JP3492839B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] [0001] The present invention relates to an image forming apparatus.
I do. [0002] 2. Description of the Related Art Light reflective marks for position detection are used.
Endless belts (hereinafter simply referred to as belts)
That the mark was detected while rotating in one direction
Perform imaging process based on information from scientific sensor
As a result, the first rotation of the belt
Creates a color toner image at the position
Based on the mark detection information from the sensor, the toner
That the toner image is overlaid with another color toner at the same position as
Repeat the cycle to create a full-color
This superimposed toner image is collectively transferred to recording paper and
There is an image forming apparatus for creating a color image. That is, in this image forming apparatus, the belt is
While continuously rotating in one direction, the first rotation of this belt
A toner image of a color at a predetermined position on the belt is formed. Twice
At the turning point, a toner image of another color is superimposed on the same position.
By repeating such a cycle, the full-color toner
Image, and transfer this superimposed toner image onto recording paper at once.
To make one full-color image. [0004] In this image forming method, color shift is prevented.
It is assumed that the imaging position on the belt is constant
Becomes However, during one revolution of the belt,
The image formation position shifts due to stretching or mechanical errors.
You. Therefore, the toner images of the respective colors are formed on the belt by the same method.
As a means of stacking on the position, attach a mark to the belt
After a predetermined time from the detection of this mark by the sensor,
In other words, starting image formation with reference to the mark
On the belt, so that the image forming position for each
The method is adopted. [0006] As described above, the mark
When trying to determine the imaging position using reflected light,
The difference from the reflectance of the belt part other than the mark
Otherwise, a detection error will occur. In addition, the light source
When the detection output at the mark part decreases due to aging,
Again, the detection of the mark position is wrong. Accordingly, the present invention provides a method for detecting a mark of a certain level.
By acquiring intelligence, a high-quality
Image forming apparatus capable of outputting a color image
The porpose is to do. [0008] The present invention achieves the above object.
To achieve, RankHas a light reflective mark for location detection
While rotating the endless belt continuously in one direction,
Based on information from the optical sensor that,
An image forming apparatus for producing a color image,Optical center
The sensor has a light emitting element and a light receiving element, and outputs from the light emitting element.
Area where the reflected light enters the light receiving element after being specularly reflected by the mark
When the length of the belt in the belt moving direction is Dr,
The amount of light detected when white paper is placed at the
Open a slit about twice the width of the Dr
When the light amount detected at the
Use(Claim 1). [0009] [0010] [0011] Embodiment (1) Multicolor image forming apparatus to which the present invention is applied As an example of a multicolor image forming apparatus suitable for carrying out the present invention,
The color image forming apparatus will be described with reference to FIG. A color image reading apparatus (hereinafter referred to as a color scanner)
It is called a canner. ) 200 is a contact glass 202
The image of the original 180 on the upper side is illuminated by the illumination lamp 205
04A, 204B, 204C, etc., and the lens 206
Image on the color sensor 207 via the
-Image information is, for example, blue (hereinafter, referred to as B),
Green (hereinafter referred to as G) Red (hereinafter referred to as R)
U. ) Is read for each color separation light and converted to an electrical image signal.
Replace. The color sensor 207 is, in this example,
B, G, R color separation means and CCD (solid-state image sensor)
And three-color simultaneous reading
It performs B, G, R obtained by the color scanner 200
Not shown based on the color separation image signal strength level of
Color conversion processing is performed by the image processing unit
Below, it is called BK. ), Cyan (hereinafter referred to as C),
Zenta (hereinafter, referred to as M) yellow (hereinafter, referred to as Y)
2) to obtain color image data including the color information. Using the color image data, the following will be described.
Color image recording device (hereinafter referred to as color printer)
U. ) 400, the image data of BK, C, M, Y
The operation method of the color scanner 200 for obtaining
A scan that takes the action and timing of the
In response to the channel start signal, the lighting
Pump 205 and mirror group 204A, 204B, 204C
Illumination / mirror optical system scans the document in the direction of the left arrow
Then, image data of one color is obtained for each scan. And that
Each time, the image is sequentially visualized by the color printer 400.
These are superimposed to form a full-color image of four colors.
To achieve. Next, an outline of the color printer 400 will be described.
explain. Writing optical unit 40 as exposure means
1 is color image data from the color scanner 200
Is converted to an optical signal, and optical writing corresponding to the original image is performed.
Then, an electrostatic latent image is formed on the photosensitive drum 414 as a latent image carrier.
Form an image. The optical writing optical unit 401 is a laser
Light emitting means 441, a light emission drive control unit for driving the light emitting means 441 (FIG.
(Not shown), polygon mirror 443, rotation for driving it
Motor 444, fθ lens 442, reflection mirror 446
It is composed of The photosensitive drum 414 is moved in the opposite direction as indicated by the arrow.
It rotates clockwise, but around it
Leaning unit 421, static elimination lamp 414M, charging
Charger 419 as means, latent image potential on photosensitive drum
Sensor 414D for detecting the pressure, a revolver developing device
420 selected developing devices, developing density pattern detector 4
14P, an intermediate transfer belt 415, and the like. The revolver developing device 420 is a BK developing device.
420K, C developing unit 420C, M developing unit 420M, Y current
The imager 420Y and each developing device are rotated counterclockwise as indicated by arrows.
Revolver rotation drive (rotating in the direction of
Abbreviation). Each of these developing units develops an electrostatic latent image
In order to make the surface of the photosensitive drum 414
Developing sleeve 420KS, 420 which rotates in contact with
CS, 420MS, 420YS and developer
It consists of a developing paddle that rotates to stir
You. In the standby state, the revolver developing device
420 is set at a position where development is performed by the BK developing device 420.
When the copy operation starts, the color scanner
Reading of BK image data from a predetermined timing at -200
Starts taking, and based on this image data,
Optical writing / latent image formation by light starts (hereinafter, BK image
An electrostatic latent image based on image data is called a BK latent image. C, M, Y
The same applies to each image data. ). It is assumed that development is possible from the leading end of the BK latent image.
Of the latent image reaches the developing position of the BK developing unit 420K
Before the rotation of the developing sleeve 420KS,
The K latent image is developed with BK toner. Thereafter, the developing operation of the BK latent image area is performed.
Continue, but when the trailing edge of the latent image passes the BK latent image position
Then, immediately from the developing position by the BK developing device 420K
Revolver developing device to developing position by next color developing unit
The device 420 is driven to rotate. This pivoting movement
At least before the leading edge of the latent image by the next image data arrives
To complete. When the image forming cycle is started, the photosensitive member
The drum 414 rotates counterclockwise as indicated by the arrow.
The intermediate transfer belt 415 is driven by a drive motor (not shown).
Thus, it rotates clockwise. As the intermediate transfer belt 415 rotates, B
K toner image formation, C toner image formation, M toner image formation, Y
The toner images are sequentially formed, and finally, BK, C, M,
The toner image is superimposed on the intermediate transfer belt 415 in the order of Y
Is done. The formation of the BK image is performed as follows.
You. The charger 419 is operated in the dark by corona discharge.
Light body drum 414 is uniformly charged to about -700 V with negative charge
I do. Subsequently, the laser diode 441 is connected to the BK signal.
Raster exposure is performed based on the signal. In this way, the raster image
When exposed, photoreceptor drum initially charged uniformly
The exposed portion 414 is proportional to the amount of exposure light.
Charge disappears and an electrostatic latent image is formed. The toner in the revolver developing device 420 is
Negatively charged by stirring with ferrite carrier
BK developing sleeve 420KS of the present developing device.
Is not shown with respect to the metal base layer of the photosensitive drum 414.
The negative DC potential and AC are superimposed by
Bias. As a result, the charge on the photosensitive drum 414 remains.
Areas where no toner adheres and where there is no charge.
Minute, that is, the BK toner is absorbed in the exposed portion.
As a result, a BK visible image similar to the latent image is formed. The intermediate transfer belt 415 is connected to the drive roller 41
5D, transfer facing roller 415T, cleaning facing low
415C and a group of driven rollers.
The drive is controlled by a drive motor that does not. The B formed on the photosensitive drum 414
The K toner image is driven at a constant speed while in contact with the photoconductor.
A belt transfer corona discharger is provided on the surface of the intermediate transfer belt 415.
(Hereinafter referred to as a belt transfer section).
It is. Hereinafter, the photosensitive drum 414 to the intermediate transfer belt 4
Transfer of the toner image to the transfer belt 15 is referred to as belt transfer. Some untransferred residue on the photosensitive drum 414
The toner is supplied to the photosensitive drum 414 in preparation for reuse.
The body is cleaned by the body cleaning unit 421. Here times
The collected toner is discharged via a collection pipe (not shown).
Stored in the toner tank. The intermediate transfer belt 415 has a photosensitive member
BK, C, M, Y toners sequentially formed on the drum 414
-The images are sequentially aligned on the same plane,
A transfer image is formed on the transfer paper.
Perform batch transfer with a copying machine. On the photosensitive drum 414 side, B
After the K image forming step, proceed to the C image forming step
From a predetermined timing to the color scanner 200
Reading of the C image data by the
The formation of the C latent image is performed by the laser light writing using The C developing device 420C moves the developing position relative to the developing position.
After the rear end of the previous BK latent image has passed, and the C latent image
Before the tip reaches, rotate the revolver
Then, the C latent image is developed with the C toner. Thereafter, development of the C latent image area is continued.
When the trailing edge of the image passes, the same as in the case of the BK developing unit
Drive the revolver developing device 420 in the
20C is sent out, and the next M developing device 420M is moved to the developing position.
Position. This operation is also the next M latent image tip
Before reaching the developing section. Each image of M and Y
The reading process of each image data
The operations of forming the latent image and developing the BK image and C image
The description is omitted because it conforms to the above. The belt cleaning device 415U has an entrance
Seals, rubber blades, discharge coils and their inlets
It is composed of a seal and a rubber blade contact / separation mechanism. 1
2nd, 3rd, 4th color after belt transfer of BK image of color
While the image is being transferred to the belt, the blade
Therefore, the entrance seal and the rubber
And other parts are kept apart. A paper transfer corona discharger (hereinafter referred to as a paper transfer device)
U. ) 417 is an overlap toner on the intermediate transfer belt 415
In order to transfer the image to the transfer paper, AC
+ DC or DC component to transfer paper and intermediate transfer belt
Is applied. In the transfer paper cassette 482 in the paper supply bank,
Contains transfer papers of various sizes, and
Remove the paper cassette from the paper cassette
Feed paper in the direction of registration roller pair 418R by b 483
・ Transported. Reference numeral 412B2 denotes OHP paper or the like.
2 illustrates a paper feed tray for manually feeding thick paper or the like. At the time when image formation is started, the transfer paper
The paper is fed from one of the paper feed trays and
It is waiting at the nip portion of the 418R. And paper transfer
The tip of the toner image on the intermediate transfer belt 415 is
Just as the leading edge of the transfer paper is just
The registration roller pair 418R is driven so as to coincide with each other,
Registration of the paper and the image is performed. In this way, the transfer paper is transferred to the intermediate transfer belt.
Paper transfer superimposed on the upper color image and connected to positive potential
Over the vessel 417. At this time, the corona discharge current
The transfer paper is charged with a positive charge, and most of the toner image is
Transcribed above. Then, on the left side of the paper transfer unit 417,
Separated static eliminator by AC + DC corona (not shown)
When the transfer paper passes, the transfer paper is discharged, and the intermediate transfer belt 4
15 and is transferred to the paper transport belt 422. Now, from the surface of the intermediate transfer belt, a four-color toner
The transfer paper on which the images are collectively transferred is transferred by a paper transport belt 422.
The sheet is conveyed to the fixing device 423 and is controlled to a predetermined temperature.
Nip between the fixing roller 423A and the pressure roller 423B
The toner image is fused and fixed by the
The paper is sent out to the outside and
Tack and get a full color copy. The photosensitive drum 414 after the belt transfer
Is a photosensitive drum composed of brush rollers, rubber blades, etc.
The surface is cleaned by the leaning unit 421,
Further, the charge is uniformly removed by the charge removing lamp 414M. Further, after the toner image is transferred to the transfer paper,
The intermediary transfer belt 415 is again moved to the cleaning unit 4.
The surface is pressed by pressing the blade with a 15U blade contact / separation mechanism.
Clean. In the case of a repeat copy, a color scan
Operation of the toner and image formation on the photoconductor
Following the eye image process, the second sheet
Proceed to the first color image process. The intermediate transfer belt 415 has one sheet.
Continued with the batch transfer process of the four-color superimposed image on the transfer paper
And the surface is cleaned with a belt cleaning device.
The second BK toner image is transferred to the belt
To do. Thereafter, the operation is the same as that of the first sheet. The above is a copy for obtaining a four-color full-color copy.
Mode was explained, but three-color copy mode and two-color
In the peak mode, the specified color and number of
Thus, the same operation as described above is performed. In the case of the single color copy mode, a predetermined
Until the number of sheets is completed, the revolver developing device 420
Only the developing device of the predetermined color is positioned at the developing position of the predetermined color and
In the image operating state, the belt cleaning device 415U
Continuous copy operation with the blade pressed against the belt
Do the work. In such an image forming apparatus, the position detecting
Mark on the outer or inner circumferential surface of the belt 415.
I can. However, for the outer peripheral surface side, belt cleaning
It is necessary to devise to avoid the pass area of the device 415U,
The above difficulties may be involved.
Provided on the surface side. The optical sensor is shown in FIG.
Although not shown, the driving roller 415 supporting the belt 415
It is provided at a position between D and the support roller 415F. (2)Reference Example 1 As shown in FIG. 3, the optical sensor 1 emits light composed of LEDs.
An electric circuit having an element 1a and a light receiving element 1b, as shown in FIG.
Driven by The light emitted from the light emitting element 1a
The amount of reflected light changes when catching the mark 2
This is detected by the light receiving element 1b, and the change in the electrical output
Thus, the presence of the mark 2 can be detected. The spectrum of light emitted from the light emitting element 1a
FIG. Also, the spectral sensitivity of the light receiving element 1b is
The degree characteristics are illustrated in FIG. 6 in the case of the solid line and the case of the broken line.
As shown in FIG. 7, the mark 2 is a rectangle of 5 mm × 5 mm.
The metal foil forming the belt is directly in the traveling direction indicated by the arrow of the belt 415.
It is provided in a form attached to the end part in the crossing direction.
You. The optical sensor 1 is driven as shown in FIG.
It is provided above the roller 415D. In FIG. 8B,
The area of the circle denoted by reference numeral 4 is an optical fixed at a predetermined position.
This is the sensitivity region of the irregularly reflected light of the sensor 1, and the symbol Od is
The center of the detection area of the irregularly reflected light is shown. Also, indicated by reference numeral 5
The area of the circle is the sensitivity area of the specular reflection light of the same optical sensor 1.
And the symbol Or indicates the center of the regular reflection light detection area.
You. In FIG. 8A, reference numeral 4a corresponds to circle 4.
The corresponding sensitivity distribution of irregularly reflected light, symbol 5a corresponds to circle 5
The sensitivity distribution of specularly reflected light is shown. The vertical axis of FIG.
Is positive, diffuse reflectance, the horizontal axis is at the edge 2M of mark 2
And the optical in the mark on the left and the belt on the right
The reflectance of the light emitted from the light emitting element 1a of the sensor 1 is specularly reflected.
FIG. 4 is a distribution diagram of a reflectance and a reflectance representing a diffuse reflectance. FIG. 8D shows the light reception of the optical sensor 1 on the vertical axis.
The output voltage (Vf) of the element 1b is shown on the horizontal axis in FIG.
When the edge 2M of the marked mark moves from left to right
5 shows the change of the output voltage (Vf). here
The optical sensor 1 is located on the horizontal axis in FIG.
It shall be fixed at the positions shown in (a) and (b).
You. In FIG. 8 (d), it was represented as a swell of a small waveform.
This is because the noise component is superimposed. In FIG. 8D, A1 is the first inflection
Point, B1 is the second inflection point, C1 is the third inflection point, D1 is
The fourth inflection point is shown. Mark edge 2M is A
When it is located to the left of 1, the regular and irregular reflection of the belt part
Light detection output appears. In the position from A1 to B1
Sometimes, in addition to the regular and irregularly reflected light from the belt,
The detection output of reflected light appears. In the position from B1 to C1
In some cases, a detection output of the regular reflection light of the mark portion appears.
When in the position from C1 to D1, the mark part is positive,
In addition to the irregularly reflected light, the detection output of the irregularly reflected light from the belt appears.
You. On the right side of D1, detection of irregularly reflected light from the mark is detected.
Power is appearing. In FIG. 8D, the optical sensor 1
The confirmation level for marking 2 is shown in FIG.
Set by the value of Vf (ON) which is the on level of the
It is. This ON point is indicated by the symbol ON. Also, once on
From the state where it turns off due to the effect of noise components
Slightly lower than the level of Vf (ON) to prevent
Vf (OF) which is the off level of the comparator 6
F) is set. Here, when Vf (ON)
The mark is detected at a certain time, and after a certain time from this point
An image is started. In FIG. 8, the value of Vf (ON) is set.
Be careful not to be affected by noise from other reflective parts
Need to be The value of Vf (ON) is B1 and C1
The specular reflection of the mark is detected during this time.
Noise due to the reflected light from the belt near B1
Must not be erroneously detected. To do that,
The regular reflectance of the mark is larger than the irregular reflectance of the mark.
Is required, and the regular reflectance of the mark
At least three times the regular reflectance is required. Further, the light emitting element 1a composed of an LED is
Since the light emission ability deteriorates due to deterioration over time, the level near C1 is reduced.
And the number of erroneous detections may be reduced.
Therefore, it is necessary to set the level of C1 high from the beginning.
Considering this point, 10,000 copies, that is,
Rotate the default 415 for 40,000 times and flash the light emitting element 40,000 times
Nevertheless, the mark of the mark should be
The regular reflectance should be at least 10 times the regular reflectance of the belt.
desirable. For example, detection in the wavelength range shown in FIGS.
When using an optical sensor that can
The relationship between the regular reflectance and the irregular reflectance of mark 2 in the appropriate wavelength range
As shown in FIG. 1, the regular reflectance of a mark is
Use a material having a reflectance larger than the irregular reflectance. And in Figure 1
The specular reflectivity of the mark shown in FIG.
Those having a relationship of 10 times or more of the reflectance are used. As described above, in this example, the optical sensor is actually
Because you are qualitatively looking at only specularly reflected light,
It is not affected by light, and the detection position is
Is determined only by the positional relationship, the optical variation of the optical sensor,
For example, for the variation in directivity for each optical sensor,
Dependencies are reduced, and false detections
This can prevent the image quality from being lowered. (3)Reference Example 2 When forming a full-color image, each color image on the belt
0.15mm
If it does not fit within the margin of error, the full color
The final image will be quite blurry. The detection of the mark is performed as shown in FIG.
If the mark is located on the support roller with the belt
The support roller is stable when
Is affected only by the degree of variation in the cylindricity of
Accuracy can be suppressed to the order of 0.01 mm. However, the sensor for detecting the mark
Figure 1 shows the location in terms of effective use of space and space efficiency.
0, the drive low
Of the belt 415 between the roller 415D and the support roller 415F.
The distance from the optical sensor 1 changes due to vibration and the detection error
It becomes a factor. Belt 415 vibrates to optical sensor 1
When approaching, mark 2 is detected earlier than the original detection point
However, if you move away due to vibration, the
Detected a leak. Or you can detect the mark
There is a case where no image is formed. In this example, as shown in FIG.
Is set inside the belt 415 and the optical sensor 1 is driven.
From an intermediate position between the roller 415D and the support roller 415F
Also located at the position on the upstream side in the rotation direction of the belt indicated by the arrow
are doing. As shown on an enlarged scale in FIG.
The vibration transmitted from the driving unit of the forming device
5 vibrates between the drive roller 415D and the support roller 415F
I do. This vibration component includes fundamental vibration and higher-order vibration.
However, since the higher-order vibrations are small in amplitude,
The reading error of the sensor may be ignored. Cannot be ignored
One is a fundamental vibration having a large amplitude. When considering such a fundamental vibration, for example,
For example, the optical sensor 1 is
If it is located upstream from the intermediate position of the
415 vibrates to mark 2 with respect to the optical sensor 1.
The optical sensor has the belt surface that has deviated above the normal position
At the opposing position of (1), when the mark rises to the right, the mark
2 moves away from the optical sensor 1 and sways downward to make the belt surface
When tilting to the lower right, it approaches the optical sensor 1 at the same time. This
Phenomenon offsets the error of mark detection by the optical sensor 1.
Result. This point will be described in detail with reference to FIG.
And a belt 41 with respect to the light receiving element 1b of the optical sensor 1.
When 5 moves upward and moves away from the optical sensor 1, the detected light amount
, The position of mark 2 is
There is a tendency for detection at a later point in time (downstream). light
In the sensor 1, the reflectance of the mark 2 is
Greater than the reflectance of the filter. Therefore, together with the belt 415
When the mark 2 passes through a position far from the optical sensor 1
When the optical sensor 1 exceeds the threshold for detecting the mark
Will come later. On the other hand, the mark 2 only looks at the regular reflectance.
The size of the optical pupil of the optical sensor 1
If is small enough, simply mark 2
The position at which the mark is detected is determined only by the angle or the angle.
Therefore, the surface of the mark 2 is inclined with respect to the light receiving axis of the optical sensor.
Mark 2 is light when there is no
Detects the presence of a mark when it comes directly above the sensor 1
You. However, as in the previous example, the optical sensor 1
The belt 415 is swung upward with respect to the optical unit and the optical sensor 1
At the same time as moving away from
When it is tilted upward by δθ,
-Δθ, equivalent to δx in distance
The presence of the mark 2 is detected earlier. As described above, when the belt 415 swings up,
Element of the tilt with respect to the optical sensor 1
And the element of moving away from the optical sensor 1 are included.
Position detection errors caused by
You. This is because if the belt 415 swings down,
I can say that. As shown in FIG. 13, the left vertical axis represents the angle.
The vertical axis on the right is the position error by distance.
Take the detection error. Considering only the error due to vibration, the curve
7, the error due to the angle corresponds to the support roller 415F
At the position of “0”, and the drive with the support roller 415F
At an intermediate position which is half the distance L between the roller 415D and the roller 415D.
0 at the position of L / 2. Also, according to curve 8, the distance
Is largest at the position of L / 2, and
It becomes minimum 0 at the position of 0 corresponding to 15F. As can be seen from FIG. 13, curves 7 and 8
At the intersection of, the angle error and the distance error
Are offset, and the position is higher than the position of L / 2.
Is also on the upstream side. Thus, the arrangement of this example
Error due to geometrical optics, so detection by vibration
Errors can be eliminated. (4) Claim1Example corresponding to As shown in FIG. 14, the optical sensor 1 is
D and the support roller 415F are located downstream of the intermediate position.
In the case of the beam, as shown in the example shown in FIG.
It is not possible to offset the error due to the vibration of. in this case
In order to minimize the detection error caused by vibration,
The constraint emitted from the element 1a is sufficient on the detection surface (belt surface).
It is necessary to be narrowed down to the minute and the tilt of the optical axis
That the luminous flux must be small enough.
is there. As a condition for satisfying this requirement, first,
The light emitted from the light emitting element 1a is specularly reflected by the mark 2
In the movement direction of the belt 415 in the area entering the light receiving element 1b
When the length is Dr, there is no slit at this belt position.
Place a blank sheet of paper and measure the amount of light detected at that time. next,
A slit 9S about twice as wide as Dr was opened in the blank paper.
Optical axis OO of optical sensor 1 and slit 9S at belt position
And the dark box 1 after this slit 9S
At 0 (see FIG. 15B), the detected light amount is measured.
Then, the detected light amount of the latter is 2 with respect to the detected light amount of the former.
In this example, the conditions are set so as to be 0% or less. A specific description will be given. FIG. 15 (a)
Reference numeral 9 indicates blank paper. In the direction of belt movement indicated by the arrow
Has a slit 9S having a width of 2Dr.
You. As shown in FIG.
Has an opening 10a wider than the opening width 2Dr of the opening 9S.
Place the dark box 10. At this time, the center of the opening 10a is
Adjust the position so that it matches the optical axis OO of the optical sensor 1.
You. FIG. 15B shows a state after such position adjustment.
are doing. In the state shown in FIG.
Optics corresponding to the moving distance while moving in the direction indicated by the arrow
The output voltage (detected light amount) of the sensor 1 is measured. This measurement
FIG. 16 shows the data in a graph. In FIG.
It is assumed that the center of the slit 9S coincides with the optical axis OO.
The output voltage of the optical sensor 1 becomes Vmin
When the camera 9S is sufficiently away from the optical axis OO, the optical sensor
1 is Vmax. Here, Vmin is 20% or less of Vmax.
It is assumed that When such a relationship is satisfied,
The specularly reflected light at step 2 sufficiently returns to the light receiving element 1a.
Therefore, the output of the optical sensor at the mark 2 is large. this
On the other hand, light reflected from a belt surface
The light is diffused by reflection and returns sufficiently to the light receiving element 1a.
Therefore, the output of the optical sensor is reduced. According to the configuration of this example, the light is sufficiently focused.
The reflected light from the mark
Thus, detection can be performed with high accuracy. Confirm this
Therefore, as shown in FIG. 17, Vmin / Vm is plotted on the vertical axis.
The ax was taken, and the detection error was taken on the horizontal axis, and an experiment was performed. You
Then, a tendency indicated by a broken line is observed, and Vmin / Vmax is
If it is 20% or less, it is the allowable value of the displacement of the superimposed image.
It has been found that 0.15 mm can be sufficiently achieved. Ma
Also, if the optical axis of the optical sensor is
In some cases, the detection error due to the vibration of the target may increase. Follow
Therefore, it is necessary to exclude the sensor whose optical axis is greatly inclined by the inspection.
is there. This is a standard (optical axis is not tilted) sensor
Determine the slit position where the output is minimum (Vmin)
And replace the sensor to be inspected with the standard sensor
The output value obtained (with the slit position as it is)
Vmin of sensor and put blank paper instead of slit
When the output value of the sensor to be inspected at the time is Vmax, Vm
When the condition that in / Vmax is 20% or less is not satisfied
Then, the sensor may be excluded as a defective product. Toes
The condition that Vmin / Vmax is not more than 20%
Sufficient condition to be satisfied for non-defective products, even for axis tilt
ing. As described above, in this example, the position of the optical sensor is
Condition to make the position upstream from the intermediate position of the support
Even if not necessarily satisfied, the characteristics of the optical sensor
/ Vmax is selected to be 20% or less.
The deviation can be made equal to or less than a predetermined value. Also according to this example
If the optical sensor is placed in the middle of the support
In terms of quality, it is possible to keep the detection error
You. [0077] According to the present invention, a certain level of mark detection accuracy can be obtained.
Output high-quality full-color images without color shift
And an image forming apparatus capable of performing the same.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a illustrated FIG reflection characteristics of the mark. 2 is a illustrated FIG reflection characteristics of the belts. FIG. 3 is a front view of an optical sensor suitable for carrying out the present invention. FIG. 4 is a drive electric circuit diagram of an optical sensor suitable for carrying out the present invention. FIG. 5 is a diagram exemplifying a spectrum distribution of output light of a light emitting element constituting the optical sensor. FIG. 6 is a diagram illustrating a spectral sensitivity characteristic of a light receiving element constituting the optical sensor. FIG. 7 is a diagram illustrating the arrangement of marks on a belt. FIG. 8 is a diagram illustrating a detection output of an optical sensor. FIG. 9 is a diagram illustrating an example of the arrangement of optical sensors. FIG. 10 is a diagram illustrating an example of the arrangement of optical sensors. FIG. 11 is a diagram schematically illustrating how a belt vibrates. FIG. 12 is a diagram illustrating the influence of belt vibration on an optical sensor. FIG. 13 is a diagram illustrating a relationship in which an error due to an angle due to vibration of a belt and an error due to a distance are offset. FIG. 14 is a diagram illustrating an example of the arrangement of optical sensors. FIG. 15 is a front view of a blank sheet having a slit formed therein and a view for explaining the arrangement thereof. FIG. 16 is an output diagram of an optical sensor. FIG. 17 is a diagram illustrating a detection error of the optical sensor. FIG. 18 is a diagram illustrating a configuration of an image forming apparatus suitable for carrying out the present invention. [Description of Signs] 1 Optical sensor 2 Mark

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-130775 (JP, A) JP-A-7-36249 (JP, A) JP-A-4-321066 (JP, A) JP-A-60-1985 102678 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/01-15/01 117 G03G 15/16

Claims (1)

(57) [Claim 1] An optical sensor that detects the mark while continuously rotating an endless belt having a light reflective mark for position detection in one direction. based on the information, the image forming apparatus to make full <br/> Rukara image, said optical sensor includes a light emitting element and a light receiving element, the light emitting
The light emitted from the element is specularly reflected by the mark and the light receiving element
And the length of the area in the belt moving direction is Dr.
The amount of light detected when a blank sheet is placed at the belt position.
Then, make a slit about twice the width of the Dr on the blank paper.
20% or less of detected light amount when placed at the belt position
An image forming apparatus characterized by using: