JP5659659B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning device as an exposure means for exposing an image carrier, an image forming apparatus such as a copying machine, a printer, a facsimile, and a plotter provided with the optical scanning device, and a multifunction device provided with at least one of them. About.

  In an image forming apparatus using the Carlson process, latent image formation, development, and transfer are performed according to the rotation of the photosensitive drum. Therefore, in the tandem multicolor image forming apparatus in which a plurality of photosensitive drums are arranged along the transfer direction of the transfer body and the toner images formed at the image forming stations of the respective colors are superimposed, the eccentricity of the photosensitive drum and the variation in the diameter of the photosensitive drum. Due to the time from latent image formation to transfer due to toner, the difference between the photosensitive drums of each color, or the meandering of the speed fluctuations of the transport belt and transfer belt that transports the recording paper, the registration error and skew of each toner image occur. The image quality is deteriorated due to displacement or color change.

Similarly, in the optical scanning device, if the change in the scanning line between the electrostatic latent images formed on the photosensitive drum (which indicates the concept of bending, tilting, bending, deformation, etc.) is not accurately aligned, The scan line to be formed is bent or skewed, which causes color shift or color change.
Conventionally, there is no distinction between the registration deviation and the skew due to the optical scanning device and those other than the optical scanning device, and the detection recorded on the transfer body as disclosed in Patent Literature 1 and Patent Literature 2 is used. Depending on the pattern, it is periodically detected at the time of start-up of the device and between jobs, and registration deviation can be corrected by changing the position of the top line by matching the timing of writing every other surface of the polygon mirror. Has been done.

As for the skew, as disclosed in Patent Document 2, the folding mirror is tilted, or as disclosed in Patent Document 3 and Patent Document 4, a scanning lens having a focusing function in the sub-scanning direction is arranged around the optical axis. The correction is performed by changing the inclination of the scanning line by rotating it to the right.
As described above, a mechanical correction function is provided in the optical scanning apparatus for registration deviation and skew, and correction is automatically performed by incorporating a pulse motor or the like.
On the other hand, correction of the bending of the scanning line is performed by bending the folding mirror as disclosed in Patent Document 2, and as disclosed in Patent Document 5, the shape along the main scanning of the scanning lens is changed in the sub-scanning direction. Also, as disclosed in Patent Document 6, mechanical correction is also performed by rotating the posture of the scanning lens around an axis orthogonal to the sub-scanning section.

In order to rotate in the vicinity of the optical axis in order to correct the tilt of the scanning lens, a fixed fulcrum is arranged at the approximate center in the main scanning direction, one end of each end is a free end, and the other end is a means for adjusting the tilt of the scanning line. In the case of the receiving point received in step 1, the scanning lens is rotated by the temperature change, and the scanning line is inclined.
This is due to the difference in the linear expansion coefficient of each member. In other words, this is due to the difference in material between the member that holds the scanning lens and the component (for example, actuator) of the tilt adjusting means.
The above tilt can be eliminated by driving the tilt adjusting means. However, if the drive frequency increases, that is, if the number of adjustments corresponding to a temperature change increases, productivity in image formation decreases and reliability decreases. Connected.

  The present invention has been made in view of the current situation as described above, and can provide an optical scanning device that can suppress the occurrence of the inclination of the scanning line due to a temperature change and contribute to improvement in productivity and reliability in image formation. Its main purpose.

In order to achieve the above object, the invention according to claim 1 is directed to a light source, a condensing optical element for converging a divergent light beam from the light source, and a light beam from the condensing optical element toward a surface to be scanned. A deflector that performs deflection scanning; and an optical element that collects a light beam from the deflector as a light spot on a surface to be scanned and scans at a constant speed, and includes at least one of the optical elements. An optical element module is configured by a holding member that holds the optical element and a means for adjusting the bending of the optical element, and the optical element module rotates about an axis orthogonal to the sub-scanning section at a substantially central position in the main scanning direction. In an optical scanning device in which possible fixed fulcrums are arranged and one end of both ends is a free end, and the other end is a receiving point received by an inclination adjusting means for adjusting the inclination of the scanning line. the inclination adjustment means may, before Body portion and composed of a fixing member for fixing the main body portion to the optical scanning device, and the fixed support, the optical element module and the tilt adjusting means for driving the abutting movable part in the optical element module, the movable portion And the fixing position of the fixing member to the optical scanning device are arranged on the same plane.

According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the fixed fulcrum and the inclination adjusting means are arranged on the same member .
According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect , the linear expansion coefficient of the fixed member and the position where the fixed member is fixed to the main body portion to the tip of the movable portion. The linear expansion coefficient of the part is the same .
According to a fourth aspect of the present invention, there is provided the optical scanning device according to any one of the first to third aspects, further comprising a pressurizing unit that pressurizes the free end portion of the optical element module toward the fixed fulcrum. In the contact position between the other end and the inclination adjusting means, the inclination adjusting means is arranged in such a direction as to directly receive the direction in which the optical element module is displaced by the pressing means. .
According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, a plurality of the light sources are provided, and a plurality of light beams emitted from these light sources correspond to each. And a plurality of the optical element groups to be imaged on the plurality of scanned surfaces, and the deflector disposed between the light source and the optical element group .

According to a sixth aspect of the present invention, in the image forming apparatus , the optical scanning device according to any one of the first to fifth aspects is provided .

According to the present invention, the influence of linear expansion of the optical element module and the inclination adjusting means can be canceled, and the inclination of the scanning line caused by the temperature change can be greatly reduced.
Since a change in scanning position due to a temperature change can be suppressed, high-quality image formation without color shift or color change can be performed in color image formation.

1 is a schematic perspective view of an optical scanning device according to an embodiment of the present invention. 1 is a schematic sectional view of an image forming apparatus. It is a general | schematic side view which shows 1st Embodiment of the support structure of an optical element. It is a general | schematic side view which shows 2nd Embodiment of the support structure of an optical element. It is a general | schematic side view which shows the prior art example of the support structure of an optical element. It is a figure which shows the detection structure of the shift | offset | difference of the sub-scanning position of a light beam. It is a perspective view of a light source unit. FIG. 6 is a block diagram showing an operation of a write control circuit. It is a timing chart at the time of delaying 1/8 clock phase. It is a figure which shows the example which divides | segments a main scanning area | region into a some area and shifts a phase for every division area. It is a block diagram which shows beam spot position shift control. It is a figure which shows the pattern of the toner patch for a detection. It is a figure which shows an optical axis change means. It is a block diagram of the circuit which controls the phase of a deflector.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The outline of the configuration of a tandem multicolor image forming apparatus 920 equipped with the optical scanning devices 900A and 900B will be described with reference to FIGS.
The color image forming apparatus 920 has an intermediate transfer belt 105 as an intermediate transfer body, and each image forming station provided with photosensitive drums 101, 102, 103, and 104 as image carriers along the moving direction thereof. Are arranged in parallel.
The image forming station having the photoconductive drum 101 has a yellow (Y) toner image, the image forming station having the photoconductive drum 102 has a magenta (M) toner image, and the image forming station having the photoconductive drum 103 has cyan (M). In the image forming station having the photosensitive drum 104, a black (Bk) toner image is formed on the toner image C).

  The image forming station for forming a yellow toner image will be described as a representative example. A charging charger 902Y for uniformly charging the surface of the photosensitive drum 101 and an optical scanning device 900A are formed around the photosensitive drum 101. A developing device 904Y provided with a developing roller 903Y that attaches a charged toner to the electrostatic latent image to be visualized is provided inside the intermediate transfer belt 105, and the toner image on the photosensitive drum 101 is transferred to the intermediate transfer belt 105. A primary transfer roller (not shown) for primary transfer and cleaning means 905Y for scraping and storing the toner remaining on the photosensitive drum 101 after transfer are disposed. Since the other image forming stations have the same configuration, they are distinguished by adding European characters for each color, and description thereof is omitted. In the following description, it is assumed that a common configuration is used without adding European characters for each color.

On the photosensitive drums 101, 102, 103, and 104, a latent image is formed simultaneously by scanning a plurality of lines (four lines in this embodiment) by scanning each surface of the polygon mirror.
The intermediate transfer belt 105 is supported by being wound around three rollers 906a, 906b, and 906c, and is rotated counterclockwise. The yellow, magenta, cyan, and black toner images are sequentially transferred onto the intermediate transfer belt 105 at the appropriate timing, and are superimposed to form a color image.
The recording paper 10 as a sheet-like recording medium is fed from the paper feed tray 907 by the paper feed roller 908 one by one in order from the top, and transferred by the registration roller pair 909 in accordance with the recording start timing in the sub-scanning direction. It is sent out to the part.

The superimposed color images on the intermediate transfer belt 105 are collectively transferred onto the recording paper 10 by a secondary transfer roller 913 as a secondary transfer unit at a transfer site. The recording paper 10 to which the color image has been transferred is sent to a fixing device 910 having a fixing roller 910a and a pressure roller 910b, where the color image is fixed. After the fixing, the recording paper 10 is discharged and stacked on a paper discharge tray 911 formed on the upper surface of the image forming apparatus main body by a pair of paper discharge rollers 912.
As shown in FIG. 1, in this embodiment, an optical scanning device 900A corresponding to yellow and magenta image forming stations and an optical scanning device 900B corresponding to cyan and black image forming stations are provided, and the scanning direction is set. It has become a method of aligning. The optical scanning device 900A and the optical scanning device 900B have exactly the same configuration.
The four photosensitive drums 101, 102, 103, and 104 are arranged at equal intervals along the moving direction of the intermediate transfer belt 105, and sequentially transfer and superimpose different color toner images to form a color image.

Optical scanning devices 900A and 900B, which are optical scanning devices 900 that scan the respective photosensitive drums 101, 102, 103, and 104, are integrally formed, and scan light beams with a polygon mirror 106 as a rotating polygon mirror. Since the rotation direction of the polygon mirror 106 is the same, the image is written so that the respective writing start positions coincide. A plurality of lines are simultaneously recorded by scanning one surface of the polygon mirror.
In the present embodiment, a pair of semiconductor lasers as light sources is provided for each of the photosensitive drums 101, 102, 103, and 104, and scanning is performed by shifting by one line pitch according to the recording density in the sub-scanning direction. Two lines are scanned simultaneously.
Since the optical scanning devices 900A and 900B have the same configuration, only one of them will be described here. The light beams 201 and 202 from the light source units 107 and 108 have portions whose emission positions are different in the sub-scanning direction for each light source unit. In this embodiment, the emission positions of the light source units 107 and 108 have a predetermined height (in this example, 6 mm), the beam from the light source unit 108 is turned back by the incident mirror 111 and directly enters the polygon mirror 106 with the main scanning direction approaching the beam from the light source unit 107 going to the polygon mirror 106. .

The cylinder lenses 113 and 114 are arranged such that one has a common curvature in the plane and the other has a common curvature in the sub-scanning direction, and the optical path lengths to the deflection points of the polygon mirror 106 are equal to each other. 202 is a deflecting surface that is converged so as to be linear in the main scanning direction, and in combination with a toroidal lens described later, the deflection point and the surface of the photoconductor are in a conjugate relationship in the sub-scanning direction so that the surface tilt correction optical system Make.
The non-parallel plate 117 is a glass substrate whose one surface is slightly inclined in the main or sub-scanning direction, and is controlled relative to the light beam from the light source unit 107 serving as a reference by controlling rotation around the optical axis. Adjust the position.
The polygon mirror 106 is a six-sided mirror, and in this embodiment, it is configured in two stages, upper and lower, and a groove is provided so that the intermediate portion not used for deflection is slightly smaller in diameter than the inscribed circle of the polygon mirror 106 to reduce windage loss. It has a shape.

The thickness of one layer of the polygon mirror 106 is about 2 mm in this example. Note that the phases of the upper and lower polygon mirrors 106 are the same. The fθ lens 120 is also integrally formed or joined in two layers, and has a non-arc surface shape that gives power so that the beam moves at a constant speed on the surface of the photosensitive member as the polygon mirror 106 rotates in the main scanning direction. Each beam is imaged in a spot shape on the surface of the photosensitive member by the toroidal lenses 122 and 123 as optical elements provided for each beam, and a latent image is recorded.
In each color station (image forming station), the photosensitive drums 101, 102, 103, which are arranged at equal intervals so that the optical path lengths from the polygon mirror 106 to the photosensitive surface as the scanning surface coincide with each other. A plurality of folding mirrors (three per station in this example) are arranged so that the incident position and the incident angle with respect to 104 are equal.

If the optical path is described for each color station, the beam 201 from the light source unit 107 serving as a reference is deflected at the upper stage of the polygon mirror 106 via the non-parallel plate 117 and the cylinder lens 113, and then the upper layer of the fθ lens 120 is passed through. Passed, reflected by the folding mirror 126, passed through the toroidal lens 122, reflected by the folding mirrors 127, 128 and guided to the photosensitive drum 102 to form a magenta image as a second image forming station.
The light beam 202 from the light source unit 108 is reflected by the incident mirror 111 through the cylinder lens 114, deflected at the lower stage of the polygon mirror 106, passes through the lower layer of the fθ lens 120, and is reflected by the folding mirror 129. The light passes through the toroidal lens 123, is reflected by the folding mirrors 130 and 131, is guided to the photosensitive drum 101, and forms a yellow image as a first image forming station.

Since the other optical scanning unit 900B has the same configuration, a description thereof will be omitted. However, the beam from the light source unit 109 serving as a reference is guided to the photosensitive drum 104, and a black image or a light source is used as the fourth image forming station. The beam from the unit 110 is guided to the photosensitive drum 103 to form a cyan image as a third image forming station.
As described above, the color image forming apparatus 920 forms an electrostatic latent image on the plurality of image carriers (photosensitive drums 101 to 104) by the optical scanning device (900A, 900B), and the electrostatic latent image. The image is developed with different color toners (yellow, magenta, cyan, and black toners) for each image carrier, and the toner images formed on each image carrier are sequentially transferred onto the intermediate transfer member (intermediate transfer belt 105). And an image forming apparatus that obtains a color image by batch transfer to a sheet-like recording medium (recording paper 10).

  Each of the optical scanning devices 900A and 900B is scanned by a light source (light source units 107 to 110), a deflection unit (polygon mirror 106) that scans light beams (201 and 202) from these light sources, and the deflection unit. An optical element (toroidal lens) having a focusing force in at least the sub-scanning direction constituting the image forming means, and an image forming means for forming an image on the scanned surface (photosensitive drums 101 to 104). 122, 123) are rotated in a plane orthogonal to the optical axis thereof, so that the inclination of the scanning line on the surface to be scanned is variable.

[Support structure of optical element]
Hereinafter, an embodiment of a support structure of optical elements constituting the optical element group will be described. In this example, the support structure of the toroidal lens will be described. Here, the toroidal lenses 122 and 123 will be described as the optical element 300.
3 is a front view showing an optical element supporting portion in an embodiment of the optical scanning device of the present invention, FIG. 4 is a front view showing an optical element supporting portion in another embodiment, and FIG. 5 is an optical element supporting portion in a conventional example. FIG.
First, a first embodiment will be described based on FIG. The optical element 300 is housed and held in a holding member 20 composed of a holding member upper 21, a holding member lower 22, and legs 23 a and 23 b located on both sides in the longitudinal direction (the horizontal direction in the drawing). Yes.

The position of the optical element 300 is determined by being attracted by the left and right positioning plate springs 24 a and 24 b fixed to the holding member top 21 with respect to the holding member top 21. Even in the central portion of the holding member upper 21, the optical element 300 is attracted by a curve adjusting plate spring 25 that is fixed to the holding member 21 and serves as an element for adjusting the bending of the optical element. Is deformed to be convex upward.
As the other element of the means for adjusting the bending of the optical element, the optical element 300 is pushed back by the potato screw 26, and the initial adjustment is made so that the bending of the optical element becomes zero.
The above elements are assembled together to form one optical element module 30.

As described above, the upper holding member 21 is connected to the lower holding member 22 via the left and right legs 23a and 23b. That is, the optical element 300 is located at the center surrounded by the upper and lower holding members and the legs.
A lower center portion of the lower holding member 22 is in contact with a convex portion 28 provided on a housing 27 as an apparatus housing, and is rotatable in the longitudinal direction. For easy understanding, the contact point between the lower holding member 22 and the convex portion 28 is indicated as a fixed fulcrum A by a surrounding dotted line.
With this configuration, the optical element module 30 can be rotated around an axis orthogonal to the sub-scanning section, and the inclination of the optical element 300 can be adjusted (γ adjustment).
The free end side of the lower holding member 22 is pressed downward in the direction of the fixed fulcrum by pressurizing means 31 such as a leaf spring fixed to the housing 27. The opposite end of the lower holding member 22 is rotationally displaced upward due to the relationship between the urging force of the pressurizing means 31 on the free end side and the fixed fulcrum A, and is received by the inclination adjusting means 32 to be balanced. .
The inclination adjusting means 32 includes a main body portion 33 such as a motor, an actuator 34 as a movable portion that is displaced by the driving force of the main body portion 33, and a fixing member 35 for fixing the main body portion 33 to the housing 27. Yes. By displacing the actuator 34, the inclination of the optical element 300 is adjusted around the fixed fulcrum A.

Here, the inclination change that occurs when there is a temperature change will be described with reference to FIG. The housing 27, the lower holding member 22, and the legs 24 are made of aluminum (hereinafter simply referred to as “aluminum”), and the actuator 34 of the tilt adjusting means 37 having the fixing member 36 is made of iron. The holding member upper 21 is also pressed downward in the direction of the fixed fulcrum by the pressing means 38 such as a leaf spring at the left end.
When the height direction of the position where the lower support member 22 is in contact with the fixed fulcrum A is used as a reference, all the components expand due to the temperature rise, but the contact position (receiving point) with the actuator 34 on the holding member 21. The height of the lower portion of the holding member 22 and the legs 24 is aluminum, and the height of the linear expansion of aluminum is increased.

On the other hand, the height of the contact position of the actuator 34 with the holding member top 21 is the height of the fixed position C (indicated by the encircled dotted line) relative to the housing 27 of the tilt adjusting means 37 from the fixed fulcrum A is the linear expansion and tilt of aluminum. From the fixed portion (fixed position C) of the adjusting means 37 to the contact position (receiving point B) with the holding member upper 21 is a linear expansion of iron.
Since the linear expansion of iron is smaller than that of aluminum, the upper part 21 of the holding member expands more. As a result, the optical element module 30 has a right-up inclination, and the optical element 300 also has a right-up inclination. End up.
Conversely, if the temperature falls, a downward slope will occur. In order to eliminate this inclination, the actuator 34 may be driven, but it is desirable that the inclination does not occur even if there is a temperature change.

Based on the above-mentioned problems of the prior art, the characteristic configuration in the first embodiment will be described based on FIG.
In the present embodiment, the tilt adjusting means 32 and the like are arranged so that the fixed fulcrum A and the receiving point B are located on the same plane.
With this configuration, no matter how much the holding member 20 or the leg 24 expands or contracts, there is no deviation in the height direction (vertical direction) between the fixed fulcrum A and the receiving point B on the same plane. Therefore, there is no tilt due to temperature change.
Further, in the present embodiment, the fixing position C of the inclination adjusting means 32 with respect to the housing 27 and the receiving point B are provided so as to be located on the same plane. With this configuration, no matter how much the fixing member 35 or the actuator 34 expands or contracts, there is no deviation in the height direction between the fixing position C and the receiving point B on the same plane. Therefore, there is no tilt due to temperature change.

As described above, since the fixed fulcrum A (convex portion 28) and the inclination adjusting means 32 are disposed in the housing 27 as the same member, a deviation in the height direction between the fixed fulcrum A and the fixed position C occurs. Absent. Therefore, there is no tilt due to temperature change.
Further, in the conventional example shown in FIG. 5, both the free end side and the opposite end of the holding member are pressed downward in the direction of the fixed fulcrum by a pressing means such as a leaf spring. On the other hand, in this embodiment, it is a simple structure in which the pressing means is reduced by reversing the direction in which the actuator 34 contacts the optical element module 30.

  The fixing member 35 and the actuator 34 may be formed of a material having the same linear expansion coefficient. By doing so, the actuator 34 extends downward by the same amount as the fixing member 35 extends upward. Therefore, there is no deviation in the height direction between the fixed position C and the receiving point B, and there is no tilt due to temperature change.

Based on FIG. 4, 2nd Embodiment about the support structure of an optical element is described.
In the present embodiment, the left end portion of the holding member upper 21 is extended so that both sides in the longitudinal direction are pressed downward by the pressurizing means 31 and 38.
In this embodiment, the fixed position C and the receiving point B are on the same plane, the fixed fulcrum A and the fixed member 35 are fixed to the same housing 27, and the fixed member 35 and the actuator 34 have the same linear expansion coefficient. And the holding member 20, the leg 24, and the housing 27 have the same linear expansion coefficient.
Therefore, if all these conditions are satisfied, the height of the receiving point B of the holding member 20 is the same as the height of the receiving point B of the actuator 24 even if there is a temperature change, and no tilt occurs.

In the description of FIG. 5, it has been described that the housing 27, the lower holding member 22 and the legs 24 are made of aluminum, and the actuator 34 is made of iron. In this case, if the actuator 34 is made of aluminum, the holding member is maintained even if the temperature changes. The height of the receiving point B and the height of the receiving point B of the actuator 34 are the same, and no tilt occurs.
In this way, the material, dimensions, and configuration of each member are combined such that the height of the receiving point B of the holding member and the height of the receiving point B of the actuator 34 are the same when the temperature changes, so that the temperature change There is no tilting due to.

[Correction in image forming apparatus]
As shown in FIG. 1, substrates 138, 139, 140, and 141 on which a photosensor is mounted for each optical scanning device are arranged on the scanning start side and the scanning end side of the image recording area, and scanned at each image forming station. Detect the beam.
In the present embodiment, the substrates 138 and 140 form a synchronization detection sensor, and the timing of each writing start is measured based on this detection signal. The substrates 139 and 141 serve as end detection sensors, and detect changes in scanning speed by measuring the time difference between detection signals from the synchronization detection sensors. Then, the reference frequency of the pixel clock that modulates each semiconductor laser is reset in inverse proportion to the detected change in scanning speed, thereby resetting the image recorded by each image forming station on the intermediate transfer belt 105. Can be stably maintained.

Further, as shown in FIG. 6, as shown in FIG. 6, any sensor is constituted by a photodiode 152 perpendicular to the main scanning direction and a non-parallel photodiode 153, so that the time difference Δt from the photodiode 152 to the photodiode 153 is reduced. By measuring, the deviation Δy of the sub-scanning position of the light beam can be detected.
The shift Δy in the sub-scanning position is expressed as Δy = (V / tan γ) · Δt using the inclination angle γ of the photodiode 153 and the scanning speed V of the light beam. In this embodiment, Δt is always constant. In addition, the rotational phase of the optical axis deflecting means (described later) or the polygon mirrors is controlled. Thereby, the irradiation position can be held so that the sub-scanning resist of each color image does not shift. Further, by disposing the sensor on both the scanning start side and the scanning end side, it is possible to detect the difference in sub-scanning position deviation between the ends, that is, the inclination of the scanning line.

FIG. 7 is a perspective view of the light source unit, and all the light source units have the same configuration.
The semiconductor lasers 501 and 502 and the coupling lenses 503 and 504 are arranged symmetrically in the main scanning direction with respect to the emission axis for each color scanning unit, and the semiconductor lasers 501 and 502 are fitted to the outer periphery of the package and are respectively base members. It press-fits into 505 and 506 from the back side.
Then, a screw 515 that passes through three points from the front side is screwed and held in contact with the back surface of the holder member 507, and the coupling lenses 503 and 504 are formed to open in a direction opposite to the holder member 507. The outer periphery is abutted against the V-groove portions 508 and 509, and is moved inward by the leaf springs 510, 51510, and 511 and fixed with screws 516.

At this time, the arrangement on the contact surface (surface orthogonal to the optical axis) of the base members 505 and 506 is fixed so that the light emitting points of the semiconductor lasers 501 and 502 are on the optical axis of the coupling lenses 503 and 504. In addition, the position on the V groove (on the optical axis) is adjusted and fixed so that the light emitted from the coupling lenses 503 and 504 becomes a parallel light beam.
The optical axes of the respective outgoing lights are inclined so as to cross each other with respect to the outgoing axes, and in this embodiment, the printed circuit board as a support member is set so that the intersection position is in the vicinity of the reflecting surface of the polygon mirror 106. An inclination of 512 is set.
The printed circuit board 512 on which the drive circuit is formed is mounted on a pedestal erected on the holder member 507 by screwing, and the lead terminals of the semiconductor lasers 501 and 502 are inserted into the through holes and soldered, whereby the light source unit 107. To 110 are integrally formed.

The light source unit inserts and positions the cylindrical portion 513 of each holder member 507 in an engagement hole formed at a different height on the wall surface of the housing that houses the optical scanning device, and abuts the contact surface 514. Screwed.
At this time, by adjusting the tilt amount γ with the cylindrical portion 513 as a reference, the beam spot interval can be adjusted to the scanning line pitch P corresponding to the recording density.

  Next, the operation of the write control circuit will be described with reference to FIG. In the pixel clock generation unit 401, the counter 403 counts the high-frequency clock VCLK generated in the high-frequency clock generation unit circuit 402, and the comparison circuit 404 sets a preset setting value L based on the count value and the duty ratio. , And the phase clock H given from the outside as the transition timing of the pixel clock and comparing with the phase data H indicating the phase shift amount, and instructing the falling edge of the pixel clock PCLK when the count value matches the set value L 1 is output, and when it coincides with the phase data H, a control signal h that instructs the rising edge of the pixel clock PCLK is output. At this time, the counter 403 is reset simultaneously with the control signal h, and a continuous pulse train is formed by counting again from zero.

In this way, the phase data H is given for each clock, and the pixel clock PCLK whose pulse cycle is sequentially changed is generated. In the present embodiment, the pixel clock PCLK is divided by 8 of the high-frequency clock VCLK so that the phase can be varied with a resolution of 1/8 clock.
FIG. 9 shows a timing chart when the phase is delayed by 1/8 clock.
If the duty is 50%, a set value L = 3 is given, and the counter 403 counts 4 and the pixel clock PCLK falls. Assuming that the 1/8 clock phase is delayed, phase data H = 6 is given and rises with 7 counts. At the same time, the counter is reset, so it falls again at 4 counts. That is, the adjacent pulse period is shortened by 1/8 clock.

The pixel clock PCLK generated in this way is supplied to the light source driving unit 406 shown in FIG. 8, and the image data read out by the image processing unit 405 is allocated to each pixel and modulated based on the pixel clock PCLK. Data is generated and the semiconductor lasers 501 and 502 are driven.
By disposing the pixels that shift the phase at a predetermined interval in this way, it is possible to correct partial magnification error distortion along the scanning direction. Such correction of electrical scanning lines is controlled by the image processing unit 405. Here, the vector image is raster-developed, the developed image is divided and shifted in the main scanning direction, and correction is performed by forming a new raster image.
Next, as shown in FIGS. 10A to 10C, the main scanning region is divided into a plurality of sections a to h, and the intervals and shift amounts of pixels for shifting the phase for each divided section are as follows. It is set as shown and given as phase data. Thereby, the positional deviation of the beam spot along the main scanning can be corrected in the same manner as when approximated by a broken line.

Now, assuming that the change in magnification with respect to the main scanning position x is L (x), the change M (x) in the beam spot position deviation is represented by its integrated value, M (x) = ∫L (x) dx.
Assuming that the beam spot position deviation is corrected to zero at the start and end points of the divided section, the deviation of the divided section width due to the change in the magnification of the arbitrary divided section is Δm, and the phase shift resolution is σ (constant) ) If the number of pixels in the divided section is N, the interval between the pixels for shifting the phase is D≈N / (Δm / σ).
However, D is represented by an integer, and the phase may be shifted by σ for each D pixel. In this embodiment, σ is 1/8 pixel.

Therefore, in this case, the beam spot position residual is maximized at an exactly middle position of the divided sections, but each divided position and the number of divided sections may be determined so that the residual is within the allowable range.
FIG. 11 is a block diagram showing beam spot position deviation control in this embodiment.
Within each optical scanning device, the scanning position of the other image forming station is aligned with the reference image form station, and the degree of image overlap between the optical forming devices serving as the reference for each optical scanning device is detected between the optical scanning devices. However, the writing timing and the period of the pixel clock are uniformly corrected for one of the optical scanning units.

The overlay accuracy of each color image is detected as a deviation from the reference station by reading the detection pattern of the toner image formed on the transfer belt 105 to detect the main scanning magnification, the sub-scanning resist, and the inclination of the scanning line. Correction control is performed.
Correction control is performed, for example, at the time of starting up the apparatus or between jobs. When the number of prints for one job increases, correction is performed by interrupting in the middle to suppress deviation due to temperature changes during that time. To do.

  As shown in FIG. 1, the detection means having the function of detecting the skew of the image transferred to the intermediate transfer member includes an illumination LED element 154, a photosensor 155 that receives reflected light, and a pair of condensing lenses 156. In this embodiment, a patch that is provided at three positions, the center and the left and right ends of the image, and that has a black, cyan, magenta, and yellow toner image along the main scanning direction and a patch that is inclined by about 45 °, A line pattern group 1410 arranged in parallel at a predetermined pitch is formed, and a detection time difference from black as a reference color is read according to the movement of the intermediate transfer belt 105.

FIG. 12 shows an example, and the toner image on the detection line is read along with the movement of the intermediate transfer member 105. The vertical direction on the drawing of FIG. 12 corresponds to the main scanning direction, and the theoretical values of the detection time differences tky, tkm, tkc from the reference color black by the line pattern formed in the order of yellow, magenta, cyan, black from the left. The deviation of the main scanning resist is obtained from the sub-scanning resist of each color based on the difference between them and the time difference between the detection times tk, tc, tm and ty with respect to the line pattern inclined by 45 ° for each color.
The scanning line tilt deviation is obtained from the sub-scanning resist difference between both ends and is corrected by tilting the toroidal lenses 122 and 123 by driving the stepping motor 315 or the like in the optical scanning device.

As described above, by adjusting the inclination of the scanning line by tilting the toroidal lenses 122 and 123 so as to correct the skew of the transferred image, a change in the inclination with time occurs due to replacement of the photosensitive drum or the like. Can be corrected, and high-quality image formation without color shift or color change can be performed.
In addition, a skew detecting means for detecting the skew of the transferred image is provided, and the inclination of the scanning line can be regularly monitored by adjusting the inclination of the scanning line based on the detection result. Correction is possible even when the inclination fluctuates, and high-quality image formation without color shift or color change can be performed.

The sub-scanning resist is obtained from the average of the respective detection values, and the writing timing in the sub-scanning direction is matched every other polygon mirror surface, that is, with one scanning line pitch P as a unit.
Further, with the recent increase in quality required for color images, it is necessary to match the registration deviation with an accuracy of one scanning line pitch P or less, so that an image forming station serving as a reference for each optical scanning device, for example, yellow and With respect to the cyan irradiation position, the magenta and black irradiation positions are finely adjusted using the optical axis changing means.
In addition, with respect to registration deviation between the optical scanning units, in other words, yellow and cyan, by controlling the rotational phase of the polygon mirrors to a predetermined value, writing out of the sub-scanning registration deviation detected by the toner image is performed. An excess of one scanning line pitch P or less that cannot be corrected by timing can be corrected.

Further, even between pages, the irradiation position can be stably maintained by using the photodiodes 152 and 153 and performing feedback correction based on the measurement values accumulated during image recording.
The main scanning magnification is obtained from the difference between the main scanning resists at the center and each end, and by adjusting the reference frequency of the pixel clock for modulating each semiconductor laser and the timing from the synchronization detection signal, the entire width of the image and the writing position are made uniform. .
Between pages, the magnification change is constantly monitored based on the detection time of the synchronization detection signal and the end detection signal, the reference frequency is corrected so that the entire width does not change even if there is a temperature change, and the left and right magnifications The expansion / contraction is adjusted with the phase data so as to be uniform.

At this time, if the magnification change for each divided section caused by the temperature change is predicted in advance and weighted phase data is stored in the data table, the distortion of the magnification can be prevented even at the intermediate image height. The magnification can be made uniform over the entire area in the main scanning direction.
In this way, in addition to periodic correction by toner image detection, fluctuations during the job are monitored, and correction is performed even between pages, so that the overlay accuracy of each color image can be achieved without interrupting the printing operation even during the job. Is maintained.

FIGS. 13A and 13B are perspective views of a support portion of a non-parallel plate that is an optical axis changing means, where FIG. 13A is an exploded perspective view and FIG. 13B is a perspective view after assembly.
In FIG. 13, a non-parallel plate 621 (same as the non-parallel plate 117 shown in FIG. 1) is fixed in a central frame of a cylindrical holder member 622 and formed on a support member 624 having a bearing portion 623 as a holder member. The pair of flange portions 626 are inserted in alignment with the notches and returned to the horizontal position so that the flange portions 626 are hooked on the back side and are held rotatably with the fitting portion 625 as a reference while being in close contact with the support member 624. The support member 624 is screwed to the housing with respect to the bottom surface, and the height H5 is set so that the rotation center of the bearing portion 623 is aligned with the emission axis of the light source unit. Can be tilted slightly.

A lever portion 627 is formed at one end of the holder member, and a feed screw formed at the shaft tip of a stepping motor 628 that is engaged and fixed to a through hole 630 formed in the support member 624 is screwed. The non-parallel plate 621 can be rotated along with the movement.
In order to eliminate backlash at this time, a tension force is applied by a spring 629 between the pin 631 of the holder member 622 and the pin 632 of the support member 624 so as to be shifted in one direction.
Here, assuming that the rotation angle is θ, the apex angle of the non-parallel plate is ε, the focal length of the coupling lens is fc, and the sub-scanning magnification of the entire optical system is ζ, the change in the sub-scanning position on the photoreceptor surface is Δy = ζ · fc · (n−1) ε · sin θ.
However, n is a refractive index of a non-parallel plate. In the range of the minute rotation angle, it can be varied substantially in proportion to the rotation angle. In this example, the apex angle ε of the non-parallel plate is about 2 °. In addition to such a non-parallel plate, the same applies when a liquid crystal deflecting element or a galvanometer mirror disclosed in the prior art is used as the optical axis changing means.

As shown in FIG. 1, the yellow and magenta image sub-scanning resists, the third and fourth stations, which are provided at the first and fourth image forming stations and are formed at the first and second image forming stations. The sub-scanning resists for cyan and black images formed in the above are maintained in a state where they are aligned by feedback control. Accordingly, the four color resists can be matched as long as the writing timing between the optical scanning devices is aligned.
FIG. 14 is a block diagram of a circuit for controlling the phase of the polygon mirror 106.
In this embodiment, each of the two image forming stations is divided into two units and scanned by different polygon scanners. Therefore, if the surface phases of the polygon mirrors are not matched, sub-scanning registration deviation occurs between the units.
Each polygon mirror 106 is mounted on a rotor 703 and is rotatably supported on a circuit board 704. In general, the rotor magnet has S and N poles arranged so as to be equally divided in the circumferential direction, and a hall element 705 serving as a rotational position detecting means is provided on the circuit board 704. A rotation position detection signal having a fixed period is generated each time the boundary between the poles passes over the Hall element as it rotates.

The polygon mirror 106 rotates when a pulse signal f0 having a constant frequency is input from the outside according to the number of rotations, and the rotation position detection signal is input by inputting this pulse signal and the rotation position detection signal to the PLL circuit. The polygon mirror 106 is rotated at a constant speed by generating a drive frequency fd whose phase is controlled so as to have a constant period.
Each polygon mirror 106 receives a pulse signal f0 having the same frequency and has the same rotation speed.
On the other hand, the light beam deflected by the polygon mirror is detected by the synchronization detection sensors 138 and 140 at the start end of each scan, and a synchronization detection signal is generated for each surface.

Since the division angle of each surface is constant, this also becomes a pulse signal with a constant period. Therefore, by setting the number of poles so that the number of faces of the polygon mirror 106 and the number of pulses of the rotation position detection signal corresponding to one rotation are equal, the frequency becomes equal and phase control becomes easy.
Usually, since the arrangement of the Hall element 705 and each surface of the polygon mirror 106 are not attached at an angle in the circumferential direction, the rotational position detection signal and the synchronization detection signal from the Hall element 705 have phases. Different.
In this embodiment, in the polygon mirror 106 in each of the optical scanning devices 900A and 900B, synchronous detection is performed at the same image height so that the rotation angle of the polygon mirror matches when the light beam passes through the synchronous detection sensors 138 and 140. Sensors 138 and 140 are arranged.

In addition, the phase of the drive frequency fd output from the PLL circuit is input by inputting the phase difference of one of the synchronization detection signals based on the polygon mirror 106 described in the upper part of the figure to the adder. The rotation phase t of the polygon mirror 106 is controlled so that the detection timing between the synchronization detection signals becomes a predetermined value.
In the present embodiment, the rotational phase t at this time is set as follows.
When the moving speed of the transfer belt is v (mm / s), the registration deviation detected on the transfer belt is d (mm), and the scanning frequency of the polygon mirror is f (Hz), the rotational phase t is t = d / v−k / f. Here, k is an integer that minimizes t.

By always controlling to satisfy this condition, it is possible to satisfactorily correct the registration deviation d between the optical scanning units to 1 line or less.
Note that the scanning frequency f is expressed as f = v · DPI / 25.4 using the recording density DPI, and the rotational speed R of the polygon mirror is R = 60 × f / n using the number of surfaces n. It becomes.
The same applies to the method of scanning the four-station optical scanning means disclosed in the prior art with a single polygon scanner, or the method of arranging four optical scanning means corresponding to each station. .

DESCRIPTION OF SYMBOLS 30 Optical element module 32 Inclination adjustment means 33 Main body part 34 Actuator as a movable part 35 Fixed member 106 Deflector 122, 123 Toroidal lens as an optical element 501, 502 Semiconductor laser as a light source 503, 504 Cup as a condensing optical element Ring lens A Fixed fulcrum B Receiving point C Fixed position

Japanese Patent Publication No.7-19084 Japanese Patent No. 3049606 Japanese Patent Laid-Open No. 11-153765 JP 2003-262816 A JP 2002-148551 A JP 2003-255245 A JP 2004-109761 A JP 2006-184526 A

Claims (6)

A light source, a condensing optical element for converging a divergent light beam from the light source, a deflector for deflecting and scanning the light beam from the condensing optical element toward a scanned surface, and a light beam from the deflector for the scanned surface An optical element that is focused as a light spot and scanned at a constant speed,
An optical element module comprising at least one optical element, a holding member for holding the optical element, and means for adjusting the bending of the optical element;
The optical element module has a fixed fulcrum rotatable around an axis orthogonal to the sub-scanning section at a substantially center in the main scanning direction, and has a free end with one of both ends floating, In the optical scanning device which becomes the receiving point received by the inclination adjusting means for adjusting the inclination of the scanning line,
The tilt adjusting means includes a movable part that contacts the optical element module, a main body that drives the movable part, and a fixing member that fixes the main body to the optical scanning device,
The fixed fulcrum, the contact position of the inclination adjusting means and the optical element module, and the fixed position of the fixing member to the optical scanning device are arranged on the same plane. Optical scanning device. The optical scanning device according to claim 1,
The optical scanning device according to claim 1, wherein the fixed fulcrum and the inclination adjusting means are disposed on the same member. The optical scanning device according to claim 1 or 2,
An optical scanning device characterized in that a linear expansion coefficient of the fixing member and a linear expansion coefficient of a portion from a position where the fixing member is fixed to the main body portion to a tip of the movable portion are the same. In the optical scanning device according to any one of claims 1 to 3,
A pressure unit that pressurizes the free end portion of the optical element module in the direction of the fixed fulcrum; and the optical element module is in contact with the other end portion and the tilt adjustment unit by the pressure unit. An optical scanning device characterized in that the tilt adjusting means is arranged in a direction to directly receive the direction in which the lens is displaced. In the optical scanning device according to any one of claims 1 to 4,
A plurality of the light source units, a plurality of optical element groups that form a plurality of light beams emitted from these light sources on a plurality of the scanned surfaces corresponding to the respective light sources, the light source and the optical element group, An optical scanning apparatus comprising the deflector disposed between the two.   An image forming apparatus comprising the optical scanning device according to claim 1.

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