JPS6113268A - Toner density controller - Google Patents

Abstract

PURPOSE:To reduce the variation of the toner density by limiting the time of the first toner supply to a certain value and inhibiting toner supply for a prescribed time till the next supply when the toner density is detected to supply the toner. CONSTITUTION:The toner density is detected by a photo diode 10 in a developing tank and is converted to a voltage by an operational amplifier 14 and a resistance 15, and noise is eliminated by an LPF18, and this voltage is amplified by a circuit consisting of an operational amplifier 19 and resistances 21 and 22 and is inputted to a comparator 22. The comparator 22 compares this input voltage with a standard voltage obtained by dividing a voltage Vc by resistaces 23 and 24 and inputs an outpt signal C to a mu computer 28. A pulse signal Ps from a synchronizing signal generating circuit 29 is inputted to the mu computer 28 also. The mu computer 28 turns on a transistor TR26 only for a prescribed time by the input signal C and the pulse Ps to operate an electromagnetic coil 27 and supplies the toner to the developing tank from a hopper omitted in the figure and inhibits toner supply for a prescribed time till the next supply. Thus, the error due to time lag is prevented to average the density.

Description

DETAILED DESCRIPTION OF THE INVENTION 149- This invention relates to a toner concentration control device for controlling the toner concentration of a developer in a developing device such as an electrophotographic copying device.

U1 Circulation A developing device of an electrophotographic copying machine using a dry two-component developer is constructed as shown in FIG. 1, for example.

To explain this simply, the two-component developer 2 consisting of toner and carrier in the developing tank 1 is stirred by an agitating blade 3 and passed through a pumping roller 4 and a developing roller 5 into a drum shape as shown by the thick arrow. It is completely supplied to the surface of the photoreceptor 6, and the electrostatic latent image on the photoreceptor 6 is developed.

The excess developer on the developing roller 5 is separated from the developing roller 5 by a separator tuff after passing through the developing position, and returns to the developing tank 1 through the duct 8.

Then, a toner concentration detector constituted by a light emitter ('LED) 9 and a light receiver (photodiode) 10,
The toner concentration of the developer is optically detected through the window 8a of the duct 8 based on the reflectance of the developer.

Further, the toner 12 in the toner tank 11 is replenished to the developer 2 in the developer tank 1 by rotation of the toner supply roller 13 .

FIG. 2 shows an example of a toner concentration control device for controlling the toner concentration of the developer in the above-described developing device.

The output of the photodiode 10 constituting the above-mentioned toner concentration detector is subjected to current-to-voltage conversion in a circuit consisting of an operational amplifier 14 and a resistor 15, passes through a low-pass filter 18 consisting of a resistor 16 and a capacitor 17, and is then connected to an operational amplifier IS and a resistor. It is amplified by an amplifier circuit consisting of 20.21, and compared with a reference level obtained by dividing the power supply voltage Vc by a resistor 23.24 by a comparator 22, and then binarized.

The output signal (concentration signal C) of this comparator 22 is applied to the base of a transistor 26 via a resistor 25, and when this signal C is at a high level (the toner concentration is light), the transistor 26 is turned on and the toner replenishment clutch 27 is driven. Then, the toner replenishing roller 13 shown in FIG. 1 is rotated to replenish toner into the developing tank 1.

That is, as shown in the flowchart of FIG. 3, this toner concentration control device turns on the replenishment clutch to replenish toner when the toner concentration is lighter than the reference value, and turns off the replenishment clutch when the toner concentration becomes higher than the reference value. The toner density of the developer is controlled by stopping toner replenishment.

By the way, since there is a response delay in detecting the concentration after toner replenishment, the first
The toner concentration of the developer directly below the toner replenishment roller 13 in the figure fluctuates as shown by the solid line A in FIG. do.

Fluctuations in the toner concentration within the duct 8 are approximately the same as fluctuations in the toner concentration of the developer supplied to the photoreceptor for image formation, so in curve 1, the image density is high near b1 where the toner concentration is high. This makes it easier for skin stains to occur.1
On the other hand, there is a problem in that near b2 where the toner density is low, the image density becomes low and a clear copy cannot be obtained.

Purpose This invention was made in view of the above-mentioned problems, and it is an object of the present invention to stably control the toner concentration in a developer to an appropriate value and obtain copies with a constant image density without background stains. The purpose is to make it possible to

■－Location The configuration of this invention will be explained below based on one embodiment.

FIG. 5 is a circuit diagram of a toner density control device showing an embodiment of the present invention.

This embodiment is obtained by adding a microcomputer and two synchronizing pulse generating circuits to the conventional toner density control device shown in FIG.

The synchronous pulse generation circuit 2 is a circuit that generates a synchronous pulse Ps in synchronization with the copying operation of the main body of the copying machine (not shown) and inputs it to the microcomputer 28. In this embodiment, one pulse is generated for each copy. do.

The microcomputer 28 inputs this synchronization pulse Ps and the concentration signal C output from the comparator 22,
Based on these signals, a first predetermined time t1 and a second predetermined time t2 are created by a preset program, and the toner concentration of the developer in the developing device is controlled by controlling on/off of the replenishment clutch. do.

That is, this microcomputer 28.

It serves as a toner replenishment control means and a replenishment time regulating means for regulating the toner replenishment time for one time.

Next, the toner density control operation during continuous copying executed by the microcomputer 28 will be specifically explained with reference to the flowchart of FIG. 6 and the timing chart of FIG. 7.

When the copier is turned on, the microcomputer 2
8 resets the internal counter that counts the synchronizing pulse Ps at 5TEP 1 and sets the count value to "0".

Then, the developer pumping clutch (not shown) is turned on, and the synchronizing pulse Ps is applied until the flow of the developer pumped up by the rotation of the pumping roller 4 in FIG. Since this does not occur, the judgment as to whether or not the synchronization pulse falls at 5TEP 2 and the judgment as to whether or not the synchronization pulse rises at 5TEP 3 are both No. 5TEP 2
Go back and repeat this.

When the copy operation starts and the synchronization pulse Ps falls, 5T
Since the judgment at EP 2 is YES and the counter has been reset, the count value of ST[EP4 is “0”.
” is also determined as YES, and the process proceeds to 5TEP 5.

Then, at 5TEP5, the density signal C output from the comparator 22 in FIG. 5 is sampled, and at 5TEP6, it is determined whether the toner density is lighter than the reference value bo shown in FIG. 7(A). The reference value of the density signal C is the toner density of the developer in the duct 8 in FIG. When it is darker, it becomes a low level -L", and when it is lighter, it becomes a high level "H".

Therefore, when the concentration signal C is "H" at the time of sampling as shown in FIG. rises, 5TEP
Execute step 8.

In this 5TEP 8, the transistor 26 shown in FIG. 5 is turned on, the replenishment clutch 27 is turned on, and the toner replenishment roller 13 shown in FIG. 1 is rotated to replenish toner into the developing tank 1.

Then, proceed to 5TEP 9, set "2" in the counter, and return to 5TEP 2.

After that, until the synchronization pulse Ps falls again, 5TEP2
and 5TEP 3 are repeated, and toner replenishment continues.

Then, when the synchronization pulse Ps falls in synchronization with the next copy operation, the process advances to 5TEP 4, but this time the counter r7J
, so proceed to 5TEPIO, decrement the counter (-1) L, and return to 5TEP 2.

Next, when the synchronization pulse Ps rises, 5TEP 2 to 5T
Proceed to EP3, 5TEPI 1, turn off the replenishment clutch at 5TEPII, stop toner replenishment, and proceed to 5TEPI
Return to 2.

Therefore, toner is replenished only during the first predetermined period t1 corresponding to one period of the synchronization pulse Ps.

Next, when the synchronization pulse Ps falls, 5TEP 2 to 5T
Proceed to EP4, the counter is rlJ, so 5T
Decrement the count value of the counter again with EPIO (
-1) and return to 5TEP 2. Therefore, at this time, the count value of the counter becomes "0".

Thereafter, when the synchronizing pulse Ps falls, the process proceeds from 5TIEP 2 to 5TEP 4, and since the counter is at "0" at this time, the process proceeds to step 5, where the density signal C is sampled again.

That is, the concentration signal is not sampled during the second predetermined time t2 corresponding to two periods of the synchronization pulse Ps,
Toner replenishment is prohibited.

If the density signal C is "H" (light) at this sampling time, toner replenishment is performed again for a first predetermined time, and then toner replenishment is prohibited for a second predetermined time.

In the example shown in FIG. 7, since the density signal is "L" (dark) at this time, toner replenishment is prohibited and the density signal becomes -H" at the fall of the primary synchronization pulse Ps, so toner is replenished. Start.

That is, toner replenishment is enabled at the time when the density signal C is sampled, and when this density signal C is H'', toner is replenished for a first predetermined time tl, and thereafter, it is set in the counter of the microcomputer 28. During a second predetermined time t2 corresponding to the period of several X synchronization pulses, the density signal C cannot be sunblinked, and toner replenishment is prohibited.

If such a replenishment time regulating means is provided to control the toner concentration, it is possible to prevent excessive toner replenishment, and the toner concentration of the developer flowing in the duct 8 is determined by the broken line L in FIG. 7(A). As shown, it is stably controlled near the reference value bo,
Since the fluctuation width ΔTC is smaller than that of the conventional example shown in FIG. 4, the image density can be kept substantially constant.

Note that the second predetermined time t2 for prohibiting toner replenishment is as follows:
It is determined according to the time it takes for the developer whose concentration has been increased by the toner replenished during the first predetermined time tl to reach the duct 8.

Then, when the toner replenishment for the first predetermined time t1 and the toner replenishment stop for the second predetermined time t2 are repeated alternately, the maximum toner replenishment amount is approximately 1 image area ratio (image area on the document/document area). The first .
By setting the second predetermined time, there will be no shortage of toner supply in continuous copying of originals with an image area ratio of 5 to 20% of normal originals.

Further, in this embodiment, the sampling of the density signal C and the ON/OFF timing of the replenishment clutch are performed according to the falling and rising edges of the synchronizing pulse, but a process signal of the main body of the copying machine or the like may also be used.

As described above, the toner density control device according to the present invention has the following features:
Toner replenishment is prohibited for a certain period of time after toner replenishment, which prevents the amount of toner replenishment from becoming excessive, and keeps the toner concentration of the developer stable at an appropriate value and reduces its fluctuation range. be able to.

As a result, it is possible to obtain a copy with a constant image quality, and also to prevent the occurrence of background stains.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an example of a developing device in a copying machine. Fig. 2 is a circuit diagram showing an example of a conventional toner concentration control device, Fig. 3 is a flowchart showing its operation, and Fig. 4 is a timing chart showing the relationship between the operation of the replenishment clutch and toner concentration. Chart diagram: FIG. 5 is a circuit diagram showing an embodiment of the present invention. FIG. 6 is a flowchart of the toner replenishment operation program executed by the microcomputer, and FIG. 7 is a timing chart for explaining the operation of the embodiment shown in FIGS. 5 and 6. 1... Developing tank 2... Two-component developer 4...
- Pumping roller 5...Developing roller 6...Photoconductor 8...Duct 9...Light emitter 1
0... Light receiver, 11... Toner tank 13...
Toner supply roller 22... Comparator 27...
Replenishment clutch 28-°° Microcomputer 2 days... Synchronous pulse generation circuit Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] 1. A toner concentration detection means for detecting the toner concentration of the developer at a predetermined location in a developer flow path in a developing device using a two-component developer, and toner replenishment controlled according to the detection result of the toner concentration detection means. and a toner replenishment control means, wherein the toner replenishment control means limits one toner replenishment time to a first predetermined time, and thereafter prohibits toner replenishment for a second predetermined time. A toner concentration control device characterized by being provided with a regulating means.