JP2000046735A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further miniaturize a sensor by which an image can be monitored with high accuracy in a noncontact on-line manner and to monitor the image with high accuracy without being affected by a change in an image recording medium. SOLUTION: Density patches 39 of a sample image 38 on a sheet of paper 37 are formed as a yellow patch, a magenta patch and a cyan patch. LED's 41 as sensor light sources are installed so as to emit blue color light, green color light and red color light. Beams of light in the respective beams of light are shone at patches in colors as their complementary colors. Beam shaping means 49 which shape the beams of light from the LED's 41 are installed at the front of the respective LED's 41. Beams of reflected light from the respective density patches 39 are received, via respective lenses 43, by respective light receiving elements 44 which are installed on focal faces on the opposite side of the side of the sheet of paper 37 of the lenses 43. The electrostatic charge amount, the exposure amount or the like of a photoreceptor is corrected by the measured result of a fixed-image density sensor 40, and the image quality of an output image is controlled.

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 using an electrophotographic method and the like, and more particularly, to a high image quality irrespective of individual differences of the apparatus, in which fluctuations in image quality due to environmental changes and aging of members are suppressed. And an image forming apparatus for controlling the image quality so as to obtain a stable image quality.

[0002]

2. Description of the Related Art With the advancement of network technology centered on computers, network printers for connecting a printer as an image output device to a network are rapidly spreading. In particular, with the colorization of the output image,
2. Description of the Related Art In recent years, development of color printers has been actively pursued, and demands for improving the maintenance stability of color image quality, uniforming color image quality among a plurality of color printers, and the like have been increasing. In particular, with regard to color reproducibility, high stability is required regardless of the installation environment, aging, and machine differences.

In general, it is known that the sensitivity of a human to color differences is extremely high. Even if the images are not temporally and distance-neighboring, the color difference of the image to be compared is L * a *
In the b * color system, if ΔE = about 5, it is possible to identify the color regardless of the observer and the situation, and to make it impossible to recognize the color difference, ΔE = about 3. References include DHAlman, RSBerns, GDSnyder and WALarsen,
Performance Testingof Color-Difference Metrics Usi
ng a Color Tolerance Dataset, COLOR research and ap
replication, vol.14, Number3, June 1989.

[0004] From such a fact, if an attempt is made to set the target level of image reproducibility below the human color difference recognition limit,
The required value for the image forming apparatus is very high, such as a color difference ΔE = 3 or less. However, as is well known,
In a conventional electrophotographic image forming apparatus, each process is unstable, and it is impossible to satisfy such a high required value. This is because electrophotography uses electrostatic phenomena in the first place, and due to environmental conditions such as temperature and humidity, and the deterioration of photoconductors and developers over time, etc. Is changed, and the image reproducibility fluctuates.

For this reason, in an electrophotographic image forming apparatus, feedback control for maintaining an optimum image density is generally used. More specifically, the most common method is to monitor the density reproduction status using a density patch, obtain an error from the target density, and multiply the error by a feedback gain to calculate a set value correction amount of the control actuator. . For example, Japanese Patent Application Laid-Open No. 1-169467 discloses that a desired image density is obtained by measuring a density patch and controlling an exposure condition and a developing bias condition.

As the density patch, an unfixed toner image immediately after the development step or a fixed image formed on an image recording medium such as paper is used. The reason why the density patch of the unfixed toner image is used may be that formation and erasing are easier than a transfer image or a fixed image formed on paper. However, although the density patch of the unfixed toner image has a high correlation with the fixed image, it is not possible to detect the influence of the fluctuation in the subsequent transfer step and fixing step.

The reason why the density patch of the fixed image is used is that the image is finally obtained by the user as an image form, and the image quality can be evaluated including the influence of fluctuations in the transfer step and the fixing step. Examples of monitoring the density of a fixed image are described in JP-A-62-296669, JP-A-63-185279, and JP-A-5-199407.
As shown in Japanese Patent Application Laid-Open Publication No. H10-163, many use an image reading unit incorporated in the apparatus.

However, in this method, in order to monitor the image density, the user has to perform the work of causing the image reading unit to read the output image once again. Hana is annoying. Further, in the case of an image forming apparatus such as a printer which does not have an image reading unit, the image density cannot be monitored in principle.

Accordingly, the applicant has disclosed in Japanese Patent Application Laid-Open No. Hei 9-17127.
No. 9 proposed a method for monitoring an image online after the fixing process. In this method, as an image monitor sensor, red, green, and blue L colors corresponding to toners of Sian, magenta, and yellow are used.
Using a special color monitor that irradiates light from ED (Light Emitting Diode) to patches of each color of Sian, Magenta and Yellow, and receives reflected light from each color patch by a light receiving element such as a photodiode for each color. It is.

Generally, the emission spectrum of an LED is RGB.
It is said that the band is narrower than the spectrum by a filter or the like, and it is difficult for an LED to spectrally separate the entire color gamut with high accuracy. However, the above-mentioned image monitor sensor is CMY
CM of density patch formed as a single patch for each color
The toner adhesion amount of each Y color alone, that is, the toner density is represented by R
Since the detection is performed by the light from the LEDs of each of the colors GB, it can be made much smaller and lower in cost than a conventional color sensor that distinguishes each color of a full-color image by dispersing the entire color gamut. Are also necessary and sufficient for an image monitor.

[0011]

However, when an output image is monitored on-line by the image forming apparatus, the vertical fluctuation of the image recording medium such as paper, that is, the fluctuation in the direction perpendicular to the traveling direction of the image recording medium is a problem. Becomes Pressing the paper with a roller or the like may cause toner peeling or misalignment, damaging the image, and requiring extra space. Is desirable. Therefore, the paper fluctuates up and down as the paper advances, and the output image cannot be accurately monitored.

When measuring a density patch on a paper surface that fluctuates up and down by a conventional sensor combining a light source, a lens, and a light receiving element, for example, if the paper surface fluctuates up and down by about 1 mm, the output of the light receiving element becomes about 15%. It is known that such a change in output makes it difficult to detect a slight difference in density between density patches on paper.

Therefore, the applicant has filed Japanese Patent Application No. 8-29721.
No. 8 (filed on October 18, 1996, reference number FN96-
00596) as the basis of the priority claim
No. 8373 (filed July 24, 1997, reference number FN9
7-00232) has proposed a measurement method capable of performing high-accuracy measurement that is not affected by fluctuations of a measurement object such as paper.

This method, which will be described in detail in an embodiment described later, irradiates light from a light source to an object to be measured, and receives reflected light from the object to be measured through a lens by a light receiving element.
In a method for measuring characteristics of a measurement target from a light receiving output of a light receiving element, particularly, reflected light from the measurement target passing through the lens is provided on a rear focal plane of the lens (a focal plane opposite to the measurement target). Is set as a specific area which is an arbitrary part of the above, and only light passing through this specific area is received by the light receiving element. This method is referred to as the prior application method.

If the method of the prior application is combined with the above-described image monitor sensor using LEDs, it is possible to realize a non-contact online high-precision image monitor.

However, in the method of the prior application, the permissible variation range of the measuring object in which the light receiving output of the light receiving element is constant irrespective of the fluctuation of the measuring object in the lens optical axis direction is almost proportional to the diameter of the lens. . Therefore, the method of the prior application and the above-mentioned LED
When an image on a sheet is monitored in combination with an image monitoring sensor that uses an image sensor, if the size of the sensor is reduced and the diameter of the lens included in the sensor is reduced, the allowable variation range of the sheet is reduced. This is an obstacle to reducing the size and cost of the entire image forming apparatus as well as the sensor.

Therefore, the present invention can realize a further miniaturization of a sensor capable of monitoring an image with high accuracy in a non-contact on-line manner, and can realize an image recording medium within a large allowable fluctuation range of an image recording medium such as paper. Thus, it is possible to realize a high-precision image monitor which is not affected by fluctuations of the image.

[0018]

According to the present invention, in an image forming apparatus for detecting an output color image and correcting image forming conditions in accordance with the detection result, an image for forming a color image with a plurality of color materials is provided. Forming means, image detecting means for detecting a sample image output by the image forming means by at least one of the plurality of color materials, and an image of the image forming means according to a detection result of the image detecting means. Control means for correcting forming conditions, wherein the image detecting means comprises: light irradiating means for irradiating the sample image with light from a light emitting diode; and reflected light from the sample image according to a density of the sample image. Light receiving means for receiving the light and outputting the detection result, wherein the light irradiating means includes a beam shaping means for shaping a light beam from the light emitting diode. Obtain, and things.

[0019] In this case, the beam shaping means may shape the light beam from the light emitting diode by an opening formed between the light emitting diode and the sample image according to the shape of the opening. .

Alternatively, the beam shaping means may be an optical lens arranged between the light emitting diode and the sample image, and may shape a light beam from the light emitting diode according to its optical characteristics. .

Alternatively, the beam shaping means may be a transmission filter disposed between the light emitting diode and the sample image, and may shape a light beam from the light emitting diode according to its optical characteristics. .

Further, the beam shaping means is a combination of a plurality of apertures, an optical lens and a transmission filter disposed between the light emitting diode and the sample image. The light beam from the light emitting diode may be shaped.

[0023]

In the image forming apparatus according to the present invention, the sectional shape of the light beam from the light emitting diode, which is the light source of the image detecting means serving as the image monitoring sensor, is formed in the opening in front of the light emitting diode. The spot area of the light beam applied to the sample image on the image recording medium is shaped into a desired shape by beam shaping means including an optical lens or a transmission filter.

Therefore, even if the image monitoring sensor is miniaturized and the diameter of the lens included therein is reduced, the light receiving output of the light receiving element becomes constant irrespective of the fluctuation of the image recording medium in the lens optical axis direction. The size of the sensor can be further reduced while maintaining the performance as a sensor capable of increasing the allowable fluctuation range of the medium and monitoring the image with high accuracy in a non-contact online manner. The size and cost of the entire device can be reduced.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Basic Configuration of Apparatus] FIG. 1 shows an image output section of an embodiment of the image forming apparatus of the present invention. The image forming apparatus according to this embodiment forms an image on a sheet by an electrophotographic method.

In an image input unit not shown in the figure, an image on the original is read by a scanner to obtain input image data, or input image data generated on an external computer is taken into the apparatus. Similarly, in an image processing unit not shown in the figure, necessary processing such as color conversion and gradation correction is performed on input image data from the image input unit, and output image data to be output by the image output unit 100. Is obtained.

A screen generator, not shown, converts the output image data from the image processing unit into a laser on / off signal whose pulse width is modulated in accordance with the pixel value. In the image output unit 100, the laser diode of the laser output unit 31 is driven by the laser on / off signal, and a laser beam modulated by the image signal is obtained from the laser output unit 31. 32.

The photoreceptor 32 is uniformly charged by a scorotron charger 33, and is irradiated with a laser beam to form an electrostatic latent image on the photoreceptor 32, and the electrostatic latent image is formed. When the developing roll of the developing device 34 comes into contact with the photoconductor 32, the electrostatic latent image is developed into a toner image.

Further, the toner image on the photoreceptor 32 is
The image is transferred onto the sheet 37 by the transfer unit 35, and the sheet 3
7 is fixed by the fixing device 36. After the toner image is transferred onto the paper 37, the photoconductor 32 is cleaned by the cleaner 38, and one image forming process is completed.

The image output unit 100 outputs a banner sheet on which a sample image is formed, as will be described later, when the image forming apparatus is turned on or when the apparatus is set up by a user operation. The image output unit 100 is provided with a fixed image density sensor 40 as an image monitor sensor for measuring a sample image formed on the paper 37 as the banner sheet at a position subsequent to the fixing device 36.

FIG. 2 shows the configuration of the image quality control section of the image forming apparatus of this embodiment. The image output unit 100 includes a light amount controller 101 for controlling the amount of laser light from the laser output unit 31, a grid power supply 102 for the scorotron charger 33, a dispense motor 103 for controlling toner supply to the developing unit 34, and the like. Having.

When the power of the apparatus is turned on or when the apparatus is set up, a sample image is formed on a sheet according to the reference pattern signal from the reference pattern generator 201 as described above. Is measured by

The image controller 50 compares the measured value of the fixed image density sensor 40 with a target value stored in the memory 202 in advance, and corrects the operation amount of the image output unit 100 based on the comparison result. I do. In this example, the grid voltage of the scorotron charger 33 and the laser output power of the laser output unit 31 are controlled, and the dispense motor 103 is driven to control the amount of toner replenishment to the developing device 34, so that the image quality of the output image is controlled. Control.

However, the manipulated variable for correction control is, for example,
The amount of charge of the photoconductor 32 by the scorotron charger 33, the amount of exposure of the photoconductor 32 by the laser output unit 31,
And at least one of the developing bias voltage, the number of rotations of the developing roll, and the toner supply coefficient.

[Sample Image and Fixed Image Density Sensor] As shown in FIG. 3, a fixed image density sensor 40 serving as an image monitoring sensor irradiates a density patch 39 of a sample image 38 formed on a paper 37 with light. An LED 41, a beam shaping unit 49 for shaping a light beam from the LED 41, a lens 43 for condensing reflected light from the density patch 39 of light shaped by the beam shaping unit 49 and applied to the density patch 39; And a light receiving element 44, such as a photodiode or a phototransistor, for receiving the reflected light transmitted through the lens 43.

The density patch 39 of the sample image 38 is formed by a single patch of each color toner. For example, when the image forming apparatus forms an image using yellow, magenta, sian, and black toners, as shown in FIG.
9M, Sian Patch 39C and Black Patch 39
It is formed by K.

As shown in FIG. 4, the LED 41 of the fixed image density sensor 40 shown in FIG. 3 has blue, complementary colors for the yellow patch 39Y, the magenta patch 39M, and the Sian patch 39C, respectively. LEDs 41B and 41G that emit green and red light,
41R is provided. Thereby, the detection accuracy of the density of each color can be improved. FIG. 5 shows the patches 39Y and 3
9M, 39C reflection spectrum and LED 41B, 41
An example of the relationship between the emission spectra of G and 41R is shown.

For the black patch 39K shown in FIG.
In principle, the LED may emit any color of blue, green, red, or white, but in this example, the LED 41RK that emits red light is provided, which has a high sensitivity of the light receiving element and is relatively inexpensive.

The reflected light from the patches 39Y, 39M, 39C, 39K is transmitted to separate light receiving elements 44Y, 44M, 44
Light is received by C and 44K. Although not shown in FIG. 4, as shown in FIG.
Beam shaping means 4 is provided in front of 1G, 41R, and 41RK.
9 and the respective light receiving elements 44Y, 44M, 44
A lens 43 is provided in front of C and 44K.

[Arrangement of Light-Receiving Elements] In the fixed image density sensor 40 shown in FIG. 3, the light emitted from the LED 41 to the density patch 39 is almost completely diffuse-reflected on the surface of the density patch 39, and the reflected light is converted into a lens. Light receiving element 44 via 43
Incident on.

In this case, as in the method of the earlier application described above,
The light receiving element 44 is connected to the rear focal plane of the lens 43 (the light receiving element 44).
Of the light reflected by the density patch 39, the lens 43
Only light that falls within a specific angle range with respect to the optical axis direction of
The light enters the light receiving element 44. Since the specific angle range does not depend on the distance between the lens 43 and the paper 37, the amount of light received by the light receiving element 44 is constant regardless of the vertical movement of the paper 37.

The principle will be described with reference to FIG. FIG.
This shows a state in which light reflected on the paper surface passes through the lens and enters a light receiving element provided on the rear focal plane 43b of the lens. FIG. 6 shows that the amount of light received by the light receiving element does not depend on the vertical fluctuation of the paper surface. However, in FIG. 6, for convenience, it is assumed that the lens has no aberration, and that the lens thickness is zero and the lens width is infinite.

In FIG. 6, point O is the center of the lens, axis 4
3a indicates the optical axis of the lens, and the surface 43c indicates the position of the lens.
The paper surfaces 201 and 202 indicate the fluctuating paper surface positions, and the image forming surfaces 301 and 302 indicate the image forming surface positions corresponding to the paper surface positions 201 and 202. Point Fa is the focal point of the lens on the paper surface side, point Fb is the focal point (rear focal point) of the lens on the light receiving element side, distance fa is the focal length of the lens as viewed on the paper surface side, and distance fb is the light receiving element side. Lens focal length, point C
Is the end of the light receiving area of the light receiving element, and the distance r is the distance between the end C of the light receiving area and the rear focal point Fb of the lens.

Here, the light is reflected at the reflection points A1 and A2 on the paper positions 201 and 202 different from each other in the direction of the optical axis 43a, passes through the lens, and forms the image formation point B on the image formation positions 301 and 302.
Considering the light that forms an image at 1 and B2, the reflection angles (angles with respect to the direction of the optical axis 43a) at the reflection points A1 and A2 when the light passes through the end C of the light receiving area of the light receiving element are s1 and s.
Let it be 2.

Further, the distances between the paper positions 201 and 202 and the lens are a1 and a2, the distances between the rear focal plane 43b and the imaging plane positions 301 and 302 are b1 and b2, and the reflection point A
Points at which light parallel to the optical axis 43a of the reflected light from the light beams A1 and A2 passes through the lens surface are L1 and L2. Then, the light is reflected at the reflection points A1 and A2, and the end C of the light receiving area of the light receiving element is obtained.
M1 and M2 are points at which light passing through the lens and forming an image at imaging points B1 and B2 passes through the lens surface. Further, the distance between the points L1 and M1 is d1, and the distance between the points L2 and M2 is d2.

From the Newton's equation in this imaging system, (a1-fa) / fa = fb / b1 (1) (a2-fa) / fa = fb / b2 (2) In addition, triangle B1L1M1 and triangle B1F
Similarity of bC, and triangle B2L2M2 and triangle B2F
From the similarity of bC, the following holds: r / b1 = d1 / (b1 + fb) (3) r / b2 = d2 / (b2 + fb) (4)

Further, in the triangle A1L1M1 and the triangle A2L2M2, using the angles s1 and s2, d1 = a1 · tan (s1) (5) d2 = a2 · tan (s2) (6)

Equations (5) and (6) are converted to equations (3)
Substituting into (4), a1 = (b1 + fb) r / (b1 · tan (s1)) (7) a2 = (b2 + fb) r / (b2 · tan (s2)) (8) By substituting the equations (7) and (8) into the equations (1) and (2), the following is obtained: r / tan (s1) = fa (9) r / tan (s2) = fa (10) .

Then, from the equations (9) and (10), s1 = s2 (11) is derived.

When this is generalized, the paper position 20
1, 202, etc., are reflected at respective reflection points Ai, such as reflection points A1, A2, on each paper surface position 20i (i is 1, 2, 3,...) Of the paper surface which fluctuates in the direction of the optical axis 43a. And imaging points B1 and B2 on the respective image plane positions 30i such as the image plane positions 301 and 302 through the lens.
Considering light that forms an image at each image forming point Bi, when this light passes through the end C of the light receiving region of the light receiving element,
Assuming that the reflection angle at the reflection point Ai is si, the reflection angle si is always constant regardless of other parameters.

That is, the reflection angle si is always constant even if the reflection area on the paper moves with the fluctuation of the paper and the reflection point Ai moves. Assuming that reflection occurs ideally, when the density at the reflection point Ai is the same, the number of rays included in the reflection angle si is considered to be constant. The amount of light incident between −C and the reflection point A is independent of the distance a between the paper surface and the lens.
An accurate light quantity corresponding to the density of i is obtained.

Therefore, the light reflected from the density patch and incident on the light receiving element does not depend on the distance between the paper surface and the light receiving element but depends on the density of the density patch.

The change in the light receiving output V of the light receiving element with respect to the distance a between the paper surface and the lens in the case of the above principle is as shown in FIG. 7, and even if the vertical fluctuation of the paper surface is 1 mm, The change in the light receiving output can be suppressed to 0.2% or less.

In FIG. 6, the lens width is assumed to be infinite. However, the lens width is actually finite. In particular, since the lens width is reduced to reduce the size of the sensor, the lens width must be considered. . Therefore, it is necessary to irradiate the light from the light source into the reflection area under the following conditions in relation to the lens width.

As shown in FIG. 8, the light reflected at each point in the reflection area 42 on the paper surface 37a and incident on the light receiving element 44 is transmitted from each point to the optical axis in accordance with the above equations (5) and (6). 43
The light is reflected in a range of an angle s on both sides in a direction parallel to a, that is, in an angle range of s × 2, and d × 2 on a lens.
Will spread to the width of.

As is apparent from FIG. 8, for the light reflected at the ends tl and tr of the reflection area 42 to pass through the lens width u and enter the light receiving element 44, t ≦ u−2 · d It is necessary to satisfy the condition of (12).

Here, d = a · tan (s) (13). From the above equations (9) and (10), tan (s) = r / fa (14). 12) is t ≦ u−2 · ar · fa / fa (15)

The lens width u, the width 2r of the light receiving element 44, and the focal length fa are fixed values.
If the width t of the reflection area 42 and the distance a between the lens and the paper 37a, which are related to the irradiation of light on the light a and the reflection of the light on the paper 37a, are within the range satisfying the condition of the expression (15). ,
There is no light that should enter the light receiving element 44 and does not pass through the lens.

Actually, since the distance d in the equation (12) is equal to or less than 1/10 of the lens width u, the width t of the reflection area 42 is
Basically, it is determined by the lens width u.

In FIG. 8, the reflection area 42 and the light receiving element 44 have the same length on both sides of the optical axis 43a, but may have different lengths on both sides of the optical axis 43a. In that case, the angle range of the light incident on the light receiving element 44 from each point in the reflection area 42 is different on both sides in the direction parallel to the optical axis 43a.

The position of the light receiving element 44 need not be the position including the optical axis 43a as long as it is within the rear focal plane 43b of the lens. In that case, in FIG. 8, the angle range of light incident on the light receiving element 44 from each point in the reflection area 42 is only on one side in a direction parallel to the optical axis 43a.

Further, since the actual optical system can be considered as a rotating body around the optical axis 43a, the optical axis 4
The distance from 3a to the end of the light receiving element 44 does not need to be constant, and the shape of the light receiving element 44 can be any shape such as a circle or a square. At this time, generally, t / 2 ≦ u / 2−ar · fa / fa (16) is satisfied.

[Beam shaping means] In the fixed image density sensor 40 shown in FIG. 3, in order to satisfy the condition of the equation (12), the sample image 38 must be within a range sufficiently smaller than the width u of the lens 43. Reflection point, LE as light source
What is necessary is just to set the spot area of the irradiation light from D41. However, the irradiation light from the LED 41 is incident on the sample image 38 with a certain spread, so that the spot area of the irradiation light actually has a certain size.

On the other hand, if the spot area is made smaller than necessary, the S / N as the sensor performance is reduced due to the decrease in the light amount. The spot area has a certain size due to the density unevenness and periodicity of the density patch 39 itself or the periodicity (resolution) of the image structure such as lines and halftone dots forming the gradation of the density patch 39. Is required.

Therefore, the spot area of the irradiation light is
It is required to be within a predetermined range that is small enough to satisfy the condition of equation (12), but not too small.

In general, in a reflection-type densitometer or colorimeter, in order to eliminate the influence of specular reflection light, irradiation light is incident at an angle of 0 ° with respect to a direction perpendicular to the sample surface, and at a 45 ° direction. A 0 ° -45 ° optical system that receives diffuse reflected light, or a 45 ° -0 ° optical system that receives diffuse reflected light in a direction of 0 ° by irradiating light at a 45 ° angle Have been.

On the other hand, in the fixed image density sensor 40, 45 ° -0
° adopt a method. That is, as shown in FIG.
Light from 1 is incident on the sample image 38 at an angle of 45 °. Therefore, the irradiation light spot area on the sample image 38 has an elliptical shape whose longitudinal direction is the optical axis direction of the LED 41 when viewed from directly above the paper 37.

However, since the spot area has an elliptical shape as described above, the spot area has a smaller diameter in the longitudinal direction.
It is necessary to satisfy the condition of the expression (12), and the obtained light amount is reduced as compared with the case where the spot area is circular. Further, by making the light from the LED 41 incident on the sample image 38 at an angle of 45 °, as shown in FIG. 9, the spot area itself moves by the same distance in a direction parallel to the paper as the paper fluctuates up and down. Therefore, the required range of the spot area is further narrowed.

For the LED, a type generally referred to as a shell type, in which a resin lens is integrally molded, is often used from the viewpoint of cost and availability.
However, it is often difficult to use the bullet-shaped LED as it is as the LED 41 as the light source of the fixed image density sensor 40 to keep the spot area within the required range.

In view of the above, according to the present invention, as shown in FIG.
A beam shaping unit 49 for shaping the light beam from the LED 41 is provided in front of the ED 41.

(When the beam shaping means is an aperture) The simplest beam shaping means is an aperture having a small thickness, that is, an optical stop. This aperture stop can prevent the irradiation light from spreading to unnecessary regions. However, since the light from the LED 41 is not a parallel light but a spread light beam, if there is a distance between the aperture stop and the sample image 38, the spread of the light beam after passing through the stop is suppressed. And it becomes difficult to limit the spot area.

Therefore, as a first example of the beam shaping means 49, as shown in FIG. 3, an opening having a certain thickness, that is, a cylindrical diaphragm is used. Accordingly, even if there is a distance between the beam shaping unit 49 and the sample image 38, the spread of the light beam after passing through the beam shaping unit 49 can be suppressed. FIG. 10 shows a spot area shape when a bullet-shaped LED is used as the LED 41 and a cylindrical aperture is provided as a beam shaping means 49 in front of the LED 41.

As described above, by providing the beam shaping means 49, the spot area shape can be defined to some extent. However, in the first example, since the opening is circular, as shown in FIG. The spot area of the irradiating light incident on the paper 37 at an angle of 45 ° is almost elliptical.

Therefore, as a second example of the beam shaping means 49, as shown in FIG. 11, the beam shaping means 49 is an oval opening. As a result, the spot area of the irradiation light becomes not a elliptical shape but a circular shape, and the light amount does not decrease so much, so that the required level can be almost satisfied.

(In the case where the beam shaping means is an optical lens) An optical lens can be used as the beam shaping means, and the same effect as when the aperture is used can be obtained. That is, the light beam from the LED 41 is condensed in a predetermined area by the lens, so that the irradiation light spot area on the paper surface can be within the required range. In addition, by using an aspherical lens or the like and converging light asymmetrically with respect to the lens optical axis, the beam spot shape can be made closer to a circle. Further, a beam shaping unit may be configured by combining an optical lens and an opening.

(When the beam shaping means is a transmission filter) A transmission filter can be used as the beam shaping means, and the same effect as when an aperture or an optical lens is used can be obtained. The transmission filter in this case is, for example, a filter having a function of diffusing a transmitted light beam and expanding the light beam at a certain angle. By using one of such filters capable of setting the diffusion angle asymmetrically with respect to the optical axis, the beam spot shape can be made closer to a circle.

Alternatively, in a filter having an in-plane density distribution, a desired spot area shape can be obtained by defining the area of the transmitted beam according to the density distribution shape. Further, the beam shaping means may be configured by combining the transmission filter and the opening, the transmission filter and the optical lens, or the transmission filter and the opening and the optical lens.

[Other Embodiments] The objects to be controlled by the detection output of the image monitor sensor are not limited to the above-described charge amount, exposure amount, developing bias voltage, developing roll rotation speed, toner supply coefficient, and drive of the transfer unit. Other operation amounts related to image formation, such as conditions, may be used. Further, the image quality may be controlled by correcting a conversion coefficient of a color conversion matrix when performing color conversion of an image signal or correcting a gradation characteristic of each color according to a detection result of the sensor.

In the above-described embodiment, the image quality is controlled by simply feeding back the difference between the measured value of the sensor and the target value. However, fuzzy control, neuro control, learning inference type control, etc. The image quality may be controlled.

The present invention can be applied not only to the electrophotographic system but also to an image forming apparatus such as an ink jet system or a thermosensitive film system.

[0081]

As described above, according to the present invention, the cross-sectional shape of the light beam from the light emitting diode as the sensor light source is shaped by the beam shaping means, so that the spot of the light beam applied to the sample image is formed. The area can be formed into a desired shape. Therefore, even if the image monitor sensor is miniaturized and the diameter of the lens included therein is reduced, the light receiving output of the light receiving element becomes constant regardless of the fluctuation of the image recording medium in the lens optical axis direction. The variation range can be increased, and the sensor can be further miniaturized while maintaining the performance as a sensor capable of monitoring an image with high accuracy in a non-contact online manner. The size and cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an image output unit of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating an image quality control portion of an embodiment of the image forming apparatus of the present invention.

FIG. 3 is a diagram illustrating an image monitoring sensor according to an embodiment of the image forming apparatus of the present invention.

FIG. 4 is a diagram showing a relationship between density patches and LEDs in the image monitoring sensor of FIG. 3;

FIG. 5 is a diagram illustrating an example of a relationship between a reflection spectrum and an emission spectrum in the case of the density patch and the LED in FIG. 4;

FIG. 6 is a diagram for explaining the principle of the optical measurement method of the prior application.

FIG. 7 is a diagram showing characteristics in the case of the optical measurement method of the prior application.

FIG. 8 is a diagram for explaining necessary conditions in the optical measurement method of the prior application.

FIG. 9 is a diagram showing the relationship between the vertical fluctuation of the paper surface and the spot area position of the light from the LED on the paper surface.

FIG. 10 is a diagram illustrating an example of a beam shaping unit of the image forming apparatus according to the present invention.

FIG. 11 is a diagram showing another example of the beam shaping means of the image forming apparatus of the present invention.

[Explanation of symbols]

 Reference Signs List 31 laser output unit 32 photoconductor 37 paper 38 sample image 39, 39Y, 39M, 39C, 39K density patch 40 fixed image density sensor 41, 41B, 41G, 41R, 41RK LED 43 lens 44 44Y, 44M, 44C, 44K: light receiving element 49: beam shaping means 50 image controller

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seigo Makita 430 Nakai-cho Sakai Nakagami-cho, Kanagawa Prefecture Inside Green Tech Nakai Fuji Xerox Co., Ltd. F term (reference) 2C061 AP01 AR01 KK12 KK25 KK28 KK32 2C262 AA05 AC03 BA09 BB03 FA12 2G059 AA01 BB10 DD12 DD20 EE02 EE13 GG01 GG02 HH02 JJ02 JJ11 KK01 MM14 5F041 AA47 EE25 FE11

Claims (11)

[Claims] 1. An image forming apparatus for detecting an output color image and correcting an image forming condition according to a result of the detection, an image forming means for forming a color image using a plurality of color materials, and the plurality of colors Image detecting means for detecting a sample image output by the image forming means by at least one of the materials, control means for correcting image forming conditions of the image forming means according to a detection result of the image detecting means; The image detecting means, light irradiating means for irradiating the sample image with light from a light emitting diode, according to the density of the sample image, receives the reflected light from the sample image, and detects the detection result Light receiving means for outputting light, and the light irradiating means includes a beam shaping means for shaping a light beam from the light emitting diode. Forming apparatus. 2. The apparatus according to claim 1, wherein said beam shaping means is an opening disposed between said light emitting diode and said sample image, and shapes a light beam from said light emitting diode according to an opening shape thereof. Item 2. The image forming apparatus according to Item 1. 3. The beam shaping means is an optical lens disposed between the light emitting diode and the sample image, and shapes a light beam from the light emitting diode according to its optical characteristics. The image forming apparatus according to claim 1. 4. The beam shaping means is a transmission filter disposed between the light emitting diode and the sample image, and shapes a light beam from the light emitting diode according to its optical characteristics. The image forming apparatus according to claim 1. 5. The beam shaping means is a combination of a plurality of apertures, optical lenses, and transmission filters disposed between the light emitting diode and the sample image. The image forming apparatus according to claim 1, wherein a light beam from the light emitting diode is shaped. 6. The image forming apparatus according to claim 1, wherein the sample image includes at least patches of each color of Sian, Magenta, and Yellow. 7. The image forming apparatus according to claim 1, wherein the light emitting diodes are at least red, green, and blue light emitting diodes. 8. An image forming apparatus according to claim 1, wherein said image detecting means is arranged at a stage subsequent to a final step of said image forming means. 9. The method according to claim 1, wherein the plurality of color materials are Sian, Magenta,
The image forming apparatus according to claim 1, wherein the image forming apparatus includes yellow and black color materials. 10. The image forming means includes at least a charger for charging a photoreceptor, an exposure unit for exposing the charged photoreceptor to form an electrostatic latent image on the photoreceptor, A developing unit for forming a toner image by using one of the plurality of color materials on the photoreceptor on which the electrostatic latent image is formed; and a transfer unit for transferring the toner image onto an image recording medium. The image forming apparatus according to claim 1. 11. The control means according to the detection result, includes: a driving condition of the charging device, an exposure amount by the exposure unit, a developing bias voltage of the developing device, a developer concentration in the developing device, and The image forming apparatus according to claim 10, wherein at least one of driving conditions of the transfer unit is corrected.