JPH0546004A - Image forming device - Google Patents

Abstract

PURPOSE:To always decide an image writing position with respect to a paper feeding direction constant without being influenced by the emitting position of a laser beam to a photosensitive body by controlling writing in a subscanning direction by utilizing a synchronizing signal for timing with a writing position in a main scanning direction. CONSTITUTION:This device is provided with a left margin control part 20 which executes the writing in the main scanning direction according to a synchronous detection signal and a top margin control part 19 which executes the writing in the subscanning direction according to the synchronous detection signal. The left margin control part instructs timing which is the writing reference of a paper by triggering the leading edge of a signal which is photoelectrically converted when the laser beam S crosses the end face of a slit plate to a light source driving control part 22. The measured value of time (t) from the leading edge to a trailing edge by a counter 18 is inputted in the top margin control part 19, and the emitting position of the laser beam S in the feeding direction is calculated based on the time (t), and the writing timing of the laser corresponding to the position is instructed to the control part 22.

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 such as an electrophotographic developing type copying machine, a printer and a facsimile machine using a laser beam, and more particularly to a writing position of a laser beam in a main scanning direction of a photoconductor. Therefore, the present invention relates to an image forming apparatus which is characterized by controlling the writing position of a sheet in the main scanning direction and the writing position in the sheet feeding direction (sub-scanning direction).

FIG. 9 is a schematic configuration diagram of an image forming apparatus according to a conventional example, FIG. 10 is a perspective view of a synchronization detection signal detecting portion, FIG. 11 is a side view thereof, and FIG. 12 is a front view thereof. Laser light S emitted from a laser light source such as a semiconductor laser diode (LD) modulated by an image signal is converted into parallel light by the first collimator lens 2 and is rotated by the cylindrical lens 3 to rotate the polyhedral surface. Mirror (polygon mirror)
Only light rays parallel to the reflecting surface of 4 form an image on the reflecting surface of the rotating polygon mirror 4. Then, the rotary polygon mirror 4 is rotated at a high speed by the motor 5, so that the reflected laser light S is reflected by the photosensitive member 11.
The mechanism is such that the surface is horizontally scanned (scanning in the main scanning direction). Here, the laser beam S reflected by the rotary polygon mirror 4
Passes through an imaging lens (fθ lens) 6 composed of one or a plurality of sheets, and is focused on the surface of the photoconductor 11 via a reflection mirror 7.

In writing the laser beam in the scanning direction, the laser beam S before scanning the photoconductor 11 enters the optical fiber 10 having an inner diameter of about 1 mm by the second cylindrical lens 9, and this optical fiber 10 is used. An electric signal (horizontal synchronizing signal) converted by a photoelectric converter (for example, a photodiode) 15 attached to the tip of is used as a reference.
The laser beam S starts writing an image based on the left margin or the lateral resist after a certain fixed time after receiving the electric signal.

Here, if the second cylindrical lens 9 is not provided, only the margin of the optical axis shift corresponding to the inner diameter of the optical fiber 10 is left, whereas the second cylindrical lens 9 is used.
By installing, there will be a considerable margin for deviation of the optical axis. Further, without using the optical fiber 10, a slit plate 16 is attached in front of the second cylindrical lens 9 in parallel with the feeding direction of the paper P to clarify the rise and fall of the signal from the photoelectric converter 15. There is also. However, the feeding direction of the paper P (sub-scanning direction of laser light)
The writing depends on the mounting accuracy of the lenses and mirrors. Reference numeral 8 is a reflection mirror for guiding the laser light S to the second cylindrical lens 9, 12 is an optical unit body, and 13 is a main body of the apparatus. The arrow A indicates the photoconductor 11.
Indicates the rotation direction of.

[0005]

The writing start position in the sheet feeding direction of the conventional image forming apparatus is determined by the alignment between the optical system device and the support of the image forming device. However, since the laser light axis emitted from the laser light source including the laser light source and the collimator lens housed in the optical system device is adjusted, it is said that the laser light axis varies within a certain range. The laser light emitted at the same time is not a perfect parallel light. Further, there are many factors that deteriorate the positional accuracy, such as the tolerance of the lens, the mirror, and the structure that holds them after the emission of the laser light, and the positioning tolerance between the optical system device and the support of the image forming apparatus.

Further, when the optical system device is replaced due to a failure of the optical system device, the laser beam does not always coincide with the emission position before the replacement. In addition, a semiconductor laser diode (L
In D), the emission angle itself changes when it is energized and heated, and as a result, the optical axis and collimating property (parallelism of laser light)
There is also a phenomenon that it is said that it is out of alignment. For the above reasons, it is very difficult to emit the laser light to the set position on the surface of the photoconductor forming the image.

However, as a recent image forming apparatus,
An image forming apparatus using a plurality of laser light sources has been developed for the purpose of increasing the image output speed or improving the image resolution, and more accurate emission position of the laser light to the photoconductor is required. Therefore, as an improvement of these, JP-A-1
In Japanese Patent Laid-Open No. 183676, the reflector of the laser light is driven to scan the laser light at a set position. However, this method requires a dedicated drive means for driving, which results in cost up and at the same time the space thereof. Will be needed.

The present invention provides an image forming apparatus capable of always determining the image writing start position in the sheet feeding direction (laser light sub-scanning direction) without being influenced by the laser light emitting position on the photosensitive member. The purpose is to do.

[0009]

SUMMARY OF THE INVENTION The above object is to provide an image forming apparatus for writing an electrostatic latent image on a photoconductor with a laser beam and visualizing the electrostatic latent image by an electrophotographic process to obtain a copy on a sheet. The slit means that varies the width of the slit along the sheet feeding direction, the photoelectric converter that converts the laser light passing through the slit means into an electric signal, and the electric signal converted by the photoelectric converter are used. This is achieved by including a left margin control unit that writes the laser light in the main scanning direction and a top margin control unit that also writes the laser light in the sub-scanning direction by this electric signal.

[0010]

According to the present invention, the synchronizing signal (electrical signal output from the photoelectric converter) for timing the writing position in the main scanning direction on the photosensitive member by the laser beam is utilized to make the sub-scanning direction (paper feeding). The writing control of (direction) is also performed.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. However, parts that are the same as or can be regarded as the same as the conventional example shown in FIG. In this embodiment, a slit plate 14 parallel to the feeding direction of the paper P is provided.

As shown in FIG. 5, the slit plate 14 has an end surface B,
One of the Cs is installed parallel to the feeding direction (the sub-scanning direction of the laser light S), and the other is installed with a certain inclination with respect to the direction. A photoelectric converter 15 is attached after the slit plate 14 in the emitting direction of the laser light S. As the photoelectric converter 15, as described in the conventional device, for example, there is a photodiode, but when the LD is used as a light source, this photodiode has a laser wavelength of LD (generally 780 nm) as shown in FIG. It is desirable to use a photo diode which meets the requirement (1).

Further, in the present embodiment, a photoelectric converter having a light receiving surface of about 4 mm (see FIG. 5) in which an emission position shift can occur is required, but a photodiode having such a light receiving surface can be obtained at low cost. Is. However, the size of the light receiving surface is not limited to the above. Here, in the related art, FIG.
If the slit is displaced in the scanning direction as shown in (S ₂ → S ₁ )
Although the range of light entering the optical fiber 10 is extremely narrowed, in this embodiment, since the light receiving surface of the photoelectric converter 15 is large, the deviation of the slit 14a of the slit plate 14 does not greatly affect the light entering width.

Now, the detection of the actual writing position will be described. In FIG. 5, the end surface B of the slit plate 14 which the laser light S first traverses is in the feeding direction (the sub-scanning direction of the laser light S).
2 shows a case in which the end face C of the slit 14a which is parallel to, and traverses afterward is inclined, and FIG.
FIG. 5 shows a block diagram after the laser light S enters.

The laser light S is first of all converted into the photoelectric conversion unit 17
Is converted into voltage by. The photoelectric conversion unit 17 uses a threshold voltage (Vs) adjusted by a resistor R ₃ to generate a voltage waveform close to a trapezoid as shown in (1) of FIG. It includes a converter 26 that shapes and amplifies as in (2). Photoelectric conversion unit 1
The signal (voltage) output from 7 is sent to the left margin control unit 20 that controls the writing position of the laser beam S in the scanning direction (horizontal direction) and the top margin control unit 19 that controls the writing in the feeding direction. ..

In the left margin control section 20, the rising edge c of the signal photoelectrically converted when the laser beam S traverses the end surface B of the slit plate 14 [(2) in FIG. 3] is used as a trigger for T ₅ [FIG. 6, FIG. 7] After that, the light source drive control unit 22 is instructed of the timing when the writing start position of the paper P is reached. The top margin control unit 19 uses the counter 18 in FIG.
(2) rising edge c to falling edge d
The measured value of the time t up to is input. Since the width of the slit 14a is proportionally different in the top margin control unit 19, the emission position of the laser beam S in the feeding direction is calculated from the time t, and the laser writing timing T _{7 corresponding} to the position is calculated. [FIG. 6, FIG. 7]
Instruct.

The timings of the counter 18 and the control units 19 and 20 are conventionally the light source drive control unit 22 and the conveyance control unit 2.
The reference clock generated from the reference clock generating unit 25 used in 1 is used as it is. The reference clock generator 25 normally uses a crystal oscillator. Although not shown, when the end surfaces B and C of the slit 14a are reversed, the writing start position of the laser light S in the scanning direction may be synchronized with the rising edge d of the waveform of FIG. 3B as a trigger. ..

It is also conceivable to use a CCD as a photoelectric converter as another embodiment, but the CCD is still expensive and the control system becomes complicated, so that it will be briefly described here. Keep it. In this case, it is not necessary to use a separate slit, and it suffices to install the CCD in parallel with the feeding direction. The rising or falling of the photoelectrically converted signal is used as a trigger for the writing position in the scanning direction of the laser light, and the laser light is used. Then, the emission position of the laser light in the feeding direction is detected by obtaining the potential of the scanned CCD. In FIG. 2, 23 is a main controller and 24 is an image data controller.

6 and 7 show timing charts in the scanning direction. This figure shows an example of the case where the image forming apparatus in which the toner is transferred to the point where the light source light is applied to the photoconductor, the image formable range of the sheet is entirely black (black solid). Here, the laser light source 1 does not turn on in the paper position range when it receives photoelectric output in the non-image portion N1. Also, it is usual that T ₇ and the image writing position do not match as shown in the figure depending on the synchronization position of the photoelectric output, but the synchronizing waveform of the photoelectric output first detected after T ₇ is considered to be the writing scanning line. Good. This is because one scanning line of the laser light S is 200 μm or less even at 200 DPI, and the writing position does not change significantly.

Further, in the figure, the registration SN (sensor)
Although it is based on the signal of, the photoelectric output is the same,
Other signals are possible. Although the rising and falling are defined above, the rising and falling may be reversed depending on the circuit in the photoelectric conversion unit 17.

FIG. 8 shows a flow chart of the operation described above. Here, T ₄ and T ₃ are constant values set from the beginning, and T ₇ is set to an initial setting value if the length determination of the synchronization signal is good. The setting of the T ₇ of the feeding shoulder stop margin as a reference for the direction of the write start position since the overlapping or omission of an image occurs before and after setting to perform during image formation is performed before writing of the paper.

First, a synchronizing signal (output of photoelectric converter 15)
Enter the works of (S1), then, in the main scanning direction write start control, detection of the waveform edge (S2), the timing the creation of T ₄ (S3), the timing the creation of the writing start position in the scanning direction (setting of T ₅₎ ( S4), timing generating (S5 of T _6), the timing the creation of T ₃ (S6) is performed.

On the other hand, in the writing control in the feeding direction (sub-scanning direction), sampling (S7) and signal length determination (S).
8), calculation of T ₇ based on the length determination result (S9), timing creation of the writing position in the feeding direction (setting of T ₇ )
(S10) is performed. Finally, the laser light source 1 is turned off (S11).

Next, an example of a sampling method of the synchronization time t of the photoelectric output which is the input signal of the top margin control of FIG. 8 will be described. The following six examples of typical sampling methods can be given. A method of sampling a laser beam scan of at least one line during a warm-up or self-diagnosis each time the power of the image forming apparatus is turned on by using a current relay circuit or the like.

A method of sampling a specific scan of at least one line of the image portion. As the specific scanning line referred to here, if a line near the leading edge line or the trailing edge line of the image in the feeding direction of the paper P is detected by counting the scanning in synchronization with the image data control unit. Easy to do. A method of sampling a scan of at least one line within a specific time after a specific time of an image portion. This is to sample the scanning line based on the time from the image writing line in the paper feeding direction in synchronization with the image data control unit, and the unit of time is to use the reference clock from the reference clock generation unit. Good.

A scan line within a specific time refers to a sync signal scanned from a first sync signal scanned after a specific time to a final sync signal within a specific time. The number of scans varies depending on the timing of the sync signal. There is no problem if the average value is used. A method of sampling scans of one line or more within a specific time period after the power is turned on. The time from the image writing line may be replaced with the time from power-on. A method of sampling a specific scan of one line or more at a specific time after the power is turned on. Although similar to the above method, this is a method of counting the number of sampling scans. A method of sampling a specific number of scans of one line or more or a scan within a specific time for each specific number of scans of laser light in a non-image portion between papers or after a specific time.

The case where the photoelectric converter sensitivity and the position of the slit plate are always determined without error has been described above. However, since there may be cases where such a case does not occur in practice, the correction method is simple. Add an explanation. First of all, a jig base including a reference laser light source is prepared, and an image forming apparatus having a slit plate mounted on the jig base is set. Then, the laser light source is caused to scan the slit on the image forming apparatus, and the deviation between the time of the synchronizing signal at that time and the set value in the jig is corrected. Since the time setting value of the synchronization signal at that time is divided beforehand,
It suffices that the time when actually scanned becomes that value.

The correction is performed by changing the resistance value of the variable resistor R ₃ shown in FIG. 2 or adjusting the shift amount by software. However, the accuracy of this jig is on the order of at least several hundreds of μm. As another method, a test pattern for outputting a continuous image in the scanning direction at a specific distance from the leading edge of the paper is input to the image forming apparatus, the image is actually output, and the deviation is measured by the variable resistor R _{3 in} FIG. There is also a method of changing the resistance value of or changing it with software.

[0029]

According to the first aspect of the present invention, it is possible to control the writing in the paper feeding direction from the signal used for synchronizing the scanning direction of the laser light, so that it is inexpensive, and a stable writing position can always be obtained. Can be set.

According to the second aspect of the present invention, the writing control in the paper feeding direction is performed when the image forming apparatus is powered on, so that a stable writing position can be set from the initial image.

According to the third aspect of the present invention, the writing control in the paper feeding direction is performed for each output of the paper regardless of the length of the image data. Therefore, a stable writing position can be set for each output of the paper. You can

According to the fourth aspect of the present invention, the scanning within the specific time range is sampled for each output of the paper, and the writing control in the paper feeding direction of the paper is performed. Therefore, the output of the paper is output without calculating the image scanning line. You can set a stable writing position for each.

According to the fifth and sixth aspects of the invention, the scanning of the laser beam is sampled every time after the power is turned on, and the writing control in the paper feeding direction is performed, so that the image is not always output. A stable writing position can be set when outputting only when necessary (when outputting intermittently).

According to the seventh aspect of the invention, since the scanning of the non-image portion between the sheets is sampled and the writing control in the sheet feeding direction is performed, a stable writing position is set immediately after the next sheet after sampling. can do.

According to the invention described in claim 8, since the correction controller is provided in the image forming apparatus, the sensitivity of the photoelectric converter,
A stable writing position can be set regardless of the mounting accuracy of the slit.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a control block diagram of the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a voltage waveform before shaping and a voltage waveform after shaping in the photoelectric conversion unit.

FIG. 4 is a spectral sensitivity characteristic diagram of a laser diode.

FIG. 5 is a plan view of a slit plate.

FIG. 6 is an overall timing chart.

FIG. 7 is an overall timing chart.

FIG. 8 is a flow chart of the control operation of the present invention.

FIG. 9 is a schematic configuration diagram of an image forming apparatus according to a conventional example.

FIG. 10 is a perspective view of a synchronization detection signal detector.

FIG. 11 is a side view of a synchronization detection signal detector.

FIG. 12 is a front view of a synchronization detection signal detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 laser light source 4 rotating polygonal mirror 11 photoconductor 14 slit plate 15 photoelectric converter 17 light source conversion unit 19 top margin control unit 20 left margin control unit 21 transport control unit 22 light source drive control unit 23 main control unit 24 image data control unit 25 Reference clock generator

Claims (8)

[Claims] 1. An image forming apparatus for writing an electrostatic latent image on a photosensitive member by a laser beam and making the electrostatic latent image visible by an electrophotographic process to obtain a copy on a sheet. The slit means varied along the direction, the photoelectric converter for converting the laser light passing through the slit means into an electric signal, and the electric signal converted by the photoelectric converter in the main scanning direction of the laser light. An image forming apparatus comprising: a left margin control unit that performs writing, and a top margin control unit that similarly performs writing in the sub-scanning direction of a laser beam using this electric signal. 2. The image forming apparatus according to claim 1, wherein each time the power of the image forming apparatus is turned on, at least one line of laser scanning is performed to sample the electric signal converted by the photoelectric converter, and the electric signal in the paper feeding direction of the laser beam is sampled. Set the export position,
An image forming apparatus characterized in that writing is performed in a paper feeding direction in which a set value is changed every time the power of the image forming apparatus is turned on. 3. The paper feeding of laser light according to claim 1, wherein at least one line of at least one sheet is subjected to a specific scan during the image output to sample the electric signal converted by the photoelectric converter. An image forming apparatus characterized in that a writing position in a direction is set and writing is performed in a sheet feeding direction in which the set value is changed for each sheet or for each specific number of sheets. 4. The sheet of laser light according to claim 1, wherein scanning of at least one or more sheets within a specified time after image output during image output samples electrical signals converted by the photoelectric converter. An image forming apparatus, characterized in that a writing position in the sheet feeding direction is set and writing is performed in the sheet feeding direction by changing the set value for each sheet or for each specific number of sheets. 5. The electric signal converted by the photoelectric conversion device according to claim 1, wherein a specific scan of one line or more is sampled every specified time after the power is turned on, and a laser beam is fed in a paper feeding direction. An image forming apparatus characterized in that a writing start position is set, and writing is performed in a paper feeding direction in which the set value is changed for each paper or for each specific number of sheets. 6. The electric signal converted by the photoelectric converter for scanning within a specific time period according to claim 1, sampling the electric signal, setting a writing start position of a laser beam in a paper feeding direction, An image forming apparatus characterized in that writing is performed in a sheet feeding direction in which the set value is changed for each sheet or for each specific number of sheets. 7. The photoelectric conversion device according to claim 1, wherein the laser light scanning of the non-image portion between the sheets is converted by the photoelectric converter for each specific number of sheets or for each first sheet after a specific time. The electric signal is sampled, the writing position of the laser beam in the paper feeding direction is set, and the setting value is changed for each paper or for each specific number of sheets, and writing is performed in the paper feeding direction. Image forming apparatus. 8. The image forming apparatus according to claim 1, further comprising a correction control unit configured to scan a known position on the slit means with a laser beam to correct the sensitivity of the photoelectric converter.