JPH08262861A - Print density control method in image forming apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] When low density printing is continued for a long period of time, it prevents the deterioration of the print quality that the toner charge amount becomes high and the image is printed more thinly. Provided is a print density control method capable of stable control. According to a print density control method in which a print density is variable by changing an exposure amount of a photoconductor 1 by an exposure source 3, in a developing device 4 when low density printing is continued for a predetermined time or longer. Increase toner density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to a method for controlling its print density.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, an exposure process for forming an electrostatic latent image corresponding to an image on the surface of a photoconductor by exposing the surface of the photoconductor, and a toner on the formed electrostatic latent image. Paper through a developing process of making the toner visible and making it visible, a transfer process of transferring the toner image generated by this development to a predetermined transfer paper, and a fixing process of applying heat to the transferred toner image to fix the paper. To form an image. These steps of exposure, development, and transfer are sequentially performed with the rotation of the photosensitive drum by the operation of the respective devices arranged in parallel around the photosensitive drum.

In general, such an image forming apparatus is provided with a function of making the print density lighter or darker in consideration of user's convenience. When controlling the change in the print density, generally, the exposure amount in the exposure process is made variable.
Specifically, when performing high-density printing, the exposure amount is set to be larger than that during normal printing, and when performing low-density printing, the exposure amount is set to be smaller than that during normal printing.

[0004]

However, when printing is performed for a long time at a low density, the amount of toner consumed from the developing device is small, so that the stirring in the developing device becomes long and the toner is The charge amount of the toner becomes high, and additives such as silica added for improving the fluidity of the toner scatter. As a result, the developability and transfer efficiency of the toner are reduced and the print quality is degraded. Thus, the method of controlling the print density by adjusting the exposure amount has a problem that the print quality is deteriorated when printing is performed for a long time at a low density.

The present invention has been made in view of the above circumstances, and it is possible to prevent deterioration of the print quality during the low density printing as described above and to stably control the low density printing. An object of the present invention is to provide a print density control method in an apparatus.

[0006]

According to a first aspect of the present invention, an electrostatic latent image corresponding to an image is formed on the surface of a photosensitive body which has been charged by exposure, and the formed electrostatic latent image is stored in a developing unit. Toner is made visible, and the toner image is transferred to paper, and the print density is controlled by changing the exposure amount and normal density printing, and low density printing in which the print density is lighter than the normal density printing. In the print density control method in the image forming apparatus capable of switching the settings of 1 and 2, when the low density printing continues for a predetermined time or longer, the toner density in the developing device is increased.

According to a second aspect of the present invention, an electrostatic latent image corresponding to an image is formed on the surface of a photoconductor charged by exposure.
The formed electrostatic latent image is visualized by adhering toner after stirring it with the carrier in the developing device, and the toner image is transferred to paper, and the print density is controlled by changing the exposure amount. In a print density control method in an image forming apparatus capable of switching between normal density printing and low density printing in which the print density is lighter than the normal density printing, the stirring time of the developing device after the low density printing is set. In accordance with the above, the toner density in the developing device is increased.

According to a third invention of the present application, an electrostatic latent image corresponding to an image is formed on the surface of a photoconductor charged by exposure.
The formed electrostatic latent image is visualized by adhering toner after stirring it with the carrier in the developing device, and the toner image is transferred to paper, and the print density is controlled by changing the exposure amount. In a print density control method in an image forming apparatus capable of switching between normal density printing and low density printing in which the print density is lower than that of the normal density printing, an exposure amount is reduced to a lower density than in the normal density printing. It is characterized in that the exposure amount is increased according to the stirring time of the developing device after the printing is set.

According to a fourth invention of the present application, an electrostatic latent image corresponding to an image is formed on the surface of a photoconductor charged by exposure.
Toner formed in the developing device is made visible by adhering the toner in the developing device to the formed electrostatic latent image, and the toner image is transferred to a sheet, and the print density is controlled by changing the exposure amount. In the print density control method in the image forming apparatus that can switch the setting between the low density print and the print density that is lighter than the normal density print, when the low density print is set for a predetermined time or more, warming up before printing is performed. ,
It is characterized in that the toner in the developing device is replaced with new toner during or after printing.

[0010]

In the first aspect of the invention, the toner density in the developing device is increased when low density printing is continued for a long time. By doing so, the toner consumption in the developing device increases, the toner replenishment in the developing device increases, and the developing state at the time of setting the low density printing is improved, and good print quality is maintained.

In the second aspect of the invention, when the setting is changed from the normal density printing to the low density printing, a timer for measuring the stirring time of the developing device is set, and when the stirring time is long, the inside of the developing device is set. Increase toner density. By doing so, the toner consumption in the developing device increases, the toner replenishment in the developing device increases, and the developing state at the time of setting the low density printing is improved, and good print quality is maintained.

In the third aspect of the invention, when the setting is changed from the normal density printing to the low density printing, a timer for measuring the stirring time of the developing device is set, and when the stirring time is long, the exposure amount is increased. To do. By doing so, the toner consumption in the developing device increases, the toner replenishment in the developing device increases, and the developing state at the time of setting the low density printing is improved, and good print quality is maintained.

According to the fourth aspect of the invention, when the low density printing is set for a predetermined time or longer, the toner in the developing device is replaced with new toner during warm-up before printing, during printing, or after printing. In this way, the toner in the developing device can be replaced efficiently, the developing state at the time of setting the low density printing is improved, and good print quality is maintained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments.

FIG. 1 is a layout view of a photosensitive member of an image forming apparatus and various members around the photosensitive member. In the drawing, reference numeral 1 is a photosensitive member rotatable in a clockwise direction. A pre-charger 2 for charging the entire surface of the photoconductor 1 around the photoconductor 1 in the order of its rotation direction, and for exposing the surface of the photoconductor 1 to form an electrostatic latent image according to an image. Exposure source 3, a developing device 4 for developing the electrostatic latent image to form a toner image, and the toner image on the paper 11
A transfer device 5 for transferring the toner to the surface of the photoconductor 1, a cleaning device 6 for removing the residual toner on the surface of the photoconductor 1, and a charge eliminator 7 for erasing the residual charge by irradiating the surface of the photoconductor 1 with light. .

The developing device 4 detects a toner concentration in the developing device 41, a developing roll 41 for adhering toner to the surface of the photoconductor 1, an agitating mechanism 42 for agitating the toner and carrier in the developing device 4, and a toner concentration in the developing device 4. A toner concentration sensor 43 for controlling toner supply to the developing device 4 according to the detection result. Further, the developing device 4 is in communication with a toner hopper 9 that stores toner via a toner replenishing roll 8 that controls a toner replenishing amount.

The developing roll 41 is a magnet roll which is disposed in close proximity to the photoconductor 1 and in which a plurality of fixed magnets are arranged side by side inside an outer cylinder made of a non-magnetic material. The stirring mechanism 42 has a configuration in which, for example, a spiral stirring plate is provided around a shaft horizontally installed in the developing device 4. Toner density sensor 43
Detects the toner concentration in the developing device 4, outputs a control voltage corresponding to the detection result to the toner replenishing roll 8, controls the number of rotations of the toner replenishing roll 8 according to the control voltage, and causes the toner hopper 9 to The amount of toner supplied to the developing device 4 can be freely controlled.

A timer 10 for measuring the stirring time in the stirring mechanism 42 is provided so as to be connected to the stirring mechanism 42, and the timer 10 is operated by the stirring mechanism 42 at a start timing when the low density printing is set. The stirring time is measured, and the measurement result is output to the toner concentration sensor 43 and the exposure source 3. The toner concentration sensor 43 changes the control voltage to the toner replenishing roll 8 according to the measured stirring time.
Further, the exposure source 3 changes the exposure amount according to the measured stirring time.

Next, the operation will be described. Photoconductor 1
Is uniformly charged over the entire surface by the pre-charger 2,
An electrostatic latent image is formed on the photoconductor 1 by light irradiation from the exposure source 3. A stirring mechanism for the toner and the carrier in the developing device 4.
The developer is agitated at 42, becomes a developer, is conveyed by the developing roll 41 and contacts the photoconductor 1, and only the toner is attracted to the photoconductor 1 and the electrostatic latent image becomes a toner image. Then, this toner image is transferred onto the paper 11 by the transfer device 5. The paper 11 on which the toner image is transferred is conveyed to a fixing device (not shown), and the toner image is fused and fixed on the paper 11. After the transfer of the toner image, the residual toner on the photoconductor 1 is scraped off by the cleaning device 6, and the residual charge is erased by the light irradiation of the static eliminator 7 to prepare for the next series of processes.

During such an operation, the toner concentration in the developing device 4 is detected by the toner concentration sensor 43, and the detection result is converted into a control voltage and output to the toner replenishing roll 8. Accordingly, the toner is supplied from the toner hopper 9 to the developing device 4 via the toner supply roll 8.

In such an operation, the exposure source 3
By varying the exposure amount by, it is possible to perform high density printing, normal density printing, and low density printing. Specifically, when performing low density printing, the exposure amount by the exposure source 3 is made smaller than that during normal printing to form an electrostatic latent image.

By the way, when low density printing is performed for a long time, as described above, the amount of toner consumed from the developing device 4 is small, so that the stirring mechanism 42 in the developing device 4 is used.
As a result of stirring for a long time, the charge amount of the toner becomes high, and additives such as silica added for improving the fluidity of the toner scatter and decrease. The charge amount of the toner gradually increases with respect to the electrical energy of the electrostatic latent image on the photoconductor 1, and the latent image charge on the photoconductor 1 is electrically neutralized with the smaller amount of toner. Have done
The amount of toner transferred from the developing device 4 to the photoconductor 1 is reduced, and as a result, the print density becomes extremely low and the print quality deteriorates. In the present invention, in order to prevent such a situation, when low density printing is performed for a long time, the toner density in the developing device 4 is increased, the exposure amount is increased, and the inside of the developing device 4 is increased. Considering the timing of toner replacement. A specific method of the present invention will be described in each of the following examples.

(First Embodiment) From the normal density printing to the low density printing, if the setting state of the low density printing continues for a predetermined time after the density setting is changed, the toner hopper 9 is operated. The toner supply amount to the developing device 4 is increased to increase the toner density in the developing device 4. FIG. 2 shows the output (control voltage) of the toner density sensor 43 (vertical axis) and the developing device 4.
2 is a graph showing the relationship with the toner density (horizontal axis) in
The linear control relationship between the two is shown. In the first embodiment, the control voltage output from the toner density sensor 43 to the toner replenishing roll 8 is changed from the normal setting level M to the high density setting level L when the setting state of low density printing continues for a predetermined time or longer. To increase the toner density in the developing device 4.

If thin printing is continued for a long period of time, the toner charge amount becomes high and the printing density becomes low. However, if the toner density is increased as in the first embodiment, the toner inside the developing device 4 will be discharged. It is possible to suppress the increase in the charge amount,
Even if the low density printing is continued for a long period of time, it is possible to prevent the print from becoming extremely thin and to continue the stable low density printing.

(Second Embodiment) When the normal density printing is set to the low density printing, the timer 10 starts measuring the stirring time by the stirring mechanism 42. Then, the measurement operation is continued as long as the setting of the low density printing is continued, and the measurement time is output to the toner density sensor 43. Toner density sensor 43
Adjusts the control voltage output to the toner replenishing roll 8 according to the measurement time to increase the toner density in the developing device 4. For example, when the measurement time reaches a predetermined time, the control voltage output from the toner density sensor 43 to the toner replenishing roll 8 is set to the normal set level M, as in the first embodiment.
Is forcibly changed to a high density set level L, and toner is replenished so as to increase the toner density in the developing device 4.

When the agitation time is long because the print is thin, the frequency with which the toner comes into contact with the carrier increases, the charge amount of the toner increases, and the print density decreases.
When the toner density is increased according to the stirring time as in the embodiment, it is possible to suppress the increase in the charge amount of the toner in the developing device 4, and even if the low density printing is continued for a long time,
Stable low density printing can be continued by preventing extremely thin. Further, in the second embodiment, since the stirring time of the developer can be measured by the timer 10, it is possible to perform the control with higher accuracy as compared with the first embodiment.

(Third Embodiment) The timer 10 starts measuring the stirring time of the toner by the stirring mechanism 42 from the time when the normal density printing is set to the low density printing. And as long as the setting of low density printing is continued, the measurement operation is continued,
The measurement time is output to the exposure source 3. The exposure source 3 increases the exposure amount according to the measurement time. FIG. 3 is a diagram showing changes in the electrostatic latent image with changes in the exposure amount.
Shows the case where the measured value of the stirring time from the time when the normal density printing is set to the low density printing has not reached the predetermined time, and FIG. 3B shows the case where the measured value reaches the predetermined time. Shows. When the stirring time of the toner reaches a predetermined time, the exposure amount is increased as shown in FIGS. 3 (A) to 3 (B).

Since the amount of exposure is reduced and printing is performed lighter than in normal printing, if the stirring time becomes longer, the toner charge amount becomes higher and the printing density becomes lighter, but as in the third embodiment, stirring is performed. When the exposure amount is increased according to the time, the photoconductor 1
In this case, the amount of charge cancellation in the toner is increased, toner consumption is promoted, the toner agitation time is shortened, and the increase in the toner charge amount in the developing device 4 can be suppressed, and low-density printing is continued for a long time. However, it is possible to prevent extremely thinning and continue stable low-density printing. Further, in the third embodiment, since the stirring time of the developer can be measured by the timer 10, it is possible to perform the control with higher accuracy as compared with the first embodiment. Further, even when the toner density is not adjusted to obtain a sufficient print density as shown in the first and second embodiments, the exposure amount is increased as in the third embodiment. Therefore, stable low density printing can be performed.

Next, a toner replacement timing example will be described in which the toner in the developing device 4 is replaced smoothly to prevent the deterioration of the print quality that occurs when the low density printing is continued for a long time. The fourth to sixth embodiments will be described. FIG. 4 is a diagram showing a general print sequence in the image forming apparatus described above. When the power is turned on, a warm-up state (warming-up state) is set, and thereafter, when a print command is input from the connected host device, printing is executed.

FIG. 5 is a warming-up sequence diagram in the fourth embodiment (corresponding to the warming-up state in FIG. 4), and FIG. 6 is a printing end sequence diagram in the fifth embodiment (corresponding to the vicinity of the end of printing in FIG. 5). FIG. 7 is a printing sequence diagram (corresponding to printing in FIG. 5) in the sixth embodiment, and each (A) of FIGS. 4, 5, and 6 shows a sequence in which toner replacement is not performed, and FIG. Each of FIGS. 5 and 6 shows a toner replacement sequence according to the present invention. When the pre-charger 2 is turned on, the surface of the photoconductor 1 is uniformly charged, and printing can be performed by applying a developing bias to the exposed portion. In such a case, if the pre-charger 2 is turned off and the developing bias is applied without charging the photoconductor 1, the image is developed in the same manner as at the time of printing. As shown in B), the pre-charger 2 is repeatedly turned on and off.

(Fourth Embodiment) In the fourth embodiment, when low density printing is set for a long period of time, as shown in the warm-up sequence of FIG. 5, during the warm-up (warming-up) of the apparatus, exposure is performed. After the electrostatic latent image on the surface of the body 1 is developed into a toner image, the toner in the developing device 4 is replaced with a new toner for the purpose of reducing the charge amount of the toner. As described above, when the toner is warmed up, the toner is replaced, so that the frequency of the control operation as in the above-described first to third embodiments is significantly reduced, or even if the control operation itself is not performed at all. It is possible to reduce the charge amount and continue stable low-density printing.

(Fifth Embodiment) In the fifth embodiment, when low density printing is set for a long period of time, as shown in the print end sequence of FIG. After developing the electrostatic latent image into a toner image,
The toner in the developing device 4 is replaced with a new toner for the purpose of reducing the amount of charge of the toner. Generally, the warm-up in the image forming apparatus is performed when the main power is turned on or when the print suspension state is continued for a predetermined time or more, so that the warm-up sequence is less likely to occur and It is conceivable that the toner cannot be sufficiently replaced by the replacement method as in the fourth embodiment. Therefore, as in the fifth embodiment, toner is replaced frequently by replacing new toner after printing is completed.

(Sixth Embodiment) In the sixth embodiment, when low-density printing is set for a long period of time and continuous printing is continued, as shown in the printing sequence of FIG. After the replacement sequence is interrupted and the electrostatic latent image on the surface of the photoconductor 1 is developed into a toner image during printing, the toner in the developing device 4 is replaced with a new toner for the purpose of reducing the charge amount of the toner. Such a sixth embodiment is carried out at the time of low density printing such that the effect of improving the print density does not appear in the above-described first to fifth embodiments.

[0034]

As described in detail above, according to the present invention, when low density printing is continued for a long period of time, the toner density in the developing device is increased, the exposure amount is increased, and the toner density in the developing device is increased. Since a sequence for sequentially replacing the toner is added, it is possible to prevent deterioration of print quality during low-density printing, which contributes to stabilization of print density control and improvement of device reliability.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image forming apparatus that implements the present invention.

FIG. 2 is a graph showing the relationship between the output of the toner density sensor and the toner density in the developing device.

FIG. 3 is a diagram showing a change in an electrostatic latent image with a change in exposure amount.

FIG. 4 is a diagram showing a general printing sequence in the image forming apparatus.

FIG. 5 is a diagram showing a warm-up sequence in the image forming apparatus.

FIG. 6 is a diagram showing a print end sequence in the image forming apparatus.

FIG. 7 is a diagram showing a printing sequence in the image forming apparatus.

[Explanation of symbols]

 1 Photoreceptor 2 Pre-charger 3 Exposure source 4 Developer 5 Transfer device 6 Cleaning device 7 Static eliminator 8 Toner replenishing roll 9 Toner hopper 10 Timer 11 Paper 41 Developing roll 42 Stirring mechanism 43 Toner density sensor

Claims (4)

[Claims] 1. An electrostatic latent image corresponding to an image is formed on the surface of a charged photoreceptor by exposure, and toner in a developing device is made to adhere to the formed electrostatic latent image to make it visible. An image forming apparatus capable of switching between normal density printing and low density printing in which the printing density is lower than the normal density printing by transferring the image onto a sheet and controlling the print density by changing the exposure amount. The print density control method in the image forming apparatus, wherein the toner density in the developing device is increased when low density printing continues for a predetermined time or longer. 2. An electrostatic latent image corresponding to an image is formed on the surface of a charged photoconductor by exposure, and toner formed after agitating with a carrier in a developing device is attached to the formed electrostatic latent image. To visualize the toner image and transfer the toner image to paper, and control the print density by changing the exposure amount to set the normal density print and the low density print in which the print density is lighter than the normal density print. A method for controlling print density in a switchable image forming apparatus, wherein the toner density in the developing device is increased according to the stirring time of the developing device after setting to low density printing. Printing density control method in. 3. An electrostatic latent image corresponding to an image is formed on the surface of a charged photoconductor by exposing the charged photoconductor, and the toner after being stirred with a carrier in a developing device is attached to the formed electrostatic latent image. To visualize the toner image and transfer the toner image to paper, and control the print density by changing the exposure amount to set the normal density print and the low density print in which the print density is lighter than the normal density print. In a print density control method in an image forming apparatus that can be switched, the exposure amount is increased in accordance with the stirring time of the developing device after setting the low density printing by reducing the exposure amount compared to the normal density printing. And a method for controlling print density in an image forming apparatus. 4. An electrostatic latent image corresponding to an image is formed on the surface of a charged photoconductor by exposing the charged photoconductor, and toner in a developing device is attached to the formed electrostatic latent image to make it visible. An image forming apparatus capable of switching between normal density printing and low density printing in which the printing density is lower than the normal density printing by transferring the image onto a sheet and controlling the print density by changing the exposure amount. In the print density control method according to the item (1), when low density printing is set for a predetermined time or more, the toner in the developing device is replaced with a new toner during warm-up before printing, during printing, or after printing. A print density control method in an image forming apparatus.