JP2010020025A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high image quality and low cost optical scanner in which variation in the beam waist position of a scanning beam is excellently corrected. <P>SOLUTION: The optical scanner includes: a light source 11; an optical scanning means 15a; a scanning optical system including variable focus means 13, 14 (or 21A, 21B); and a scanning beam focus detection means which detects the focus shift and the shift direction of the scanning beam on a scanning face 17, wherein the variable focus means can independently vary a main scanning direction and a sub scanning direction, and the scanning beam focus detection means is disposed in a region in which an image is not recorded on the scanning face or equivalent face of scanning, and independently detects the focus shift amount and the shift direction of the scanning beam in the main scanning direction and the sub scanning direction. Thus, the focus shift amount and the shift direction of the scanning beam in the main scanning direction and in the sub scanning direction are individually detected, and the variable focus means corrects the focus shift amount in the main scanning direction and that in the sub scanning direction independently and simultaneously. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus and an image forming apparatus such as a digital copying machine, a printer, a plotter, a facsimile, or a multifunction machine including the optical scanning apparatus.

  In general, an optical scanning device known in relation to a laser printer or the like generally deflects a light beam from a light source such as a semiconductor laser by an optical deflector such as a polygon mirror or a galvanometer mirror, and forms an imaging optical device such as an fθ lens. The system is configured to collect light toward the surface to be scanned to form a light spot on the surface to be scanned, and to scan the surface to be scanned with this light spot. The optical scanning direction is referred to as the main scanning direction, and the direction orthogonal to the main scanning direction is referred to as the sub-scanning direction. Further, what forms the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member.

The following is mentioned as the performance required for the optical scanning apparatus as described above.
1. Uniformity of the beam spot diameter in the image forming area on the surface to be scanned.
2. Constant velocity of scanning speed on the surface to be scanned (fθ characteristic).
A rotating polygon mirror called a polygon mirror is widely used as an optical deflector of an optical scanning device. However, when optical scanning is performed using a polygon mirror, the end of the image forming area scans more than the center. Since the speed is increased and the fθ characteristic cannot be realized, and the optical path length is different between the end portion and the central portion of the image forming region, field curvature occurs and the uniformity of the beam spot diameter cannot be maintained. The fθ lens corrects the fθ characteristic and the curvature of field, and the performances 1 and 2 are satisfied by the fθ lens.
Further, in order to further improve the performance of the fθ lens and reduce the cost, a lens aspherical using a resin is used.
For this reason, the lens surface shape and the refractive index of the lens vary due to temperature variation, which tends to cause beam waist position variation, and the beam spot diameter on the surface to be scanned tends to increase. Further, the increase in the beam spot diameter causes a large quality degradation of the output image. For this reason, it is difficult to further improve the performance of the optical scanning device.

In connection with the optical scanning device,
(1) “A pair of knife edges are arranged on the scanning plane and the signal detected by the light receiving element placed behind the knife edges is differentiated to detect the deviation of the beam condensing position” (2 "In the optical scanning optical system, the focal shift of the scanning surface due to the ambient temperature is corrected using a variable focus lens or a variable focus lens. For the correction, the scanning beam on the scanning surface is detected by detecting the scanning beam on the scanning surface. The focal point of the variable focus lens or the variable focus lens is varied so that the focus is minimized, and the focus state of the scanning beam is placed on the scanning surface, and the positive and negative in the optical axis direction with respect to the scanning surface. Detects the rise and fall of the amount of transmitted light that has scanned two knife edges placed at symmetrical positions, and compares the rise and fall times to detect the condensing state of the scanning light. Etc. are known.

Here, as a known example, for example, Patent Document 1 (Japanese Patent Laid-Open No. 4-155304) discloses a “condensing position detecting device”, which is a laser beam focused and scanned on a scanning surface. The scanning laser beam scans a pair of knife edges which are condensing position detectors and are arranged at different positions from the scanning plane. The light transmitted through the knife edge is detected by a light receiving element placed behind and generates a light reception signal. An output peak value of a signal obtained by differentiating the detected light reception signal or a time width of the signal is detected to detect a deviation amount of the condensing position of the laser beam from the scanning surface.
In this known example, the amount and direction of deviation of the condensing position of the scanning laser beam can be detected only in the main scanning direction, and there is no disclosure about detection in the sub-scanning direction.

Patent Document 2 (Japanese Patent Laid-Open No. 7-20395) discloses a “laser beam scanning optical device”, which includes light placed at a scanning start end or a scanning end end of a surface equivalent to a scanning surface. The scanning beam condensing state is detected by the sensor, and as a result, the lens in the scanning beam is displaced to correct the focal point.
The optical sensor that detects the scanning beam condensing state detects the beam that has passed through the flat slit plate placed on the scanning equivalent plane by the photoelectric conversion element. There are slits that are perpendicular to the main scanning and those that are inclined, and the beam diameter in the main scanning direction is first adjusted by detecting the beam that has passed through the orthogonal slit, and then the secondary beam is detected by detecting the beam that has passed through the inclined slit. The beam diameter in the scanning direction is adjusted.
According to this known example, when the beam diameter is adjusted by the output of the optical sensor, the displacement direction (correction direction) of the lens of the scanning lens system is not known from the output of the optical sensor. For this reason, trial and error correction operation is required, and it is difficult to perform quick correction.

Patent Document 3 (Japanese Patent Application Laid-Open No. 6-289304) discloses a “condensing position detection device”, which is reflected by two mirrors arranged at different positions outside the scanning region of the scanning beam. The scanned beam is received by a common light detecting means, and the differential signal of the received light signal is peak-held to detect the converging position deviation of the scanned beam.
Even in this known example, the amount and direction of deviation of the condensing position of the scanning laser beam can be detected only in the main scanning direction, and there is no disclosure about detection in the sub-scanning direction. In addition, there is a drawback that the position of the two mirrors needs to be adjusted.

Patent Document 4 (Japanese Patent Application Laid-Open No. 2006-258838) discloses an “optical scanning device and a multicolor image forming device”, which is a scanning surface spot diameter and sub-scanning direction scanning in the optical scanning device. The position is detected, and the spot diameter and the scanning position are corrected by a liquid lens which is a variable focus deflection means. Spot diameter detection measures the time between two points at the start and end of scanning, detects the focal length variation of the fθ lens, and converts the spot diameter change therefrom.
However, with this method, the spot diameter is not actual but can only be calculated indirectly, and only the converted value based on the change in the focal length of the fθ lens is known (the change in focus due to the lens before the polygon mirror, such as a collimator lens, is not known). Further, in the specification of Patent Document 4, as a variable focus deflection means, it is disclosed as a feature that a liquid lens can have a variable focus and a deflection function with one element.

JP-A-4-155304 Japanese Patent Laid-Open No. 7-20395 JP-A-6-289304 JP 2006-258838 A

FIG. 21 shows an embodiment described in Patent Document 1 as a known example. FIG. 21A is a cross-sectional view, and FIG. 21B is a plan view. A pair of knife edges 7a and 7b are disposed outside the photosensitive region on the same surface as the photosensitive member 9 that is the scanning surface. Has been. A light receiving element 1 is disposed below the light receiving element 1 to detect a change in the amount of light of the scanning laser beam transmitted through the knife edge. The signal detected by the light receiving element is differentiated, and the peak value or pulse width of the two generated differential signals is compared to detect the condensing deviation and the deviation direction of the scanning beam.
According to this known example, it is possible to detect the deviation of the condensing position and the deviation direction of the scanning laser beam. However, only the condensing position shift and the shift direction in the main scanning direction can be detected, and information in the sub-scanning direction cannot be obtained.

The present invention has been made in view of the above circumstances, and an object of the present invention is to satisfactorily correct a beam waist position variation of a scanning beam, and to provide a high-quality and low-cost optical scanning device and its optical scanning. An object of the present invention is to provide a high-quality image forming apparatus provided with the apparatus.
More specifically,
(1) To detect defocus of the scanning beam due to temperature fluctuations of the optical scanning device, correct the defocus by the variable focus means, and always enable optical scanning without defocus even if there is an environmental change,
(2) Scanning beam detection detects both the amount of defocus and the direction of defocus in the main and sub-scan directions, and simultaneously corrects the defocus in the main and sub-scan directions independently by the variable focus means. Speeding up,
(3) The positioning accuracy of the defocus detection means in the scanning optical system is loose, and no special position adjustment is required during installation.
(4) Providing a configuration that can be downsized by integrating defocus detection in the main scanning direction and the sub-scanning direction;
Is the purpose (issue).

In order to achieve the above object, the present invention employs the following solutions.
The first means of the present invention is an optical scanning device, and “a light source, an optical scanning unit that scans a light beam from the light source, and a scanning beam that is scanned by the optical scanning unit is condensed on a scanning surface. A scanning optical system including a variable focus unit, and a scanning beam focus detection unit for detecting a defocus and a shift direction of the scanning beam on the scanning surface. ”“ The variable focus unit is independent of the main scanning direction and the sub-scanning direction ” "The scanning beam focus detection means is arranged in an area where no image is recorded on the scanning plane or the scanning equivalent plane, and is shifted from the scanning plane or the scanning equivalent plane in the beam traveling direction in the positive and negative directions. A pair of knife edge pairs, one set of knife edge pairs having an edge line perpendicular to the main scanning direction and the other set having edge lines inclined with respect to the main scanning direction. Transparent A light detector for detecting the beam ”,“ when the condensed light beam on the scanning surface has a condensing diameter in the main scanning direction equal to or smaller than the condensing diameter in the sub-scanning direction, an edge perpendicular to the main scanning direction ” The focus shift in the main scanning direction is corrected from the output of the scanning beam focus detection means having a line by the main scanning variable focus means, and the sub-scan is detected from the output of the scanning beam focus detection means having a knife edge line inclined with respect to the main scanning direction. The focus shift in the sub-scanning direction is corrected by the scanning variable focus means ”.

According to a second means of the present invention, in the optical scanning device according to the first means, when the condensing diameter in the main scanning direction is larger than the condensing diameter in the sub scanning direction with respect to the condensing beam on the scanning surface, The scanning beam focal point having an edge line perpendicular to the main scanning direction, and the inclination angle α of the knife edge of the scanning beam focal point detecting means having an edge line inclined with respect to the main scanning direction is smaller than 45 ° with respect to the main scanning direction. The main scanning variable focus means corrects the defocus in the main scanning direction based on the output of the detecting means, and the sub-scanning variable focus based on the output of the scanning beam focus detecting means having an edge line inclined with respect to the main scanning direction. It is characterized in that the defocus in the sub-scanning direction is corrected by the means.
According to a third means of the present invention, in the optical scanning device according to the first or second means, the scanning beam focus detection means is mainly composed of a pair of knife edge pairs arranged so as to be shifted in the beam traveling direction. A knife edge having an edge line perpendicular to the scanning direction and the other set having an edge line inclined with respect to the main scanning direction, and being displaced in the same direction from the scanning plane with respect to the beam traveling direction in each group Are formed on a common substrate, and one photodetector for detecting a transmitted beam is arranged in common for each knife edge group and detected.

According to a fourth means of the present invention, in the optical scanning device according to any one of the first to third means, the variable focus means changes a focus by applying a voltage, and a main scanning direction and a sub-scanning direction. Are arranged so that the focus can be controlled independently.
According to a fifth means of the present invention, in the optical scanning device according to any one of the first to third means, the main scanning direction variable focus means includes a cylindrical lens having a bus in the sub-scanning direction and the cylindrical lens. The sub-scanning direction variable focal point means is composed of a cylindrical lens having a generating line in the main scanning direction and an optical axis direction moving means of the cylindrical lens.

  According to a sixth means of the present invention, in the image forming apparatus that scans the surface of the image carrier (scanning surface) with a light beam to form a latent image and develops the latent image to make it visible, the light beam is scanned. As the means, the optical scanning device for correcting the defocus described in any one of the first to fifth means is used.

In the optical scanning device of the first means, when the condensed beam on the scanning surface has a condensing diameter in the main scanning direction equal to or smaller than the condensing diameter in the sub-scanning direction, the scanning laser beam focal points in the main scanning direction and the sub-scanning direction The amount of deviation and the direction of deviation can be detected individually, and the main focus and sub-scan independent variable focus means can independently and simultaneously correct the defocus in the main and sub-scan directions. Correction becomes possible.
In addition, the arrangement accuracy of the knife edge pair placed on the scanning plane may be loose, and there is an advantage that no special position adjustment is required at the time of installation.

In the optical scanning device of the second means, the scanning laser beam focal points in the main scanning direction and the sub-scanning direction even when the condensed beam diameter in the main scanning direction is larger than the condensed beam diameter in the sub-scanning direction. The amount of deviation and the direction of deviation can be detected individually, and the main focus and sub-scan independent variable focus means can independently and simultaneously correct the defocus in the main and sub-scan directions. Correction becomes possible.
Further, in the optical scanning device of the third means, the light provided with the scanning laser beam focus detection means that enables independent detection by integrating the main-scanning and sub-scanning defocus detection, and can be simplified and miniaturized. A scanning device can be provided.

In the optical scanning device of the fourth means, there is no mechanical movement, and simultaneous defocus correction can be made electronically independent in the main scanning and sub-scanning directions.
In the optical scanning device of the fifth means, simultaneous defocus correction can be performed independently of the main scanning and sub-scanning directions by a method different from the fourth means.

  In the image forming apparatus of the sixth means, by using the optical scanning apparatus capable of correcting the defocus as the optical beam scanning means, it is possible to satisfactorily correct the beam waist position fluctuation of the scanning beam. In addition, it is possible to provide a single-color or multicolor image forming apparatus with high image quality and low cost.

  Hereinafter, the configuration, operation, and effects of the present invention will be described in detail based on the illustrated embodiments.

[Example 1]
1 and 2 show an embodiment of a scanning optical system of an optical scanning apparatus to which the present invention is applied. FIG. 1 is a plan view (main scanning sectional view) showing an arrangement example of optical systems after the rotary polygon mirror 15 as an optical deflector which is an optical scanning means of the optical scanning device, and FIGS. ) Represents a side view (sub-scan sectional view) showing an example of the arrangement of the optical system from the semiconductor laser (LD) 11 as the light source to the scanning surface 17.
In FIG. 1, the laser beam deflected by the rotary polygon mirror 15 is focused by the fθ lens 16, condensed as a small light spot on the scanning surface 17, and scanned in the main scanning direction A. The fθ lens 16 has a single lens configuration in FIG. 1 and is an anamorphic lens having different focal lengths in the main scanning direction and the sub-scanning direction. Moreover, it is not limited to this, and there are many variations such as a two-group two-lens configuration, or an anamorphic one-lens configuration + a long cylindrical lens configuration.

2A and 2B, a semiconductor laser (LD) 11 that is a light source and a coupling lens 12 that takes in diverging light from the LD 11 into an optical system, a reflecting surface 15a of a rotary polygon mirror, an fθ lens 16, and The scanning surface 17 is common and is illustrated in a similar arrangement.
FIG. 2A shows a cylindrical lens 13 having a generating line in the sub-scanning direction and a main scanning as a variable focus means capable of independently changing the main scanning direction and the sub-scanning direction between the coupling lens 12 and the rotary polygon mirror 15. A cylindrical lens 14 having a generating line in the direction is arranged. The front cylindrical lens 13 has a function of collimating the divergent beam from the LD 11 into a parallel beam in cooperation with the coupling lens 12 in the main scanning direction, and the rear cylindrical lens 14 is a rotating polygon mirror only in the sub-scanning direction. It has a function of condensing on the reflecting surface 15a.

  The fθ lens 16 condenses parallel beams on the scanning surface in the main scanning direction, and in the sub-scanning direction, the reflecting surface 15a re-images the beam condensed on the reflecting surface 15a of the rotary polygon mirror on the scanning surface 17. And the scanning plane 17 have a function of a so-called rotating polygon mirror surface tilt correction optical system in which the imaging is conjugate. The variable focus function in the scanning optical system is performed by moving means for moving the cylindrical lens 13 back and forth in the optical axis direction a in the main scanning direction. As the moving means, linear feeding by a linear motor, a rotary motor, a piezoelectric body or the like is performed. Further, the sub-scanning direction is performed by moving means for moving the cylindrical lens 14 back and forth in the optical axis direction b. In this way, by moving the two cylindrical lenses 13 and 14 whose buses are orthogonal to each other in the optical axis directions a and b, it is possible to perform independent variable focus in both main scanning and sub-scanning.

In FIG. 2B, the diverging light from the LD 11 is converted into a parallel beam only by the coupling lens 12. The cylindrical lens 14 is the same as the cylindrical lens 14 having a bus in the main scanning direction in FIG. Here, the variable focus means includes a main scanning focus variable element 21A and a sub scanning focus variable element 21B that can independently change main scanning and sub scanning, and is disposed between the coupling lens 12 and the cylindrical lens 14. The arrangement location is not limited to this, and is not particularly limited as long as it is between the light source 11 and the rotary polygon mirror 15.
Both the main scanning focus variable element 21A and the sub-scanning focus variable element 21B are variable in focus by the voltage applied to the elements, and can be variably controlled independently. Specifically, these elements include a liquid crystal lens that uses a change in refractive index due to the voltage of the liquid crystal, or a liquid lens that changes the lens surface shape by changing the wettability of the liquid by the voltage and performs a variable focus lens action.

  Here, in both cases of FIGS. 2A and 2B, the scanning of the present application is performed at a scanning start portion outside the effective scanning area (image recording area) for printing the image on the scanning surface 17 (or scanning equivalent surface) of FIG. The beam focus detection means 18 is arranged to detect the defocus of the scanning beam on the scanning surface 17. The scanning beam focus detection means 18 of the present invention can detect both the defocus and the shift direction of the scanning beam. In addition, it is possible to detect a defocus in the main scanning direction and the sub scanning direction. FIG. 1 shows an embodiment in which a single scanning beam focus detection means 18 can detect a defocus in both main scanning and sub-scanning directions.

On the other hand, the embodiment shown in FIG. 6 or FIG. 7 is an embodiment using two devices that can detect a defocus in one direction by one scanning beam focus detection means.
Here, in the configuration of the embodiment of FIG. 6, the scanning beam focus detection means 18-1 detects the defocus in the main scanning direction and the scanning beam focus detection means 18-2 detects the defocus in the sub-scanning direction. (Equivalent surface) is disposed at the scanning start portion outside the effective scanning area where the image is printed, and the focus shift in the main scanning direction and the sub scanning direction is individually detected.

  Further, in the configuration of the embodiment of FIG. 7, the scanning beam focus detection means 18-1 detects the defocus in the main scanning direction, and the scanning beam focus detection means 18-2 detects the defocus in the sub scanning direction. -1 is located at the scanning start end outside the effective scanning area, and the scanning beam focus detection means 18-2 is located at the scanning end end, and individually detects the defocus in the main scanning direction and the sub scanning direction.

  Next, an embodiment of the scanning beam focus detection means will be described. To detect a scanning beam defocus in the main scanning direction, an edge line is provided in the direction perpendicular to the main scanning direction as shown in the known example of FIG. This is done by means consisting of a pair of knife edges arranged offset from the front and back of the scanning plane and a photodetector arranged behind the edges. Although known so far, in order to detect the scanning beam defocus in the sub-scanning direction, as shown in FIGS. 3 and 4, it has an edge line inclined obliquely with respect to the main scanning direction, and the front and back of the scanning surface. This is performed by a configuration of a pair of knife edges 1 and 2 which are arranged to be shifted to each other and a photodetector 20 which is arranged behind the knife edges 1 and 2. FIG. 3 is a view showing an embodiment of the scanning beam focus detection means, and is a plan view of the knife edge pair as seen from the light source side. 4 is a sectional view in the main scanning direction of the optical system from the knife edge pair of the scanning beam focus detection means shown in FIG. 3 to the photodetector.

  FIG. 3 shows a case where the direction of the edge line of the pair of knife edges 1 and 2 is inclined at 45 ° with respect to the main scanning direction. The knife edge 1 and the knife edge 2 are arranged in parallel to each other and shifted from the scanning plane to a position that is symmetric with respect to the beam traveling direction. The scanning beam that has passed through the knife edges 1 and 2 is received by the photodetector 20 via the condenser lens 19. In addition, the condensing lens 19 is not essential and the structure which does not use the condensing lens 19 may be sufficient. The advantage of using the condensing lens 19 is that the size of the light receiving surface of the light receiving light detector 20 is small, and the light receiving signal rises and rises when the scanning beam for detecting defocusing crosses the knife edges 1 and 2. By being able to accurately detect the downstream waveform, it is possible to improve defocus detection accuracy.

  FIG. 4 is a plan view of the cross section in the main scanning direction (cross section in the main scanning direction), and the scanning beam scans from the top to the bottom of the figure. FIG. 4A shows a state where the scanning beam is just focused on the scanning surface 17, and the light is shielded by the knife edge 1 along with the scanning → transmission starts from the knife edge 1 → the entire transmission is not applied to the knife edge 1. → The light is shielded by the knife edge 2 → The light is shielded by the knife edge 2. 4B shows a state where light is condensed toward the light source side from the scanning surface 17 (forward focusing), and FIG. 4C shows a state where light is condensed farther than the scanning surface 17 (backward focusing). Represents.

  FIG. 5 is a diagram showing the relationship of waveforms detected by the photodetector 20 of the scanning beam focus detection means of FIG. The horizontal axis in the figure is the time axis t, and the vertical axis is the signal amplitude. FIG. 5A shows a light reception waveform of the photodetector 20 behind the knife edge. The left figure in FIG. 5A shows the forward-focused state, the middle figure in FIG. 5A shows the scanning beam just focused on the scanning surface, and the right-hand figure in FIG. 5A shows the rear-focused state. Is the received light waveform. Comparing the three diagrams of FIG. 5A, the waveform of the central diagram focused on the scanning plane shows that the rise time of the signal transmitted through the knife edge 1 is equal to the fall time of the knife edge 2, and the forward focusing and In the left diagram of FIG. 5A, the rise time of the signal transmitted through the knife edge 1 is short, and the fall time by the knife edge 2 is long. Further, in the right diagram of FIG. 5A, which is the rear focusing, the rise time of the signal transmitted through the knife edge 1 is long and the fall time by the knife edge 2 is short.

  This situation becomes clear in FIG. 5 (b) obtained by time-differentiating the received light waveform of FIG. 5 (a). FIG. 5B obtained by time differentiation shows a waveform similar to the beam shape of the scanning beam on the knife edge surface. That is, the differential waveform in the center diagram of FIG. 5B that is just focused on the scanning plane has the same beam shape as the differential waveform at knife edge 1 and knife edge 2, and FIG. In the left figure of (), the beam shape at the knife edge 1 is thin, and the beam shape at the knife edge 2 is thick. Further, in the right view of FIG. 5B, which is the back focus, the beam shape at the knife edge 1 is thick and the beam shape at the knife edge 2 is thin.

In order to detect the focus shift and the shift direction from this differential waveform, the threshold value is processed from the differential waveform with a threshold value (horizontal line in the differential waveform in FIG. 5B), and binarized. 5 (c). The pulse width of the central pulse waveform in FIG. 5C focused on the scanning plane is equal, and the binarized pulse width at the knife edge 1 is shown in the left diagram of FIG. The binarized pulse width at the knife edge 2 is larger, and in the right diagram of FIG. 5 (c) where the converging state is backward focused, the binarized pulse width at the knife edge 1 is binary at the knife edge 2. Greater than the pulse width. From the above, assuming that the binarized pulse width at the knife edge 1 is t3 and the pulse width at the knife edge 2 is t4, the focus error signal F is
F = t3-t4
Then, F indicates the defocus and shift direction.
That is, when F = 0, the light is focused on the scanning surface. When F <0, the light converging position is shifted to the light source side, and when F> 0, the light source is focused. It is in the state of back focusing that is shifted in the opposite direction, and the amount of defocus and the direction of shift can be known from the value of F and positive / negative.

Based on the focus error signal F, variable focus means in the scanning optical system (moving means for the cylindrical lenses 13 and 14 in FIG. 2A, or main scanning focus variable element 21A in FIG. 2B, sub-scanning focus). The variable focus control is performed so that the focus error signal F becomes zero by feeding back to the driving means of the variable element 21B.
In addition to this, as disclosed in Patent Document 1, the method of detecting the scanning beam defocus from the light reception signal from the knife edge pair holds the peak value of the differential signal and rises the light reception signal. And the peak voltage of the differential peak corresponding to the falling edge can also be calculated.

  Next, it will be described that scanning beam focus detection in the sub-scanning direction can be performed by a pair of knife edges inclined obliquely with respect to the main scanning direction. FIG. 14 shows a light reception waveform of the knife edge transmitted light detection signal of the present invention when the beam shape of the scanning laser beam is circular. A broken line 1 written in the scanning laser beam indicates a scanning beam detection direction detected by a knife edge perpendicular to the main scanning, and a lower figure shows a light reception signal corresponding to the knife edge pair perpendicular to the main scanning. A broken line 2 indicates a scanning beam detection direction detected by a knife edge inclined with respect to the main scanning, and a lower right diagram shows a light reception signal corresponding to the inclined knife edge pair. In the figure, a light reception signal by a knife edge inclined by 45 ° with respect to the main scanning direction is shown. As described with reference to FIG. 5, detection of defocus from these received light signals can be performed by differentiating the received light signals with respect to time, obtaining signals similar to the scanning beam shape, and performing threshold processing thereof. From the figure, when the beam shape of the scanning laser beam is circular, the scanning beam defocus in the main scanning direction is obtained from a pair of knife edges perpendicular to the main scanning. The scanning beam defocus in the sub-scanning direction is obtained from a pair of knife edges inclined with respect to the main scanning.

  Further, as shown in FIG. 15, when the condensing diameter of the scanning laser beam in the main scanning direction is smaller than the condensing diameter in the sub-scanning direction, the light reception signal obtained from the knife edge pair inclined with respect to the main scanning direction is from the main scanning direction. The signal based on the beam shape in the sub-scanning direction is the main, and scanning beam defocus detection in the sub-scanning direction can be approximately obtained from a pair of knife edges inclined with respect to the main scanning.

From the above, when the condensing diameter in the main scanning direction is equal to or smaller than the condensing diameter in the sub-scanning direction with respect to the condensing beam on the scanning surface, the scanning beam focus detection means having an edge line perpendicular to the main scanning direction ( For example, the scanning beam focus detection means (for example, FIG. 6, FIG. 6), which has a knife edge line inclined from the output of the scanning beam focus detection means 18-1) in FIGS. Defocus in the sub-scanning direction can be detected independently from the output of the scanning beam focus detection means 18-2) in FIG.
Since the defocus detection in the main scanning direction and the sub-scanning direction can be performed independently, the correction is performed from the main scanning focus sensor (main scanning Fo sensor) of the scanning beam focus detection means as shown in the flowchart of FIG. Based on the output focus shift signal (main scanning focus error signal Fo1) in the main scanning direction, the main scanning direction focus variable means (for example, main scanning focus variable element (main scanning variable focus lens) 21A in FIG. 2B) is driven. ) To correct the defocus in the main scanning direction. Further, as shown in FIG. 19B, an approximate sub-scanning defocus signal (approximate sub-scanning focus error signal Fo2) output from the sub-scanning focus sensor (approximate sub-scanning Fo sensor) of the scanning beam focus detection means. ) To control the sub-scanning direction focus changing means (for example, driving the sub-scanning focus changing element (sub-scanning variable focus lens) 21B in FIG. 2B) to correct the defocus in the sub-scanning direction. This correction is performed independently and simultaneously in parallel. However, t1 and t2 in FIG. 19 (a) are the pulse widths of two binarized pulses obtained from the differential waveform of the received light output of the knife edge pair transmitted light perpendicular to the main scanning direction, and in FIG. 19 (b). t3 and t4 are the pulse widths of two binarized pulses obtained from the differential waveform of the received light output of the knife edge pair transmitted light inclined with respect to the main scanning direction.

  As described above, independent defocus correction in the main scanning direction and the sub-scanning direction is performed independently for each of the main scanning focus variable element 21A and the sub-scanning focus variable element 21B for voltage application control shown in FIG. , Fo2 signals are fed back to perform defocus correction simultaneously with main scanning and sub scanning.

  As another method, the focus shift unit shown in FIG. 2A is used for independent defocus correction in the main scanning direction and the sub-scanning direction. In the main scanning direction, the preceding cylindrical lens 13 is adjusted based on Fo1. It is performed by moving means for moving back and forth in the optical axis direction a, and the sub-scanning direction is performed by moving means for moving the subsequent cylindrical lens 14 back and forth in the optical axis direction b based on Fo2.

According to this embodiment, it is possible to individually detect the scanning laser beam defocus amount and the misalignment direction in the main scanning direction and the sub-scanning direction, and the main scanning direction and the sub-scanning direction by the variable focus means independent of the main scanning and sub-scanning. This makes it possible to perform corrections that quickly and independently reduce the defocusing.
Further, according to the present embodiment, the arrangement accuracy of the knife edge pair in the vicinity of the scanning surface may be loose, and no special position adjustment is required when the scanning beam focus detection means is installed.

[Example 2]
Next, FIG. 16 shows an embodiment in which the main scanning direction condensing diameter is larger than the sub scanning direction condensing diameter with respect to the condensing beam on the scanning surface. In this case, the light reception signal by the knife edge pair having the edge line inclined obliquely with respect to the main scanning direction (45 ° direction in FIG. 16) is mainly the defocus signal in the main scanning direction from the sub scanning direction. The scanning beam defocus detection in the sub-scanning direction cannot be obtained from the signal by the inclined knife edge pair.

  Thus, when the main scanning direction condensing diameter is larger than the sub-scanning direction condensing diameter, a knife edge pair as shown in FIG. 17 is used. FIG. 17A shows a knife edge pair for detecting a defocus in the main scanning direction, which is the same as the conventional one. FIG. 17B shows a knife edge pair having an edge line inclined with respect to the main scanning direction in order to detect a defocus in the sub scanning direction, and the inclination angles of the knife edges 3 and 4 of the scanning beam focus detection means. α is set to an angle smaller than 45 ° with respect to the main scanning direction. FIG. 17B shows a case where α≈10 ° is set. This makes the knife edge line as close as possible to the main scanning direction as shown in the figure.

  FIG. 18 shows a received light waveform of the transmitted light detection signal corresponding to the knife edge of FIG. 17 when the main scanning direction condensing diameter is larger than the sub-scanning direction condensing diameter. The broken line 1 written in the scanning laser beam indicates the direction of the scanning beam shape detected by the knife edge perpendicular to the main scanning in FIG. 17A, and the lower figure corresponds to the knife edge pair perpendicular to the main scanning. Received light signal. A broken line 2 indicates the direction of the scanning beam shape detected by the knife edges 3 and 4 inclined with respect to the main scan in FIG. 17B, and the lower right figure shows a light reception signal corresponding to the inclined knife edge pair. . As shown in FIG. 18, when the tilt angle α of the knife edge of the scanning beam focus detection means is set to an angle smaller than 45 ° with respect to the main scanning direction, the received light signal is a signal based on the beam shape in the sub-scanning direction from the main scanning direction. Scanning beam defocus detection in the main and sub-scanning directions can be approximately obtained from a pair of knife edges inclined at α <45 ° with respect to the main scanning.

With the configuration of the present embodiment, even when the condensing diameter in the main scanning direction is larger than the condensing diameter in the sub scanning direction, defocus detection in the main scanning direction and the sub scanning direction can be performed independently, and the correction is performed as shown in FIG. , (B), the main scanning and the sub-scanning can be performed simultaneously at the same time.
As described above, also in this embodiment, the scanning laser beam defocus amount and the misalignment direction in the main scanning direction and the sub-scanning direction can be detected individually, and the main scanning direction can be detected by the variable focus means independent of the main scanning and sub-scanning. Thus, it is possible to perform corrections that simultaneously and quickly accelerate the defocus in the sub-scanning direction.
Further, according to the present embodiment, the arrangement accuracy of the knife edge pair placed in the vicinity of the scanning surface may be loose, and no special position adjustment is required at the time of installation.

[Example 3]
Next, another embodiment is shown in FIGS. This embodiment is a configuration example of a scanning beam focus detection means that integrates main-scan and sub-scan focus shift detection and enables independent detection. FIG. 8 shows a configuration example when the knife edge group of the scanning beam focus detection means is viewed from the light source direction. The knife edges 1 and 2 have edge lines perpendicular to the main scanning direction, and are knife edge pairs for detecting defocus in the main scanning direction. The knife edges 3 and 4 have edge lines inclined in the main scanning direction, This is a knife edge pair for detecting defocus in the scanning direction. FIG. 9 is a sectional view in the main scanning direction (plan view of the main scanning section) of the optical system from the knife edge group of the scanning beam focus detection means shown in FIG. 4 is arranged shifted to the light source side, and knife edges 2 and 3 are arranged shifted in the opposite direction to the light source. The beam that has passed through the knife edge is condensed on the photodetector 20 by the condenser lens 19. Here, the knife edges 2 and 3 are formed on the same substrate end, thereby simplifying.

  FIG. 10A shows the relationship of the waveform of the received light signal detected by the photodetector 20 shown in FIG. The horizontal axis is time t, and the vertical axis is output amplitude. In this figure, the scanning beam is focused on the scanning surface and is a signal when there is no defocus. The first peak of the light reception signal in FIG. 10A is a light reception signal for detecting a defocus in the main scanning direction due to the knife edge pairs 1 and 2, and the next peak is in the sub scanning direction due to the knife edge pairs 3 and 4. It is a light reception signal for detecting defocus. 10B is a signal obtained by time-differentiating FIG. 10A, and FIG. 10C is a pulse output obtained by binarizing the differentiated signal with a threshold corresponding to the horizontal line in FIG. 10B. . Of these pulse trains, the pulse widths of two pulses by the first knife edge pair 1 and 2 related to the main scanning are t1 and t2, respectively. The pulse widths of the knife edge pairs 3 and 4 related to the sub-scan are t3 and t4, respectively.

  These pulse trains change depending on the defocus state of the scanning laser beam. FIG. 11 shows how the pulse trains t1 and t2 change. In FIG. 11, “a” in FIG. 11 is a forward focusing state where the scanning laser beam condensing position is on the light source side, and the pulse width is t1 <t2. 11 b is just when focused on the scanning plane, the pulse width is t 1 = t 2, c in FIG. 11 is the back-focused state, and the pulse width is t 1> t 2.

Here, if the focus error signal for detecting the defocus in the main scanning direction is Fo1,
Fo1 = t1-t2
And
Further, if the focus error signal for detecting the defocus in the sub-scanning direction is Fo2,
Fo2 = t3-t4
And

FIG. 12 shows the relationship between the focus error signal and the defocus. When Fo1 = 0 and Fo2 = 0, the light is focused on the scanning surface. When Fo1 <0 and Fo2 <0, the focal position is shifted forward toward the light source side, Fo1 The case of> 0, Fo2> 0 is a back-focused state shifted in the opposite direction of the light source, and the amount of defocus and the direction of shift can be known by the values of Fo1, Fo2 and positive / negative.
In FIG. 12A, the focus error signal Fo1 in the main scanning direction is the vertical axis, the horizontal axis is the coordinate z in the optical axis direction, and Z = 0 represents the scanning surface position. In FIG. 12B, the focus error signal Fo2 in the sub-scanning direction is the vertical axis, the horizontal axis is the coordinate z in the optical axis direction, and z = 0 represents the scanning surface position. Accordingly, variable focus means in the main and sub-scanning directions (moving means for the cylindrical lenses 13 and 14 in FIG. 2A, so that the focus error signals Fo1 and Fo2 in FIGS. Alternatively, the main scanning focus variable element 21A and the sub-scanning focus variable element 21B in FIG. 2B are simultaneously and independently driven to correct the defocus of the scanning optical system.

  In addition to this, as disclosed in Patent Document 1, the method of detecting the scanning beam defocus from the light reception signal from the knife edge pair holds the peak value of the differential signal and rises the light reception signal. And the peak voltage corresponding to the falling edge is also obtained by comparison calculation.

FIG. 13 shows a structural example of a sensor that actually configures the scanning beam focus detection means of the present embodiment. FIG. 13A shows a configuration example when the condensing lens 19 is provided. The left diagram of FIG. 13A is a plan view of the knife edge group of the scanning beam focus detection sensor as viewed from the light source direction, and FIG. ) Is a main scanning sectional view of the scanning beam focus detection sensor. The knife edges 2 and 3 are respectively formed on the same substrate end. FIG. 13B shows a configuration example when no condensing lens is used, and the left figure of FIG. 13B is a plan view of the knife edge group of the scanning beam focus detection sensor viewed from the light source direction, and FIG. ) Is a main scanning sectional view of the scanning beam focus detection sensor. In the configuration of FIG. 13B, the size can be further reduced as compared with FIG. Further, in the configuration example of FIG. 13, not only the knife edges 2 and 3 are formed on the same substrate end, but also the knife edges 1 and 4 are formed on the same substrate, so that the simplification can be further simplified.
By using the scanning beam focus detection sensor having the configuration shown in FIG. 13, it is possible to integrate the main scanning and sub-scanning defocus detection to enable independent detection, and to simplify and miniaturize the optical scanning device. Can be provided.

[Example 4]
Next, an embodiment of an image forming apparatus including the optical scanning device described in the first to third embodiments will be described.
FIG. 20 illustrates a multicolor image forming apparatus 100 including a plurality of optical scanning devices described in the first to third embodiments. The multicolor image forming apparatus 100 is an image forming apparatus that prints out a full color image, and includes four photoconductors 120Y, 120M, 120C, and 120K (hereinafter, subscripts Y, M, and C corresponding to reference numerals) corresponding to the respective colors in the apparatus. , K as appropriate, and Y: yellow, M: magenta, C: cyan, and K: black) are arranged in parallel).
In this image forming apparatus, the optical scanning device 105, the developing device 106, the photosensitive member 120, the intermediate transfer belt 121, the fixing device 114, the feeding device to which any of the configurations described in the first to third embodiments are applied in order from the top. A paper cassette 111 and the like are laid out.
Although not shown, when this image forming apparatus is used as a digital copying machine, a facsimile machine, or a multifunction machine, a scanner device (document reading device) (not shown) is disposed above or separately from the optical scanning device 105. Monkey.

Photoconductors 120Y, 120M, 120C, and 120K corresponding to the respective colors are arranged on the upper surface side of the intermediate transfer belt 121 at equal intervals in the parallel order.
The photoconductors 120Y, 120M, 120C, and 120K are formed to have the same diameter, and constituent members for forming an image according to an electrophotographic process are sequentially arranged around the photoconductors 120Y, 120M, 120C, and 120K.
That is, only the developing device 106 is shown in FIG. 20, but the explanation will be made by taking the photoconductor 120Y as an example. Actually, a charging device (charging charger, charging roller, charging brush, etc.) not shown around the photoconductor 120Y. A laser beam LY emitted from the optical scanning device 105 based on image information, a developing device 106Y, a transfer device (not shown) (transfer charger, transfer roller, transfer brush, etc.), a cleaning device (not shown), and the like are sequentially arranged. . Similar members are also provided for the other photoconductors 120M, 120C, and 120K.

  In this embodiment, the photoconductive photoconductors 120Y, 120M, 120C, and 120K are used as scanning surfaces set for the respective colors, and the respective photoconductors (scanning surfaces) 120Y, 120M, 120C, and 120K are used. The laser beams LY, LM, LC, and LK from the optical scanning device 105 are provided so as to correspond.

The photoconductor 120Y uniformly charged by a charging device (not shown) rotates in the direction of arrow A, thereby sub-scanning the laser beam LY, and an electrostatic latent image is formed on the photoconductor 120Y.
Further, a developing device 106Y for supplying toner to the photoconductor 120Y is disposed downstream of the irradiation position of the laser beam LY by the optical scanning device 105, so that yellow (Y) toner is supplied. The
The toner supplied from the developing device 106Y adheres to the portion where the electrostatic latent image is formed, and a Y toner image is formed.
Similarly, charging, latent image formation, and development are performed on the photoconductors 120M, 120C, and 120K, and M, C, and K monochromatic toner images are formed, respectively.

An intermediate transfer belt 121 is arranged further downstream in the rotation direction than the arrangement positions of the developing devices 106Y, 106M, 106C, and 106K of the photosensitive members 120Y, 120M, 120C, and 120K.
The intermediate transfer belt 121 is supported around a plurality of rollers 102a, 102b, and 102c, and is moved and conveyed in the direction of arrow B by driving a motor (not shown).
By this conveyance, the intermediate transfer belt 121 is sequentially moved to the photoconductors 120Y, 120M, 120C, and 120K.
The single color images developed by the photoconductors 120Y, 120M, 120C, and 120K are sequentially superimposed and transferred onto the intermediate transfer belt 121, and a color image is formed on the intermediate transfer belt 121.

Thereafter, the transfer paper is fed from the paper feed tray 111 and conveyed in the direction of arrow C via the secondary transfer roller 112, and the color image is transferred from the intermediate transfer belt 121 to the transfer paper.
The transfer paper on which the color image is formed is heated and pressed by the fixing device 114 and fixed, and then discharged as a full-color image print onto a paper discharge tray 110 at the top of the image forming device.

The multi-color image forming apparatus 100 using the optical scanning apparatus having the above-described configuration can provide a high-quality color image that does not change color even during continuous output.
Although not shown, for example, the optical scanning device of the present invention can also be applied to a monochrome image forming apparatus composed of only K: black.

In the multi-color image forming apparatus configured as described above, the beam spot diameter of the laser beam by the optical scanning device is preferably controlled for each optical scanning device with the initial (factory shipment state) as a target.
If the beam spot diameter is corrected during image formation, the image quality may be locally degraded due to slight ripples (slight fluctuations in the beam spot diameter and beam spot position immediately after the operation) caused by the operation of the above-mentioned focus varying means. There is.
In addition, there is little variation in the beam spot diameter in the time required to output one image. However, during continuous output, environmental fluctuations in the multicolor image forming apparatus are severe, and therefore it is desirable to perform correction in the shortest possible cycle.
From the above, the correction of the beam spot diameter is preferably performed between sheets during continuous printing. For this reason, using the configuration and detection / correction method of the present invention, independent detection in the main scanning and sub-scanning directions of the scanning laser beam defocus and independent correction in the main scanning and sub-scanning directions by feedback to the variable focus means are performed. Accordingly, it is possible to quickly detect and correct the defocusing in a short time between the sheets.
In addition, the above-described defocus detection and correction can be appropriately performed when starting up the image forming apparatus, when recovering from the sleep mode, during process control, and the like.

It is a figure which shows one Example of this invention, Comprising: It is the top view (main scanning sectional drawing) which showed the example of arrangement | positioning of the optical system after the optical deflector (rotating polygon mirror) of an optical scanning device. (A), (b) is the side view (sub-scanning sectional view) which showed the example of arrangement | positioning of the optical system from the light source (semiconductor laser (LD)) of an optical scanning device to a scanning surface, respectively. It is a figure which shows one Example of a scanning beam focus detection means, and is a top view of the knife edge pair seen from the light source side. FIG. 4 is a cross-sectional view in the main scanning direction of the optical system from the knife edge pair of the scanning beam focus detection means shown in FIG. 3 to the photodetector. It is a figure which shows the relationship of the signal waveform detected with the photodetector of the scanning beam focus detection means of FIG. It is a figure which shows another Example of this invention, Comprising: It is the top view (main scanning sectional drawing) which showed the example of arrangement | positioning of the optical system after the optical deflector (rotating polygon mirror) of an optical scanning device. It is a figure which shows another Example of this invention, Comprising: It is the top view (main scanning sectional drawing) which showed the example of arrangement | positioning of the optical system after the optical deflector (rotating polygon mirror) of an optical scanning device. It is a figure which shows another Example of this invention, and saw the knife edge group of the scanning beam focus detection means of the structure which integrated the main-scanning and sub-scanning focus shift detection, and enabled the independent detection from the light source direction. It is a top view which shows the example of a structure at the time. FIG. 9 is a cross-sectional view in the main scanning direction of the optical system from the knife edge group of the scanning beam focus detection means shown in FIG. 8 to the photodetector. It is a figure which shows the relationship of the signal waveform detected with the photodetector of the scanning beam focus detection means of FIG. It is the figure which showed a mode that pulse train t1, t2 of FIG.10 (c) changed with the focus shift | offset | difference states of a scanning laser beam. (A) is a diagram showing the relationship between the focus error signal in the main scanning direction and defocus, and (b) is a diagram showing the relationship between the focus error signal in the sub-scanning direction and defocus. It is a figure which shows the structural example of the sensor which actually comprised the scanning beam focus detection means of Example 3. FIG. It is a figure which shows the light reception waveform of the knife edge transmitted light detection signal of this invention when the beam shape of a scanning laser beam is circular. It is a figure which shows the light reception waveform of the knife edge transmitted light detection signal of this invention when the main scanning direction condensing diameter of a scanning laser beam is smaller than a sub scanning direction condensing diameter. It is a figure which shows the light-receiving waveform of the knife edge transmitted light detection signal of this invention when the main scanning direction condensing diameter of a scanning laser beam is larger than a sub-scanning direction condensing diameter. It is explanatory drawing of the knife edge pair which shows another Example of this invention, (a) is a top view when the knife edge pair which detects the focus shift | offset | difference of the main scanning direction is seen from the light source direction, (b) FIG. 5 is a plan view when a knife edge pair having an edge line inclined with respect to the main scanning direction is viewed from the light source direction in order to detect defocus in the sub scanning direction. It is a figure which shows the light reception waveform of the transmitted light detection signal corresponding to the knife edge of FIG. 17 when a main scanning direction condensing diameter is larger than a sub-scanning direction condensing diameter. It is a flowchart which shows an example of the focus shift detection and the correction | amendment method of the main scanning direction which concerns on this invention, and a subscanning direction. 1 is a schematic configuration diagram of a multicolor image forming apparatus including a plurality of optical scanning devices described in Embodiments 1 to 3. FIG. It is a copy of the figure which shows the Example described in patent document 1.

Explanation of symbols

1, 2, 3, 4: Knife edge 11: Light source (semiconductor laser (LD))
12: Coupling lens 13: Cylindrical lens having a bus in the sub-scanning direction 14: Cylindrical lens having a bus in the main scanning direction 15: Rotating polygon mirror (optical scanning means)
15a: Reflecting surface 16: fθ lens 17: Scanning surface 18: Scanning beam focus detection means 18-1: Scanning beam focus detection means in the main scanning direction 18-2: Scanning beam focus detection means in the sub-scanning direction 19: Condensing lens 20: photodetector 21A: main scanning variable focus element (main scanning variable focus means)
21B: Sub-scanning variable focus element (sub-scanning variable focus means)
DESCRIPTION OF SYMBOLS 100: Multicolor image forming apparatus 102a, 102b, 102c: Roller 105: Optical scanning apparatus 106Y, 106M, 106C, 106K: Developing apparatus 110: Paper discharge tray 111: Paper feed cassette 112: Secondary transfer roller 114: Fixing apparatus 120Y , 120M, 120C, 120K: photoconductor 121: intermediate transfer belt LY, LM, LC, LK: laser beam

Claims (6)

A scanning optical system including a light source, an optical scanning unit that scans a light beam from the light source, a variable focus unit that focuses the scanning beam scanned by the optical scanning unit on a scanning surface, and a scanning beam on the scanning surface And a scanning beam focus detection means for detecting a defocus and a shift direction of
The variable focus means can independently change the main scanning direction and the sub-scanning direction,
The scanning beam focus detection means is arranged in a region where no image is recorded on the scanning plane or scanning equivalent plane, and a pair of knife edges arranged in the positive and negative directions in the beam traveling direction from the scanning plane or scanning equivalent plane. One pair of knife edge pairs has an edge line perpendicular to the main scanning direction, and the other pair has an edge line inclined with respect to the main scanning direction, and detects a beam transmitted through the knife edge pair. Equipped with a photodetector,
When the condensed light beam on the scanning surface has a condensing diameter in the main scanning direction equal to or smaller than the condensing diameter in the sub-scanning direction, the main scanning variable can be made from the output of the scanning beam focus detection means having an edge line perpendicular to the main scanning direction. The focus means corrects the defocus in the main scanning direction, and corrects the defocus in the sub-scanning direction by the sub-scanning variable focus means from the output of the scanning beam focus detecting means having the knife edge line inclined with respect to the main scanning direction. An optical scanning device. The optical scanning device according to claim 1,
When the condensing diameter in the main scanning direction is larger than the condensing diameter in the sub-scanning direction with respect to the condensing beam on the scanning surface, the inclination angle α of the knife edge of the scanning beam focus detection means having the edge line inclined with respect to the main scanning direction Is an angle smaller than 45 ° with respect to the main scanning direction, and the focus shift in the main scanning direction is corrected by the main scanning variable focusing means based on the output of the scanning beam focus detecting means having an edge line perpendicular to the main scanning direction And an optical scanning device characterized in that the sub-scanning variable focus means corrects the defocus in the sub-scanning direction based on the output of the scanning beam focus detection means having an edge line inclined with respect to the main scanning direction. The optical scanning device according to claim 1 or 2,
In the scanning beam focus detection means, a pair of knife edge pairs which are arranged shifted in the beam traveling direction has an edge line perpendicular to the main scanning direction, and the other pair has an edge line inclined with respect to the main scanning direction. In each set, at least one knife edge arranged in the same direction from the scanning plane with respect to the beam traveling direction is formed on a common substrate, and a photodetector for detecting the transmitted beam is provided for each set of knife edges. On the other hand, an optical scanning device characterized in that one common detector is arranged and detected. In the optical scanning device according to any one of claims 1 to 3,
The optical scanning device according to claim 1, wherein the variable focus means is arranged so that the focus can be varied by applying a voltage, and the main scanning direction and the sub-scanning direction can be independently controlled in variable focus. In the optical scanning device according to any one of claims 1 to 3,
The main scanning direction variable focus means includes a cylindrical lens having a bus line in the sub-scanning direction and an optical axis direction moving means of the cylindrical lens, and the sub-scanning direction variable focus means has a cylindrical lens having a bus line in the main scanning direction and the cylindrical lens. An optical scanning device comprising a lens optical axis direction moving means. In an image forming apparatus that forms a latent image by scanning an image carrier surface (scanning surface) with a light beam, and develops the latent image into a visible image.
An image forming apparatus using the optical scanning device for correcting defocusing according to claim 1 as the light beam scanning means.

Images