JP3364533B2 - Color density sensor and image forming apparatus using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color density sensor suitable for use in an image forming apparatus such as a copying machine or a printer capable of forming an image in full color.

[0002]

2. Description of the Related Art A copying machine for forming an image with toner,
In image forming apparatuses such as printers, toner is usually attached to an electrostatic latent image formed on a photosensitive drum, and an image is formed by transferring the attached toner to plain paper. There is. Conventionally, only black toner has been used as toner, but recently, cyan (C
y), magenta (Mg), and yellow (Ye) color toners are used to form a full-color image.

In such an image forming apparatus, when the remaining amount of toner becomes small, the density of the formed image decreases, so that the density of the toner adhering to the photosensitive drum is detected. . In an image forming apparatus using black toner, for example, when a predetermined number of copying operations are performed, the black toner is attached onto the non-image area of the photosensitive drum, and the black toner is irradiated with light from a light source. The reflected light is received by a light receiving element such as a photodiode, and the amount of reflected light from the black toner received by the light receiving element is measured. When the amount of black toner attached to the photoconductor drum is large, the amount of reflected light from the black toner is small, and the output current of the light receiving element decreases. Conversely, when the amount of black toner attached is small, the amount of black toner The amount of reflected light is large and the output current of the light receiving element increases. Then, when the output current from the light receiving element becomes equal to or higher than a predetermined value, it is informed that the toner density needs to be replenished because the remaining toner amount is low. It is like this.

Also in the case of an image forming apparatus using color toners, similarly, cyan, magenta, and yellow toners are sequentially adhered to the photosensitive drum so that the respective color toners captured by the light receiving element are changed. The density of each color toner is detected based on the output current of the light receiving element corresponding to the amount of reflected light.

[0005]

FIG. 9 is a graph showing the spectral reflectances of the black toner and the surface of the photosensitive drum. Spectral reflectance of black toner is 400-700
It has a low constant value for light having a wavelength of nm. On the other hand, the spectral reflectance of the surface of the photosensitive drum is 400
It has a large constant value for light with a wavelength of up to 700 nm. Therefore, the spectral reflectance of the surface of the photosensitive drum and the spectral reflectance of the black toner are greatly different, and in a low density state where a small amount of black toner adheres to the surface of the photosensitive drum, due to the influence of the surface of the photosensitive drum, While the amount of reflected light tends to increase, in the high-concentration state where a large amount of black toner adheres to the surface of the photoconductor drum, there is almost no increase in the amount of reflected light due to the effect of the photoconductor drum surface. The amount of reflected light of is reduced. As a result, the amount of light received by the light receiving element greatly changes in accordance with the amount of black toner attached to the surface of the photoconductor drum, and the density of the black toner attached to the surface of the photoconductor drum can be accurately detected.

On the other hand, in the case of color toner,
The amount of reflected light from each color toner may not be accurately captured by the light receiving element.

FIG. 10A is a graph showing the spectral reflectance of cyan toner, FIG. 10B is a graph showing the spectral reflectance of magenta toner, and FIG. 10C is a graph showing the spectral reflectance of yellow toner. Is. The cyan toner has a low spectral reflectance with respect to red light having a wavelength of 600 nm or more, and the magenta toner has a spectral reflectance of 500 to 6 wavelengths.
It is low for green light of about 00 nm. Further, the spectral reflectance of the yellow toner is low for blue light having a wavelength of about 500 nm or less.

As described above, the characteristics of the spectral reflectance of each color toner are different from each other. On the other hand, since the spectral reflectance of the surface of the photoconductor drum is a high constant value, the density of each color toner may be different depending on the wavelength of the light irradiated to each color toner attached to the surface of the photoconductor drum. It may not be detected accurately.

For example, in the case of cyan toner, which has a large spectral reflectance for light having a wavelength of about 600 nm or less, 60
With light having a wavelength of about 0 nm or less, the difference from the spectral reflectance on the surface of the photosensitive drum becomes small. When the amount of reflected light from the surface of the photoconductor drum is equal to the amount of reflected light from the cyan toner for each wavelength, the light of each wavelength is reflected on the surface of the photoconductor drum as indicated by the broken line in FIG. It is considered that the average reflectance of the spectral reflectance of 1 and the spectral reflectance of cyan toner is obtained. Therefore, for light with a wavelength of 600 to 700 nm, when the amount of cyan toner adhering to the surface of the photoconductor drum increases, the amount of light reflected from the cyan toner greatly decreases in accordance with the amount of cyan toner, but with a wavelength of 600 nm.
Even if the amount of cyan toner on the surface of the photosensitive drum is large, the amount of reflected light does not decrease significantly for light of a certain level or less. As a result, there is a problem that the amount (density) of the cyan toner attached to the photoconductor drum cannot be accurately measured with light having a wavelength of 400 to 600 nm.

Similarly, wavelengths 400-500 nm and 6
With the light of 00 to 700 nm, the density of the magenta toner adhered to the surface of the photoconductor drum cannot be measured with high accuracy, and with the light of the wavelength of 500 to 700 nm, the density of the yellow toner adhered to the surface of the photoconductor drum. Cannot be measured with high accuracy.

The present invention solves such a problem, and an object thereof is to provide a color density sensor capable of measuring the density of color toner adhering to the surface of a photoconductor with high accuracy, and a color density sensor using the same. Another object of the present invention is to provide such an image forming apparatus.

[0012]

The color density sensor of the present invention is a color density sensor for measuring the toner density of each of cyan, magenta and yellow. A light source for irradiating light, each light receiving element that receives reflected light or transmitted light from each toner, and detects the amount of received light in each wavelength region of blue, red, and green, and a light receiving element corresponding to the wavelength region of red Of the light receiving element corresponding to the blue wavelength region and the light receiving element corresponding to the green wavelength region. The toner density of cyan is determined based on the ratio calculated by the first calculating means and the second calculating means for calculating the ratio to the detected output, and the cyan toner density is determined based on the ratio calculated by the second calculating means. It is characterized in comprising a determination means for each of the toner concentration of printer and yellow, the object is achieved.

Further, in the color density sensor of the present invention,
The first calculation means obtains a ratio obtained by dividing the detection output of the light receiving element corresponding to the green wavelength range by the detection output of the light receiving element corresponding to the red wavelength range, and the second calculation means determines the ratio to the green wavelength range. The ratio obtained by dividing the detection output of the corresponding light receiving element by the detection output of the light receiving element corresponding to the blue wavelength region is obtained.

Further, in the color density sensor of the present invention,
When the respective toner densities of cyan, magenta, and yellow are optimally set, a storage unit for storing the ratio calculated by the first calculation unit and the ratio calculated by the second calculation unit is provided, and each toner density is provided. Is stored in the storage means, the respective ratios are obtained again by the first and second calculation means, and the determination means is obtained by the first calculation means in the storage means. The toner density of cyan is determined based on the calculated ratio and the ratio calculated again by the first calculating device, and the cyan toner density is determined by the ratio calculated by the second calculating device and the ratio calculated again by the second calculating device in the storage device. Based on this, the toner densities of magenta and yellow are determined.

The image forming apparatus of the present invention is an image forming apparatus in which an image is formed on a photoconductor with color toner, and the light emitted from the light source of the color density sensor adheres on the photoconductor. It is characterized in that it is provided so as to be reflected by the color toner and received by each light receiving element, whereby the above object is achieved.

Further, in the image forming apparatus of the present invention, when determining the toner density of cyan, each light receiving element corresponding to each wavelength region of red and green and the first calculation means are selected, and magenta and yellow are selected. When determining the respective toner densities, the respective light receiving elements and the second calculation means corresponding to the respective blue and green wavelength regions are selected.

[0017]

In the color density sensor of the present invention, the reflected light or transmitted light from each of the cyan, magenta, and yellow toners is received by each light receiving element. The respective light receiving elements have respective spectral sensitivities set in different wavelength regions, and respectively output signals corresponding to the amount of received light.
Then, the ratio of the signals output from each light receiving element is calculated by the calculating means. Since the wavelength regions of the light received by the respective light receiving elements are different from each other, the ratio of the output signal corresponding to the amount of light received by each light receiving element calculated by the calculation means becomes large. Therefore, the color density of the object to be measured can be measured with high accuracy based on the calculation result of the calculation means.

The calculation results of the first and second calculation means are selectively stored in the storage section, and thereafter, the calculation results of the first and second calculation means repeatedly executed are stored in the storage section. By comparing with the calculation result, it is possible to measure the change with time of the color density of the measured object.

Since the spectral sensitivity of the light receiving element is in the wavelength region of red light, green light, and blue light which are the three primary colors of light, the densities of cyan, magenta, and yellow colors can be measured. it can. When measuring the color density of cyan, a light-receiving element with spectral sensitivity in the wavelength range of red light and green light is selected.When measuring the color density of magenta and yellow, the wavelengths of green light and blue light are selected. A light receiving element having a spectral sensitivity in the area is selected.

The color density sensor of the present invention is preferably used in an image forming apparatus such as a copying machine or a printer which forms an image with cyan toner, magenta toner and yellow toner. That is, when measuring the density of cyan toner, a light receiving element whose spectral sensitivity is in the wavelength region of red light and green light is used, and the ratio of the amount of reflected light from the cyan toner received by each light receiving element is used. The density of the cyan toner is measured based on Similarly, in the case of magenta toner and yellow toner, based on the ratio of the amount of reflected light from each color toner received by the light receiving element having a spectral sensitivity in each wavelength region of green light and blue light, respectively, The density of the color toner is measured.

[0021]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 is a schematic perspective view of a photosensitive drum and its vicinity in a full-color copying machine which is an example of an image forming apparatus equipped with a color density sensor of the present invention.
Is a schematic side view thereof.

The color density detecting apparatus of the present invention comprises a halogen lamp 20 as a light source, which is disposed opposite to an image non-forming area provided at one end of the surface of the photosensitive drum 10, and the halogen lamp 20. The light receiving unit 30 is arranged so as to receive the light that is irradiated and reflected on the surface of the photosensitive drum 10. Photoconductor drum 10
Rotate in the direction indicated by arrow A. In the image non-forming area of the photoconductor drum 10, for example, when a predetermined number of images are formed, a square cyan (Cy)
The toner pattern 12, the magenta (Mg) toner pattern 13, and the yellow (Ye) toner pattern 14 are
Each is formed in order.

FIG. 3 is a block diagram of the control system of the color density sensor of the present invention. As shown in FIG.
0 indicates three light receiving elements 31, 3 having different spectral sensitivities from each other.
It has 2, 33. Each light receiving element 31, 32, 33
Is cyan (Cy), magenta (Mg), yellow (Y
e) complementary colors of red (R), green (G),
Each photodiode is configured by a blue (B) filter whose light receiving surface is covered.

FIG. 4 is a graph showing the spectral sensitivity characteristics of the light receiving elements 31, 32, 33. The light receiving element 31 is shown in FIG.
4A, it has sensitivity to red light having a wavelength of 600 nm, and the light receiving element 32 has spectral sensitivity to green light having a wavelength of 530 nm, as shown in FIG. 4B. As shown in FIG. 4C, the light receiving element 33 is
It has spectral sensitivity to blue light with a wavelength of 60 nm.

As shown in FIG. 3, each light receiving element 31, 3
The outputs of 2, 33 are amplified by amplifiers 34, 35, 36, respectively, and output to analog / digital (A / D) converters 37, 38, 39, respectively. Each A / D
The converters 37, 38, 39 convert the analog signals output from the amplifiers 34, 35, 36 into digital signals. The output IR of the A / D converter 37 obtained by digitally converting the output of the light receiving element 31 having sensitivity to red light is given to the first division circuit 41, and the output IR of the light receiving element 32 having sensitivity to green light. The output IG of the A / D converter 38 obtained by digitally converting the output is given to the first division circuit 41 and the second division circuit 42, respectively. The output IB of the A / D converter 39 obtained by digitally converting the output of the light receiving element 33 having sensitivity to blue light is given to the second division circuit 42.

The first division circuit 41 calculates the ratio (IG / IR) of the output IG of the A / D converter 38 to the output IR of the A / D converter 37. Similarly, the second division circuit 42
Calculates the ratio (IB / IG) of the output IG of the A / D converter 38 and the output IB of the A / D converter 39.

First division circuit 41 and second division circuit 42
A storage unit 43 for selectively storing the respective outputs IG / IR and IB / IG is connected to, and a comparison operation unit 44 to which the respective outputs IG / IR and IB / IG are given is connected. . The storage unit 43 is composed of, for example, an EEPROM, and is set to store the outputs of the first division circuit 41 and the second division circuit 42 when predetermined storage is to be performed. The storage unit 43 stores the first division circuit 41 and the second division circuit when optimum color reproducibility is obtained, for example, when the color copying machine is maintained or when the color copying machine is reinforced with toner. The output of the arithmetic circuit 42 is stored.

First division circuit 41 and second division circuit 42
The output of is output to the comparison calculation unit 44, except when it is stored in the storage unit 43. Storage unit 4
The outputs of the first division circuit 41 and the second division circuit 42 stored in 3 are synchronized with each other when the outputs of the division circuits 41 and 42 are output to the comparison operation unit 44. 44
It is designed to be output to. The comparison calculation unit 44 includes each division circuit 4 based on the output of each light receiving element 31, 32, 33.
The outputs of 1 and 42 are compared with the outputs of the division circuits 41 and 42 stored in the storage unit 43, and a predetermined signal is output based on the comparison result.

Each light receiving element 31, 32, 33 and each division circuit 41, 42 in such a color density sensor.
The relationship of the outputs will be described. Each light receiving element 31, 3
The output characteristics of Nos. 2 and 33 were examined using a plurality of standard color chips manufactured by Nippon Color Research Institute Co., Ltd. (based on JIS Z8721-1958). As the color chart, one having a constant hue and lightness but different saturation was selected.

In order to check the output characteristics of each of the light receiving elements 31, 32 and 33 for cyan (Cy) toner, hue 5B is used.
G, lightness 4, and a plurality of color charts having different saturations (color depths) only are used, and the light from the halogen lamp 20 is reflected on each color chart so that each light receiving element 31, 32, 33 receives. Upon receiving light, the output from each of the light receiving elements 31, 32, and 33 has the result shown in FIG.

As shown in FIG. 5D, the light receiving element 31 sensitive to red light has an output current value IR as the saturation (density) of cyan (Cy) increases (darkens).
Is smaller, the light receiving element 32 is sensitive to green light and the light receiving element 33 is sensitive to blue light.
As shown in FIGS. 5E and 5F, cyan (C
As the saturation (density) of y) increases, the output current value I
G and IB are getting larger. However, the respective changes in the output current values IR, IG and IB of the respective light receiving elements 31, 32 and 33 are small. For example, while the output current of the light receiving element 31 at the saturation 8 is 0.018 μA, The output current of the light receiving element 31 at a degree N (achromatic color) is 0.025 μA, and the ratio of both (0.018 /
0.025) is only 1 / 1.38.

Each division circuit 41 and 4 in this case
The output result of No. 2 is shown in FIG. FIG. 6G shows the output (IG / I) of the first division circuit 41 indicating the ratio of red light and green light.
FIG. 6 (h) shows the output (IB / IG) of the second division circuit 42 indicating the ratio of green light and blue light. When the density (saturation) of cyan Cy increases, the output current IR of the light receiving element 31 sensitive to red light decreases, whereas the output current IG of the light receiving element 32 sensitive to green light increases. Then, the output (IG / IR) of the first division circuit 41 increases (see (g) in FIG. 6). The output of the first division circuit 41 is 1.44 when the saturation is 8, while it is 0.80 when the saturation is N (achromatic color).
The rate of increase in the output of the first division circuit 41 is 1.80 / 1.

Thus, the output of the first division circuit 41 (I
Cyan (Cy) density (saturation) based on G / IR
Can be measured.

Similarly, for magenta (Mg) toner, a plurality of color chips having a hue of 10 P and a lightness of 4 and different in saturation (color density) are used, and the outputs of the division circuits 41 and 42 are used. The results were measured. The results are shown in Fig. 7. FIG. 7 (i) shows a first division circuit 4 showing the ratio of red light to green light.
1 output (IG / IR) is shown in FIG. 7 (j).
Indicates the output (IB / IG) of the second division circuit 42 indicating the ratio of green light and blue light. When the density (saturation) of magenta (Mg) increases, the output IG of the light receiving element 32 sensitive to green light decreases, whereas the output current IR and the blue light of the light receiving element 31 sensitive to red light decrease. Since the output current IB of the light receiving element 33 having sensitivity to increases, as shown in (i) of FIG. 7, the output (IG / IR) of the first division circuit 41 decreases and As shown in j), the output (IB / IG) of the second division circuit 42 increases. The rate of change of the second division circuit 42 is the first division circuit 4
The rate of change is greater than 1, and therefore the magenta (Mg) concentration can be measured based on the output (IB / IG) of the second division circuit 42.

Similarly, with respect to the yellow (Ye) toner, a plurality of color chips having hue 5Y and lightness 8 and different in saturation (color density) are used, and each of the division circuits 41 and 42 has a color chart. The output result was measured. The results are shown in Fig. 8. FIG. 8K shows the first division circuit 4 indicating the ratio of red light and green light.
1 output (IG / IR) is shown in FIG. 8 (m).
Indicates the output (IB / IG) of the second division circuit 42 indicating the ratio of green light to blue light. When the density (saturation) of yellow (Ye) increases, the output current IB of the light receiving element 33 sensitive to blue light decreases, while the output current IR and the green color of the light receiving element 31 sensitive to red light decrease. Since the output current IG of the light receiving element 32 having light sensitivity is increased, the output (IG / IR) of the first division circuit 41 is decreased and the output current IG of FIG. (M)
As shown in, the output of the second division circuit 42 (IB / IG)
Is reduced. The change rate of the second division circuit 42 is larger than that of the first division circuit 41, and the density of yellow (Ye) is measured based on the output (IB / IG) of the second division circuit 42. You can

In the color copying machine provided with the color density detecting device of the present invention, for example, when a predetermined number of images are formed and when each color toner is replenished,
A rectangular cyan toner pattern 12, a magenta toner pattern 13, and a yellow toner pattern 14 are sequentially formed in the image non-forming area of the photosensitive drum 10. Then, by the rotation of the photosensitive drum 10,
Light is emitted from the halogen lamp 20 to the toner patterns 12 to 14, and the light reflected by the toner patterns 12 to 14 is sequentially received by the light receiving unit 30.

Each light receiving element 31, 32, 33 of the light receiving section 30.
Outputs a predetermined current value on the basis of the amount of light reflected from the cyan toner pattern 12, and each amplifier 34, 35, 36
A / D converters 37, 38, 3 after being amplified by
It is converted into a digital signal by 9. First division circuit 41
And the second division circuit 42 includes the A / D converters 37, 3
An output ratio IG / IR between the pair of light receiving elements 31 and 32 and an output ratio IB / IG between the pair of light receiving elements 32 and 33 are calculated based on the outputs IR, IG, and IB of the eight and thirty-nine. Then, regarding the cyan toner pattern 12,
The calculation result IG / IR of the first division circuit 41 is cyan (C
y) It is output to the comparison calculation unit 44 or the storage unit 43 as the calculation result regarding the toner.

The storage unit 43 stores the output of the first division circuit 41 immediately after the cyan toner is replenished, and the comparison operation unit 44 stores a predetermined number of other images, The output of the first division circuit 41 is output. And
In synchronization with the output from the first division circuit 41 to the comparison calculation unit 44, the storage value regarding the cyan toner is output from the storage unit 43 to the comparison calculation unit 44. Then, the comparison calculation unit is
The output of the division circuit 41 is compared with the stored value of the cyan toner stored in the storage unit 43. If the difference between the two is greater than or equal to a predetermined value, the density of the cyan toner decreases. If so, an appropriate alarm is issued to replenish the cyan toner.

Similarly, when the magenta toner pattern 13 on the photosensitive drum 10 is irradiated with the light from the halogen lamp 20 and the reflected light is received by the light receiving section 30, the division circuits 41 and 42 respectively. , Each light receiving element 31, 32, 3
Based on the outputs of the A / D converters 37, 38, 39 corresponding to 3, the respective division circuits 41 and 42 operate. Then, for the magenta toner pattern 13, the calculation result IB / IG of the second division circuit 42 is selectively output to the storage unit 43 and the comparison calculation unit 44 as the calculation result for the magenta (Mg) toner.

The calculation result of the second division circuit 42 stored in the storage unit 43 immediately after the magenta toner is replenished is calculated by the second division circuit 42 immediately after the predetermined number of images are formed. The result is compared with the comparison calculation unit 44, and when the two values are different from each other by a predetermined value or more, it is determined that the density of the magenta toner is low, and an appropriate alarm for replenishing the magenta toner is issued.

Further, regarding the yellow toner pattern 14, the storage unit 43 also stores the calculation result I of the second division circuit 42.
B / IG is selectively output to the storage unit 43 and the comparison calculation unit 44 as the calculation result regarding the yellow (Ye) toner.

The calculation result of the second division circuit 42 stored in the storage unit 43 immediately after the yellow toner is replenished is calculated by the second division circuit 42 immediately after the predetermined number of images are formed. The result is compared with the comparison calculation unit 44, and when the two values are different from each other by a predetermined value or more, it is determined that the density of the yellow toner has decreased, and an appropriate alarm for replenishing the yellow toner is issued.

In the above embodiment, the density of each color toner is measured immediately after a predetermined number of images are formed. However, for example, immediately after the color copying machine is powered on, The density of each color toner may be measured. Further, although the storage unit 43 stores the calculation result of the first division circuit 41 or the second division circuit 42 immediately after each color toner is replenished, the color copying machine is maintained. Immediately after that, it may be stored in the storage unit 43.

Although the halogen lamp 20 is used as the light source, a tungsten lamp or a fluorescent lamp having a spectrum in the wavelength range of 400 to 700 nm may be used.

Further, although the color copying machine has been described in the above embodiment, the present invention can be applied to an image forming apparatus such as a color printer or a color facsimile.

[0047]

As described above, the color density sensor of the present invention measures the color density of the object to be measured based on the ratio of the output signals of the light receiving elements having the spectral sensitivity in different wavelength regions. Therefore, the color density of the measured object can be accurately measured. In particular, even the density of each color toner attached on the photoconductor in an image forming apparatus such as a copying machine or a printer can be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a photosensitive drum and its vicinity in a full-color copying machine that is an image forming apparatus equipped with a color density sensor of the present invention.

FIG. 2 is a schematic side view thereof.

FIG. 3 is a block diagram of a control system of the color density sensor of the present invention.

FIG. 4 is a graph showing the spectral sensitivity characteristics of each light receiving element used in the color density sensor of the present invention.

FIG. 5 is a graph showing an output current with respect to cyan toner of each light receiving element used in the color density sensor of the present invention.

FIG. 6 is a graph showing the calculation result of each division circuit used in the color density sensor of the present invention with respect to the density of cyan toner.

FIG. 7 is a graph showing the calculation result of each division circuit used in the color density sensor of the present invention with respect to the density of magenta toner.

FIG. 8 is a graph showing the calculation result of each division circuit used in the color density sensor of the present invention with respect to the density of yellow toner.

FIG. 9 is a graph showing the spectral reflectance with respect to the wavelength of the photosensitive drum surface and the black toner in the copying machine.

10A is a graph showing the spectral reflectance of the photosensitive drum surface of the copying machine with respect to the wavelength of cyan toner, and FIG. 10B is the spectral reflectance of the photosensitive drum surface of the copying machine with respect to the wavelength of magenta toner. Graph,
(C) is a graph showing the spectral reflectance with respect to the wavelength of the photosensitive drum surface and the magenta toner in the copying machine.

[Explanation of symbols]

10 Photoconductor toner 12 Cyan toner pattern 13 magenta toner pattern 14 Yellow toner pattern 20 halogen lamp 30 Light receiving part 31 Light receiving element 32 light receiving element 33 Light receiving element 41 First Division Circuit 42 Second division circuit 43 storage 44 Comparison operation unit

Continuation of front page (56) Reference JP-A-5-5655 (JP, A) JP-A-5-118924 (JP, A) JP-A-58-186022 (JP, A) JP-A-5-333650 (JP , A) JP-A-3-174173 (JP, A) JP-A-3-110450 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01J 3/46-3/51 G01N 21/00-21/01 G01N 21/17-21/61 G03G 15/01 G03G 15/08 115 G03G 21/00 370 H04N 9/04-9/11

Claims (5)

(57) [Claims] 1. A color density sensor for measuring the toner density of each of cyan, magenta, and yellow, wherein the light source irradiates each of the cyan, magenta, and yellow toners with light, and the reflected light from each toner. Or it receives the transmitted light and outputs blue, red,
First, a ratio of each light receiving element that detects the amount of received light in each of the green and green wavelength regions and the ratio between the detection output of the light receiving element corresponding to the red wavelength region and the detection output of the light receiving element corresponding to the green wavelength region
Second calculating means for calculating a ratio between the detection output of the light receiving element corresponding to the blue wavelength region and the detection output of the light receiving element corresponding to the green wavelength region
Judgment for determining the toner density of cyan based on the ratio calculated by the calculating means and the first calculating means, and judging for judging the toner density of each of magenta and yellow based on the ratio calculated by the second calculating means. A color density sensor comprising: 2. The first calculation means obtains a ratio obtained by dividing the detection output of the light receiving element corresponding to the green wavelength region by the detection output of the light receiving element corresponding to the red wavelength region, and the second calculation means is The color density sensor according to claim 1, wherein a ratio obtained by dividing a detection output of the light receiving element corresponding to the green wavelength region by a detection output of the light receiving element corresponding to the blue wavelength region is obtained. 3. A storage unit for storing the ratio calculated by the first calculation unit and the ratio calculated by the second calculation unit when the respective toner densities of cyan, magenta, and yellow are optimally set. After storing the respective ratios when the respective toner densities are optimally set in the storage means, the respective ratios are again obtained by the first and second calculation means, and the determination means is the first means in the storage means. The toner density of cyan is determined based on the ratio obtained by the calculating means and the ratio obtained again by the first calculating means, and the ratio obtained by the second calculating means in the storage means and again by the second calculating means. The color density sensor according to claim 1, wherein the toner density of each of magenta and yellow is determined based on the obtained ratio. 4. An image forming apparatus in which an image is formed on a photoconductor with color toner, wherein the color density sensor according to claim 1 is a color in which light emitted from the light source adheres to the photoconductor. An image forming apparatus, which is provided so as to be reflected by toner and received by each light receiving element. 5. When determining the toner densities of cyan, each light receiving element corresponding to each wavelength region of red and green and the first calculating means are selected to determine the toner densities of magenta and yellow respectively. 5. The image forming apparatus according to claim 4, wherein each light receiving element corresponding to each wavelength region of blue and green and the second calculation unit are selected.