JP2006145772A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image free from distortion regardless of manufacturing variation and environmental change. <P>SOLUTION: This image forming apparatus is equipped with a resonance oscillating scanning mirror 3, a clock modulator 16, an ambient temperature measuring device 20, a temperature compensator 21, and a comparison arithmetic processor 22. By the ambient temperature measuring device 20 and the temperature compensator 21, a resonance frequency is determined for the resonance oscillating scanning mirror 3 at the temperature, with the comparison arithmetic processor 22 computing a deviation from a predetermined basic frequency of the resonance frequency as a correction. This correction is inputted in the clock modulator 16. The clock modulator 16, on the basis of the inputted correction, modulates the cycle of the image basic clock so that no image forming width is deviated from a prescribed width in the main scanning direction on account of a change or variance of the resonance frequency. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a resonance oscillation scanning mirror that scans a light beam by reflecting the light beam and generating resonance oscillation.

  In a laser beam printer, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum by scanning the laser beam, and this electrostatic latent image is developed with toner to form a visible toner image. The output image is obtained by transferring the toner image onto a sheet. The laser beam is scanned on the photosensitive drum in the axial direction (main scanning direction) of the photosensitive drum. A two-dimensional electrostatic latent image is formed on the peripheral surface of the photosensitive drum by rotating the photosensitive drum about its axis in accordance with the scanning of the laser beam.

  As means for scanning a laser beam, a polygon mirror having a plurality of reflecting surfaces and rotating at high speed is generally used. However, since the polygon mirror has, for example, six reflecting surfaces, it is difficult to reduce the size itself. In addition, since a motor for rotating the polygon mirror is necessary, it is difficult to reduce the size of such a laser beam printer.

  Therefore, as a means for scanning the laser beam, a laser beam printer having a resonance oscillation scanning mirror that scans the laser beam by reflecting the laser beam and generating resonance oscillation has attracted attention. The resonant vibration scanning mirror has an axis substantially parallel to the reflecting surface, and resonates by an electrostatic driving force, for example, and sine vibrates around the axis. As a result, the laser beam incident on the reflecting surface can be scanned.

  The laser beam is generated by a laser oscillator in synchronization with an image basic clock having a fixed period based on image data. This image basic clock is set so that an image having a predetermined width in the main scanning direction can be obtained when the resonant vibration scanning mirror vibrates at a predetermined resonance frequency. For this reason, when the resonance frequency of the resonant vibration scanning mirror deviates from a predetermined frequency, the image forming width deviates from the predetermined width in the main scanning direction. That is, the magnification in the main scanning direction deviates from a predetermined magnification, and the output image is distorted.

  Further, the photosensitive drum is rotated around its axis at a constant rotational speed (circumferential speed) corresponding to the paper transport speed, that is, the image forming (printing) speed. The rotational speed of the photosensitive drum is set so that the scanning line interval of the laser beam on the circumferential surface of the photosensitive drum becomes a predetermined interval when the resonant vibration scanning mirror vibrates at a predetermined resonant frequency. For this reason, when the resonance frequency deviates from a predetermined frequency, the scanning line interval is deviated from the predetermined interval with respect to the sub-scanning direction that is the circumferential direction of the photosensitive drum. As a result, the magnification in the sub-scanning direction deviates from a predetermined magnification, and the output image is distorted.

Therefore, the resonant vibration scanning mirror must vibrate regularly.
By the way, the resonance frequency of the resonant vibration scanning mirror varies depending on the mass distribution (moment) around the axis, for example, the size (including thickness) of the resonant vibration scanning mirror. The resonant vibration scanning mirror is finely processed with high accuracy. However, due to manufacturing variations, the mass distribution around the axis may deviate from the predetermined distribution, and the resonant vibration scanning mirror may not have the predetermined resonance frequency. In an image forming apparatus having such a resonant vibration scanning mirror, the output image is distorted.

Therefore, Patent Document 1 below proposes a resonant vibration scanning mirror that has a removable mass adjusting section and can adjust the resonance frequency by cutting the mass adjusting section.
JP-A-8-75475

However, the resonance frequency cannot be finely adjusted by excising the mass adjusting portion, and the resonance frequency cannot be adjusted with high reproducibility due to the cutting accuracy of the mass adjusting portion or burrs generated during cutting. Further, by making such adjustment, the cost of the resonant vibration scanning mirror is increased.
Furthermore, the resonance frequency fluctuates not only by the mass distribution around the axis of the resonant vibration scanning mirror but also by environmental changes such as changes in ambient temperature.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of forming an image without distortion regardless of manufacturing variations and environmental changes.

  In order to achieve the above object, an invention according to claim 1 has a resonance vibration scanning mirror that generates a predetermined resonance vibration, and the resonance vibration scanning mirror reflects a light beam output based on image data. In the image forming apparatus having a mechanism for scanning on the photosensitive member, a correction value generation unit that generates a correction value of the resonance frequency that exists individually for each resonance vibration scanning mirror, and a correction that the correction value generation unit generates An image forming apparatus comprising: a first correction unit that modulates an image basic clock for synchronously outputting a light beam based on image data according to a value.

  According to the present invention, the correction value generating means can generate a correction value that exists individually for each resonant vibration scanning mirror due to manufacturing variations and environmental changes. Then, based on this correction value, the period of the image basic clock is modulated (corrected) so that the image forming width in the main scanning direction does not deviate from a predetermined width due to fluctuations and variations in the resonance frequency. . That is, the magnification in the main scanning direction in the output image (image formed on the paper) can be set to a predetermined magnification.

Therefore, this image forming apparatus can form an image free from distortion (magnification shift in the main scanning direction) regardless of manufacturing variations and environmental changes.
2. The image forming apparatus according to claim 1, further comprising: a second correcting unit that corrects a process speed for forming an image on a sheet based on the correction value generated by the correction value generating unit. Device.

Examples of the process speed include a moving speed of the photosensitive member in the sub-scanning direction (for example, a peripheral speed of the photosensitive drum) and a paper conveyance speed.
The second correction means corrects the moving speed of the photosensitive member in the sub-scanning direction based on the correction value so that the scanning line interval in the sub-scanning direction does not deviate from a predetermined interval due to fluctuations and variations in the resonance frequency. can do. Further, the second correction unit can correct the sheet conveyance speed to match the movement speed of the photosensitive member in the sub-scanning direction based on the correction value.

Thereby, the magnification in the sub-scanning direction in the output image can be set to a predetermined magnification. Therefore, an image free from distortion (magnification shift in the main scanning direction and sub-scanning direction) can be formed regardless of manufacturing variations and environmental changes.
According to a third aspect of the present invention, the correction value generation means applies a correction value by applying a temperature measurement means for measuring an ambient temperature, and a temperature table of a resonance frequency stored in advance to the temperature measured by the temperature measurement means. The image forming apparatus according to claim 1, further comprising:

According to the present invention, it is possible to correct the change in the resonance frequency due to the change in the ambient temperature as the environmental change.
The image forming apparatus may further include a storage device that stores a resonance frequency measured at a predetermined temperature of a resonant vibration scanning mirror mounted on the image forming apparatus. In this case, the temperature table includes a predetermined temperature. The temperature may be associated with the resonance frequency for each resonance frequency.

In this case, the correction value can be obtained by fitting the temperature measured by the temperature measuring means and the actual measurement value of the resonance frequency stored in the storage device to the temperature table. Thereby, it is possible to obtain a correction value that takes into account variations in the resonance frequency due to manufacturing variations.
According to a fourth aspect of the present invention, the correction value generation means detects a light beam reflected by the resonance vibration scanning mirror and measures fluctuation or variation of the resonance vibration, and based on the measurement result. The image forming apparatus according to claim 1, further comprising a calculation unit that calculates a correction value.

According to the present invention, the actual resonance frequency (hereinafter referred to as “measured resonance frequency”) of the resonance vibration scanning mirror can be directly obtained by detecting the light beam reflected by the resonance vibration scanning mirror. Therefore, the calculation means can obtain a correction value reflecting all factors of resonance frequency variation or fluctuation, such as manufacturing variation and environmental change.
The calculating means may calculate a deviation of the actually measured resonance frequency from the reference frequency as a correction value. In this case, the reference frequency is, for example, a predetermined fixed resonance frequency. Alternatively, it may be an average value of the actually measured resonance frequencies of the latest predetermined number of times (for example, 50 times).

The image forming apparatus may include a light receiving sensor used to control the output timing of the light beam in the main scanning direction. In this case, the means for measuring fluctuation or variation in the resonance frequency is the light receiving sensor. The measured resonance frequency may be obtained from the time interval at which the light beam is detected.
A fifth aspect of the present invention is the image forming apparatus according to the fourth aspect, wherein the first correction unit feeds back the correction value calculated by the calculation unit to the image basic clock.

  According to the present invention, since the correction value is fed back to the image basic clock, for example, the environment around the resonant vibration scanning mirror such as the ambient temperature changes during the operation of the image forming apparatus, and the resonance vibration scanning mirror Even if the resonance frequency changes, an image without distortion can be formed by synchronizing the light beam with an image basic clock based on the changed resonance frequency.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing the structure of an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 reflects a laser oscillator 2 that outputs a laser beam L based on image data, and reflects the laser beam L output from the laser oscillator 2 and causes resonance vibration to generate the laser beam L. Resonant vibration scanning mirror 3 for scanning, and photosensitive drum 4 on which an electrostatic latent image is formed on the peripheral surface by irradiation with laser beam L scanned by resonance vibration scanning mirror 3 are provided. .

The laser oscillator 2 includes a laser diode (LD).
The resonant oscillation scanning mirror 3 has a reflection surface M that reflects the laser beam L. The laser beam L reflected by the reflecting surface M is reflected by the folding mirror 6 and guided to the peripheral surface of the photosensitive drum 4.
The resonant vibration scanning mirror 3 has an axis A substantially parallel to the reflection plane M, and is resonated in, for example, a torsion mode and sinusoidally vibrated around the axis A when an electrostatic driving force is applied. Thus, the laser beam L incident on the reflection plane M is scanned in a plane perpendicular to the axis A, and the arrival position of the laser beam L on the photosensitive drum 4 is a direction along the axis B of the photosensitive drum 4. (Main scanning direction; indicated by a double arrow H in FIG. 1). The folding mirror 6 has a longitudinal shape in the scanning direction of the laser beam L so that the scanned laser beam L can be guided to the entire image forming region set on the peripheral surface of the photosensitive drum 4. Yes.

A shaping optical system 5 is disposed on the optical path of the laser beam L between the laser oscillator 2 and the resonant oscillation scanning mirror 3. The cross-sectional shape of the laser beam L output from the laser oscillator 2 is shaped by the shaping optical system 5 (for example, an aperture, a collimator lens, a cylindrical lens, etc.).
A condensing lens 7 is disposed on the optical path of the laser beam L between the resonant oscillation scanning mirror 3 and the folding mirror 6. By passing through the condenser lens 7, the laser beam L scans the photosensitive drum 4 at a constant speed.

  At the time of image formation, the photosensitive drum 4 is rotated around its axis B (the direction of rotation is indicated by an arrow V in FIG. 1), and on the peripheral surface of the photosensitive drum 4, the upstream side of the irradiation position of the laser beam L. Are uniformly charged. The charged peripheral surface is repeatedly scanned in the main scanning direction by the laser beam L, so that a two-dimensional electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4. The electrostatic latent image is developed with toner to form a visible toner image, and the toner image is transferred onto a sheet to obtain an output image. The rotation of the photosensitive drum 4 around the axis B is controlled by the image forming process control device 10.

A light receiving sensor 8 is provided in the vicinity of one end in the scanning direction between the condenser lens 7 and the folding mirror 6 within the scanning range of the laser beam L by the sine vibration of the resonant vibration scanning mirror 3. . When receiving the laser beam L, the light receiving sensor 8 outputs a timing signal for controlling the timing of main scanning.
A timing signal output from the light receiving sensor 8 is input to the control unit 11. The controller 11 controls the output timing of the laser beam L of the laser oscillator 2 based on this timing signal. The control unit 11 generates an image basic clock, and the laser oscillator 2 outputs a laser beam L based on image data in synchronization with the image basic clock.

FIG. 2 is a timing chart of the image basic clock, the output of the laser beam L, and the timing signal.
Referring to FIGS. 1 and 2, the light receiving sensor 8 receives the laser beam L and outputs a timing signal. When this timing signal is input to the control unit 11, the control unit 11 performs a predetermined number of image basics. The clock is counted. During this time, the irradiation position of the laser beam L on the photosensitive drum 4 enters the image forming area (printing area) by scanning with the laser beam L.

  Subsequently, output of the laser beam L based on the image data is started in synchronization with the image basic clock. The output of the laser beam L is stopped after continuing the irradiation position of the laser beam L from one end to the other end of the image forming area based on the image basic clock. The output of the laser beam L during this period corresponds to one scanning line in the image forming area (printing area) on the photosensitive drum 4.

  Subsequently, when a predetermined number of image basic clocks are counted and the scanned laser beam L is directed to the light receiving sensor 8, the laser oscillator 2 outputs an output (forced lighting) unrelated to image formation by the control unit 11. ) Is controlled. The laser beam L by the forced lighting is received by the light receiving sensor 8 and a timing signal is output. After the control unit 11 counts a predetermined number of image basic clocks, the output of the laser beam L corresponding to the next scanning line is output. Be started.

FIG. 3 is a block diagram of a control system of the image forming apparatus 1.
The control unit 11 includes an image basic clock generator 15, a clock modulator 16, an image data transfer device 17, and a laser diode (LD) oscillation / control device 18.
The image basic clock generator 15 generates an image basic clock having a fixed period and outputs it to the clock modulator 16. The image basic clock is modulated by the clock modulator 16 so as to have a predetermined period. The image basic clock generated by the image basic clock generator 15 is set so that an output image having a predetermined width in the main scanning direction can be obtained when the resonant oscillation scanning mirror 3 is resonantly oscillating at a predetermined resonance frequency. ing.

  The image basic clock modulated by the clock modulation device 16 is input to the image data transfer device 17. The image data transfer device 17 is configured to receive and store image data output from an image data input unit (not shown) (for example, a document reading unit). The image data transfer device 17 outputs (transfers) the image data to the LD oscillation / control device 18 in synchronization with the image basic clock modulated by the clock modulation device 16.

The LD oscillation / control device 18 controls the laser oscillator 2 to output the laser beam L corresponding to the image data input from the image data transfer device 17.
The laser beam L output from the laser oscillator 2 is reflected by the resonant oscillation scanning mirror 3 and scanned. The laser beam L reflected in a predetermined angular direction is received by a light receiving sensor 8 as a synchronization detecting device. When receiving the laser beam L, the light receiving sensor 8 outputs a timing signal to the image data transfer device 17. Based on this timing signal, the image data transfer device 17 controls the start timing of image data transfer for each scanning line (see FIG. 2).

The image forming apparatus 1 includes an ambient temperature measuring device 20 that measures the temperature inside (preferably near the resonant vibration scanning mirror 3).
The control unit 11 includes a temperature correction unit 21 and a comparison calculation device 22. The temperature correction unit 21 includes a storage device in which data of a temperature table 21T of resonance frequencies is stored. In the temperature table 21 of the resonance frequency, the temperature and the resonance frequency of the resonance vibration scanning mirror 3 at that temperature are associated with each other.

  The temperature correction unit 21 is supplied with temperature data measured from the ambient temperature measurement device 20. The temperature correction unit 21 applies the temperature to the temperature table 21 of the resonance frequency, obtains the resonance frequency of the resonance vibration scanning mirror 3 at the temperature, and outputs the data of the resonance frequency to the comparison calculation device 22. The comparison calculation device 22 calculates a deviation of the resonance frequency from a predetermined basic frequency as a correction value that exists individually for each resonance vibration scanning mirror 3.

  The correction value calculated by the comparison operation device 22 is input to the clock modulation device 16. Based on the input correction value, the clock modulation device 16 modulates the period of the image basic clock so that the image forming width in the main scanning direction does not deviate from a predetermined width due to fluctuations and variations in the resonance frequency. Thereby, the magnification in the main scanning direction in the output image can be set to a predetermined magnification.

  Further, the correction value calculated by the comparison calculation device 22 is input to the image forming process control device 10. When the correction value is input, the image forming process control device 10 is configured so that the scanning line interval in the sub-scanning direction does not deviate from a predetermined interval based on the input correction value due to variations and variations in the resonance frequency. The number of rotations (circumferential speed) around the axis B of the photosensitive drum 4 is controlled. Thereby, the magnification in the sub-scanning direction of the electrostatic latent image and the toner image formed on the peripheral surface of the photosensitive drum 4 can be set to a predetermined magnification.

  The image forming apparatus 1 further controls the sheet conveying apparatus 25 that conveys the sheet for transferring the toner image formed on the photosensitive drum 4 and the operation (for example, the sheet conveying speed) of the sheet conveying apparatus 25. A sheet conveyance control device 26 is provided. The correction value calculated by the comparison calculation device 22 is also input to the paper transport control device 26. The paper transport control device 26 controls the paper transport device 25 so as to transport paper according to the peripheral speed of the photosensitive drum 4 based on the input correction value. Thereby, the magnification in the sub-scanning direction in the output image can be set to a predetermined magnification.

As described above, the image forming apparatus 1 can obtain a distortion-free output image having a predetermined magnification in the main scanning direction and the sub-scanning direction.
FIG. 4 is a block diagram of a control system of the image forming apparatus according to the second embodiment of the present invention. 4, parts corresponding to those shown in FIG. 3 are denoted by the same reference numerals as those in FIG.

The control unit 31 of the image forming apparatus includes a resonance frequency detection device 33 and a comparison operation device 34.
The timing signal from the light receiving sensor 8 is output to the resonance frequency detection device 33 in addition to the image data transfer device 17. The resonance frequency detection device 33 obtains the actual resonance frequency (hereinafter referred to as “measured resonance frequency”) of the resonance vibration scanning mirror 3 from the time interval when the timing signal is input.

The data of the measured resonance frequency is input to the comparison calculation device 34. The comparison calculation device 34 calculates a deviation of the actually measured resonance frequency from the reference frequency as a correction value. The reference frequency may be a predetermined constant resonance frequency, or may be an average value of the measured resonance frequencies of the latest predetermined number of times (for example, 50 times).
The correction value is output from the comparison calculation device 34 to the clock modulation device 16, the image forming process control device 10, and the paper transport control device 26 as in the case of the first embodiment (see FIG. 3). Thereby, the modulation of the image basic clock, the control of the peripheral speed of the photosensitive drum 4 and the control of the paper conveyance speed are performed, respectively, and the magnification in the main scanning direction and the sub scanning direction in the output image formed on the paper is predetermined. Magnification. That is, an image without distortion can be formed.

In this image forming apparatus, by obtaining the actually measured resonance frequency, it is possible to obtain a correction value that reflects all factors of resonance frequency variation or fluctuation, such as manufacturing variation and environmental change.
Further, the correction value calculated by the comparison operation device 34 is periodically input (feedback) to the clock modulation device 16. Therefore, for example, even if the environment around the resonant vibration scanning mirror 3 such as the ambient temperature changes during the operation of the image forming apparatus, the laser beam L changes even if the resonant frequency of the resonant vibration scanning mirror 3 changes. By outputting in synchronization with an image basic clock based on the later resonance frequency, an image without distortion can be formed.

  The above is an example of an embodiment of the present invention, and the present invention is not limited to this. For example, the image forming apparatus 1 according to the first embodiment further includes a storage device that stores a resonance frequency (actually measured value) measured at a predetermined temperature of the resonant vibration scanning mirror 3 mounted on the image forming apparatus 1. You may have. In this case, the temperature table 21 may be a table in which a temperature and a resonance frequency are associated with each other at a predetermined frequency.

In this case, the correction value can be obtained by fitting the temperature measured by the ambient temperature measurement device 20 and the actual measurement value of the resonance frequency stored in the storage device to the temperature table. Thereby, it is possible to obtain a correction value that takes into account variations in the resonance frequency due to manufacturing variations.
In addition, various design changes can be made within the scope of matters described in the claims.

1 is a perspective view showing a structure of an image forming apparatus according to an embodiment of the present invention. 4 is a timing chart of an image basic clock, a laser beam output, and a timing signal. FIG. 2 is a block diagram of a control system of the image forming apparatus shown in FIG. 1. FIG. 5 is a block diagram of a control system of an image forming apparatus according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Resonant vibration scanning mirror 10 Image forming process control apparatus 11, 31 Control part 16 Clock modulation apparatus 20 Ambient temperature measuring apparatus 21 Resonance frequency temperature table 22, 34 Comparison calculating means 26 Paper conveyance control apparatus L Laser beam

Claims (5)

In an image forming apparatus having a resonance vibration scanning mirror that generates a predetermined resonance vibration, and having a mechanism that reflects a light beam output based on image data by the resonance vibration scanning mirror and scans it onto a photoconductor.
Correction value generating means for generating a correction value of the resonance frequency that exists individually for each of the resonance vibration scanning mirrors;
An image forming apparatus comprising: a first correction unit that modulates an image basic clock for synchronously outputting a light beam based on image data by a correction value generated by the correction value generation unit.   The image forming apparatus according to claim 1, further comprising a second correction unit that corrects a process speed for forming an image on a sheet based on a correction value generated by the correction value generation unit. The correction value generating means includes
Temperature measuring means for measuring the ambient temperature;
3. The image forming apparatus according to claim 1, further comprising: a means for calculating a correction value by applying the temperature measured by the temperature measuring means to a temperature table of resonance frequencies stored in advance. The correction value generating means detects a light beam reflected by the resonant vibration scanning mirror, and measures a fluctuation or variation of the resonant vibration;
The image forming apparatus according to claim 1, further comprising a calculation unit that calculates a correction value based on the measurement result.   The image forming apparatus according to claim 4, wherein the first correction unit feeds back the correction value calculated by the calculation unit to the image basic clock.

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