JPH10288911A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the wasteful generation of heat in a thermal fixing device and to prevent the rise of temperature in the device by setting required thermal fixing temperature in accordance with fixed toner quantity. SOLUTION: When a CPU 31 receives a printing command from a host computer 48, it gets under specified printing control. In such a case, the CPU 31 counts the number of black dots out of the specified number of lines of printing data received from the host computer 48 and judges based on the counted value whether or not the toner quantity to be transferred to recording paper is small. Namely, when the toner quantity to be transferred to the recording paper is large such as when the number of the black dots is equal to or above the specified value, the large quantity of heat is required for the thermal fixing of the toner, so that the toner is thermally fixed at the ordinary thermal fixing temperature. Meanwhile, when the toner quantity to be transferred to the recording paper is small such as when the number of the black dots is not equal to or above the specified value, the toner is thermally fixed at the lower temperature than the ordinary thermal fixing temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus having an electrophotographic process mechanism for thermally fixing toner transferred to a recording medium.

[0002]

2. Description of the Related Art As an image forming apparatus of this type, for example, there is a laser printer. This laser printer is provided with a light source such as a charging unit and a laser diode around a photosensitive drum provided in the middle of a paper transport path in the main body of the apparatus. An exposure apparatus provided with
An electrophotographic process mechanism including a developing device, a transfer device, and the like is provided. Further, a heat fixing device is provided downstream of the electrophotographic process mechanism on the sheet conveying path to thermally fix the toner image transferred onto the recording paper by the electrophotographic process mechanism.

In such a laser printer, print control as shown in FIG. 4 is performed by a CPU (not shown) constituting a control unit main body. That is,
When the CPU receives a print command and print data from a host computer connected by a communication cable, for example,
The print data is received one dot at a time for a predetermined number of lines. Subsequently, the temperature of the heater of the thermal fixing device is set to a predetermined set temperature (about 180 ° C. to 190 ° C.), and the following printing process is performed.

The surface of the photosensitive drum is charged by a charging unit,
An electrostatic latent image is formed on the surface of the photosensitive drum by exposure from an exposure device based on print data, and the electrostatic latent image is visualized with toner from a developing device. Is transferred, and the toner image is heat-fixed by the heat fixing device at the set temperature to form an image on recording paper.

[0005]

Generally, the temperature required for heat fixing of the toner varies depending on the amount of heat taken by the toner, and therefore varies depending on the amount of the toner to be transferred to the recording paper. That is, if the number of black dots in the print data is small, the amount of toner to be transferred to the recording paper is also small, so that the amount of heat deprived by the toner can be small, and the heat fixing temperature of toner (11
(0 ° C. to 120 ° C.), it is considered that the toner can be sufficiently fixed.

However, in the conventional electrophotographic apparatus as described above, since the amount of toner is not taken into consideration when heat fixing the toner, the temperature is always constant regardless of the number of black dots in the print data. (180 ° C ~ 19
(About 0 ° C.).
For this reason, when printing print data with few black dots, there is a problem in that heat generated in the thermal fixing device is wasted and the temperature inside the apparatus increases.

Therefore, according to the present invention, since a necessary heat fixing temperature can be set according to the amount of toner to be fixed, it is possible to prevent wasteful heat from being generated in the heat fixing device and increase the temperature inside the apparatus. It is an object of the present invention to provide an electrophotographic apparatus capable of preventing such a situation.

[0008]

According to the present invention, the surface of an electrostatic latent image holding member is charged, an electrostatic latent image is formed by exposure, the electrostatic latent image is visualized, and the image is recorded on a recording medium. In an electrophotographic apparatus in which a visualized toner image is transferred and the toner is heat-fixed by a heat fixing device, the number of black dots in print data for a predetermined number of lines to be printed is counted, and the black dots are counted. When determining whether the count value of the number falls in at least one of the ranges divided by one or more threshold values, and performing heat fixing in the heat fixing unit in the lower range than in the upper range according to each range. The heat fixing temperature is set so that the temperature becomes low.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a laser printer will be described below with reference to the drawings.
FIG. 1 is an overall configuration diagram of a laser printer according to the present embodiment, in which a photosensitive drum 2 is disposed substantially at the center of a housing 1. The photosensitive drum 2 is driven to rotate in the direction of the arrow in the figure.

Around the photosensitive drum 2, as an electrophotographic process mechanism, a charging unit 4 for uniformly charging the photosensitive layer on the surface of the photosensitive drum 2, and a host computer (described later) is charged to the photosensitive layer charged by the charging unit 4. Exposure device 5 that irradiates a laser beam based on print data from 48 to form an electrostatic latent image, and develops by attaching toner to the electrostatic latent image formed on the photosensitive layer of photosensitive drum 2 and developing the image. Device 6,
A transfer unit 7 for transferring an image developed by the developing device 6 to transfer paper conveyed on a conveyance path, and a cleaning unit 8 for removing residual toner from the photosensitive drum 2 are sequentially arranged.

The transfer section 7 is disposed below the photosensitive drum 2. The recording paper is conveyed at a predetermined timing toward the transfer unit 7 from the paper feed cassette 10a or the manual insertion slot 10b provided on one side of the housing 1 by the operation of the conveyance roller 11 such as a pickup roller. It has become.

The conveyed recording paper is heat-fixed by a heat fixing device 13 after the transfer section 7 transfers the toner image on the photosensitive drum 2. The heat fixing device 13 includes a heat roller 13a formed of a metal roller having a built-in heat fixing device heater 42 formed of, for example, a halogen lamp, and a press roller 13b formed of elastic silicon. The resin of the toner on the recording paper is melted by the heat of the surface of the heat roller 13a due to the heat generated by the heat fixing device heater 42 and the pressure of the press roller 13b, and the toner is fixed and fixed on the recording paper. Then, the fixed recording paper is discharged to the outside of the housing 1 by the discharge roller 14.

At the time of the image forming operation of the laser printer constructed as described above, the laser beam from the exposure device 5 is turned on / off based on print data from a host computer 48 to be described later which is externally connected. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 2. The electrostatic latent image is visualized by the toner attached by the developing device 6. Thereafter, the transfer unit 7 transfers the toner image on the photosensitive drum 2 to the recording medium conveyed at a predetermined timing. Then, the toner image is thermally fixed by the heat fixing device 13 and is discharged to the outside of the housing 1.

FIG. 2 is a block diagram showing the configuration of the control unit of the laser printer shown in FIG. 1. Reference numeral 31 denotes a CPU (central processing unit) constituting the control unit main body, and 32 denotes a program for the CPU 31 to control each unit. ROM (read only memory) in which data and the like are stored in advance, 33 is the CPU
A random access memory (RAM) provided with various memory areas for temporarily storing data to be processed by the counter 31 and a counter 33a for counting the number of black dots in the print data.
Access memory), 34 is an I / O port. The CPU 31, the ROM 32, the RAM 33, and the I / O port 34 are interconnected via bus lines 35 such as an address bus, a data bus, and a control bus.

The I / O port 34 is provided with a high-voltage power supply circuit 36 for supplying a high voltage to the charging unit 4 and the transfer unit 7, and a laser diode for driving a laser diode 37 for oscillating laser light, which is provided in the exposure device 5. A drive circuit 38; a motor drive circuit 40 for controlling the driving of various motors 39 such as a transport motor for driving the photosensitive drum 2;
3. A sensor circuit 45 for connecting various sensors 44 such as a sheet detection sensor for detecting the presence or absence of a sheet, and an I / F (interface) 46 are connected. A host computer 48 for communicating print data and various kinds of processing data is connected to the I / F 46 via a communication cable.

The CPU 31 is connected to the host computer 4
When a print command is received from the printer 8, print control as shown in FIG. 3 is performed. That is, the CPU 31
Is the host computer 48 in ST (step) 11.
Print data for one dot.

Subsequently, in ST12, it is determined whether or not the received print data is a black dot (data for one dot for irradiating a laser beam from the exposure device 5 to deposit toner on the photosensitive drum 2). Here, the black dots are white dots (the photosensitive drum 2 is not irradiated with the laser beam from the exposure device 5).
Data other than the one-dot data on which no toner is attached), not only black dot data when binarized, but also half-tone data when the dot is expressed in 256 tones Is also included.

If it is determined in ST12 that the received print data is not a black dot, the process proceeds to ST14. If it is determined that the received print data is a black dot, the count value of the counter 33a of the RAM 33 is incremented in ST13. The counter 33a of the RAM 33 is cleared by an initial setting performed when the power of the main body of the laser printer is turned on.

Subsequently, in ST14, it is determined whether print data for a predetermined number of lines has been received. Here, the print data for the predetermined number of lines is a data amount for performing the heat fixing at the heat fixing temperature of 1. The predetermined number of lines is determined based on, for example, a relationship with a predetermined black dot threshold value described later.
Specifically, considering that the temperature of the thermal fixing device fluctuates due to heat deprived by the toner fixing operation, it is preferable to increase the predetermined number of lines when the predetermined threshold value of the black dot is increased.

If it is determined in ST14 that the print data for the predetermined number of lines has not been received, the process returns to ST11. If it is determined that the print data for the predetermined number of lines has been received, the process returns to ST15. It is determined whether or not the count value of the counter 33a is equal to or more than a predetermined value (a predetermined threshold value of a black dot).

If it is determined in ST15 that the count value is equal to or greater than the predetermined value (it is in the upper range), the temperature of the thermal fixing device heater 42 is set to a normal set temperature, for example, the same thermal fixing as in the prior art, in ST16. The temperature is set at 180 ° C to 190 ° C. Then, the counter 33a is cleared in ST17, and the printing process is performed in ST18. In this printing process, when the recording paper to which the toner has been transferred in the electrophotographic process as described above is conveyed to the thermal fixing device 13, the recording paper is thermally fixed at a normal thermal fixing temperature and the recording paper is discharged out of the housing 1. Is done.

On the other hand, in ST15, the counter 33
If it is determined that the count value of “a” is not equal to or more than the predetermined value (it is in the lower range), the heat fixing device heater 4 is determined in ST19.
2 is set to a temperature lower than the normal set temperature. As a result, the heat fixing device heater 42 is controlled to reach the set temperature. The lower temperature mentioned here is a temperature higher than the heat fixing temperature of the toner of 110 ° C. to 120 ° C., and even if the temperature is lowered due to the loss of heat by the toner or the recording paper, the temperature is kept at 110 ° C. to 120 ° C. Set the temperature so that it does not become lower. Specifically, it is necessary to set an appropriate temperature depending on the transport speed of the recording paper, the ambient temperature of the thermal fixing device 13, and the like. For example, 160 ° C. to 170 ° C., which is about 20 ° C. lower than the normal thermal fixing temperature. It is preferable to set to ° C.

Then, the counter 33a is cleared in ST17, and the printing process is performed in ST18. In this printing process, when the recording paper to which the toner has been transferred in the above-described electrophotographic process is conveyed to the thermal fixing device 13, the recording paper is thermally fixed at a temperature lower than a normal thermal fixing temperature, and the recording paper is encased. It is discharged out of the body 1.

In the embodiment of the present invention having such a configuration, whether or not the amount of toner transferred to the recording sheet is small is determined by determining whether the amount of toner transferred from the host computer 48 is equal to the predetermined number of lines of black data. The number of dots is counted, and judgment is made based on the count value. That is, when the amount of toner transferred to the recording paper whose number of black dots is equal to or more than a predetermined value is large, a large amount of heat is required for heat fixing of the toner. Perform heat fixing.

On the other hand, when the amount of the toner transferred to the recording paper is small such that the number of black dots is not more than the predetermined value, the amount of heat required for heat fixing of the toner is small, and the The fixing is performed at a temperature lower than the normal heat fixing temperature. Thereby, the necessary heat fixing temperature can be set according to the amount of the toner to be fixed, so that the heat fixing of the toner can be performed efficiently, and unnecessary heat generation in the heat fixing device can be prevented. It is also possible to prevent the temperature inside the device from rising.

Although the present embodiment has been described in connection with the case where dot data (image data) is received from the host computer 48 and the number of black dots is counted, the present invention is not limited to this. It may receive code data and the like from the computer 48 and count black dots in dot data obtained by developing the code data.

In the embodiment of the present invention, whether the amount of toner transferred to recording paper is small or not is determined by determining the number of black dots in the print data of a predetermined number of lines received from the host computer 48. The description has been given of the case where the counting is performed and the judgment is made based on the count value. However, the present invention is not limited to this. For example, the number of irradiations of the laser beam from the exposure apparatus 5 may be counted.

Further, in the present embodiment, the case where the count value of the number of black dots is determined by dividing the count value by one threshold and the two types of heat fixing temperatures are selectively set has been described. Instead, three or more heat fixing temperatures may be selectively set. That is, the count value of the number of black dots is determined by dividing the count value by two or more thresholds, and the heat fixing temperature is set so that the lower range has a lower temperature for heat fixing than the upper range according to each range. It may be set selectively.

[0029]

As described in detail above, according to the present invention, the necessary heat fixing temperature can be set according to the amount of toner to be fixed, so that the toner can be efficiently heat-fixed. It is possible to provide an electrophotographic apparatus capable of preventing the generation of useless heat in the apparatus and preventing the temperature in the apparatus from rising.

[Brief description of the drawings]

FIG. 1 is an overall sectional view showing a configuration of a laser printer according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a control unit in the embodiment.

FIG. 3 is a flowchart showing print control performed by a CPU shown in FIG. 2;

FIG. 4 is a flowchart showing print control performed by a CPU of a conventional laser printer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 2 ... Photosensitive drum (electrostatic latent image holding body) 4 ... Charging part 5 ... Exposure device 6 ... Developing device 13 ... Thermal fixing device 31 ... CPU 33a ... Counter 42 ... Heat fixing device heater

Claims (1)

[Claims] An electrostatic latent image is formed by charging a surface of an electrostatic latent image holding member, forming an electrostatic latent image by exposure, visualizing the electrostatic latent image, and displaying the visualized toner image on a recording medium. In an electrophotographic apparatus for transferring the toner and thermally fixing the toner with a heat fixing device,
The number of black dots in the print data for the predetermined number of lines to be printed is counted, and it is determined whether the count value of the number of black dots falls within a range divided by at least one or more threshold values, An electrophotographic apparatus, wherein the thermal fixing temperature is set such that the lower fixing range has a lower temperature for heat fixing by the thermal fixing device than the upper range according to each range.