JP2005208460A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which energy is saved by efficiently controlling a driving signal and a surface to be scanned is stably scanned with a light beam, and to provide an image forming apparatus using the optical scanner. <P>SOLUTION: The driving frequency of a deflection mirror face is increased as a resonance frequency increases, the rocking amplitude of the deflection mirror face is reduced (Θ1 to Θ2), the scanning time from the light beam detection position A to the light beam detection position B becomes PT, thus, the scanning time becomes substantially equal to that before the resonance frequency increases. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical scanning apparatus that scans a light beam on a surface to be scanned in a main scanning direction, and an image forming apparatus that forms an electrostatic latent image using the apparatus.

  Examples of apparatuses using this type of optical scanning apparatus include image forming apparatuses such as laser printers, copiers, and facsimile machines. For example, in Patent Document 1, a laser beam modulated according to image data is incident on a deflector via a collimator lens, a cylindrical lens, and a reflection mirror and deflected. More specifically, the optical scanning device provided in this conventional apparatus is configured as follows.

  In this optical scanning device, a laser beam emitted from a semiconductor laser is passed through a collimator lens and a cylindrical lens, so that the cross-sectional shape thereof is shaped into a horizontally long elliptical shape extending in the main scanning direction. Then, the laser beam is incident on the reflecting mirror of the deflector along the main scanning plane.

  In this apparatus, a deflector manufactured using a micromachining technique is used in order to solve various problems that occur particularly when a polygon mirror or a galvanometer mirror is used as a deflector. That is, a mirror vibrator in which a drive coil, a reflection mirror, and a ligament are integrally formed on a frame is processed using a photolithographic technique and an etching technique on a substrate such as quartz or silicon. Then, by applying a drive signal to the drive coil, the reflection mirror is swung about a swing axis that is substantially orthogonal to the main scanning direction, and the laser beam incident on the reflection mirror is deflected.

  The laser beam deflected in this way forms an image on a photosensitive member (corresponding to the “latent image carrier” of the present invention) through a scanning lens and a cylindrical lens. Thus, an electrostatic latent image corresponding to the image data is formed.

JP-A-1-302317 (second page, FIGS. 2-4)

  By the way, the resonance frequency of the mirror vibrator may vary depending on the processing method when manufacturing the mirror vibrator. Therefore, in order to eliminate this problem, the frequency of the drive signal applied to the drive coil is adjusted according to the resonance frequency of each mirror vibrator so that the drive frequency of the mirror vibrator substantially matches the resonance frequency of the mirror vibrator. The oscillation amplitude of the reflecting mirror is always set to the maximum value. Further, an arc / sin lens is used as a scanning lens, and the laser beam is scanned at a constant scanning width at a constant speed by controlling the amplitude of the driving signal applied to the driving coil.

  Specifically (see Patent Document 1 and FIG. 2), when the resonance frequency of the mirror vibrator is lower than a predetermined design value, the frequency of the drive signal is decreased according to the resonance frequency. The drive frequency of the mirror vibrator is lowered from a predetermined value to substantially match the value of the resonance frequency. At this time, as the drive frequency decreases, the scanning time during which the light beam scans a predetermined scanning width varies from a predetermined value. Therefore, not only reducing the frequency of the drive signal applied to the mirror vibrator, but also increasing the amplitude to increase the swinging amplitude of the reflecting mirror of the mirror vibrator, thereby making it approximately equal to the predetermined scanning time. ing. On the other hand, when the resonance frequency of the mirror vibrator is higher than a predetermined value, the drive frequency of the mirror vibrator is increased to substantially match the resonance frequency, and the oscillation amplitude of the reflection mirror of the mirror vibrator is increased. By reducing the scanning time, the scanning time during which the light beam scans the predetermined scanning width is made substantially equal to the predetermined value.

  As described above, in the above-described control of the frequency and amplitude of the drive signal, the drive signal energy must be increased to increase the amplitude of the drive signal. Therefore, there is a demand for a technique that can realize energy saving of the optical scanning device by more efficiently controlling the frequency and amplitude of the drive signal.

  Furthermore, in the conventional device, there is a problem of variation in the resonance frequency due to the manufacturing method of the mirror vibrator. However, even when the same mirror vibrator is used, the resonance frequency fluctuates due to fluctuations in the use environment. May end up. Therefore, there is a demand for a technique that can stably scan the light beam not only with respect to variations in the resonance frequency due to the manufacturing method but also with respect to variations in the resonance frequency due to variations in the use environment.

  The present invention has been made in view of the above problems, and realizes an energy saving by efficiently controlling a drive signal, and an optical scanning device capable of stably scanning a light beam on a surface to be scanned and the scanning device. An object of the present invention is to provide an image forming apparatus using the apparatus.

  In order to achieve the above object, an optical scanning device according to the present invention is an optical scanning device that scans a light beam in an effective scanning region on a surface to be scanned in a main scanning direction. A deflector having a deflecting mirror surface which is provided so as to be swingable about a swing axis substantially orthogonal to the scanning direction and which reflects the light beam emitted from the light source and deflects it in the main scanning direction; and the deflector And a mirror driving means for swinging the deflecting mirror surface about the swing axis by supplying a drive signal to the light source, and scanning the light beam at least over the effective scanning region by resonating and swinging the deflecting mirror surface. When the frequency band of the drive signal is an optical scanning effective band, the mirror driving means sets the frequency of the driving signal within the optical scanning effective band according to the resonance frequency of the deflection mirror surface. Moreover, the adjustment is performed while satisfying the condition that the resonance frequency is lower than the resonance frequency, and the drive signal amplitude and the swing amplitude of the deflection mirror surface are adjusted by adjusting the amplitude of the drive signal. It is said.

  In the invention configured as above, the frequency of the drive signal for driving the deflecting mirror surface is adjusted while satisfying the condition that it is within the optical scanning effective band and lower than the resonance frequency, and the drive signal By adjusting the amplitude, the driving frequency and the swing amplitude of the deflection mirror surface are adjusted. Therefore, by adjusting the drive frequency and oscillation amplitude of the deflection mirror surface by adjusting the frequency and amplitude of the drive signal for driving the deflection mirror surface according to the variation and fluctuation of the resonance frequency of the deflection mirror surface, The scanning time during which the light beam scans the effective scanning area on the surface to be scanned can be kept substantially constant. In addition, the scanning time can be kept substantially constant by reducing the amplitude of the drive signal, regardless of whether the resonance frequency fluctuates to the high frequency side or to the low frequency side due to the effects described in detail later. Can do. That is, it is not necessary to increase the swing amplitude of the deflection mirror surface by increasing the amplitude (energy) of the drive signal. By efficiently controlling the drive signal as described above, energy saving of the optical scanning device can be realized, and the light beam can be stably scanned on the surface to be scanned. In the present invention, the oscillation frequency of the deflection mirror surface is set lower than the maximum value by setting the frequency of the drive signal to be different from the resonance frequency of the deflection mirror surface. Therefore, the light beam can be scanned over the entire effective scanning area. In the present invention, “adjusting the frequency of the drive signal within the optical scanning effective band while satisfying the condition of being lower than the resonance frequency according to the resonance frequency of the deflection mirror surface” This means that when the resonance frequency fluctuates, the frequency of the drive signal is changed as necessary or the frequency is maintained as it is. That is, as will be described in detail later, there are cases where the frequency of the drive signal needs to be changed depending on the variation of the resonance frequency, and there are cases where it is preferable to maintain the frequency. Therefore, in this specification, “the frequency of the drive signal is adjusted according to the resonance frequency of the deflecting mirror surface while satisfying the condition that it is within the optical scanning effective band and lower than the resonance frequency”. Is defined as above.

  Further, the mirror driving means may be configured to increase the frequency of the driving signal and decrease the amplitude of the driving signal as the resonance frequency increases. In the invention configured as described above, the drive signal can be controlled more efficiently, and the energy saving of the optical scanning device can be further improved.

  The mirror driving means may be configured to reduce the amplitude of the drive signal while keeping the frequency of the drive signal substantially constant as the resonance frequency decreases. In the invention configured as described above, the drive signal is controlled more efficiently. Further, the frequency of the drive signal for driving the deflection mirror surface is made substantially constant, and only the amplitude of the drive signal is reduced. Therefore, the energy saving of the optical scanning device can be further improved and the control of the drive signal can be simplified.

  In addition, the apparatus further includes a scanning time measuring unit that measures a scanning time during which the light beam scans the effective scanning region and has at least one light beam detection element, and the mirror driving unit is configured to output the scanning time by the output from the scanning time measuring unit. The scanning time may be substantially constant by adjusting the frequency and amplitude of the driving signal. In the invention configured as described above, the frequency and amplitude of the drive signal for driving the deflection mirror surface can be automatically set to the optimum frequency and amplitude by using the output from the scanning time measuring means. Therefore, not only the individual difference of the resonance frequency of the deflection mirror surface caused by the manufacturing error of the deflector but also the fluctuation of the resonance frequency of the deflection mirror surface due to the change of the use environment can be dealt with in real time. Therefore, the scanning time during which the light beam scans the effective scanning region can be made constant with higher accuracy.

  The light beam detecting element may be arranged outside a sweep surface formed by sweeping the light beam when scanning the effective scanning region. In the invention configured as described above, since the light beam detecting element does not become an obstacle when the light beam scans the effective scanning region, it is not necessary to add a beam splitter or the like, and a simple structure can be realized.

  Further, the scanning time measuring means has two light beam detection elements, and each of the light beam detection elements has an optical axis when the light beam scans substantially the center of the effective scanning area. It is good also as a structure arrange | positioned substantially symmetrically. In the invention configured as described above, it is possible to easily calculate the scanning time for the light beam to scan the effective scanning region from the time for the light beam to pass through the light beam detecting element.

  Further, the output of the light beam detecting element may be used as a horizontal synchronization signal when the light beam scans the effective scanning area. In the invention configured as described above, it is not necessary to add a light beam detecting element in order to obtain a horizontal synchronization signal, and the apparatus configuration can be simplified.

  The image forming apparatus according to the present invention has the same configuration as the latent image carrier and the optical scanning device described above, and scans a light beam with a predetermined area on the surface of the latent image carrier as the effective scanning area. The image forming apparatus includes an exposure unit that forms an electrostatic latent image on the latent image carrier, and a developing unit that develops the electrostatic latent image with toner to form a toner image. In the invention configured as described above, an electrostatic latent image is stably formed on the latent image carrier by the optical scanning device described above, and the electrostatic latent image is developed with toner. Therefore, an image can be obtained stably.

<Basic Operation of Optical Scanning Device According to the Present Invention>
First, the first basic operation of the optical scanning device according to the present invention will be described in detail with reference to FIGS. FIG. 1 shows a resonance curve of the oscillation amplitude of the deflection mirror surface, and FIG. 2 shows the oscillation frequency of the deflection mirror surface and the oscillation of the deflection mirror surface as the frequency and amplitude of the drive signal for driving the deflection mirror surface are adjusted. It is a figure which shows a mode that an amplitude fluctuates. FIG. 1 shows a case where the resonance frequency of the deflecting mirror surface of the deflector having the resonance frequency f01 increases to the resonance frequency f02 due to fluctuations in the temperature or the like of the usage environment, and the resonance curve increases with the increase of the resonance frequency. Figure 2 also shows how fluctuations occur.

  In FIG. 1, the vertical axis represents the oscillation amplitude (Θ) of the deflecting mirror surface of the deflector, and the horizontal axis represents the driving frequency of the deflecting mirror surface. The resonance curves R1 and R2 and the resonance curve R3 of the oscillation amplitude of the deflection mirror surface when the amplitude of the drive signal for driving the deflection mirror surface having the resonance curve R2 is decreased are shown. As shown in FIG. 1, the deflection mirror surface has resonance frequencies f01 and f02 before and after the change of the resonance frequency, and when it is driven to oscillate at a drive frequency within the optical scanning effective band, a predetermined oscillation amplitude Θ0 or more. The oscillation amplitude is as follows. The oscillation amplitude Θ0 is a value required for the deflector to scan at least the effective scanning area on the surface to be scanned with the light beam deflected by the deflecting mirror surface. Note that the value is determined by the arrangement relationship of each component of the optical scanning device. In the figure, FB indicates an optical scanning effective band when the deflection mirror surface has the resonance frequency f01, and an optical scanning effective band when the deflection mirror surface has the resonance frequency f02 is not shown.

  In FIG. 2, the vertical axis is the swing amplitude (Θ) of the deflecting mirror surface of the deflector and the horizontal axis is time (t), and the swing when the deflecting mirror surface whose resonance curve is shown in FIG. A dynamic amplitude waveform is shown. More specifically, when the deflection mirror surface having the resonance characteristic of the resonance curve R1 is oscillated and driven at the drive frequency f1 before the resonance frequency is increased, the oscillation amplitude waveform F1 of the deflection mirror surface, and the resonance curve after the resonance frequency is increased. When the deflection mirror surface having the resonance characteristic of R2 is oscillated and driven at the drive frequency f2, the oscillation amplitude waveform F2 of the deflection mirror surface, and the drive for driving the deflection mirror surface having the resonance characteristic of the resonance curve R2 after the resonance frequency is increased. A swing amplitude waveform F3 of the deflection mirror surface when the deflection mirror surface having the resonance characteristic of the resonance curve R3 is driven to swing at the drive frequency f2 by decreasing the signal amplitude is shown. In the drawing, for easy understanding of the explanation, at the time t 0, the points where the swing amplitude is 0 overlap in each swing amplitude waveform.

  In the optical scanning device according to the present invention, the deflection mirror surface having the resonance frequency f01 is oscillated and driven at a drive frequency f1 lower than the resonance frequency f01 and within the optical scanning effective band FB. Therefore, the maximum value of the swing amplitude of the deflection mirror surface is Θ1 (see FIGS. 1 and 2). Similarly, when the resonance frequency of the deflection mirror surface increases to the resonance frequency f02, the deflection mirror surface is oscillated at a drive frequency f2 that is lower than the resonance frequency f02 of the deflection mirror surface and within the optical scanning effective band (not shown). Driving. Therefore, the oscillation amplitude of the deflection mirror surface is Θ1 (see FIGS. 1 and 2). That is, by increasing the frequency of the drive signal for driving the deflection mirror surface in accordance with the increase in the resonance frequency, the oscillation amplitude of the deflection mirror surface is set to a substantially constant value before and after the fluctuation of the resonance frequency of the deflection mirror surface ( Θ1).

  Next, as described above, the frequency of the drive signal for driving the deflecting mirror surface is adjusted, and the amplitude of the drive signal is reduced to reduce the scanning time for scanning the effective scanning area on the surface to be scanned with the light beam. The principle of adjustment will be described in detail.

  If the deflection mirror surface having the resonance characteristic of the resonance curve R1 is oscillated and driven at the drive frequency f1 before the resonance frequency is increased, the deflection mirror surface is oscillated and driven as the oscillation amplitude waveform F1. At this time, the light beam deflected by the deflection mirror surface at time t11 passes through the light beam detection position A and is detected by the light beam detection sensor (light beam detection element). Further, the light beam deflected by the deflecting mirror surface at time t12 passes through the light beam detection position B and is detected by the light beam detection sensor. In this case, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT.

  Next, when the resonance frequency f01 of the deflecting mirror surface increases to the resonance frequency f02 (resonance curve R2) due to fluctuations in the temperature or the like of the use environment of the deflector, at the same drive frequency f1 as before the increase of the resonance frequency. When the deflection mirror surface is driven to swing, the swing amplitude of the deflection mirror surface fluctuates (decreases), so that the scanning time during which the light beam scans the effective scanning area on the surface to be scanned fluctuates. That is, the scanning time during which the light beam scans from the light beam detection position A to the light beam detection position B varies. At this time, the scanning time can be adjusted by increasing the frequency of the drive signal for driving the deflection mirror surface and decreasing the amplitude of the drive signal (see waveform F2 and waveform F3).

  In FIG. 2, as shown by the oscillation amplitude waveforms F2 and F3, the frequency of the drive signal for driving the deflection mirror surface is adjusted (increased) so that the drive frequency of the deflection mirror surface is higher than the drive frequency f1. While the frequency f2 is adjusted (see FIG. 1), the oscillation amplitude of the deflection mirror surface is reduced by reducing the amplitude of the drive signal for driving the deflection mirror surface. Thus, as the resonance frequency increases, the drive signal frequency is adjusted to increase the drive frequency of the deflecting mirror surface, and the drive signal amplitude is decreased to reduce the swing amplitude of the deflecting mirror surface. Thus (Θ1 → Θ2), the light beam deflected by the deflecting mirror surface passes through the light beam detection position A at time t11 and passes through the light beam detection position B at time t12. That is, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT, which is substantially equal to the scanning time PT before the resonance frequency is increased. Thus, by increasing the frequency of the drive signal for driving the deflection mirror surface and decreasing the amplitude of the drive signal, the drive frequency of the deflection mirror surface and the swing amplitude of the deflection mirror surface are adjusted, The time during which the light beam scans from the light beam detection position A to the light beam detection position B can be made substantially constant before and after the resonance frequency of the deflection mirror surface is increased.

  Although the case where the resonance frequency increases due to fluctuations in the temperature or the like of the usage environment has been described, the above method is also applied to the variation in the resonance frequency of the deflection mirror surface caused by the manufacturing method of the deflector, and the surface to be scanned The scanning time during which the light beam scans the upper effective scanning area can be adjusted to be substantially constant. Therefore, even if the resonance frequency varies or fluctuates, it can be appropriately dealt with by adjusting the frequency of the drive signal and reducing the amplitude of the drive signal. Thus, by efficiently controlling the drive signal for driving the deflection mirror surface, energy saving can be realized and the light beam can be stably scanned on the surface to be scanned.

  Next, the second basic operation of the optical scanning device according to the present invention will be described in detail with reference to FIGS. 3 shows a resonance curve of the oscillation amplitude of the deflection mirror surface, and FIG. 4 shows the oscillation frequency of the deflection mirror surface and the oscillation of the deflection mirror surface as the frequency and amplitude of the drive signal for driving the deflection mirror surface are adjusted. It is a figure which shows a mode that an amplitude fluctuates. FIG. 3 shows a case where the resonance frequency of the deflecting mirror surface of the deflector having the resonance frequency f01 is decreased to the resonance frequency f03 due to fluctuations in the temperature or the like of the use environment, and a resonance curve with a decrease in the resonance frequency. Figure 2 also shows how fluctuations occur.

  In FIG. 3, the vertical axis represents the oscillation amplitude (Θ) of the deflecting mirror surface of the deflector, and the horizontal axis represents the driving frequency of the deflecting mirror surface. The resonance curves R1 and R4 and the resonance curve R5 of the oscillation amplitude of the deflection mirror surface when the amplitude of the drive signal for driving the deflection mirror surface having the resonance curve R4 is decreased are shown. As shown in FIG. 3, the deflection mirror surface has resonance frequencies f01 and f03 before and after the fluctuation of the resonance frequency, and when it is driven to oscillate at a driving frequency within the optical scanning effective band, it is greater than a predetermined oscillation amplitude Θ0. The oscillation amplitude is as follows. As described above, the oscillation amplitude Θ0 is a value required for the deflector to scan at least the effective scanning area on the surface to be scanned with the light beam deflected by the deflection mirror surface. In the figure, FB indicates an optical scanning effective band when the deflecting mirror surface has the resonance frequency f01, and an optical scanning effective band when the deflection mirror surface has the resonance frequency f03 is not shown.

  In FIG. 4, the vertical axis is the swing amplitude (Θ) of the deflecting mirror surface of the deflector, and the horizontal axis is time (t), and the swing when the deflecting mirror surface whose resonance curve is shown in FIG. A dynamic amplitude waveform is shown. More specifically, when the deflection mirror surface having the resonance characteristic of the resonance curve R1 is oscillated and driven at the drive frequency f1 before the resonance frequency is decreased, the oscillation amplitude waveform F1 of the deflection mirror surface, and the resonance curve after the resonance frequency is decreased. When the deflection mirror surface having the resonance characteristic of R4 is oscillated and driven at the drive frequency f1, the oscillation amplitude waveform F4 of the deflection mirror surface, and the drive for driving the deflection mirror surface having the resonance characteristic of the resonance curve R4 after the resonance frequency is decreased. A swing amplitude waveform F5 of the deflection mirror surface when the deflection mirror surface having the resonance characteristic of the resonance curve R5 is driven to swing at the drive frequency f1 by decreasing the amplitude of the signal is shown. In the figure, for easy understanding of the description, at the time t 0, the points where the swing amplitude is 0 overlap in each swing amplitude waveform. Further, the oscillation amplitude waveforms F1 and F5 are drawn in an overlapping manner because the driving frequency and amplitude of the deflecting mirror surface are substantially equal.

  In the optical scanning device according to the present invention, the deflection mirror surface having the resonance frequency f01 is oscillated and driven at a drive frequency f1 lower than the resonance frequency f01 and within the optical scanning effective band FB. Therefore, the maximum value of the swing amplitude of the deflection mirror surface is Θ1 (see FIGS. 3 and 4). Similarly, when the resonance frequency of the deflection mirror surface decreases to the resonance frequency f03, the deflection mirror surface is oscillated at a drive frequency f1 that is lower than the resonance frequency f02 of the deflection mirror surface and within the optical scanning effective band (not shown). Driving. Therefore, the oscillation amplitude of the deflection mirror surface is Θ3 (see FIGS. 3 and 4). That is, even if the resonance frequency decreases, the oscillation amplitude of the deflection mirror surface is larger than before the resonance frequency of the deflection mirror surface increases by making the frequency of the drive signal for driving the deflection mirror surface substantially constant. Value (Θ3).

  Next, as described above, as the resonance frequency of the deflecting mirror surface decreases, the frequency of the driving signal for driving the deflecting mirror surface is made substantially constant and the amplitude of the driving signal is reduced, so that The principle of adjusting the scanning time for scanning the effective scanning area with the light beam will be described in detail.

  When the deflection mirror surface having the resonance characteristic of the resonance curve R1 is oscillated and driven at the drive frequency f1 before the resonance frequency is decreased, the deflection mirror surface is oscillated and driven as the oscillation amplitude waveform F1. At this time, the light beam deflected by the deflection mirror surface at time t11 passes through the light beam detection position A and is detected by the light beam detection sensor (light beam detection element). Further, the light beam deflected by the deflecting mirror surface at time t12 passes through the light beam detection position B and is detected by the light beam detection sensor. In this case, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT.

  Next, when the resonance frequency f01 of the deflecting mirror surface decreases to the resonance frequency f03 (resonance curve R4) due to fluctuations in the temperature or the like of the use environment of the deflector, the drive frequency f1 is the same as before the resonance frequency is decreased. When the deflection mirror surface is driven to swing, the swing amplitude of the deflection mirror surface fluctuates (increases), so that the scanning time during which the light beam scans the effective scanning area on the surface to be scanned fluctuates. That is, the scanning time during which the light beam scans from the light beam detection position A to the light beam detection position B varies. At this time, the scanning time can be adjusted by reducing the amplitude of the drive signal while keeping the frequency of the drive signal for driving the deflection mirror surface substantially constant (see waveform F4 and waveform F5).

  In FIG. 4, as shown by the oscillation amplitude waveforms F4 and F5, the amplitude of the drive signal for driving the deflection mirror surface is decreased while the frequency of the drive signal for driving the deflection mirror surface is substantially constant (see FIG. 3). This shows how the oscillation amplitude of the deflection mirror surface decreases. As described above, as the resonance frequency is reduced, the frequency of the drive signal is made substantially constant, and the amplitude of the drive signal is reduced to reduce the oscillation amplitude of the deflection mirror surface, thereby being deflected by the deflection mirror surface. The light beam passes through the light beam detection position A at time t11 and passes through the light beam detection position B at time t12. That is, the time during which the light beam scans from the light beam detection position A to the light beam detection position B is PT, which is substantially equal to the scanning time PT before the resonance frequency is decreased. In this way, by adjusting the oscillation amplitude of the deflection mirror surface by reducing the amplitude of the drive signal (Θ3 → Θ1) while making the frequency of the drive signal of the deflection mirror surface substantially constant, the deflection mirror surface Before and after the resonance frequency is decreased, the time during which the light beam scans from the light beam detection position A to the light beam detection position B can be made substantially constant.

  In addition, although the case where the resonance frequency is reduced due to fluctuations in the temperature or the like of the usage environment has been described, the above method is also applied to the variation in the resonance frequency of the deflection mirror surface caused by the manufacturing method of the deflector, and the surface to be scanned The scanning time during which the light beam scans the upper effective scanning region can be adjusted to be substantially constant. Therefore, even if the resonance frequency varies or fluctuates, it can be appropriately handled by reducing the amplitude of the drive signal while keeping the frequency of the drive signal substantially constant. Thus, by efficiently controlling the drive signal for driving the deflection mirror surface, energy saving can be realized and the light beam can be stably scanned on the surface to be scanned. Further, the scanning time for the light beam to scan the effective scanning area on the surface to be scanned can be adjusted to be substantially constant by reducing only the amplitude of the driving signal while keeping the frequency of the driving signal substantially constant. Therefore, the control of the drive signal can be simplified.

  In the second basic operation, “adjustment of the frequency of the drive signal” is performed in which the frequency of the drive signal is not changed and the frequency before the change is maintained despite the change in the resonance frequency. Of course, the frequency of the drive signal may be changed while satisfying the condition that it is within the optical scanning effective band and lower than the resonance frequency wave number, and the amplitude of the drive signal may be decreased accordingly.

  In all of the embodiments described below, the frequency of the drive signal for the deflection mirror surface is set and adjusted as described above.

<First Embodiment>
FIG. 5 is a view showing an image forming apparatus equipped with an exposure unit according to the first embodiment of the optical scanning apparatus of the present invention. FIG. 6 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus is a so-called four-cycle color printer. In this image forming apparatus, when a print command is given to the main controller 11 from an external device such as a host computer in response to an image formation request from the user, the engine controller 10 responds to the print command from the CPU 111 of the main controller 11. The engine unit EG is controlled to form an image corresponding to the print command on a sheet such as copy paper, transfer paper, paper, and OHP transparent sheet.

  In this engine unit EG, a photosensitive member 2 (corresponding to a “latent image carrier” of the present invention) is provided so as to be rotatable in the arrow direction (sub-scanning direction) in FIG. Further, a charging unit 3, a rotary developing unit 4, and a cleaning unit (not shown) are arranged around the photoconductor 2 along the rotation direction. A charging controller 103 is electrically connected to the charging unit 3 and applies a predetermined charging bias. By applying this bias, the outer peripheral surface of the photoreceptor 2 is uniformly charged to a predetermined surface potential. Further, the photosensitive member 2, the charging unit 3, and the cleaning unit integrally constitute a photosensitive member cartridge, and the photosensitive member cartridge is integrally detachable from the apparatus main body 5.

  Then, the light beam L is irradiated from the exposure unit 6 corresponding to the optical scanning device (exposure means) of the present invention toward the outer peripheral surface of the photoreceptor 2 charged by the charging unit 3. The exposure unit 6 exposes a light beam L on the surface of the photosensitive member 2 (corresponding to the “scanned surface” of the present invention) in accordance with an image signal given from an external device, and outputs electrostatic light corresponding to the image signal. A latent image is formed. The configuration and operation of the exposure unit 6 will be described in detail later.

  The electrostatic latent image thus formed is developed with toner by the developing unit 4 (corresponding to the “developing means” of the present invention). That is, in this embodiment, the developing unit 4 is configured as a support frame 40 that is rotatably provided around the axis, and a cartridge that is detachable with respect to the support frame 40, and for yellow that contains toner of each color. A developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4K are provided. Then, based on a control command from the developing device controller 104 of the engine controller 10, the developing unit 4 is rotationally driven and these developing devices 4Y, 4M, 4C, 4K are selectively brought into contact with the photosensitive member 2. Alternatively, when positioned at a predetermined developing position facing each other with a predetermined gap, toner is applied to the surface of the photoreceptor 2 from a developing roller provided in the developing unit and carrying toner of a selected color. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color.

  The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 that is stretched over a plurality of rollers 72, 73, and the like, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction by rotationally driving the roller 73. It has.

  In the vicinity of the roller 72, a transfer belt cleaner (not shown), a density sensor 76 (FIG. 6), and a vertical synchronization sensor 77 (FIG. 6) are arranged. Among these, the density sensor 76 is provided facing the surface of the intermediate transfer belt 71 and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71. The vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71, and is a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71 in the sub-scanning direction, that is, a vertical synchronization signal. It functions as a vertical sync sensor for obtaining Vsync. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and to superimpose toner images of each color accurately.

  When transferring a color image to a sheet, each color toner image formed on the photoreceptor 2 is superimposed on the intermediate transfer belt 71 to form a color image and taken out from the cassette 8 one by one. The color image is secondarily transferred onto the sheet conveyed along the conveyance path F to the secondary transfer region TR2.

  At this time, in order to correctly transfer the image on the intermediate transfer belt 71 to a predetermined position on the sheet, the timing of feeding the sheet to the secondary transfer region TR2 is managed. Specifically, a gate roller 81 is provided on the transport path F on the front side of the secondary transfer region TR2, and the gate roller 81 rotates in accordance with the timing of the circumferential movement of the intermediate transfer belt 71. Are sent to the secondary transfer region TR2 at a predetermined timing.

  Further, the sheet on which the color image is formed in this way is conveyed to the discharge tray portion 51 provided on the upper surface portion of the apparatus main body 5 via the fixing unit 9 and the discharge roller 82. Further, when images are formed on both sides of the sheet, the sheet on which the image is formed on one side as described above is switched back by the discharge roller 82. As a result, the sheet is conveyed along the reverse conveyance path FR. Then, it is put again on the transport path F before the gate roller 81. At this time, the image is transferred to the surface of the sheet that is in contact with the intermediate transfer belt 71 and transfers the image in the secondary transfer region TR2. The surface is the opposite of the surface. In this way, images can be formed on both sides of the sheet.

  In FIG. 6, reference numeral 113 denotes an image memory provided in the main controller 11 for storing image data given from an external device such as a host computer via the interface 112, and reference numeral 106 is executed by the CPU 101. A ROM for storing calculation data, control data for controlling the engine unit EG, and the like, and a reference numeral 107 are RAMs for temporarily storing calculation results in the CPU 101 and other data.

  7 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 5, and FIG. 8 is a diagram showing a configuration of an exposure unit and an exposure control unit of the image forming apparatus of FIG. 9 and 10 are diagrams showing a deflector as one component of the exposure unit, FIG. 11 is a schematic diagram for calculating the scanning time of the light beam in this embodiment, and FIG. 12 is a drive signal in this embodiment. It is a flowchart which shows the control procedure of a frequency and an amplitude. Hereinafter, the configuration and operation of the exposure unit will be described in detail with reference to these drawings.

  The exposure unit 6 has an exposure housing 61. A single laser light source 62 is fixed to the exposure housing 61 so that a light beam can be emitted from the laser light source 62. The laser light source 62 is electrically connected to the light source driving unit 102a of the exposure control unit 102. For this reason, the light source driving unit 102a controls the laser light source 62 on / off according to the image data, and the laser light source 62 emits a light beam modulated according to the image data.

  Further, in the exposure housing 61, a collimator lens 631, a cylindrical lens 632, a deflector 65, a scanning lens are used to scan and expose the light beam from the laser light source 62 onto the surface (not shown) of the photoreceptor 2. 66 is provided. That is, the light beam from the laser light source 62 is shaped into collimated light of an appropriate size by the collimator lens 631 and then incident on the cylindrical lens 632 having power only in the sub-scanning direction Y. Then, by adjusting the cylindrical lens 632, the collimated light is imaged in the vicinity of the deflection mirror surface 651 of the deflector 65 in the sub-scanning direction Y. Thus, in this embodiment, the collimator lens 631 and the cylindrical lens 632 function as the beam shaping system 63 that shapes the light beam from the laser light source 62.

  The deflector 65 is formed by using a micromachining technique in which a micromachine is integrally formed on a semiconductor substrate by applying a semiconductor manufacturing technique. The deflector 65 reflects the light beam reflected by the deflection mirror surface 651 in the main scanning direction X. Deflection is possible. More specifically, the deflector 65 is configured as follows.

  As shown in FIG. 9, in this deflector 65, a silicon substrate 652 functions as a support member, and a movable plate 656 is provided by processing a part of the silicon substrate 652. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and is swingable about a swing axis AX1 extending substantially parallel to the sub-scanning direction Y. Further, a planar coil 655 that is electrically connected to a pair of outer electrode terminals (not shown) formed on the upper surface of the silicon substrate 652 via a torsion spring 657 is coated on the upper surface of the movable plate 656 with an insulating layer. It has been. In addition, an aluminum film or the like is formed as a deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  Further, as shown in FIG. 10, a concave portion 652a is provided at a substantially central portion of the silicon substrate 652 so that the movable plate 656 can swing around the swing axis AX1. Then, permanent magnets 659a and 659b are fixed to the inner bottom surface of the recess 652a in positions different from each other at both ends of the movable plate 656 in different orientations. Further, the planar coil 655 is electrically connected to the drive unit 102b of the exposure control unit 102, and the Lorentz depends on the direction of the current flowing through the planar coil 655 by the energization of the coil 655 and the direction of the magnetic flux by the permanent magnets 659a and 659b. A force acts and a moment for rotating the movable plate 656 is generated. As a result, the movable plate 656 (deflection mirror surface 651) swings with the torsion spring 657 as the swing axis AX1. Here, if the current flowing through the planar coil 655 is an alternating current and is continuously repeated, the deflection mirror surface 651 can be reciprocally oscillated with the torsion spring 657 as the swing axis AX1.

  As described above, in the deflector 65, the driving unit 102b of the exposure control unit 102 functions as the “mirror driving unit” of the present invention, and controls the driving unit 102b, thereby “the basic operation of the optical scanning device according to the present invention”. As described in the section, the deflecting mirror surface 651 (deflector 65) due to variations in the resonance frequency of the deflecting mirror surface 651 (deflector 65) due to the manufacturing method of the deflector 65, temperature of the use environment, and the like. By adjusting the frequency and amplitude of the drive signal for driving the deflecting mirror surface 651 (current flowing through the planar coil 655) in accordance with the fluctuation of the resonance frequency, the driving frequency and oscillation amplitude of the deflecting mirror surface 651 are adjusted. . In this manner, the light beam is deflected and scanned in the main scanning direction X by swinging the deflection mirror surface 651 about the swing axis AX.

  The light beam deflected by the deflecting mirror surface 651 of the deflector 65 configured as described above is deflected toward the scanning lens 66. In this embodiment, the scanning lens 66 is configured so that the F values are substantially the same over the entire effective scanning area PA (see FIG. 11) on the surface of the photoreceptor 2. Therefore, the light beam deflected toward the scanning lens 66 is focused on the effective scanning area PA on the surface of the photoreceptor 2 with the substantially same spot diameter via the scanning lens. As a result, a light beam is scanned in parallel with the main scanning direction X, and a line-like latent image extending in the main scanning direction X is formed on the surface of the photoreceptor 2.

  Further, in this embodiment, as shown in FIG. 7, the start or end of the scanning light beam from the deflector 65 is turned back by mirrors 69a and 69b to synchronize sensors 60A and 60B (corresponding to “beam detecting element” in the present invention) Leading to. These folding mirrors 69a and 69b and the synchronization sensors 60A and 60B are disposed outside the sweep surface formed by sweeping the light beam when scanning the effective scanning area PA. The folding mirrors 69a and 69b are disposed substantially symmetrically with respect to the optical axis L0 when the light beam scans the substantial center of the effective scanning area PA. Therefore, as schematically shown in FIG. 11, the synchronization sensors 60A and 60B can be considered to be equivalent to being arranged substantially symmetrically with respect to the optical axis L0.

  The detection signals of the light beams from the synchronization sensors 60A and 60B are transmitted to the measuring unit 102c of the exposure control unit 102, and the scanning time for scanning the effective scanning area PA with the light beam is calculated in the measuring unit. Then, the scanning time calculated in the measuring unit 102c is transmitted to the driving unit 102b (mirror driving means), and the driving unit 102b drives the deflection mirror surface 651 according to the transmitted scanning time. And determine the amplitude. That is, the folding mirrors 69a and 69b, the synchronization sensors 60A and 60B, and the measuring unit 102c function as the scanning time measuring unit of the present invention. Further, in this embodiment, the synchronization sensors 60A and 60B function as a horizontal synchronization read sensor for obtaining a synchronization signal when the light beam scans the effective scanning area PA in the main scanning direction X, that is, the horizontal synchronization signal Hsync. I am letting.

  Next, the operation of the exposure unit 6 (optical scanning device) configured as described above will be described with reference to FIG. FIG. 12 is a flowchart showing the operation of the exposure unit 6 of FIG. The exposure unit 6 performs control to adjust the frequency and amplitude of the drive signal for driving the deflection mirror surface 651 to the frequency and amplitude corresponding to the resonance frequency of the deflection mirror surface 651 (deflector 65).

  First, the laser light source 62 is turned on (step S1), and optical scanning of the surface (scanned surface) of the photoreceptor 2 is started. Then, the time Δts during which the light beam passes through the two synchronization sensors 60A and 60B is measured from the time when the light beam is incident on the synchronization sensors 60A and 60B (step S2), and then the measurement value Δts in step S2 is used. Then, a scanning time Δtp during which the light beam scans the effective scanning area PA on the surface of the photosensitive member 2 is calculated (step S3).

  In step 3, first, the maximum swing amplitude Θm of the deflection mirror surface 651 (deflector 65) is calculated using the measured value Δts in step 2 (Equation 1).

そして、数１によって算出された偏向ミラー面６５１（偏向器６５）の最大揺動振幅Θmより、光ビームが感光体２の表面の有効走査領域ＰＡを走査する走査時間Δtpを算出する（数２）。

Then, from the maximum swing amplitude Θm of the deflecting mirror surface 651 (deflector 65) calculated by Equation 1, a scanning time Δtp for scanning the effective scanning area PA of the surface of the photoreceptor 2 by the light beam is calculated (Equation 2 ).

なお、数１、数２中における各記号は以下の通りである（図１１参照）。

In addition, each symbol in Formula 1 and Formula 2 is as follows (refer FIG. 11).

Θs: rotation angle of the deflection mirror surface when the synchronous sensor detects the light beam (a known value from the arrangement relationship of the components constituting the exposure unit)
Θp: rotation angle of the deflecting mirror surface when the end of the effective scanning area is scanned by the light beam (a known value from the arrangement relationship of the components constituting the exposure unit)
f: Deflector drive frequency Θm: Maximum swing amplitude of deflector (deflection mirror surface) Δts: Time for light beam to pass through two synchronous sensors Δtp: Scanning time for light beam to scan effective scanning area PA Δts is a time measured by the synchronous sensors 60A and 60B, and Δtp is a time calculated by the measuring unit 102c of the exposure control unit 102.

  The scanning time Δtp calculated in step S3 is transmitted to the driving unit 102b of the exposure control unit 102, and an error e with respect to the preset value Δtp0 of the scanning time of the effective scanning area PA set in advance in the driving unit 102b is calculated. (Step S4). If the error e is smaller than a preset error allowable value e0, the optical scanning of the surface of the photosensitive member 2 is continued with the frequency and amplitude of the drive signal as it is.

  However, if the error e calculated in step S4 is larger than the allowable error value e0, the frequency value and amplitude value of a new drive signal are calculated (step S6). Then, according to the frequency value and the amplitude value calculated in step S6, the drive unit 102b (mirror drive means) adjusts the frequency and amplitude of the drive signal for driving the deflection mirror surface 651 (deflector 65) (step S7). Thereafter, the operation from step S3 is repeated until the error e becomes smaller than the allowable error value e0.

  As described above, according to this embodiment, the drive unit 102b (mirror drive unit) of the exposure control unit 102 sets the frequency of the drive signal for driving the deflection mirror surface 651 (deflector 65) to the deflection mirror surface 651. According to the resonance frequency, adjustment is performed while satisfying the condition that the resonance frequency is lower than the resonance frequency, and the amplitude of the drive signal is adjusted. As described above, scanning in which the light beam scans the effective scanning area PA, which is fluctuated due to variations in the resonance frequency due to variations in the resonance frequency of the deflection mirror surface 651 due to the manufacturing method of the deflector 65 and variations in the temperature of the usage environment, etc. The time Δtp is adjusted to be within a predetermined error range e0 of the preset scanning time Δtp0 by adjusting the frequency and amplitude of the drive signal for driving the deflection mirror surface 651 (deflector 65). Yes. Therefore, even if the resonance frequency of the deflecting mirror surface 651 fluctuates due to variations in the resonance frequency of the deflecting mirror surface 651 due to manufacturing errors of the deflector 65, or due to fluctuations in the temperature of the environment in which the deflector 65 is used, the present invention By reducing the amplitude (energy) of the drive signal by the action and effect described in detail in the section “Basic operation of the optical scanning device according to the above”, the scanning time during which the light beam scans the effective scanning area PA is kept substantially constant, The light beam is stably scanned over the effective scanning area PA. As described above, by efficiently controlling the drive signal, energy saving of the optical scanning device can be realized, and the light beam can be stably scanned on the surface to be scanned. Furthermore, since the frequency of the drive signal is set within the optical scanning effective band, the light beam can be scanned over the entire effective scanning region.

  In this embodiment, the frequency of the drive signal is increased and the amplitude of the drive signal is decreased as the resonance frequency is increased. Therefore, since the drive signal is controlled more efficiently, the energy saving of the optical scanning device can be further improved.

  In this embodiment, the amplitude of the drive signal is reduced while keeping the frequency of the drive signal substantially constant as the resonance frequency is reduced. As described above, the drive signal is controlled more efficiently, and the frequency of the drive signal for driving the deflecting mirror surface 651 is made substantially constant, and only the amplitude of the drive signal is reduced. Can be further improved, and the control of the drive signal can be simplified.

  In this embodiment, the time Δtp during which the light beam scans the effective scanning area PA is calculated from the outputs of the synchronization sensors 60A and 60B, and Δtp is set within a predetermined error range e0 of Δtp0 set in advance. The frequency and amplitude of the drive signal for driving the deflection mirror surface 651 (deflector 65) are adjusted. Therefore, not only the individual difference of the resonance frequency caused by the manufacturing error of the deflector but also the change of the resonance frequency due to the change of the use environment can be dealt with in real time. Therefore, the scanning time during which the light beam scans the effective scanning area PA can be made substantially constant with higher accuracy.

  Further, in this embodiment, the folding mirrors 69a and 69b and the synchronization sensors 60A and 60B are disposed outside the sweep surface formed by sweeping when the light beam scans the effective scanning area PA. Accordingly, the folding mirrors 69a and 69b and the synchronization sensors 60A and 60B do not become obstacles when the light beam scans the effective scanning area PA, so that it is not necessary to add a beam splitter or the like, and a simple configuration can be realized.

  In this embodiment, the two synchronization sensors 60A and 60B are disposed substantially symmetrically with respect to the optical axis when the light beam scans the substantial center of the effective scanning area PA (see FIG. 11). . Therefore, it is easy to calculate the scanning time Δtp during which the light beam scans the effective scanning area PA using the time Δts that is measured by the two synchronization sensors and passes through the two synchronization sensors 60A and 60B. It can be carried out.

  In this embodiment, the synchronization sensors 60A and 60B function as a horizontal synchronization reading sensor for obtaining a synchronization signal when the light beam scans the effective scanning area PA in the main scanning direction X, that is, the horizontal synchronization signal Hsync. I am letting. Therefore, it is not necessary to add a new sensor to obtain Hsync, and the apparatus configuration can be simplified.

  Further, according to this embodiment, the electrostatic latent image stably formed by the exposure unit described above is developed with toner. Therefore, a stable image can be obtained.

Second Embodiment
FIG. 13 is a diagram showing a second embodiment of the optical scanning device according to the present invention. The second embodiment is greatly different from the first embodiment in that the deflection mirror surface 651 is driven to swing using electrostatic force, and other configurations are the same as those in the first embodiment. is there. In addition, the same code | symbol is attached | subjected to the structure same as 1st Embodiment.

  In the deflector 65, as shown in FIG. 13, a movable plate 656 is provided by processing a part of the silicon substrate 652. The movable plate 656 is formed in a flat plate shape, is elastically supported on the silicon substrate 652 by a torsion spring 657, and is swingable about a swing axis AX1 extending substantially parallel to the sub-scanning direction Y. In addition, an aluminum film or the like is formed as a deflection mirror surface 651 at the center of the upper surface of the movable plate 656.

  Further, as shown in FIG. 13, a recess 652a is provided at a substantially central portion of the silicon substrate 652 so that the movable plate 656 can swing around the swing axis AX1. Electrodes 658a and 658b are respectively fixed to positions on the inner bottom surface of the recess 652a that face both ends of the movable plate 656. These two electrodes 658a and 658b function as electrodes for driving the movable plate 656 to swing around the swing axis AX1. That is, these electrodes 658 a and 658 b are electrically connected to a drive unit (not shown) of the exposure control unit 102, and electrostatic adsorption force is applied between the electrode and the deflecting mirror surface 651 by applying a voltage to the electrode. Acts to draw one end of the deflecting mirror surface 651 toward the electrode. Therefore, when a predetermined voltage is alternately applied to the electrodes 658a and 658b from the driving unit, the deflection mirror surface 651 (movable plate 656) can be reciprocally oscillated using the torsion spring 657 as the swing axis AX1. In this embodiment, the deflection mirror surface 651 (movable plate 656) is driven to swing as described in the section "Basic operation of the optical scanning device according to the invention". Therefore, it has the same effect as the first embodiment.

  In order to swing the deflecting mirror surface 651 in this way, electromagnetic force, electrostatic force or the like is used, but it goes without saying that any of them may be used. However, since each driving method has the following characteristics, it is desirable to adopt them appropriately in consideration of them. That is, when an electromagnetic force is used as a driving force for driving the deflection mirror surface 651 to swing, the deflection mirror surface 651 can be driven to swing with a lower driving voltage than when an electrostatic attraction force is generated. Thus, voltage control is facilitated, and the positional accuracy of the scanning light beam can be increased. On the other hand, when the electrostatic attraction force is used as the driving force, there is no need to form a coil pattern, the deflector 65 can be further miniaturized, and the deflection scanning can be further speeded up.

<Third Embodiment>
FIG. 14 is a diagram showing a third embodiment of the optical scanning device according to the present invention. The third embodiment is greatly different from the first and second embodiments in that the scanning time of the light beam is measured by one synchronization sensor 60C and folding mirrors 69c to 69e. Other configurations are the same as those in the first and second embodiments.

  Also in this case, since the deflector 65 is controlled as in the first and second embodiments, the same operation and effect are obtained.

<Others>
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, the relationship between the resonance frequency, the frequency of the drive signal, the amplitude of the drive signal, and the scanning time Δtp is stored in advance in the ROM 106 or the like, and the deflection mirror surface 651 (deflector 65) is set based on these stored values. It is good also as a structure which adjusts the frequency and amplitude of the drive signal to drive substantially. Such a configuration also has the same effects as the above embodiment.

  In this case, the synchronization sensors 60A to 60C may not be provided. Even with such a configuration, it is possible to realize an optical scanning device having the same effect as the above-described embodiment and having a simple configuration in which no synchronization sensor is provided.

  In the above embodiment, the optical scanning device according to the present invention is used as the exposure unit of the color image forming apparatus, but the application target of the present invention is not limited to this. That is, as an exposure unit of an image forming apparatus that scans a light beam on a latent image carrier such as a photoconductor to form an electrostatic latent image and develops the electrostatic latent image with toner to form a toner image. Can be used. Of course, the application target of the optical scanning device is not limited to the exposure means provided in the image forming apparatus, but can be applied to all optical scanning devices that scan the surface to be scanned with the light beam.

It is a figure which shows the resonance curve of the oscillation amplitude of a deflection | deviation mirror surface. It is a figure which shows a mode that the drive frequency and rocking | fluctuation amplitude of a deflection | deviation mirror surface are changed with adjustment of the frequency and amplitude of a drive signal. It is a figure which shows the resonance curve of the oscillation amplitude of a deflection | deviation mirror surface. It is a figure which shows a mode that the drive frequency and rocking | fluctuation amplitude of a deflection | deviation mirror surface are changed with adjustment of the frequency and amplitude of a drive signal. 1 is a diagram illustrating an image forming apparatus equipped with an exposure unit according to a first embodiment of an optical scanning device according to the present invention. FIG. 6 is a block diagram illustrating an electrical configuration of the image forming apparatus in FIG. 5. FIG. 6 is a main scanning sectional view showing a configuration of an exposure unit (optical scanning device) provided in the image forming apparatus of FIG. 5. It is a block diagram which shows the structure of the exposure unit and exposure control part of FIG. It is a figure which shows the deflector which is one component of an exposure unit. It is a figure which shows the deflector which is one component of an exposure unit. It is a schematic diagram for calculating the scanning time of the light beam. It is a flowchart which shows the control procedure of the frequency and amplitude of a drive signal. It is a figure which shows the deflector which is one component of the exposure unit which is 2nd Embodiment of the optical scanning device concerning this invention. It is a main scanning sectional view showing a third embodiment of the optical scanning device according to the present invention.

Explanation of symbols

2 ... photosensitive body (latent image carrier), 4 ... developing unit (developing means), 6 ... exposure unit (optical scanning device), 60A, 60B, 60C ... synchronous sensor (scanning time measuring means), 69a, 69b, 69c , 69d, 69e ... folding mirror (scanning time measuring means), 65 ... deflector, 651 ... deflecting mirror surface, 102b ... driving unit (mirror driving means), 102c ... measuring unit (scanning time measuring means), AX1 ... swinging Axis, PA: Effective scanning area, FB: Optical scanning effective band, f01, f02, f03 ... Resonance frequency, f1, f2 ... Drive frequency, X ... Main scanning direction, Y ... Sub scanning direction

Claims (8)

In an optical scanning device that scans a light beam in a main scanning direction within an effective scanning area on a surface to be scanned,
A light source that emits a light beam;
A deflector having a deflecting mirror surface provided so as to be swingable about a swing axis substantially orthogonal to the main scanning direction and reflecting a light beam emitted from the light source to deflect the light beam in the main scanning direction;
Mirror driving means for applying a drive signal to the deflector to swing the deflection mirror surface about the swing axis;
When the frequency band of the drive signal can be scanned at least over the entire effective scanning region by resonating and swinging the deflection mirror surface, and the optical scanning effective band,
The mirror driving means adjusts the frequency of the drive signal in the optical scanning effective band in accordance with the resonance frequency of the deflecting mirror surface while satisfying the condition that it is lower than the resonance frequency, and An optical scanning device characterized by adjusting an amplitude of a drive signal to adjust a drive frequency of the deflection mirror surface and an oscillation amplitude of the deflection mirror surface.   The optical scanning device according to claim 1, wherein the mirror driving unit increases the frequency of the driving signal and decreases the amplitude of the driving signal as the resonance frequency increases.   2. The optical scanning device according to claim 1, wherein the mirror driving unit reduces the amplitude of the drive signal while keeping the frequency of the drive signal substantially constant as the resonance frequency decreases.   The apparatus further comprises scanning time measuring means for measuring a scanning time during which the light beam scans the effective scanning area and having at least one light beam detecting element, and the mirror driving means is driven by the output from the scanning time measuring means. 4. The optical scanning device according to claim 1, wherein the scanning time is made substantially constant by adjusting the frequency and amplitude of a signal.   The optical scanning device according to claim 4, wherein the light beam detection element is disposed outside a sweep surface formed by sweeping the light beam when scanning the effective scanning region.   The scanning time measuring means has two light beam detection elements, and each of the light beam detection elements is substantially symmetric with respect to an optical axis when the light beam scans a substantial center of the effective scanning region. The optical scanning device according to claim 4, wherein the optical scanning device is disposed on the surface.   7. The optical scanning device according to claim 4, wherein an output of the light beam detecting element is used as a horizontal synchronizing signal when the light beam scans the effective scanning area. A latent image carrier;
8. The optical scanning device according to claim 1, wherein the optical scanning device is configured to scan a light beam with a predetermined region on the surface of the latent image carrier as the effective scanning region, and to scan the latent image carrier on the latent image carrier. Exposure means for forming an electrostatic latent image on
An image forming apparatus comprising: developing means for developing the electrostatic latent image with toner to form a toner image.

Images