JP3033075B2 - Toner density control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer, and more particularly, to a toner density in an image forming apparatus using a two-component developing device. The present invention relates to a control device.

[Conventional technology]

In this type of image forming apparatus, toner density control is performed in which a toner density in a developing device of a developing device is detected, and toner for replenishment is appropriately supplied to the developing device in accordance with the detection result. When the toner concentration detecting means for detecting the toner concentration is installed in the developing device, the developer always flows through the toner concentration detecting device in order to avoid erroneous detection due to the stagnation of the developer in the developing device. Is installed at the location where it is located. Specifically, it is installed between the developing roller and the paddle roller at the bottom of the developing device.

A certain type of toner concentration sensor, which is sensitive to the amount of magnetic material in the developer, has a temperature dependency such that the output decreases as the temperature increases, as shown in FIG. 3, for example. In FIG. 3, the vertical axis indicates the output of the toner density sensor, and the horizontal axis indicates the toner density of the developing device. The characteristic a is obtained when the temperature is T ₀ , and the characteristic is obtained when the temperature is T ₀ ′, which is higher than this.

However, as described above, since the toner density sensor is installed at the bottom of the developing device or the like, the temperature may change for the following reasons.

If the pre-transfer exposure source is located directly below the developing unit,
It becomes a heat source and raises the temperature of the developing device.

When a heat source is disposed inside the photoconductor in order to keep the characteristics of the photoconductor serving as the image carrier constant, the heat source indirectly increases the temperature of the developing device.

When the power supply unit is disposed near the developing device due to layout, heat from the heat radiating member of the power supply unit increases the temperature of the developing device.

When the apparatus is used continuously, the kinetic energy of the developing device and the developer is converted into heat energy, and the temperature of the developing device is raised.

When the temperature of the toner density sensor changes in this way,
The following problems occurred.

That is, for example, when a toner density sensor having characteristics as shown in FIG. 3 is used, even though the toner density in the developing device is the target toner density D ₀ corresponding to the control reference value V ₀ , the temperature becomes T ₀ 'properties of the toner density sensor is changed from the characteristic a to the characteristic b in order to increase the detection value as a result is V ₀ from V _0' T ₀ after becoming high toner density D than the toner density D _{0 0} "is erroneously detected. Due to such erroneous detection, the toner density is
Until the toner concentration becomes D ₀ ′, which is considerably lower than D ₀ , the toner is not replenished and the toner concentration is reduced. As a result, there is a problem that the image density is reduced.

On the other hand, the developing ability is detected by detecting the amount of toner adhering to the actually developed predetermined potential portion by an optical sensor or the like, and the amount of toner adhering to the predetermined potential portion is determined to be a target amount (the target potential of the predetermined potential portion). so that the reference amount of adhered is an image corresponding to the density), it corrects the reference value V ₀ which is the control of toner replenishment, thereby, there is known so as to obtain a constant image density.

According to this, detecting the actual developing ability of the developer, so to correct the reference value V ₀ which control the toner supply, erroneous toner density characteristics of the toner density sensor as described above varies with the temperature sensing , A constant image density can be obtained, and as a result, the above problem is solved.

[Problems to be solved by the invention]

However, in the above-described conventional technology, when the image forming operation is continuously performed and the temperature of the toner density sensor becomes relatively high (for example, T ₀ ′ in FIG. 3), the predetermined potential actually developed is used. The reference value V ₀ of the toner replenishment control is corrected (for example, corrected to V ₀ ′ in FIG. 3) so that the toner adhesion amount to the portion becomes the reference adhesion amount, and the image forming operation is performed as it is. If, for example, the image forming operation is not performed until the next day, the following problem occurs when the image forming is started on the next day.

That is, when the image formation on the next day is started, the temperature of the toner density sensor is considerably lower than the temperature at the end of the image formation on the previous day (for example, T _{0 in} FIG. 3). Also, it is far from the one at the end of the image formation on the previous day (for example, b in FIG. 3) (for example, a in FIG. 3). Therefore, even if the toner concentration is the target toner concentration (for example, D _{0 in} FIG. 3), the comparison with the final reference value V ₀ ′ indicates that the toner concentration is extremely low. As a result, the maximum toner replenishment is continuously performed, and the image becomes dirty and the toner is scattered. Further, in the case where the presence / absence of the remaining amount of the replenishment toner is determined based on the difference between the detected value and the control reference value, it is erroneously detected that there is no remaining amount even though the replenishment toner remains, There is a problem that processing such as toner end display and machine stop is performed.

In order to solve the problem based on the temperature dependency of the toner density sensor, the temperature of the developer is detected, and the control reference value of the toner replenishment control using the toner density sensor is corrected according to the detected value. It has been proposed to provide a developing device with a temperature controller to keep the temperature of the developer constant (see Japanese Patent Application Laid-Open No. 1-161349). It is necessary to provide a temperature sensor and a heater constituting the temperature control unit only to solve the problem based on the above, and there is a problem that the number of parts increases and the cost increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and an object of the present invention is to perform rapid toner replenishment control by using a temperature-dependent toner concentration detection unit. An object of the present invention is to provide a toner density control device capable of preventing the image from becoming dirty and scattering toner even when a temperature change occurs.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a toner concentration detecting means for detecting a toner concentration of a developing device, and comparing a detection value of the toner concentration detecting device with a control reference value to supply toner to the developing device. Replenishing control means for controlling replenishment; adhering amount detecting means for detecting an adhering amount of toner on a predetermined potential portion developed by the developing device; comparing the detected value of the adhering amount detecting means with an adhering amount reference value; First correction means for correcting the control reference value based on the comparison result, storage means for storing a detection value of the toner density detection means, detection value of the toner density detection means and stored in the storage means A second correction unit that compares the detected value with the detected reference value and corrects the control reference value when a difference between the detected value of the toner density detecting unit and the detected value stored in the storage unit exceeds a predetermined value. Are provided.

[Action]

The present invention compares the detection output of the toner density detection means with the detection output at the time of toner density detection by the previous toner density detection means stored in the storage means, so that the difference between the two detection outputs is a normal value. The presence or absence of a rapid temperature change is determined based on whether or not the toner density detection output is within the range of the toner density detection output based on the variation of the toner density in the image forming operation, and it is determined that a rapid temperature change has occurred since the previous toner density detection. In this case, the control reference value is corrected to prevent an excessive toner supply.

〔Example〕

An embodiment in which the present invention is applied to a toner density control device of an electrophotographic copying machine as an image forming apparatus will be described.

FIG. 1 is a schematic configuration diagram of an electrophotographic copying machine according to the present embodiment.

 First, an outline of the entire copying machine will be described.

In FIG. 1, a document (not shown) on a contact glass 1 is already moved by a uniform charger 2 by an optical system (not shown) including a document irradiation lamp for irradiating a document while moving in parallel to the document. An image is formed and projected on a drum-shaped photoconductor 3 which is a uniformly charged latent image carrier, whereby an electrostatic latent image is formed on the photoconductor 3. This electrostatic latent image is formed into a toner image by the toner of the developing device 4 provided on the right side of the photoconductor. Here, the developing device 4 is a developing device using a two-component developer, and includes a developing roller 5 and a paddle roller 6.
And the like, and a cartridge 8 for accommodating toner for replenishment. The developing roller 5 at the bottom is located at a position where the flow of the developer in the developing device 7 is good.
A toner density sensor 9 serving as a toner density detecting unit is provided between the paddle roller 6 and the paddle roller 6. Further, a replenishing roller 16 for replenishing toner in the developing device 7 is provided below the cartridge 8. This developing device 4
Is transferred by the transfer charger 10 to transfer paper conveyed from the paper supply unit. The transfer paper on which the toner image has been transferred is separated from the photoreceptor 3 by the separation charger 11, and is discharged outside the machine as a copy paper through a fixing device (not shown).

On the other hand, the residual toner is removed from the surface of the photoreceptor 3 after transfer by the cleaning device 12 provided on the left side, and then the residual charge is removed by the charge removing lamp 13 to prepare for the next charging by the uniform charger 2. Can be

The photoconductor 1 is attached to one end of the contact glass.
A reference density plate 11 for forming a reference pattern latent image which is a predetermined potential portion is provided thereon. An optical sensor 15 is provided between the developing device 4 and the transfer charger 10 so as to detect the amount of toner adhering to the toner image by developing the reference pattern with the developing device 4. It is provided.

Next, the toner density control in this example will be described.

In the block diagram of the electrical unit shown in FIG. 2, the toner density sensor 9 and the optical sensor 15 provided in the developing device are
Connected to I / O unit 17. ROM18 and RAM for CPU18
The ROM 19 stores a toner density control program described later. A motor (motor drive circuit) 21 for driving the toner supply roller 16 is connected to the I / O unit 17.

In this example, the supply control means includes a toner supply roller 16.
The necessity of toner replenishment by rotationally driving the detection value V _P of the I / O unit 17 of the toner density sensor 9 for each copy
From loading, control the replenishment of the replenishment toner by the detected value V _P is determined by comparison whether greater than the control reference value V ₀ read from RAM 20, for a predetermined time driving the toner supply roller is greater I do. It This predetermined time may be fixed in a certain time may be set based on the differentially between the detection value V _P and the control reference value V _0.

Then, the first correction means in this example, the control reference value V _0, is corrected based on the output value of the optical sensor 15 for detecting the change in sensitivity of the developing ability and the photosensitive member of the developer.

Hereinafter, the control reference value V ₀ using the output value of the optical sensor 15
Will be described.

In an exposure scanning step of an original to be copied, an image of a reference density plate 11 provided at one end of a contact glass is irradiated by an irradiation lamp of an exposure optical system, and a reference pattern latent image is formed on the photoreceptor 1. Is formed outside the original image area. The reference pattern latent image is developed by the developing device 4 and an optical sensor
At 15, the toner adhesion amount is detected. This optical sensor characteristic is shown in the second quadrant of FIG. As you can see,
There is an exponential relationship between the toner adhesion amount and the sensor output. Therefore, if the optimum values of the developing potential and the toner adhesion amount shown in the first quadrant of FIG. 1 are determined, the density of the reference density plate and the application of the developing roller during the development of the reference pattern latent image are adjusted so that the developing potential becomes appropriate. By setting the voltage, forming and developing the reference pattern latent image under these conditions, and detecting the amount of toner adhered thereto, it is possible to determine what state the current developer capacity is in. . By utilizing this fact, the excess or deficiency of the developing ability is corrected by feeding back to the toner density of the developing device. Specifically, the toner density control standard value V ₀ which toner supply control when at higher developability control reference value V ₀ which toner replenishment control in the direction in which the toner density is low, low developer capability conversely Is corrected in the direction that becomes higher.

By the above, it is shifted toner concentration is lower direction corresponding to the control reference value V ₀ gone by detecting the fact than increasing the toner concentration by the temperature dependence of the toner density sensor 9, a reduction in development performance with it is fed back to the control reference value V ₀ is detected by an optical sensor, which is corrected in the direction in which the toner density is high, it is possible to maintain the toner concentration constant.

However, in this state, it is not possible to sufficiently cope with a sudden temperature change as described above. In particular, detection by the optical sensor 15 is performed, for example, by taking into account the toner consumption due to the development of the reference pattern and the load on the cleaning device.
If the copying is performed once for each copy, the control reference value V ₀ which is inappropriate due to a rapid temperature change
From the control reference value using the output value of the optical sensor 15
To not meet the deadline, but the correction of the V _0, would run a large amount of toner replenishment in the control reference value V ₀ deviated from the proper value.

Accordingly, in this embodiment, by detecting the presence or absence of sudden changes in temperature, when the sudden change in temperature has occurred, apart from the correction of the control reference value V ₀ using the output value of the optical sensor 15, quickly to be capable of correcting the control reference value V ₀ to the ones appropriate to.

For this reason, the detection value of the toner density sensor 9 is always
The data is stored while being updated in the RAM as the storage means. And
The second correction unit in this example calculates the difference between the previous detection value of the toner density sensor 9 that is the stored detection value and the detection value of the current (current) toner density sensor 9.
Correcting the control reference value V ₀ which is the toner density sensor 9.

 Hereinafter, this correction control will be described.

Normally, the detection of the toner density by the toner density sensor 9 is performed for each image forming cycle in the developing device. Therefore, the change in the toner density in the detection interval is caused by the toner consumed by the image forming and the replenished toner. And the amount of change should fall within a predetermined range obtained through experiments or the like. Therefore, when the difference between the detection values of at least two consecutive toner density detections exceeds such a predetermined range, the toner density has not changed and the detection characteristics of the toner density sensor 9 have changed. It can be determined that the sensitivity has changed. Therefore, in such a case, to maintain the toner concentration constant, to correct the control reference value V ₀ to the value of the current detection value or the vicinity thereof.

This will be specifically described with reference to FIG. 3. First, after the power is turned on, the temperature of the toner density sensor 9 is T ₀ , the control reference value V ₀ is V ₀ , and the toner density sensor 9 is controlled to the target toner density D ₀ . It is assumed that it is. After the power is turned on, the temperature of the toner density sensor 9 rises to T ₀ ′ over time (due to heat release from the fixing device, etc.), and if the control reference value V ₀ remains at V ₀ , the toner density becomes D ₀ ′. Will be controlled. However, this shift causes the control reference value V ₀ of the toner density sensor 9 to be corrected to V ₀ ′ by detecting the amount of toner adhered by the optical sensor 15, so that the substantial toner density continues to be controlled to D ₀ .
For example, when the next day the power is turned on in a state where the use of day powered down ends, the temperature of the toner concentration sensor 9 is returned to T _0, the detection value V _P is met around V ₀ 'day ones is shifted around in the V ₁ Figure 3. Therefore, storing the detected value Vb of the final toner concentration sensor 9, a sudden without detection value V _P or toner density is controlled by correcting the value around the current toner density sensor 9 varies toner It is possible to prevent erroneous detection of replenishment and toner end.

FIG. 5 is a flowchart of control of the replenishment control means and the second correction means in this example.

In a first step, the toner density sensor 9 is detected, and in a second step, the absolute value of the difference between this detected value _VP and the previous detected value Vb of the toner density sensor 9 is a predetermined value ΔV
Is determined.

Here, when it is determined that the difference does not exceed ΔV, the third
Proceeds to step, the detection value V _P is determined whether or not the toner supply on whether greater control reference value V _0, in the case of supplementation needed by ON toner supply drive motor in a fourth step, a sixth Proceeds to a step where the current detection value _VP is stored in the RAM
To memorize.

In the second step the contrary, if it is determined that no more than this ΔV, the flow proceeds to the fifth step, corrected by setting the current detection value V _P as the control reference value V _0, the necessity of the toner replenishing without judgment, it proceeds to the sixth step, storing the current detection value V _P in the RAM.

As described above, in the present embodiment, the predetermined potential portion is formed using the reference density plate. Alternatively, for example, a portion that is charged and not irradiated with light may be used as the predetermined potential portion. Also, in a reversal developing system using a laser optical system, a predetermined potential portion may be formed by irradiating this laser beam. Further, an electrode portion to which a predetermined potential is applied may be provided close to the surface of the photoconductor, and this may be used as the predetermined potential portion.

Further, the amount of toner adhered to the developed predetermined potential portion is detected on the predetermined potential portion. Alternatively, the toner may be transferred to a transfer paper and detected on the transfer paper.

〔The invention's effect〕

As described above, according to the present invention, the presence / absence of a rapid temperature change is determined, and when it is determined that a rapid temperature change has occurred since the previous toner concentration detection, the control reference value is corrected. As a result, it is possible to prevent the toner from being replenished excessively, so that there is an excellent effect that it is possible to prevent the image from becoming dirty and the toner from scattering.

[Brief description of the drawings]

FIG. 1 is a front view showing a configuration of a main part of an electrophotographic copying machine according to an embodiment of the present invention. FIG. 2 is a block diagram of the electrical unit. FIG. 3 is a characteristic diagram showing output characteristics of the toner density sensor. FIG. 4 is a characteristic diagram showing output characteristics of the optical sensor. FIG. 5 is a flowchart of the toner supply control in this embodiment. 3 photoreceptor, 7 developing device 8 cartridge 9 toner concentration sensor 14 reference density plate 15, optical sensor

Claims (1)

(57) [Claims] A toner density detecting means for detecting a toner density of a developing device; and a replenishing control for controlling replenishment of replenishing toner to the developing device by comparing a detected value of the toner density detecting means with a control reference value. Means, an adhesion amount detecting means for detecting an adhesion amount of the toner to a predetermined potential portion developed by the developing device, and comparing the detected value of the adhesion amount detecting means with the adhesion amount reference value,
First correction means for correcting the control reference value based on the comparison result, storage means for storing a detection value of the toner density detection means, detection value of the toner density detection means and stored in the storage means A second correction unit that compares the detected value with the detected reference value and corrects the control reference value when a difference between the detected value of the toner density detecting unit and the detected value stored in the storage unit exceeds a predetermined value. And a toner concentration control device.