JP4730354B2 - Image forming apparatus and program - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an electrostatic latent image on an image carrier using a vibrating mirror that oscillates in a reciprocating manner and forms an image by an electrophotographic method. In the present specification, vibration caused by reciprocating rotation such as a galvanometer mirror is referred to as reciprocating rotational vibration in order to distinguish it from linear reciprocating vibration.

In recent years, an image forming apparatus that forms an image by an electrophotographic method uses a polygon mirror that rotates at a constant speed to scan an image carrier by deflecting a light beam. It has been proposed to perform scanning using a vibrating mirror such as a galvanomirror that is rotationally oscillated. In such an image forming apparatus using a vibrating mirror, a resonant vibrating mirror that is driven at the resonant frequency of the vibrating mirror is often used to increase the vibration amplitude. The amplitude of the oscillating mirror may deviate from the reference value. Therefore, it is proposed to monitor the scanning state of the laser beam through a fixed mirror and a photo sensor, and to control the amplitude by controlling the drive current of the semiconductor galvano mirror according to the detection interval of the laser beam by the photo sensor. (For example, refer to Patent Document 1).
JP 2001-228434 A

  However, if such control is performed during printing, there is a possibility that a problem such as distortion of the image may occur. For example, if the above-described control is performed while an image having ruled lines in the sub-scanning direction is formed, the ruled lines may swell in the scanning direction. In view of the above, an object of the present invention is to provide an image forming apparatus capable of accurately controlling the amplitude of a vibrating mirror while suppressing distortion of an image to be formed to form an accurate image.

The image forming apparatus of the present invention made to achieve the above object includes a light source that emits a light beam, a vibrating mirror that reflects the light beam emitted from the light source while reciprocatingly oscillating, and reflected by the vibrating mirror. An image carrier on which an electrostatic latent image is formed by irradiation of the light beam, developing means for developing the electrostatic latent image formed on the image carrier by attaching a developer, and Transfer means for transferring the developer adhered by the developing means to the recording medium, timing detection means for detecting timing corresponding to a blank line of print data, and the timing detection of the amplitude of the light beam by the vibrating mirror And amplitude adjusting means for adjusting at the timing detected by the means.

  In the image forming apparatus of the present invention configured as described above, the light beam emitted from the light source is reflected by the vibrating mirror that oscillates in a reciprocating manner, and is applied to the image carrier. By this light beam irradiation, an electrostatic latent image is formed on the image carrier, and the electrostatic latent image is developed with the developer attached by the developing means, and further, the developer is applied to the recording medium by the transferring means. The image is formed by being transferred.

In the present invention, the timing detection unit detects the timing corresponding to the blank line of the print data , and the amplitude adjustment unit adjusts the amplitude of the light beam by the vibrating mirror at the timing. For this reason, in the present invention, the amplitude of the oscillating mirror is adjusted at the timing when the electrostatic latent image is not formed on the image carrier, so that the amplitude is accurately controlled while suppressing the distortion in the image due to the amplitude adjustment. As a result, an accurate image can be formed.

Moreover, in the timing corresponding to blank lines of print data the electrostatic latent image on the image bearing member is not formed, it is possible to satisfactorily suppress the distortion of the image generated by the adjustment of the amplitude.

  The image forming apparatus of the present invention is irradiated with a light source that emits a light beam, a vibrating mirror that reflects the light beam emitted from the light source while reciprocatingly oscillating, and a light beam reflected by the vibrating mirror. An image bearing member on which an electrostatic latent image is formed, a developing means for developing the electrostatic latent image formed on the image bearing member by attaching a developer, and the developing means Transfer means for transferring the developer to a recording medium; timing detection means for detecting the timing at which an electrostatic latent image is formed on the image carrier only at a position corresponding to the center of vibration of the vibration mirror; An amplitude adjusting unit that adjusts the amplitude of the light beam by the vibrating mirror at the timing detected by the timing detecting unit may be provided.

  Also in the image forming apparatus of the present invention configured as described above, the light beam emitted from the light source is reflected by the vibrating mirror that vibrates in a reciprocating manner, and is irradiated onto the image carrier. By this light beam irradiation, an electrostatic latent image is formed on the image carrier, and the electrostatic latent image is developed with the developer attached by the developing means, and further, the developer is applied to the recording medium by the transferring means. The image is formed by being transferred.

  In the present invention, the timing detection means detects the timing at which the electrostatic latent image is formed on the image carrier only at the position corresponding to the center of vibration of the vibration mirror, and at that timing, the amplitude adjustment means Adjusts the amplitude of the light beam by the vibrating mirror. The center of vibration of the vibrating mirror is constant regardless of the amplitude. In the present invention, the amplitude of the oscillating mirror is adjusted at the timing when the electrostatic latent image is formed only at the position corresponding to the center of vibration, so that the amplitude can be accurately adjusted while suppressing distortion in the image due to the amplitude adjustment. By controlling, an accurate image can be formed. The center of vibration in the present invention may have a certain width depending on the required resolution and the like.

  Further, in each of the image forming apparatuses, the modulation control means for controlling the modulation of the light beam based on the print data, the vibration mirror and the image carrier are disposed between the image forming apparatus and the vibration mirror. When the amplitude of the light beam is a reference value, an optical system adjusted so that the light beam reflected by the vibrating mirror is scanned at a constant speed on the image carrier, and within a scanning range of the light beam. A light beam detection means for detecting the light beam at at least one point; a detection time of the light beam two times consecutively by the light beam detection means; and a detection time when the amplitude is a reference value. And a timing correction means for correcting the modulation timing by the modulation control means.

  In this case, the optical system disposed between the vibrating mirror and the position where the image carrier is formed has a light beam reflected by the vibrating mirror when the amplitude of the light beam by the vibrating mirror is a reference value. The image carrier is adjusted to be scanned at a constant speed. Therefore, when the amplitude of the light beam is a reference value, the emission time of the light beam corresponding to each pixel set with a constant width on the image carrier is a fixed time. Further, the light beam detection means detects the light beam at at least one point within the scanning range of the light beam, and the modulation control means controls the modulation of the light beam based on the print data.

  In the present invention, based on the detection time of the light beam twice in succession by the detection means and the detection time when the amplitude is a reference value, the timing correction means has the modulation by the modulation control means. Correct the timing. As described above, according to the present invention, the modulation timing is corrected based on the actually detected two times of the light beam detection time and the detection time when the amplitude is the reference value. That is, in the present invention, the light beam modulation timing is corrected based on the actual light beam detection interval on the premise of the presence of the optical system, so that a more accurate image can be formed.

  In this case, the amplitude adjusting means further adjusts the amplitude of the vibrating mirror to a specific range centered on the reference value, and the timing correcting means corrects the modulation timing to thereby adjust the image carrier. Further detailed adjustment of the position irradiated with the light beam may be performed.

  In this case, rough adjustment can be performed by amplitude control of the oscillating mirror by the amplitude adjustment unit, and more detailed adjustment can be performed by correcting the modulation timing by the timing correction unit, so that adjustment for forming an accurate image is more efficient. Can be done automatically.

  A program of the present invention is characterized by causing a computer to operate as any one of the timing detection means and the amplitude adjustment means described above. For this reason, if the computer which controls the image forming apparatus provided with the light source, the vibrating mirror, the image carrier, the developing unit, and the transfer unit is caused to execute the program of the present invention, the image forming apparatus according to any one of the above can be easily performed. Can be configured.

[Entire configuration of laser printer 1]
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram schematically showing the configuration of a laser printer 1 as an example of an image forming apparatus to which the present invention is applied. As shown in FIG. 1, the laser printer 1 includes a pair of transport rollers 2 that transport a sheet P as an example of a recording medium supplied one by one from a paper feed tray (not shown). The sheet P conveyed by the conveying roller 2 passes between a photosensitive drum 3 as an example of an image carrier and a transfer roller 4 as an example of a transfer unit, and further, a heating roller 5 and a pressure roller 6. Are discharged to a paper discharge tray (not shown) provided on the upper surface of the laser printer 1.

  The photosensitive drum 3 is grounded, and a positively chargeable photosensitive layer made of an organic photosensitive material such as polycarbonate is formed on the surface thereof. Is supported so as to be rotatable in the clockwise direction.

  In addition to the transfer roller 4, a charger 9, a laser scanner unit 10, and a developing unit 20 as an example of a developing unit are disposed on the outer periphery of the photosensitive drum 3 from the upstream side in the rotation direction. . The charger 9 is a positively charged scorotron charger that generates corona discharge from a charging wire such as tungsten, and is configured to uniformly charge the surface of the photosensitive drum 3 to a positive polarity. The laser scanner unit 10 scans and exposes the photosensitive drum 3 with laser light L by a mechanism described later. The developing unit 20 supplies positively charged toner (not shown) via the developing roller 21 to the surface of the photosensitive drum 3. In this embodiment, a positively chargeable non-magnetic one-component polymer toner is used as the toner.

  For this reason, the surface of the photosensitive drum 3 is first uniformly charged positively by the charger 9 as the photosensitive drum 3 rotates, and then is scanned by the laser beam L from the laser scanner unit 10 at high speed. It is exposed to form an electrostatic latent image corresponding to the print data. Next, when positively charged toner is supplied from the developing unit 20 to the photosensitive drum 3, the toner is an electrostatic latent image formed on the surface of the photosensitive drum 3, that is, uniformly positive. The surface of the charged photosensitive drum 3 is supplied to the exposed portion exposed to the laser beam L and the potential is lowered, and is selectively attached to be visualized, thereby forming a toner image. Is done.

  The transfer roller 4 is supported by the laser printer 1 so as to be rotatable counterclockwise in FIG. The transfer roller 4 has a metal roller shaft covered with a roller made of an ion conductive rubber material, and a transfer bias (transfer forward bias) is applied from a transfer bias application power source (not shown) at the time of transfer. It is configured. Therefore, the toner adhered on the surface of the photosensitive drum 3 is transferred to the paper P while the paper P passes between the photosensitive drum 3 and the transfer roller 4. The sheet P after the toner transfer is sandwiched between the heating roller 5 and the pressure roller 6 so that the toner is heat-fixed and then discharged onto the discharge tray.

[Configuration of Laser Scanner Unit 10]
Next, FIG. 2 is a perspective view showing the internal configuration of the laser scanner unit 10. As shown in FIG. 2, the laser scanner unit 10 includes a vibration mirror 11 that reciprocally rotates and vibrates by a known vibration element (not shown), and a laser as an example of a light source that emits laser light L toward the vibration mirror 11. And a diode 12.

  For this reason, the laser beam L reflected by the oscillating mirror 11 is scanned with a predetermined amplitude (hereinafter also referred to as scanning amplitude). The laser beam L reflected by the vibrating mirror 11 passes through an F arc sine θ lens 13 as an example of an optical system, is reflected by a reflecting mirror 14, and then reaches the photosensitive drum 3. The F arc sine θ lens 13 is a lens in which the incident angle θ and the imaging position r have a relationship of r = f · arcsin θ (f is the focal length of the lens), and when the scanning amplitude is a reference value, The light L is adjusted so that the photosensitive drum 3 disposed on the scanning line is scanned at a constant speed in the main scanning direction (the axial direction of the photosensitive drum 3). The vibrating mirror 11 described above may be reciprocatingly oscillating around the vertical axis. However, the direction of the scanning line formed on the photosensitive drum 3 is 2 so that the direction of the scanning line is parallel to the forward path and the backward path. It may vibrate around an axis.

  Further, a BD mirror that reflects the laser light L in a region inside the scanning amplitude and outside a range reflected by the reflecting mirror 14 toward the photosensitive drum 3 (hereinafter also referred to as a printing width). 17 is disposed. Further, the laser scanner unit 10 includes a BD sensor 18 as an example of a light beam detection unit that detects the laser light L reflected by the BD mirror 17. Therefore, the modulation timing of the laser diode 12 can be adjusted based on the timing at which the BD sensor 18 detects the laser light L.

[Configuration and Control of Laser Printer 1 Control System]
FIG. 3 is a block diagram showing the configuration of the control unit 30 of the laser printer 1 with a portion related to the laser scanner unit 10 as a center. As shown in FIG. 3, the control unit 30 includes a LAN interface (LAN I / F) 31 for connecting to a LAN (not shown), a CPU 32 that executes various operations, and a memory 33 via a bus 34. Are configured as connected microcomputers. Further, the bus 34 has an image memory 35 in which print data input via the LAN interface 31 is developed as a two-dimensional image, a vibration mirror drive circuit 36 for driving the vibration mirror 11, and a BD sensor (BD) 18. As an example of the modulation control means for instructing the light emission timing of the laser diode 12 to the BD detection circuit 37 that reads the output signal of the laser and compares it with a predetermined threshold value, and the LD drive circuit 38 that drives the laser diode (LD) 12 The timing control circuit 39 is connected. A common reference clock 40 is input to the oscillating mirror drive circuit 36, the BD detection circuit 37, and the timing control circuit 39, and each unit drives the oscillating mirror 11 and outputs an output signal from the BD sensor 18 based on this clock. Sampling or control of the light emission timing is executed.

  Next, processing executed by the control unit 30 will be described with reference to the flowchart of FIG. As shown in FIG. 4, in this process, first, in S1 (S represents a step: the same applies hereinafter), it is determined whether or not a print command has been input via the LAN interface 31. If a print command has not been input (S1: N), the process stands by in S1, and if a print command is input (S1: Y), the process proceeds to S2. In S <b> 2, the oscillating mirror 11 is activated via the oscillating mirror drive circuit 36. In this process, after the vibration mirror 11 is activated, it waits for a predetermined time until the amplitude is stabilized to some extent, and when the predetermined time elapses, in the subsequent S3, the BD detection circuit 37 performs the following BD detection interval. A certain BD interval (IBD) is detected.

  That is, assuming that there is no F arc sine θ lens 13, the laser beam L is scanned on the scanning line in a sine wave shape by the vibrating mirror 11. For this reason, the movement of the scanning position can be considered as an orthogonal projection of the circular motion onto the scanning line SS, as illustrated in FIG. Further, as described above, since the BD mirror 17 is disposed in an area inside the scanning amplitude and outside the printing width, the scanning position is a position detected by the BD sensor 18 (hereinafter also referred to as a BD position). Pass) twice during period T. Therefore, in S3, the difference between td1 and td2 of two consecutive passage times (hereinafter also referred to as BD passage times) of the BD position is detected as a BD interval (IBD). However, when td1 <td2 and td2-td1 <T / 2, IBD = td2-td1.

  In S4, it is determined whether the IBD is larger than the printable BD interval minimum value IMIN and smaller than the printable BD interval maximum value IMAX. When IBD ≦ IMIN, that is, when the amplitude of the vibrating mirror 11 is smaller than the printable range, or when IMAX ≦ IBD, that is, when the amplitude of the vibrating mirror 11 is larger than the printable range (S4: N), the process proceeds to S5. In S5, by changing the voltage applied by the oscillating mirror drive circuit 36, the amplitude of the oscillating mirror 11 is adjusted toward the reference value set between IMIN and IMAX. In subsequent S6, the process waits until the elapsed time tp from the last amplitude adjustment in S5 becomes equal to or longer than the time tp0 sufficient for the amplitude to stabilize (S6: N), and when the elapsed time tp becomes equal to or longer than the time tp0 ( S6: Y), the process proceeds to S3 described above. Thus, if IMIN <IBD <IMAX is satisfied while the processes of S3 to S6 are repeatedly executed (S4: Y), the process proceeds to S7.

In S7, printing is started by driving various rollers and the like. In S8 as an example of the subsequent claim 1 Symbol mounting timing detecting means, the region of a few lines to be made from now scanned by the vibration mirror 11, whether the blank area as illustrated in FIG. 6 (A) To be judged. If the area of several lines to be scanned is not a blank area (S8: N), in S9 as an example of the timing detecting means according to claim 2 , the area of several lines to be scanned is It is determined whether or not it is the central print area where printing is performed only for the print area. The central printing area is not limited to an area where printing is performed on only one central point, and may have a certain width depending on a required resolution or the like. Here, as illustrated in FIG. 6B, a range where the print area exists only in an area within 10% of the paper width is set as the central print area.

  If the area of several lines to be scanned is not the central printing area (S9: N), the process proceeds to S11, and the above-described BD passage times td1 and td2 are detected. In S12 as an example of a further subsequent timing correction means, the light emission timing of the laser diode 12 is calculated as follows.

  That is, φ (t) where φ (t) is the transition angle of the laser beam L, T is the vibration period of the oscillating mirror 11, θc is the maximum oscillation angle, Dc is the vibration delay time of the oscillating mirror 11, and t is the time. Can be generally represented by the following equation (1).

Here, if the swing angle corresponding to the BD position is φ, the following simultaneous equations can be established because the BD passage time is td1, td2, and the solution of (2) is obtained by solving this. Can do.

Then, φ (t) can be expressed by the following equation (3) by substituting the solution of (2) into the above equation (1).

Next, when the amplitude is the reference value, that is, when the maximum swing angle θc is the reference value θ0, the F arc sine θ lens 13 is a photoconductor in which the laser light L is disposed on the scanning line. The drum 3 is adjusted so as to be scanned at a constant speed in the scanning direction of the drum 3 (axial direction of the drum). If the BD passage times td1 and td2 when the amplitude is the reference value are td01 and td02 (td01 <td02), the following equation (4) holds. Φ0 (t) is a transition angle when the amplitude is a reference value.

However, in general, the actual amplitude may not match the reference value. In this case, the BD passage time is different from td01 and td02, and the scanning line cannot be scanned at a constant speed. Therefore, in the present embodiment, tc satisfying φ (tc) = φ0 (t) is obtained as follows. That is,

And solving this equation for tc yields the following solution:

If the time t is converted to tc by this equation and the laser diode 12 is caused to emit light at the timing corresponding to the converted time tc, whether the F arc sine θ lens 13 is adjusted to the above amplitude at that time. Can be performed. More specifically, for example, if the laser diode 12 is caused to emit light at the timing when the time t engraved at equal intervals is converted into tc by the above equation, electrostatic latent images are formed on the photosensitive drum 3 at equal intervals. be able to. In S12, such a conversion formula for tc is calculated.

  This conversion formula may be calculated by creating a table for the values of td1 and td2, and reading the corresponding table value in S12. In this case, the calculation can be further speeded up. it can.

  As a specific form of this table, for example, the following form can be considered. Even if the BD passage times td1 and td2 are timed based on the driving clock set so as to rise once for one vibration period T by dividing the reference clock 40, td1 and td2 The combination will be enormous. Therefore, if the above equation 7 is arranged for two parameters (td1 -td2) and (td1 + td2),

It becomes. Therefore, if only the term of f (td1 -td2) is obtained from the table and the term of (td1 + td2) / 2 is calculated at any time, the table can be made smaller. Note that the above f (td1 -td2) is given as a series of values each having a value corresponding to each dot formed on the photosensitive drum 3.

  Further, this number sequence need not be obtained for the entire vibration period T. If the number sequence A for a quarter period is obtained, the next quarter period is T / 2-A, and the next The quarter cycle is represented by T / 2 + A, and the next quarter cycle is represented by TA. The table does not need to have data in units of dots, and the table has only data every several dots, and the dots in between can be complemented by linear approximation or the like to further reduce the table.

  For example, when an image is formed on the photosensitive drum 3 with 4960 dots in one way (reciprocation, that is, 9920 dots per vibration period T), if data is acquired from the table every 16 dots, it is exemplified in the following Table 1. Use a table that does this.

That is, in the table of Table 1, as described above, the value of f (td1 -td2) for the 0 to 2480th dots for a quarter period is set at an interval of 16 dots, and a desired value obtained from this table is obtained. By adding the above (td1 + td2) / 2 to the value for the dot, the time tc for forming the dot can be calculated (see next S13).

  In subsequent S13, the conversion formula or table value of tc calculated in S12 is input to the timing control circuit 39, and the timing control circuit 39 is instructed to read the image memory 35, whereby the image memory 35 is read. The laser diode 12 emits light at a timing according to the developed print data and the above tc. As described above, in the processes of S11 to S13, by correcting the light emission timing of the laser diode 12 using the above-described conversion formula of tc, a good image without distortion can be obtained by accurately aligning the pixel positions on the paper P. Can be formed. In subsequent S14, it is determined whether or not printing for one page has been completed. If it has not been completed (S14: N), the process proceeds to S8 described above.

  On the other hand, if it is determined during execution of the processes of S8 to S14 that several lines of areas to be scanned are blank areas (S8: Y), the process proceeds to S15. In S15, the amplitude of the oscillating mirror 11 is adjusted toward the reference value by changing the voltage applied by the oscillating mirror drive circuit 36 by the following oscillating mirror amplitude adjustment process. Migrate to Also, when it is determined that the area of several lines to be scanned is the central print area during the execution of the processes of S8 to S14 (S9: Y), the process similarly proceeds to S15, and the vibrating mirror After the amplitude of 11 is adjusted toward the reference value, the process proceeds to S14 described above.

FIG. 7 is a flowchart showing in detail the vibration mirror amplitude adjustment process of S15. As shown in FIG. 7, in this process, first, in S151, the elapsed time tp from the last amplitude adjustment is compared with the time tp0 sufficient for the amplitude to stabilize, as in S6 described above. If the time tp is less than the above time tp0 (S151: N), the process proceeds to S14 as it is. On the other hand, if the elapsed time tp is equal to or greater than the above time tp0 (S151: Y), the SBD is detected in S152 as in S3 described above, and the amplitude is determined in S153 as in S5 described above. Is adjusted, and the process proceeds to S14. That is, the process of S15 shifted from S8 corresponds to the amplitude adjusting means described in claim 1, and the process of S15 transferred from S9 corresponds to the amplitude adjusting means described in claim 2 . The several blank areas in S8 and the central print area of several lines in S9 are accurately performed during a time (tp0) sufficient for the amplitude to stabilize after the amplitude is adjusted. This refers to the case where there is a blank area or a central print area that is more than the number of scans.

  For this reason, in the processes of S8 to S15, whenever there is a blank area or a central print area (S8: Y or S9: Y), a process of bringing the aforementioned maximum swing angle θc close to the reference value θ0 in S15 is executed. Furthermore, the light emission timing of the laser diode 12 is corrected at any time according to the deviation of θc and θ0 by the processes of S11 to S13. Therefore, it is possible to form a good image without distortion on the paper P by accurately aligning the positions of the pixels formed on the photosensitive drum 3.

When printing for one page is completed (S14: Y), it is determined in S21 whether printing of all pages for which a print command has been issued has been completed. If printing of all the pages has not been completed (S21: N) , after the amplitude is adjusted by the vibration mirror amplitude adjustment process similar to S15 shown in FIG. 7 in S22, the process proceeds to S8. . Then, printing of the next page is started.

Thus, in the present embodiment, since the adjustment of the amplitude is performed at timing corresponding to the switching of the pages, the sheet P can form a better image. Their to, the printing of all the pages is completed: after (S21 Y), the vibrating mirror 11 at S23, is stopped, the process proceeds to the above-mentioned S1, waiting is made until the next print command.

[Effects of the present embodiment]
As described above, in the present embodiment, the control for adjusting the amplitude of the oscillating mirror 11 toward the reference value is executed as needed (S15, S22), and according to the deviation between the adjusted amplitude and the reference value. The light emission timing of the laser diode 12 is corrected (S11 to S13). For this reason, it is possible to accurately align the positions of the pixels formed on the photosensitive drum 3 and form a good image without distortion on the paper P.

  In addition, the amplitude adjustment is performed at a timing corresponding to a blank area (S8: Y) or page switching (S21: N) where no electrostatic latent image is formed on the photosensitive drum 3, or a position corresponding to the center of vibration. This is executed at a timing corresponding to the central printing area (S9: Y) in which only the electrostatic latent image is formed. For this reason, it is possible to form an accurate image regardless of a temperature change or the like by accurately controlling the amplitude while suppressing distortion in the image due to the amplitude adjustment. In particular, if the light emission timing is corrected by the processing of S11 to S13, the center dot position hardly changes even if the amplitude changes, so that the image distortion when the amplitude adjustment is performed in the central printing area is further improved. Can be suppressed.

  In the present embodiment, after adjusting the amplitude as described above, the light emission timing of the laser diode 12 is corrected using the conversion formula of tc, so that the pixel position on the paper P is more accurately determined. It is possible to form a good image without distortion.

  In addition, in this embodiment, the common reference clock 40 is input to the oscillating mirror drive circuit 36, the BD detection circuit 37, and the timing control circuit 39, whereby the drive timing of the oscillating mirror 11 and the BD sensor 18 are controlled. The sampling timing of the output signal and the light emission timing of the laser diode 12 are synchronized. Therefore, a more accurate image can be formed by suppressing a shift in modulation timing due to error accumulation. Further, in the present embodiment, since the above correction is performed by repeatedly detecting td1 and td2 during printing (see S13), for example, it can cope with fluctuations in the amplitude caused by temperature changes or the like during printing of one page. Thus, an even more accurate image can be formed. In addition, the laser printer 1 according to the present embodiment uses the vibrating mirror 11 and thus can be easily downsized as compared with the case where a polygon mirror is used.

  In addition, this invention is not limited to the said embodiment at all, It can implement with a various form in the range which does not deviate from the summary of this invention. For example, in the above embodiment, the modulation is performed by controlling the LD drive circuit 38 by the timing control circuit 39, but the laser diode is always caused to emit light, and the modulation is performed by the shutter provided in front of the laser diode. Also good. In the above embodiment, the monochrome laser printer 1 has been described as an example. However, the image forming apparatus of the present invention can also be applied to a color printer, and in this case, the effect of aligning the pixel positions as described above. Appears more prominently.

  Furthermore, if the temperature change in the vicinity of the vibrating mirror 11 is suppressed by covering the laser scanner unit 10 with a heat insulating material or the like, the change in amplitude itself can be suppressed, and a more accurate image can be formed. Furthermore, the present invention can also be applied to a laser scanner unit provided with a pair of BD mirrors 17 and a BD sensor 18 on both sides of the print width. In this case, timing correction similar to the above can be performed based on the timing at which the pair of BD sensors 18 sequentially detect the laser light L, but the calculation formula in that case needs to be changed as appropriate. Since such a change in calculation formula is well known, the description thereof is omitted here.

It is explanatory drawing which represents roughly the structure of the laser printer to which this invention was applied. It is a perspective view showing the internal structure of the laser scanner unit of the printer. It is a block diagram showing the structure of the control system of the printer. It is a flowchart showing the process performed with the control system. It is explanatory drawing which represents typically the view of the light emission timing control in the process. It is explanatory drawing showing the timing of amplitude adjustment in the process. It is a flowchart showing the detail of the vibration mirror amplitude adjustment process in the process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser printer 3 ... Photosensitive drum 4 ... Transfer roller 5 ... Heating roller 6 ... Pressure roller 9 ... Charger 10 ... Laser scanner unit 11 ... Vibrating mirror 12 ... Laser diode 13 ... F arc sine (theta) lens 14 ... Reflective mirror DESCRIPTION OF SYMBOLS 17 ... BD mirror 18 ... BD sensor 20 ... Development unit 30 ... Control part 31 ... LAN interface 32 ... CPU 33 ... Memory 35 ... Image memory 36 ... Vibration mirror drive circuit 37 ... BD detection circuit 38 ... LD drive circuit 39 ... Timing control Circuit 40 ... Reference clock L ... Laser beam P ... Paper

Claims (5)

A light source that emits a light beam;
A vibrating mirror that reflects the light beam emitted from the light source while reciprocatingly oscillating;
An image carrier on which an electrostatic latent image is formed by irradiation with the light beam reflected by the vibrating mirror;
Developing means for developing the electrostatic latent image formed on the image carrier by attaching a developer;
Transfer means for transferring the developer adhered by the developing means to a recording medium;
Timing detection means for detecting timing corresponding to a blank line of print data ;
Amplitude adjusting means for adjusting the amplitude of the light beam by the vibrating mirror at the timing detected by the timing detecting means;
An image forming apparatus comprising: A light source that emits a light beam;
A vibrating mirror that reflects the light beam emitted from the light source while reciprocatingly oscillating;
An image carrier on which an electrostatic latent image is formed by irradiating the light beam reflected on the vibrating mirror;
Developing means for developing the electrostatic latent image formed on the image carrier by attaching a developer;
Transfer means for transferring the developer adhered by the developing means to a recording medium;
Timing detection means for detecting a timing at which an electrostatic latent image is formed only on a position corresponding to the center of vibration of the vibrating mirror on the image carrier;
Amplitude adjusting means for adjusting the amplitude of the light beam by the vibrating mirror at the timing detected by the timing detecting means;
An image forming apparatus comprising: Modulation control means for controlling the modulation of the light beam based on print data;
When the amplitude of the light beam by the vibrating mirror is a reference value, the light beam reflected by the vibrating mirror is moved at a constant speed on the image carrier. An optical system adjusted to be scanned at
A light beam detecting means for detecting the light beam at at least one point within the scanning range of the light beam;
Timing correction means for correcting the modulation timing by the modulation control means based on the detection time of the light beam twice in succession by the light beam detection means and the detection time when the amplitude is a reference value; ,
The image forming apparatus according to any one of claims 1 to 2, further comprising a. The amplitude adjusting means adjusts the amplitude of the vibrating mirror to a specific range centered on the reference value,
4. The image forming apparatus according to claim 3 , wherein the timing correction unit performs further detailed adjustment of a position where the light beam is applied to the image carrier by correcting the modulation timing. A program for causing a computer to operate as the timing detection means and the amplitude adjustment means according to any one of claims 1 to 4 .