JPH0419766A - Toner concentration controller for image forming device - Google Patents

Abstract

PURPOSE:To carry out accurate toner concentration control by measuring the output characteristic change in a toner concentration sensor based on the degree of a change in a concentration detecting signal when the toner of a fixed quantity is replenished, and carrying out a correction with respect to a reference value. CONSTITUTION:The concentration detecting signal detected after the toner of the fixed quantity is replenished into a developer and the concentration detecting signal before the toner is replenished are compared. Thus, the output characteristic change of the toner concentration sensor 7 caused by a bulk density change, a spent phenomenon, further, the stain of the surface of a transparent plate 44, etc., is measured and considered, so that the correction with respect to the reference value is properly carried out. Thus, the deviation of the detected and actual toner concentration is resolved and accurate toner concentration control can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner density control device for an image forming apparatus.

The branch two-component developer is composed of a toner that visualizes an electrostatic latent image on a photoreceptor, and a carrier that applies an electric charge to the toner through triboelectric charging and transports the toner to a development area. The carrier is not consumed during continuous printing and is always retained in a constant amount in the developing device. On the other hand, toner is consumed during continuous printing.

When the toner in the developer is consumed, the toner density changes and affects the image density, so it is necessary to control this constant. Therefore, changes in toner density are detected by magnetic changes or changes in the amount of reflected light, and toner is replenished based on the results to control the toner density to be constant.

A method using magnetism is a method of detecting toner concentration by detecting changes in the amount of carrier per unit volume present in the developer as changes in magnetic permeability, converting the detected magnetic permeability into voltage, This is compared with a reference voltage, and the required amount of toner is replenished based on the comparison result.

The method using light is a method in which the developer is irradiated with light and the amount of reflected light is detected to detect the toner density.
The detected amount of reflected light is converted into a voltage change, and as described above,
This is compared with a reference voltage, and toner is replenished based on the comparison result.

However, the method using magnetism described above detects the toner concentration from the amount of carrier in the developer, and is not a method for detecting the amount of toner itself. The detection result of toner density will change due to factors other than printing, that is, factors other than toner consumption.In the method using light, as mentioned above, causes other than printing durability, that is, toner consumption will change. The toner density detection result changes due to other factors.

The main causes of changes in detection results other than the above-mentioned toner consumption include the following.

(2) The toner is subjected to post-treatment to improve toner fluidity and stabilize charging. Usually, about 0.2% to 1% of silica is dispersed in the toner as a post-processing agent. Silica may be attached to the initially replenished toner, or the post-processing agent may be removed from the toner as it is agitated. For this reason, as the developer is used up, the bulk density changes, and in the magnetic toner concentration detection method that detects the amount of carrier, the toner concentration indicated by the detection result is higher than the actual toner concentration. .

(2) When the toner is consumed relatively quickly, the time during which it is stirred in the developing device is shortened, so that less of the post-processing agent is removed. That is, the degree of deviation between the actual toner concentration and the detection result varies depending on whether the toner is consumed quickly or not.

■As the developing process consumes the toner starting from the one with the lowest charge amount, the toner with the higher charge amount, that is, the toner with a smaller particle size, accumulates during continuous printing. The bulk density changes, and the toner concentration indicated by the detection result is higher than the actual toner concentration.

(2) Particularly problematic in optical detection methods is the spent phenomenon of carriers. What is the spent phenomenon?
As the developer is used, the toner gets crushed and adheres to the carrier, causing the carrier that should normally absorb light to reflect light. In this case, as well, the detection result is The displayed toner density is higher than the actual toner density.

■Furthermore, this is also a problem with the optical detection method, as toner adheres to the surface of the optical sensor, and the optical sensor detects the toner concentration from the reflected light from this adhered toner. There is a problem that the toner concentration indicated by the detection result is higher than the actual toner concentration.

As described above, as the developer is used up, the bulk density changes, and the toner concentration value indicated by the detection result changes toward a higher value than the actual toner concentration. Therefore, if constant toner density control is performed based on this detection result, there is a drawback that the image density gradually becomes thinner.

Therefore, there is a known method in which the change in bulk density is predicted from the cumulative number of copies, the operating time of the developing device, etc., and the reference voltage is corrected (see Japanese Patent Laid-Open No. 5773771).

However, since the conventional reference value correction described above is based on the predicted bulk density, the reference value tends to be corrected by predicting a bulk density that is different from the actual change in bulk density. The problem is that toner density cannot be controlled.

In view of the above circumstances, the present invention measures changes in the output characteristics of a toner density sensor based on the degree of change in the density detection signal when a certain amount of toner is replenished, and appropriately corrects the reference value. The object of the present invention is to provide a toner density control device for an image forming apparatus.

In order to solve the above-mentioned problem, the toner density control device for an image forming apparatus according to the present invention for controlling i's uses a density detection signal that changes according to a change in toner density of a two-component developer as a reference value. In the toner density control device of an image forming apparatus, which controls the toner density by replenishing an appropriate amount of toner based on the comparison result, the density detection signal detected after a certain amount of toner is replenished into the developer and the toner The apparatus is characterized by comprising a correction means for correcting the relative relationship between the concentration detection signal and a reference value based on the degree of difference from the concentration detection signal before replenishment.

According to the above configuration, changes in the output characteristics of the toner concentration sensor due to changes in bulk density, spent phenomenon, and dirt on the surface of the toner concentration sensor are measured, and by taking these changes in output characteristics into consideration, Correction to the reference value is appropriately performed. This eliminates the discrepancy between the detected toner density and the actual toner density, making it possible to perform accurate toner density control.

! -Ship-■ An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

FIG. 1 shows a photosensitive drum 1, a developing device 2, an exposure light source 3,
FIG. 2 is an explanatory diagram showing mutual connections and arrangement relationships among a light source drive section 4, a mirror 5, a control system 6, an optical toner concentration sensor 7, a toner replenishment drive device 8, and the like.

The developing device 2 includes a magnet roller 10 for conveying the two-component developer to a position facing the circumferential surface of the photoreceptor drum 1 and supplying toner to the photoreceptor drum l, and a transfer agitation section 11 for stirring the developer while conveying it. , a toner replenishment roller 12 driven by the toner replenishment drive device 8, and a toner replenishment hopper 13 for storing toner.

The transfer agitation section 11 includes two transfer screws 25.
．． 26 are arranged in parallel with a partition plate 27 in between, and the developer is transferred and circulated and stirred by driving the transfer screws 25 and 26. The toner concentration sensor 7 is composed of an infrared LED 41, a photodiode 42, a housing 43, and a transparent plate 44, as shown in FIG. 2(a). As shown in the same character (b), the toner concentration sensor 7 has a transparent plate 44 connected to the transfer stirring section 1
1 as desired.

The control system 6 includes an input interface section 20, an output interface section 21, a ROM 22, a CPU 23,
It is configured to include a timer 35. Said CPU23
In addition to controlling the entire copying machine, it also plays a central role in controlling toner density.

Further, the ROM 22 stores various types of fillers necessary when the CPLi 23 performs toner density control.

FIG. 3 mainly shows a comparison part and a part for correcting the reference voltage. The comparison section includes a comparator 31 that compares the density detection signal (sensor output) output from the toner density sensor 7 with a reference voltage. The reference voltage generator 32 changes the reference voltage based on a correction signal from the CPU 23. As will be described in detail later, the CPU 23 detects the difference between a density detection signal detected when a certain amount of toner is replenished into the developer and is sufficiently stirred in the developer, and a density detection signal before toner is replenished. The relative relationship between the concentration detection signal and the reference value is corrected based on the degree of .

FIG. 4 is a flowchart schematically showing the operation of the copying machine. First, initial settings are made (S1), and then a reference value correction process for toner density control is performed (S2). Next, accept key input and perform settings based on this key (S3
). Next, determine whether the print switch is turned on or not! , (S4), if it is OFF, it moves to step 3, while if it is ON, it starts the copying operation and (3, 5)
, counting the number of copies (S7). Then, it is determined whether the number of copies has reached the number set manually with the key (S7), and if it has reached the number, it is determined that it is finished and moves to step 3, whereas if it has not reached the number, the copying operation continues. As soon as possible, proceed to step 5.

Figure 5 shows the AT for toner density control in step 2 of Figure 4.
It is a flowchart which shows DC reference value correction processing. First, the timer 35 is used to set the time T1 (5ll), and the transfer screws 25 and 26 are started to be driven (S12).
. Next, it is determined whether the time T1 has ended (S13
), if the process has not been completed, the process proceeds to step 12, while if it has been completed, the process proceeds to step 14. That is, in the steps 11 to 13, the time T is applied to the developer.
1 pre-stirring will be performed. In step 14, the output v1 of the toner concentration sensor 7 is measured.

Next, a certain amount of toner is replenished into the transfer stirring section ll (515), and a time T2 is set by the timer 35 (51).
6) Start driving the transfer screws 25, 26 (
517).

The amount of toner supplied is, for example, about 1 g. Here, when 700 g of developer exists in the transfer stirring section 11 with a toner concentration of 8%, the amount of toner is 56
The amount of change in toner density will increase from 1.5 g to 57 g, but the change in toner concentration is only about 0.13%, which is small.
It does not adversely affect toner density control.

Next, it is determined whether or not time T2 has ended (S18).
If the process has not been completed, the process proceeds to step 17, while if it has been completed, the process proceeds to step 19. That is, in steps 16 to 18, the replenished toner is uniformly mixed with the developer by stirring.

When the time T2 expires, the output V2 of the toner concentration sensor 7 is measured (319). Next, the difference Δ between the output ■1 before toner replenishment and the output v2 after toner replenishment
(2) is calculated' (S20), and a correction value is calculated from this ΔV (321).

FIG. 6 is a graph showing the output characteristics of the optical toner density sensor with respect to toner density, and uses the degree of dirt on the transparent plate 44 as a parameter. The degree of dirt is A<B<C<
As shown by D, the slope of the output characteristic changes more gradually as the dirt becomes dirty. Note that the straight line indicated by A indicates a state in which the transparent plate 44 is not soiled.

Table 1 shows the relationship between the sensor output voltage change when the toner concentration changes by 1% and Δ■ when 1 g of toner is replenished in each case for the degree of contamination A to D. This is a table showing

Table For example, when the toner concentration is controlled to be constant at 8%, and the above Δ■ is 0.13 mV, the sensor output value when the toner concentration is 8% in the output characteristics of dirt D is used as the reference voltage. You can correct it accordingly. The value of the reference voltage is
The values are set as shown in Table 2 based on the sensor output when the toner concentration is 8% as determined by the graph of FIG. 6, and are selected according to the measured value of Δ■.

Table 7 (range of ΔV includes upper limit) FIG. 7 is a graph showing the output characteristics of the magnetic toner concentration sensor with respect to toner concentration, using bulk density as a parameter. When the bulk density is high and when the bulk density is low, the slope of the output characteristics is gentler when the bulk density is higher.

In this case as well, the reference voltage can be corrected based on the obtained output characteristics, as described above.

According to the above configuration, changes in the output characteristics of the toner concentration sensor 7 due to changes in bulk density, spent phenomenon, and dirt on the surface of the transparent plate 44 are measured, and by taking these changes in output characteristics into account, the reference value is determined. corrections are made appropriately. This eliminates the discrepancy between the detected toner density and the actual toner density, making it possible to perform accurate toner density control.

In addition, in a color copying machine, changes in toner density affect the hue, and accurate toner density control is required. Therefore, the toner density control device of the present invention is particularly useful in a color copying machine. Become something. In this case, the correction amount may be calculated by measuring the change in the output characteristics of the toner density sensor provided in each color developing device, and the reference voltage may be corrected using each correction amount.

The light reflection characteristics of each color toner (yellow, magenta, cyan) with respect to the wavelength of light are shown in Figure 8 (a) and (b).
) and (c), respectively. In this embodiment, an infrared LED 41 is used as a light emitting element, but each sensor may also use a light emitting element that emits light of a complementary color to the toner color.

Furthermore, the object of correction is not limited to the reference value, but may also be a concentration detection signal or a comparison result passed through the comparator 31.

According to the present invention of 4. Lessons F and 1 or more, the change in the output characteristics of the toner concentration sensor is measured, and this change in the output characteristics is taken into consideration.
Correction to the reference value is appropriately performed. This eliminates the discrepancy between the detected toner concentration and the actual toner concentration, and provides the effect of accurate toner concentration control.

[Brief explanation of the drawing]

1 to 8 show one embodiment of the present invention, and FIG. 1 shows the mutual connections and arrangement relationships of each functional member around the photoreceptor drum, the control system, the toner concentration sensor, etc. 2(a) is a sectional view of the optical toner concentration sensor, FIG. 2(b) is a sectional view showing the arrangement of the sensor, and FIG. 3 is a schematic configuration diagram showing the reference voltage correction section. , FIG. 4 is a flowchart showing the operation of the copying machine, FIG. 5 is a flowchart showing the operation of toner density control, FIG. 6 is a graph showing the relationship between the sensor output and toner density in the optical toner density sensor, and FIG. 7 8 is a graph showing the relationship between the sensor output and toner density in a magnetic toner density sensor, FIG. 8(a) is a graph showing the light reflectance of yellow toner, and FIG. 8(b) is a graph showing the light reflectance of magenta toner. The graph (c) is a graph showing the light reflectance of cyan toner. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 2... Developing device, 3... Light source, 6... Control system, 7... Toner density sensor, 8...
・Toner replenishment drive device, 11...Transfer stirring section, 22.
...ROM, 23...CPU, 25.26...Transfer screw 31...Comparator, 32...Reference voltage generator, 35...Timer. Patent applicant: Minolta Camera Co., Ltd. Figure 2 Figure 4 Figure 5 Figure 6 Figure 7 Toner production (wt'/s+)

Claims (1)

[Claims] (1) Toner in an image forming apparatus that compares a density detection signal that changes according to changes in toner density of a two-component developer with a reference value, and controls the toner density by replenishing an appropriate amount of toner based on the comparison result. In the density control device, the relative relationship between the density detection signal and a reference value is determined based on the degree of difference between the density detection signal detected after a certain amount of toner is replenished into the developer and the density detection signal detected before toner is replenished. 1. A toner density control device for an image forming apparatus, comprising a correction means for correcting.