JPH08136838A - Image forming device - Google Patents

Abstract

PURPOSE: To automatically correct a magnification when a scan optical system is changed due to environmental fluctuation, etc. CONSTITUTION: A beam scanning on a photosensitive body 5 is detected by a photodetector DETP1 detecting a scan start and the DETP2 detecting a scan end. A polygon mirror 3 is rotated by a polygon motor M, and the polygon motor M is driven by a polygon motor drive circuit 6, and the rotational speed of the polygon mirror 3 is controlled by a magnification correction circuit 7 through the polygon motor drive circuit 6. The magnification correction circuit 7 controls the rotational speed of the polygon mirror 3 so that the deflection speed of the light beam between two points becomes a fixed value based on respective detection signals detected by two photodetectors DETP1, DETP2, and controls a phase of a laser beam by controlling a laser drive circuit 2 through a phase synchronizing circuit 8. The rotational speed of the photosensitive body 5 is controlled by a main body drive circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by rotating a polygon mirror.

[0002]

2. Description of the Related Art In this type of image forming apparatus, a laser beam is modulated by image data, and a polygon mirror is rotated to deflect at a constant angular velocity in the main scanning direction. It is configured to scan on the photoconductor by performing correction, etc.

[0003]

However, the conventional apparatus has a problem that the magnification is changed when the scanning optical system changes due to environmental changes or the like.

As an apparatus of this type, for example, as shown in Japanese Patent Laid-Open No. 60-58774, photodetectors are provided at arbitrary two points on the main scanning line, and a light beam scans between the two points. A method has been proposed in which the timing is detected by two photodetectors and controlled so that a constant sync pulse is always output within this scanning time.

Further, as shown in JP-A-60-74767 and JP-A-5-19204, light receiving elements are arranged at a writing reference position, a writing start position and a writing end position, and signals detected by the respective light receiving elements are detected. A method of adjusting the position of an optical system including a lens is proposed based on the temporal correlation of.

Further, as disclosed in Japanese Patent Laid-Open No. 3-110512, it is necessary to measure the time required for the light beam to pass between two predetermined points on the scanning line and the distance the light beam moves within the predetermined time. Measuring the periodic variation of the scanning speed,
A method has been proposed in which the phase and period of the clock are changed so as to suppress the influence of the jitter error on the change of the pixel clock.

In view of the above-mentioned conventional problems, it is an object of the present invention to provide an image forming apparatus capable of automatically correcting the magnification when the scanning optical system changes due to environmental changes or the like.

[0008]

In order to achieve the above object, the first means is a deflecting means for deflecting a light beam modulated according to an image signal in the main scanning direction, and is deflected by the deflecting means. The first and second light detecting means for detecting the light beam between two points on the main scanning line and the deflection speed of the light beam between the two points detected by the first and second light detecting means are constant. And a control means for controlling the deflecting means.

In the second means, the control means in the first means counts two clocks having a constant frequency while the light beam is detected by the first and second photodetection means. It is characterized by comprising a counter for measuring the scanning time of the light beam between them.

A third means is characterized in that the clock in the second means is a write clock for an image signal written by the light beam.

A fourth means is characterized in that the control means controls the deflection speed of the light beam based on a scanning time when the deflection speed of the light beam is initially controlled in the second or third means.

In a fifth means, in the first to fourth means, the control means controls the deflection speed to a certain constant speed and ends the control of the deflection speed when an error occurs during the control of the deflection speed. It is characterized by doing.

A sixth means is characterized in that the certain constant speed in the fifth means is a deflection speed immediately before an error occurs.

A seventh means is characterized in that the certain constant speed in the fifth means is a deflection speed when the deflection speed of the light beam is initially controlled.

In an eighth means, in the second to seventh means, the deflecting means has a polygon mirror, and the scanning time of the light beam is a total of scanning times corresponding to an integral multiple of the number of surfaces of the polygon mirror. It is characterized by being.

A ninth means is characterized in that, in the second to seventh means, the deflecting means has a polygon mirror, and the scanning time of the light beam is a scanning time of a specific surface of the polygon mirror. To do.

A tenth means comprises a photosensitive member which moves in the sub-scanning direction in the first to ninth means, and the control means controls the moving speed of the photosensitive member according to the deflection speed of the light beam. It is characterized by

The eleventh means is the ninth means, wherein the moving speed v _p and the deflection speed v of the photoconductor are v _p / v = a
(A: a constant corresponding to the writing density).

[0019]

In the first means, the deflecting means is controlled so that the deflection speed of the light beam between the two points detected by the first and second light detecting means becomes constant, so that the scanning optical system is kept in the environment. The magnification in the main scanning direction can be automatically corrected when it changes due to fluctuations or the like.

In the second means, the scanning time of the light beam between two points is detected by counting the clock of a constant frequency while the light beam is detected by the first and second light detecting means. Therefore, the magnification in the main scanning direction can be automatically corrected with a simple circuit.

In the third means, since the clock counted by the counter is the writing clock of the image data written by the light beam, the magnification in the main scanning direction can be automatically corrected with a simple circuit.

In the fourth means, since the control is performed based on the scanning time when the deflection speed of the light beam is initially controlled, the correction can be performed quickly.

In the fifth means, when an error occurs during the control of the deflection speed, the deflection speed is controlled to a certain constant speed and the control of the deflection speed is terminated, so that the image formation is continued even if the error occurs. can do.

According to the sixth means, since the certain constant speed is the deflection speed immediately before the occurrence of the error, it is possible to prevent the image quality from being remarkably deteriorated.

In the seventh means, since a certain constant speed is the deflection speed when the deflection speed of the light beam is initially controlled,
It is possible to prevent the image quality from significantly deteriorating.

In the eighth means, the scanning time of the light beam is measured by totaling the scanning times corresponding to an integral multiple of the number of surfaces of the polygon mirror. Therefore, the scanning time of the light beam can be determined even if the surface of the polygon mirror varies. Can be measured accurately.

In the ninth means, since the scanning time of the light beam is measured by the scanning time of the specific surface of the polygon mirror, the scanning time of the light beam can be accurately measured even if the surface of the polygon mirror varies. You can

In the tenth means, since the moving speed of the photosensitive member is controlled according to the deflection speed of the light beam, the magnification in the main scanning direction and the sub-scanning direction is automatically adjusted when the scanning optical system changes due to environmental changes. Can be corrected dynamically.

In the eleventh means, the moving speed of the photosensitive member is controlled according to the constant according to the writing density and the deflection speed of the light beam. Therefore, when the scanning optical system changes due to environmental changes, etc. The magnification in the sub-scanning direction can be automatically corrected.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a block diagram showing the magnification correction circuit of FIG. 1 in detail, and FIG. 3 is a schematic view of magnification correction operation of the image forming apparatus of FIG. 4 is a flowchart for explaining the magnification correction operation of the image forming apparatus of FIG. 1 in detail, and FIG. 5 is a beam scanning time obtained by summing the scanning times for an integral multiple of the number of polygon mirror surfaces. 6 is an explanatory view showing a method for measuring the beam scanning time by the scanning time of a specific surface of the polygon mirror, and FIG. 7 is a beam scanning time by the scanning time of a specific surface of the polygon mirror. Explanatory drawing which shows the other method of measuring
Is a block diagram showing a magnification correction circuit for correcting the magnification in the sub-scanning direction, FIG. 9 is a block diagram showing a modification of FIG.
10 is a configuration diagram showing a driving mechanism of the photoconductor, FIG. 11 is an explanatory diagram showing a method of measuring a beam scanning time by a detection signal of one photodetector, and FIG. 12 is a beam by a detection signal of one photodetector. FIG. 13 is an explanatory view showing another method for measuring the scanning time, and FIG. 13 is an explanatory view showing still another method for measuring the beam scanning time by the detection signal of one photodetector.

In FIG. 1, the beam emitted from the laser diode 1 is modulated by the laser drive circuit 2 in accordance with the image signal and the writing clock CLK, and the like by the polygon mirror 3 rotated by the polygon motor M (see FIG. 2). After the angular velocity is deflected, the f-θ lens 4 corrects the constant velocity deflection and corrects the surface tilt, and scans the photoconductor 5 in the main scanning direction. A photodetector DETP1 for detecting the start of scanning and a photodetector DETP2 for detecting the end of scanning are arranged in the vicinity of both ends of the photoconductor 5 along the main scanning direction.
Beams scanning above are photodetectors DETP1 and DETP2
Is detected by

The polygon motor M is driven by a polygon motor drive circuit 6, and the rotation speed of the polygon mirror 3 is controlled by a write clock generation circuit (magnification correction circuit) 7 via the polygon motor drive circuit 6. The magnification correction circuit 7 controls the rotational speed of the polygon mirror M based on the detection signals detected by the two photodetectors DETP1 and DETP2 so that the deflection speed of the light beam between the two points becomes constant, and the phase is corrected. The phase of the write clock CLK is controlled by controlling the laser drive circuit 2 via the synchronizing circuit 8. Further, the rotation speed of the photoconductor 5 is determined by the main body drive circuit 9
Controlled by.

As shown in FIG. 2, the magnification correction circuit 7 includes a counter 71, a D flip-flop (DFF) 72, a control circuit 73, a clock generating circuit 74 having a PLL configuration, and a D.
It is composed of FFs 75 and 76. The counter 71 is cleared by the scanning start detection signal of the photodetector DETP1 and counts the clock ICLK. Photodetector DET
The scanning end detection signal of P2 is latched by the DFFs 75 and 76 in synchronization with the clock ICLK and applied to the DFF 72. The DFF 72 latches the count value of the counter 71 with the scanning end detection signal of the photodetector DETP2.
Therefore, the count value latched by the DFF 72 corresponds to the scanning time T of the laser beam between the two photodetectors DETP1 and DETP2.

The control circuit 73 performs control relating to image formation, and particularly during magnification correction, the / OC terminal of the DFF 72 (hereinafter,
"/" Is used for the inverted signal. ) Is set from "H" to "L", and the count value latched by the DFF 72 is fetched (step S1 shown in FIG. 3). The polygon motor drive circuit 6 controls the deflection speed v from the control circuit 73.
The rotation speed v of the polygon motor M is controlled so that the scanning time T (the count value of the counter 71) becomes the constant time T ₀ based on the control signal (step S2 → S3).

When the control circuit 73 also takes in the data latched by the DFF 72, it determines whether the count value is normal (step S4), and if it is not normal, it performs error processing (step S5).

The magnification correction will be described in detail with reference to FIG. First, the control circuit 73 causes the scanning time T (counter 7
The frequency for measuring 1) is set (step S11), and then the initial value v ₀ of the rotation speed of the polygon motor M is set in the polygon motor drive circuit 6 (step S12). Then, the scanning time T is measured by the counter 71 (step S13), and the scanning time T is fetched by the control circuit 73 (step S14).

Next, if a measurement error occurs, error processing is performed (steps S15 → S16), while if no measurement error occurs, the scanning time T is set to T ₁ (steps S15 → S17). . Next, when the initial magnification adjustment has not been completed, the value v ₀ calculated from the theoretical value is set as the rotation speed of the polygon motor M (step S
18 → S19), on the other hand, if the initial magnification adjustment has been completed, the stored value v _mem is set (steps S18 → S2).
0).

Then, the polygon motor drive circuit 6 controls the rotation speed of the polygon motor M (step S2).
1). Next, if a calculation error occurs, error processing is performed (steps S22 → S23). On the other hand, if no calculation has occurred, initial magnification adjustment is performed if initial magnification adjustment has not been completed (steps S24 → S25). , And the rotation speed v is stored as a stored value v _mem (step S2
6). Then, the processes shown in steps S21 to S26 are performed until the scanning time T reaches the constant time T ₀ (step S2).
7).

With such a configuration, the polygon mirrors 3 and f for focusing and scanning the laser beam on the photoconductor 5
The magnification can be corrected according to the change of the optical characteristics due to the environmental change of the scanning optical system such as the −θ lens 4. Also,
Since the control circuit 73 stores the correction data of the rotation speed v of the polygon motor M at the time of initial magnification correction, the initial magnification correction and the temporal magnification correction can be performed with the same configuration. Further, by detecting the laser beam that has passed through the f-θ lens 4, the magnification correction can be performed according to the change in the optical characteristics of the f-θ lens 4.

Here, the counter 71 outputs the clock ICLK.
By counting the two photodetectors DETP1,
When measuring the scanning time T of the laser beam during the DETP2, the count value processing (normal / abnormal) and correction calculation) become complicated if the frequency of the clock ICLK changes. Therefore, the processing of the control circuit 73 can be significantly reduced by using the constant clock ICLK.

Returning to FIG. 2, the clock generation circuit 74 outputs clocks having different phases to the phase synchronization circuit 8 based on the output data and the control signal from the control circuit 73. As shown in FIG. 1, the phase synchronization circuit 8 is also applied with the scanning start detection signal of the photodetector DETP1 and selects one of the clocks whose phases are different from each other and has a phase closer to the scanning start detection signal to select the write clock. It is applied to the laser drive circuit 2 as CLK.

Therefore, the phase of the write clock CLK is corrected every time the main scanning direction is scanned. Further, this writing clock CL which is corrected every time the main scanning direction is scanned
By using K as the input clock ICLK, it is possible to prevent counting errors and measure the scanning time T with high accuracy. Furthermore, by measuring the scanning time T based on the write clock CLK, the write clock CLK according to the print condition can be used even if the print condition changes, so the control circuit 73 can be changed according to the model. Can be reduced to improve versatility.

Further, it is desirable that the polygon motor M is controlled at a rotation speed at which a correct magnification is obtained, but the scanning time T can be measured immediately at a constant rotation speed.

If any error occurs during the magnification correction, for example, if the correction range is exceeded, the magnification correction is interrupted and the rotation speed of the polygon motor M (for example, theoretical By setting the value v ₀ ) calculated from the value, it is possible to prevent the image formation from becoming impossible, and it is possible to operate the apparatus until the error that has occurred is eliminated.

Further, by setting the frequency of the write clock CLK to a frequency corresponding to the rotation speed of the polygon motor M determined immediately before the occurrence of an error, unless the power of the apparatus is turned off or the apparatus is set to the initial state. It is possible to prevent the image quality from significantly deteriorating.

In the above embodiment, when an error that does not significantly affect the image formation occurs during magnification correction, it can be temporarily avoided. However, when such a large error occurs, if processing is performed in the magnification correction circuit 7, the upper control unit (not shown) does not recognize this error and performs control assuming that the image forming apparatus is in a normal state. It will be. Therefore, by notifying the upper control unit as a message of the content of the error that occurred, the upper control unit can promptly avoid the error by issuing a warning to the operator or a higher system in response to the error. it can.

Further, as shown in FIG. 1, two photodetectors D are provided.
In the configuration using ETP1 and DETP2, the main scanning synchronization signal can be obtained even when one of them fails, so that the main scanning synchronization signal can be used as the phase synchronization of the write clock CLK and the main scanning synchronization signal for image formation.

Further, in the configuration shown in FIG. 2, since the counter 71 is latched by the scanning start detection signal and the count value of the counter 71 is latched by the scanning end detection signal, it is necessary to measure the scanning time T except when the magnification is corrected. If there is no light, the laser beam is prevented from reaching the two photodetectors DETP1 and DETP2 so that the laser beam is not emitted unnecessarily, and the laser diode 1, the photodetectors DETP1 and DETP2, the photoconductor 5, etc. The life of can be extended.

In the configuration shown in FIG. 2, the photodetector D
When the scanning end detection signal is obtained by ETP2,
The measurement result is controlled by the control circuit 7 when the write clock CLK is corrected.
If the timing of capturing in 3 coincides with the scanning end detection signal, the capture of the measurement result may not be performed normally. Therefore, in such a case, it is necessary to perform processing such as synchronizing the capture timing and the output timing of the scan end detection signal so that the measurement result can be captured normally. Therefore, by preventing the laser beam from reaching the photodetector DETP2, the above timing control becomes unnecessary and the control circuit 73 can be simplified.

Further, when the scanning time T, which is the basis of the control, is taken in, even if the rotation speed of the motor M is constant, the scanning speed of each surface as shown in FIG. Vary. Therefore, as shown in FIG. 5, the scanning time T for an integral multiple of the number of surfaces is summed to change the total time A, so that the detection accuracy of the scanning speed due to a change over time can be increased.

Further, as shown in FIG. 6, the polygon mirror 3
The scanning time T of only a specific surface (second surface in the figure) of the polygon mirror 3 may be taken in. In this method, as shown in FIG. 1 may be turned on.

Further, by controlling the rotation speed of the polygon mirror 3 as described above, it is possible to permanently obtain an image with high magnification accuracy in the main scanning direction, but the rotation of the photoconductor 5 in the sub scanning direction. When the speed is constant, some expansion and contraction occurs. Therefore, as shown in the following formula,
By controlling the process linear velocity v _p in accordance with the deflection velocity v of the polygon motor M, expansion and contraction in the sub-scanning direction can be prevented.

V _p / v = a (a: constant according to writing density) Such control is performed by the main body drive circuit 9 from the polygon motor drive circuit 6 to the deflection speed v of the polygon motor M as shown in FIG. It can be realized by obtaining. Also,
As another method for obtaining the deflection speed v, the encoder of the polygon motor M and the frequency of the scanning start detection signal can be obtained from the control circuit 73 as shown in FIG. When controlling the process linear velocity v _p of the photoconductor 5, the drive mechanism of the photoconductor 5 as shown in FIG. 10 is controlled.

The output timing of the scanning start detection signal varies depending on the accuracy of each surface of the polygon mirror 3. Therefore, as shown in FIG. 11, the interval B that is an integral multiple of the number of surfaces is counted and the change is used. Yes, and also Figure 1
As shown in FIG. 2, it is possible to use the sum of the intervals which is an integral multiple of the number of continuous surfaces. Further, as shown in FIG. 13, when the laser diode 1 is turned on only on a specific surface (first surface), The detection signal can be used.

[0055]

As described above, according to the first aspect of the invention, the light detected by the first and second light detecting means 2
Since the deflection means is controlled so that the deflection speed of the light beam between the points becomes constant, the magnification in the main scanning direction can be automatically corrected when the scanning optical system changes due to environmental changes or the like.

According to the second aspect of the invention, the first and second aspects are provided.
Since the scanning time of the light beam between two points is detected by counting the clock of a constant frequency while the light beam is detected by the light detecting means, the magnification in the main scanning direction is automatically adjusted by a simple circuit. Can be corrected to.

According to the third aspect of the invention, since the clock counted by the counter is the writing clock of the image data written by the light beam, the magnification in the main scanning direction can be automatically corrected with a simple circuit. it can.

According to the fourth aspect of the invention, since the control is performed based on the scanning time when the deflection speed of the light beam is initially controlled, the correction can be performed quickly.

According to the fifth aspect of the present invention, when an error occurs during the control of the deflection speed, the deflection speed is controlled to a certain constant speed and the control of the deflection speed is ended. Therefore, even if an error occurs. Image formation can be continued.

According to the sixth aspect of the invention, since the certain constant speed is the deflection speed immediately before the occurrence of the error, it is possible to prevent the quality of the image from being significantly deteriorated.

According to the seventh aspect of the invention, since the certain constant speed is the deflection speed when the deflection speed of the light beam is initially controlled, it is possible to prevent the image quality from being significantly deteriorated.

According to the eighth aspect of the present invention, the scanning time of the light beam is measured by totaling the scanning times corresponding to an integral multiple of the number of surfaces of the polygon mirror. Therefore, even if the surface of the polygon mirror varies, Can be accurately measured.

According to the ninth aspect of the invention, since the scanning time of the light beam is measured by the scanning time of the specific surface of the polygon mirror, the scanning time of the light beam is accurate even if the surface of the polygon mirror varies. Can be measured.

According to the tenth aspect of the invention, since the moving speed of the photoconductor is controlled according to the deflection speed of the light beam,
When the scanning optical system changes due to environmental changes or the like, the magnifications in the main scanning direction and the sub scanning direction can be automatically corrected.

According to the eleventh aspect of the present invention, since the moving speed of the photosensitive member is controlled according to the constant according to the writing density and the deflection speed of the light beam, when the scanning optical system changes due to environmental changes or the like. The magnification in the main scanning direction and the sub-scanning direction can be automatically corrected.

[0066]

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram showing the magnification correction circuit of FIG. 1 in detail.

3 is a flowchart for explaining an outline of a magnification correction operation of the image forming apparatus in FIG.

FIG. 4 is a flowchart for explaining a magnification correction operation of the image forming apparatus in FIG. 1 in detail.

FIG. 5 is an explanatory diagram showing a method of measuring a beam scanning time by totaling scanning times for an integer multiple of the number of faces of a polygon mirror.

FIG. 6 is an explanatory diagram showing a method of measuring a beam scanning time by a scanning time of a specific surface of a polygon mirror.

FIG. 7 is an explanatory diagram showing another method of measuring the beam scanning time by the scanning time of a specific surface of a polygon mirror.

FIG. 8 is a block diagram showing a magnification correction circuit for correcting the magnification in the sub-scanning direction.

9 is a block diagram showing a modified example of FIG.

FIG. 10 is a configuration diagram showing a drive mechanism of a photoconductor.

FIG. 11 is an explanatory diagram showing a method of measuring a beam scanning time by a detection signal of one photodetector.

FIG. 12 is an explanatory diagram showing another method of measuring the beam scanning time by the detection signal of one photodetector.

FIG. 13 is an explanatory diagram showing still another method of measuring the beam scanning time by the detection signal of one photodetector.

[Explanation of symbols]

 1 Laser diode 2 Laser drive circuit 3 Polygon mirror 4 f-θ lens 5 Photoconductor 6 Polygon motor drive circuit 7 Write clock generation circuit 8 Phase synchronization circuit 9 Main body drive circuit M Polygon motor DETP1, DETP2 Photodetector

Claims (11)

[Claims] 1. An image forming apparatus for forming an image by scanning a light beam, wherein the light beam modulated according to an image signal is deflected in a main scanning direction, and the light deflected by the deflecting means. First and second light detecting means for detecting the beam between two points on the main scanning line, and a deflection speed of the light beam between the two points detected by the first and second light detecting means becomes constant. An image forming apparatus comprising: a control unit that controls the deflection unit. 2. The control means measures a scanning time of the light beam between two points by counting a clock having a constant frequency while the light beam is detected by the first and second light detecting means. The image forming apparatus according to claim 1, further comprising: 3. The image forming apparatus according to claim 2, wherein the clock is a writing clock of an image signal written by the light beam. 4. The image forming apparatus according to claim 2, wherein the control means controls the deflection speed of the light beam based on a scanning time when the deflection speed is initially controlled. 5. The control means ends the control of the deflection speed by controlling the deflection speed to a certain constant speed when an error occurs during the control of the deflection speed.
5. The image forming apparatus according to any one of 4 to 4. 6. The image forming apparatus according to claim 5, wherein the certain constant speed is a deflection speed immediately before an error occurs. 7. The image forming apparatus according to claim 5, wherein the certain constant speed is a deflection speed when the deflection speed of the light beam is initially controlled. 8. The deflecting means includes a polygon mirror,
8. The image forming apparatus according to claim 2, wherein the scanning time of the light beam is a total of scanning times for an integral multiple of the number of faces of the polygon mirror. 9. The deflecting means includes a polygon mirror,
8. The scanning time of the light beam is a scanning time of a specific surface of the polygon mirror.
The image forming apparatus according to any one of 1. 10. A photosensitive member moving in the sub-scanning direction,
10. The image forming apparatus according to claim 1, wherein the control unit controls the moving speed of the photoconductor according to the deflection speed of the light beam. 11. The image forming apparatus according to claim 10, wherein the moving speed v _p and the deflection speed v of the photoconductor are v _p / v = a (a: a constant corresponding to the writing density). .