JP2006162672A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device which continuously stabilizes fixing a roller surface temperature within a permissible range even in long-time continuous printing operation and prevents a productivity decrease and fixation defects due to a down time of the device. <P>SOLUTION: The fixing device is equipped with: a fixing means having a plurality of heating bodies differing in light distribution; a pressing means opposed to the fixing means for press contacting; a fixation period calculating means of calculating when a recording material carrying an unfixed image passes through the fixing device; and a voltage ratio variation control means of variably controlling the ratio of voltages applied to a plurality of heaters according to the passage timing of the recording material calculated by the fixation period calculating means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device of an image forming apparatus, and more particularly to a fixing device using a carbon heater and a control method thereof.

  Conventionally, in a fixing device having heaters with different light distributions, a stable temperature is maintained in the paper passing area, and the power ratio of the heater depends on the paper type so as not to overheat in the non-paper passing area (edge). It is decided in advance. In particular, with conventional halogen heaters, variably controlling the applied voltage affects the life, and frequent ON / OFF control causes problems such as flicker and harmonics. Therefore, the heater ON / OFF predetermined for each paper type is problematic. The power ratio is optimized by controlling based on the OFF duty.

  In general, providing a plurality of heaters with different light distributions increases the cost of the apparatus, so usually two of them are provided for all paper types (see Patent Documents 1 and 2).

JP 05-281877 A Japanese Patent Laid-Open No. 07-114294

  However, since the temperature adjustment control during the printing operation is optimized for the sheet passing area, it is difficult to stably maintain the temperature of the non-sheet passing area on the end side, and the longer the continuous printing operation becomes, the longer the continuous printing operation becomes. A temperature difference occurs between the center and the edge of the surface of the fixing roller. As a result, in a printing operation that takes a long time, there is a possibility that a temperature difference occurs between the end and the center even in the sheet passing area, and the fixing property may differ between the center and the end of the sheet.

  Also, recently, the technical trend of the fixing roller has changed from a conventional thick-walled resin to a structure using a thin-walled resin material, but because the thin-walled system has poor heat conduction in the main scanning direction compared to the thick-walled system, In particular, the above problem is likely to occur. If a roller with a relatively large heat capacity is used even in a thin-walled system, the heat taken away by the sheet cannot be compensated for between the sheets, and the temperature of the sheet passing area also falls outside the predetermined range if continuous sheet feeding continues for a long time. Resulting in.

  In the conventional halogen heater, in response to the above problems, when the temperature at the center or at the edge is higher than a predetermined value or lower than a predetermined value, the paper interval is widened, or a down sequence is inserted so that the paper is not passed through the fixing device for a while. Thus, measures have been taken by providing a time to adjust the temperature of the entire roller to be within a predetermined range (see Japanese Patent Application Laid-Open Nos. 09-114318 and 10-020718). However, in this case, the problem is that the productivity of the apparatus is lowered.

  The present invention has been made in view of the above problems, and the object of the present invention is that the fixing roller surface temperature can be continuously stabilized within an allowable range even during a long-time continuous printing operation. It is an object of the present invention to provide a fixing device that can prevent a decrease in productivity and occurrence of fixing failure.

  Therefore, in the present invention, a fixing device including a plurality of heating elements having different light distributions and a pressure unit that is pressed against the fixing unit (particularly, in the present invention, like a carbon heater). A fixing structure using a heater that does not affect the life even if the applied voltage is variably controlled), means for calculating the timing at which the recording material passes through the fixing portion, and a plurality of types based on the passage timing. By providing a means for variably controlling the voltage ratio applied to the heater, the voltage ratio can be controlled at an optimal timing during continuous printing. This is done by grasping the timing when the recording material passes through the fixing nip portion that is in pressure contact with the fixing roller and the pressure roller, so that the voltage is switched while the toner image is fixed on the target recording material. Prevents the temperature of the roller surface from changing rapidly.

  Further, by performing the voltage ratio variable control based on the detection result of the number of recording materials passing through the fixing unit and the surface temperature of the fixing roller, the control can be performed at a timing more suitable for the apparatus.

  Furthermore, by performing the above-described voltage ratio variable control within the maximum power that can be supplied to the fixing device, it is possible to secure power supply to other than the fixing device so as not to hinder the operation of the entire device. To do.

  By the above means, the temperature difference between the center and the edge caused by continuous paper feeding can be reduced, and excessive temperature rise of the edge temperature can also be prevented. Therefore, the surface temperature of the fixing roller can be continuously stabilized within an allowable range even during a long continuous printing operation, and the above-described problems such as productivity reduction and fixing failure due to the downtime of the apparatus are solved.

  According to the present invention, in a fixing device using a plurality of heaters having different light distributions, a temperature difference between a paper passing area and a non-paper passing area caused by a continuous printing operation is caused to cause downtime of the apparatus as in the conventional case. Without reduction. Therefore, according to the present invention, it is possible to ensure stable fixing image quality and improve the operation rate and productivity of the apparatus.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
FIG. 1 is a schematic cross-sectional view of a fixing device according to Embodiment 1 of the present invention.

  In the illustrated fixing device, a fixing roller 101 provided with a carbon heater as a heat source therein, a pressure roller 102 that rotates while being pressed against the fixing roller 101, and a recording material carrying an unfixed image enter the fixing device. A fixing entrance SNS1 and a temperature sensor TH1 for detecting the surface temperature of the fixing roller 101.

  Thus, the recording material carrying the unfixed image passes through the pressure contact portion formed by the fixing roller 101 and the pressure roller 102, whereby the toner image is fixed to the recording material by heat and pressure. At this time, the surface temperature of the fixing roller 101 is controlled by an electric circuit (not shown) based on the detection result of the temperature sensor TH1 so that the surface temperature is stabilized within a predetermined range.

  Next, the configuration of the carbon heater provided in the fixing roller 101 will be described with reference to FIG.

  As shown in FIG. 2, two heaters having different configurations are provided. The heater 1 has a length of 200 mm at the center of the heater portion 201 located at the center with respect to the fixing roller, and has a specification of 800 W at 100V. The shape is plate-like, and heat is radiated mainly in a direction orthogonal to the plate surface. The heater 2 has heater portions 202 and 203 having a length of 50 mm at both ends with respect to the fixing roller, and has a specification of 100 W and 400 W (200 W × 2). The shape is plate like the heater 1. As shown in the lower side of FIG. 2, the light distribution of the heaters 1 and 2 is distributed in the center portion of the fixing roller, the heater 2 is distributed at both ends, and in an area substantially equal to the length of the heater portion. ing. The feature of the carbon heater used in the present embodiment is that it is a carbon-based resistor, so that there is no inrush current and lighting of 0 to 100% is possible.

  FIG. 3 is a schematic diagram of a circuit block related to fixing heater control including a voltage ratio control circuit 304 which is a feature of the present invention. The function will be described below.

  From the CPU 301 that executes various control processing operations over the entire apparatus, the ROM 303 and RAM 302 that store software programs and the like for operating the CPU 301, the voltage ratio control circuit 304, which is a feature of the present invention, and the voltage ratio control circuit 304 And a peak value control circuit 305 for controlling the peak value of the voltage applied to the heaters 1 and 2 based on the above signal and the information of the temperature sensor TH1.

  The voltage ratio control circuit 304 operates the peak value control circuit 305 so that the applied voltage of the heaters 1 and 2 is predetermined for each paper type based on the paper type information of the recording material transmitted from the CPU 301. Based on the paper type information and the signal from the fixing entrance sensor SNS1, the timing at which the recording material carrying the unfixed image passes through the fixing nip portion is calculated. In the present embodiment, a counter (not shown) that further counts the number of recording materials passing therethrough is provided, and the voltage applied to the heaters 1 and 2 is switched and controlled for each predetermined number of sheets.

  Here, FIG. 4 shows a state of temperature change in the sheet passing area and the non-sheet passing area in the conventional heater control, and the problem will be described below. FIG. 5 shows the temperature distribution on the surface of the fixing roller in question. FIG. 6 shows general power control in a fixing configuration using a conventional halogen heater.

  First, a conventional heater control method will be described. Since a conventional heater generally uses a halogen heater, the rated power is 1500 W for the entire apparatus (Japanese power outlet specifications are 100 V, 15 A). If the applied voltage is not fixed and used according to the power supply specifications, the heater life may be deteriorated. For this reason, it is difficult to keep all the heaters ON during continuous paper feeding, and the lighting control is performed for each of the two heaters except when the machine operation other than the fixing unit is stopped as in warm-up. Is common. The control method is such that the ON / OFF duty of the heaters 1 and 2 is determined so as to obtain a predetermined power ratio for each paper size, and is provided in the vicinity of the center of the fixing roller based on the detection result of the temperature sensor. It was controlled to be within the temperature range.

  In addition, the amount of heat stored depends on the thickness of the rubber material of the fixing roller, and this thickness is related to the amount of heat required for fixing. However, in the conventional halogen heater control method, frequent ON / OFF is not possible. In order to influence flicker and harmonics, a rubber roller having a relatively high heat capacity is used so that it can be easily controlled with a period of about 1 second to 4 seconds. For this reason, the heat taken by the paper passing cannot be compensated between the papers, and the temperature in the paper passing region tends to decrease as the continuous paper passing continues. At this time, in the non-sheet passing area on the end side, since the heat taken away by the sheet passing is small, the temperature tends to increase.

  Conventionally, as a means for solving such a problem, when one of the temperature sensors disposed near the center and near the end of the fixing roller is outside a predetermined temperature range, the sheet passing is stopped and the fixing roller is idled. As a result, a time for acclimatization was provided so that the temperature of the roller surface was uniform, but this had the problem of a reduction in productivity due to downtime of the apparatus.

  Furthermore, as a member used for the fixing roller recently, for the purpose of shortening the warm-up time or the like, a member having a higher thermal conductivity in the direction orthogonal to the roller axial direction is used, In this case, since the thermal conductivity in the axial direction is deteriorated, the temperature difference between the end side temperature which is a non-sheet passing region and the sheet passing region becomes larger. Therefore, the problem described above is more serious.

  Therefore, in the present embodiment, the above problem is solved by performing the heater control as shown in FIG. Hereinafter, the control method will be described.

First, electric power is supplied from the peak value control circuit 305 to the heaters 1 and 2 based on the voltage ratio of the heaters 1 and 2 predetermined according to the paper type by the voltage ratio control circuit 304 of FIG. Since the carbon heater in the present embodiment can supply power from 0 to 100% with respect to the rated voltage, the power supply ratio to the two heaters is controlled not by the ON / OFF duty but by the crest value control of the AC voltage. Is controlling. Conventionally, as shown in FIG. 6, the required power of the large size paper is 800 W × 1.3 sec × 3 ÷ 200 mm≈16 W / mm in 10 seconds in the heater 1. Also for the heater 2, 400 W × 1.3 sec × 3 ÷ 100 mm≈16 W / mm, and the same amount is necessary. Therefore, in the control in the present embodiment, heater 1 = 16 W / mm × 200 mm ÷ 10 sec = 320 W, heater 2 = 16 W / mm × 100 mm ÷ 10 sec = 160 W (see FIG. 7). This is the optimum power ratio for the target paper type. However, as described above, if the power ratio is kept constant during continuous paper feeding as in the conventional case, the power ratio is not near the center of the paper feeding area. A temperature difference occurs between the vicinity of the end of the paper passing area.
Therefore, in this embodiment, the voltage ratio control circuit 304 counts the number of sheets through which the recording material passes, and performs control to switch the previous power ratio every time it reaches 20. Further, the switching timing is performed at the time of non-sheet passing based on the timing at which the recording material passes, thereby avoiding a sudden temperature fluctuation at the time of sheet feeding. The power ratio at this time is 600 W for heater 1 and 100 W for heater 2. In the present embodiment, the power ratio at the time of switching is obtained as a result of examination, and is preset according to the paper type and the number of sheets.

  As described above, by controlling the switching of the power ratio to a plurality of heaters with different light distributions at the desired timing during continuous paper feeding, the problem is that continuous operation continues even at a predetermined optimal power ratio. It becomes possible to reduce the temperature difference between the sheet passing area and the non-sheet passing area.

  Next, the overall flow of the function of the first embodiment described above will be described with reference to the flowchart shown in FIG.

  First, the recording material is stored in the paper supply unit or the print job ticket is sent to recognize the paper type (S101). Then, when JOB starts (S102) and a recording material carrying an unfixed image is conveyed, it is detected that the recording material has entered by a sensor arranged near the entrance of the fixing device (S103). Based on the detection timing, the timing at which the recording material passes through the fixing nip is calculated (S104). In this embodiment, the number of sheets through which the recording material passes is counted (S105), and when the number exceeds the predetermined number (20 sheets in this embodiment) (S106), the paper type information recognized in S101 is added. Based on this, control is performed to obtain a predetermined voltage ratio (S107). Thereafter, when JOB continues, a series of sequences from detection of entry into the fixing entrance is repeatedly executed, and the voltage ratio is switched every predetermined number of sheets.

  As a feature of the present embodiment, since voltage switching control is performed based on the number of recording materials passing through the fixing unit, it is necessary to predict the temperature of the actual roller surface, and a study for that is required. Become. However, conversely, the heat capacity of the fixing roller member is small, the change in the roller surface temperature is fast, and it is considered suitable for a fixing configuration that is difficult to control with a temperature sensor.

<Embodiment 2>
In the second embodiment, description of the same configurations and functions as those of the first embodiment will be omitted.

  In this embodiment, as shown in FIG. 9, temperature sensors TH1, TH2, and TH3 are disposed near the center and near the end of the surface of the fixing roller, and the detected temperature and end of TH1 located at the center are detected. Based on the detected temperatures of TH2 and TH3 located at, the temperature difference calculation circuit 1002 calculates the temperature difference between the center TH1 and the end portions TH2 and TH3. If either one is equal to or greater than the predetermined value, a request signal is output to the voltage ratio control circuit 304 to change the applied voltage ratio (see FIG. 10). In response, the voltage ratio control circuit 304 executes switching control to a voltage ratio predetermined for each paper type.

  By the above control, as in the first embodiment, it is possible to reduce the temperature difference between the sheet passing area and the non-sheet passing area during continuous sheet passing.

  Next, the overall flow of the function of the second embodiment described above will be described with reference to the flowchart shown in FIG.

  First, the recording material is stored in the paper supply unit or a print job ticket is sent to recognize the paper type (S201). Then, JOB starts (S202), and when a recording material carrying an unfixed image is conveyed, the sensor disposed near the entrance of the fixing device detects that the recording material has entered (S203). Based on the detection timing, the timing at which the recording material passes through the fixing nip is calculated (S204). Then, in the present embodiment, based on the temperature detection results of the temperature sensor TH1 disposed near the center of the fixing roller surface and the TH2 and TH3 disposed at both ends (S205), the center TH1 and the ends TH2 and TH3 are detected. And when it is determined that either (TH2-TH1) or (TH3-TH1) is equal to or greater than a predetermined value N (S206), voltage ratio switching control is performed (S206). S207). Since the above flow is continued until JOB is completed, the voltage ratio is switched every time the temperature difference between the center and the end of the fixing roller surface exceeds a predetermined value in step S206.

  Since the present embodiment is controlled while detecting the temperature of the roller surface as a feature different from the first embodiment, voltage switching control can be performed at a more optimal timing. However, in general, from the viewpoint of the responsiveness of the temperature sensor, a slight time lag occurs between the actual roller surface temperature and the detection result of the temperature sensor. I think that it is suitable for the structure where the temperature change of the surface is gentle.

1 is a schematic cross-sectional configuration diagram of a fixing device according to an embodiment of the present invention. The structure and light distribution of the carbon heater in embodiment of this invention are shown. 1 is a schematic configuration of a block diagram including a voltage ratio control circuit which is a feature of the present invention. 6 is a graph showing changes in fixing roller surface temperature in conventional control. FIG. 6 is a diagram illustrating a temperature distribution on the surface of a fixing roller which is a problem in conventional control. The power control with a conventional halogen heater is shown. The power control in Embodiment 1 of this invention is shown. It is the graph which showed the roller surface temperature change by control in Embodiment 1 shown in FIG. FIG. 6 is a layout diagram of temperature sensors in the vicinity of a fixing roller in Embodiment 2 of the present invention. FIG. 3 is a partial block diagram of a control circuit according to Embodiment 2 of the present invention. It is the flowchart which showed a series of operation | movement sequences in Embodiment 1 of this invention. It is the flowchart which showed a series of operation | movement sequences in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Fixing roller 102 Pressure roller 201 Heater part 202 Heater part 203 Heater part 301 CPU
302 RAM
303 ROM
304 Voltage ratio control circuit 305 Crest value control circuit SNS1 Fixing entrance sensor TH1 Temperature sensor

Claims (4)

In a fixing device including a fixing unit including a plurality of heating elements having different light distributions, and a pressing unit that presses against the fixing unit.
A fixing period calculating means for calculating a timing at which a recording material carrying an unfixed image passes through the fixing device; and a ratio of voltages applied to the plurality of heaters based on the passing timing of the recording material calculated by the fixing period calculating means And a voltage ratio variable control means for variably controlling the fixing device.   The fixing period calculating means is provided with means for counting the number of passing sheets of recording material, and when the counted number of sheets reaches a predetermined value, the voltage ratio is switched and controlled based on the passing timing by the fixing period calculating means. The fixing device according to claim 1, wherein:   The fixing means has an endlessly movable surface, the plurality of heating elements are arranged inside, and a plurality of temperature detecting means are arranged to detect the surface temperature near the center and the end in the axial direction of the fixing means. 2. The fixing device according to claim 1, wherein the voltage ratio variably controlled by the voltage ratio variable control means is determined based on a detection result of the temperature detection means.   The voltage ratio that is variably controlled by the voltage ratio variable control means is determined such that the total power supplied to the plurality of heating elements is equal to or less than a predetermined power. Fixing device.

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