JPH0962168A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing a failure such as a hot offset phenomenon or a cold offset phenomenon, etc., even when a printing speed changes depending on a printed resolution. SOLUTION: The image forming device having two or more kinds of print speeds is provided with a CPU 23, a fan 16, a rotation speed control means 27 to control the fan 16 at more than two kinds of speeds at least, and a power supply means 24. And, the number of revolution changeover signal is outputted from CPU 23 to the number of revolutions control means 27 according to the print speed, and the number of revolutions control means 27 changes over the power supply to the fan 16 supplied from the power supply means 24 according to the number of revolutions changeover control signal and changes the number of revolutions of the fan.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for printing by an electrophotographic process.

[0002]

2. Description of the Related Art Conventionally, various image forming apparatuses have been proposed as output terminals for personal computers and workstations.

In recent years, electrophotographic processes, which are highly advantageous in terms of recording speed and printing quality, and laser beam printers using laser technology have rapidly become popular. An image forming apparatus such as a laser beam printer performs a charging process, an exposure process, a developing process, a transfer process, and a fixing process, performs printing, and discharges a recording paper to the outside of the machine.

Recently, laser beam printers have become highly functional in order to cope with a plurality of printing speeds and resolutions of external host devices such as scanners and personal computers, or to cope with user's applications, and the laser beam printer itself. There is also a growing demand for printers that can print at multiple printing speeds and various resolutions.

The structure and operation of the conventional image forming apparatus will be described below. FIG. 3 is a block diagram showing the configuration of a conventional image forming apparatus. FIG. 4 is a block diagram of a control unit of a fan of a conventional image forming apparatus.

As shown in FIG. 3, in the conventional laser beam printer, a display / operation unit 2, a controller unit 3, a photosensitive drum 4, and a laser beam printer main body 1 are provided.
Charging device 5, exposure optical system 6, developing device 7, transfer roller 8, static eliminator 9, fixing device 15, fan 16, cassette 11, paper feed roller 13, face-down paper ejection tray 20 and a face-up discharge tray 22.

The operation / display unit 2 is generally provided on the upper surface of the laser beam printer main body 1 and is composed of a display means such as a liquid crystal display panel and an emitting diode and an operation means such as an input switch, and sets various operating environment conditions concerning printing. And display. The controller unit 3 controls input / output of data to / from an external host device, performs image processing of image data to be transmitted, and sets various operating environments related to printing according to data input from the operation / display unit 2. To do. The photosensitive drum 4 is formed by adhering an organic photoconductive substance on an electrode thin film on the surface of a metal drum such as aluminum. Then, by the charger 5, along the rotation direction of the photosensitive drum 4,
The surface of the photosensitive drum 4 is charged (charging process). Further, the surface of the photosensitive drum 4 charged by the charger 5 is irradiated with the exposure light beam 10 from the exposure optical system 6. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 4 by projecting the image of the original as a light image (exposure step). The developing device 7 adsorbs toner on the electrostatic latent image (development process). The transfer roller 8 is
The toner image formed by the developing device 7 on the surface of the photosensitive drum 4 is transferred to the recording paper 12 (transfer process). The static eliminator 9 removes the toner remaining on the surface of the photosensitive drum 4 after transferring the toner image onto the recording paper by the transfer roller 8. Fixing device 15
Has a heating roller 17 and a pressure roller 18, and fixes the toner image on the recording paper 12 after transfer onto the recording paper 12 by the heating roller 17 and the pressure roller 18 (fixing process). The fan 16 radiates heat generated from the heating roller 17 and a drive motor (not shown) to the outside of the laser beam printer body 1. The recording paper 12 is stored in the cassette 11. The paper feed roller 13 feeds the recording paper 12 one by one from the cassette 11 and conveys it to the paper conveyance path 14. The face-down discharge tray 20 is used when the user selects face-down as the discharge method, and receives the recording paper 12 that has passed through the face-down transport path 19. On the other hand, when the user selects face-up as the paper discharge method, the face-up paper discharge tray 22 is used to receive the recording paper 12 that has passed through the face-up conveyance path 21.

Next, the structure and operation of the part that controls the fan 16 will be described in more detail. As shown in FIG. 4, control of the fan 16 is performed by a central processing unit (hereinafter referred to as CP
23), power supply means 24, power ON / OFF
It is performed by the control means 25 and an external host device 26 such as a personal computer.

An external host device 26 such as a personal computer
Sets various operating environments of the CPU 23 in the laser beam printer body 1. The CPU 23 controls the timing of image formation of the entire apparatus, and also determines errors and controls them. The power supply means 24 is a constant voltage source for applying to the fan 16. The power ON / OFF control means 25 controls ON / OFF of the connection between the power supply means 24 and the fan 16 according to a control signal from the CPU 23.

By the way, as described above, the fan 16 is rotated by the heating roller 17 or a drive motor (not shown) when performing a normal image forming process including a charging process, an exposing process, a developing process, a transferring process, and a fixing process. This is because the heat generated from such a heat source and the ozone generated by the corona discharge are emitted to the outside of the laser beam printer main body 1.

When the fan 16 is rotated, the CPU is first input by the user from the external host device 26 such as a personal computer or a scanner or the display / operation unit 2.
23 sets various operating environments. When the image forming process starts, the CPU 23 outputs an ON control signal to the power ON / OFF control unit 25. And power ON / O
The FF control means 25 connects the power supply means 24 and the fan 16, the power is supplied to the fan 16, and the fan 16 rotates. Normally, the fan 16 is a DC motor, and the rotation speed of the fan is originally changed by the power supplied from the power supply means 24 to the fan 16. However, the power supply means 24 in the conventional image forming apparatus has a single operation. Since there are only modes, the fan 16 can only take a certain number of rotations in a steady state. On the other hand, when the fan 16 is not rotated, CP
The U23 outputs an OFF control signal to the power ON / OFF control means 25, and the power ON / OFF control means 25 shuts off the power supply means 24 and the fan 16. As a result, fan 16
Since no power is supplied to the fan 16, the fan 16 does not rotate.

The operation of the conventional laser beam printer constructed as above will be described below. Before printing, the user makes various settings according to the setting contents of the printing environment displayed on the display / operation unit 2. Controller part 3
When the character / image data is received from the external host device 26 such as a personal computer and the image processing is performed, the photosensitive drum 4 repeats the following process while rotating, and performs the printing operation. In the charging process, a high voltage is applied to the charging wire in the charger 5 in a direct current manner, and corona discharge is performed to radiate charge and electrostatic energy, and the surface of the rotating photosensitive drum 4 is about -700V. To be uniformly charged. In the exposure process, the laser beam emitted from the exposure optical system 6 is modulated according to the print pattern data transmitted from the controller unit 3, and the exposure light beam 10 is modulated by the exposure beam 10.
Irradiate the surface of. Since the portion irradiated with the exposure light beam 10 has increased electric conductivity, the electric charge disappears only in that portion, and an electrostatic latent image is formed on the surface of the photosensitive drum 4. In the developing process, the developing device 7 charges the toner to about −300V. When the photosensitive drum 4 reaches the developing device 7, the negatively charged toner is adsorbed to a portion of the surface of the photosensitive drum 4 where the electric charge is removed by the irradiation of the exposure light beam 10, and the negative positive process is performed. In the transfer process, the recording paper 12 is fed from the cassette 11 by the paper feed roller 13 and conveyed to the transfer roller 8 through the paper conveyance path 14. The electrostatic Coulomb force of the transfer roller 8 applied with a voltage of about +1000 V on the surface transfers the toner adsorbed on the surface of the photosensitive drum 4 to the recording paper 12. After the transfer, the toner remaining on the surface of the photosensitive drum 4 is removed by the static eliminator 11. During the fixing process, the recording paper 12 is heated by the holding pressure of the pressure roller 18 and the heat of the heating roller 17 in the fixing device 15.
The toner image on the surface of is fixed. The fan 16 is controlled by the CPU 23 or the like as described above and rotates at a constant rotation speed, and heat generated from the heating roller 17 and a driving motor (not shown) and ozone generated by corona discharge are generated in the laser beam printer main body 1. Release to the outside. Chart paper 1
There are two methods of discharging the sheet, face down and face up. When the user selects face down as the paper discharge method, the recording paper 12 is discharged to the face down paper discharge tray 20 through the face down transport path 19. On the other hand, when the user selects face-up, the recording paper 1
The sheet 2 passes through the face-up transport path 21 and is discharged to the face-up sheet discharge tray 22. The printing operation on one sheet of recording paper 12 is completed by the printing process as described above.

[0013]

However, the conventional image forming apparatus has the following problems. That is, depending on the image forming apparatus, the printing speed changes depending on the printing resolution (for example, 1200
Some have a function of (dpi: 9 ppm, 600 dpi: 18 ppm). With this printer, the drive motor rotation speed and the heating roller set temperature of the fixing device change according to the printing speed, and as a result, the amount of heat generated from the driving motor and the heating roller of the fixing device changes at each printing speed. The temperature inside the beam printer body also changes. In order to fix the toner transferred to the recording paper, a certain amount of heat energy must be applied to the toner, so at low printing speed, the toner contacts the heating roller for a relatively long time. Must be set low. On the contrary, at a high printing speed, the time during which the toner is in contact with the heating roller is short, so it is necessary to set the temperature of the heating roller high. In this way, constant heat is applied to the toner even if the printing speed changes. Therefore, the temperature inside the laser beam printer main body at a high printing speed is higher than the temperature inside the laser beam printer main body at a low printing speed. At this time, the fan that rotates at a constant rotation speed cannot cool the inside of the laser beam printer main body in the high temperature state at high printing speed to an allowable level, and causes a hot offset phenomenon caused by overheating the toner during fixing. However, heat causes the deterioration of the process unit such as the fusion of the toner. Also,
Even when the temperature inside the laser beam printer body is low at low printing speed, the fan rotates at a constant rotation speed, so the fan rotates at an air volume that is higher than necessary and consumes extra power. This causes a cold offset phenomenon or the like caused by insufficient heating of the toner.

Therefore, an object of the present invention is to provide an image forming apparatus capable of preventing problems such as a hot offset phenomenon and a cold offset phenomenon even when the printing speed changes depending on the printing resolution.

[0015]

An image forming apparatus of the present invention is an image forming apparatus for performing printing at two or more kinds of printing speeds, and comprises a central processing unit for controlling image forming timing and an image forming process. The central processing unit has a fan for discharging generated heat to the outside, a rotation speed control means for controlling the fan at at least two rotation speeds, and a power supply means for supplying energy to the fan. A rotation speed switching control signal is output to the rotation speed control means according to the speed to change the rotation speed of the fan.

[0016]

With the above structure, the central processing means outputs the rotation speed switching control signal to the rotation speed control means according to the printing speed, and the rotation speed control means supplies the power from the power supply means to the fan by the rotation speed switching control signal. The fan speed changes depending on the printing speed. Here, at a high printing speed, the temperature inside the laser beam printer main body is high, so the fan is rotated at a high rotational speed to improve the cooling capacity. On the other hand, when the printing speed is low, the temperature inside the laser beam printer main body is low, so the fan is rotated at a low speed to reduce the cooling capacity. This allows
At each print speed of the laser beam printer, the fan rotates at the optimum air flow rate, so the offset phenomenon due to heat at high print speeds, deterioration of the process unit, etc. It is possible to prevent the power consumption and the cold offset phenomenon due to the rotation in the.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are control block diagrams of a fan of an image forming apparatus according to an embodiment of the present invention. The same components as those shown in FIGS. 3 and 4 showing the conventional image forming apparatus are designated by the same reference numerals and the description thereof will be omitted.

As shown in FIG. 1, the control unit of the fan 16 of the laser beam printer main body 1 is an external host device 26 for setting various operating environments of the CPU 23, and the CPU 23 for controlling the image forming timing of the entire device. And C
There is provided a rotation speed control means 27 for switching the power supplied from the power supply means 24 to the fan 16 according to the rotation speed switching control signal output from the PU 23. External host device 26
Sets various operating environments for printing by the CPU 23, and the CPU 23 outputs a rotation speed switching control signal corresponding to each set printing speed to the rotation speed control means 27. The rotation speed control means 27 switches the power supply supplied from the power supply means 24 to the fan 16 according to the rotation speed switching control signal output from the CPU 23 to supply different power to the fan 16. In this way, the power supplied to the fan 16 is made different depending on the printing speed, and the rotation speed of the fan 16 is changed. At a high printing speed, the temperature of the heating roller 17 in the fixing device 15 is high and the temperature in the laser beam printer main body 1 is high. Therefore, the fan 16 is rotated at a high rotational speed to improve the cooling capacity. . On the other hand, when the printing speed is low, the temperature inside the laser beam printer main body 1 is low, so the fan 16 is rotated at a low rotation speed to lower the cooling capacity.

More specifically, as shown in FIG. 2, when the fan 16 is set to two rotation speeds, a high rotation speed and a low rotation speed, the rotation speed control means 27 includes a PNP type transistor 28 and a transistor 29. It can be easily constructed by switching and. The power supply means 24 includes two power supplies H corresponding to two rotation speeds of the fan 16, respectively.
i (power supply voltage: large) and Lo (power supply voltage: small) are provided and connected to the emitter terminals of the transistor 28 and the transistor 29, respectively. The magnitudes of the power supply voltage Hi and the power supply voltage Lo are determined in advance so that the fan 16 rotates at an optimum air volume for the corresponding printing speed. The collector terminals of the transistor 28 and the transistor 29 are both connected to one terminal of the fan 16, and the other terminal of the fan 16 is grounded. Then, one of the transistors is selectively turned on, and the power source of the transistor in the on state is connected to the fan 16. The base terminals of the transistors 28 and 29 are connected to the output port of the CPU 23. CP at high printing speed
U23 outputs a rotation speed switching control signal for turning on the transistor 28 and turning off the transistor 29,
The power Hi is supplied to the fan 16, and the fan 16 rotates at a high rotation speed. On the other hand, when the printing speed is low, the CPU 23
From the transistor 28 to the OFF state, the transistor 29
A rotation speed switching control signal for turning on is output, the power source Lo is supplied to the fan 16, and the fan 16 rotates at a low rotation speed. In this way, the fan 16 can be rotated at the rotation speed of the optimum air volume for each printing speed, and problems such as the hot offset phenomenon and the cold offset phenomenon can be prevented. Of course, other switching elements may be used instead of the transistors 28 and 29.

Further, the power supply means 24 in FIG. 1 may be provided with two or more kinds of current values. At this time, as in the above description, the rotation speed switching control signal is set to CP in accordance with the printing speed.
Output from U23 to the rotation speed control means 27, and the rotation speed control means 27 switches the power supply current supplied to the fan 16,
The rotation speed of the fan 16 can be switched. Also at this time, the energy supplied to the fan 16 eventually changes according to the printing speed, and the above-mentioned problems can be prevented.

[0021]

According to the image forming apparatus of the present invention, even when the printing speed changes, the fan rotates at the optimum air flow speed for each printing speed, so that the heat is generated at high printing speed. It is possible to prevent the hot offset phenomenon and deterioration of the process unit due to the above, and to prevent the power consumption and the cold offset phenomenon due to the rotation of the fan with an air volume more than necessary at a low printing speed.

[Brief description of drawings]

FIG. 1 is a control block diagram of a fan of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a control block diagram of a fan of the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a conventional image forming apparatus.

FIG. 4 is a block diagram of a fan control unit of a conventional image forming apparatus.

[Explanation of symbols]

 1 Laser Beam Printer Main Body 2 Display / Operation Unit 16 Fan 23 CPU 24 Power Supply Means 25 Power ON / OFF Control Means 26 External Host Equipment 27 Rotation Speed Control Means 28 Transistors 29 Transistors

Claims (3)

[Claims] 1. An image forming apparatus for printing at least two kinds of printing speeds, comprising a central processing unit for controlling image forming timing, and a fan for discharging heat generated in the image forming process to the outside. And a rotation speed control means for controlling the fan at at least two rotation speeds,
The central processing unit outputs a rotation speed switching control signal to the rotation speed control unit according to the printing speed to change the rotation speed of the fan. A characteristic image forming apparatus. 2. The power supply means generates at least two types of voltages, and the rotation speed control means changes the voltage supplied to the fan to change the rotation speed of the fan. The image forming apparatus described. 3. The power supply means generates at least two kinds of currents, and the rotation speed control means changes the current supplied to the fan to change the rotation speed of the fan. The image forming apparatus described.