JP3172557B2 - Transfer current automatic variable device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic transfer current varying device for automatically varying a transfer current of a transfer unit for transferring a toner image on an image carrier onto a medium in an image forming apparatus such as an electrophotographic apparatus. It is about.

[0002]

2. Description of the Related Art In general, when printing is repeated in an electrophotographic apparatus or the like, the charge amount of a developer gradually changes. When the charge amount changes, the optimum value of the transfer current flowing to the transfer charger changes in order to transfer the toner image from the image carrier to the print medium, but printing is performed while the transfer current is always kept constant. Was.

As described in JP-A-59-121364, the charge amount of a toner is measured (to be precise,
Bias current) and determine the transfer current.

[0004]

When printing is performed with the above-mentioned conventional transfer current constantly kept constant, the charge amount of the developer gradually changes as printing is repeated, and the toner is transferred from the photosensitive drum to the print medium on the print medium. When an image is transferred, there is a problem that the optimum value of the transfer current flowing through the transfer charger changes, but the transfer current becomes constant, and the optimum printing cannot be performed as printing is repeated.

If the charge amount (bias current) of the toner is measured and the transfer current is controlled based on the measured charge amount, good printing can be performed. However, a mechanism for detecting the charge amount of the toner is required. Therefore, there is a problem that the size of the apparatus is increased and the cost is increased.

According to the present invention, an optimum transfer current corresponding to a change in specific charge due to use of a developing device is measured in advance, and based on the measured value, an optimum transfer current corresponding to use of the developing device is set. An object of the present invention is to make it possible to always transfer an optimal toner image to a medium without depending on the number of printed sheets.

[0007]

Means for solving the problem will be described with reference to FIG. In FIG. 1, the transfer current table 22 is a table in which an optimum transfer current associated with a change in the specific charge of the toner is obtained in advance and stored in association with the number of prints corresponding to the stirring of the developer.

[0008] The number-of-printed-sheets measuring unit 23 measures the number of printed sheets corresponding to the stirring of the developer. The transfer current setting section 24 sets the optimal transfer current from the high voltage power supply to the transfer charger 5 with reference to the transfer table 22 based on the number of prints measured by the print number measurement section 23. is there.

[0009]

According to the present invention, as shown in FIG. 1, an optimum transfer current associated with a change in the specific charge of the toner is determined in advance in the transfer current table 22 in association with the number of prints corresponding to the stirring of the developer. The number of prints is measured by the number-of-prints measuring unit 23 and the transfer current setting unit 24 refers to the transfer table 22 based on the number of prints measured by the number-of-prints-number measuring unit 23. Then, an optimal transfer current is supplied from the high-voltage power supply to the transfer charger 5, so that an optimal toner image is transferred onto the medium.

Here, a developer consisting of two components of a carrier and a toner, or a developer consisting of one component of a toner is used. Measurement is started.

Therefore, the optimum transfer current corresponding to the change of the specific charge due to the stirring of the developer is measured in advance, and based on this, the optimum transfer current corresponding to the use of the developing device is set. Therefore, it is possible to always transfer the optimum toner image to the medium without depending on the number of printed sheets.

[0012]

Next, the structure and operation of an embodiment of the present invention will be sequentially described in detail with reference to FIGS.

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 1A shows a block diagram. In FIG. 1A, a ROM 21 stores a table and a program in advance. Here, a transfer current table 22 is used as a table, and a printed sheet counting unit 2 is used as a program.
3. The transfer current setting unit 24 and the like are stored in advance. These programs are read and executed by the MPU 25 to measure the number of printed sheets (S2 in FIG. 3).
To S6), and an optimal transfer current is set (see S8 in FIG. 3).

The transfer current table 22 is a table in which an optimum transfer current associated with a change in the specific charge of the toner is previously found and stored in association with the number of prints corresponding to the stirring of the developer. As shown in FIG. 2A, the optimum transfer current is previously measured and stored in association with the number of prints.

The number-of-prints measuring unit 23 measures the number of prints corresponding to the stirring of the developer (S2 in FIG. 3).
To S6). The transfer current setting unit 24 refers to the transfer table 22 based on the number of prints measured by the number-of-prints measurement unit 23, and sets a predetermined value in the DA converter 28. By setting a predetermined value in the DA converter 28, a high voltage is applied from the high voltage power supply 29 to the transfer charger 5, and a predetermined transfer current is supplied. As a result, the toner image on the photosensitive drum 2 can always be transferred onto the sheet 4 in a good state.

The MPU 25 is a microprocessor which reads out and executes a program stored in the ROM 21 and performs a predetermined process. Here, the number of printed sheets is measured based on the rotation signal of the drum, or the time for printing one sheet on the paper 4 (for example, 1 In the case of an electrophotographic apparatus that prints 50 sheets per minute, 1.2
(Seconds), the number of printed sheets is counted as one. In the latter case, since the change in the specific charge of the toner in the developer 11 in the developing device 1 is determined by the time for stirring the toner, the time for stirring the toner is divided by 1.2 seconds, and the number of sheets printed on the paper 4 is calculated. The number of prints is converted and measured.

The RAM 26 is a random access memory and has a backup power supply. This RAM 26
A print number counter 27 is provided therein, and S2 in FIG.
To S6, the number of prints is measured.

The DA converter 28 converts the transfer current value sent from the MPU 25 into an analog DC voltage and sends it to the high-voltage power supply 29. The high voltage power supply 29
A high voltage is generated so that a current corresponding to the transfer current value sent from the DA converter 28 flows to the transfer charger 5. The generated high voltage is applied to the corona wire of the transfer charger 5 to flow a predetermined transfer current.

FIG. 1B is a configuration diagram (cross section) of the electrophotographic apparatus. In FIG. 1B, the developing device 1 includes:
The toner of the developer (magnetic carrier and toner) is attached to the latent image on the photosensitive drum 2 by the magnet roll 13 while stirring the developer 11.
At this time, the developer 11 is rotated by the stirring roller 12 in the direction of the arrow shown in the figure, and the screw 11 (not shown) mutually agitates the developer 11 in the front and rear directions. With respect to the developer 11 thus stirred, the toner is adhered to the magnet roll 13 together with a magnetic carrier and rotated as shown in the drawing, and further formed into a thin uniform layer by a blade. Is developed by attaching toner only. Thus, the developer 11
, The toner specific charge changes as measured by the experiment of FIG. 2 described later.

Further, the developer 11 is replenished from the cartridge mounting portion 1-1 by a replenishing roller 1-2 as needed. To replace the developer 11, the developer bottom plate is opened, and the developer 11 is discharged into the developer disposal bottle 15. After discharging, the developer bottom plate is closed, and a new developer (carrier and toner) 11 is supplied from a supply port (not shown). The developing device bottom plate open detection switch 14 is operated (ON / OFF) by the replacement operation of the developer 11, and notifies the MPU 25 of the replacement completion signal.
The MPU 25 that has received the notification of the exchange completion signal resets the number-of-printed-sheets counter 27 with YES in S2 of FIG.

The photosensitive drum 2 is exposed according to the image and character information to be printed to form an electrostatic latent image.
This is developed by the developing device 1 to attach toner, and a voltage having a polarity opposite to that of the toner is applied by the transfer charger 5, so that the toner image on the photosensitive drum 2 is transferred to the paper 4. The toner image transferred to the sheet 4 is transferred to a heat roller 7.
And heat to fuse and fix.

The pre-charger 3 charges the photosensitive layer whose conductivity changes in response to light irradiated on the photosensitive drum 2. The paper 4 is a paper on which the toner image on the photosensitive drum 2 is transferred and printed.

The transfer charger 5 reversely charges the toner image on the photosensitive drum 2 and transfers the toner image onto the paper 4. The backup roller 6 transports the sheet 4 in the direction of the arrow.

The heat roller 7 transports the paper 4 in the direction of the arrow and heats the paper 4 to fix the toner image on the paper 4. FIG. 2 shows an operation explanatory diagram of the present invention.

FIG. 2A shows the transfer current table 22. In this method, a new developer and a developer printed with the indicated number of sheets are prepared, and the optimum transfer current and the charge amount of the toner are actually measured. Here, the optimum transfer current is determined when the print density and quality on the paper 4 are optimized.
The current (μA) supplied to the transfer charger 5 was measured.

FIG. 2B shows the current supplied to the transfer charger 5 based on the measurement result of FIG. 700 μA from initial to 10,000 sheets, 62 from 10,000 to 30,000 sheets
0 μA, 550 μA from 30,000 to 50,000 sheets, FIG.
The printing was performed up to 500,000 sheets by setting as in the experimental result of (a). The result is shown in FIG.

FIG. 2C shows a printing result printed under the transfer current shown in FIG. Here, the variable is shown in FIG.
(B) is a printing result printed under the transfer current.
“Constant” is a printing result printed under a conventional constant transfer current. As can be seen from these printing results, in the case of the variable of the present invention, ◎ (good) printing quality was obtained from the initial stage to 200,000 sheets, and even at 200,000 sheets or more, the printing quality was improved compared to the conventional case. It can be seen that good print quality was obtained over a wide range of the number of prints, as compared with the conventional case where the transfer current was constant.

FIG. 3 shows an example of the transfer current of the present invention. This is one in which the transfer current is changed continuously instead of the step-like transfer current in FIG. As described above, the transfer current may be continuously and sequentially set in accordance with the number of prints, and the transfer current may be changed more finely in accordance with the number of prints to improve the print quality.

Next, the operation of the configuration of FIG. 1 will be described in detail according to the order shown in the flowchart of FIG. In FIG. 4, in step S1, data of the number of prints to be subjected to the transfer current switching process and the transfer current at that time are read from the ROM. In this case, for example, the number of printed sheets and the optimum transfer current (μA) shown in FIG. 2A are read from the transfer current table 22 in the ROM 21 in FIG.

In step S2, it is determined whether or not the developer replacement completion signal has been received. If YES, the number of prints counter 27 in S3
Is reset, and the process proceeds to S4. In the case of NO, the process proceeds to S4. In S4, it is determined whether or not the developing device 1 has rotated for 1.2 seconds or more. This is because the developing unit 1 prints one sheet from 1.2 seconds, that is, 60 seconds / 50 sheets = 1.2 seconds / sheet as an electronic copying apparatus capable of printing 50 sheets per minute. During this time, it is determined whether or not the developer 11 has been stirred by the stirring roller 12 of the developing device 1. Y
In the case of ES, the process proceeds to S5. If NO, the process stands by at S4.

In step S5, the rotation time of the developing device 1 is reset to 0 second. In step S6, the number of printed sheets is read from the RAM 26. This reads the value of the number of prints of the print number counter 27 of the RMA 26 in FIG.

In S7, +1 is added to the number of printed sheets read in S6.
I do. In step S8, the number of prints is written back to the RAM 26. In this case, the value of the number-of-printed-sheets counter 27 of the RAM 26 is incremented by 1 and rewritten.

In step S9, it is determined whether or not the number of prints matches the number of prints for performing the transfer switching process. This is because the number of printed sheets counted from S6 to S8 is, for example, (a) in FIG.
It is determined whether or not the number of prints matches the value of the number of prints in the transfer current table 22 of FIG. YES
In the case of (1), a signal is sent to the DA converter 28 so as to set the transfer current according to the number of prints in S10. Thereby, a high voltage is applied to the transfer charger 5 from the high voltage power supply 29,
The set transfer current is caused to flow, and the optimum transfer current is caused to flow. Then, the process returns to S2. On the other hand, if NO, the process returns to S2.

As described above, the rotation time of the developing device 1 is 1.
The number of printed sheets is measured by adding the number of printed sheets to 2 seconds (one sheet, time for printing), and the measured number of printed sheets is obtained and stored in advance, for example, in the transfer current table 2 shown in FIG.
When the number of printed sheets coincides with 2, the corresponding optimal transfer current is caused to flow to the transfer charger 5, and the toner image is transferred from the photosensitive drum 2 to the paper 4 with good quality.

FIG. 5 shows another configuration diagram (one component) of the present invention. This is a configuration in the case where the developing device 1 uses the one-component developer 11. In the case of the one-component developer 11, the replacement of the developer 11 is not a two-component one, but a cartridge replacement (replacement of the developing device 1). The replacement is detected by a cartridge replacement detection switch 16 shown in FIG. 1 (a) is notified to the MPU 25, and the number-of-printed-sheets counter 27 is reset (YES in S2 in FIG. 4, S
3). The other configuration is the same as that shown in FIG.

[0036]

As described above, according to the present invention,
Because the optimal transfer current corresponding to the change in specific charge due to the stirring of the developer is measured in advance, and based on this, the optimal transfer current corresponding to the use of the developing device is set. In addition, an optimum transfer current can be supplied to the transfer charger 5 without depending on the number of printed sheets, so that a good quality toner image can always be transferred to a medium. Thereby, even if the charge amount of the toner is changed by repeating the printing, the transfer is always performed with the optimum transfer current, so that a good toner image can be stably obtained. Also, by measuring the change in charge amount in advance,
Since the optimal transfer current corresponding to this is stored, there is no need to provide a means for measuring the optimal transfer current of the toner, and the configuration is simpler than an apparatus having a mechanism for measuring the toner charge amount. Thus, the cost can be reduced and the size can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of the present invention.

FIG. 2 is a diagram illustrating the operation of the present invention.

FIG. 3 is an example of a transfer current according to the present invention.

FIG. 4 is an operation explanatory flowchart of the present invention.

FIG. 5 is another configuration diagram (one component) of the present invention.

[Explanation of symbols]

 1: developing unit 11: developer 12: stirring roller 13: magnet roll 14: developing unit bottom plate open detection switch 16: cartridge replacement detection switch 2: photosensitive drum 3: pre-charger 4: paper 5: transfer charger 7: heat Roller 21: ROM 22: Transfer current table 23: Print number measuring unit 24: Transfer current setting unit 25: MPU 26: RAM 27: Print number counter 28: DA converter 29: High voltage power supply

Claims (2)

(57) [Claims] 1. A automatically variable to transfer current automated variable device transfer current of the image forming apparatus, in association with the number of printed sheets corresponding to the stirring number of printed sheets or the developer, and inversely proportional to the transition of the toner specific charge a transfer current table to previously obtained and stored the optimum transfer current, and a measuring unit for measuring the number of printed sheets corresponding to a stirred number of printed sheets or the developer, the said number of printed sheets measured by the measuring unit based on An automatic transfer current varying device, wherein a high voltage is applied to a transfer charger so that an optimum transfer current is obtained by referring to a transfer current table. 2. The transfer according to claim 1, wherein the measuring section starts measuring the number of printed sheets or the number of printed sheets corresponding to the stirring of the developer starting from the point when the developer is replaced. Automatic current variable device.