JP4422235B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a high-speed laser beam printer apparatus or a digital copying apparatus capable of forming a high-speed image by exposing a plurality of light beams at once.
[0002]
[Prior art]
In an image forming apparatus such as a high-speed laser beam printer or a digital copying apparatus, as one of techniques for increasing the image forming speed, the amount of image data formed by one exposure using two or more laser beams. A method of increasing the value has already been put into practical use. In this case, two or more laser diodes are used as light sources, and the distance (interval) between the beam spots of the laser beams emitted from the respective laser diodes is a distance (interval) corresponding to the required resolution. Each laser diode is arranged in such a manner.
[0003]
By the way, as a method of setting the interval between the beam spots of the laser beams to an interval corresponding to the required resolution, a “number of light sources + 1” photodetector is used, and the first (from the first laser diode) is used. The position of the first laser diode is adjusted so that the first laser beam is positioned between the first and second photodetectors, and the second laser beam (from the second laser diode) is adjusted by, for example, a galvanometer mirror or an active prism. There is known a method of adjusting a position through which a laser beam from a second laser diode passes so as to be positioned between the second and third photodetectors.
[0004]
For example, when the resolution is 600 dpi (dots per inch), for example, the photodetector is usually arranged at a position where the beam spot of the laser beam is minimized, and therefore, as shown in FIG. , PD2 and PD3 are arranged at intervals of 42 μm.
[0005]
[Problems to be solved by the invention]
However, for example, when the resolution is 600 dpi, there is a problem that the cost of the photodetector increases because high positional accuracy is required in the step of arranging the intervals between the photodetectors at 42 μm.
[0006]
Further, as shown in FIG. 8B, the diameter of the beam spot of the laser beam is 60 to 70 μm. Therefore, three photodetectors arranged at intervals of 42 μm and a detection circuit as shown in FIG. 8C. As shown in FIG. 8D, there is a problem that the two beam spots are overlapped and accurate positioning becomes difficult and accuracy is lowered. 8C integrates the difference signal out1 obtained by the operational amplifiers OP1 and OP1 that detect the difference signal between the output of PD1 and the output of PD2 for the detection timing time defined by the switch SW1. Integration circuit C1-OP3, from integration circuit C2-OP4 that integrates difference signal out2 obtained by operational amplifiers OP2 and OP2 for detecting the difference signal between the output of PD2 and the output of PD3 for the detection timing time defined by switch SW1. Composed. Also, 1 to 3 in FIG. 8D are outputs when the beam spot is located at the center of PD1 and PD2, outputs when the beam spot is located biased to PD1, and Each output is shown when the beam spot is located further on the PD3 than the PD2, and the output of the difference signal OP1 is unevenly distributed at 0V, minus (−), and plus (+) minute, respectively. Output.
[0007]
An object of the present invention is to provide an image forming apparatus capable of appropriately setting an interval between two laser beams and improving an image.
[0008]
[Means for Solving the Problems]
The present invention has been made based on the above-described problems. Arranged so that the polarization directions of the laser beams emitted from each of them are orthogonal to each other Provided between the first and second laser diodes, the first optical means for directing the laser beams from the respective laser diodes in the same direction, and the second laser diode and the first optical means. The second optical means for shifting the optical path of the laser beam from the second laser diode in parallel, and the respective laser beams directed in the same direction by the first optical means are continuously provided in a predetermined direction. Rotation reflecting means for reflecting on A polarization beam splitter, having a polarization plane to which polarization in a direction orthogonal to the polarization direction of the laser beam emitted from the second laser diode is given; Separating means for separating the respective laser beams reflected by the rotary reflecting means in different directions and a plurality of detection regions, and detecting each laser beam separated by the separating means to detect laser Light detection means for outputting an electric signal having a magnitude corresponding to the light intensity of the beam; The laser beam from the second laser diode separated by the separation means between the separation means and the light detection means is compared with the laser beam from the first laser diode on the light detection means. A third optical means for guiding the outer periphery on the photosensitive member so as to have a predetermined interval in the sub-scanning direction; Drive means for rotating the second optical means by a predetermined amount based on an electric signal generated by a laser beam from the second laser diode among electric signals obtained by the light detection means. An image forming apparatus having a two-beam exposure apparatus is provided.
[0009]
Further, the present invention irradiates light toward a photosensitive member that is formed in a rotatable cylindrical shape, and the charge held by the light is selectively attenuated to generate an electrostatic image. The first and second laser diodes in which the planes of polarization of the light emitted from each of them are orthogonal to each other and the lines connecting them are arranged in a plane parallel to the axial direction of the photoreceptor; A parallel flat glass that translates the direction in which the light from one of the first and second laser diodes travels in the axial direction of the photosensitive member, and each of the light that has passed through the parallel flat glass and the other one of the light. A prism that is directed in the same direction, a prism unit that aligns light from the respective laser diodes in a direction perpendicular to the axial direction of the photosensitive member, and a plurality of reflecting surfaces that are rotatably formed A polygonal mirror that continuously reflects the respective light aligned by the prism unit in the axial direction of the photoconductor, and polarization in a direction orthogonal to the direction of polarization of the light that has passed through the parallel plate glass. A polarizing beam splitter that has a given polarization plane and separates light that has passed through the parallel plate glass out of the respective lights reflected by the polygonal mirror, and a plurality of detection regions, and the polarization A detector that detects each of the lights separated by a beam splitter and outputs an electric signal having a magnitude corresponding to the light intensity of the light; and is disposed between the polarizing beam splitter and the photodetector, and the polarized beam. The light separated by the splitter is reflected on the detection surface of the photodetector. light For light that has passed through the beam splitter, At a predetermined interval in the sub-scanning direction on the outer periphery of the photoconductor And a driving means for rotating the prism by a predetermined amount based on an electric signal generated by light separated by the polarization beam splitter among electric signals obtained by the photodetector. An image forming apparatus having a two-beam exposure apparatus is provided.
[0010]
Furthermore, the present invention irradiates light toward a photoconductor that is formed in a rotatable cylindrical shape, and the charge held by the light is selectively attenuated to generate an electrostatic image. The first and second laser diodes in which the planes of polarization of the light emitted from each of them are orthogonal to each other and the lines connecting them are arranged in a plane parallel to the axial direction of the photoreceptor; A parallel flat glass that translates the direction in which the light from one of the first and second laser diodes travels in the axial direction of the photosensitive member, and each of the light that has passed through the parallel flat glass and the other one of the light. A prism that is directed in the same direction, a prism unit that aligns light from the respective laser diodes in a direction orthogonal to the axial direction of the photosensitive member, and a plurality of reflecting surfaces that are rotatably formed. The polygonal mirror that continuously reflects the respective lights aligned by the prism unit in the axial direction of the photoconductor, and the polarization in the direction orthogonal to the polarization direction of the light that has passed through the parallel plate glass A polarizing beam splitter that separates light that has passed through the parallel plate glass out of the respective light reflected by the polygonal mirror, and a plurality of detection regions, A photodetector that detects the respective lights separated by the polarization beam splitter and outputs an electric signal having a magnitude corresponding to the light intensity of the light, and is disposed between the polarization beam splitter and the photodetector, and the polarization The light separated by the beam splitter is reflected on the detection surface of the photodetector. light For light that has passed through the beam splitter, In the sub-scanning direction which is the axial direction of the photoconductor by the polygon mirror A prism mirror that guides to a position separated by 100 μm, and an amount by which the prism should be rotated is set based on an electrical signal generated by light separated by the polarization beam splitter among electrical signals obtained by the photodetector. A two-beam exposure apparatus comprising: a signal processing unit for driving the actuator that rotates the prism according to an amount of rotation of the prism generated by the signal processing unit. An image forming apparatus is provided.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 schematically shows an image forming apparatus, that is, a digital copying apparatus having a two-beam exposure apparatus according to an embodiment of the present invention.
[0013]
As shown in FIG. 1, the digital copying apparatus 1 includes a scanner unit 10 that reads a document image and a printer unit 20 that is an image forming unit.
[0014]
The scanner unit 10 has predetermined imaging characteristics for light from the first carriage 11 formed to be movable in the direction of the arrow, the second carriage 12 that is moved by following the first carriage 11, and the light from the second carriage 12. A reduction lens 13 to be applied, a photoelectric conversion element (CCD sensor) 14 that photoelectrically converts light given predetermined imaging characteristics by the reduction lens 13 and outputs an electrical signal, a document table 15 that holds a document O, a document table 15 A document cover 16 and the like for pressing the document O against the document are provided.
[0015]
The document O set on the document table 15 is illuminated by light from the light source 17 provided on the first carriage 11 and reflects reflected light in which light and dark corresponding to the presence or absence of an image is distributed. This reflected light is incident on the reduction lens 13 as image information of the document O via the mirror 11a of the first carriage and the 12a and 12b of the second carriage.
[0016]
The reflected light from the document O guided to the reduction lens 13 is condensed on the light receiving surface of the CCD sensor (photoelectric conversion element) 14 by the reduction lens 13.
[0017]
Thereafter, a carriage driving motor (not shown) is rotated, and the first carriage 11 and the second carriage 12 are moved along the document table 15 so that the image information of the document O, that is, reflected light, is extended from the mirror 11a. The image is sequentially taken out in a direction orthogonal to the direction in which the mirror 11a extends with a predetermined width along the direction in which the image is drawn, and all image information of the document O is guided to the CCD sensor.
[0018]
As described above, the image of the document O placed on the document table 15 is captured by the CCD sensor 14 for each line along the first direction in which the mirror 11a extends, and image processing is performed. The circuit 17 converts the image into a digital image signal indicating the density of the image.
[0019]
The printer unit 20 includes a two-beam exposure apparatus 100 described below with reference to FIG. 2 and an electrophotographic image forming unit 21 capable of forming an image on a recording paper P that is an image forming medium.
[0020]
The two laser diodes of the two-beam exposure apparatus 100 emit light while changing the light intensity in order to form a latent image on the photosensitive drum 22 in accordance with the laser modulation signal generated based on the digital image signal described above. The light from the laser diode is continuously reflected by the polygonal mirror described below in the same direction as the reading line when the scanner unit 10 reads an image, and the exposure position X on the outer peripheral surface of the photosensitive drum 22 is reflected. Thus, the light is sequentially irradiated in the axial direction of the photosensitive drum 22.
[0021]
Thereafter, the photosensitive drum 22 is rotated at a predetermined speed in the direction of the arrow, so that two laser beams sequentially deflected by the deflecting device are exposed on the outer periphery of the photosensitive drum 22 at predetermined intervals.
[0022]
In this way, an electrostatic latent image corresponding to the image signal is formed on the outer periphery of the photosensitive drum 22.
[0023]
The electrostatic latent image formed on the outer periphery of the photosensitive drum 22 is developed with toner from the developing device 23, conveyed to a position facing the transfer device 24 by rotation of the photosensitive drum 22, and supplied from the paper cassette 25. One sheet is taken out by the paper roller 26 and the separation roller 27, and is transferred by the electric field from the transfer device 24 onto the recording paper P supplied with the timing aligned by the aligning roller 28.
[0024]
The recording paper P to which the toner image is transferred is separated together with the toner by the separation device 29 and guided to the fixing device 31 by the transport device 30.
[0025]
The recording paper P guided to the fixing device 31 is discharged onto the tray 33 by the paper discharge roller 32 after the toner (toner image) is fixed by heat and pressure from the fixing device 31.
[0026]
On the other hand, the photosensitive drum 22 after the toner image (toner) is transferred to the recording paper P by the transfer device 24 is opposed to the cleaning device 34 as a result of the subsequent rotation, and the transfer residual toner (residual toner) remaining on the outer periphery. ) Is removed, and the state before the surface potential is supplied by the charging device 35 is returned to the initial state, and the next image formation becomes possible.
[0027]
By repeating the above process, a continuous image forming operation can be performed.
[0028]
As described above, the document O set on the document table 15 is read by the scanner unit 10, and the read image information is converted into a toner image by the printer unit 20 and output to the recording paper P. Copied.
[0029]
2 is a schematic diagram illustrating a state in which image light (laser beam) is irradiated onto the photosensitive drum 22 by the two-beam exposure apparatus 100 in the image forming apparatus shown in FIG.
[0030]
As shown in FIG. 2, in the two-beam exposure apparatus 100, the laser beams LA and LB emitted from the first laser diode LD1 and the second laser diode LD2 are individually applied to the respective laser diodes. The two collimator lenses CL1 and CL2 are collimated, and the traveling direction is aligned by the first prism PR1. A second prism (parallel plate glass) that can shift in parallel the traveling direction of the laser beam emitted by the laser diode LD2 between the CL2 that collimates the laser beam from the laser diode LD2 and the prism PR1. ) PR2 is provided. Each laser diode LD1, LD2 is on the same plane, and the direction of the polarization plane (polarization plane) of the laser beam LA from the laser diode LD1 and the polarization plane (polarization plane) of the laser beam LB from the laser diode LD2. ) Are arranged so that the directions are perpendicular to each other. At this time, the first and second laser diodes LD1 and LD2 are arranged so that the plane in which each is disposed and the axial direction of the photosensitive drum 22 are parallel to each other.
[0031]
The two laser beams LA and LB whose traveling directions are aligned by the first prism PR1 are mutually positioned by a prism unit including the third and fourth prisms PR3 and PR4 described in detail with reference to FIG. Is converted from the direction parallel to the axis of the photosensitive drum 22 (lateral direction) to the rotational direction (vertical direction) of the outer periphery of the photosensitive drum 22. That is, when the image is exposed in the axial direction of the photosensitive drum 22, two lines of images can be exposed simultaneously.
[0032]
The two beams converted into the vertical columns are collected by the cylindrical lens C1 infinitely with respect to the axial direction of the reflecting surface of the polygonal mirror POL (the vertical direction, ie, the direction orthogonal to the axial direction of the photosensitive drum 22). The light is guided to an arbitrary reflecting surface of the mirror POL and reflected toward the photosensitive drum 22.
[0033]
The respective laser beams LA and LB reflected by an arbitrary reflecting surface of the polygonal mirror POL are rotated by the first and second fθ lenses fθ1 and fθ2 and the rotation angle θ of each reflecting surface of the polygonal mirror POL and two A predetermined convergence is given so that the relationship with the focal length f defined by the fθ lenses fθ1 and fθ2 satisfies the image height h, that is, “h = fθ” is satisfied.
[0034]
The respective laser beams LA and LB that have passed through the first and second fθ lenses fθ1 and fθ2 are reflected by the second cylindrical lens C2 from the reflection surface of the polygonal mirror POL when incident on the first cylindrical lens C1. The influence of the difference in inclination with respect to the axis is removed, bent by the output mirror M, and exposed to a predetermined position (X shown in FIG. 1) of the photosensitive drum 22 along with the rotation of the polygonal mirror POL. Irradiation is sequentially performed in the axial direction of the body drum 22. At this time, the distance between the first and second laser beams LA and LB from the first and second laser diodes LD1 and LD2 is defined according to the required resolution, for example, 600 dpi (dot per In inch), it is approximately 42 μm. Note that the interval between the laser beams LA and LB is determined based on the first laser beam LA detected by the detection method described below with reference to FIG. Is corrected to the target value (set value).
[0035]
When the two laser beams LA and LB are reflected by an arbitrary reflecting surface of the polygonal mirror POL, they are reflected to a non-image area, that is, an area outside the width of the effective image area of the photosensitive drum 22 to be cylindrical. Respective laser beams LA and LB that have passed through the lens C2 are modulated in intensity by the image information from the image processing circuit 17 to form the latent image on the photosensitive drum 22 by modulating the intensity of the laser beams LA and LB. In order to define, it enters into the photodetector PD which detects at least one of the laser beams LA and LB. Note that the photodetector PD includes three detection areas arranged at predetermined intervals and a fourth detection area provided in a direction orthogonal to the three areas, as will be described below with reference to FIG. It is a split photo detector.
[0036]
Between the photo detector PD and the second cylindrical lens C2, a condensing lens OL for condensing the laser beams LA and LB to be detected and a polarization beam splitter PBS are provided on the light receiving surface of the photo detector PD. Thereby, the laser beams LA and LB condensed to a predetermined beam spot diameter are incident on the photodetector PD after being separated at a predetermined interval. That is, the laser beam separated by the polarization beam splitter PBS is a mirror that guides the separated laser beam at a predetermined interval compared to the position where the laser beam that has passed through the polarization beam splitter is focused on the photodetector PD. The light is reflected by the prism (reflection mirror) PR5 and irradiated to the photodetector PD. In the example shown in FIG. 2, the polarization direction of the polarization plane of the polarization beam splitter PBS and the polarization plane of the laser beam LB are matched so that the second laser beam LB is separated by the polarization beam splitter PBS. Yes.
[0037]
The output of the photodetector PD is converted into a difference signal between the light intensity of the laser beam LA and the light intensity of the laser beam LB by the differential circuit 111, integrated by the integration circuit 112, and processed by the main control circuit 110 by the AD converter 113. (Recognized) is converted into a possible digital signal. Since the difference signal of the output of the photodetector PD thus obtained corresponds to the distance between the two laser beams LA and LB, the second prism PR2 is operated by the operation of the actuator 114 under the control of the main control circuit 110. Is rotated by a predetermined amount, the interval between the laser beams LA and LB is set to a predetermined amount. That is, the position of the second laser beam LB can be set to a position at a predetermined interval with respect to the first laser beam LA.
[0038]
The output of the photodetector PD is also synthesized by the summing circuit 115 and binarized by the binarization circuit 116, and used as a horizontal synchronization signal “H-SYNC” for defining the exposure timing of the photosensitive drum 22. The
[0039]
FIG. 3 shows the third and third embodiments of the two-beam exposure apparatus 100 shown in FIG. Second FIG. 6 is a schematic diagram illustrating the configuration and operation of four prisms PR3 and PR4.
[0040]
As shown in FIG. 3 (a), the prisms PR3 and PR4 which are seen as one overlapping when viewed from above are third prisms as shown in FIGS. 3 (b) and 3 (c). The laser beams LA and LB reflected by the inclined surface of the right-angle prism PR3 are incident on the inclined surface of the right-angle prism PR4, which is the fourth prism that is in close contact with the third prism PR3, with the inclined surface rotated by 90 °. As shown three-dimensionally in FIG. 3D, the arrangement direction of the two laser beams LA and LB is changed from horizontal to vertical and emitted from the fourth prism PR4.
[0041]
FIGS. 3E and 3F are schematic views for explaining another embodiment of the prism unit shown in FIGS. 3B to 3D. The laser beams LA and LB are those of the third prism PR3. The light is reflected on the slope without passing through the prism PR3, and is similarly reflected on the slope of the fourth prism PR4 without passing through the prism PR4. That is, as shown in FIG. 3G, the arrangement direction of the two laser beams LA and LB is changed from horizontal to vertical without passing through the prism. It is to be noted that the reflecting surfaces of the two prisms are arranged in a positional relationship rotated by 90 ° as in the example described above. Further, according to this configuration, the respective laser beams LA and LB are not damaged by both prisms.
[0042]
FIG. 4 is a schematic diagram for explaining the photodetector PD and its output circuit of the two-beam exposure apparatus 100 shown in FIG.
[0043]
As shown in FIG. 4, the photodetector PD includes first to third detection areas a, b, and c in which the width in the sub-scanning direction, that is, the rotation axis direction of the polygonal mirror POL is 100 μm, and the detection area a , B, and c have a fourth detection region d provided so as to be in contact with each detection region at one end in the short side direction. The first to third detection areas a, b, and c are arranged so that the long side direction is in contact with each other. Therefore, the interval between the first detection area a and the third detection area c is approximately 100 μm.
[0044]
In this photodetector PD, the outputs of the first and second detection areas a and b are differentially output to the output terminal out1, and the outputs of the second and third detection areas b and c are differentially output to the output terminal out2. Is output as That is, OP1 and OP2 in FIG. 4 correspond to the differential circuit 111 described in FIG.
[0045]
The outputs of the output terminals out1 and out2 are integrated for a certain time defined by the switches sw1 and sw2 by an integrating circuit including C1 and C2, respectively, and output to the output terminals out4 and out5 (integrating circuit 112).
[0046]
Outputs from the output terminals out4 and out5 are A / D converted by the AD converter shown in FIG. 2 and input to the main control circuit 110, respectively. Thereby, the operation amount of the actuator 115 for rotating the prism PR2 is determined, and the prism PR2 is rotated by a predetermined angle.
[0047]
The outputs of the first to third detection areas a, b, and c of the photodetector PD are simply added independently from the components output to the output terminals out1 and out2. The added output is combined with the output of the fourth detection region d, which is current-voltaged by OP7, by OP6 as a summing circuit, and is output to the output terminal out3. The output of the output terminal 3 is used as a horizontal synchronization signal H-SYNC. H-SYNC is defined by a zero cross obtained by masking a signal obtained by binarizing the output of the output end out3 with a signal obtained by binarizing the sum of outputs from the first to fourth detection regions. Is done.
[0048]
Next, a method for setting the interval between the two laser beams LA and Lb, which are exposure beams emitted from the two-beam exposure apparatus 100 toward the photosensitive drum 22, using the four-divided photodetector PD shown in FIG. Will be explained.
[0049]
First, only LD1 is caused to emit light, and LD1 is positioned and fixed while referring to the outputs of the first and second detection areas a and b of the photodetector PD. That is, the position of LD1 is set so that the output of the output end out1 which is the differential output of the outputs of the first and second detection regions a and b becomes “0”.
[0050]
Next, the actuator 115 is energized so that the laser beam LB from the LD 2 is positioned at the center of the second and third detection regions while referring to the outputs of the second and third detection regions b and c of the photodetector PD. Thus, the rotation amount of the prism PR2 is changed. That is, the position of LD2 is set so that the output of the output end out2 which is the differential output of the outputs of the second and third detection regions b and c becomes “0” as shown by out2 (b) in FIG. To do. In FIG. 5, out2 (a) shows a state where the laser beam LB is shifted to the second detection region b side, and out2 (c) shows a state where the laser beam LB is shifted to the third detection region c side. Yes.
[0051]
As described above, the adjustment work is simplified by adopting a method of shifting the optical path of the laser beam LB from the LD 2 in parallel after fixing the position of the LD 1. Further, in the photodetector PD, the interval between the boundary portion between the first detection region a and the second detection region b and the boundary portion between the second detection region b and the third detection region c is 100 μm. The photodetector PD can be easily manufactured, and the component cost is reduced.
[0052]
FIG. 6 is a schematic diagram for explaining an embodiment different from that shown in FIG. 4 of the photodetector PD applicable to the two-beam exposure apparatus 100 shown in FIG. 2 and its output circuit.
[0053]
As shown in FIG. 6, the photodetector PD includes first to fourth detection areas a, b, c, and d each having a width of 100 μm in the sub-scanning direction, that is, the rotational axis direction of the polygonal mirror POL, respectively. Detection regions a, b, c, and d have a fifth detection region e provided in contact with each detection region at one end in the short side direction. The first to fourth detection areas a, b, c, and d are arranged so that the long side directions thereof are in contact with each other.
[0054]
In this photodetector PD, the outputs of the first and second detection areas a and b are output to the output end out1, and the outputs of the third and fourth detection areas c and d are output to the output end out2, respectively. Is output as
[0055]
Outputs from the output terminals out1 and out2 are integrated for a predetermined time defined by the switches sw1 and sw2 by an integrating circuit including C1 and C2, respectively, and output to the output terminals out4 and out5.
[0056]
Outputs from the output terminals out4 and out5 are A / D converted by the AD converter shown in FIG. 2 and input to the main control circuit 110, respectively. Thereby, the operation amount of the actuator 115 for rotating the prism PR2 is determined, and the prism PR2 is rotated by a predetermined angle.
[0057]
The outputs of the first to fourth detection areas a, b, c, and d of the photodetector PD are added independently of the components output to the output terminals out1 and out2. This added output is combined with the output of the fifth detection region e that is current-voltaged by OP7 by OP6 as a summing circuit, and is output to the output terminal out3. The output of the output terminal 3 is used as a horizontal synchronization signal H-SYNC. The H-SYNC is based on a zero cross obtained by masking a signal obtained by binarizing the output of the output terminal out3 with a signal obtained by binarizing the sum of outputs from the first to fifth detection regions. Defined.
[0058]
Next, a method for setting the interval between the two laser beams LA and Lb, which are exposure beams emitted from the two-beam exposure apparatus 100 toward the photosensitive drum 22, using the five-divided photodetector PD shown in FIG. Will be explained.
[0059]
First, the LD 1 is positioned and fixed while referring to the outputs of the first and second detection areas a and b of the photodetector PD. That is, the position of LD1 is set so that the output of the output end out1 which is the differential output of the outputs of the first and second detection regions a and b becomes “0”.
[0060]
Next, the actuator 115 is energized so that the laser beam LB from the LD 2 is positioned at the center of the third and fourth detection regions while referring to the outputs of the third and fourth detection regions c and d of the photodetector PD. Thus, the rotation amount of the prism PR2 is changed. That is, the position of LD2 is set so that the output of the output end out2 which is the differential output of the outputs of the third and fourth detection regions c and d becomes “0” as shown in out2 (b) in FIG. To do. In FIG. 7, out2 (a) shows a state where the laser beam LB is shifted to the second detection region b side, and out2 (c) shows a state where the laser beam LB is shifted to the third detection region c side. Yes.
[0061]
In this way, the position of the laser diode LD1 is set by detecting the laser beam LA emitted from the first laser diode LD1 using the photodetector PD having a plurality of detection areas with a large pitch that can be easily manufactured. The laser beam LB emitted from the second laser diode LD2 is guided to a predetermined position of the photodetector PD with the laser beam LA as a reference while the beam LA is detected by the photodetector PD under a predetermined condition. By shifting the optical path of the beam LB by the rotation of the parallel prism, the interval between the two laser beams can be accurately set to a reference interval. As a result, density differences and jitter that may occur in the electrostatic latent image formed on the photosensitive drum 22 are suppressed.
[0062]
【The invention's effect】
As described above, according to the present invention, in the electronic copying apparatus as the image forming apparatus, one of the two laser beams emitted from the two-beam exposure apparatus as the exposure unit is used as a plurality of detection areas. By detecting in a predetermined detection area of the photodetector to identify the position of the laser diode and shifting the optical path of the laser beam in parallel so that other laser beams can be detected in the predetermined detection area, the sub-scanning direction The beam interval can be kept constant. This facilitates assembly adjustment and reduces the adjustment time. Further, since the distance between the beams is kept constant, the image quality is improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the configuration of a digital copying apparatus according to the present invention.
FIG. 2 is a schematic view showing a two-beam exposure apparatus incorporated in the copying apparatus shown in FIG.
FIG. 3 is a schematic diagram illustrating the configuration of third and fourth prisms PR3 and PR4 of the two-beam exposure apparatus shown in FIG.
4 is a schematic diagram showing a photodetector and its output circuit of the two-beam exposure apparatus shown in FIG. 2. FIG.
FIG. 5 is a schematic diagram showing characteristics of an output signal output by the photodetector and the output circuit shown in FIG. 4;
6 is a schematic diagram showing another embodiment of the photodetector and its output circuit shown in FIG. 4; FIG.
7 is a schematic diagram showing characteristics of an output signal output by the photodetector and the output circuit shown in FIG. 6;
FIG. 8 is a schematic diagram showing an output signal output by a conventional photodetector and its output circuit.
[Explanation of symbols]
1 ... Digital copying machine,
10: Scanner unit,
14 ... CCD sensor,
15 ... manuscript table,
17 Image processing circuit
20: Printer section,
22 ... photosensitive drum,
23. Developing device,
24 ... Transfer device,
31. Fixing device,
100 ... 2 beam exposure apparatus,
110 ... main control circuit,
111... Differential circuit,
112... Integration circuit,
113 ... AD converter,
114 ... Actuator,
115...
116... Binarization circuit,
LD1... First laser diode,
LD2 ... second laser diode,
PR1 ... Prism,
PR2 ... Parallel plate prism,
PR5 ... Mirror prism,
PBS ・ ・ ・ Polarizing beam splitter,
PD: Photo detector.

Claims (7)

First and second laser diodes arranged such that the directions of polarization of the laser beams emitted by each are orthogonal to each other ;
First optical means for directing laser beams from the respective laser diodes in the same direction;
A second optical means provided between the second laser diode and the first optical means for shifting in parallel the optical path of the laser beam from the second laser diode;
Rotational reflecting means for continuously reflecting the respective laser beams directed in the same direction by the first optical means in a predetermined direction;
A polarization beam splitter, the polarization beam splitter having a polarization plane to which a polarization in a direction orthogonal to a polarization direction of a laser beam emitted from the second laser diode is provided, and each of which is reflected by the rotary reflection unit Separating means for separating the laser beams in different directions;
A light detection means that has a plurality of detection regions, detects each of the laser beams separated by the separation means, and outputs an electrical signal having a magnitude corresponding to the light intensity of the laser beam;
The laser beam from the second laser diode separated by the separation means between the separation means and the light detection means is compared with the laser beam from the first laser diode on the light detection means. A third optical means for guiding the outer periphery on the photosensitive member so as to have a predetermined interval in the sub-scanning direction;
Drive means for rotating the second optical means by a predetermined amount based on an electric signal generated by a laser beam from the second laser diode among electric signals obtained by the light detection means;
An image forming apparatus having a two-beam exposure apparatus comprising: 2. The image forming apparatus according to claim 1 , wherein an interval in the sub-scanning direction of the second laser beam with respect to the first laser beam on the light detection unit is 100 μm . It is formed in a rotatable cylindrical shape, and the electric charge held by light irradiation is selectively attenuated to irradiate light toward a photoconductor that generates an electrostatic image, each radiating First and second laser diodes in which the planes of polarization of light are orthogonal to each other, and the lines connecting them are arranged in a plane parallel to the axial direction of the photoreceptor;
A parallel plate glass that translates the direction in which the light from one of the first and second laser diodes travels in the axial direction of the photoreceptor;
A prism that directs each of the light that has passed through the parallel plate glass and the other one of the light in the same direction;
A prism unit that aligns the light from each of the laser diodes in a direction perpendicular to the axial direction of the photoreceptor;
A polygonal mirror that is formed so that a plurality of reflecting surfaces are rotatable, and each of the lights aligned by the prism unit is continuously reflected in the axial direction of the photosensitive member;
It has a polarization plane given polarization in a direction orthogonal to the direction of polarization of light that has passed through the parallel flat glass, and has passed through the parallel flat glass of the respective light reflected by the polygonal mirror. A polarizing beam splitter that separates the light;
A photodetector having a plurality of detection regions, detecting each of the lights separated by the polarization beam splitter, and outputting an electric signal having a magnitude corresponding to the light intensity of the light;
The light arranged between the polarization beam splitter and the photodetector and separated by the polarization beam splitter is arranged on the detection surface of the photodetector with respect to the light that has passed through the polarization beam splitter. A prism mirror that guides at a predetermined interval in the sub-scanning direction,
Drive means for rotating the prism by a predetermined amount based on an electrical signal generated by the light separated by the polarization beam splitter among the electrical signals obtained by the photodetector;
An image forming apparatus having a two-beam exposure apparatus comprising: The prism mirror is configured such that light separated by the polarization beam splitter on the detection surface of the photodetector has an interval of 100 μm in the sub-scanning direction with respect to light that has passed through the polarization beam splitter. The image forming apparatus according to claim 3. The photodetector includes first to third detection areas along a direction in which the light is reflected by the polygonal mirror, and a fourth detection area in contact with one end of each of the first to third detection areas. 5. The image forming apparatus according to claim 4, wherein the prism is rotated so that a difference signal between the output of the second detection area and the output of the third detection area becomes “0”. . The photodetector includes first to fourth detection areas along a direction in which the light is reflected by the polygonal mirror, and a fifth detection area in contact with one end of each of the first to fourth detection areas. 5. The image forming apparatus according to claim 4 , wherein the prism is rotated so that a difference signal between the output of the third detection region and the output of the fourth detection region becomes “0”. . It is formed in a rotatable cylindrical shape, and the electric charge held by light irradiation is selectively attenuated to irradiate light toward a photoconductor that generates an electrostatic image, each radiating First and second laser diodes in which the planes of polarization of light are orthogonal to each other, and the lines connecting them are arranged in a plane parallel to the axial direction of the photoreceptor;
A parallel plate glass that translates the direction in which the light from one of the first and second laser diodes travels in the axial direction of the photoreceptor;
A prism that directs each of the light that has passed through the parallel plate glass and the other one of the light in the same direction;
A prism unit that aligns the light from each of the laser diodes in a direction perpendicular to the axial direction of the photoreceptor;
A polygonal mirror that is formed so that a plurality of reflecting surfaces are rotatable, and each of the lights aligned by the prism unit is continuously reflected in the axial direction of the photosensitive member;
It has a polarization plane given polarization in a direction orthogonal to the direction of polarization of light that has passed through the parallel flat glass, and has passed through the parallel flat glass of the respective light reflected by the polygonal mirror. A polarizing beam splitter that separates the light;
A photodetector having a plurality of detection regions, detecting each of the lights separated by the polarization beam splitter, and outputting an electric signal having a magnitude corresponding to the light intensity of the light;
Light that is disposed between the polarization beam splitter and the photodetector and separated by the polarization beam splitter is reflected by the polygon mirror with respect to the light that has passed through the polarization beam splitter on the detection surface of the photodetector. A prism mirror that guides to a position separated by 100 μm in the sub-scanning direction that is the axial direction of the photoconductor;
Signal processing means for setting an amount by which the prism should be rotated based on an electric signal generated by the light separated by the polarization beam splitter among the electric signal obtained by the photodetector;
Driving means for driving an actuator for rotating the prism in accordance with an amount of rotation of the prism generated by the signal processing means;
An image forming apparatus having a two-beam exposure apparatus comprising:

Images