JP3530747B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image by an electrophotographic method, and more particularly, to temperature control for a fixing device. 2. Description of the Related Art An electrophotographic image forming apparatus includes a photosensitive drum, a developing device, a fixing device, and the like. The photoconductor drum is a device for forming an electrostatic latent image corresponding to exposure by exposing a surface charged to a constant potential. The developing device is a device for developing the electrostatic latent image formed on the photosensitive drum into a toner image.
The fixing device is a device for fixing the toner image transferred to the sheet after the toner image on the photosensitive drum is transferred to the sheet. In this type of image forming apparatus, in order to form a good image, the potential of the photosensitive drum is adjusted, for example, when the power is turned on or after a predetermined number (for example, 3000) of images are formed. . Further, when toner is supplied to the developing device, an adjustment operation is performed for a predetermined time in order to sufficiently stir the toner. [0004] During these potential adjustments and adjustment operations during toner replenishment (hereinafter referred to as "aging"), due to the structure of the image forming apparatus, the fixing device is also operated with no load (in a state where paper is not supplied). It has become. [0005] However, when the fixing device is operated for a long time without load, there is a problem that the peripheral surface of the pressure roller included in the fixing device is stained with toner or the like. [0006] The inventors of the present application have studied the cause of this, and have found the following. [0007] The fixing device generally includes a roller pair of a heat roller and a pressure roller, and each roller is provided with a cleaning roller. The surface of the pressure roller is cleaned by the cleaning roller. However, it has been found that if the temperature of the pressure roller is too high, the dirt such as toner adhered to the cleaned cleaning roller returns to the pressure roller again. Normally, when a load is applied to the fixing device, that is, when a sheet is given to the fixing device, the heat of the heat roller and the pressure roller is removed by the sheet passing between the heat roller and the pressure roller. Therefore, the temperature of the pressure roller does not rise so much. For this reason, the pressure roller is always satisfactorily cleaned by the cleaning roller when a load is applied, but the above-described problem occurs when the pressure roller is driven for a long time with no load. The present invention has been made in view of such a background, and an object of the present invention is to provide an improved image forming apparatus which does not cause a problem in a fixing device during aging. SUMMARY OF THE INVENTION The present invention relates to an image forming apparatus having a fixing device for forming a toner image by electrophotography, transferring the toner image to a sheet, and fixing the toner image transferred to the sheet. Therefore, the fixing device includes a roller pair of a heat roller and a pressure roller, and the sheet is passed between the rollers,
Are those toner image on the sheet is fixed by heat and pressure, furthermore, in the image forming apparatus is heating means for heating the heat roller is provided, predetermined adjustment processing
And the image cannot be formed during the adjustment process.
In response to the aging signal to the effect that performs the aging process to be given, and the timer means starts counting, after the timer means has timed the specified time period, the Ejin
And control means for lowering the heating temperature by the heating means by a certain temperature until the adjustment process in response to the switching signal is completed. According to the above arrangement, after a predetermined time has passed after the predetermined adjustment signal has been given, the heating temperature of the heating means is reduced by a certain temperature until the adjustment is completed. For example, usually, the heating means uses a heat roller of 195.
° C, but this temperature is reduced to, for example, 175 ° C. As a result, during the adjustment, the fixing device is operated with no load, but the temperature of the heat roller heated by the heating means is lowered, so that the temperature of the pressure roller does not become too high. Therefore, no trouble such as toner returning from the cleaning roller to the pressure roller does not occur, and the pressure roller is maintained in a clean state when the adjustment operation is completed. Therefore, there is no problem such as soiling of the back surface of the sheet in image formation after the end of the adjustment operation. Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is an illustrative block diagram showing a configuration of a characteristic portion of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, the fixing device 1 includes a roller pair of a heat roller 2 and a pressure roller 3. A heater 4 is provided inside the heat roller 2 as a heating unit for heating the heat roller 2. The energization of the heater 4 is controlled by a control circuit 8. In addition, a temperature sensor 9 is provided near the peripheral surface of the heat roller 2 so that the peripheral surface temperature of the heat roller 2 is measured. The signal of the temperature sensor 9 is also provided to the control circuit 8. The paper P on which the toner image has been transferred passes between the heat roller 2 and the pressure roller 3, so that the toner is heated by the heat roller 2 and is sandwiched between the heat roller 2 and the pressure roller 3. Is pressed, and the toner image is fixed on the sheet. Then, the sheet P on which the toner has been fixed is discharged from the left side in FIG. An oil application roller 5 and a cleaning roller 6 are provided around the heat roller 2 so as to be in contact with the peripheral surface of the heat roller 2. The oil application roller 5 is
Heat roller 2 before contacting paper P on which toner image is to be fixed
Is a roller for applying, for example, silicone oil as a release liquid to the surface of the roller. While the paper P passes between the heat roller 2 and the pressure roller 3, the paper P may be stuck to the peripheral surface of the heat roller 2 and may not be smoothly separated from the heat roller 2. Therefore, by applying a releasing oil to the peripheral surface of the heat roller 2 in advance, the paper that has passed between the heat roller 2 and the pressure roller 3 is easily separated from the heat roller 2. The cleaning roller 6 is a roller for cleaning the peripheral surface of the heat roller 2 after the sheet is separated. When the paper P is heated and pressed by the heat roller 2 and the pressure roller 3, a very small part of the toner transferred to the paper P may adhere to the peripheral surface of the heat roller 2. The cleaning roller 6 is provided for cleaning toner and the like adhered to the peripheral surface of the heat roller 2. In the present embodiment, the peripheral surface of the pressure roller 3 is of a conductive type in which carbon is kneaded into a Teflon tube. When the peripheral surface of the pressure roller 3 is made of Teflon as a main material and of a conductive type, there is an advantage that static electricity is hardly generated on the paper P passing between the heat roller 2 and the pressure roller 3. This is because the toner transferred to the paper P is generally positively charged, and the peripheral surface of the pressure roller 3 made of Teflon is negatively charged. Then, since the pressure roller 3 is conductive, the charge is released, so that the positive charge on the paper is combined with the negative charge of Teflon, and the charge is released. Therefore, static electricity hardly remains on the paper P. The cleaning roller 7 is also in contact with the peripheral surface of the pressure roller 3 and is rotated. The cleaning roller 7 is a roller for cleaning dirt such as toner adhered to the peripheral surface of the pressure roller 3. When the surface temperature of the pressure roller 3 rises as described in the section of the prior art, even if the cleaning roller 7 removes dirt such as toner from the surface of the pressure roller 3, even if the cleaning roller 7 cleans the circumference of the cleaning roller 7, Dirt transferred to the surface,
It has been found that the pressure roller 3 may return to the peripheral surface again. The case where the peripheral surface temperature of the pressure roller 3 is excessively raised is a case where the fixing device 1 is operated for a long time with no load. When a load is applied to the fixing device 1, that is, when a sheet is sent to the fixing device 1, while the sheet P passes between the heat roller 2 and the pressure roller 3, the heat roller 2 and the pressure roller 3 Heat is removed by the paper P and the pressure roller 3
Does not rise above its predetermined temperature. However, if the vehicle is operated for a long time with no load,
In some cases, the heat of the heat roller 2 is transmitted to the pressure roller 3 as it is, and the peripheral surface temperature of the pressure roller 3 rises too much. A case where the operation is performed for a long time with no load includes aging. Therefore, in this embodiment, as described below, a special temperature control is applied to the heater 4 during aging. In FIG. 1, other components usually provided in an image forming apparatus such as a photosensitive drum, a developing device, a transfer device, and a sheet conveying device are not shown. In addition, since these configurations are already known, description thereof will be omitted. In FIG. 1, the control circuit 8 is supplied with an adjustment signal from an adjustment signal input unit 10. The adjustment signal input section 10 is a section for inputting a start signal when aging is performed. The control circuit 8 includes a timer 11 for measuring time. This timer 11
The timer may be a hardware timer or a so-called software timer. The display unit 12 is further connected to the control circuit 8. The display unit 12 is provided on an operation panel or the like of the image forming apparatus and is a unit for performing necessary display for a user. FIG. 2 is a flowchart for explaining the control operation of control circuit 8 in FIG. A description will be given along the flow of FIG. When the control operation starts, the control circuit 8 controls the adjustment signal input unit 10
It is determined whether or not an aging signal has been input from (step S1). If no aging signal is provided, the process ends. When an aging signal is given from the adjustment signal input unit 10, that is, when toner is supplied or when a predetermined number of images are formed and the potential of the photosensitive drum needs to be adjusted, the adjustment signal input unit An aging signal is provided from 10. When the control circuit 8 detects the input of the aging signal, the timer 1
1 is started (step S2), and the display section 12 displays, for example, "Please wait for a while." (Step S3). Then, a predetermined aging process is performed (Step S4). As described above, the aging process is a process of adjusting the potential of the photosensitive drum or a process of sufficiently stirring the toner in the developing device when the toner is supplied. After the aging process is started, the control circuit 8 determines whether or not the aging process has been completed (step S5). This determination is made, for example, when a signal indicating that the surface potential of the photosensitive drum is stabilized is given from the sensor. If the aging process has not been completed, the control circuit 8 determines whether or not the timer 11 has counted, for example, two minutes (step S6). If the aging is completed before the timer 11 counts 2 minutes, the process proceeds to step S10, and the display on the display unit 12 is changed from "Please wait" to "I can copy" (step S10), the process ends. If the timer 11 measures 2 minutes in step S6, the control circuit 8 lowers the temperature of the heater 4 from, for example, 195.degree. C. which has been controlled up to 175.degree. C. (step S7). Then, the temperature of the heater 4 is set to 175 ° C.
And wait for the aging to be completed (step S8). When the aging is completed, the temperature of the heater 4 is increased again from 175 ° C. to 195 ° C. (Step S)
9). Then, the display on the display unit 12 is changed to "copy is possible" (step S10), and the process is terminated. In step S7, the temperature of the heater 4 is set to 175 ° C.
Therefore, even if the temperature of the heat roller 2 is transmitted to the pressure roller 3, the peripheral surface temperature of the pressure roller 3 does not increase until dirt and the like are adsorbed from the cleaning roller 7 again. The temperature of the heater 4 is set to a temperature (175 ° C. in this embodiment) at which the no-load heat roller 2 can be sufficiently heated depending on the temperature. Therefore, immediately after the aging process is completed, the fixing device 1 is brought into a state in which the fixing device 1 can operate normally. The control temperature of 195 ° C. or 175 ° C. of the heater 4 in the above-described embodiment is merely an example, and is not limited to this. The time measured by the timer 11 is not limited to 2 minutes, but may be changed depending on the type of the device. Since the present invention is configured as described above, there is no problem that the peripheral surface of the pressure roller 3 is overheated during aging and dirt adheres to the surface. In this case, the fixing device can be operated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustrative block diagram showing a main configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining the operation of the control circuit shown in FIG. 1; [Description of Signs] 1 Fixing device 2 Heat roller 3 Pressure roller 4 Heater 7 Cleaning roller 8 Control circuit 10 Adjustment signal input unit 11 Timer

Claims (1)

(57) An image forming apparatus having a fixing device for forming a toner image by electrophotography, transferring the toner image to a sheet, and fixing the toner image transferred to the sheet, The fixing device includes a roller pair of a heat roller and a pressure roller, and the toner image on the sheet is heated and pressed to be fixed by passing the sheet therebetween, and further, the heat roller is heated. In an image forming apparatus provided with a heating unit that performs heating, a predetermined adjustment process is performed.
Aging treatment that can not be formed
In response to the aging signal is given, the timer means starts counting, after the timer means has timed the specified time period, until the adjustment process in response to the aging signal <br/> No. is completed only, the image forming apparatus characterized by comprising a control means for lowering by a constant temperature heating temperature by the heating means.