JPS61215570A - Controller for toner density - Google Patents

Abstract

PURPOSE:To detect and control invariably accurate toner density by obtaining reference toner density data with a reference developer having constant toner density, calculating the maximum and minimum values and their mean value, and performing toner density control on the basis of those values. CONSTITUTION:The reference developer which has constant toner density is put in a developing device 7 previously and toner density is detected specific times to find the maximum value A and minimum value B, which are stored in a RAM 40. Then, every time an interruption is allowed, the maximum value A and minimum value B are read out to calculate their mean value C, which compared with toner density data D obtained by A/D conversion. Then, when D=C, a solenoid 39 is turned on to supply toner and when D>C, the data D is compared with the maximum value A; when D<=A, the solenoid 39 is turned on and when D>A, the solenoid is turned off. Further, when D<C, the data D is compared with the minimum value B; when D>=B, the solenoid is turned on and when D<B, the solenoid is turned off. Consequently, a reference value for density decision making is given a specific range and invariably accurate toner density is detected and controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a toner concentration control device for controlling the toner concentration of a developer contained in a developing device in an image forming apparatus such as a copying machine.

[Technical Background of the Invention] In general, for example, copying machines often use a developing device that develops an electrostatic latent image on a photoreceptor by a magnetic brush method using a two-component developer consisting of toner and carrier. In a copying machine using such a developing device, the toner concentration of the developer contained in the developing device is detected by a density detector such as a magnetic sensor, and the output voltage of the density detector is determined by a preset unit voltage. The developer is compared with one reference voltage and the toner replenishing means is turned on or off depending on the comparison result to replenish the toner and control the toner concentration in the developer to be a constant value.

[Problems with the Background Art] However, in the past, the reference voltage was set using hardware, but according to this setting method, it can be set as long as it is within the range of the reference voltage, so accurate setting is difficult. It was impossible. In addition, the output voltage of the concentration detector generally fluctuates depending on the stirring state of the developer in the developing device (that is, the amplitude of the output voltage changes minutely).
. Therefore, depending on how the reference voltage is set, the output voltage may deviate from the set range due to fluctuations in the output voltage. Therefore, the conventional control method has a problem in that it is not always possible to accurately detect and control the toner density.

[Object of the Invention] The present invention has been made in view of the above circumstances, and an object thereof is to provide a toner concentration control device that can always accurately detect and control toner concentration.

[Summary of the Invention] In order to achieve the above object, the present invention obtains reference toner density data in advance using a reference developer with a constant toner density, and calculates the maximum value, minimum value, and average value of this toner density data. are determined, respectively, and toner density control is performed based on the determined maximum value, minimum value, and average value.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 5 shows a copying machine as an example of an image forming apparatus according to the present invention. That is, 1 is a housing, and a photosensitive drum 2 that rotates in the direction of arrow a in the figure is provided approximately at the center of the housing. Further, in the upper part of the housing 1, a document table 3 for supporting a document is provided so as to be able to reciprocate in the direction indicated by the arrow in the figure. By moving the document table 3 in synchronization with the rotation of the photoreceptor drum 2, the light emitted from the exposure lamp 4 is reflected by the document on the document table 3, and the reflected light is transmitted through convergent light transmission. An image is formed on the photoreceptor drum 2 by the body 5, and is reflected on the photoreceptor drum 2 as an inverted image of the document. At this time, by charging the surface of the photoreceptor drum 2 with the charging device 6, an inverted image of the original is formed on the photoreceptor drum 2 as an electrostatic latent image, and this electrostatic latent image is developed. It is configured to be visualized by applying toner with a container 7.

On the other hand, a paper feed device 8 is provided at a lower portion of the housing 1 to supply paper to the lower part of the photoreceptor drum 2 (image transfer section 14). The paper feed device 8 includes a paper feed cassette 9 which is removably attached to the left side of the housing 1 and stores a plurality of sheets of paper, and a manual feed cassette 9 which is protruded from the right side of the housing 1 and is used to feed paper manually. 1 sheet of paper from the paper table 10 and the paper feed cassette 9
It has a paper feed roller 11 that feeds sheets one by one, and a transport roller 12 that transports the paper sent out by the paper feed roller 11. At the same time as stopping the
The configuration includes a registration roller 13 that corrects the inclination of the leading edge of the paper and sends the paper to the image transfer unit 14 at a timing such that the leading edge of the paper and the leading edge of the toner image on the photoreceptor drum 2 coincide. There is.

The paper conveyed by the registration rollers 13 is sent to the image transfer section 14. The paper sent to the image transfer unit 14 comes into close contact with the surface of the photoreceptor drum 2 at the transfer charger 15, and the toner image on the photoreceptor drum 2 is then charged by the charger 15. is transcribed. After the transfer, the photosensitive drum 2 is configured so that residual toner on the surface thereof is removed by a cleaner 16 and the photosensitive drum 2 returns to its initial state. On the other hand, the paper after transfer is transferred to the transport roller 1.
7 to a heat roller 18 as a fixing device,
By passing through the fixing roller 18, the transferred image is heated and fixed. Then, the paper after fixing is transferred to the paper ejection roller 1.
9, the paper is discharged onto a tray 20 outside the housing 1.

The developing device 7 performs development using a two-component developer consisting of toner and carrier, and by forming a magnetic brush of the developer on the surface, the developer is applied to the area to be developed, that is, the photosensitive drum 2. A magnetic roller (
(developing roller) 21. In addition, 22 is the developing device 7
This is a developer stirring body that stirs the developer inside. A magnetic sensor 2 as a density detection means is mounted on the side wall of the developing device 7.
3 is mounted with its detection head 24 portion exposed inside the developing device 7, and the toner concentration of the developer in the developing device 7 is detected by a change in the magnetic permeability of the developer. Further, a toner hopper 25 containing replenishment toner is provided above the developing device 7, and as a toner replenishing roller 26 provided at the bottom thereof rotates, the toner in the toner hopper 25 is transferred to the developing device 7. It is designed to be replenished internally. The toner supply roller 26 is rotatably driven by a solenoid (not shown) via a rotation mechanism (not shown).

FIG. 1 shows a toner density control circuit.

That is, the magnetic sensor 23 includes a detection head 24 that includes an adjustment coil and a detection coil that come into contact with the developer in the developing device 7 and detect the magnetic permeability of the developer.
an oscillator 31 that drives the oscillator and outputs a reference phase signal, an amplifier 32 that amplifies the minute output signal from the detection head 24, and a detection signal amplified by this amplifier 32 and a reference phase signal output from the oscillator 31. a phase comparator 33 that compares the phase difference between the two, and a low-pass filter 34 that shapes the waveform of the signal output from the phase comparator 33.
It consists of The characteristics of the output voltage with respect to the toner concentration of this magnetic sensor 23 are shown in FIG.
The output voltage increases as the toner concentration decreases. The output voltage of the magnetic sensor 23 is supplied as an analog signal to an 8-bit A/D conversion circuit 35. This A
The /D conversion circuit 35 starts a conversion operation when a conversion command signal is supplied from a microcomputer (hereinafter simply referred to as microcomputer) 36 that controls the entire copying machine, and converts the input analog signal into digital data. The data is then supplied to the microcomputer 36 as multi-stage toner density data. Further, an auto toner set mode switch 37 is connected to the microcomputer 36, and by turning on this switch 37, the auto toner set mode is set. Further, a solenoid drive circuit 38 is connected to the microcomputer 36, and this drive circuit 38 drives a toner replenishment solenoid 39. Note that the toner replenishing solenoid 39 is used to rotationally drive the toner replenishing roller 26.

Furthermore, the microcomputer 36 has a RAM for storing reference data.
(Random access memory) 40 is connected, and this RAM 40 is backed up by a backup power source 41 such as a battery.

Next, the operation in the above configuration will be explained. First, the operation of the main program will be explained with reference to the flowchart shown in FIG. Now, when the copy key (not shown) is turned on, the process proceeds to step A1, where it is determined whether the mode is normal copy mode or auto toner set mode based on the state of switch 37. If it is normal copy mode (if switch 37 is off) Proceed to step A2. In step A2, an external interrupt timer is set to permit external interrupts at intervals of 10 m5ec, for example, and the process proceeds to step A3 for normal copy control. Note that when an interrupt is permitted by the external interrupt timer, an interrupt program for the automatic toner detection mode, which will be described later, is executed. On the other hand, in step A1, if the auto toner set mode is selected (if the switch 37 is in the on state), step A
The process proceeds to Step 4, where a timer is set for, for example, 3 minutes to stir the developer, and the process proceeds to Step A5. In step A5, it is determined whether 3 minutes have elapsed or not, and when the 3 minutes have elapsed, the process proceeds to step A6. In step 86, for example, 35Q
Set the msec timer and proceed to step A7. In step A7, it is determined whether 350 m5 ec has elapsed or not, and when 350 m5 ec has elapsed, the process proceeds to step 88. In step 88, the microcomputer 36 starts A/D conversion by supplying a conversion command signal to the A/D conversion circuit 35, and the process proceeds to step A9. In step 80, the above A
It is determined whether the /D conversion operation is the first operation, and if it is the first operation, the process advances to step A10. In step AIO, the toner density data obtained by the A/D conversion is stored in the first area of the RAM 40, and the process proceeds to step A11. In step A9, if it is not the first operation, the process advances to step A12. In step A12, it is determined whether or not the current A/D converted toner density data is greater than the previous toner density data, and if so, the process advances to step A13. In step A13, the current toner density data is stored in the second area of the RAM 40 as the maximum value A, and the previous data is rewritten), and the process proceeds to step A11. In step A12, if the toner density data is not greater than the previous toner density data, the process advances to step A14. In step A14, it is determined whether the current A/D converted toner density data is smaller than the previous toner density data,
If it is smaller, proceed to step A15.

In step A15, the current toner density data is stored in the third area of the RAM 40 as the minimum value B, and the previous data is rewritten), and the process proceeds to step A11. In step A14, if the toner density data is not smaller than the previous toner density data, the process advances to step A11. In step A11,
It is determined whether or not the auto toner set mode is set. If the mode is not the auto toner set mode (if the switch 37 is off), the process returns to step A2. If the auto toner set mode is selected, the process returns to step 86. Repeat the same action. Note that step A12. The judgment in A14 is that when the second operation is performed, the RA during the first operation is
This is done by comparing the data with the data stored in the first area of M40, and from the third time onwards, the data is compared with the data stored in the second area of RAM40.
This is done by comparing the maximum value A and the minimum value B stored in the third area. After repeating this a predetermined number of times every 350 msec, the switch 37 is turned off to end the auto toner set mode operation, and the RAM 4
Maximum value A and minimum value B are stored in 0. In the case of this automatic toner set mode, a reference developer with a constant toner concentration is stored in the developing device 7 in advance, and the toner concentration is detected as described above and its maximum value A and minimum value B are determined. Each is what they are looking for.

Next, the operation of the interrupt program will be explained with reference to the flowchart shown in FIG. As described above, this operation is performed every time an interrupt is enabled by the external interrupt timer at intervals of 10 m5ec. If the interrupt is permitted, the process proceeds to step B1 to start A/D conversion, and the process proceeds to step B2. In step B2, the maximum value A and minimum value B stored in the RAM 40 are read out, and in step B
Proceed to step 3. In step B3, the maximum value A and the minimum value B read from the RAM 40 are added (A+8) and divided by 2 to obtain the average value C, and the process proceeds to step B4. In step B4, the toner density data D obtained by the A/D conversion is compared with the average value C obtained above.
If =C, proceed to step B5. In step B5,
Turn on the solenoid 39 to replenish toner and return to the main program. In step B4 above, D>C
If so, proceed to step B6. In step B6, the toner density data D obtained by the above A/D conversion and the above RA
A comparison is made with the maximum value A read from M40, and D≦A.
If so, proceed to step B5 and turn on the solenoid 39, and if D>A, proceed to step B7. In step B7, the solenoid 3'9 is turned off and the process returns to the main program. Further, in step B4, if it is DEC, the process proceeds to step B8. In step B8, the toner density data D obtained through the A/D conversion is compared with the minimum value B read out from the RAM 40, and if D≧B, the process proceeds to step B5, where the solenoid 39 is turned on, and D< 8
If so, proceed to step B9.

In step B9, the solenoid 39 is turned off and the process returns to the main program.

In the above embodiment, a case was explained in which the toner concentration of the developer is controlled in a copying machine, but the present invention is not limited to this, and development may be performed using a two-component developer consisting of toner and carrier. The invention can be applied to image forming apparatuses (for example, laser printers, electronic printers, etc.) equipped with a developing device that performs this process, as long as the toner concentration of the developer is controlled.

[Effects of the Invention] As detailed above, according to the present invention, reference toner density data is obtained in advance using a reference developer having a constant toner density, and the maximum value, minimum value, and average value of this toner density data are calculated. By determining each value and performing toner concentration control based on the determined maximum, minimum, and average values, it is possible to set the reference value for density determination within a predetermined range, thus solving the conventional problem. It is possible to provide a toner concentration control device that can eliminate spots and always accurately detect and control toner concentration.

[Brief explanation of the drawing]

The figures are for explaining one embodiment of the present invention, and FIG. 1 is a configuration diagram of a toner concentration control circuit, FIG. 2 is a diagram showing characteristics of output voltage with respect to toner concentration of a magnetic sensor, and FIG. FIG. 4 is a flowchart for explaining the operation of the main program, FIG. 4 is a flowchart for explaining the operation of the interrupt program, and FIG. 5 is a side view schematically showing the configuration of the copying machine. 2... Photosensitive drum, 7... Developing device, 21... Magnetic roller, 23... Magnetic sensor (density detection means), 2
4...Detection head, 25...Toner hopper, 26.
... Toner supply roller, 35 ... A/D conversion circuit, 3
6... Microcomputer, 38... Solenoid drive circuit, 3
9...Solenoid for toner replenishment, 40...RAM.

Claims (5)

[Claims] (1) In an image forming apparatus that performs image formation using a developing device equipped with a developer conveying means for conveying a two-component developer consisting of toner and carrier to a developing area, a developing device housed in the developing device A concentration detection means for detecting the toner concentration of the agent and converting it into an analog electric signal, a conversion means for obtaining multi-level toner concentration data by converting the output signal of the concentration detection means into digital data, and the conversion means means for respectively obtaining the maximum value, minimum value, and average value of the toner density data for the reference developer having a constant toner density obtained in , and the maximum value, minimum value, and average value obtained by this means and the converting means. A toner characterized by comprising a comparison means for comparing the obtained toner concentration data with the actual developer, and a toner replenishment means for replenishing the toner to the developing device according to the comparison result of the comparison means. Concentration control device. (2) The toner concentration control device according to claim 1, wherein the concentration detection means is a magnetic sensor that detects the toner concentration of the developer by magnetically detecting a change in the magnetic permeability of the developer. (3) The toner density control device according to claim 1, wherein the developer conveying means is a magnetic roller that conveys the developer while rotating. (4) The toner density control device according to claim 1, wherein the image forming device is a copying machine. (5) The toner density control device according to claim 4, wherein the developing area is a surface of a photoreceptor on which an electrostatic latent image is formed.