JP3515246B2 - Density detection apparatus and density detection method used in image forming apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in an image forming apparatus for forming an image by an electrophotographic process, such as an electrostatic copying machine, and in order to keep the formed image in high quality, it is charged. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a density detecting device and a density detecting method for outputting density data used when adjusting image forming conditions such as an amount, an exposure amount, and a developing bias.

[0002]

2. Description of the Related Art In an electrostatic copying machine, a copied image is formed as follows. That is, the actual document placed on the document table is illuminated and scanned. The reflected light of the actual document is guided to the photosensitive drum that is rotated in synchronization with the illumination scanning. As a result, the photosensitive drum is exposed. The surface of the photosensitive drum before exposure is uniformly charged by the charger. Then, an electrostatic latent image corresponding to the actual original image is formed on the surface of the photosensitive drum by the selective charge removal by exposure.

The formed electrostatic latent image is developed into a toner image by a developing device to which toner is supplied from a toner hopper. This toner image is transferred to the copy sheet by corona discharge in the transfer corona discharger. The copy sheet after the transfer of the toner image is guided to the fixing device, and the toner is fixed on the copy sheet to complete the copy. By the way, in order to stably obtain a high-quality image in the electrostatic copying machine, the image forming conditions such as the exposure amount and charge amount of the photosensitive drum, the developing bias, and the toner amount to be replenished to the developing device are set. It needs to be adjusted appropriately.

The adjustment of the image forming conditions is performed at predetermined intervals such as during maintenance. When adjusting the image forming conditions, a pseudo original (density reference original) such as white or black placed in an area other than the illumination scanning area of the actual original is tentatively illuminated, and the toner image corresponding to the pseudo original is lit. Is formed. At this time, the exposure amount, the surface potential, the toner image density on the surface of the photosensitive drum, and the like are detected, and the image forming conditions are automatically adjusted based on the detection result. Specifically, for example, when a pure white pseudo document is illuminated and a toner image is formed, if so-called fogging is detected based on the detected toner image density, the exposure amount is increased. Also, when a black pseudo document is illuminated and a toner image is formed, if it is determined that the density is insufficient based on the detection result of the toner image density, the toner is automatically supplied from the toner hopper to the developing device. It

In order to detect the toner image density on the surface of the photoconductor drum, a reflection type photosensor composed of a pair of a light emitting element and a light receiving element arranged facing the photoconductor drum is generally applied. That is, a predetermined amount of irradiation light is emitted from the light emitting element to the photosensitive drum, and density data corresponding to the reflected light amount is output from the light receiving element. Since the amount of reflected light corresponds to the density of the toner image on the surface of the photosensitive drum, the density of the toner image on the surface of the photosensitive drum can be detected based on the density data.

By the way, at the time of initial setting immediately after the manufacture of the copying machine, there are two types of light amount to be emitted from the light emitting element of the reflection type photosensor toward the photosensitive drum, for example, a low density irradiation light amount and a high density irradiation light amount. The irradiation light amount of is set. The low-concentration irradiation light amount is the amount of light to be emitted from the light emitting element toward the photosensitive drum when detecting fogging. Further, the high-concentration irradiation light amount is the light amount that should be irradiated when solid black is detected.

The reason why the amount of light to be irradiated is changed when detecting fog and when detecting solid black is as follows. That is, when detecting fog, the pseudo original on which a pure white image is formed is illuminated, so that toner hardly adheres to the photosensitive drum. Therefore, the amount of light received by the light receiving element is relatively high. On the other hand, the light receiving element has a property that its output is saturated when the amount of received light increases. Therefore, the amount of light to be emitted when detecting fogging needs to be relatively low in order to suppress the amount of light reflected from the photosensitive drum.

Further, when solid black is detected, since a pseudo original on which a black image is formed is illuminated, a large amount of toner adheres to the photosensitive drum. Therefore, most of the light emitted from the light emitting element is absorbed by the toner on the surface of the photosensitive drum, so that the amount of light received by the light receiving element is relatively low. On the other hand, the light receiving element cannot detect a subtle change in the received light amount when the received light amount is small. Therefore, the amount of light to be emitted when detecting solid black needs to be relatively high in order to increase the amount of reflected light.

FIG. 7 is a diagram showing the relationship between the toner image density on the surface of the photosensitive drum and the density data output from the reflective photosensor when the low density set light amount is set. Referring to FIG. 7, the density data output from the reflective photosensor relatively linearly changes in the low density area E1, whereas the high density area E2 changes.
Then it hardly changes. That is, the reflection type photosensor can detect the density change in the low density region E1 with high accuracy when the low density set light amount is set. Therefore, fogging can be detected with high accuracy.

FIG. 8 is a diagram showing the relationship between the toner image density on the surface of the photosensitive drum and the density data output from the reflection type photosensor when the high density set light amount is set. Referring to FIG. 8, the density data output from the reflective photosensor hardly changes in the low density area E1, but relatively linearly changes in the high density area E2. That is, the reflection type photosensor can detect the density change in the high density region E2 with high accuracy when the high density set light amount is set. Therefore, solid black can be detected with high accuracy.

[0011]

The constant low-density setting light amount and the high-density setting light amount set at the time of initial setting are also utilized in the image forming condition adjusting process performed every predetermined period. However, the state around the reflective photosensor and the state of the copying machine are different between the initial setting and the image forming condition adjustment processing. Therefore, the toner image density cannot always be accurately detected even if the constant set light amount obtained during the initial setting is applied during the image forming condition adjustment processing. Therefore, the image forming conditions may not be properly adjusted, and a high quality image may not be obtained.

An object of the present invention is to use a high density light amount characteristic curve obtained at the time of initial setting at the time of density detection,
It is an object of the present invention to provide a density detecting device capable of accurately detecting the density of a toner image. Another object of the present invention is to provide a density detection method capable of accurately detecting the density of a toner image while using the high density light amount characteristic curve obtained at the time of initial setting during density detection.

[0013]

According to a first aspect of the present invention for achieving the above object, a photosensitive member on which an electrostatic latent image is formed, and an electrostatic latent image formed on the photosensitive member are toner particles. A density detecting device for detecting the density of a toner image formed by an image forming apparatus including a developing device for developing an image, wherein light is radiated toward the photoconductor to change the amount of light reflected from the photoconductor. A density sensor that outputs corresponding density data, in which the light amount of the light emitted toward the photoconductor is variable, and as the light amount of the light emitted toward the photoconductor at the time of initial setting. The first low-density light amount for detecting the toner image density in the low-density region is set, and further, the density of the toner image of which the density is known is detected by the density sensor. First to obtain the light intensity characteristic curve A low-density curve acquisition unit and a first high-density light amount for detecting the toner image density in a high-density region as the light amount of the light irradiated toward the photoconductor at the time of initial setting, and further, Is detected by the density sensor to obtain a high density light quantity characteristic curve of the density sensor, and high density curve acquisition means is provided for the first density data in the first low density light quantity characteristic curve. First reference density acquisition means for acquiring the corresponding toner image density as the first reference density, and first for acquiring density data corresponding to the first reference density in the high density light amount characteristic curve as the first correction reference data. Correction reference data acquisition means, low density light amount acquisition means for obtaining a second low density light quantity for detecting a toner image in a low density area at the time of density detection, and density detection In the above, the high-density light amount acquisition means for obtaining the second high-density light amount for detecting the toner image in the high-density region, and the second low-density light amount as the light amount of the light radiated toward the photoreceptor. Set
Further, a second low density curve acquisition unit for acquiring a second low density light quantity characteristic curve of the density sensor by detecting the density of the toner image of known density by the density sensor, and the second low density light quantity characteristic. In the curve, as a second reference density acquisition means for acquiring the toner image density corresponding to the second density data substantially equal to the first density data as the second reference density, and as the light amount of the light irradiated toward the photoconductor. By setting the second high density light amount and further detecting the toner image of the second reference density by the density sensor, the density data output by the density sensor at this time is used as the second correction reference data. When the second correction reference data acquisition unit for acquiring and the second high density light amount are set and the toner image density is detected by the density sensor,
Density data correction means for correcting the density data output by the density sensor based on the first correction reference data and the second correction reference data and outputting corrected density data, and the corrected density data for the high density A density detecting device, comprising: a density acquisition unit that acquires a toner image density by applying the light intensity characteristic curve. Contract
The invention described in claim 2 is a pseudo original as a density reference original.
And a light source for illuminating this pseudo original and controlling this light source.
Control circuit that changes the exposure amount by
Include the above light source to illuminate the pseudo document and
When the light source is controlled by the control circuit to change the exposure amount,
In addition, the reflected light from the pseudo original is guided to the photoconductor.
The toner image of the above-mentioned density is formed on the photoreceptor by
It is designed to be formed in
It is the concentration detection device according to 1.

According to a third aspect of the invention, an image forming apparatus includes a photoconductor on which an electrostatic latent image is formed, and a developing device for developing the electrostatic latent image formed on the photoconductor into a toner image. A method for detecting the density of a toner image by using a density sensor that irradiates a variable amount of light toward the photoconductor and outputs density data corresponding to the amount of light reflected from the photoconductor In the initial setting, the first low-density light amount for detecting the toner image density in the low-density area is set as the light amount of the light emitted from the density sensor toward the photoconductor. Obtaining a first low density light amount characteristic curve of the density sensor by detecting the density of a known toner image by the density sensor in which the light amount for the first low density is set, and irradiating the photoconductor to the photoconductor. As the amount of light By setting the first high density light amount for detecting the toner image density in the density region, and by detecting the density of the toner image of known density by the density sensor in which the first high density light amount is set. Acquiring a high density light amount characteristic curve of the density sensor, acquiring a toner image density corresponding to the first density data in the first low density light amount characteristic curve as a first reference density, the high density light amount characteristic curve In step 1, the density data corresponding to the first reference density is acquired as the first correction reference data, and when the density is detected, the second low density light amount for detecting the toner image in the low density area is calculated. Determining a second high-density light amount for detecting the toner image in the density region, and setting the second low-density light amount as the light amount of the light irradiated toward the photoconductor. To obtain a second low-density light amount characteristic curve of the density sensor by detecting the density of the toner image of known density by the density sensor to which the second low-density light amount is set. In the light quantity characteristic curve, the toner image density corresponding to the second density data that is substantially equal to the first density data is acquired as the second reference density, and the second high value is obtained as the light quantity of the light irradiated toward the photoconductor. By setting the density light amount and detecting the toner image of the second reference density by the density sensor having the second high density light amount set, the density data output by the density sensor at this time is 2 Obtain as correction reference data, the second
When the high density light amount is set and the toner image density is detected by the density sensor, the density data output by the density sensor is corrected based on the first correction reference data and the second correction reference data. And a method of applying the corrected density data to the high density light amount characteristic curve to obtain a toner image density, which is a density detecting method. The invention according to claim 4 is
Illuminating a pseudo original as a standard original with a light source
In both cases, the light source is controlled to change the exposure amount and
By guiding the reflected light from a similar document to the photoconductor,
Forming a toner image of known density on the photoconductor
The concentration detection according to claim 3, further comprising:
Is the way.

According to the present invention, at the time of initial setting, first, the first for detecting the toner image density in the low density area as the light quantity of the light emitted from the density sensor toward the photosensitive member.
The light amount for low density is set. Then, the density of the toner image whose density is known is detected by the density sensor. As a result, the first low-density light amount characteristic curve, which is the input / output characteristic for the first low-density light amount of the density sensor, is acquired. Then
A first high-density light amount for detecting the toner image density in the high-density region is set as the light amount of the light emitted toward the photoconductor. Then, the density of the toner image whose density is known is detected by the density sensor. As a result, the first density sensor
A high density light amount characteristic curve which is an input / output characteristic with respect to the high density light amount is acquired.

In the first low density light amount characteristic curve, the first
The toner image density corresponding to the density data is set as the first reference density. Then, the density data corresponding to the first reference density in the high density light amount characteristic curve is acquired as the first correction reference data. On the other hand, at the time of density detection, the second light amount for low density for detecting the toner image in the low density area is newly obtained. Further, the second high density light amount for detecting the toner image in the high density area is obtained. Then, the second low-density light amount is set as the light amount of the light emitted toward the photoconductor. In this state, the density of the toner image whose density is known is detected by the density sensor. As a result, the second low-density light amount characteristic curve of the density sensor is acquired. This second
In the low-density light amount characteristic curve, the toner image density corresponding to the second density data that is almost equal to the first density data is the second
The standard concentration is used. Then, the second high-density light amount is set as the light amount of the light emitted toward the photoconductor. In this state, the toner image of the second reference density is detected by the density sensor. At this time, the density data output by the density sensor is used as the second correction reference data.

When the second high density light amount is set and the toner image density is detected by the density sensor, the density sensor outputs on the basis of the first correction reference data and the second correction reference data. The density data to be corrected is corrected. Then, by applying the corrected density data to the high density light amount characteristic curve, the toner image density is acquired.
As described above, according to the present invention, the first and second correction reference data are obtained at the initial setting and the density detection, respectively. Both the first and second reference data for correction correspond to the light amount for high density. Since the first density data and the second density data are almost equal, the first and second density data
The correction reference data is output data of the density sensor corresponding to almost the same toner image density. That is, if the first correction reference data and the second correction reference data are different,
This means that the input / output characteristics of the density sensor corresponding to the light amount for high density differ between the initial setting and the density detection.
Therefore, in the present invention, by correcting the output density data of the density sensor based on the first and second correction reference data, the density sensor is used while using the high density light amount characteristic curve obtained at the time of initial setting. The concentration can be detected accurately.

Further, according to the present invention, when the density is detected, the second low-density light amount and the second high-density light amount are newly obtained. This also eliminates the influence of the difference in mechanical conditions between the initial setting and the concentration detection, and the concentration can be measured accurately. The correction of the density data may be achieved by correcting the high density light amount characteristic curve based on the first and second correction reference data. In this case, the density can be obtained by applying the density data output by the density sensor to the corrected high density light amount characteristic curve.

Specifically, a plurality of density data D _S DAT
When stores the high density light amount characteristic curve represented by a plurality of density values corresponding to the plurality of density data D _S DAT to the first storage means. In correcting the density data, the plurality of density data D _S DAT are respectively corrected based on the first and second correction reference data D _ST and D _SF based on the following equations, and the corrected density data D _S DAT ′
To get.

D_SDAT '= K × D_SDAT However, K = D_ST/ D_{science fiction}Is. Then, the corrected density data D_SDAT 'and density before correction
Data D_SIt is stored in the second storage means in association with DAT.
Keep it. When acquiring the density, the density sensor outputs
Concentration data closest to the concentration data of the second storage means
Density data D before correction_SFound in DAT.
This found density data D before correction _SDAT compatible
Corrected density data D_SDAT 'is from the second storage means
Read out. In addition, the read corrected density data
TA D_SIs the density value corresponding to DAT 'the first storage means?
Read from.

Alternatively, the density data output by the density sensor may be corrected based on the ratio between the first correction reference data and the second correction reference data. Specifically, based on the first correction reference data D _ST and the second correction reference data D _SF , the density data D _S output by the density sensor is corrected according to the following equation to obtain corrected density data D _S ″. You can do it like this.

D _S ″ = K × D _S , where K = D _ST / D _SF . Note that the first low-density light amount is from the above-mentioned density sensor to the photoconductor on which toner is not attached at the time of initial setting. In this case, when the light of a plurality of levels is emitted, the density data output from the density sensor may be the maximum level of light amount that is equal to or higher than a predetermined value. It may be a light amount obtained by substituting the light amount for low density into a predetermined conversion formula.

The second low-density light amount is acquired by determining that the density data output by the density sensor is equal to or more than a predetermined value when the photoconductor having no toner adhered thereto is irradiated with light in a plurality of stages. The maximum light amount at which the light amount is obtained may be acquired as the second low-density light amount. In this case, the second high-density light amount may be obtained by substituting the second low-density light amount into the predetermined conversion formula.

By the way, the relationship between the low-density light amount and the high-density light amount differs between the initial setting and the density detection. The main cause thereof is, for example, toner or paper dust attached to the light receiving surface of the density sensor. Therefore, even if the second high-density light amount is obtained by substituting the second low-density light amount into a certain conversion formula, the second high-density light amount is not always an appropriate value. Therefore, the input / output characteristic of the density sensor in which the second high-density light amount is set (see the broken line in FIG. 8) is the input / output characteristic of the density sensor in which the first high-density light amount is set (see FIG. 8). 8 (see the solid line). Therefore, if the high density light amount characteristic curve acquired at the time of initial setting is used as it is, erroneous detection of density occurs. Therefore, if the output density data of the density sensor is corrected according to the present invention, while using the high density light amount characteristic curve obtained at the time of initial setting,
The detection accuracy of the concentration can be improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a conceptual diagram showing a schematic configuration of an electrostatic copying machine to which an embodiment of the present invention is applied. Below the original placing table 2 on which the actual original 1 made of transparent glass or the like is to be placed, the original placing table 2 is placed.
A light source 4 is provided for illuminating and scanning the surface of the real document 1 placed on. The light source 4 is composed of a halogen lamp or the like, and is conveyed at a constant speed in the arrow 3 direction during the image forming operation.

The reflected light from the original is reflected by mirrors 5, 6, 7,
It is guided to the exposure area 11 on the surface of the photosensitive drum 10 via the zoom lens 8 and the zoom lens 9. On the other hand, the surface of the photosensitive drum 10 before reaching the exposure area 11 is a corona discharger 12 for charging.
Are uniformly charged by. As a result, an electrostatic latent image corresponding to the actual original 1 is formed on the surface of the photosensitive drum 10.

During the image forming operation, the reflecting mirror 5 is carried together with the light source 4, and the reflecting mirrors 6 and 7 are carried in the direction of arrow 3 at a speed half the carrying speed of the light source 4. In addition, the photosensitive drum 10 is synchronized with the movement of the light source 4 by the arrow 21.
Driven to rotate. The electrostatic latent image formed on the surface of the photosensitive drum 10 is developed into a toner image by the developing device 14 in which toner is supplied from the toner hopper 13. The developed toner image is transferred to the surface of the copy paper 16 in the transfer corona discharger 15. The copy paper 16 on which the toner image has been transferred is separated from the photoconductor drum 10 by the separation discharge device 17, and then guided to the fixing device 19 by the conveyor belt 18. Then, the toner is heated and fixed on the surface of the copy paper 16 in the fixing device 19, and the copy is completed.

The photosensitive drum 1 after the transfer of the toner image
The toner remaining on the surface of No. 0 is removed by the cleaning device 20 and prepared for the next copying. Pseudo originals 22a and 22b, which are density reference originals on which pure white and pure black images are formed, are provided on both sides of the original placing table 2 and inside the main body of the copying machine. The pseudo originals 22a and 22b are used as the copy paper 1 as described later.
It is used when adjusting the density of the image to be formed in No. 6.

A portion of a density detecting device 23, which will be described below, is provided at a position near the photosensitive drum 10 between the separating discharger 17 and the cleaning device 20 so as to face the photosensitive drum 10. Reflective photo sensor 24
Is provided. FIG. 2 is a block diagram showing an electrical configuration of the concentration detecting device 23. This concentration detector 23
Is used at the time of the image forming condition adjusting process described later in order to adjust the density of the image to be formed on the copy paper 16. During the image forming condition adjustment processing, the pseudo original 22
Either a or 22b is tentatively illuminated, and a toner image having a density corresponding to the pseudo original is formed on the photosensitive drum 10. The density of the formed toner image is detected by the density detecting device 23.
The image forming conditions such as the exposure amount and the amount of toner to be supplied to the developing device 14 are adjusted based on the detection result.

As described above, the density detecting device 23 includes the reflection type photo sensor 24. The reflection type photo sensor 24 includes a light emitting element 24a including a light emitting diode (LED) for irradiating the photosensitive drum 10 with a predetermined amount of light, and a Darlington type photo sensor for receiving the reflected light from the photosensitive drum 10. The light-receiving element 24b includes a transistor and the like, and is driven by the drive circuit 25.

A code represented by a binary code corresponding to the voltage to be supplied to the light emitting element 24a is given to the drive circuit 25 from the control circuit 26. The control circuit 26 generates a code corresponding to the voltage to be applied to the light emitting element 24a according to a predetermined program. The drive circuit 25 is
A voltage corresponding to the given code is applied to the light emitting element 24a. Therefore, the light emitting element 24a irradiates the photoconductor drum 10 with a light amount corresponding to the above voltage.

The light applied to the photosensitive drum 10 is partially reflected by the surface of the photosensitive drum 10, and the remaining portion is absorbed by the toner on the surface of the photosensitive drum 10. Therefore, when the toner image density is relatively low, a relatively high amount of light is reflected, and when the toner image density is relatively high, a relatively low amount of light is reflected. The reflected light is received by the light receiving element 24b. Light receiving element 24b
Generates density data inversely proportional to the amount of reflected light and supplies it to the control circuit 26. That is, the control circuit 26 is provided with density data corresponding to the toner image density.

The control circuit 26 is, for example, a CPU.
(Central processing unit), RAM (Random access memory)
32 and a microcomputer including a ROM (Read Only Memory). In the present embodiment,
Density curve acquisition means, first reference density acquisition means, first correction reference data acquisition means, light intensity acquisition means, second reference density acquisition means, second correction reference data acquisition means, density data correction means, density acquisition means, etc. Function as. The control circuit 26 performs an initial setting process and an image forming condition adjusting process, which will be described later, based on the density data output from the light receiving element 24b. The control circuit 26 is connected to a writable nonvolatile memory 31 for storing data regarding the input / output characteristics of the reflective photosensor 24.
The non-volatile memory 31 may be composed of, for example, a RAM with a backup power supply or an EEPROM (electrically erasable / writable ROM).

FIG. 3 is a flow chart for explaining the initial setting process performed before the copying machine is used by the user. In this initial setting process, first, density data is acquired (step S1). More specifically, in a state where the undeveloped (that is, toner-free) photoconductor drum 10 is stationary, the maximum irradiation light amount L _max and the minimum irradiation light amount L of the plurality of predetermined irradiation light amounts L are set. Light having an irradiation light amount L _min is emitted from the light emitting element 24a of the reflective photosensor 24 to the photosensitive drum 10. Then, the density data D _smin and D _smax respectively corresponding to the reflected light when the maximum irradiation light amount L _max and the minimum irradiation light amount L _min are irradiated are acquired.

Then, the light of the irradiation light quantity L which is sequentially incremented by one step from the minimum irradiation light quantity L _min is emitted from the light emitting element 2.
The photosensitive drum 10 is irradiated with light from 4a. This allows
A plurality of density data D _s respectively corresponding to a plurality of levels of irradiation light amount L are acquired. When the irradiation light amount L is incremented by one step it will acquire the density data D _s of each stage, whether the density data D _s satisfies the following equation (1) is examined.

D _s <D _smin + V ₀ (1) However, for example, V ₀ = 0.2 (V) When the above equation (1) is satisfied, the irradiation light amount L immediately before is equal to the reference light amount L ₀ . The density data D _s obtained at the reference light amount L ₀ is set as the density data D _s 1.
That is, the maximum irradiation light amount that satisfies D _s ≧ D _smin + V ₀ is the reference light amount L ₀ . When D _s <D _smin + V ₀ , the sensor output is saturated, and even if the irradiation light amount is increased after this condition is satisfied, the density data D _s hardly changes. Therefore, the reference light amount L ₀ is slightly lower than the light amount at which the sensor output is saturated. The above constant V
₀ is experimentally determined so that the reference light amount L ₀ is set to a light amount at which the output of the sensor 24 shows a sufficiently large change with respect to the density change.

Next, the photosensitive drum 10 is rotated,
The light of the reference light amount L ₀ is emitted from the light emitting element 24a to the rotating photosensitive drum 10. At this time, the light emitting element 24a is caused to emit light a plurality of times during one rotation of the photosensitive drum 10. The average of the plurality of density data D _s acquired at this time is calculated, and the average density data D _sav
It is said that Then, the average density data D _sav, based on the density data D _smax corresponding to the density data corresponding to the reference light quantity L ₀ D _s 1 and minimum light quantity L _min, a plurality of stages on the photosensitive drum 10 of the stationary state The plurality of density data D _s respectively obtained by irradiating the light of the light amount of are corrected. Specifically, the corrected density data D _s ′
Is given by equation (2) below.

D _s ′ = D _s (D _smax −D _sav ) / (D _smax −D _s 1) + D _smax (D _sav −D _s 1) / (D _smax −D _s 1) ... (2) This As a result, appropriate density data can be obtained in consideration of variations in the circumferential direction of the photoconductor drum 10. In this way, the density data is acquired in each part of the photosensitive drum 10 over one round only for the reference light amount L ₀ of the irradiation light amount L in a plurality of stages. Therefore, regarding the irradiation light amount L at all stages,
The time required to acquire the density data can be shortened as compared with the case where the density data is acquired at each part of the photosensitive drum 10 over one round. Moreover, since the total amount of light applied to the photoconductor drum 10 is small, light fatigue of the photoconductor drum 10 can be reduced.

When the density data is acquired, the first low-density setting light amount LN ₁ and the first high-density setting light amount LX ₁ are obtained (step S2). Specifically, of the corrected density data D _s ′, D _s ′ ≧ D _smin + V ₀ ′ (3) where, for example, the minimum density data D that satisfies V ₀ ′ = 0.4 (V) _The light quantity corresponding to _s ′ (the maximum light quantity that satisfies the above expression (3)) is the first low-density setting light quantity LN ₁ . It is preferable not to use the density data D _s ′ that does not satisfy the above (3) because it is the data in the region where the sensor output is saturated. The constant V ₀ ′ is experimentally determined so that the light amount capable of sufficiently increasing the change in the output of the sensor 24 with respect to the change in density is the first low-density set light amount LN ₁ .

On the other hand, the first high density set light amount LX₁Is above
Obtained first low-density setting light amount LN ₁Into a predetermined conversion formula
It is obtained by substituting. For example, the amount of irradiation light
When L is set in 64 steps from 0 to 63, the first high density
Degree setting light intensity LX₁Is the first conversion value
Quantity LN₁May be obtained by substituting     LN₁= 0 to 15 LX₁= 2LN₁+2 (4)     LN₁= 16 to 23 LX₁= 0.108 (LN₁)²−0.28LN₁+11                                                             ‥‥(Five) Hello LN₁If> 23, the high-density setting light amount LX₁
Must be set to a value of 64 or more, and the setting is
It will be impossible. In such a case, the concentration detection device 23
It is considered that some abnormality has occurred in the.

In creating the above conversion formula, an appropriate first high-density setting light amount LX ₁ is obtained by an experiment with respect to a plurality of values of the first low-density setting light amount LN ₁ . Then, the above conversion formula is determined so that this experimental result can be approximated. For example, an intermediate density between the toner image density of the undeveloped photosensitive drum 10 and the solid black toner image density is referred to as an intermediate density. The low-density setting light amount LN is preferably set so that the output of the reflection type photosensor 24 becomes maximum (capacitated) at an intermediate density. Further, it is preferable that the high-density set light amount LX is set so that the output of the reflection type photosensor 24 rises at an intermediate density and becomes maximum (topped) in solid black.

At the time of the image forming condition adjusting process described later, the second low density setting light amount LN ₂ is obtained in the same manner as the first low density setting light amount LN _1, and the second low density setting light amount LX ₁ is obtained in the same manner as the first high density setting light amount LX ₁ . The high density set light amount LX ₂ is obtained. Then, the head detection, the second low concentration setting amount LN ₂ or the second high concentration setting light amount LX ₂ is used, the solid black detection, the second high concentration setting light amount LX ₂ used.

When adjusting the image forming conditions, as described above, one of the pseudo originals 22a and 22b is illuminated, and the toner image is formed on the surface of the photosensitive drum 10. However, even if the pseudo originals 22a and 22b are illuminated and the actual original 1 is illuminated and scanned,
Even if the densities of the real manuscript 1 and the pseudo manuscripts 22a and 22b are equal, the amount of reflected light (exposure amount) guided to the photoconductor drum 10 due to structural factors of each electrostatic copying machine such as the difference in the installation position. ) Are different from each other. For example, pseudo original 2
When 2a and 22b are closer to the light source 4 than the actual document 1, the exposure amount is larger when the actual document 1 is illuminated and scanned. This is because the light source 4 is usually designed so that the light is focused on the actual document surface. Therefore, for example, the density of the toner image formed by illuminating and scanning the pure white area of the real original 1 and the pseudo original 2 having the pure white image formed thereon
There is a difference in the density of the toner image formed by illuminating 2a. Therefore, even under the condition that the pure white image of the real original 1 can be reproduced without causing fog, the pseudo original 22
The toner image corresponding to may have a relatively high density. Therefore, depending on the machine, the second low density setting light amount
Even if LN ₂ is used, the density of the toner image corresponding to the pseudo original 22a may not be accurately detected.

Therefore, in the initial setting process of this embodiment,
As shown in FIG. 3, a real original 1 on which a pure white image is formed
Toner image formed by illuminating the image and a pure white pseudo original 2
The density difference from the toner image formed by illuminating 2a is obtained (step S3). Based on whether or not the obtained density difference is equal to or more than a predetermined threshold value, the second low density setting light amount LN ₂ or the second high density setting light amount L is set.
Which one of X ₂ is used as the irradiation light amount for fogging detection is selected (step S4).

For example, when the density difference is equal to or more than the threshold value, the density of the toner image formed by illuminating the pseudo original 22a is relatively high, and therefore the second high density setting light amount LX ₂ is detected as fog. It is the amount of irradiation light. If the density difference is less than the threshold value, the pseudo original 22a is
The density of the toner image formed by illuminating is not so high. Therefore, the second low-density set light amount LN ₂ is adopted for fogging detection.

Next, the correction reference data D for generating the correction reference data D _ST which is the first correction reference data.
_ST generation processing is performed (step S5). The correction reference data D _ST is used to correct the density data output from the reflective photosensor 24 when the second high density setting light amount LX ₂ is set as the irradiation light amount of the light emitting element 24a during the image forming condition adjustment processing. It is data for doing.

When the correction reference data D _ST is obtained, the initial setting process ends. FIG. 4 is a flowchart for explaining the correction reference data D _ST generation process. In the correction reference data D _ST generation process, first, the reference density ID ₀
Is required (step T1). More specifically, the first value obtained in step S2 of the initial setting process will be described.
The low-density set light amount LN ₁ is set in the reflective photosensor 24, and the pseudo original 22a is illuminated by the light source 4. As a result, the reflected light from the pseudo original 22a is
It is guided to the photoconductor drum 10. At this time, the light source 4 controls
While being controlled by the circuit 26 to change the exposure amount,
The photosensitive drum 21 is rotated, and the toner image forming operation is performed by the action of the developing device 14 and the like. As a result, a toner image having a plurality of regions having mutually different densities is formed on the surface of the photoconductor drum 10. The density of each area of the toner image is detected by the reflective photosensor 24, and the density data output by the sensor 24 is acquired for each area. Since the actual density of the toner image in each area corresponds to the exposure amount corresponding to each area, it is known
Therefore, the low density setting data curve M1 of FIG. 6 showing the relationship between the known toner image density and the density data can be obtained. In this low density setting data curve M1, predetermined first density data D ₀ (for example, D ₀ = 4.35 ± 0.04
The toner image density ID corresponding to (V)) is the first reference density I
It is set to D ₀ . The low density setting data curve M1 described above is stored in the non-volatile memory 31 and is utilized during the image forming condition adjustment processing.

When the first reference density ID ₀ is obtained, this time, the first reference density ID ₀ obtained at step S2 of the initialization processing is obtained.
The high-density set light amount LX ₁ is set in the reflective photosensor 24. Then, in the same manner as above, the high density setting data curve M2 as shown in FIG. 6 is acquired. In the high density setting data curve M2, the density data D _s corresponding to the reference density ID ₀ is set as the correction reference data D _ST (step T2). That is, the correction reference data D _ST
Is density data in the first high density setting light quantity LX ₁ corresponding to the first reference density ID ₀ with which the first density data D ₀ can be obtained in the first low density setting light quantity LN ₁ . The high density setting data curve M2 is also stored in the non-volatile memory 31 and is used during the image forming condition adjustment processing.

The first density data D ₀ is preferably set to be slightly lower than the saturation point of the output of the reflective photosensor 24 when the first low density setting light amount LN ₁ is set. With this configuration, the first reference density ID ₀ is set to the first low-density setting light amount LN ₁ and the first high-density setting light amount LX.
_In either case, the density can be set so that the output of the reflective photosensor 24 is not saturated.

FIG. 5 is a flow chart for explaining the image forming condition adjusting process. The image forming condition adjusting process is performed every predetermined period (for example, every 60,000 sheets), such as during maintenance. More specifically, first, the same processing as the density data acquisition processing and the set light amount acquisition processing described in FIG. 3 is performed. Based on this, a second low density set amount of light LN ₂ is determined in the same manner as in the first low density set amount of light LN _1, first
The second high-density setting light amount LX ₂ is acquired in the same manner as the high-density setting light amount LX ₁ (steps P1 and P2). Then, the second reference concentration ID ₁ is obtained (step P
3). The second reference concentration ID ₁ is the first reference concentration I
It is obtained almost in the same manner as D ₀ . That is, the reflective photosensor 24 in which the second low-density setting light amount LN ₂ is set
The density data that is slightly lower than the saturation point of the output of is the second density data D ₁ . Then, the second low-density setting light amount LN ₂
In, the toner image density corresponding to the second density data D ₁ is set as the second reference density ID ₁ . This second reference concentration I
D ₁ has almost the same density as the first reference density ID ₀ . The second density data D ₁ has an accuracy range D ₀ ± of ± α (for example, α = 0.02 (V)) with respect to the first density data D ₀ .
It is a value within α.

When the second reference density ID ₁ is obtained, when the first high density setting light amount LX ₁ is set in the reflective photosensor 24 in the initial setting, the reflective photosensor 2
The density data output from No. 4 is corrected (step P4). In other words, the plurality of density data D _S DAT acquired for the toner images of a plurality of levels of density with the first high density setting light amount LX ₁ set during the initial setting process are corrected. The density data D _S DAT is data that forms the above-described high density setting data curve M2, and is stored in the nonvolatile memory 31.

When the second low-density setting light amount LN ₂ is set, the input / output characteristics of the reflective photosensor 24 are not so different from the input / output characteristics when the first low-density setting light amount LN ₁ is set at the initial setting. There is no. Therefore, when the toner image density is detected by setting the second low-density setting light amount LN ₂ , the low-density setting data curve M obtained at the initial setting is set.
It is safe to refer to 1. On the other hand, the input / output characteristics of the sensor 24 when the second high-density setting light amount LX ₂ is set during the image forming condition adjustment processing are the same as when the first high-density setting light amount LX ₁ is set during the initial setting processing. It deviates considerably from the input / output characteristics of 24. This is because the low density setting light amounts LN ₁ and LN ₂ are set based on the actual density detection result, while the high density setting light amounts LX ₁ and LX are set.
_This is because ₂ is obtained by substituting the low density set light amounts LN ₁ and LN ₂ into the conversion formula. That is, the appropriate relationship between the low-density set light amount and the high-density set light amount differs between the initial setting and the image forming condition adjustment processing. The main cause thereof is toner or paper dust attached to the light emitting surface or the light receiving surface of the reflective photosensor 24.

Therefore, when the second high density setting light amount LX ₂ is set during the image forming condition adjusting process,
High concentration setting data curve M2 acquired at the time of initial setting processing
Cannot be referred to as is. What is performed there is the process of step P4 based on the correction reference data _DST acquired at the time of initial setting. More specifically, first, the pseudo original 22a is illuminated with the exposure amount corresponding to the second reference density ID ₁ . Then, the developing device 14
The surface of the photoconductor drum 10 can be
A toner image having the reference density ID ₁ is formed. The density of the toner image of the second reference density ID ₁ is the second high density setting light amount L
The output density data detected by the reflective photosensor 24 in which X ₂ is set is the second correction reference data.
The correction reference data D _SF is used.

The input / output characteristic of the reflection type photosensor 24 corresponding to the second high density set light amount LX ₂ is, for example, as shown in FIG. 6 due to the influence of toner or paper dust attached to the light emitting surface and the light receiving surface.
The high-density-setting data curve M2a is different from the characteristic when the first high-density setting light amount LX ₁ is set in the initial setting. In this high density setting data curve M2a, the density data corresponding to the second reference density ID ₁ is supplemented.
It is normal use reference data D _SF .

[0055] When the correction reference data D _SF is obtained, this accessory
Based on the normal use reference data D _SF and the correction reference data D _ST obtained during the initial setting processing, the correction coefficient K is obtained by K = D _ST / D _SF (6). Then, the plurality of density data D _S DAT acquired during the initial setting process are used in a form corrected based on the correction coefficient K. That is, at the time of the image forming condition adjustment processing, the plurality of density data acquired at the initial setting are treated as the corrected density data D _S DAT ′ shown in the following expression (7). D after correction
_S DAT ′ is associated with the uncorrected data D _S DAT,
It is stored in the RAM 32 in the control circuit 26.

D _S DAT ′ = K × D _S DAT (7) For example, the actual output data of the reflective photosensor 24 for the reference density ID ₀ is D _SF . The density data corresponding to the density data D _SF , which has been acquired during the initial setting process and has been corrected, is as follows when calculated according to the above equation (7).

D _S DAT ′ = K × D _SF = (D _ST / D _SF ) × D _SF = D _ST (8) The data D _S DAT ′ (= D _ST ) after this correction is processed at the time of initial setting processing. If it is regarded as the acquired data and is applied to the high density setting data curve M2 acquired during the initial setting processing, the toner image density ID ₀ is obtained. Thus, even if the input / output characteristics of the reflective photosensor 24 are different from the high density setting data curve M2 stored in the non-volatile memory 31, the density data D _S DAT obtained at the initial setting is corrected by the above correction. Can be used to accurately detect the density of the toner image.

When the correction of the density data D _S DAT is completed (step P4), it is next detected whether or not fog has occurred (step P5). That is, the pseudo original 22a on which a pure white image is formed is illuminated and
The toner image forming operation is performed. Reflective photo sensor 24
The amount of light to be irradiated from the photosensitive drum 10 to the photoconductor drum 10 is the set amount of light selected from the second low-density set light amount LN ₂ or the second high-density set light amount LX _{2 as} the fog detection light amount in the initial setting process. Then, the reflective photo sensor 24
Whether or not fogging has occurred is detected based on the density data output from.

As a result, when it is detected that fogging has occurred, the amount of light to be generated from the light source 4 is increased (step P6). Next, solid black detection is performed (step P7). That is, the pseudo original 22b on which a black image is formed is illuminated, and a toner image corresponding to the pseudo original 22b is formed on the surface of the photoconductor drum 10. Then, the density of the formed toner image is detected by the reflective photosensor 24. At this time, the amount of light to be emitted from the reflective photosensor 24 is the second high-density setting light amount LX ₂
Is set to. Then, based on the density data output by the reflective photosensor 24, it is detected whether or not solid black.

As a result, when it is detected that the solid black is not obtained,
The toner hopper 13 is controlled. Specifically, the amount of toner to be supplied from the toner hopper 13 to the developing device 14 is increased (step P8). As a result, the adjustment of the image forming conditions is achieved, and it becomes possible to stably obtain a high quality image.

When the second high-density setting light amount LX ₂ is set, the density data D _S acquired at the initial setting is set.
The DAT that is closest to the output data of the reflective photosensor 24 is found. And this density data D
_The corrected density data D _S DAT ′ corresponding to _S DAT is read from the RAM 32 in the control circuit 26. further,
In the high density setting data curve M2, the toner image density corresponding to the read corrected data D _S DAT ′ is found. This toner image density is regarded as the density of the toner image to be detected.

That is, as a result, when the first high-density setting light amount LX ₁ is set in the reflective photosensor 24, the output data D _S of the reflective photosensor 24 is calculated according to the following expression (9). Will be corrected. Then, the toner image density is detected by applying the corrected data D _S ″ to the input / output characteristics at the time of initial setting. D _S ″ = K × D _S (9) As described above In addition, according to the electrostatic copying machine of the present embodiment, the second high-density setting light amount LX is set during the image forming condition adjustment processing.
_{When 2} is set in the reflection type photo sensor 24 to detect the toner image density, toner image densities ID ₀ and I which are almost equal
D initialization processing and during image forming condition adjusting process when the correcting reference data D _ST and which are respectively obtained for ₁
The density data of the reflective photosensor 24 is corrected based on D _SF . Thereby, the reflective photo sensor 24
Even if the input / output characteristics of the reflective photosensor 24 are different from those at the time of initial setting due to the adherence of the floating toner or the like on the light emitting surface or the light receiving surface of the same, it is possible to eliminate the influence and detect the toner image density well You can Therefore, even when the second high-density setting light amount LX ₂ is set in the reflective photosensor 24, the toner image density can always be accurately detected.
Therefore, the image forming conditions can be adjusted accurately, and a high quality image can be stably obtained.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. For example, although the electrostatic copying machine has been described as an example in the above embodiment, the present invention is applicable to any image forming apparatus such as a laser printer or a facsimile machine in which an image is formed by an electrophotographic process. Can also be applied.

Besides, various modifications can be made within the scope of the technical matters described in the claims.

[0065]

As described above, according to the present invention, the output density data of the density sensor is calculated based on the first and second correction reference data which are the output data of the density sensor corresponding to the toner image densities which are substantially equal to each other. By performing the correction, it is possible to accurately detect the density by the density sensor while using the high density light amount characteristic curve obtained at the initial setting.

Further, according to the present invention, when the density is detected, the second low-density light amount and the second high-density light amount are newly obtained. This also eliminates the influence of the difference in mechanical conditions between the initial setting and the concentration detection, and the concentration can be measured with high accuracy. The relationship between the low-density light amount and the high-density light amount differs between the initial setting and the density detection. Therefore, even if the second high-density light amount is obtained by substituting the second low-density light amount into a certain conversion formula, the second high-density light amount is not always an appropriate value. Therefore, if the high density light amount characteristic curve acquired at the time of initial setting is used as it is, erroneous detection of density occurs. Therefore, by correcting the output density data of the density sensor according to the present invention, it is possible to improve the density detection accuracy while using the high density light amount characteristic curve.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a schematic configuration of an electrostatic copying machine to which a density detecting device according to an embodiment of the present invention is applied.

FIG. 2 is a block diagram showing an electrical configuration of a density detecting device which constitutes a part of the electrostatic copying machine.

FIG. 3 is a flowchart for explaining an initial setting process in the electrostatic copying machine.

FIG. 4 is a reference data D for correction in the electrostatic copying machine.
₇ is a flowchart for explaining _ST generation processing.

FIG. 5 is a flowchart for explaining an image forming condition adjusting process in the electrostatic copying machine.

FIG. 6 shows a low density setting data curve and a high density setting data curve which are outputs of the reflection type photosensor when the first low density setting light amount and the first high density setting light amount are set in the reflection type photosensor. It is a figure.

FIG. 7 is a diagram showing a relationship between a toner image density and density data output from the reflective photosensor when a low density set light amount is set.

FIG. 8 is a diagram showing a relationship between a toner image density and density data output from the reflective photosensor when a high density set light amount is set.

[Explanation of symbols]

4 light sources 10 Photosensitive drum 13 Toner hopper 14 Developing device 23 Concentration detector 24 Reflective Photo Sensor 24a light emitting element 24b light receiving element 26 Control circuit 31 non-volatile memory 32 RAM

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 15/00 303 G03G 21/00 370-540

Claims (4)

(57) [Claims] 1. A density of a toner image formed by an image forming apparatus including a photoconductor on which an electrostatic latent image is formed and a developing device for developing the electrostatic latent image formed on the photoconductor into a toner image. A density detection device for detecting light, which is a density sensor for irradiating light to the photoconductor and outputting density data corresponding to the amount of light reflected from the photoconductor. A density sensor having a variable amount of light to be emitted, and a first low-density light amount for detecting the toner image density in a low-density region as the amount of light emitted toward the photoconductor at the time of initial setting. Further, a first low-density curve acquisition means for acquiring the first low-density light amount characteristic curve of the density sensor by detecting the density of the toner image of known density by the density sensor, and at the time of initial setting, Towards the photoconductor By setting the first high-density light amount for detecting the toner image density in the high-density region as the light amount of the emitted light, and further detecting the density of the toner image of known density by the density sensor, High density curve acquisition means for acquiring a high density light quantity characteristic curve of the density sensor, and first reference density acquisition for acquiring a toner image density corresponding to the first density data in the first low density light quantity characteristic curve as a first reference density. Means, first correction reference data acquisition means for acquiring density data corresponding to the first reference density in the high density light amount characteristic curve as first correction reference data, and toner in a low density region at the time of density detection. Light amount acquisition means for low density for obtaining a second light amount for low density for detecting an image, and second light for high density for detecting a toner image in a high density area at the time of density detection And the high-density light quantity acquisition means for obtaining, the second as a quantity of light irradiated toward the photosensitive member
By setting the light amount for low density and further detecting the density of the toner image of known density by the density sensor,
Second low density curve acquisition means for acquiring a second low density light quantity characteristic curve of the density sensor, and a toner image corresponding to second density data substantially equal to the first density data in the second low density light quantity characteristic curve. Second reference density acquisition means for acquiring the density as the second reference density, and the second reference density as the light amount of the light irradiated toward the photoconductor.
By setting the amount of light for high density and further detecting the toner image of the second reference density by the density sensor,
At this time, the density data output by the density sensor
A second correction reference data acquisition unit that acquires the correction reference data; and the first correction reference data and the first correction reference data when the toner image density is detected by the density sensor by setting the second high density light amount. 2 based on the correction reference data, the density data output from the density sensor is corrected, and the density data correction means for outputting the corrected density data; and the corrected density data is applied to the high density light amount characteristic curve to obtain the toner. A density detecting device, comprising: a density acquiring unit for acquiring image density. 2. A pseudo original as a density reference original, a light source for illuminating the pseudo original, and a control for varying the exposure amount by controlling the light source.
A control circuit for illuminating the pseudo document with the light source, and the control circuit.
Control the light source to change the exposure amount,
By guiding the reflected light from the pseudo document to the photoconductor,
A toner image of known density is formed on the photoreceptor.
2. The method according to claim 1, wherein
Concentration detector. 3. An image forming apparatus including a photoconductor on which an electrostatic latent image is formed and a developing device for developing the electrostatic latent image formed on the photoconductor into a toner image. This is a method of detecting the density of a toner image using a density sensor that irradiates a variable amount of light that can be set toward the target and outputs density data corresponding to the amount of light reflected from the photoconductor. A first for detecting a toner image density in a low density area as a light quantity of light emitted from the density sensor toward the photoconductor
By setting the low density light amount, and by detecting the density of the toner image of known density by the density sensor having the first low density light amount set, the first low density light amount characteristic curve of the density sensor is calculated. Acquiring, setting a first high-density light amount for detecting the toner image density in a high-density region as the light amount of the light radiated toward the photoconductor, the density of the toner image of known density The high density light amount characteristic curve of the density sensor is obtained by detecting the first high density light amount set by the density sensor, and the toner corresponding to the first density data in the first low density light amount characteristic curve. Acquiring the image density as the first reference density, acquiring the density data corresponding to the first reference density in the high density light amount characteristic curve as the first correction reference data, Determining a second light amount for low density for detecting a toner image in a low density region, a second light amount for high density for detecting a toner image in a high density region, The second amount of light emitted toward the second
By setting the light amount for low density, and detecting the density of the toner image of known density by the density sensor having the light amount for second low density set, the second low density light amount characteristic curve of the density sensor is obtained. Acquiring, as a second reference density, a toner image density corresponding to second density data that is substantially equal to the first density data in the second low density light amount characteristic curve, and is irradiated toward the photoconductor. The second amount of light
By setting the high density light amount, and by detecting the toner image of the second reference density by the density sensor in which the second high density light amount is set, the density data output by the density sensor at this time is obtained. To obtain the second correction reference data, and when the second high density light amount is set and the toner image density is detected by the density sensor, the first correction reference data and the second correction reference data are obtained. A density detecting method, comprising: correcting the density data output from the density sensor based on the above, and applying the corrected density data to the high density light amount characteristic curve to obtain the toner image density. . 4. A light source is used as a pseudo original as a density reference original.
Illumination and control the light source to adjust the exposure
And guide the reflected light from the pseudo document to the photoconductor.
By doing so, the toner image with the known density is formed on the photoreceptor.
4. The method according to claim 3, further comprising forming
The concentration detection method described.