to claim 3 , wherein the driving voltage is applied in a range not exceeding a period from the amplitude peak of the vibrating mirror to the amplitude of 0 . A light source, light source driving means for modulating the light source according to image information, a vibration mirror that reciprocally vibrates about a torsion beam as a rotation axis, and scans a light beam from the light source, and a drive frequency of the vibration mirror An optical scanning device having vibration mirror driving means that changes in accordance with a resonance frequency unique to the vibration mirror, a photosensitive member on which an electrostatic image is formed by the optical scanning device, and the electrostatic image is visualized with toner. An image forming apparatus comprising: a developing unit that forms an image; and a transfer unit that transfers a visualized toner image onto a recording sheet.
The oscillating mirror has a period from θS to −θS (0 <θS <θ) in the forward period from the scanning angle θ0 as a starting point until it reaches −θ0, and only according to the image information in the scanning direction in the same direction. Used for recording images,
When the scanning angle θS is the search start end and the scanning angle −θS is the scanning end, a synchronization detection sensor that detects the synchronization of the scanning start end and a scanning end detection sensor that detects the beam at the scanning end Provided with amplitude detection means for detecting the amplitude of the vibrating mirror by measuring the time difference between the synchronization detection signal generated from the synchronization detection sensor and the termination detection signal generated from the scanning end detection sensor,
Based on the amplitude of the oscillating mirror detected by the amplitude detection means, Change the drive frequency of the oscillating mirror so that the amplitude remains above a predetermined value,
The light source driving means detects a change in the scanning speed of the vibrating mirror based on the amplitude of the vibrating mirror detected by the amplitude detecting means for the pixel clock that modulates the light source, and the detected scanning speed fluctuation In response to this, phase synchronization means for selecting one cycle of the reference clock of the pixel clock from a plurality of clocks delayed by 1 / n is newly generated based on the synchronization detection signal output from the synchronization detection sensor. An image forming apparatus, wherein an image is recorded by changing a clock. 6. The optical scanning device according to claim 5 , further comprising a speed variable unit that changes a moving speed of the photoconductor, and performs image recording by changing the moving speed of the photoconductor according to a driving frequency of the vibrating mirror. An image forming apparatus. 7. The image forming apparatus according to claim 5, wherein a plurality of the optical scanning devices are provided, and image recording is performed by resonating and vibrating each vibrating mirror at a common drive frequency.

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