JP3611269B2 - Image recording device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image recording apparatus such as a printer, a facsimile, and a copying machine using an electrophotographic system, and more particularly to a temperature control mechanism of a fixing unit.
[0002]
[Prior art]
An example of an image recording apparatus (monocolor image recording apparatus) will be described with reference to FIG. The image recording apparatus includes a paper feeding unit 92 that feeds recording materials P one by one, an image forming unit 91 that forms a toner image on the recording material based on image information, and image formation while conveying the recording material. The image forming apparatus includes a transfer conveyance unit 93 that transfers the toner image formed on the portion 91 and a fixing unit 100 that fixes the toner image on the recording material after transfer by heat.
[0003]
The fixing unit 100 includes, for example, a fixing roller 101A having a built-in halogen heater 102 and a pressure roller 101B pressed against the fixing roller 101A, and a recording material is sandwiched between the rollers 101A and 101B. It is fixed while being conveyed. Then, the temperature detection sensor 103 detects the surface temperature of the fixing roller 101A, and the halogen heater 102 is ON / OFF controlled in accordance with the detected temperature to keep the surface temperature of the fixing roller 101A constant.
[0004]
However, for example, if a malfunction of the temperature detection sensor 103 occurs, temperature control cannot be performed, so that the halogen heater 102 continues to be turned on (ON), and there is a possibility that excessive temperature rise will occur. Therefore, in order to prevent this, an excessive temperature rise prevention means for cutting off the energization to the halogen heater 102 when a predetermined temperature is exceeded is provided. As such an excessive temperature rise prevention means, for example, a thermo switch or a thermal fuse is used.
[0005]
Among them, the thermo switch 104 is a switch for turning on / off a contact for energizing the halogen heater 102 by displacement of the bimetal. The thermo switch 104 is normally disposed in contact with the surface of the fixing roller 101A (contact method).
[0006]
[Problems to be solved by the invention]
However, in this contact method, since the thermo switch 104 is used for a long time in a state of being in contact with the fixing roller 101A, the contact portion on the surface of the fixing roller 101A is deteriorated, which causes a reduction in roller life.
[0007]
In particular, in a full-color image recording apparatus that has been rapidly put into practical use in recent years, the problem of the roller life reduction becomes more prominent as follows compared to the case of a monocolor image recording apparatus. In order to reliably fix the four-color toner on the recording material without offsetting the toner onto the fixing roller, it is necessary to apply a release agent to the surface of the fixing roller. Since the fixing roller has a surface layer in which the release agent is easy to adjust, it is inevitable that the wear resistance of the surface layer is lowered. Therefore, the deterioration of the surface of the fixing roller due to the contact of the thermo switch becomes remarkable. In addition, in the case of full color, even a slight deterioration of the surface of the fixing roller tends to stand out as an image defect.
[0008]
In addition, if the recording material is wound around the fixing roller for some reason when the contact method is used, the thermal responsiveness of the thermo switch decreases due to the recording material being sandwiched between the fixing roller and the thermo switch, There is also a risk that the specified performance cannot be achieved.
[0009]
On the other hand, in order to deal with the problem of the decrease in the roller life due to the deterioration of the surface of the fixing roller and the problem of the decrease in the thermal responsiveness due to the recording material being wound around the fixing roller, the portion corresponding to the image surface of the recording material in the fixing roller ( It has been proposed and put into practical use that a thermoswitch is brought into contact with a portion that is off the image portion. However, in this case, it is necessary to increase the length of the fixing roller in order to provide a contact portion with the thermo switch in a portion other than the image portion of the fixing roller. This leads to an adverse effect of increasing the size of the apparatus.
[0010]
In view of the problem of such a contact method, it is desired to replace the contact method with a non-contact method, that is, to dispose the thermo switch away from the surface of the fixing roller.
[0011]
However, the non-contact method is not good in thermal response. Therefore, it is conventionally difficult to maintain the specified overheat prevention performance (when the temperature of the fixing roller exceeds the set temperature, the operation for preventing the overheat in a predetermined time is executed) by the non-contact method. It is believed that.
[0012]
In recent years, in order to prevent the user from waiting as much as possible, there is an increasing demand for the apparatus to be put into a standby state sooner after the apparatus is turned on. For this reason, the fixing roller is also regarded as important to reach the temperature control temperature in a shorter time (shortening the warm-up time). When the temperature rise rate of the fixing roller is increased in this way, the thermo switch needs to have high followability of the temperature rise with respect to the fixing roller for safety.
[0013]
In short, although the contact method is widely used, there are various problems. On the other hand, the non-contact method has a problem of thermal follow-up, and maintains specified performance in terms of thermal response. Is seen as difficult.
[0014]
The present invention was devised in view of the circumstances as described above, and solves the problems of the non-contact method while adopting the non-contact method as an excessive temperature rise prevention means, and is ideal. This is to realize the function to prevent overheating.
[0015]
In other words, the object of the present invention is to prevent the temperature rise of the fixing roller by reducing the life of the fixing roller and preventing the enlargement of the apparatus by adopting a non-contact method, and also reducing the warm-up time of the fixing roller. An object of the present invention is to provide an image recording apparatus that maintains specified performance.
[0018]
[Means for Solving the Problems]
According to the present invention, the object is to fix the toner image on the recording material by heat, a temperature detecting unit for detecting the surface temperature of the fixing unit of the fixing unit, and fixing in the vicinity of the fixing unit. In an image recording apparatus having an excessive temperature rise prevention unit that is disposed in a non-contact state with the image forming unit and prevents an excessive temperature rise in the fixing unit, the over temperature rise prevention unit is cooledWhenA cooling unit that discharges heat from the fixing unit to the outside of the apparatus, and a cooling target switching unit that switches a cooling target by the cooling unit to cool only the fixing unit or both the fixing unit and the overheating prevention unit, While the fixing unit does not reach the temperature control temperature, the cooling target switching unit only cools the fixing unit, and when the fixing unit reaches the temperature control temperature, the cooling target switching unit cools both the fixing unit and the excessive temperature rise prevention unit. This is achieved by having the control means.
[0021]
In the present invention, while the temperature adjustment temperature is not reached, the cooling target switching means is set so as to cool only the fixing means, and when the temperature adjustment temperature is reached, both the fixing means and the excessive temperature rise prevention means are cooled. Cut to letChangeYeah. That is, the heat discharging operation of the fixing unit is started independently from the warm-up stage.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to FIGS.
[0023]
(First embodiment)
First, a first embodiment of the present invention will be described with reference to FIGS.
[0024]
FIG. 1 shows a color image recording apparatus as an embodiment of the present invention.
[0025]
The image recording apparatus includes a sheet feeding unit 20 that feeds recording materials P one by one, an image forming unit 10 that forms a toner image based on image information, and an image forming unit 10 that conveys the recording material. A transfer / conveying unit 30 for transferring the transferred toner image, a fixing unit 40 as fixing means for fixing the toner image on the recording material after transfer by heat and pressure, and a control unit for controlling each part of the apparatus. Have.
[0026]
Here, the paper feeding unit 20 includes a cassette 21 for storing recording materials, a roller group 23 for feeding recording materials from the cassette 21 one by one, and a paper feeding guide 24.
[0027]
In the image forming unit 10, four stations 10A to 10D are sequentially arranged corresponding to four colors of yellow, cyan, magenta, and black. Each of the stations 10 </ b> A to 10 </ b> D includes a photosensitive drum 11 as an image carrier, and a primary charger 12, an optical system 13, a developing device 14, and a cleaning device 15 that are disposed to face the outer peripheral surface of the photosensitive drum 11. doing.
[0028]
The transfer conveyance unit 30 has a transfer belt 31 wound around a plurality of rollers. The driving roller 32 in the roller group is disposed at the end of the transfer belt 31 near the fixing unit 40.
[0029]
The fixing unit 40 detects a fixing roller 41A as a fixing unit including a fixing heater such as a halogen heater 49, a pressure roller 41B pressed against the fixing roller 41A, and a surface temperature of the fixing roller 41A. A thermistor 46 as a temperature detecting means, a thermo switch 47 as an example of an excessive temperature rise preventing means arranged in a non-contact state in the vicinity of the fixing roller 41B, and a recording material are guided to the nip portions of both rollers 41A and 41B. The inlet guide 43C and the inner discharge roller 44 and the outer discharge roller 45 that guide the recording material discharged from the roller pair 41A and 41B to the outside of the apparatus are configured. These members are covered by a fixing unit frame 42 shown in FIG.
[0030]
Since the thermo switch 47 is a non-contact type, the surface portion of the fixing roller 41A is not deteriorated. Further, since there is no problem of a decrease in thermal response due to the recording material being involved, there is no need to extend the length of the fixing roller 41A in order to bring the contact-type thermo switch into contact with an area other than the image portion of the fixing roller 41A. There is no need to increase the size of the device.
[0031]
The exhaust fan 61 cools the thermo switch 47 and exhausts the atmosphere around the fixing unit 40 to the outside of the apparatus. The reason for cooling the thermo switch 47 is to lower the operating temperature of the thermo switch 47 and thereby increase the thermal response. Also, the reason why the exhaust heat of the fixing unit 40 is discharged outside the apparatus is that when the heat of the fixing unit 40 is released into the apparatus, the internal temperature of the apparatus rises and the image forming unit 10 and the transfer conveyance unit 30 This is to prevent the performance from changing.
[0032]
The control unit includes a control circuit 70, motor drive boards 71, 72, and the like, and controls operations of the units 20, 10, 30, 40 described above.
[0033]
The operation of the image recording apparatus will be described. The recording materials sent one by one from the cassette 21 are sequentially conveyed by the transfer conveyance unit 30 and then sequentially passed through the stations 10A to 10D of the image forming unit 10 to form four color toner images. Is then transferred between the fixing roller 41 </ b> A and the pressure roller 41 </ b> B of the fixing unit 40, and the toner image is fixed by being heated and pressurized while being conveyed between the fixing roller 41 </ b> A and the pressure roller 41 </ b> B.
[0034]
Next, a configuration that characterizes the present embodiment will be described.
[0035]
An electric control system of the fixing unit 40 is shown in FIG. The detailed structure around the fixing unit 40 is shown in FIGS.
[0036]
As shown in FIG. 2, the electric control system of the fixing unit receives a detection temperature from the thermistor 46 for detecting the temperature of the fixing roller, and a detection temperature from the thermistor 46, and a detected temperature and a specified temperature (temperature control temperature). In comparison, a control circuit 70 that outputs a heater drive signal and a fan drive signal, an SSR 73 that performs heater ON / OFF control by a heater drive signal from the control circuit 70, and a halogen heater 49 driven by the SSR 73 And a power source 53 of the halogen heater 49, a thermo switch 47 for cutting off the energization of the halogen heater 49, and an exhaust fan 61 driven by a fan drive signal from the control circuit 70.
[0037]
The control circuit 70 receives the fixing roller detection temperature signal from the thermistor 46, compares the detected temperature with a specified temperature (temperature control temperature), and controls ON / OFF of the halogen heater 49 by the SSR 73 based on the result. Set to do.
[0038]
On the other hand, the thermo switch 47 is disposed in a non-contact state in the vicinity of the surface of the fixing roller 41A. In this embodiment, the distance between the fixing roller 41A and the thermo switch 47 is set to an error range of 0.7 mm ± 0.2 mm. When the surface temperature of the fixing roller 41A further rises beyond the normal temperature control temperature due to some cause, for example, the detection failure of the thermistor 46 or the operation failure of the SSR 73, the internal temperature of the thermo switch 47 increases accordingly, Thus, when the bimetal in the thermo switch 47 is displaced and the contact for energizing the halogen heater 49 is separated, the energization of the halogen heater 49 is interrupted.
[0039]
By the way, if the fixing roller 41A is temperature-controlled, for example, at a temperature close to 200 ° C. (175 ° C. in this embodiment), the heat in the fixing unit 40 is gradually released to the outside of the unit to raise the temperature inside the apparatus. To go. Then, the toner in the image forming unit 10 is warmed and easily fused, thereby causing a problem that the development efficiency and the transfer efficiency are lowered, and good image quality is not maintained. In particular, when the distance between the image forming unit 10 and the fixing unit 40 is reduced in order to reduce the size of the apparatus, or when a low-melting toner is used for energy saving, a larger problem occurs. .
[0040]
In addition, there are the following problems. The driving roller 32 of the transfer / conveying unit 30 is usually disposed downstream of the final image transfer region (contact point between the photosensitive drum 11 and the transfer belt 31) T. The reason is as follows. By setting the transfer belt 31 to the pulling side in all image transfer regions, it is possible to prevent the transfer belt 31 from being loosened as much as possible, thereby preventing image transfer failure and transfer position deviation. For this reason, the driving roller 32 is disposed in the vicinity of the fixing unit 40, and a certain temperature increase cannot be avoided. Therefore, the drive roller 32 is thermally expanded, and the transfer speed of the transfer belt 31 is increased. When the speed change exceeds a certain value, the transfer image expands and contracts and the color shift of the multicolor image appears. In particular, in the case of color misregistration, a problem occurs even if the speed changes by about 0.1%. That is, the diameter of the drive roller 32 should not change by more than 0.1%.
[0041]
However, in order to drive the transfer belt 31 without slipping, the drive roller 32 is usually configured such that a layer having a high friction coefficient, for example, a rubber layer is wound around the roller surface. However, in general, these materials have a large coefficient of linear expansion. More specifically, when the temperature of the driving roller increases by about 20 degrees, the diameter increases by 0.1%.
[0042]
In view of this, an exhaust heat mechanism (exhaust means) of the fixing unit 40 is provided to discharge the atmosphere around the fixing unit 40 to the outside of the apparatus so as to prevent the temperature rise in the apparatus as much as possible. In this embodiment, the thermoswitch cooling means also serves as the fixing unit heat exhausting means. That is, as shown in FIGS. 3 and 4, the fixing unit exhaust heat means is provided between the front side plate 1 and the rear side plate 2 of the apparatus main body so as to cover the sheet feeding side surface and the upper part of the fixing unit 40. Exhaust duct 62, exhaust openings 1A and 2A provided at positions corresponding to exhaust duct 62 in front plate 1 and rear plate 2, respectively, and exhaust fan 61 provided in opening 2A of rear plate 2 are provided. doing.
[0043]
With the rotation of the exhaust fan 61, fresh air is taken in from the opening 1A of the front side plate 1 while discharging the air in the exhaust duct 62 from the opening 2A of the rear side plate 2 to the outside of the device (see arrow Fu in FIG. 3). At the same time, air is sucked from the vicinity of the sheet feeding side of the fixing unit 40 and discharged out of the apparatus (see arrow Ff in FIG. 4).
[0044]
As a result, it is possible to prevent heat from diffusing from the opening on the paper feed side of the fixing unit 40 into the apparatus, thereby preventing temperature rise in the apparatus as much as possible and always obtaining a good image.
[0045]
Further, the thermo switch 47 has a structure as shown in FIGS. 3 and 4 in order to be cooled. The thermo switch 47 is attached to the fixing unit frame 42 via a metal thermo switch mounting plate 48. A part of the thermo switch mounting plate 48 protrudes into the exhaust duct 62 from an opening 42A formed on the upper surface of the fixing unit frame 42 (this protruding portion is referred to as a protruding portion 48A). . Therefore, when the exhaust fan 61 operates, the protrusion 48A of the thermo switch mounting plate 48 is cooled, and the thermo switch 47 is also cooled accordingly. In order to increase the cooling effect, for example, aluminum having high thermal conductivity is suitable as the material of the thermoswitch mounting plate 48.
[0046]
Further, the exhaust fan 61 is controlled by the control circuit 70 (see FIG. 2) so as not to operate until the fixing roller 41A reaches a specified temperature (temperature control temperature) after the halogen heater 49 is turned on. Yes. The reason for such control will be described below based on the graph of FIG.
[0047]
This graph shows temporal changes in the surface temperature of the fixing roller 41A and the temperature of the thermo switch 47 when the apparatus is turned on at room temperature of 25 ° C. and started up. The halogen heater 49 starts to light, and the surface of the fixing roller 41A reaches a temperature adjustment temperature of 175 ° C. in 100 seconds. Usually, after that, the temperature enters the temperature control temperature and continues to change as shown by curve A. Further, the temperature of the thermo switch 47 at that time follows the temperature change (curve A) of the halogen heater 49 and becomes a steady state at about 95 ° C. after rising as shown by the curve B. In response to this, the temperature Tb at which the thermo switch 47 operates to cut off the energization of the halogen heater 49 is set to 105 ° C., which is 10 degrees higher than the steady temperature.
[0048]
Here, the exhaust fan 61 does not operate until the fixing roller 41A reaches the temperature adjustment temperature 175 ° C. (up to 100 sec), that is, during the warm-up, and operates after entering the temperature adjustment state (from 100 sec). It is to be controlled. That is, since the cooling of the thermo switch 47 is started from 100 sec after entering the temperature control state, the temperature followability of the thermo switch 47 is enhanced during the warm-up.
[0049]
If the surface temperature of the fixing roller 41A is not accurately detected due to a defect in the thermistor 46, the halogen heater 49 continues to be fully lit even after 100 seconds. As a result, the temperature of the fixing roller 41A is 175 as shown by the curve D. It is considered that the temperature rises further above the temperature. During this temperature control abnormality, since the apparatus determines that the fixing roller 41A has not reached the temperature control temperature, the exhaust fan 61 is not operated. Therefore, since the thermo switch 47 is not cooled, the temperature change has higher followability than that during cooling. That is, the thermo switch 47 changes as shown by the curve E, and the bimetal is displaced and operated at the time tb when the set temperature Tb (105 ° C.) is reached, and the halogen heater 49 is turned off. At this time, the fixing roller 41A has a temperature of about 250 ° C., and does not damage the fixing roller 41A itself and surrounding parts.
[0050]
On the other hand, for comparison with the present embodiment, a case where the thermo switch 47 is not configured to be cooled will be described. In this case, the steady temperature of the thermo switch 47 is increased by the amount that is not cooled, so that the curve C is obtained, which is about 125 ° C. The operating temperature Tc of the thermo switch 47 must be set to 135 ° C. according to the steady temperature 125 ° C., and accordingly, the time until the thermo switch 47 operates in the event of an abnormality is increased to tc. At this time, the temperature of the fixing roller 41A exceeds 300 ° C., and the fixing roller 41A itself and surrounding parts (for example, a bearing and a cleaning unit) are damaged.
[0051]
As described above, when the means for cooling the thermo switch 47 is provided, the operating temperature of the thermo switch 47 can be set lower than in the case where there is no cooling means, and the cooling means is set as described above. By controlling so as not to operate during warm-up, the temperature rise of the thermo switch 47 can follow the temperature rise of the halogen heater 49 during warm-up. Therefore, the time until the thermo switch 47 enters a switch operable state can be shortened, so that safety can be improved.
[0052]
For example, even with the fixing roller 41A having a fast warm-up time such as 100 sec, it is not cooled before reaching the temperature control temperature (at the time of warm-up), and starts cooling when the temperature reaches the temperature control temperature. Even the switch 47 can maintain the specified performance.
[0053]
Next, a modification of this embodiment will be described.
[0054]
When the location of the thermo switch 47 is touched, in this embodiment, as shown in FIGS. 3 and 4, the thermo switch 47 is arranged almost directly above the fixing roller 41A. This is to efficiently absorb the heat released from the fixing roller 41A. In the non-contact method, the temperature rises mainly by absorbing radiant heat from the surface of the fixing roller 41A, but partly receives heat from air convection.
[0055]
However, it does not necessarily have to be on the vertical line at the center of the fixing roller 41A, and there is no significant difference as long as it does not deviate from the projection area of the fixing roller 41A even if it is slightly shifted in the horizontal direction.
[0056]
In the above-described embodiment, a part 48 </ b> A of the thermo switch mounting plate 48 protrudes from the fixing unit frame 42 into the exhaust duct 62 in order to cool the thermo switch 47. According to this, since the thermo switch 47 is indirectly cooled through one component called the thermo switch mounting plate 48, there is room for improvement in terms of cooling efficiency. In order to improve cooling efficiency, for example, as shown in FIG. 6, a part of the upper surface of the fixing unit frame 42 is formed with a concave portion 42A that gently slopes from both sides to the center, and a thermo switch is formed through an opening formed in the center. 47 can be inserted and fixed from above. According to this modification, since the thermo switch 47 itself is directly cooled by touching the air flow in the exhaust duct, the cooling effect is improved, and the switch operating temperature of the thermo switch 47 is set higher than the above-described Tb (see FIG. 5). It can be set to a lower value, and as a result, the thermal response can be further improved.
[0057]
Here, the reason why the upper surface of the fixing unit 40 is not used as the mounting surface of the thermo switch 47 is that it is usually necessary to secure a space around the fixing roller 41A for arranging some parts such as a separation claw and a cleaning mechanism. Because there is. If this space is not necessary in some cases, the mounting surface of the thermo switch can be made coincident with the upper surface of the fixing unit frame 42, and the shape of the fixing unit frame 42 can be simplified.
[0058]
In the above-described embodiment, the cooling means of the thermo switch 47 is configured to also serve as the heat exhaust mechanism of the fixing unit 40, but the present invention is not limited thereto. If there is no problem in cost and space, the thermoswitch cooling means and the fixing unit heat discharging mechanism may be provided independently, or only the fixing unit heat discharging mechanism may be omitted for reasons such as high cost. .
[0059]
In this embodiment, the timing for operating the thermoswitch cooling means is set when the fixing roller 41A reaches the temperature control temperature, but the switch operation is set after a certain fixed time has elapsed from the temperature control temperature. These are also substantially included in the present invention.
[0060]
In addition, although the abnormal operation has been described with a rise from room temperature, the same effect can be obtained even in an abnormal operation from a temperature control state or an intermediate temperature between the room temperature and the temperature control state. Of course.
[0061]
Moreover, although the thermo switch 47 was illustrated as an excessive temperature rise prevention means (safety device), not only this but a thermal fuse (illustration omitted) may be used, for example.
[0062]
Further, although the full-color image recording apparatus is exemplified as the image recording apparatus, the present invention is not limited to this, and a mono-color image recording apparatus may be used.
[0063]
(Second Embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG.
[0064]
In the first embodiment described above, the operation of cooling the thermo switch 47 and the heat exhausting operation of the fixing unit 40 are performed simultaneously. According to this, if the heat exhausting operation of the fixing unit 40 is performed even during the warm-up, the thermo switch 47 is also cooled, and the temperature followability of the thermo switch 47 during the warm-up is lowered. Will end up. On the other hand, if a cooling means dedicated to the thermo switch 47 is provided separately, this problem can be dealt with, but this is often difficult in terms of space and cost.
[0065]
Therefore, a configuration example in which the cooling operation of the thermo switch 47 and the exhaust heat operation of the fixing unit 40 can be performed independently without any difficulty in space and cost will be described with reference to FIG.
[0066]
This is obtained by adding cooling target switching means for switching only the fixing unit 40 or both the fixing unit 40 and the thermo switch 47 to the configuration of FIG. In this embodiment, the cooling target switching means includes a pair of wall surfaces 49 provided on the left and right sides of the upper surface of the fixing unit frame 42 with the protrusion 48A of the thermo switch mounting plate 48 interposed therebetween, and an upstream of the pair of wall surfaces 49 in the exhaust direction. It has an opening / closing member 50 provided to open and close the side, and a solenoid 52 connected to the opening / closing member 50 via a link 51. The solenoid 52 is connected to the control circuit 70 (see FIG. 2).
[0067]
The wall surface 49 forms an air flow path that passes through the protrusion 48A. The opening / closing member 50 is provided so as to be able to stand or fall over by connecting the end surfaces of both wall surfaces 49. The solenoid 52 stands up and falls over the opening / closing member 50 via the link 51. When the solenoid 52 is not energized, the opening / closing member 50 is pulled down and laid down by an urging force of a spring (not shown), and the air flow path is opened. On the other hand, when the solenoid 52 is energized, the solenoid 52 pushes the open / close member 50 to stand and close the air flow path.
[0068]
The control circuit 70 energizes the solenoid 52 before the temperature adjustment temperature is reached (warm-up), closes the air flow path, and after reaching the temperature adjustment temperature, deenergizes the solenoid 52 to set the air flow path. It is set to open.
[0069]
According to the flow path object switching means configured as described above, the cooling object is switched before and after the temperature control temperature as follows.
[0070]
When the apparatus power switch is turned on, the halogen heater 49 is turned on, and at the same time, the exhaust fan 61 starts to rotate and exhaust is started. Here, the solenoid 52 is energized, the open / close member 50 is raised, and the air flow path is closed. Therefore, the air flow generated by the exhaust fan 62 bypasses the thermo switch mounting plate 48 and flows as indicated by the arrow Fb. Therefore, only the exhaust heat of the fixing unit 40 is performed, and the thermo switch 47 is not cooled. Since the thermo switch 47 is not cooled, the temperature followability of the thermo switch 47 during warm-up is maintained.
[0071]
When the surface temperature of the halogen heater 49 rises and reaches a temperature adjustment temperature of 175 ° C., the temperature adjustment control mode of the halogen heater 49 is entered, and at that time, the energization to the solenoid 52 is stopped. Then, the opening / closing member 50 is laid down by the spring force, the air flow path is opened, and cooling of the thermo switch 47 is started.
[0072]
As described above, since the heat exhausting operation of the fixing unit 40 is started from the warm-up stage, the temperature rise of surrounding parts and the atmosphere is further reduced. Therefore, the degree of transfer image density reduction and color misregistration is further improved, and a high-quality image can be maintained. Further, since it is not necessary to provide independent cooling means according to the thermo switch 47 and the fixing unit 40, the space is saved and the cost is low.
[0075]
【The invention's effect】
According to the present invention, the cooling target switching unit is set to cool only the fixing unit while the temperature adjustment temperature is not reached. When the temperature adjustment temperature is reached, both the fixing unit and the excessive temperature rise prevention unit are set. Cut to coolChangeYeah. That is, since the heat discharging operation of the fixing unit can be started independently from the warm-up stage, the temperature rise of the parts and atmosphere around the fixing unit can be further reduced. Therefore, the degree of transfer image density reduction and color shift is further improved, and a high-quality image can be maintained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the entire image recording apparatus according to a first embodiment of the present invention.
2 is a block diagram showing an electric control circuit related to a fixing unit of the image recording apparatus of FIG. 1;
FIG. 3 is a partially broken perspective view showing the periphery of the fixing unit of the image recording apparatus of FIG.
4 is a longitudinal sectional view around a fixing unit in FIG. 3;
5 is a graph showing changes in time-temperature of each part of the image recording apparatus in FIG.
6 is a perspective view showing a modification of the fixing unit shown in FIG.
FIG. 7 is a perspective view showing the periphery of a fixing unit of the second embodiment of the image recording apparatus of the present invention.
FIG. 8 is a schematic cross-sectional view showing an entire example of a conventional image recording apparatus.
[Explanation of symbols]
P Recording material
40 Fixing unit (fixing means)
41A Fixing roller (fixing part)
42 Fixing unit frame
46 thermistor (temperature detection means)
47 Thermo switch (Preventing excessive temperature rise)
48 Thermo switch mounting plate
48A Protrusion of thermo switch mounting plate
49 Wall surface (cooling object switching means)
50 Opening and closing member (cooling object switching means)
51 link (cooling target switching means)
52 Solenoid (Cooling target switching means)
61 Exhaust fan (cooling means)
62 Exhaust duct (cooling means)
70 Control circuit (control means)

Claims (1)

Fixing means for fixing the toner image on the recording material by heat, temperature detecting means for detecting the surface temperature of the fixing portion of the fixing means, and fixing in a non-contact state with the fixing portion in the vicinity of the fixing portion an image recording apparatus having an overheat protection means for preventing excessive Atsushi Nobori of the parts, cooling means for discharging to the outside of the heat dissipation device of both fixing means cooling the overheat protection means, by the cooling means The cooling target switching means for switching the cooling target only to the fixing means or both the fixing means and the excessive temperature rise prevention means, and the fixing means for cooling only the fixing means while the fixing means does not reach the temperature control temperature. An image recording apparatus comprising: a control means for causing the cooling target switching means to cool both the fixing means and the excessive temperature rise prevention means when the means reaches the temperature control temperature.

Images