JPH09185191A - Toner concentration detector and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color density detector with a simple constitution, capable of optically detecting the quantity of color toner stuck onto an image carrier (surface density), with high accuracy, especially, in a high-sticking region such as a region where the surface of the image carrier is completely covered with toner. SOLUTION: Both of a light emitting element 2 and a light receiving element 3 have directivity. These light emitting and receiving elements 2 and 3 are disposed to place a point P where the optical axes of the light emitting and receiving elements 2 and 3 intersect each other, on the surface of the image carrier 4C or in its vicinity and be at an angle ψ formed in such a manner that an optical axial plane S1 including both optical axes of the light emitting and receiving elements 2 and 3 is inclined with respect to a normal h from the surface of the image carrier 4C passing through the intersection P by a fixed angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner density detecting device for detecting the color toner density on an image carrier by means of a light emitting element and a light receiving element, and an image forming represented by a color copying machine equipped with this toner density detecting device. It relates to the device.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as a copying machine or a printer, which develops an electrostatic latent image formed on a surface of a photoconductor as an image carrier using a developer containing toner, the electrostatic latent image is formed. Since the toner contained in the developer accommodated in the developing device is consumed with the development of the above, in order to keep the density of the copy image constant at all times, a new toner is added depending on the consumption amount of the developer. Toner must be replenished.

Therefore, conventionally, focusing on the fact that the toner concentration in the developer and the development concentration (toner adhesion amount to the photoconductor) are in a fixed proportional relationship, a platen glass for placing a document to be copied. A reference chart with a certain density provided near the is exposed and developed on the photoconductor to form a reference pattern image for toner density detection, and the density is optically detected, and according to the detected value. The amount of toner replenishment is controlled. Specifically, the density of a predetermined set value of the reference pattern image is compared with the density of the reference pattern image detected for toner replenishment control, and if the latter is higher, the toner replenishment is stopped or replenished. If the amount is reduced, the toner replenishment is restarted or the amount of replenishment is increased if the amount is low.

On the other hand, in recent years, the development of mono-color copying machines for red, blue, etc. has been promoted.
A system in which a black toner developing device and a color toner developing device are exchanged arbitrarily, a system in which both developing devices are installed side by side and their operation is arbitrarily switched and controlled, and a method in which development is performed using a full color developing device are adopted. ing.

Conventionally, the optical means for detecting the density of the reference pattern image used in the black toner copying machine is composed of a light emitting element and a light receiving element, and the light receiving element detects the regular reflection light from the light emitting element. The optical axis plane including the respective optical axes of the received and emitted light fluxes coincides with the plane including the normal line of the image carrier.

However, during development with color toner, since the color toner causes diffuse reflection, there is almost no difference in the reflectance between the photoconductor as the image carrier and the color toner. As shown in FIG. The color toner shown (solid line is black toner) cannot obtain a correlation between the toner density and the light receiving element output (amount of specular reflection light), and it is difficult to detect the density of the reference pattern image by the color toner.

As a measure against this, Japanese Patent Laid-Open No. 61-20947
In JP-A-0, at least one of a light emitting element and a light receiving element is used so that the light receiving element receives specularly reflected light when black toner is used for development, and color toner is used for development. In this case, there is disclosed a toner concentration detecting device in which the light receiving element can rotate and switch in the optical axis plane so as to receive irregularly reflected light.

Further, in Japanese Patent Laid-Open No. 62-164066, the image density is increased for a monocolor toner having the output characteristic of a quadratic curve infrared photosensor in accordance with the toner adhesion amount on the image carrier. At times, there is a method of controlling in a color characteristic region where the sensor output also increases, and limiting the replenishment of toner when the sensor output exceeds a certain value. Further, Japanese Patent Laid-Open No. 62-209476 discloses a light receiving element. A method is disclosed in which two are used, one is arranged to receive specularly reflected light and the other is to receive irregularly reflected light, and the toner supply amount of the developing device is controlled in accordance with the difference between the output signals of both light receiving elements. .

[0009]

However, in the above-described conventional color density detecting method or apparatus, the image carrier and the optical axis plane including the optical axes of the light emitting and receiving light fluxes of the light emitting element and the light receiving element are the image carrier. The configuration is the same as the plane including the normal line, and this is achieved by changing the angles of the light emitting element and the light receiving element in the plane of the optical axis. When the light emitting element and the light receiving element as the toner concentration detecting device are provided at positions that coincide with the plane including the normal line of the image carrier and the toner concentration is to be detected, they are formed on the image carrier. Since the reflected light from the color toner image is irregularly reflected light, the amount of the light becomes very weak. Therefore, in order to detect the reflected light, the light emitting element and the light receiving element are brought close to the image carrier (detected surface), Further, it is necessary to increase the size of the light receiving surface / light emitting surface of the light emitting element and the light receiving element so that the reflected light can be sufficiently detected. However, when the light emitting element and the light receiving element are brought closer to the image carrier (detected surface), or the size of the light receiving surface / light emitting surface of the light emitting element and the light receiving element is increased, the light emitting element and the light receiving element are formed on the image carrier. There is a problem that a large amount of specularly reflected light from the reflected light from the toner image is mixedly input and the density value of the color toner image cannot be accurately detected.

Further, the light emitting element and the light receiving element are brought closer to the image carrier (the surface to be detected) in order to detect diffused reflection light, and the size of the light receiving surface / light emitting surface of the light emitting element and the light receiving element is increased. In that case, there is a problem that the mechanism has to be incorporated in a narrow space and the configuration is complicated, and a simpler configuration has been desired.

Therefore, an object of the present invention is to solve the above-mentioned conventional problems and to detect the amount (area density) of color toner adhered on the image carrier with high optical accuracy. In particular, it is an object of the present invention to provide a color density detecting device having a simple structure capable of detecting with high accuracy in a high adhesion region where toner completely covers the surface of an image carrier.

[0012]

According to a first aspect of the invention, an image forming condition is obtained by irradiating a toner pattern image formed on an image carrier with light from a light emitting element and detecting the reflected light with a light receiving element. In the image forming apparatus including a toner density detecting device for controlling the image carrying device, the light emitting element and the light receiving element both have directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect is the image carrier. An optical axis plane, which is on the body surface or near the carrier surface and includes both optical axes of the light emitting element and the light receiving element, is predetermined with respect to a normal line from the carrier surface passing through the intersection. In the image forming apparatus, the light emitting element and the light receiving element are arranged at an inclined angle.

According to a second aspect of the present invention, there is provided a toner density detecting device for irradiating a toner pattern image formed on an object to be measured with light from a light emitting element and detecting the reflected light with a light receiving element.
The light emitting element and the light receiving element have both directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect, on the surface of the measured object, or in the vicinity of the surface of the carrier, An optical axis plane including both optical axes of the light emitting element and the light receiving element, the light emitting element and the light receiving element at an angle inclined by a predetermined angle with respect to a normal line from the surface of the measured object passing through the intersection. The toner concentration detecting apparatus is characterized in that

According to a third aspect of the present invention, the directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the normal line and the optical axis plane are set. Is defined as ψ, the diameter of the light emitting surface of the light receiving element is D1, the diameter of the light receiving surface of the light receiving element is D2, and the optical path length connecting the center of the light emitting surface and the center of the light receiving surface is When ρ, ψ> φ1 + tan ~ ¹ (D2 /
2. The image forming apparatus according to claim 1, wherein the light emitting element and the light receiving element are arranged so as to satisfy either one of 2ρ) or ψ> φ2 + tan ~ ¹ (D1 / 2ρ). It is in.

According to a fourth aspect of the present invention, the directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the normal line and the optical axis plane are set. Is defined as ψ, the diameter of the light emitting surface of the light receiving element is D1, the diameter of the light receiving surface of the light receiving element is D2, and the optical path length connecting the center of the light emitting surface and the center of the light receiving surface is When ρ, ψ> 1/2 ・ φ1 + tan ~
¹ (D2 / 2ρ) or ψ> 1/2 ・ φ2 + tan ~
3. The image forming apparatus according to claim 2, wherein the light emitting element and the light receiving element are arranged so as to satisfy any one of ¹ (D1 / 2ρ).

According to a fifth aspect of the invention, the light emitting element and the light receiving element are unitized by a supporting member so that both optical axes of the light emitting element and the light receiving element are included in the same plane, and the light emitting element or the light receiving element is united. 5. An image forming apparatus according to claim 1, wherein a condensing optical element is provided in front of at least one of the above.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a color image forming apparatus to which the present invention is applied. In FIG. 1, image information converted into a digital signal in a scanner unit (not shown) is sent to a writing unit 22 that forms a visible image pattern. To be The writing unit 22 emits laser light 22Y, 22M, 22C, 22BK including image information of each color to the recording units 23Y, 23M, 23C, 23BK, and the recording units 23Y, 23M, 23C, 23.
The BKs are arranged on the same plane at regular intervals. Each of the recording units 23Y, 23M, 23C, and 23BK has the same electrophotographic system configuration although the developing colors are different. For example, the recording unit 23C includes a photoconductor drum 24C and a charger 25C. Cyan light formed on the photoconductor drum 4C by exposing the photoconductor drum 4C by irradiating the laser beam 22C from the writing unit 22 with modulated light according to image information to uniformly charge the photoconductor drum 4C. The electrostatic latent image of the image is developed by the developing unit 26C and visualized.

The transfer paper sent from a paper supply unit (not shown)
The registration roller 30 sends the toner image to the transfer belt 1 supported by the driving roller 34 and the driven roller 35 at the same timing and the toner images in order by the photoconductor drums 4BK, 4C, 4M, and 4Y while being conveyed leftward in the drawing. After being transferred, it is fixed by the fixing roller 32 and discharged.

In this transfer belt 1, as shown in FIG. 2, a light emitting element 2 and a light receiving element 3 form an angle formed by a perpendicular line s at a predetermined point P on the belt 1 and its optical axis 2a and optical axis 3a. Are arranged so as to be θ ₁ and θ _2, respectively.
The light emitting element 2 and the light receiving element 3 used in this embodiment both have a relatively wide directivity. That is, in the present embodiment, the light amount of the emitted light of the light emitting element 2 or the angle at which the sensitivity of the light receiving area of the light receiving element 3 becomes 1/2 is φ1 = 30 ° for the light emitting element, In case of φ2 = 20
Is 0 ° (φ1 and φ2 respectively represent the spread angle of each element).

Here, the directivity of both elements means that the emission intensity and the sensitivity intensity in the emitted light or the received light of the elements are 1
It means the distribution area of light that becomes / 2. And arrow A in FIG.
As shown in FIG. 3 when viewed from the direction, the light emitting element 2 and the light receiving element 3 are arranged such that the normal line h at the point P and the plane S1 including both the optical axis 2a and the optical axis 3a form an angle ψ. In this embodiment, ψ = 30 ° is set. FIG. 4 shows changes in the output voltage of the light receiving element 3 when the angle ψ formed by the normal line h at the point P and the plane S1 is changed in this configuration. In FIG. 4, characteristics when the transfer belt 1 is completely covered with color toner are shown by a characteristic line 40 and a characteristic line 41 when the toner is not attached. As shown in FIG. 4, since the color toner causes irregular reflection, when the inclination angle ψ of the plane including the optical axes of the light emitting element 2 and the light receiving element 3 with respect to the normal line h is −10 degrees to 10 degrees, The difference in the change in the output voltage of the light receiving element 3 between the case where the toner is completely covered and the case where the toner is not adhered is small, and the detection of the toner concentration has low sensitivity. On the other hand, outside the above range, the change is most noticeable as a difference between the values of the two characteristic lines. That is, in this embodiment, the planes including both optical axes of the light emitting element 2 and the light receiving element 3 are tilted so that the angle ψ is larger than 10 degrees or smaller than −10 degrees. It is possible to increase the difference in the output voltage of the light receiving element 3 between the case where the toner is completely covered and the case where the toner is not adhered, and the toner concentration can be detected with high sensitivity. Here, in the directivity between the light emitting element 2 and the light receiving element 3,
There is an error between each light emitting element 2 and each light receiving element 3. That is, the directional spread angle between the light emitting element 2 and the light receiving element 3 is
Due to subtle errors, the above angle ψ is │ψ in the actual design.
It is desirable that | ≧ 25 °.

[0021]

[Equation 1]

Means

In this embodiment, since the angle ψ = 30 °, it is possible to provide a highly sensitive toner concentration detecting device without being affected by the error between the light emitting element 2 and the light receiving element 3.

The second embodiment will be described below.

In the above embodiment, the case where the transfer belt 1 is used as the image carrier and the light emitting element 2 and the light receiving element 3 are elements having a relatively wide directivity is described. Next, as another embodiment, an image is formed. A case will be described in which a photosensitive drum is used as a carrier, and a light emitting element and a light receiving element are used as elements having a medium directivity.

As shown in FIG. 5, the light emitting element 2 and the light receiving element 3 are connected to the photosensitive drum 4C (photosensitive drum B shown in FIG. 1).
K, 4C, 4M, and 4Y), so that the angles formed by the perpendicular line s to the photosensitive drum 4C and its optical axes 2a and 3a at a predetermined point P are θ ₁ and θ ₂ , respectively. It is arranged. Both the light emitting element 2 and the light receiving element 3 used in this embodiment have a narrow directivity in the middle of the spread of the received and emitted luminous flux. That is, the amount of light emitted from the light emitting element 2 or the sensitivity of the light receiving area of the light receiving element 3 is 1 or less.
Angle of 1/2, φ1 = 8 ° for light emitting element, φ2 =
It is 12 degrees. (Φ1 and φ respectively indicate the spread angle.) Then, as shown in FIG. 6 viewed from the direction of arrow A in FIG.
The light emitting element 2 and the light receiving element 3 are arranged so that the normal line h at the point P and the optical axis plane S1 including both optical axes of the optical axis 2a and the optical axis 3a form an angle ψ. FIG. 7 shows changes in the output voltage of the light emitting element 2 when the angle ψ is changed, and FIG. 8 shows the output voltage of the light receiving element with respect to the toner adhesion amount of the image carrier when the angle ψ = 0 °. Shows the change.
In FIG. 7, the output characteristic when the photosensitive drum 4C is completely covered with color toner is a characteristic curve 42, and the output characteristic when some toner is attached is a characteristic curve 43.
A characteristic curve 44 shows the characteristic when there is no toner adhesion. In this case, in the vicinity of the angle ψ = 0 °, the output voltage difference remarkably appears regardless of the degree of toner adhesion. However, as shown in FIG. 8, when the angle ψ = 0 °, the amount of toner adhered on the image carrier changed from the time when the toner adhered on the image carrier exceeded 0.5 mg / cm ² . However, the difference in the output voltage of the light receiving element is reduced.

On the other hand, the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 is set at an angle ψ with respect to the normal line of the image carrier.
= 10 °, the change in the output voltage of the light receiving element 3 with respect to the change in the amount of adhered toner on the image carrier is as shown in FIG.
It appears remarkably as shown in. Therefore, the angle ψ is 1
By arranging the light emitting element 2 and the light receiving element 3 so as to be inclined at an angle larger than 0 degree or smaller than -10 degrees, the difference in the output voltage of the light receiving element between the above output characteristics becomes remarkable. The amount of adhered color toner can be detected with high sensitivity. In the case of this embodiment, the angle ψ = 30 ° is set.

Next, a third embodiment will be described. In the above two embodiments, the optical axis 2a of the light emitting element 2 and the optical axis 3 of the light receiving element 3 are used.
The case where the point P where a intersects with the image bearing member is on the surface of the image carrier has been described, but as another embodiment, the point P ′ where the optical axis 2a of the light emitting element 2 and the optical axis 3a of the light receiving element 3 intersect is described. A case will be described where the image carrier is set to a position displaced inward from the surface of the image carrier, that is, in the vicinity of the surface of the image carrier.

In FIG. 10, a point P'where the optical axis 2a of the light emitting element 2 and the optical axis 3a of the light receiving element 3 intersect is on the normal line h on the photosensitive drum 4C and inside the photosensitive drum 4C. The optical axis 2a of the light emitting element 2 and the optical axis 3a of the light receiving element 3 and the normal line h passing through the point P ′ are arranged so as to be θ1 and θ2, respectively. . The light emitting element 2 and the light receiving element 3 used in this embodiment both have relatively narrow directivity. That is, the amount of light emitted from the light emitting element 2 or the light receiving sensitivity of the light receiving element 3 is φ1 = 8 ° for the light emitting element 2 and φ2 = 12 ° for the light receiving element 3 (angle θ1, θ2 indicates the spread angle, respectively.) Then, as shown in FIG. 12 viewed in the direction of arrow A in FIG.
A plane St that includes the point P ′ and is orthogonal to the rotation axis of the photoconductor drum 4C (that is, a plane that includes a normal line passing through the surface of the photoconductor drum 4C that passes through the point P ′) St and the light emitting element 2 and the light receiving element 3 The angle ψ formed by the plane S including both optical axes is the angle ψ = 30.
The light emitting element 2 and the light receiving element 3 are arranged so as to form an angle of °.

Even in this case, there is no problem in detecting irregularly reflected light of the color toner in the toner density detecting device including the light emitting element 2 and the light receiving element 3. The reason is described below.

FIG. 12 shows a state in which the light-emitting element 2 and the light-receiving element 3 are arranged so as to be inclined with respect to the normal line of the image carrier so that the latent image forming surface (detected surface) of the image carrier is shown. The light emitting element 2 and the light receiving element 3 will be described with reference to a diagram in which the light emitting element 2 and the light receiving element 3 are virtually arranged at the positions of the phase targets.

In FIG. 12, the light emitting element 2 and the light receiving element 3
, 2φ1 and 2φ2 respectively, the light amount of the light emitting element 2 and the sensitivity of the light receiving element 3 are "1" inside the directivity spread 2φ1 and 2φ2 of both elements, and the outside is "0".
And

When the reflecting surface of the detected surface L changes from the first position L1 in FIG. 12 to the second position L2 in FIG. 12, the area of the light received by the light receiving element from the detected surface is: The light emitting area SI of the first detected surface L1 of the light emitting element 2 is reduced and changed to the light emitting area S2 of the second detected surface. The illuminance in the light emitting area S2 on the detection surface is SI / S2 times. It becomes equal to the relationship between the distance r1 from the first detected surface L1 to the light receiving point PDi of the light receiving element 3 and the distance r2 from the second detected surface L2 to the light receiving point PDi of the light receiving element 3, and in the end, The change in illuminance on the detection surface changes in inverse proportion to the square of the distance from the light receiving element to the detection surface. That is, the following equation holds.

[0034]

[Equation 2]

This means that the detected surface is the first detected surface L.
Although the light receiving sensitivity to the light receiving element is lowered even if the light receiving element changes from 1 to the second detected surface L2, the toner concentration detecting device including the light emitting element 2 and the light receiving element 3 detects the light emitted from the light emitting element on the detected surface. Since the reflected light is reflected by the light receiving element and the light receiving element receives the change in the light receiving degree to determine the toner density, even if the reflected light changes, the measurement is not hindered.

Even if the detected surface changes from the first detected surface L1 to the third detected surface L3, the area of the light received by the light receiving element from the detected surface is now the light emitting element 2 The light emitting area SI 'on the first detected surface L1 is reduced to the light emitting area S3 on the third detected surface. Light emitting area S3 on the detection surface
The illuminance inside is SI '/ S3 times. It is the distance r1 from the first detected surface L1 to the light receiving point PDi of the light receiving element 3.
And the distance r3 from the third detected surface L3 to the light receiving point PDi of the light receiving element 3 are equal, and eventually, the change in illuminance on the detected surface is 2 times the distance from the light receiving element to the detected surface. It will change in inverse proportion to the power. That is, the following equation holds.

[0037]

(Equation 3)

This means that the light receiving sensitivity of the light receiving element 3 increases conversely, but the fact that the detected surface changes to the third detected surface L3 means that the reflected light diffuses outside the light receiving range of the light receiving element. As a result, the received light of the reflected light in the light receiving area will be totally reduced. However, similarly to the case where the detection surface is displaced from the second detection surface L2, the change in the light receiving ability of the light receiving element 3 is not affected.

Next, a fourth embodiment will be described. As shown in FIG. 13, the light emitting element 2 and the light receiving element 3 are fixed and supported by a supporting member 61 of the light emitting and receiving element unit 60. A Fresnel lens 62 as a condensing optical system is provided in front of the light emitting element 2.
However, dust-proof glass 63 is arranged in front of the light receiving element 3. The Fresnel lens 62 irradiates a light beam which is narrowed down on the surface of the image carrier 1 to the point P, and the light receiving element 3 is arranged so that the light receiving element 3 receives the light spot at the point P through the dustproof glass 63. In the light emitting / receiving element unit 60, the example in which the Fresnel lens 62 is provided on the light emitting element 2 side is shown, but it may be provided on the light receiving element 3 side.

FIG. 14 shows a state in which the light-emitting element 2 and the light-receiving element 3 are arranged so as to be inclined with respect to the normal line of the image carrier, and the latent image forming surface (detected surface) of the image carrier is shown. It is the figure which virtually arranged the light emitting element 2 and the light receiving element 3 in the position of a phase object as a reference.

In FIG. 14, the directivity which is the spread of the luminous flux of the light emitting element 2 is φ1 and the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the light emitting element 2 and the light receiving element 3 are shown.
The angle between the normal line h passing through the intersection point P where the two optical axes intersect and the optical axis plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 is an angle ψ, and the diameter of the light emitting surface 2b of the light emitting element 2 is Is D1 and the optical path length connecting the center Ps of the light emitting surface 2b of the light emitting element 2 and the center PD of the light receiving surface 3b of the light receiving element 3 is ρ, the light emitting element 2 and the light emitting element 2 satisfy the following equation. The plane S1 including both optical axes of the light receiving element 3 is arranged so as to be inclined by an angle ψ with respect to the normal line h.

[0042] ^{ψ> φ1 + tan ~ 1 (} D2 / 2ρ) In this case, the emission intensity of the light emitted directional .phi.1 from the light emitting element 2 emission optical axis is half the optical axis direction.

Here, the relationship between the emission intensity of the emitted light having the directivity φ1 of the light emitting element 2 and the intensities of specular reflection light and irregular reflection light will be described.

In FIG. 14, line segments LA0, LA1 and L from the center point Psi of light emission of the light emitting element 2 to the reflecting surface L are shown.
A2 indicates the light emitted from the light emitting element 2, and this line segment LA
1 ', LA2 and LA0', which are extensions of the reflecting surface L
Line segments LA1 ', LA2 and LA located closer to the light receiving element 3 side
Reference numeral 0'indicates the lights LA0, LA1 and LA2 that are specularly reflected by the reflecting surface L, respectively.

Here, it is known that the intensity of specularly reflected light changes in proportion to the light emission intensity distribution of the light emitting element. On the other hand, it is known that the intensity of the diffusely reflected light is proportional to the solid angle of the light receiving surface of the light receiving element 3 viewed from the point P. Therefore, if the size of the light receiving surface of the light emitting element 3 is constant, The intensity does not change if the distance from the point P to the light receiving element 3 is constant.

Since the areas on the line segments LA1 'and LA2' coincide with the area of the directivity φ1, in this area, the intensity of the specularly reflected light is the optical axis LA0 '(the intensity of the most specularly reflected light) of the light emitting element 2. Is a half of the strength on the (higher area). Therefore, if the light receiving element 3 is arranged outside the region surrounded by the line segments LA1 'and LA2' on the light receiving surface of the light receiving element 3, the light receiving element 3 is
Only specular reflection light having an intensity of / 2 or less can be detected, and diffuse reflection light can be detected without weakening the intensity.

Although the above relationship has been described with reference to the light emitting element 2, the light emitting surface is arranged outside the region of the directivity φ2 of the light receiving element 2 even when the light receiving element 3 described later based on FIG. 15 is used as a reference. By doing so, the intensity of the specularly reflected light received by the light receiving element 3 becomes 1/2 or less, while the intensity of the irregularly reflected light does not change, as in the case where the light emitting element 2 is used as a reference.

The optical path length ρ of the light emitting element 2 and the light receiving element 3 is determined from the point Ps on the light emitting element surface of the optical axis of the light emitting element 2 to the light receiving element 3
Represents the shortest distance of light passing through the surface to be detected up to the point P _D on the light receiving element surface of the optical axis.

In this case, the center point Psi of light emission when defining the directivity of the light emitting element 2 is generally positioned slightly inside the surface of the light emitting element 2 from the surface of the element.

Therefore, the central point Ps of light emission of the light emitting element is
The distance from i to the point P _D on the light receiving element surface of the light receiving element 3 is from the point Ps on the light emitting element surface of the light emitting element 2 to the point P _D on the light receiving element surface of the light receiving element 3. Longer than the distance to. That is,

[0051]

(Equation 4)

It becomes

The angle ψ formed by the center of the light receiving element 3 and the end 3A of the light receiving element 3 viewed from the center point of the light emission of the light emitting element 2.
Satisfies the following equation.

[0054]

(Equation 5)

[0055]

(Equation 6)

However, D ₂ is the diameter of the light-receiving surface of the light-receiving element 3. The light-receiving element 3 is arranged such that the light-receiving surface is located outside the luminous flux φ1 of the light-emitting element 2.

Therefore,

[0058]

(Equation 7)

And the tilt angles ψ with respect to the normal line h of the optical axis plane S1 of both optical axes of the light emitting element 2 and the light receiving element 3 satisfy the above expression, both optical axes of the light emitting element 2 and the light receiving element 3 are satisfied. If the optical axis plane S1 of is inclined with respect to the normal line h,
Most of the regular reflection light LA emitted from the light emitting element 2 is shown in FIG.
As shown in FIG. 4, the light is not emitted to the outside of the light receiving surface of the light receiving element 3 and does not enter the light receiving element 3.

The tilt angle ψ with respect to the normal line h of the optical axis plane S1 of both optical axes of the light emitting element 2 and the light receiving element 3 has been described above with reference to the light emitting element. The same applies to the light emitting element.

In FIG. 15, the directivity φ2 which is the spread of the light beam received by the light receiving element 3 is set, and the light emitting surface 2b of the light emitting element 2 is set.
Let D1 be the diameter of.

In this case, the light receiving intensity of the light received with the directivity φ2 from the light receiving optical axis of the light receiving element 3 is ½ of the optical axis direction.
The optical path length ρ of the light emitting element 2 and the light receiving element 3 passes through a detected surface from a point PD on the light receiving element surface of the optical axis of the light receiving element 3 to Ps on the light emitting surface of the light emitting element of the optical axis of the light emitting element 2. Indicates the shortest distance of light.

In this case, generally, the center point PDi of light reception when defining the directivity of the light receiving element 3 is located slightly inside the surface of the light receiving element 3 from the surface of the element. Therefore, from the distance from the center point Ps of light emission of the light emitting element to the point PD on the light receiving element surface of the light receiving element 3 from the point PDi on the light receiving element surface of the light receiving element 3 to the optical axis of the light emitting element 2. The distance to PS on the light emitting element surface is long. That is,

[0064]

(Equation 8)

It becomes

When viewed from the light receiving center point PDi of the light receiving element, PDi on the light emitting element surface of the optical axis of the light emitting element 2 and the end 2A of the tip of the light emitting element 2 on the normal line h side are formed. Angle δ
However, the light receiving element 3 is arranged so as to satisfy the following equation.

[0067]

[Equation 9]

[0068]

(Equation 10)

The light emitting element 2 is arranged so that the light emitting surface is located outside the light emitting beam φ2 of the light receiving element 3. Therefore,

[0070]

[Equation 11]

And the tilt angles ψ with respect to the normal line h of the optical axis plane S1 of both optical axes of the light emitting element 2 and the light receiving element 3 satisfy the above expression, both optical axes of the light emitting element 2 and the light receiving element 3 are satisfied. If the optical axis plane S1 of is inclined with respect to the normal line h,
Most of the regular reflection light LA from the light emitting element 2 is emitted to the outside of the light receiving surface of the light receiving element 3, as shown in FIG.
Light is not incident on the light receiving element 3.

As is clear from the above description, the light-receiving element 3 is arranged such that the light-receiving surface of the light-receiving element 3 is located outside of the luminous flux φ1 of the light-emitting element 2, or the light-emitting surface of the light-emitting element 2 is arranged so that The light emitting element 2 is arranged so as to be located outside the received light beam φ2 of the light receiving element 3. That is,

[0073]

(Equation 12)

Or

[0075]

(Equation 13)

If the light emitting element 2 and the light receiving element 3 are arranged so as to satisfy either one of the above, the light receiving element 3 does not receive most of the specularly reflected light but receives the irregularly reflected light. The amount of adhered color toner can be accurately detected without being confused by the noise of reflected light.

A specific example of the toner concentration detecting device in the above embodiment will be shown below. In FIG. 16, the toner concentration detecting device is a light receiving element 3 having a light receiving area of 4 mm in diameter.
And a light emitting element 2 having a directivity φ1 of 20 °,
The distance from the center of the light emitting surface of the light emitting element to the center of the light receiving surface of the light receiving element 3 is 4 mm, which is equidistant from the surface to be detected. That is, the distance ρ from the center of the light emitting surface of the light emitting element to the center of the light receiving surface of the light receiving element 3 is ρ = 8 mm. In this toner concentration detecting device, the inclination angle ψ with respect to the normal line h of the plane S1 including both optical axes of the light-emitting element 2 and the light-receiving element 3 is defined as a large part of specular reflection light from the reflection surface of the image carrier (detection target). Is not input to the light receiving element 3

[0078]

[Equation 14]

However, if the actual numerical value is substituted for this,

[0080]

(Equation 15)

And this value is φ1 + tan ~ ¹ (D2 /
2ρ)

[0082]

(Equation 16)

Here, the inclination angle ψ'with respect to the normal line h of the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 is temporarily

[0084]

[Equation 17]

If set to, the value and the light regularly reflected from the reflecting surface of the image carrier (detection object) are not directly inputted to the light receiving element 3 and the light receiving element 2 and the light receiving element 3.
Comparing with the inclination angle ψ with respect to the normal line h of the plane S1 including both optical axes, ψ′≈37 °> ψ = 34 °, which is the positive angle from the reflection surface of the image carrier (detection target). Most of the reflected light is not directly input to the light receiving element 3, and both light beams of the light emitting element 2 and the light receiving element 3 are actually obtained from the inclination angle ψ with respect to the normal line h of the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3. Since the inclination angle ψ'with respect to the normal line h of the plane S1 including the axis is set to be large, the toner density can be detected without being confused by the noise of the specular reflection light.

FIG. 17 shows a case where the light emitting element 2 has a narrow directivity, specifically, FIGS. 13 to 15 when φ1 = 2 °.
The relationship between the normal line h at the intersection point P of the image carrier 1, the angle ψ formed by the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 and the sensor output voltage (corresponding to the detected light amount) is shown. Where φ
2 = 30 °. A curve 70 is a characteristic curve of the output voltage when there is no toner, and B′AB is a region where the regular reflection of the image carrier 1 can be mainly detected, and C′B ′ and B
C is an area in which only irregular reflection of the image carrier 1 can be detected. A curve 71 shows the characteristic when the toner adheres to the entire surface. The output voltage characteristic curve 71 has little dependence on the angle ψ. The same applies to the diffused reflection light component of the image carrier 1 when there is no toner.

In FIG. 17, in the vicinity of the angle ψ = 0 °,
The output voltage difference remarkably appears regardless of the degree of toner adhesion. However, as shown in FIG. 8, when the angle ψ = 0 °, the difference in the output voltage of the light receiving element 3 becomes small even if the toner adhesion amount on the image carrier changes.

On the other hand, the plane including both the optical axes of the light emitting element 2 and the light receiving element 3 is angle ψ with respect to the normal line of the image carrier.
When it is arranged at an angle larger than ± 1 °, it has sufficient sensitivity up to a region where a large amount of toner adheres on the image carrier as shown in FIG.

Therefore, the light emitting element 2 and the light receiving element 3
Is larger than ± 1 °, and in this embodiment, the angle ψ =
By arranging at an angle of 2 °, the toner color adhesion amount can be detected with high sensitivity without being disturbed by noise of specular reflection light.

Now, the difference in the output characteristics of the light receiving element with respect to the difference in directivity between the light emitting element 2 and the light receiving element 3 will be described.

FIG. 4 shows that when the directivity of the light receiving element 3 and the light emitting element 2 is relatively wide, specifically, φ1 = 30 °, φ2.
FIG. 7 is a diagram showing the output characteristics of the light receiving element with respect to changes in the inclination angle ψ of the normal line h of the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 in the case of 20 °, and FIG. When the light emitting element 2 has a medium directivity, specifically,
FIG. 7 is a diagram showing output characteristics of a light receiving element with respect to changes in an inclination angle ψ of a normal line h of a plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 when φ1 = 8 ° and φ2 = 12 °. Also,
FIG. 17 shows the inclination of the normal line h of the plane S1 including both optical axes of the light emitting element 2 and the light receiving element 3 when the directivity of the light receiving element 3 or the light emitting element 2 is narrow, specifically, φ1 = 2 °. It is a figure which shows the output characteristic of a light receiving element with respect to the change of angle (psi).

[0092]

As described above, according to the invention of claim 1, the light emitting element and the light receiving element both have directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect with each other, On the surface of the image carrier, or in the vicinity of the surface of the image carrier, an optical axis plane including both optical axes of the light emitting element and the light receiving element,
Since the light emitting element and the light receiving element are arranged at an angle inclined by a predetermined angle with respect to a normal line from the surface of the carrier passing through the intersection, irregular reflection formed on the surface to be detected of the image carrier. It is possible to provide the image forming apparatus capable of capturing the reflection characteristic light of the color toner by cutting the noise of the regular reflection light and accurately detecting the color toner density. Further, in the present invention, the concentration can be detected with a simple configuration in which the plane optical axis planes including both the optical axes of the light emitting element and the light receiving element are inclined with respect to the normal line, so that the concentration can be detected like a conventional detection device. There is no need for a cumbersome mechanism to process the results electronically.

According to the second aspect of the invention, the light emitting element and the light receiving element both have directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect is on the surface of the object to be measured, or An optical axis plane including both optical axes of the light emitting element and the light receiving element in the vicinity of the surface of the object to be measured is inclined at a predetermined angle with respect to a normal line from the surface of the object to be measured passing through the intersection. Since the light emitting element and the light receiving element are arranged at an angle to detect the toner density, the reflection characteristic light of the diffusely reflected color toner formed on the detection surface of the object to be measured is cut into the noise of the specular reflection light. You can make it take in,
Accurate detection of color toner density is possible. Further, in the present invention, the concentration can be detected with a simple configuration in which the plane optical axis planes including both the optical axes of the light emitting element and the light receiving element are inclined with respect to the normal line, so that the concentration can be detected like a conventional detection device. There is no need for a cumbersome mechanism to process the results electronically.

According to the third aspect of the present invention, the directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the normal line and the optical axis plane are set. Is defined as ψ, the diameter of the light emitting surface of the light receiving element is D1, the diameter of the light receiving surface of the light receiving element is D2, and the optical path length connecting the center of the light emitting surface and the center of the light receiving surface is When ρ, the light emitting element and the light receiving element are arranged so that either ψ> φ1 + tan ~ ¹ (D2 / 2ρ) or ψ> φ2 + tan ~ ¹ (D1 / 2ρ) is satisfied. The reflection characteristic light of the color toner that is diffusely reflected and formed on the surface to be detected of the image carrier can be taken in by cutting the noise of the specular reflection light, and the color toner density can be accurately detected.

According to the fourth aspect of the invention, the directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the normal line and the light An angle formed with the axial plane is ψ, a diameter of a light emitting surface of the light receiving element is D1, a diameter of a light receiving surface of the light receiving element is D2, and an optical path connecting a center of the light emitting surface and a center of the light receiving surface. When the length is ρ, the light emitting element and the light receiving element are arranged so that either ψ> φ1 + tan ~ ¹ (D2 / 2ρ) or ψ> φ2 + tan ~ ¹ (D1 / 2ρ) is satisfied. In addition, it is possible to cut the noise of the specular reflection light into the reflection characteristic light of the color toner that is diffusely reflected and is formed on the surface to be detected of the object to be measured, and to accurately detect the color toner concentration.

According to the invention of claim 5, the light emitting element and the light receiving element are unitized by a supporting member so that both optical axes of the optical element and the light receiving element are included in the same plane, and the light emitting element or the light receiving element is united. Since the condensing optical element is provided in front of at least one of the above, the emitted light or the reflected light is condensed and used for detection, so that the detection accuracy can be improved.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram of a light emitting element and a light receiving element that constitute the color density detection device of the first embodiment as seen from the front of an image carrier.

FIG. 3 is a configuration diagram of a color density detection device in a state where the light emitting element 2 and the light receiving element 3 are viewed from the direction A in FIG.

FIG. 4 is a diagram illustrating a case where the light receiving element and the light emitting element have a relatively wide directivity, the amount of toner adhered to the image carrier and the light receiving element with respect to a change in an inclination angle of a normal line of a plane including both optical axes of the light emitting element and the light receiving element. It is a characteristic diagram which shows the relationship of the output voltage from.

FIG. 5 is a configuration diagram showing a light emitting element and a light receiving element of an example based on the second example.

FIG. 6 is a configuration diagram showing a color density detection device when FIG. 5 is viewed from the direction A.

FIG. 7 shows the amount of toner adhering to the image carrier with respect to the change in the inclination angle of the normal line of the plane including both the optical axes of the light emitting element and the light receiving element when the directivity of the light receiving element and the light emitting element is medium. FIG. 4 is a characteristic diagram showing the relationship between the output voltage from the light receiving element and the output voltage.

FIG. 8 is a characteristic diagram showing the relationship between the toner adhesion amount on the image carrier and the output voltage from the light receiving element.

FIG. 9 is a characteristic showing the relationship between the toner adhesion amount on the image carrier and the output voltage from the light receiving element when the planes including both the optical axes of the light emitting element and the light receiving element are arranged at an angle ψ with respect to the normal line. It is a diagram.

FIG. 10 is a configuration diagram showing a light emitting element and a light receiving element of an example based on the third example.

FIG. 11 is a configuration diagram of a toner concentration detecting device in a state in which planes including both optical axes of a light emitting element and a light receiving element of an example based on the third example are arranged with an inclination with respect to a normal line.

FIG. 12 shows a state in which a light emitting element and a light receiving element are arranged so as to be inclined with respect to a normal line of an image carrier, and the light emitting element and the light receiving element are matched with each other with reference to the latent image forming surface of the image carrier. FIG. 3 is a configuration diagram of a light emitting element and a light receiving element, which is virtually arranged at a target position and illustrates a state in which the position of the image carrier is displaced.

FIG. 13 is a side view showing an example of a light emitting / receiving element unit in which a light emitting element and a light receiving element according to the fourth embodiment are integrated by a supporting member.

FIG. 14 is a state in which a light emitting element and a light receiving element of an example based on the fourth example are arranged so as to be inclined with respect to a normal line of the image carrier, with reference to the latent image forming surface of the image carrier. FIG. 3 is an explanatory configuration diagram for explaining a degree of inclination with a light emitting element and a light receiving element virtually arranged at positions of phase symmetry, and the light emitting element as a reference.

FIG. 15 is a state in which the light emitting element and the light receiving element of the embodiment based on the fourth embodiment are arranged so as to be inclined with respect to the normal line of the image carrier, with reference to the latent image forming surface of the image carrier. FIG. 7 is an explanatory configuration diagram for explaining a degree of inclination with a light emitting element and a light receiving element virtually arranged at positions of phase symmetry, and the light receiving element as a reference.

FIG. 16 is an explanatory configuration diagram explaining a light emitting element and a light receiving element of an example based on the fourth example by applying specific numerical values.

FIG. 17 is a characteristic curve showing the relationship between the inclination angle of the density detection sensor with respect to the surface of the image carrier and the sensor output voltage when a light emitting element and a light receiving element having narrow directivity are used.

FIG. 18 is a characteristic showing the relationship between the toner adhesion amount on the image carrier and the output voltage from the light receiving element when the planes including both the optical axes of the light emitting element and the light receiving element are arranged at an angle ψ with respect to the normal line. It is a diagram.

FIG. 19 is a characteristic diagram showing a relationship between an output voltage of a conventional light receiving element and a toner adhesion amount on an image carrier.

[Explanation of symbols]

1 Photoconductor drum 4C Transfer belt 62 Fresnel lens φ1 Directivity that is the spread of the luminous flux of the light emitting element φ2 Directivity that is the spread of the received luminous flux of the light receiving element d Diameter of the light receiving and emitting surface of the light receiving and emitting element D1 Light emitting surface of the light receiving element Diameter D2 diameter of the light receiving surface of the light receiving element ψ angle between the normal line and the optical axis plane ρ optical path length connecting the center of the light emitting surface and the center of the light receiving surface

Claims (5)

[Claims] 1. An image provided with a toner density detecting device for irradiating light of a light emitting element on a toner pattern image formed on an image carrier and detecting the reflected light by a light receiving element to control an image forming condition. In the forming apparatus, the light emitting element and the light receiving element both have directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect is on the surface of the image carrier or in the vicinity of the surface of the carrier. Where the optical axis plane including both optical axes of the light emitting element and the light receiving element is inclined at a predetermined angle with respect to a normal line from the surface of the carrier passing through the intersection, An image forming apparatus comprising: a light receiving element. 2. A toner concentration detecting device for irradiating a toner pattern image formed on an object to be measured with light from a light emitting element and detecting the reflected light with a light receiving element, wherein both the light emitting element and the light receiving element are Both the light emitting element and the light receiving element have directivity, and the point where the optical axes of the light emitting element and the light receiving element intersect is on the surface of the object to be measured or in the vicinity of the surface of the carrier. An optical axis plane including an axis is characterized in that the light emitting element and the light receiving element are arranged at an angle inclined by a predetermined angle with respect to a normal line from the surface of the measured object passing through the intersection. Toner concentration detecting device. 3. The directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the angle formed by the normal and the plane of the optical axis is set. ψ, the diameter of the light emitting surface of the light receiving element is D1, the diameter of the light receiving surface of the light receiving element is D2, and the optical path length connecting the center of the light emitting surface and the center of the light receiving surface is ρ, The light emitting element and the light receiving element are arranged so as to satisfy either ψ> φ1 + tan ~ ¹ (D2 / 2ρ) or ψ> φ2 + tan ~ ¹ (D1 / 2ρ). The image forming apparatus according to claim 1. 4. The directivity which is the spread of the luminous flux of the light emitting element is φ1, the directivity which is the spread of the received luminous flux of the light receiving element is φ2, and the angle between the normal and the plane of the optical axis is set. ψ, the diameter of the light emitting surface of the light receiving element is D1, the diameter of the light receiving surface of the light receiving element is D2, and the optical path length connecting the center of the light emitting surface and the center of the light receiving surface is ρ, The light emitting element and the light receiving element are arranged so as to satisfy either ψ> φ1 + tan ~ ¹ (D2 / 2ρ) or ψ> φ2 + tan ~ ¹ (D1 / 2ρ). The toner concentration detecting device according to claim 2. 5. The light emitting element and the light receiving element are unitized by a supporting member so that both optical axes of the light emitting element and the light receiving element are included in the same plane, and at least one of the light emitting element and the light receiving element is provided in front of the light emitting element and the light receiving element. The image forming apparatus according to claim 1, 2, 3, or 4, wherein a condensing optical element is provided in the.