JP2001265157A - Fixing machine for electrophotographic printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing machine for an electrophotographic printer, capable of performing a fixing operation in accordance with a printing speed of about 40 to 50 PPM such as that of a copying machine. SOLUTION: A thermistor 1 is arranged at a point B outside the maximum printing area, and constitutes a 1st temperature detecting means for controlling a temperature in contact with the coated surface of the heat roller 2. A thermistor 3 is arranged near the central part of the heat roller 2 in a noncontact state, and functions as a 2nd temperature detecting means with leaving a gap of about 1 mm between the heat roller 2 and the thermistor 3. Two halogen lamps 4 and 5 are assembled as heating sources inside the heat roller 2. The halogen lamp 4 functions as a heating source with a light-emitting area, having an effective length corresponding to the whole printing area and for printing a wide paper, and the halogen lamp 5 functions as a heating source with the light-emitting area, which is as wide as the vertically placed A4 sized paper (about 210 mm in width) and for printing a narrow paper.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fixing device for an electrophotographic printer.

[0002]

2. Description of the Related Art In an electrophotographic printer, a roller fixing means comprising a heated heat roller and a backup roller which is in pressure contact with the heat roller is used. In this roller fixing means, the transfer paper is heated by a pair of heated and pressurized rollers (heat roller and backup roller), and the unfixed toner image formed on the surface thereof is instantaneously fixed. A fixing device using such a roller fixing unit has a very high thermal efficiency, and can easily increase the fixing speed as compared with other fixing methods.
It has a number of advantages. Therefore, in recent electrophotographic printers, a fixing method using a roller has become mainstream.

FIG. 2 is a side view showing the structure of a fixing means using a conventional heat roller. 50 is a heat roller,
Reference numeral 51 denotes a backup roller made of silicon rubber having a low hardness, and reference numeral 52 denotes a separation claw for separating transfer paper from the heat roller 50 after fixing. Backup roller 51
Is pressed against the heat roller 50 by a pressure spring 55 via a bearing 60 to which both ends of the rotating shaft are fitted.

Usually, the heat roller 50 is made of an aluminum metal pipe, and since the roller surface comes into direct contact with the unfixed toner image, the heat roller 50 has a sufficient releasability from the toner on the surface of the transfer paper. The surface is coated with a non-adhesive substance such as a fluororesin (Teflon (registered trademark) coating). Separation claw 52
A plurality (about 4 to 6) are provided in the axial direction of the heat roller 50 in accordance with the allowable paper size on which printing can be performed, and are rotatably held with respect to the fixing device cover 53 by means (not shown). The compression coil spring 54 contacts the peripheral surface of the heat roller 50 with an appropriate pressing force.

[0005] Reference numeral 56 denotes a heater (for example, a halogen lamp or the like) incorporated in the heat roller 50. The heater 56 is energized to heat the heat roller 50. A temperature control thermistor 57 rubs on the surface of the heat roller 50, and the temperature of the heat roller 50 is controlled by the thermistor 57 so that the fixing temperature can be maintained at a constant temperature. Reference numeral 58 denotes a cleaning felt impregnated with silicone oil. The cleaning felt 58 also rubs on the surface of the heat roller 50. The cleaning felt 58 has a function of removing offset toner on the surface of the heat roller 50, and maintains the releasability of the heat roller 50 from the surface toner on the transfer paper 59 for a long period of time. This prevents the offset toner from adhering and accumulating on the rubbing thermistor 57.

In the fixing device having the above configuration, the transfer roller 59 having unfixed toner on its surface is heated by a heat roller 50.
When the toner image passes through the space between the roller and the backup roller 51, heat and pressure are applied to fuse the toner image.

FIG. 3 is a plan view showing the positional relationship between the thermistor and the transfer paper in the fixing device. In a normal fixing device, the transfer paper is configured to travel and print with center distribution. Therefore, the thermistor 57 for temperature control is provided within the minimum paper width region of the allowable printable paper size, for example, the center position of the heat roller 50. Is disposed at point A in the vicinity. In such a fixing device, since the surface temperature of the heat roller 50 decreases due to the paper passing, and the temperature tends to be the highest at the center of the heat roller 50, that is, near the center position, all types of transfer paper are used. This is because the temperature control becomes easier if the thermistor 57 is disposed in the area where the light passes. Here, the minimum paper width is A6 (equivalent to postcard).

In the fixing device having the above-described structure, the temperature control is easy, but the thermistor 57 is in the printing area of the paper and rubs against the surface of the heat roller 50. Therefore, although the cleaning felt 58 is provided, the toner easily adheres and accumulates on the rubbing surface of the thermistor 57 with the heat roller 50, and the adhering and accumulating toner causes the coating layer on the surface of the heat roller 50 to quickly wear. In addition, the releasability is reduced, and the print quality is deteriorated. Further, the deposited toner is carried away by the rotation of the heat roller 50, and is re-transferred onto the transfer paper, thereby deteriorating print quality and causing unstable temperature control.

Further, the cleaning felt 58 impregnated with silicone oil needs to be periodically replaced. However, if the cleaning felt 58 is to be used continuously even when its life has expired, the toner collected by the cleaning felt 58 is It is carried away by the rotation of the heat roller 50 and is offset by the transfer paper to lower the print quality. Further, the operability is poor because the cleaning felt 58 is a regular replacement part.
There was also a problem that running costs increased.

In view of these problems, the thermistor 5
7 is not the point A in the minimum sheet width area, but the position shown in FIG.
A fixing device that does not require a cleaning felt has been already proposed by disposing it at a position outside the printing area shown in FIG. However, when a narrow sheet is continuously printed by a fixing device in which the arrangement position of the thermistor 57 is located outside the printing area, the temperature drop at the point B of the heat roller 50 distant from the central portion where the sheet passes. And the temperature drop at the center becomes remarkable as compared with that, and it becomes impossible to secure a good fixing property. Therefore, the size data of the printing paper supplied from the paper size detecting means, which will be described later, provided in accordance with the selection of the paper cassette, or the size data input by the operator from the operation panel is detected in advance, and according to the paper size. The fixing temperature control is switched to prevent the fixing failure.

FIG. 4 is a block diagram showing a circuit configuration for performing conventional fixing temperature control. Here, the paper size information detected by the paper size detection switch 61 or the like, or the paper size information printed by the operator input from the operation panel 62 is transmitted to the control unit CPU 63.
Is input to The control unit CPU 63 has a program ROM
A fixing temperature control program corresponding to each sheet size, which is set in advance in 64, is read and transmitted to the fixing temperature control circuit 65. The fixing temperature control circuit 65 converts information from the program ROM 64 into a signal, transmits the signal to the heater driving circuit 66, monitors the temperature of the heater 56 via the thermistor 57, and turns on / off the AC voltage supply to the heater 56. By turning it off, temperature control is performed. The heater drive circuit 66 supplies an AC voltage to the heater 56 based on a signal from the fixing temperature control circuit 65, and
(FIG. 2) is heated.

However, the above-mentioned fixing temperature control method is not technically satisfactory, for example, the fixing temperature setting reliability is poor and the operability is extremely poor. This is because even if the size of the paper to be printed can be recognized, it cannot be detected by the thickness of the paper, and even when input by an operator, a fixing temperature setting corresponding to the thickness is selected from the operation panel 62. This is because it is necessary.
In other words, even for paper of the same size, the thickness of the paper varies depending on various uses, from a paper continuous amount of about 45 kg to a paper continuous amount of 135 kg or more, such as a postcard. When a pattern having a high print duty is continuously printed on a sheet, there is a problem that the temperature drop at the center of the heat roller becomes remarkable, and good fixability cannot be obtained.

In recent years, the allowable paper width on which printing can be performed has been increased, and register marks (marks indicating printing positions) have been formed on A3 paper.
May be printed on paper one size larger than the conventional A3 paper. Therefore, if the position of the thermistor for controlling the temperature is set outside the printing area of the paper, and the narrow paper is continuously printed, the detection by the thermistor at the position distant from the center where the paper passes as described above. It is difficult to ensure good fixing properties, for example, the temperature does not decrease, and the temperature decreases more and more only in the central part. In addition, diversification of printing media has led to many demands for printing thick paper having a thickness of 0.2 mm or more using a front feeder, and it has become difficult to control the temperature to ensure good fixability.

FIG. 5 is a diagram showing a temperature distribution of a conventional heat roller. As shown on the lower side of the horizontal axis in the figure, the thermistor 57 used for temperature control is disposed outside the printable area of the heat roller 50 (point B at the left end). A temperature distribution curve indicated by a broken line in the graph is a temperature distribution curve in a standby state (standby state waiting for printing). This curve is
The light distribution characteristic of the halogen lamp constituting the heater 56, that is, the temperature distribution slightly changes depending on the state of distribution of the heat generating portion. Become. The temperature distribution curve shown by the solid line is
5 is a graph showing a saturated temperature distribution curve of the heat roller 50 during continuous printing. In this curve, the temperature Tc in the vicinity of the center of the heat roller 50 is the lowest, and the control temperature T12 by the thermistor 57 during continuous printing is (T12−T12).
The temperature is lowered only by c).

Next, control of the fixing temperature by the conventional electrophotographic printer will be described. In general, as the sheet thickness increases and the sheet width decreases, for example, as in a postcard or an envelope, the above-described temperature drop (T12−Tc) becomes more remarkable, and it becomes more difficult to secure good fixing properties. Also,
In order to save energy and prevent the temperature inside the apparatus from rising, the above-described standby control temperature T11 is set lower than the print control temperature T12, and the control temperature is quickly set to T11 when printing starts.
From T2 to T12.

FIG. 6A is a diagram showing a temperature change on the surface of a heat roller in a conventional fixing device, and FIG. 6B is a diagram showing an on / off state of a heater. As shown in the lower part of the horizontal axis (time axis) in FIG. 7A, here, the temperature of the fixing device is controlled in a process from the preparation state to the continuous printing through the standby state. In the figure, the temperature curve indicated by the solid line is the temperature change at the thermistor portion B which is the temperature control position shown in FIG. 5, the temperature curve indicated by the dashed line is the temperature change at the center C point, and the temperature curve indicated by the broken line is the maximum. This is a temperature change at a point D near the right end of the print effective area.

An example of the conventional temperature control will be described below with reference to FIG. When the main switch is turned on, the heater is energized at the same time as when the main switch is turned on. The heater is energized until the standby temperature T10 is reached.
By repeating the F operation, the heat roller is controlled at a temperature near the standby temperature T10. When a print signal is received at time tp to start printing, the set temperature of the heat roller is switched to the control temperature T20 higher than the standby temperature T10.
Accordingly, the heater is continuously turned on, and the surface temperature of the heat roller rises. After reaching the predetermined temperature T20 at time tq, temperature control is performed before and after the control temperature T20. The time to (= tp−tq) from the start of printing to the control temperature T20 may be equal to or shorter than the time from the start of printing to the end of the transfer paper reaching the heat roller. is necessary.

[0018]

As described above, it is desirable that the temperature reaches the control temperature T20 necessary for ensuring good fixing performance before the leading edge of the transfer paper reaches the heat roller. The surface temperature of the heat roller at the point C at the center and the point D at the right end also rises when printing starts, and after time tq, the temperature gradually decreases due to continuous printing, and eventually reaches the saturation temperature. At this time, the temperature drop (−Δt = T20−Tc) with respect to the control temperature Tc at the central point C is greater as the thickness of the sheet becomes smaller as described above, and in some cases, becomes lower than the standby control temperature T10. For this reason, there has been a problem that good fixability cannot be obtained during continuous printing.

Therefore, when there is a print command for narrow paper, the standby control temperature is set to a higher value than the conventional set temperature in anticipation of the temperature decrease during continuous printing to avoid this problem. It is also considered to do. However, if the waiting time is long, the internal temperature of the printer device rises, adversely affecting the toner in the developing device, and the heat roller, backup roller, etc. are deteriorated, and the life of the device is shortened. In addition, there is another problem that the set temperature at the initial stage of printing is high, so that the paper is likely to be wrinkled. Further, a method of gradually lowering the thermistor control temperature during continuous printing so as to prevent a temperature drop in a central portion has been attempted. However, when printing narrow paper continuously, there is a problem that the temperature at both ends of the heat roller, which is outside the paper passing area and has a very small temperature drop, rises sharply.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object the purpose of a four-copy printer.
An object of the present invention is to provide a fixing device of an electrophotographic printer capable of performing a fixing operation corresponding to a printing speed of about 0 PPM to 50 PPM.

[0021]

SUMMARY OF THE INVENTION A fixing device for an electrophotographic printer according to the present invention has a first heating source having an effective length corresponding to the entire printing area of the electrophotographic printer, and an effective heating source shorter than the first heating source. A heat roller including a second heat source having a length, a first temperature detecting means disposed to be in contact with the heat roller at an end outside the printing area, and detecting a temperature; A second temperature detecting means that is disposed in a non-contact manner at the center of the printing area and detects a temperature; and a temperature of the heat roller based on the temperatures detected by the first and second temperature detecting means. And temperature control means for controlling the temperature.

Further, in the fixing device for an electrophotographic printer according to the present invention, the temperature control means may include:
Temperature control is performed based on the temperature detected by the first temperature detecting means, and when continuous printing of narrow paper is instructed, temperature control is performed based on the temperature detected by the second temperature detecting means. It is.

In the fixing device for an electrophotographic printer according to the present invention, the temperature control means turns on the second heating source with priority to heat the heat roller during continuous printing on narrow paper, When the temperature at the end of the heat roller drops below the limit temperature, the first heating source is turned on at the same time.

Also, in the fixing device of the electrophotographic printer according to the present invention, the size of the gap between the second temperature detecting means and the heat roller is determined by the temperature detected by the first and second temperature detecting means. And a fixing control program for correcting the fixing control temperature of the heat roller by inferring from the surface temperature of the heat roller measured in advance.

Further, the fixing device of the electrophotographic printer according to the present invention obtains a ripple width of a temperature change based on the ripple width of the temperature detected by the second temperature detecting means, and determines a ripple width of the temperature change according to the ripple width. And a ripple correction program for correcting the fixing control temperature of the heat roller.

[0026]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

Embodiment 1 FIG. 1 is a front sectional view showing a mounting positional relationship between the heat roller and the halogen lamp according to the first embodiment.

The thermistor 1 is disposed outside the maximum printing area (here, the A3-size printing area), for example, at a point B near the left end in FIG. 1, and contacts the coating surface of the heat roller 2 to control the temperature. This constitutes a first temperature detecting means for performing the following. Thermistor 3 is a heat roller 2
Is a second temperature detecting means which is disposed in a non-contact manner in the vicinity of a central portion of the first roller and which has a gap of about 1 mm from the heat roller 2. Inside the heat roller 2, two halogen lamps 4 and 5 are incorporated as heat sources.
Among these, the halogen lamp 4 has a heating source (first heating source) for printing wide paper having an effective length light emitting region corresponding to the entire printing region, and the halogen lamp 5 has a width (approximately 210 mm) when A4 is placed vertically. This is a heating source (second heating source) for printing narrow paper having a light emitting area. The overall configuration of the fixing device is the same as that of the conventional device shown in FIG.

FIG. 7 is a block diagram showing a circuit configuration for controlling the fixing temperature in the fixing device according to the first embodiment. Here, as in the case of the conventional device of FIG.
It comprises a paper size detection switch 11, an operation panel 12, a control CPU 13, a program ROM 14, a fixing temperature control circuit 15, a heater drive circuit 16, and a fixing device 17. The fixing temperature control circuit 15 converts the information from the program ROM 14 into a signal and transmits the signal to the heater drive circuit 16 to control the light emission of the two halogen lamps 4 and 5, and to control the two contact / non-contact thermistors. 1,3
The heater control circuit 16 monitors the temperature of the heat roller 2 through the heater drive circuit 16 and turns on / off the AC voltage supply to control the temperature.

FIG. 8 is a diagram showing how the fixing temperature is controlled by the heat roller according to the first embodiment.
The temperature change on the surface of the heat roller will be described in detail below.

FIG. 8A shows the temperature change on the surface of the heat roller, and FIG. 8B shows the on / off state of the wide halogen lamp 4 and the narrow halogen lamp 5, respectively. Here, as in the case of FIG. 6, the temperature control state of the fixing device in the process from the preparation state to the continuous printing through the standby state is shown. In the figure, the temperature curve indicated by the solid line is the temperature detected by the non-contact type thermistor 3 which is the temperature control position in FIG. 1, and the temperature curve indicated by the dashed line is the position at the mounting position of the non-contact type thermistor 3 (the center of the heat roller). The surface temperature of the heat roller 2 and the temperature curve indicated by the broken line are the temperature detected by the contact thermistor 1, that is, the surface temperature of the heat roller 2 at the left end of the heat roller where the thermistor 1 is mounted.

The vertical axis of FIG. 8A shows the standby temperature T0 at the left end of the heat roller 2, the standby temperature T1 at the center, and the temperature T detected by the non-contact thermistor 3, respectively.
2. The control temperature T3 at the non-contact type thermistor 3 after the start of printing, the control temperature T4 at the center required to secure good fixing performance, and the limit temperature T5 at the left end of the heat roller 2. It is shown.

First, when the main switch is turned on,
At the same time, energization of the heaters (halogen lamps 4 and 5) is started. As a result, the temperature of the heat roller 2 is increased,
The temperature detected by the contact thermistor 1 is a predetermined standby temperature T
Reach 0. At this time, the temperature control in the preparation state from the start-up to the standby state is performed by the contact thermistor 1 disposed at the left end of the heat roller 2. Two halogen lamps 4 and 5 are used only for the heater to emit light immediately after startup. Thereafter, as the temperature of the heat roller 2 rises, the narrow-width halogen lamp 5 is turned off to prevent overshoot from occurring when the temperature rises. In order to reduce the overshoot and to shorten the warm-up time at the time of start-up, two halogen lamps are used for an optimum time according to the power of the halogen lamps 4 and 5 and the heat capacity of the heat roller 2. Lamp 4,
5 may be emitted simultaneously. This time is determined experimentally.

Next, when shifting from the ready state to the standby state, the standby temperature T0 at the left end of the heat roller 2 is located at the center.
The standby temperature T1 is maintained at a slightly higher level, but the temperature is controlled by the thermistor 1 as in the preparation state. This temperature difference (T1-T0) corresponds to the actual temperature difference between the center and the left end of the heat roller 2 heated by the halogen lamp 4. The heat roller 2 has a peak-shaped temperature distribution at the center of the heat roller 2. However, since the non-contact type thermistor 3 is provided with a gap of about 1 mm from the heat roller 2, The detected temperature at the center of the roller 2 is the actual surface temperature T of the heat roller 2.
It is detected as a temperature T2 lower than 1.

Next, when continuous printing of narrow paper is started in the standby state, temperature control is performed by the non-contact type thermistor 3 disposed at the center of the heat roller 2. The temperature control from the start-up to the standby state was performed by the contact-type thermistor 1. In continuous printing, however, the paper size detection switch 11 shown in FIG.
When the paper size smaller than the A4 vertical width is detected by the operator input from, the temperature control in the control unit CPU 13 is executed based on the temperature detected by the non-contact type thermistor 3 at the center.

Returning to FIG. 8, at time tp, the control unit CPU1
When a print signal is input into the heat roller 3 and the printing is started after the standby state is over, the contact type thermistor 1 at the left end of the heat roller 2 shifts to the temperature control by the non-contact type thermistor 3 at the center and the control unit. The CPU 13 reads a fixing temperature control program set in advance in the program ROM 14 corresponding to each sheet size, and transmits the program to the fixing temperature control circuit 15. Here, the control temperature of the non-contact type thermistor 3 is switched to the control temperature T3 higher than the detected temperature T2. If the printing paper is a print signal for a narrow paper (A4 length or less), the wide halogen lamp 4 is turned off and the narrow halogen lamp 5 is turned off.
Only light up. Thus, even after the surface temperature of the heat roller 2 rises and reaches a predetermined control temperature T3 at time tq, the temperature control is performed by the non-contact thermistor 3 before and after the same control temperature T3. At this time, the actual surface temperature at the center of the heat roller 2 rises from the standby temperature T1 to T4, and is controlled so that the surface temperature changes before and after the temperature T4.

Here, in order to ensure good fixability in the fixing device, the heat roller 2 must reach a predetermined control temperature T4 (T3) before the leading edge of the transfer paper reaches the heat roller 2. Is desirable. For that purpose, the time t0 (= from the start of printing until the control temperature T3 is reached).
tp-tq) needs to be equal to or shorter than the time from the start of printing until the leading edge of the transfer paper reaches the heat roller 2. In the first embodiment, the control temperature is increased from T2 to T3 (the surface temperature of the heat roller is increased from T1 to T4) after the start of printing. If the standby temperature T1 is previously set equal to the appropriate temperature T4 for printing (T1 = T4), the temperature detected by the thermistor 3 may be made to match the control temperature T3. This method is effective when the printing speed of the electrophotographic printer is high and the time until the leading edge of the transfer paper reaches the heat roller is short.

During continuous printing, the width of the halogen lamp 5 is reduced, and the temperature of the sheet passing portion can be controlled by the non-contact type thermistor 3. Therefore, it is possible to reliably maintain the appropriate control temperature T4 without lowering the surface temperature of the heat roller 2. However, heat roller 2
When only the narrow halogen lamp 5 is used to heat the heat roller 2, the temperature at both ends of the heat roller 2 gradually decreases during continuous printing. Continuous printing of narrow paper is completed,
Considering the case where a wide sheet is printed immediately, it is necessary to suppress the temperature drop at both ends of the heat roller 2 within a certain range. Therefore, the lower limit temperature T at the left end of the heat roller 2
5, when the contact-type thermistor 1 detects the limit temperature T5, the wide halogen lamp 4 is caused to emit light at the same time, and the surface temperature at both ends of the heat roller 2 becomes T.
Control is performed so that it does not become 5 or less. Thus, in continuous printing, two (contact / non-contact) thermistors 1, 3
It is also effective to execute the temperature control by using.

Next, at the time tr when the continuous printing is completed, the temperature control of the heat roller 2 is switched to the control by the contact thermistor 1. At this time, if the detected temperature of the thermistor 1 is lower than the control temperature T0 in the standby state, the wide halogen lamp 4 is caused to emit light and the temperature is raised to T0. At this time, by causing the wide halogen lamp 4 to emit light, the non-contact thermistor 3 is turned on.
, And the surface temperature at the center of the heat roller 2 are higher than the control temperatures T3 and T4 during continuous printing, respectively. In order to suppress this temperature rise, it is necessary to set the lower limit temperature T5 at the left end of the heat roller 2 to a temperature that is not much lower than the control temperature T0 in the standby state.

The contact thermistor 1 during continuous printing
Depends on the heat capacity of the heat roller 2 and the electric power of the halogen lamp 4, for example, the lower limit temperature T5 may be set equal to the control temperature T0 in the standby state or set to a value within -10 ° C. from the control temperature T0. Preferably. Thus, it has been experimentally confirmed that the temperature rise in the central portion of the heat roller 2 is suppressed within an allowable range and a good fixing result is obtained.

As described above, in the fixing device of the electrophotographic printer according to Embodiment 1 of the present invention, the non-contact type thermistor 3 is disposed at the center of the heat roller 2.
When shifting from the standby state to continuous printing of narrow paper, the temperature control by the contact-type thermistor 1 at the left end is switched to the temperature control by the non-contact thermistor 3.
For this reason, the narrow halogen lamp 5 of the two halogen lamps 4 and 5 incorporated in the heat roller 2 during the continuous printing is preferentially emitted and heated, whereby
Compared with the conventional temperature control using only a single contact-type thermistor, there is no temperature drop at the center of the heat roller 2 and excessive temperature at both ends of the heat roller 2 outside the paper passing area. It is possible to prevent a rise and always secure good fixing properties.

Further, since the non-contact type thermistor 3 is disposed at the center of the printing area, the toner offset on the heat roller 2 at the time of fixing does not adhere to and deposit on the thermistor. It is possible to prevent the printing paper from being stained or to make the temperature control unstable. In other words, a cleaning member such as a cleaning felt mounted on the thermistor at the time of the conventional temperature control is not required, and maintenance related to silicon oil or the like is not required, so that good print quality can always be ensured.

Further, the heat roller 2 and the thermistor 3
Since there is no rubbing, the inconvenience that the coating layer on the surface of the heat roller 2 is worn away at an early stage is eliminated, and the effects such as securing the print quality and extending the service life of the components can be expected.

Embodiment 2 In the first embodiment, it is assumed that the gap (gap) between the surface of the heat roller 2 and the non-contact type thermistor 3 is adjusted to about 1 mm when the non-contact thermistor 3 is disposed at the center of the heat roller 2. Was. The detected temperature T2 of the non-contact thermistor 3 is about 1 m
m, so that the heat roller 2
Is lower than the actual surface temperature T1. Therefore, the temperature control in the first embodiment is based on the premise that the non-contact thermistor 3 is mounted on the heat roller 2 so that the gap is always constant.

However, it is difficult to eliminate a gap mounting error when assembling the fixing device, and fluctuation over time is inevitable. That is, when assembling the fixing device, it is difficult to maintain the gap amount of the non-contact type thermistor 3 at a constant value and thereafter keep the gap as it is, and it is inevitable that the gap size changes. When the size of the gap changes, the temperature difference between the temperature detected by the non-contact type thermistor 3 and the actual surface temperature of the heat roller also changes.

In the temperature detection performed during continuous printing, since the heat roller 2 is constantly rotating, air convection occurs in the gap. If an exhaust fan or the like is mounted in the vicinity of the fixing device, it is inevitable that air flows in the gap. Therefore, in order to minimize these effects, the mounting position of the non-contact type thermistor 3 is taken into consideration, and the gap between the thermistor 3 and the heat roller 2 is not changed when a paper jam occurs. Therefore, a device for mounting is required. However, it is most effective to perform the control temperature correction as described below according to the gap amount between the thermistor and the heat roller.

Hereinafter, a method for correcting the control temperature of the non-contact type thermistor in the fixing device according to the second embodiment will be described in detail.

FIG. 9 is a graph showing the relationship between the gap of a non-contact type thermistor and the temperature measured on the surface of the heat roller. The figure shows the results of measuring the surface temperature while changing the control temperature of the heat roller 2 in a plurality of ways in a standby state before the start of printing. The thermistor 3 when the control temperature of the heat roller 2 is 170 ° C. Gap (horizontal axis)
, The measured value of the surface temperature (vertical axis) of the heat roller 2 is indicated by Δ, the measured value at 180 ° C. is indicated by Δ, and the measured value at 190 ° C. is indicated by Δ. In this experiment,
As the heat roller 2 shown in FIG. 1, the outer diameter Φ is 36 mm,
An aluminum pipe material having a thickness of 1.2 mm is used, and the heating source is an A4 vertical width (about 210 m) of electric power of 600 W.
A halogen lamp 5 having a light emission length of m) is used.

As can be seen from FIG. 9, at any control temperature, there is linearity in the amount of change in the surface temperature of the heat roller 2 with respect to the gap. For example, when the control temperature of the non-contact type thermistor 3 is 180 ° C., if the gap is 1 mm, the surface temperature of the heat roller is 19 °.
It changes around 6 ° C, and if the gap is 0.7 mm,
The surface temperature of the heat roller fluctuates around 190 ° C., and the gap becomes l. If it is 3 mm, the surface temperature of the heat roller fluctuates around 202.5 ° C., so that the difference between the control temperature and the surface temperature is large for a large gap, and small for a small gap. . Regardless of the control temperature, when the gap is 0.7 mm, the heat roller surface temperature is about +9 to + 10 ° C. with respect to the control temperature, and when the gap is 1 mm, the heat roller surface temperature is +15 with respect to the control temperature. It can be seen that there is a temperature difference of about + 16 ° C. Therefore, the surface temperature data of the heat roller with respect to the gap of the non-contact type thermistor 3 is stored in advance in the program ROM 14 (see FIG. 7) as the fixing temperature control program A for each control temperature.

FIG. 10 is a diagram showing the surface temperature at the center of the heat roller when the temperature is controlled by a contact-type thermistor. Here, a contact type thermistor 1 and a heat roller 2
This indicates that the surface temperature of the heat roller 2 at the mounting position (central portion) of the non-contact type thermistor 3 changes linearly with respect to the control temperature. FIG. 10 shows the measured surface temperature (vertical axis) of the heat roller 2 for each control temperature (horizontal axis) at the mounting position of the non-contact type thermistor 3. The conditions such as the shape and material of the heat roller 2 are the same as in the case of FIG. Standby state (when temperature is controlled by contact thermistor)
In FIG. 5, the surface temperature of the heat roller 2 has, as shown in FIG.

According to the actual measurement results shown in FIG. 10, the temperature distribution shape itself changes depending on the heat capacity of the heat roller 2, the power of the halogen lamps 4 and 5 and the light distribution, but is the mounting position of the non-contact type thermistor 3. It can be seen that the temperature at the center is about 14 to 16 ° C. higher than the temperature at the ends. Therefore, the relationship between the end surface temperature and the center surface temperature obtained from the actual measurement result is stored in advance in the program ROM 14 (see FIG. 7) as the fixing temperature control program B.

As described above, the fixing temperature control programs A and B are stored in the program ROM 14, and the temperature at the left end is detected by the thermistor 1, and the temperature is detected by the non-contact type thermistor 3 at the center. By doing so, the size of the gap can be estimated based on the correlation between the detected temperatures of the two thermistors 1 and 3 and the surface temperature at the center of the heat roller 2.

Next, a method for correcting the control temperature of the non-contact type thermistor 3 will be described. Here, for the non-contact type thermistor 3, the default value of the gap 1 mm at the control temperature of 180 ° C. is stored in the control programs A and B.

When the temperature correction is performed by the fixing device in the standby state, if the control temperature of the contact thermistor 1 is, for example, 180 ° C., the program RO
By reading the control program B (FIG. 10) from M14, it can be seen that the actual surface temperature at the center of the heat roller 2 fluctuates about 196 ° C. At this time, assuming that the temperature measured by the non-contact thermistor 3 (detected temperature T2) is detected as 170 ° C., the control program A (FIG. 9) is read from the program ROM 14 and the actual temperature and the detected temperature are calculated. The comparison shows that the gap between the heat roller 2 and the thermistor 3 is 1.6 mm. Therefore, it can be estimated that the gap of the non-contact type thermistor 3 of this fixing device is shifted from the default value (1 mm) by about 0.6 mm.

In such a fixing device, when continuous printing of narrow paper is started and the temperature control as described in the first embodiment is performed, the non-contact type thermistor 3 is switched to the control temperature T3, for example. When the temperature is controlled at 190 ° C., the default gap is 1 mm as shown in FIG.
Is maintained, the surface temperature at the center of the heat roller is controlled to about 205 ° C. However, in an actual fixing device, since the gap amount is estimated to be 1.6 mm, the control temperature T3 is set to 190 ° C.
Is performed, the surface temperature becomes about 215 ° C. as shown in FIG. 9 and becomes about 10 ° C. higher than the target temperature. Therefore, in order to perform the temperature control of the heat roller 2 at the set temperature (205 ° C.) when the gap is 1 mm and the control temperature T3 is 190 ° C., based on the assumed value of 1.6 mm gap, From FIG. 9, it can be seen that the temperature control may be performed by correcting the control temperature T3 to 180 ° C. That is, the actual surface temperature of the heat roller 2 is set to 20 ° C. which is closest to 205 ° C.
It can be controlled at 7 ° C.

As described above, in the fixing device according to the second embodiment,
The heat roller 2 is always fixed satisfactorily irrespective of the fluctuation of the gap in the non-contact type thermistor 3 by correcting the control temperature set value to the closest value based on the comparison operation processing results of the read control programs A and B. It is possible to perform temperature control to set the temperature.

In the method of correcting the control temperature described above,
As a distribution line of the heat roller surface temperature, FIG. 9 shows that the control temperature of the non-contact type thermistor 3 is 170/180/1.
Although only three cases of 90 ° C. are shown, the control resolution of the thermistor is actually about 2 to 3 ° C., and a distribution straight line corresponding to the resolution can be obtained.

Further, it is possible to automatically execute the above-described control temperature correction. For example, if the gap value is set to 1 mm as a default value when the product is shipped from the factory, and the correction is automatically performed immediately before shifting from the print standby state to the heater OFF mode, the temperature is always maintained at an appropriate fixing temperature. Control becomes possible.

Embodiment 3 In the third embodiment, the control temperature level of the non-contact type thermistor 3 is increased based on the detected temperature of the heat roller 2 detected by the non-contact type thermistor 3 according to the magnitude of the temperature change (ripple width). It is to let.

When the temperature is controlled by the non-contact type thermistor 3, air convection occurs in the gap between the heat roller and the air flow of the exhaust fan or the like. Therefore, the thermal responsiveness of the thermal element used in the non-contact type thermistor tends to be worse than that of the contact type thermistor 1. In recent years, as this kind of heat-sensitive element, a small bead element or a thin-film element having a small heat capacity has been used, and a heat-sensitive element having the same thermal response as a contact-type thermistor has been developed. However, in a non-contact thermistor, the thermal responsiveness tends to deteriorate as the gap increases, and the temperature ripple during control increases as compared with a contact thermistor.

FIG. 11 is a diagram for explaining the outline of the procedure for correcting the temperature ripple. As shown in FIG.
When the resolution of the temperature control by the contact thermistor 2 is 2 ° C., the temperature ripple width is the ON of the halogen lamp.
The temperature changes within a range of / OFF temperature (resolution 2 ° C.) or a temperature range slightly exceeding the range. On the other hand, the temperature ripple when the temperature is controlled by the non-contact type thermistor 3 is considerably larger than that of the contact type thermistor 2, as shown in FIG. Moreover, the ripple generated by the non-contact type thermistor 3 may be equal or amplified on the actual heat roller surface and may become large. Therefore, in the case where a temperature ripple occurs about 5 times larger than the resolution (2 ° C.) of the contact-type thermistor 2, for example, a width of 10 ° C. or more, when the print fixing is performed at the lower limit temperature of the ripple. In addition, good fixability may not be obtained. Therefore, especially when special paper such as postcards and envelopes is used and the thickness of the paper is considerably large, the ripple width greatly affects the fixing property.

A specific temperature control method according to the third embodiment will be described based on a circuit configuration for performing the fixing temperature control shown in FIG. 7, as in the fixing device according to the first embodiment. The fixing temperature control circuit 15 detects the ripple width of the temperature detected by the non-contact thermistor 3 during continuous printing. The program ROM 14 stores a ripple correction program (not shown) separately from the fixing temperature control program.

Now, the temperature ripple in the non-contact type thermistor 3 is, for example, 10 ° C. (in FIG. 11, the resolution is 2 ° C.).
Then, the set temperature is raised by two levels with respect to the original control temperature. When the ripple width is six levels, the level is increased by three levels in the same manner, and thereafter, every time the ripple width increases by one level, the set temperature is also increased by one level. In the fixing temperature control circuit 15, the set temperature rise level is determined based on the ripple correction program called by the control unit CPU 13, converted into a predetermined temperature command signal, and transmitted to the heater drive circuit 16.

In the case of temperature control by the non-contact type thermistor 3, the actual surface temperature of the heat roller gradually decreases, though slightly, due to the influence of the gap. Even in such a case, the control temperature of the non-contact type thermistor 3 is increased stepwise by a method similar to the method described above.

As described above, in the fixing device according to the third embodiment, even if a ripple occurs in the detected temperature during the temperature control, a decrease in the fixing temperature can be prevented, and good fixing performance can always be ensured. . In addition, since the control temperature of the non-contact type thermistor can be increased stepwise by the same temperature control method, the deviation between the non-contact type thermistor and the actual heat roller surface temperature is corrected by a correction program. Thus, it is possible to always maintain a stable fixing temperature and secure good fixing properties.

[0066]

Since the present invention is configured as described above, it has the following effects.

In the fixing device for an electrophotographic printer according to the first and second aspects of the present invention, the fixing device may have a 40 to 50 PPM equivalent to a copier.
The fixing operation can be performed at a printing speed of about PPM, and a cleaning member such as a cleaning felt mounted on the thermistor at the time of the conventional temperature control is not required. Good print quality can be ensured. In addition, the disadvantage that the coating layer on the surface of the heat roller is worn away at an early stage is eliminated, and effects such as securing print quality and extending the service life of components can be expected.

According to the fixing device of the electrophotographic printer according to the third aspect, compared with the conventional temperature control using only a single contact-type thermistor, the temperature of the central portion of the heat roller does not decrease, and Excessive temperature rise at both ends of the heat roller outside the paper passing area can be prevented, and good fixability can always be ensured.

According to the fixing device of the electrophotographic printer according to the fourth aspect, it is possible to perform temperature control such that the heat roller is always set to a favorable fixing temperature regardless of the fluctuation of the gap in the non-contact type thermistor. .

According to the fixing device of the electrophotographic printer according to the fifth aspect, based on the temperature of the heat roller detected by the non-contact type thermistor, the non-contact type according to the magnitude of the temperature change (ripple width). The control temperature level of the mold thermistor can be increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a heat roller according to Embodiment 1 of the present invention.

FIG. 2 is a side view showing a configuration of a fixing unit using a conventional heat roller.

FIG. 3 is a plan view showing a positional relationship between a thermistor and a transfer sheet.

FIG. 4 is a block diagram showing a circuit configuration for performing conventional fixing temperature control.

FIG. 5 is a diagram showing a temperature distribution by a conventional heat roller.

FIG. 6 is a diagram illustrating a temperature change of a fixing device in a conventional temperature control.

FIG. 7 is a block diagram illustrating a fixing temperature control unit according to the present invention.

FIG. 8 is a diagram showing a temperature control method according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a measured value of a heat roller surface temperature with respect to a gap amount of a non-contact type thermistor in a standby state.

FIG. 10 is a diagram showing measured values of the surface temperature of the heat roller at the non-contact type thermistor mounting position with respect to the control temperature of the contact type thermistor during temperature control.

FIG. 11 is a schematic explanatory diagram showing a temperature ripple correction method according to Embodiment 3 of the present invention.

[Explanation of symbols]

1 contact thermistor, 2 heat roller, 3
Non-contact type thermistor, 4 Wide halogen lamp, 5 Narrow halogen lamp, 11 Paper size detection switch, 12 Operation panel, 13 Control CPU, 14 Program ROM, 15 Fixing temperature control circuit, 16 Heater drive Circuit, 17 fixing device.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2H033 AA24 BB01 CA04 CA27 CA30 CA47 CA48 3K058 AA02 AA04 AA42 AA45 AA72 AA73 AA86 BA18 CA23 CA61 CA70 CB02 DA02 DA22 5H323 AA35 BB01 CA08 CB04 CB42 DA01 FF04 GG02 MM09

Claims (5)

[Claims] 1. A heat roller including a first heating source having an effective length corresponding to the entire printing area of an electrophotographic printer, and a second heating source having an effective length shorter than the first heating source; A first temperature detecting unit that is disposed so as to be in contact with the roller at an end outside the printing area and detects the temperature; and is disposed in a non-contact manner at a central part of the printing area in proximity to the heat roller. And a temperature control unit for controlling the temperature of the heat roller based on the temperatures detected by the first and second temperature detection units. Fixing device for photo printer. 2. The temperature control unit controls the temperature based on the temperature detected by the first temperature detection unit during a printing standby, and when the continuous printing of narrow paper is instructed, the second temperature control unit executes the second temperature control. 2. The fixing device according to claim 1, wherein the temperature is controlled based on the temperature detected by the temperature detecting unit. 3. The temperature control means, during continuous printing of narrow paper, turns on a second heating source with priority and heats the heat roller, and the temperature at the end of the heat roller is a critical temperature. If the number falls below
2. A fixing device for an electrophotographic printer according to claim 1, wherein said heating sources are turned on simultaneously. 4. The temperature of the gap between the second temperature detecting means and the heat roller detected by the first and second temperature detecting means, and the surface temperature of the heat roller previously measured. 4. The fixing device for an electrophotographic printer according to claim 1, further comprising a fixing control program for correcting the fixing control temperature of the heat roller, as estimated from the following. 5. A ripple correction program for determining a ripple width of a temperature change based on the temperature detected by the second temperature detection means, and correcting a fixing control temperature of the heat roller according to the ripple width. 4. A fixing device for an electrophotographic printer according to claim 1, wherein: