JPH1058746A - Multi-beam scanning type image forming apparatus / scanning line pitch unevenness detecting method / scanning line pitch unevenness detecting device and scanning line pitch unevenness correcting device - Google Patents

Abstract

(57) Abstract: In a multi-beam scanning type image forming apparatus, unevenness in scanning line pitch is easily detected. Multi-beam scanning for converging light beams from a plurality of light sources on a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction and simultaneously scanning the photoconductor with the plurality of light spots. A method for detecting pitch unevenness of a scanning line simultaneously scanned by a plurality of light spots in a mold image forming apparatus, wherein a simultaneous scanning by all light spots is repeatedly performed to detect a latent image pattern for pitch unevenness detection. Is formed, and the average potential of the latent image pattern is detected by the potential sensor 49B.
Is compared with a predetermined comparison value, thereby detecting the pitch unevenness of the scanning line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam scanning type image forming apparatus, a scanning line pitch unevenness detecting method, a scanning line pitch unevenness detecting device, and a scanning line pitch unevenness correcting device.

[0002]

2. Description of the Related Art A beam scanning type image forming apparatus that deflects a light beam whose intensity is modulated by an image signal and scans a surface to be scanned for image formation is widely known as a digital copying machine, various optical printers, and the like. . Recently, a “multi-beam scanning type image forming apparatus” that simultaneously scans a plurality of scanning lines at a time has been proposed in order to speed up scanning.

One of the important points to note in image formation by multi-beam scanning is that the scanning line pitch for determining the recording density in the sub-scanning direction must be properly set. If the scanning line pitch is not appropriate, the recording density or image density of the written recorded image fluctuates periodically in the sub-scanning direction, causing image quality deterioration of the recorded image.

The scanning line pitch is determined by the relative positional relationship between the light sources in the light source unit, the imaging magnification of an optical system between the light source unit and the surface to be scanned, and the like. The imaging magnification and the like are often slightly different due to a small assembling error when assembling the optical system to each multi-beam scanning device,
Even if the assembling adjustment is performed as designed, it is conceivable that the imaging magnification changes with time due to the influence of vibrations and the like accompanying the actual use of the multi-beam scanning device. Regarding the relative positional relationship between the plurality of light sources in the light source section, aside from the monolithic structure such as an LD (semiconductor laser) array, in a light source section in which a plurality of independent semiconductor lasers are combined, An assembling error or a change with time is considered.

[0005] For these reasons, in order to realize an appropriate scanning line pitch, it is necessary to detect "whether or not the scanning line pitch is uneven" as needed.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel "scanning line pitch unevenness detection method" which can easily detect scanning line pitch unevenness. Another object of the present invention is to realize a “scanning line pitch unevenness detecting device” for implementing the above-described pitch unevenness detecting method.

Another object of the present invention is to provide a method for detecting unevenness in scanning line pitch based on the method for detecting unevenness in scanning line pitch.
It is an object of the present invention to realize a “scanning line pitch unevenness correction device” that corrects scanning line pitch unevenness.

Still another object of the present invention is to realize a "multi-beam scanning type image forming apparatus" having a scanning line pitch unevenness detecting function or a scanning line pitch unevenness detecting function and a scanning line pitch unevenness correcting function.

[0009]

According to a first aspect of the present invention, there is provided a method for detecting unevenness in scanning line pitch, wherein a plurality of light spots obtained by separating light beams from a plurality of light sources on a photoconductive photosensitive member in a sub-scanning direction. In a multi-beam scanning type image forming apparatus that condenses light and scans the photosensitive member simultaneously with the plurality of light spots, a method for detecting uneven pitches of scanning lines simultaneously scanned by the plurality of light spots is used.

The scanning line pitch unevenness detecting method according to the first aspect has the following features. That is, the simultaneous scanning by all the light spots is repeated to form a "latent image pattern for detecting uneven pitch", and the "average potential" of the latent image pattern is detected by a potential sensor. Then, the unevenness of the scanning line pitch is detected by comparing the value detected by the potential sensor with a predetermined comparison value.

The method for detecting uneven scanning line pitch according to claim 2 is characterized by the following points. That is, the simultaneous scanning by all the light spots is repeatedly performed to form a “latent image pattern for detecting uneven pitch”, and the toner pattern obtained by developing this latent image pattern under “predetermined development conditions” The reflection intensity of the area region is detected by the optical sensor, and the detected value of the optical sensor is compared with a predetermined comparison value to detect the scanning line pitch unevenness.

In the first and second aspects of the present invention, the latent image pattern for detecting uneven pitch formed by repeatedly performing simultaneous scanning with all the light spots is a pattern corresponding to a so-called "solid portion". If there is no scanning line pitch unevenness, the potential of the latent image pattern is uniformly lower than the surroundings in absolute value.

However, when the scanning line pitch is uneven, the formed latent image pattern periodically includes a portion where the scanning line pitch becomes large and a portion where the scanning line pitch becomes small in the sub-scanning direction. Is higher in absolute value where the scanning line pitch is large.

For this reason, when the scanning line pitch unevenness exists, the potential of the latent image pattern for detecting the unevenness of the pitch becomes "in average" higher in absolute value than the potential when there is no scanning line pitch unevenness. .

The "potential sensor" detects the potential on the surface of the photoreceptor. In general, the detected potential is not an accurate fine potential distribution on the surface of the photoreceptor, but an average of such potential distribution. Average potential ". Therefore, the presence or absence of the scanning line pitch unevenness and the degree thereof can be known from the magnitude of the detection potential from the latent image pattern. That is, the “average detected potential” from the latent image pattern formed in a state where the scanning line pitch unevenness is completely corrected is set as a “predetermined comparison value”, and the potential detected at the time of detection is compared with the comparison value. This makes it possible to know the degree of the scanning line pitch unevenness (the larger the difference between the detected potential and the reference value, the more noticeable the scanning line pitch unevenness).

The "toner pattern" obtained by (reversing) developing the latent image pattern is an appropriate "solid pattern" if the scanning line pitch is not uneven, and its image density is uniform. However, if there is unevenness in the scanning line pitch, the shading of the image periodically fluctuates in the sub-scanning direction. For this reason, the “reflection intensity” when light is applied to the area area of the toner pattern (an area having a certain two-dimensional spread (at least about several mm ² )) is smaller than that of a proper toner pattern. Since the reflection intensity is detected by an optical sensor, the presence or absence of the scanning line pitch unevenness can be detected because the scanning line pitch unevenness is larger. The detection value when the reflection intensity is detected by the optical sensor is defined as a “predetermined comparison value”, and the detection value detected at the time of detection is compared with the comparison value to determine the degree of the scanning line pitch unevenness (the detected reflection intensity). The greater the difference between the scanning line pitch and the reference value, the more noticeable the scanning line pitch unevenness is.)

In the case of the second aspect of the present invention, if the developing conditions for developing the latent image pattern are not fixed, the density of the toner pattern to be formed fluctuates depending on the developing conditions. It becomes an error. Therefore, it is necessary to keep development conditions constant. In the invention according to claim 2,
The reflection intensity of the toner pattern transferred to the intermediate transfer medium such as the intermediate transfer belt may be detected.

According to a third aspect of the present invention, there is provided a method of detecting unevenness in scanning line pitch, comprising: condensing light beams from a plurality of light sources on a photoconductive photosensitive member as a plurality of light spots separated in a sub-scanning direction;
In a multi-beam scanning type image forming apparatus that simultaneously scans the photoconductor with the plurality of light spots, a method for detecting pitch unevenness of scanning lines simultaneously scanned by any two light sources adjacent to each other is described. This is common in that a second latent image pattern is formed.

In this case, the number of light sources may be two or three or more. When the number of light sources is two, these two are the above-mentioned "arbitrary two light sources adjacent to each other", but when the number of light sources is three or more, any one of these light sources and this If another light source adjacent to the light source constitutes "arbitrary two light sources adjacent to each other" and the number of light sources is three or more, the light sources other than the two light sources are turned off and the scanning line pitch unevenness is detected.

The first and second latent image patterns are for "for detecting pitch unevenness". The “first latent image pattern” is formed by simultaneously turning on the two light sources and simultaneously scanning with two light spots every predetermined number of scanning lines.

The “second latent image pattern” is a second light spot (an even-numbered scan line, where the numbers of the scan lines sequentially scanned by the two light spots are 1, 2, 3,...) Is formed by repeating a scan with a light spot that scans the first light spot) and a subsequent scan with a scan spot with the first light spot every predetermined number of scan lines.

For example, if the predetermined number is 2, the above 1, 2, 3,. . When considering the th scan line,
The first latent image pattern includes first, second, fifth, sixth, ninth,
Tenth,. . The second scan line is formed by scanning the
Are the second, third, sixth, seventh, tenth,
Eleventh,. . The scan line is formed by scanning the scan line.

According to a third aspect of the present invention, there is provided a scanning line pitch unevenness detecting method which is characterized by the following points. That is, the first and second
The "average potential" of each of the latent image patterns is detected by a potential sensor, and the unevenness of the scanning line pitch is detected by comparing two obtained detection values.

According to a fourth aspect of the present invention, there is provided a scanning line pitch unevenness detecting method having the following features. That is, the first and second
The “reflection intensity of the area area” of each of the first and second toner patterns obtained by developing the latent image pattern of “1” under “predetermined development conditions” is detected by an optical sensor, and the first and second toner patterns are Pitch unevenness of the scanning line is detected by comparing two obtained detection values.

As described above, the potentials of the first and second latent image patterns change in the sub-scanning direction in the form of stripes having a width of two scanning lines. When the interval between the first and second light spots in the sub-scanning direction is equal to the predetermined scanning line pitch, the first and second latent image patterns are shifted from each other by one scanning line in the sub-scanning direction. In this case, the “average potential” detected by the potential sensor or the “reflection intensity” of the toner pattern obtained by developing each latent image pattern is:
It is the same for each latent image pattern.

However, if the interval between the first and second light spots in the sub-scanning direction is slightly larger (smaller) than the predetermined scanning line pitch, the "predetermined number of scanning lines" are not scanned.
The width of the minute becomes smaller (larger) in the first latent image pattern, and larger (smaller) in the second latent image pattern. Accordingly, when the distance between the two light spots in the sub-scanning direction deviates from the predetermined scanning line pitch, a difference is generated between the average potentials of the first and second latent image patterns. Therefore, by detecting the difference between the average potential and the reflection intensity, it is possible to know the presence or absence of the scanning line pitch unevenness and the “degree of unevenness”.

In the scanning line pitch unevenness detecting method according to the fourth aspect, the reflection intensity may be detected by transferring the first and second toner patterns onto the intermediate transfer medium (claim 5). Further, in the method for detecting uneven scanning line pitch according to claim 3, 4 or 5, the first and second latent image patterns may be “formed so as to be arranged in the sub-scanning direction” (in this case, the potential The sensor or the optical sensor can be used in common for the first and second latent image patterns or the toner pattern) (claim 6), or may be "formed so as to be arranged in the main scanning direction" (claim 7). .

[0028] In the scanning line pitch unevenness detecting method according to any one of claims 3 to 7, the first and second latent image patterns may include a recording scanning area (a writing area) of a writable area by a light spot. It may be formed outside the area in the main scanning direction where the image to be recorded is written (in this case, the scanning line pitch unevenness can be detected irrespective of whether or not the image is being written). It may be formed in the recording scanning area (claim 8). In the case of the invention described in claim 8, scanning line pitch unevenness can be detected in the "area where image formation is actually performed".

When the first and second latent image patterns are formed in the recording scanning area in this manner, a plurality of pairs of the first and second latent image patterns can be formed in the main scanning direction. Accordingly, the scanning line pitch unevenness can be detected at a plurality of different positions in the main scanning direction (claim 9).

A "scanning line pitch unevenness detecting device" according to a tenth aspect is an apparatus for implementing the scanning line pitch unevenness detecting method according to the third aspect. It has "one or more potential sensors" for detecting an average potential of the first and second latent image patterns, and "pitch unevenness detecting means" for detecting scanning line pitch unevenness based on an output of the potential sensor.

According to an eleventh aspect of the present invention, there is provided a scanning line pitch unevenness detecting apparatus for performing the scanning line pitch unevenness detecting method according to the fourth aspect. It has "one or more optical sensors" for detecting the reflection intensity of each area of the second toner pattern, and "pitch unevenness detecting means" for detecting scanning line pitch unevenness based on the output of the optical sensor.

According to a twelfth aspect of the present invention, there is provided a scanning line pitch unevenness correcting apparatus, wherein: "light beams from a plurality of light sources are condensed on a photoconductive photosensitive member as a plurality of light spots separated in a sub-scanning direction; A multi-beam scanning type image forming apparatus that simultaneously scans the photoconductors, wherein a device for correcting scanning line pitch unevenness is provided, and a pitch control unit for adjusting the scanning line pitch and a pitch control unit for controlling the pitch adjusting unit. Means for correcting pitch unevenness by adjusting the pitch adjusting means by the pitch control means in accordance with the pitch unevenness detected by the scanning line pitch unevenness detecting method according to any one of claims 3 to 9. It is characterized by doing so.

According to a thirteenth aspect of the present invention, there is provided a multi-beam scanning type image forming apparatus comprising: a light beam from a plurality of light sources is condensed on a photoconductive photosensitive member as a plurality of light spots separated in a sub-scanning direction; A multi-beam scanning type image forming apparatus for simultaneously scanning the photoconductor with a spot has a scanning line pitch unevenness detecting device according to claim 10 or 11.

According to a fourteenth aspect of the present invention, there is provided a multi-beam scanning type image forming apparatus, wherein "light beams from a plurality of light sources are condensed on a photoconductive photosensitive member as a plurality of light spots separated in a sub-scanning direction, and these light beams are condensed. A scanning line pitch unevenness detecting device according to claim 10 or 11, wherein:
A scanning line pitch unevenness correcting device according to claim 12 is provided.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below by taking as an example a case where the number of light sources in a light source section is two (two-beam scanning). In FIG. 2A, two light beams for two-beam scanning are obtained from a “light source unit” indicated by reference numeral 10.
Each is emitted as a parallel beam. The two radiated light beams pass through the opening of the aperture plate 20 for shaping the light spot, enter the cylinder lens 43, and correspond to the sub-scanning direction (a virtual path obtained by linearly developing the optical path from the light source to the surface to be scanned). The direction parallel to the sub-scanning direction on the optical path, and the direction parallel to the main scanning direction on the virtual optical path is called the main scanning corresponding direction). An image is formed as a “long line image in the main scanning corresponding direction” in the vicinity of the deflecting reflection surface 44 of the polygon mirror 40 which is a container.

When the polygon mirror 40 rotates at a constant speed in the direction of the arrow, the two light beams reflected by the deflecting / reflecting surface 44 become deflecting light beams, and are scanned by the action of the fθ lens 45 and the long toroidal lens 46 for correcting surface tilt. The light is condensed as two light spots on the photoconductive photoconductor 48 whose peripheral surface is matched with the surface, and the photoconductor 48 is scanned.

As shown in FIG. 2B, the light source 10
Two semiconductor lasers 11 and 12 are provided in a casing 18.
And the two collimating lenses 13 and 14 and a half that rotates the polarization plane of the light beam from the semiconductor laser 11 by 90 degrees.
A wave plate 15, a beam combining prism 16 for combining light beams from the semiconductor lasers 11 and 12, and a quarter wave plate for changing the polarization state of the combined two light beams into a circularly polarized state for "shading correction". 17 are provided.

Each light beam emitted from the semiconductor lasers 11 and 12 is converted into a parallel light beam by the corresponding collimator lenses 13 and 14 and then enters the beam combining prism 16. The light beam from the semiconductor laser 11 is
The light passes through the polarization beam splitter film 162 at the point, and exits from the beam combining prism 16. The light beam from the semiconductor laser 12 is internally reflected by the inclined surface 161 of the beam combining prism 16, is reflected by the polarization beam splitter film 162, and exits from the beam combining prism 16.

In FIG. 2B, the collimating lens 1
Both 3 and 14 are “in the same plane parallel to the main scanning corresponding direction”. At least one of the semiconductor lasers 11 and 12 is slightly displaced from the optical axis of the corresponding collimator lens in the main / sub scanning corresponding direction. In FIG. 2B, the deviation of the semiconductor laser 12 from the optical axis of the collimator lens 14 in the sub-scanning corresponding direction is illustrated “exaggeratedly”. That is, the straight line in the main scanning corresponding direction and the fine angular connecting the light emitting portion of the semiconductor laser 11, 12: form a theta _A, square: the slope of theta _A, 2 a light beam emitted from the beam combining prism 16 is scan-corresponding to each other It is slightly inclined in the direction.

Due to the small angle, two light spots condensed on the scanning surface 50 (SP1 and SP2 in FIG. 2C).
The gap in the sub-scanning direction indicated by 2): P _S is determined. Due to a slight shift of the semiconductor lasers 11 and 12 from the optical axis of the corresponding collimating lens in the main scanning direction, the light beam emitted from the beam combining prism 16 in the main scanning direction is as shown in FIG. Make a small angle θ _B with each other. The light is condensed on the scanned surface 50 by this angle: θ _B 2
Interval between two light spots in the main scanning direction: P _M (FIG. 2
(C)) is determined.

By rotating the light source unit 10 around the optical axis of the collimating lens 13,
One of the spacing of the light spot while keeping constant the direction connecting these spots can be rotated, by utilizing this fact, the interval: P _S, it is possible to adjust the P _M.

In FIG. 2B, the two light beams emitted from the beam combining prism 16 have linearly polarized planes of polarization orthogonal to each other. Are caused to pass through the quarter-wave plate 17 to make them circularly polarized. In this manner, the two light beams that have been combined and subjected to shading correction are emitted from the light source unit 10.

The light emitted from the light source unit 10 is
The two light beams deflected by 0 are deflected toward the scanning region. On the way to the scanning region, they enter the light receiving element (not shown) via the fθ lens 45 and are detected, and are used to generate a synchronization signal for starting scanning. You.

In FIG. 2A, reference numeral 49 denotes a "sensor".
And the output of the sensor 49 is input to the detection unit 50. The detection unit 50 is, for example, a microcomputer. The sensor 49 can be a “potential sensor or an optical sensor”.

FIG. 1A shows an embodiment in which the sensor 49 in FIG. 2A is implemented as a potential sensor 49A. Reference numeral 491 indicates a probe of the potential sensor 49A. The position of the probe 491 is set between a scanning position by a light spot and a developing unit (not shown).

FIG. 1B shows an embodiment in which the sensor 49 in FIG. 2A is implemented as an optical sensor 49B. The position of the optical sensor 49B is determined by the developing unit 60.
Is set on the downstream side of

Hereinafter, a method of detecting uneven scanning line pitch according to the second aspect of the present invention will be described with reference to the embodiment of FIG. In the multi-beam scanning type image forming apparatus shown in FIG.
Is uniformly charged, and the simultaneous scanning by the two light spots SP1 and SP2 is repeated to form a “latent image pattern for detecting pitch unevenness”. To obtain a toner pattern.

FIGS. 1 (c) to 1 (e) are illustrations showing the toner patterns thus obtained. Code 1,
1 ′ and 1 ″ indicate toner images (line images) obtained by scanning the light spot SP1, and reference numerals 2, 2 ′ and 2 ″ indicate toner images obtained by scanning the light spot SP2.
Note that “the toner pattern actually formed when the scanning line pitch unevenness is detected” is practically about 10 mm × 10 mm, and therefore, the toner pattern is formed by about 100 scanning lines. FIGS. 1C to 1E are explanatory diagrams, and show only six scanning lines.

In an ideal state where there is no scanning line pitch unevenness, the toner pattern formed as described above has a uniform toner image density as shown in FIG. Light is emitted from the light emitting source 493 of the optical sensor 49B to the area of such an ideal toner pattern, and the reflection intensity of the area is detected as the amount of light received by the light receiving unit 494. Then, the detected value at this time is defined as a predetermined “comparison value”,
It is stored in advance in the detection unit 50 shown in FIG.

When the distance between the two light spots SP1 and SP2 in the sub-scanning direction: P _S (FIG. 2C) is smaller than a predetermined scanning line pitch, the upper part of the scanning line formed by the light spot SP2 is formed by the light spot SP1. Since the toner pattern overlaps the lower part of the scanning line, the toner pattern to be formed is as shown in FIG.
Occurs. When the distance between the two light spots SP1 and SP2 in the sub-scanning direction: P _S is larger than a predetermined scanning line pitch, the upper part of the scanning line formed by the light spot SP1 overlaps the lower part of the scanning line formed by the light spot SP2. As shown in FIG. 1 (e), a portion where no toner is present also occurs.

Therefore, if there is scanning line pitch unevenness,
As shown in FIGS. 1D and 1E, the obtained toner pattern includes a portion where the surface of the photoreceptor is not covered with the toner, and the reflection intensity increases in this portion. The average reflection intensity within the detected area becomes larger than the “comparison value”.

Therefore, by comparing the value detected by the optical sensor 49B with the "predetermined comparison value", it is possible to detect the presence of scanning line pitch unevenness when the detection value is larger than the comparison value.

The detection unit 50 shown in FIG.
An operation of subtracting the "comparison value" from the output of the line 9B is performed. If the result of the operation exceeds a predetermined allowable value, it is determined that the scanning line pitch unevenness exceeds the actual allowable amount, and a display (not shown) is displayed. Indicate this in the section.

Above, the reflection intensity of the toner pattern obtained by developing the formed “latent image pattern for detecting uneven pitch” was detected by a sensor, but the average potential of the latent image pattern was detected by a potential sensor. Scanning line pitch unevenness can also be detected by detecting with 49A (claim 1).

That is, in the case of a latent image pattern such that a toner pattern as shown in FIG.
Are small in absolute value, and this is stored in the detection unit 50 in advance as a “comparison value”.
In the case of the latent image pattern in which the toner pattern is as shown in FIGS. 1D and 1E, the remaining scan portion (for example, FIG. 1D)
, The average potential detected by the potential sensor 49A becomes larger in absolute value than the comparison value due to the effect of the residual potential in the region between the portions indicated by reference numerals 2 and 1 '). Therefore, the detection unit 50 executes an operation of subtracting the “comparison value” from the output of the potential sensor 49A, and when the result of the operation exceeds a predetermined allowable value, the scanning line pitch unevenness exceeds the actual allowable amount. The presence of scanning line pitch unevenness can be detected.
When such scanning line pitch unevenness exists, the detecting unit 5
“0” indicates that fact on a display unit (not shown).

The inventions according to the first and second aspects are effective for detecting a somewhat large scanning line pitch unevenness. However, in these methods, the cause of the scanning line pitch unevenness, the light spot SP1, SP1 interval: P _S is, whether it is because the increased, it is impossible to know in order to become small.

[0057] scan line pitch irregularity detection method according to claim 3-9, wherein to be described below, causes the scanning line pitch unevenness, spacing of the light spot SP1, SP1: whether P _S is because increased, decreased This is useful for detecting when the scan line pitch unevenness is small.

Hereinafter, embodiments of the present invention will be described with reference to the multi-beam scanning type image forming apparatus shown in FIG.

As the sensor 49 shown in FIG. 2A, the potential sensor 49A shown in FIG. 1A or the optical sensor 49B can be used.

In FIG. 3A, reference numerals SP11, SP
Reference numeral 22 denotes a light intensity distribution of the two light spots SP1 and SP2, respectively, and reference numeral Lv denotes a photosensitive member 48 (FIG. 2A).
2 shows a threshold value at which the photoconductivity of the liquid crystal occurs. Note that the horizontal direction in FIG. 3A is the sub-scanning direction.

FIG. 3A shows two light spots SP1 and SP1.
SP2 in the sub-scanning direction: P _S is appropriate.
At this time, a “latent image having a width of two scanning lines: L ₀ ” is formed on the photoconductor 48.

As shown in FIG. 3B, the light spot SP
1, the gap in the sub-scanning direction is a regular spacing SP2: smaller from P _S only [Delta] d, Interval: When becomes P _S -Δd, latent obtained by scanning simultaneously with a light spot SP1, SP2 of the time image width: L ₁ is normal width: less than L _0. In this case, scanning with the light spot SP2 is performed first, and then scanning with the light spot SP1 is performed.
Latent image width formed by the scanning: L ₂ is regular width: greater than L _0. That is, L ₁ <L ₀ <L ₂ .

Therefore, the "first" for detecting pitch unevenness, which is obtained by simultaneously turning on two light sources and simultaneously scanning by two light spots SP1 and SP2 every two scanning lines (a predetermined number of scanning lines), is obtained. Latent image pattern ", scanning by the second light spot SP2, and the subsequent first light spot S
A "second latent image pattern" for detecting pitch unevenness, which is obtained by repeating the scanning by P1 every two scanning lines, is formed.

That is, in the first latent image pattern, scanning by the light spots SP1 and SP2 is performed simultaneously, and the order of the scanning lines is 1, 2, 3,. . . Then, the scanning lines 1 and 2 are scanned, the scanning lines 3 and 4 are not scanned, the scanning lines 5 and 6 are scanned, and so on.
(C) A latent image pattern as shown in (c) (six scanning lines are drawn for simplicity of description, but a latent image pattern actually formed is suitably about 10 mm × 10 mm). In the figure, run 1 to run 6 indicate scanning line numbers 1 to 6.

FIG. 3C shows a first latent image pattern in an ideal case where there is no scanning line pitch unevenness, and the optically scanned portion (hatched portion) and the non-scanned portion are the regular two. The width of the scanning line: L ₀ is alternately arranged in the sub-scanning direction (vertical direction in the figure) in a stripe pattern.

FIG. 3D shows light spots SP1 and SP2.
Is the first latent image pattern formed when P _S is smaller than the proper interval, and the width of the hatched portion to be scanned is L ₁ (<L ₀ ). Thus, the width of the unscanned portion is L ₂ (> L ₀ ). At this time, the second latent image pattern (scanning is first performed with the light spot SP2, then scanning is performed with the light spot SP1, and after scanning is stopped, scanning with the light spot SP2 is performed. repeat the process said performing), as shown in FIG. 3 (e), the width of the scanned portion (portion hatched are in L _2, the width of the scanned portion not become L _1.

The photosensitive member is first uniformly charged, and the absolute value of the potential drops in the scanned portion. Therefore, the absolute value of the potential detected by the potential sensor 49A as the average potential of the latent image pattern is calculated as "the portion not scanned". 3 (d) and 3 (e), the detected potential of the “first latent image pattern” shown in FIG.
(Absolute value) than the detected potential of the second latent image pattern shown in FIG.

Hereinafter, it is assumed that the photosensitive member is positively charged and the detection potential is a positive potential for the sake of specificity of the description. The potentials detected from the first and second latent image patterns are denoted by V ₁ and V ₂ , respectively.
Then, in the above case, V ₁ > V ₂ . Conversely, spacing of the light spots SP1, SP2: a V _2> V ₁ if P _S is greater than the appropriate value.

Accordingly, the detecting section 50 in FIG.
When the operation: V ₂ −V ₁ is performed, the scanning line pitch unevenness is “interval: P _S is reduced” due to the sign of the result.
It is possible to know whether this is due to the fact or “interval: P _S has increased”, and it is possible to know “the degree of scan line pitch unevenness” based on the magnitude of the calculation result.

The above is an explanation of the embodiment of the third aspect of the present invention.

When the first and second electrostatic latent images are developed under predetermined developing conditions, the “average reflection intensity in the area area” that can be detected by the optical sensor 49B is large as the area of the non-scanned portion is large. From the optical sensor 49B
The detection results of Studies on the first and second toner patterns, if respectively P ₁ and P _2, calculated by the detection unit 50: Doing P ₂ -P _1, the sign of the result, the scanning line pitch It is possible to know whether the unevenness is due to “interval: P _S has decreased” or “interval: P _S has increased”, and to know the degree of scanning line pitch unevenness according to the magnitude of the calculation result. be able to. The above is the description of the embodiment of the invention described in claim 4. In the first to fourth aspects of the present invention, the latent image pattern or the generation pattern of the first and second latent image patterns is stored in the control unit of the scanning device.

The detecting section 50 constitutes "pitch unevenness detecting means" in the scanning line pitch unevenness detecting apparatus according to the tenth and eleventh aspects of the present invention.

The detected scanning line pitch unevenness may be displayed on a suitable display means, or may be used as “scanning line pitch unevenness correction data” as described below.

In the above-described embodiment,
The first and second latent image patterns are formed so as to be arranged in the sub-scanning direction (claim 6). Therefore, there is one sensor 49 (potential sensor 49A or optical sensor 49B),
The average potential of the latent image pattern or the average reflection intensity of the toner pattern is sequentially detected.

Further, the first and second latent image patterns are formed in the recording scanning area (claim 8). Therefore, it is possible to detect the presence of scanning line pitch unevenness in an area where image recording is actually performed. However, on the other hand, when scanning for image formation is performed, it is not possible to detect scanning line pitch unevenness. In such a case, the "scanning line pitch unevenness detection" is forcibly performed every predetermined number of times (for example, 100 times) of the image forming process, or every time the main switch of the image forming apparatus is turned on. May be performed prior to the execution.

An embodiment of the scanning line pitch unevenness correcting apparatus according to the twelfth aspect will be described below.

In FIG. 2A, the rotation mechanism 80 is composed of a stepping motor and a rotation transmission mechanism (gear, chain, wire, etc.) for transmitting the rotation of the stepping motor to the light source unit 10. It is designed to rotate around the optical axis. When the light source unit 10 is rotated in this manner, the light spot SP in FIG.
Since 1, the arrangement direction of SP2 is rotated on the surface to be scanned, the sub-scanning direction between the light spot SP1, SP2 By utilizing this: to adjust the P _S.

Therefore, the rotation mechanism 80 constitutes "pitch adjusting means for adjusting the scanning line pitch" in the twelfth aspect of the present invention. The rotation mechanism 80 is controlled by the pitch control unit 70. Therefore, the pitch control section 70 constitutes "pitch control means for controlling the rotation mechanism 80 as pitch adjustment means". As described above, the detection unit 50 can be constituted by a microcomputer. Therefore, the detection unit 30 and the pitch control unit 70, which are separately illustrated in FIG. 2A, can be collectively configured by a microcomputer.

The correction of the scanning line pitch unevenness is performed by correcting the “scanning line pitch unevenness” detected by the detection unit 30 by the method using the first and second latent image patterns as described above. Input to the control unit 70, the pitch control unit 70 controls the rotation mechanism 80, and the light source unit 10
Is rotated around the optical axis of the collimating lens 13.

The procedure for correcting the scanning line pitch unevenness will be described with reference to the flowchart of FIG. The first step of the scanning line pitch unevenness correction is “scanning line pitch unevenness detection”. The detection of the scanning line pitch unevenness is performed by the method according to the third or fourth aspect of the present invention. That is, the average potential of the first and second latent image patterns: the difference between V ₁ and V ₂ and its sign, or the average reflection intensity of the first and second toner patterns:
The P _1, the difference between P ₂ and its negative, and the degree of the scanning line pitch unevenness, the cause Interval: or P _S is due to greater than the proper value, known either by small.

According to whether the interval: P _S is larger or smaller than the appropriate value, the direction of rotation of the light source unit 10 by the rotating mechanism 80 (counterclockwise or counterclockwise) determines clockwise or), the difference between V _1, V _2, or the "degree of scanning line pitch unevenness" which is known by the difference of P _1, P _2, determined by the rotation angle (pitch control unit 70 of the light source unit 10 (In this determination, the “difference” and the rotation angle may be determined in advance as a table and may be determined by a table, or may be determined by calculating using an appropriate arithmetic expression.) The rotation mechanism 80 is controlled by the pitch control unit 70 so as to realize the determined rotation angle so that the interval P _{S in} the sub-scanning direction between the light spots SP1 and SP2 is realized.

If necessary, after the correction of the scanning line pitch unevenness, the scanning line pitch unevenness may be detected again, and if the correction result is not sufficient, the above correction process may be repeated.

Alternatively, the correction of the scanning line pitch unevenness may be performed according to the procedure shown in FIG. That is, for example, the potentials: V ₁ and V ₂ are detected, and the absolute value of the difference: | ΔV |
And A is a value corresponding to the permissible limit of scanning line pitch unevenness:
It is determined whether or not it is larger than S. When A <S, the scanning line pitch unevenness is within the allowable limit, and there is no need to perform “scanning line pitch unevenness correction”.

When A> S, the light source unit is rotated by a predetermined angle in a predetermined (+) direction, and | ΔV | = B is newly detected. When B <S, the correction is terminated. When B> S, it is determined whether or not B <A. When B <A, the process returns to step S1 by loop: α, rotates the light source unit by a predetermined angle in the (+) direction, and scans again. Detects line pitch unevenness. This process is repeated until B <S.

When B> A, the light source unit is rotated by a predetermined angle in the (-) direction to detect scanning line pitch unevenness.
It is determined whether ΔV | = C is “whether or not S <C”. If S <C, the process returns to step S2 in a loop β, and C
<S is determined, and if S <C, a loop: β
To return to step S2, rotate the light source unit by a predetermined angle in the (-) direction, and detect the scanning line pitch unevenness again. This process is repeated until C <S. Each time the process returns to steps S1 and S2 in the loop α and β, the rotation angle of the light source unit is appropriately set to a smaller value.

Thus, the embodiment shown in FIG. 2A is an embodiment of the "multi-beam scanning type image forming apparatus". In the embodiment described with reference to FIG. 2, when an “optical sensor” is used as the sensor 49, the reflection intensity of the toner pattern is detected on the photoreceptor 48, but as shown in FIG. Alternatively, the toner pattern may be transferred from the photoreceptor 48 to the intermediate transfer belt 51 as an “intermediate transfer medium”, and the reflection intensity of the toner pattern on the transfer belt 51 may be detected by the optical sensor 49B. ). In FIG. 6, reference numeral 52 denotes a transfer roller.

In the embodiment shown in FIG. 2A,
The first and second latent image patterns are formed so as to be arranged in the main scanning direction, and an average potential thereof or an average reflection intensity of a toner pattern obtained by developing them is detected by two sensors. In this case, the “scanning line pitch unevenness detection speed” can be increased.

Further, "plural pairs" of the first and second latent image patterns may be formed in the main scanning direction, and a plurality of sensors may be used for these. For example, each pair can be provided at three positions in the center and both ends in the scan recording area. In such a case, the scanning line pitch unevenness can be corrected so that the average of the scanning line pitches at the three locations becomes a predetermined scanning line pitch.

As described above, the inventions of claims 3 to 9 can be extended to the case where the number of light sources is three or more (when the light source of the light source unit is an LD array or the like). In such a case, an arbitrary “two adjacent to each other” for which scanning line pitch unevenness is to be detected.
With only the `` light source '' turned on and the other light sources turned off,
The scanning line pitch unevenness can be detected by the method described in the above embodiment.

[0090]

As described above, according to the present invention, a multi-beam scanning type image forming apparatus, a scanning line pitch unevenness detecting method, a scanning line pitch unevenness detecting apparatus, and a scanning line pitch unevenness correcting apparatus in this apparatus are provided. Can be provided.

According to the scanning line pitch unevenness detecting method and apparatus of the present invention, scanning line pitch unevenness in a multi-beam scanning type image forming apparatus can be easily and reliably detected.

According to the scanning line pitch unevenness correction apparatus, the scanning line pitch unevenness can be effectively corrected based on the scanning line pitch unevenness detected as described above.

According to the multi-beam scanning type image forming apparatus of the present invention, it is possible to properly set the scanning line pitch by accurately detecting the scanning line pitch unevenness, thereby realizing good multi-beam scanning.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the invention described in claims 1 and 2;

FIG. 2 is a diagram for explaining an embodiment of a multi-beam scanning type image forming apparatus according to the present invention.

FIG. 3 is a diagram for explaining an embodiment of the invention described in claims 3 and 4;

FIG. 4 is a flowchart illustrating an example of a procedure for correcting scanning line pitch unevenness.

FIG. 5 is a flowchart for explaining another example of the procedure for correcting the scanning line pitch unevenness.

FIG. 6 is a view for explaining an embodiment of the invention described in claim 5;

[Explanation of symbols]

 48 Photoconductor 49A Potential sensor 49B Optical sensor

Claims (14)

[Claims] 1. A multi-beam that converges light beams from a plurality of light sources onto a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction and scans the photoconductor simultaneously with the plurality of light spots. In a scanning type image forming apparatus, a method for detecting pitch unevenness of a scanning line simultaneously scanned by a plurality of light spots, wherein the simultaneous scanning by all the light spots is repeatedly performed to detect a latent image for detecting pitch unevenness. Forming a pattern, detecting an average potential of the latent image pattern by a potential sensor, and comparing the detection value of the potential sensor with a predetermined comparison value to detect pitch line unevenness of a scanning line. Scanning line pitch unevenness detection method. 2. A multi-beam for converging light beams from a plurality of light sources on a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction and scanning the photoconductor simultaneously with the plurality of light spots. In a scanning type image forming apparatus, a method for detecting pitch unevenness of a scanning line simultaneously scanned by a plurality of light spots, wherein the simultaneous scanning by all the light spots is repeatedly performed to detect a latent image for detecting pitch unevenness. A pattern is formed, and the reflection intensity of the area of the toner pattern obtained by developing the latent image pattern under predetermined development conditions is detected by an optical sensor, and the value detected by the optical sensor is compared with a predetermined comparison value. Scanning line pitch unevenness detecting method for detecting scanning line pitch unevenness. 3. A multi-beam for converging light beams from a plurality of light sources on a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction, and scanning the photoconductor simultaneously with the plurality of light spots. In a scanning type image forming apparatus, a method for detecting pitch unevenness of a scanning line simultaneously scanned by any two light sources adjacent to each other, comprising: A first latent image pattern for detecting pitch unevenness, which is obtained by repeating every other scanning line, a scan by the second light spot, and a subsequent scan by the first light spot are repeated every predetermined number of scanning lines. And forming a second latent image pattern for detecting pitch unevenness obtained by the above-described method. An average potential of each of the first and second latent image patterns is detected by a potential sensor. Scanning line pitch unevenness detecting method and detecting the pitch unevenness of scanning lines by comparing the two detected values is. 4. A multi-beam that converges light beams from a plurality of light sources onto a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction, and scans the photoconductor simultaneously with the plurality of light spots. In a scanning type image forming apparatus, a method for detecting pitch unevenness of a scanning line simultaneously scanned by any two light sources adjacent to each other, comprising: A first latent image pattern for detecting pitch unevenness, which is obtained by repeating every other scanning line, a scan by the second light spot, and a subsequent scan by the first light spot are repeated every predetermined number of scanning lines. And a second latent image pattern for detecting pitch unevenness, which is obtained by developing the first and second latent image patterns under predetermined developing conditions. A scanning line pitch detecting a reflection intensity of an area area of each of the toner patterns by an optical sensor, and detecting a scanning line pitch unevenness by comparing two detection values obtained from the first and second toner patterns; Unevenness detection method. 5. The scanning line pitch unevenness detecting method according to claim 4, wherein the first and second toner patterns are transferred onto an intermediate transfer medium and the reflection intensity is detected. Unevenness detection method. 6. The scanning line pitch unevenness detecting method according to claim 3, wherein the first and second latent image patterns are formed so as to be arranged in the sub-scanning direction. Pitch unevenness detection method. 7. A scanning line pitch unevenness detecting method according to claim 3, wherein the first and second latent image patterns are formed so as to be arranged in the main scanning direction. Pitch unevenness detection method. 8. The scanning line pitch unevenness detecting method according to claim 3, wherein the first and second latent image patterns are formed in a recording scanning area. Line pitch unevenness detection method. 9. A method according to claim 8, wherein a plurality of pairs of the first and second latent image patterns are formed in the main scanning direction. . 10. An apparatus for implementing the scanning line pitch unevenness detecting method according to claim 3, wherein an average potential of the first and second latent image patterns formed for detecting pitch unevenness is detected. A scanning line pitch unevenness detecting device, comprising: at least one potential sensor that performs scanning; and a pitch unevenness detecting unit that detects scanning line pitch unevenness based on an output of the one or more potential sensors. 11. An apparatus for implementing the scanning line pitch unevenness detecting method according to claim 4, wherein the reflection intensity of each area of the first and second toner patterns formed for detecting the pitch unevenness is detected. A scanning line pitch unevenness detecting device, comprising: at least one optical sensor; and pitch line unevenness detecting means for detecting a scanning line pitch unevenness based on an output of the one or more optical sensors. 12. A multi-beam scanning system in which light beams from a plurality of light sources are converged on a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction, and the photoconductors are simultaneously scanned by these light spots. A type image forming apparatus, comprising: a pitch adjusting unit for adjusting a scanning line pitch; and a pitch controlling unit for controlling the pitch adjusting unit. The method according to any one of claims 3 to 9, wherein: A scanning line pitch unevenness correction apparatus, wherein the pitch adjusting means is adjusted by the pitch control means in accordance with the detected scanning line pitch unevenness to perform pitch unevenness correction. 13. A multi-beam scanning system in which light beams from a plurality of light sources are converged on a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction, and the photoconductors are simultaneously scanned by these light spots. A multi-beam scanning type image forming apparatus, comprising: the scanning line pitch unevenness detecting apparatus according to claim 10. 14. A multi-beam scanning device for converging light beams from a plurality of light sources onto a photoconductive photoconductor as a plurality of light spots separated in a sub-scanning direction and scanning the photoconductor simultaneously with these light spots. A multi-beam scanning image forming apparatus, comprising: a scanning line pitch unevenness detecting device according to claim 10; and a scanning line pitch unevenness correcting device according to claim 12.