JPH0362269B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for controlling image density in a copying machine using a two-component developer and an apparatus for carrying out the method.

Prior Art Conventional image density measurement involves placing a patch at a constant density on a platen support, scanning it to form a patch latent image on the drum surface, detecting its optical density, and comparing it with a reference level. This was done by However, since this method forms patch latent images on the drum surface, it is affected by changes in the charging properties of the photoreceptor. Specifically, the charging characteristics of the photoreceptor change depending on its fatigue state, and particularly in a continuous copying process, the charging potential of the photoreceptor gradually decreases as the number of copies increases. To compensate for this, copying machines equipped with conventional image density measuring devices
Since the toner concentration is increased to compensate for the charging characteristics, the resulting toner concentration is high, causing fogging in the background and dirt inside the machine due to toner blowing out.

Purpose of the Invention Therefore, the present invention has been made in view of the above-mentioned drawbacks, and by making various improvements to the conventional image density control method, it is possible to stably achieve image density without being affected by the charging characteristics of the photoreceptor. An object of the present invention is to provide a method for maintaining image density and an apparatus for carrying out the method.

Structure of the Invention The above object is to control image density by forming a patch latent image of a constant size on the surface of a photoreceptor drum, measuring the optical density of the patch image after development, and controlling the amount of toner replenishment by comparing it with a reference level. A method, comprising: a) measuring the density of the patch image in a preparation cycle before the start of the copying process; b) comparing the measured patch density with a reference value;
In response to the result, one is selected from a plurality of preset toner supply amounts, c. cumulatively calculates the copying area based on the copy size and number of copies during the copying process, and d) the cumulative copying area is a constant value. This can be achieved by supplying the amount of toner selected in b above into the developing machine each time the amount of toner is reached.

Further, the apparatus for carrying out the above method forms a patch latent image of a fixed size on the surface of the photoreceptor, measures the optical density of the patch image after development, and controls the amount of toner replenishment by comparing it with a reference level. The image density measuring device measures the density of a patch image in a preparation cycle before the copying process, and comprises a patch density sensor consisting of a light emitting element and a light receiving element, and a patch density sensor connected to the output of the sensor. The outputs of the paper size sensor and paper transport switch are inputted to a comparison circuit that compares the density value with the paper setting reference density value, a toner supply amount setting circuit that sets the toner supply amount based on the comparison circuit, and a toner supply amount setting circuit that sets the toner supply amount based on the comparison circuit. The relative area ratio is counted for each output of the paper travel switch,
An integrating circuit that includes a counter that generates an output when the counted value reaches a set value, and in response to the output of the integrating circuit, the amount of toner corresponding to the output of the toner supply amount setting circuit is supplied from the toner replenisher to the developing machine. This can be achieved by comprising a motor drive control circuit that controls the toner drive motor and the toner drive motor.

EXAMPLES The present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory diagram of a copying machine that uses a two-component developer and is equipped with an image density control device according to the present invention. 5, a transfer corotron 6, a static elimination corotron 7, a cleaning device 8, and a static elimination lamp 9 are shown. In a normal copying process, after the photosensitive drum 2 is charged with a charging corotron 3, a latent image corresponding to a document (not shown) placed on the document table 1 is exposed to an exposure lamp 4.
formed by. This latent image is visualized by a developing device 5, and is transferred from a paper tray 10 to a suitable conveyance path 1.
Transfer corotron onto paper fed through 1 and 6
Transcribed by. Thereafter, the photosensitive drum is cleaned by a cleaning device 8 and static electricity is eliminated by a static elimination lamp 9. On the other hand, on the paper, the developed image transferred by the transfer corotron 6 is transferred to the static eliminating corotron 7.
After the static electricity is removed by the image forming apparatus, the image is transported to a fixing device (not shown), where it is fixed, and then discharged from the copying machine. The above is a general one copy cycle, but
In the present invention, in the so-called dead cycle before the normal copy cycle starts,
A patch 12 provided in a non-image area of the document platen 1 is made into a latent image on the photoreceptor drum 2, and made into a visible image by the developing device 5.
A transfer corotron 6 transports the toner without transferring it to paper, and a patch density sensor on the transport path measures the toner density. Thereafter, the developing toner is collected by a cleaning device 8.

In this way, in the present invention, toner density measurement is performed during the preparation cycle (dead cycle) before the start of the (continuous) copying cycle, instead of the conventional method of measuring toner concentration in the dead cycle of the continuous copying cycle. By doing this, it is possible to prevent changes in charging characteristics (decrease in charging voltage) due to fatigue of the photoreceptor drum surface that occurs when measuring toner concentration during continuous copying cycles, and also to prevent changes in charging characteristics (decrease in charging voltage) that occur as a result of high toner concentration. It is possible to prevent fogging of the background area and dirt inside the machine due to toner blowing out.

More specifically, when a print start button (not shown) of a copying machine is pressed, the photosensitive drum 2 starts rotating, and when the rotation reaches a steady state, the charging corotron 3 starts discharging. When the print start button is pressed, the exposure lamp 3 lights up in a stationary state, and the patch 12 is irradiated onto the photoreceptor drum 2. However, since the exposure lamp 3 is stationary, the patch 12 is illuminated in a stationary state, but since the exposure lamp 3 is stationary, the patch 12 is illuminated in a stationary state. A latent image is formed. This band-shaped patch is erased by an unnecessary latent image erasing lamp (not shown) provided above the developing section, except for the portion necessary for density measurement, which will be described later, to form a patch image for measurement. This image is visualized with toner from the developing device 5, passes through a transfer and charge removal corotron area, and is then conveyed to the patch density sensor section. This sensor is composed of a known device, and has a structure in which a light emitting element and a light receiving element are paired, and the amount of light reflected from the drum in a clean state without toner and the relative amount of reflection from the developed patch. is measured and its output is supplied to one input of the comparator circuit 13. The other input of the comparator circuit 13 is set to a predetermined reference concentration. The output of the comparison circuit 13 is supplied to a toner supply amount setting circuit 14. Therefore, if the reference value is t ₁ and the measured value is t ₂ , when t ₁ = t ₂ , the output of the circuit 14 is a signal that supplies the average usage amount (N: normal), and t ₁ > t When t 1 <t ₂ , a signal representing a usage amount below the average usage amount (L: decrease) is output, and when t ₁ <t ₂ , a signal representing the usage amount above the average usage amount (H: increase) is output. This output signal is supplied to the motor drive control circuit 15.

The present invention is further configured such that the number of copies is accumulated at an area ratio proportional to the copy size, and when the accumulation reaches a predetermined value, it is supplied to the above-mentioned motor drive control circuit. has been done.

In this configuration, in the diagram shown in FIG. 1, the output of the paper size sensor 20 provided near the paper storage tray 10 is connected to one input of the integration circuit 16, and the output is provided in the middle of the paper conveyance path. The output of the paper transport switch 17 is connected to the other input of the integration circuit 16. The integrating circuit 16 has a counter inside, and for each signal input from the paper transport switch, the signal from the paper storage tray 10 is 10 if it is A3, 8 if it is B4, and 8 if it is A4. It is configured to count integers according to the relative area ratio, such as 5 for B5 and 4 for B5. (It is also possible to calculate and accumulate the area ratio more accurately, but in this case, the counting means becomes large.) Then, by presetting this counter to, for example, 40,
The motor drive circuit 1 is configured to generate an output every time it counts or every time the count exceeds 40.
Supply to 5. The motor drive control circuit 15 supplies an amount of toner corresponding to the signal from the circuit 14 to the developing machine 5 from the toner replenisher 18 every time the signal from the circuit 16 is output.
Electric power is supplied to the toner drive motor 19 so that the toner drive motor 19 is supplied with electric power.

In the above configuration, in the case of continuous copying, the toner amount corresponding to the output of the toner supply amount setting circuit corresponding to the first measured toner density is changed every time the output signal from the integration circuit 16 is generated. Then, the toner is supplied from the toner replenisher 18 to the developing device 5. Also, in the case of single and small number of copies, the measured toner density is updated each time and therefore corresponds to the toner density measured before the start of the copy cycle when the set count value is reached. The toner is supplied when the amount of toner reaches the count value when copying each copy or a small number of copies. This will be explained using FIG.

Figure 2 shows two B4 sheets first, then five A3 sheets,
It also shows the cumulative count and toner supply when 10 sheets of B5 are copied. During the dead cycle when copying two sheets of B4, a signal representing H (increase) in the patch measurement result is supplied from the setting circuit 14 to the control circuit 1, and at the same time, a signal representing the paper size B4 is sent to one input of the integrating circuit 16. A signal is being input. Therefore, in response to a signal from paper transport switch 17 inputted to the other side of circuit 16, circuit 1
The counter inside 6 counts 8, 16. When the copying cycle ends and the copying machine stops, the toner supply amount signal from the setting circuit 14 to the control circuit 15 is reset, but the count value of the counter inside the integrating circuit 16 is held. Next, when a copy cycle for copying five A3 sheets is started, a new toner supply amount instruction signal is supplied from the setting circuit 14 to the control circuit 15 in response to the patch density measured in the dead cycle. On the other hand, integration circuit 16
Since a signal representing the A3 size is supplied to one input, in response to the output from the paper transport switch 17, the counter in the integrating circuit 16 adds the value (16) to 26, 36. , 46. Here, the counter is reset by the preset means, and when the value reaches (exceeds) 40, the counter is reset and a signal is output to the motor drive control circuit 15. Therefore, from the 4th card onwards, the counter is 10,
Count to 20. On the other hand, when the motor drive control circuit 15 receives the signal from the circuit 16, the desired toner (L: an amount smaller than the average usage amount) is supplied from the toner replenisher to the developing device 5 based on the signal from the circuit 14. Electric power is supplied to the toner drive motor 19 so that the toner drive motor 19 This timing is shown in the figure as "toner supply" in relation to the copy cycle.
Similarly, when B5 size copying is started, the patch density is measured in the dead cycle, and when the count value of the counter of the integration circuit 16 reaches 40, the desired value of toner (H: (more than the average usage amount) is supplied.

In the above configuration, the output of the integrating circuit 16 is input to the toner supply amount setting circuit 14, and when a signal from the circuit 16 is generated, the desired value of toner is supplied from the circuit 14 to the toner drive motor. It is also possible to omit the motor drive control circuit 15 by arranging a structure in which power is supplied only for the time required for the motor drive control circuit 15.

Effects of the Invention As described above, the present invention improves the conventional image density measurement method in various ways to measure toner density without being affected by changes in charging characteristics due to photoreceptor drum fatigue, etc. Since it can be measured, there is no high toner concentration inside the developing machine, and therefore copies can be obtained without fogging in the background, and since toner does not blow out, the inside of the developing machine is not contaminated. .

In addition, in the present invention, the toner supply is cumulatively counted based on the relative area ratio of the number of copies, and when the counted value reaches a constant value, the required amount of toner can be supplied, so that the number of copies can be adjusted according to the copy size. Regardless of the situation, the required amount can be supplied more accurately when needed than before.

[Brief explanation of drawings]

FIG. 1 is a schematic illustration of a copying machine 1 equipped with an image density control device according to the present invention, and FIG. 2 shows patch density measurement, area accumulation according to copy size, and toner supply in relation to a copy cycle. This is a diagram. Symbols in the figure, 1: Original table, 2: Photosensitive drum,
3: Charging corotron, 4: Exposure lamp, 5: Developing machine, 6: Transfer corotron, 7: Eliminating corotron,
8: Cleaning device, 9: Static elimination lamp, 10:
Paper tray, 11: Conveyance path, 12: Patch, 1
3: Comparison circuit, 14: Toner supply setting circuit, 1
5: Motor drive control circuit, 16: Integration circuit, 1
7: Paper travel switch, 18: Toner supply device, 1
9: Toner drive motor, 20: Paper size sensor.

Claims (1)

[Scope of Claims] 1 Image density control in which a patch latent image of a fixed size is formed on the surface of a photoreceptor drum, the optical density of the patch image after development is measured, and the amount of toner replenishment is controlled by comparing it with a reference level. A method, comprising: a) measuring the density of the patch image in a preparation cycle before the start of the copying process; b) comparing the measured patch density with a reference value;
In response to the result, one is selected from a plurality of preset toner supply amounts, c. cumulatively calculates the copying area based on the copy size and number of copies during the copying process, and d) the cumulative copying area is a constant value. An image density control method characterized in that the amount of toner selected in b is supplied into a developing machine each time the amount of toner is reached. 2. An image density control device that controls the amount of toner replenishment by forming a patch latent image of a certain size on the surface of a photoreceptor, measuring the optical density of the patch image after development, and comparing it with a reference level, The method measures the density of patch images in the preparation cycle before the copying process, and includes a patch density sensor consisting of a light emitting element and a light receiving element, and a comparison device connected to the output of the sensor to compare it with a set standard density value. A toner supply amount setting circuit that sets the toner supply amount based on the comparison circuit, and the outputs of the paper size sensor and the paper transport switch are input, and the relative area ratio is determined by the paper transport switch according to the paper size. An integrating circuit that includes a counter that counts each output and generates an output when the counted value reaches a set value, and supplies toner with an amount of toner corresponding to the output of the toner supply amount setting circuit in response to the output of the integrating circuit. 1. An image density measuring device comprising: a motor drive control circuit for controlling a toner drive motor for supplying toner from a toner to a developing device; and the toner drive motor.