JPH08292681A - Image forming device - Google Patents

Abstract

PURPOSE: To always keep sufficient fixing characteristic without being influenced by environment and to form an image in the best condition by prolonging an interval time for when the surface temperature of a heating body is lower than a second set temperature. CONSTITUTION: The surface temperature of a heating roller is returned so as to be always positioned inside fixable areas (T1, T2) by means of the previously set interval (ta), even though the image is consecutively formed as shown in figure (A) in the case of normal temperature. In the case of a low temperature environment, the interval is prolonged to previously set time (tb) by means of a control circuit when the surface temperature of the heating roller is lower than second set temperature Tp as shown in figure (D). The temperature of the heating roller rises to first set temperature (ts) or to the temperature which is not <=T1 by the idly driving of the heating roller even though next image forming is performed in the middle of interval. Thus, the next image forming is performed after the surface temperature of the heating roller rises.

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 such as a copying machine or a printer, and more particularly to a case where the surface temperature of a heating roller of a fixing device is deprived of a predetermined amount by a passing transfer material and lowered. In particular, the present invention relates to an image forming apparatus capable of forming a plurality of continuous images without fixing defects by controlling an interval of passage of a transfer material.

[0002]

2. Description of the Related Art A toner image is transferred by a well-known electrophotographic process to a fixing device composed of a heating roller having a heating means and a pressure roller which is pressed against the heating roller and is driven or interlocked with the heating roller. There is known an image forming apparatus that forms a permanent image by passing a material, melting a toner image on a transfer material and thermally fixing the toner image. Such an image forming apparatus is
By repeating the steps of charging, exposing, developing, transferring, and fixing, it is possible to continuously form a plurality of images.

Usually, the temperature of the transfer material itself is almost equal to the air temperature used in the apparatus, and is much lower than the surface temperature of the heating roller of the fixing apparatus. For this reason, when the transfer material comes into contact with the heating roller and passes through the fixing device, the transfer material absorbs heat from the heating roller, and the surface temperature of the heating roller decreases. In order to compensate for this decrease in the surface temperature of the heating roller, it is sufficient to supply sufficient heat necessary for recovering the decreased temperature in a short time. Therefore, as a heating means of the heating roller, a relatively large capacity is required. It is possible to return to the set temperature in a short time by applying a high voltage to this heater using the above heater.

As for the process speed of how many images can be formed in a unit time, as shown in FIG.
It is determined by the sum of the copy time tc at which an image is actually formed and the interval ta under the condition that the predetermined value Ts within 1, T2) is controlled. Interval ta
Is the time from the trailing edge of the Nth transfer material to the leading edge of the (N + 1) th transfer material in a plurality of continuous image formations.
For example, the interval ta depends on the time for synchronizing the conveyance of the transfer material and the image data on the image carrier, the time for the optical system in the fixed-document-type image forming apparatus to return to a predetermined position after scanning the original, and the like. Is determined.

On the other hand, energy saving is spreading in image forming apparatuses. In particular, the fixing device has the highest power consumption in the image forming apparatus. By replacing the heater of the fixing device with a low power heater,
Inrush current when power is input to the heater can be suppressed, and overheating due to overshoot of the heating roller surface temperature due to heater on / off control can be suppressed, reducing heater power consumption and effective energy saving Can be realized. Further, by reducing the power consumption of the heater of the fixing device, it becomes possible to install the image forming apparatus even from a power source for general households that supplies only a small amount of power.

If a suitable image forming condition is set and the copy time tc is kept constant, the shorter the interval ta, the faster the process speed. However, when the above-mentioned low power heater is used, the recovery of the surface temperature of the heating roller may not catch up and a fixing failure may occur. Therefore, as shown in FIG. Must. In particular, since the surface temperature of the heating roller takes a different time to recover depending on the ambient environment temperature and the amount of heat taken by the transfer material, it is necessary to set the interval ta according to the condition that the room temperature is low. For example, using a household power source of 100 V and 15 A, the interval Ti is t so as to correspond to a normal room temperature.
In the image forming apparatus set to a, when image formation is performed in a low temperature environment of 10 ° C. or lower, the temperature control of the heating roller cannot keep up and the fixing temperature becomes lower than T1 as shown in FIG. 3B. As a result, fixing failure occurs.

The voltage has a permissible range, and a constant voltage is not always supplied. For example, even if the voltage is 100 V, only 90 V is supplied and the ambient temperature is normal. However, it may not be possible to maintain the heating roller at the set temperature.

[0008]

As described above, the low voltage,
If the interval is set to ta on the basis of conditions such as a low temperature environment, the process speed becomes slower, and under the above conditions during normal temperature environment or the formation of one image, the control of the surface temperature of the heating roller becomes conversely marginal. , It will not be possible to exert sufficient performance.

The present invention solves the above-mentioned problems and does not depend on the environment (room temperature) even when the heater of the fixing device is replaced with a low power heater adapted for household power. It is an object of the present invention to provide an image forming apparatus that always has a sufficient fixing property and can form an image under the best conditions.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is a roller or belt type heating body provided with a heating means controlled to a first set temperature, and pressure-contacted to this heating body. An image forming apparatus for fixing by passing a transfer material carrying a toner image to a fixing device composed of a roller or a belt type pressurizing body, wherein a predetermined time interval is provided between image formation. In an image forming apparatus capable of forming a plurality of continuous images, a second preset temperature lower than the first preset temperature is provided, and when the surface temperature of the heating body becomes lower than the second preset temperature, The second set temperature is located within a temperature range in which there is no problem with the fixing property of the transfer material, and is located near the lower limit of this temperature range. To.

[0011]

In such a structure, the heating element of the fixing device provided in the image forming apparatus is controlled to the first set temperature within the temperature range having a good fixing property. The image forming apparatus is capable of forming a plurality of continuous images, and a predetermined time interval is set. In a normal environment (room temperature), the transfer material is controlled so as to maintain the first set temperature even if the transfer material deprives the heat of the heating body. In an environment where the room temperature is low, the heat absorption of the transfer material is better than the heating of the heater of the fixing device, and it becomes impossible to control to the set temperature of the heating element.
The fixing temperature gradually decreases. When the temperature sensor detects the surface temperature of the heating element and becomes equal to or lower than the second preset temperature, the interval time is extended to return to the first preset temperature, and then the next image formation is performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an example of the basic configuration of an image forming apparatus in which the present invention is preferably used. The image forming apparatus 1 includes, as an image forming unit 2, a photosensitive drum 3 having a photosensitive member on its surface and rotating in the direction of arrow A, and a corona charger that charges the photosensitive drum 3 around the photosensitive drum 3 in the direction of rotation. 4. An optical projection device 5 such as an LED for projecting an optical image based on subordinate gift data output from a computer or the like onto the charged surface of the photosensitive drum 3 to form a latent image on the photosensitive drum 3. A developing device 6 that develops a latent image to form a toner image, a transfer corona discharger 8 that transfers a toner image to a transfer material that is sent from a paper feeding unit 7 that is loaded with roll paper or cut paper, and a transfer from a photosensitive drum 3. An AC separation corona discharger 9 that separates the material, a cleaning device 10 that removes the developer remaining on the surface of the photosensitive drum 3 after transfer, and a cleaning device that uniformly removes the surface potential of the surface of the photosensitive drum 3. And a Saranpu 11, it is provided so as to act sequentially the surface of the photosensitive drum 3. Further, a fixing device 15 described later is arranged to fix the transferred toner image on the transfer material as a permanent image.

As an image forming operation, image data sent from the outside is projected onto the uniformly charged photosensitive drum 3 by the optical projection device 5 to form an electrostatic latent image on the photosensitive drum 3. This electrostatic latent image is visualized by the toner in the developing device 6 to form a toner image on the photosensitive drum 3. The transfer material (roll paper) is interlocked with the transfer corona discharger 8 by interlocking so that the front end of the transfer material and the front end of the image formed on the photosensitive drum coincide with each other by providing a predetermined interval for the operation up to the toner image formation. The toner image is conveyed to and from the photosensitive drum 3, and the toner image is transferred to the transfer material. After that, the transfer material is electrostatically neutralized by the separation corona discharger 9,
It is separated from the photosensitive drum 3 at a predetermined separation position. Then, it is guided by the conveying means 13 and further conveyed to the fixing device 15. The toner image is fixed by the fixing device 15 and discharged from the discharge port 16 to the outside of the device. During this time, a cutter (not shown) detects the size of the document and cuts the transfer material into a desired size.

After the transfer of the photosensitive drum 3, the cleaning device 9 cleans the toner remaining on the surface of the photosensitive drum 3, and the eraser lamp 11 discharges the surface of the photosensitive drum 3 to prepare for the next image formation. To do.

FIG. 2 shows an example of the fixing device 15. The fixing device 15 is provided in contact with the heating roller 17 as a heating body and the heating roller 17 with an appropriate pressure.
A pressure roller 18 as a pressure member that is driven or interlocked with the heater, a heater 19, and a temperature sensor 20 that contacts the heating roller 17 and detects the surface temperature of the heating roller 17. The heating roller 17 is formed of a hollow cylindrical metal cylinder, has a surface coated with a fluorine resin or the like for preventing offset, and has a heater 19 inside.
The heater 19 is compatible with 100 V and 15 A, for example. The temperature of the surface of the heating roller 17 is controlled by the temperature sensor 20.
The surface temperature is detected by the control circuit 2
1 to control the temperature to reach the first set temperature Ts. The pressure roller 18 forms an elastic body such as silicon rubber around the metal shaft and contacts the heating roller 17 with an appropriate pressure to form a nip. Heating roller 7
Is driven by an external drive source to uniformly transfer the heat of the heating roller 17 to the pressure roller 18.
The transfer material carrying the toner image in the image forming section 2 is passed between the heating roller 17 and the pressure roller 18 to form a permanent image by heat and pressure.

FIG. 3 is a diagram showing the relationship between the surface temperature of the heating roller 17 and time. The image formation is performed between image formation when the temperature of the heating roller is lowered more than a predetermined value due to a change in environmental temperature or the like. The control of the interval will be described. The vertical axis represents the surface temperature (T) of the heating roller, and the horizontal axis represents time (t). A region between T1 and T2 is a region where good fixing property can be obtained. When the image forming apparatus is in the ready state, the surface temperature of the heating roller is controlled so as to reach the first set temperature Ts. When the image is formed, the surface temperature of the heating roller 17 is lowered by the passage of the transfer material due to the first copy. After that, the interval ta (tb)
The heating roller is idled for the period of time to raise the surface temperature. Next, the second copy is performed with the timing of the image data and the transfer material, and the surface temperature of the heating roller is lowered by the passage of the transfer material. In this way, image formation is continuously performed.

The surface temperature of the heating roller 17 is controlled to a set temperature, but since the heater is for a low voltage, it is easily influenced by the external environmental temperature. Normal temperature is shown in Fig. 3.
Even if continuous image formation is performed as shown in (A), the heating roller 1 is driven by the preset interval ta.
Within the area where the surface temperature of 7 returns and can be fixed (T1, T2)
Can always be located in. FIG. 3D shows the surface temperature (T) and time (t) of the heating roller in a low temperature environment.
When the surface temperature of the heating roller 17 becomes lower than the second set temperature Tp, the control circuit (not shown) extends the interval to a preset time tb. During the interval, the heating roller idles to raise the temperature to the first set temperature ts or to a temperature that does not become T1 or less even if the next image formation is performed. After the surface temperature of the heating roller 17 rises in this way, the next image formation is performed.

As a preferable example of the interval control, when the normal interval ta in continuous image formation is set to 1 second, the interval tb is set to about 2 to 3 seconds when the temperature of the fixing device is lowered. ing. As described above, the interval ta is set in advance under the best condition at room temperature, and the interval tb at which the image formation is possible is set according to the environmental temperature, so that the temperature of the fixing device capable of stable fixing is controlled at all times. . Since the intervals ta and tb differ depending on the image forming apparatus used, the set value is appropriately selected. Further, the interval tb may be set according to the size of the transfer material.

Although the heating roller is used as the heating element and the pressure roller is used as the pressing element in the embodiments, a belt on which the heating element moves or a fixed belt (including a film) may be used. A belt in which the pressing body moves or a fixed belt may be used, and the same effect as that of the embodiment can be obtained.

[0020]

As described above, according to the present invention, it is possible to provide the image forming apparatus having the best process speed in accordance with the environment such as the room temperature by the power saving, and the image forming apparatus is ready. It is possible to continuously perform image formation on the transfer material.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a fixing device of the image forming apparatus according to the present invention.

3A, 3B, 3C, and 3D are diagrams showing the relationship between the surface temperature of the heating roller of the image forming apparatus according to the present invention and time.

[Explanation of symbols]

 1 Image Forming Apparatus 2 Image Forming Section 3 Photosensitive Drum 4 Corona Charging Device 5 Optical Projecting Device 6 Developing Device 7 Paper Feeding Section 8 Transfer Corona Discharging Device 9 Separation Corona Discharging Device 10 Cleaning Device 11 Eraser Lamp 12 Document Conveying Device 13 Conveying Means 15 Fixing device 16 Discharge port 17 Heating roller 18 Pressure roller 19 Heater 20 Sensor 21 Control circuit

Claims (2)

[Claims] 1. A toner image is formed on a fixing device including a roller or belt type heating body having a heating unit controlled to a first set temperature, and a roller or belt type pressure body pressingly contacting the heating body. An image forming apparatus that allows a carried transfer material to pass therethrough and fix the image, wherein the image forming apparatus is capable of forming a plurality of continuous images by providing an interval of a predetermined time between image formations. A second preset temperature lower than the preset temperature is provided, and the interval time is extended when the surface temperature of the heating element becomes lower than the second preset temperature. 2. The image forming according to claim 1, wherein the second set temperature is located within a temperature range where there is no problem with the fixing property of the transfer material, and is located near the lower limit of this temperature range. apparatus.