Patent Application
20180118488
The present disclosure relates to a sheet detection mechanism to be mounted on an image forming apparatus, such as a printer and a copying machine using an electrophotographic technique and an image forming apparatus equipped therewith.
Image forming apparatuses using an electrophotographic technique are equipped with sheet detection mechanisms for detecting moving sheets and fixing units for heat fixing images on sheets. However, if the sheet detection mechanism exists near the fixing unit, there is a possibility that water vapor generated from a sheet by heat fixing causes dew condensation in the sheet detection mechanism, and the sheet detection mechanism is thermally damaged by radiation heat from the fixing unit.
Japanese Patent Application Laid-Open No. 2007-33520 describes a configuration for cooling a sensor for detecting a sheet by blowing air thereto.
As a type of a sheet detection mechanism for detecting a sheet by illuminating a sheet with light, there is a configuration in which a part of a sensor unit is disposed on both of two guide units disposed to face each other across a sheet conveyance path. For example, a light-emitting unit is arranged on one of the guide units, and a light-receiving unit for receiving light and converting it into an electrical signal is arranged on the other guide unit. When a conveyed sheet blocks the light, presence of the sheet is detected. However, when the sensor unit is cooled by being blown by air in the configuration in which the part of the sensor unit is disposed on both of the two guide units, at least two air ducts are required, and the apparatus becomes larger.
Thus, the present disclosure is directed to a sheet detection mechanism in which an air blow configuration to a sensor unit is miniaturized and the provision of an image forming apparatus equipped therewith.
A sheet detection mechanism includes a guide unit including a first guide unit and a second guide unit facing the first guide unit across a space in which a sheet moves and configured to guide a sheet, and a sensor unit installed in the guide unit and configured to detect a sheet moving along the guide unit, wherein the sensor unit includes a first optical element unit installed inside of the first guide unit and a second optical element unit installed inside of the second guide unit and configured to optically detect a sheet in cooperation with the first optical element unit, wherein the first guide unit is provided with a first opening portion through which light in an optical path connecting the first optical element unit and the second optical element unit passes, and the second guide unit is provided with a second opening portion through which light in an optical path connecting the first optical element unit and the second optical element unit passes, the first guide unit is provided with a duct for sending air to the first optical element unit, and air coming out from the first opening portion hits the second optical element unit via the second opening portion.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A configuration of an image forming apparatus according to a first exemplary embodiment is described with reference to
A main body (printer main body) 100 of the image forming apparatus illustrated in
A belt unit 10 includes an intermediate transfer belt 12 stretched around a drive roller 13 and a tension roller 14. The tension roller 14 applies a tensile force to the intermediate transfer belt 12 in a direction of an arrow T. Each of the photosensitive drums 1Y, 1M, 1C, and 1K rotates clockwise and the intermediate transfer belt 12 rotates counterclockwise in
After transfer of the toner images, the toners remaining on the photosensitive drums 1Y, 1M, 1C, and 1K are respectively removed by the drum cleaners 8Y, 8M, 8C, and 8K. Further, the toners remaining on the intermediate transfer belt 12 after the secondary transfer to a sheet S are removed by a belt cleaner 26 and collected to a waste toner collecting container, which is not illustrated.
The sheet feeding unit is constituted of a sheet feeding roller 24 mounted on the main body 100 and a sheet feeding cassette 23 detachable from the main body 100. The sheet feeding roller 24 rotates by power from a driving unit, which is not illustrated. The sheet S is separated by the sheet feeding roller 24 one by one from the sheet feeding cassette 23 and conveyed to a registration roller pair 17. The registration roller pair 17 finally corrects skew feeding of the sheet S. Further, the registration roller pair 17 matches a timing of scanning the photosensitive drum with a laser beam with a timing of sheet conveyance.
The sheet S fed from the sheet feeding unit is conveyed to the secondary transfer unit 15 by the registration roller pair 17. A bias voltage is applied to a secondary transfer roller 16 in the secondary transfer unit 15, and accordingly the four color toner images on the intermediate transfer belt 12 are secondary transferred to the sheet S.
The sheet S after toner image transfer is conveyed to a fixing unit 18. The toner image on a sheet S surface is heated and fixed to the sheet S at a fixing nip portion N formed between a fixing film 19a and a pressure roller 19b.
A sheet detection mechanism 20 detects the sheet S nipped and conveyed by the fixing unit 18. The sheet detection mechanism 20 detects the sheet S passing through the fixing nip portion N and transmits detected information to a control unit, which is not illustrated. The control unit performs conveyance control of the sheet S and annunciation of a jam of the sheet S based on the detected information received from the sheet detection mechanism 20. The sheet detection mechanism is installed immediately behind the fixing unit.
The sheet S passed through the sheet detection mechanism 20 is conveyed by a roller pair 27. The sheet S passed through the roller pair 27 is conveyed by a sheet discharge roller pair 21 and discharged onto a sheet discharge tray 22. The sheet S according to the present exemplary embodiment is a material which does not transmit light and reflect it on a sheet surface like plain paper.
As illustrated in
The sheet detection mechanism 20 is disposed on downstream of the fixing nip portion N in the sheet conveyance direction. In addition, the sheet detection mechanism 20 is disposed above the fixing nip portion in a vertical direction. The sheet detection mechanism 20 and the roller pair 27 are unitized as a sheet discharge unit 70. As illustrated in
The fixing film 19a has a three layer structure including a base layer, an elastic layer, and a surface layer in the order from an inner side. An outer diameter of the fixing film 19a according to the present exemplary embodiment is 24 mm. The base layer is made of polyimide and has a thickness of 70 μm. The elastic layer is made of silicon rubber and has a thickness of 200 μm. The surface layer is made of perfluoroalkyl vinyl ether copolymer (PFA) and has a thickness of 15 μm. The pressure roller 19b has a three layer structure including a core metal, an elastic layer, and a release layer in the order from the center. An outer diameter of the pressure roller 19b according to the present exemplary embodiment is 25 mm. A material of the core metal is stainless steel (SUS). The elastic layer has a thickness of 4 mm and is made of silicon rubber. The release layer is made of PFA and has a thickness of 30 μm.
The heater 50 has a function of raising a temperature of the fixing film 19a to that necessary for fixing the toner on the sheet S thereto. According to the present exemplary embodiment, the heater 50 is a ceramic heater in which a heat generation resistor is printed on a ceramic substrate. In this regard, the heating method is not limited to the above-described one, and a heat roller method and induction heating (IH) method may be adopted.
A basic configuration of the sheet detection mechanism 20 according to the present exemplary embodiment is described.
The guide units (30 and 31) includes a first guide unit 30 and a second guide unit 31 facing the first guide unit 30 across a space in which the sheet S moves. The first guide unit 30 faces a non-printing surface of the sheet S in the case of one-side print, and the second guide unit 31 faces a printing surface of the sheet S in the case of the one-side print. The first guide unit 30 includes a sheet passing portion 30a and a bottom surface portion 30b. The second guide unit 31 includes a sheet passing portion 31a and a bottom surface portion 31b. The sheet S to be conveyed passes through a sheet conveyance path (the space in which the sheet moves) formed between the sheet passing portion 30a of the first guide unit 30 and the sheet passing portion 31a of the second guide unit 31 and is discharged.
The sensor units (28 and 29) include a first optical element unit 28 which is disposed inside of the first guide unit 30 and a second optical element unit 29 which is disposed inside of the second guide unit 31 and optically detects the sheet S in cooperation with the first optical element unit 28. In the apparatus according to the present exemplary embodiment, the first optical element unit 28 is a light-emitting unit, and the second optical element unit 29 is a light-receiving unit. The light-emitting unit 28 is formed by attaching a light emitting element on an electrical substrate. The light-receiving unit 29 is formed by attaching a light receiving element on an electrical substrate. The light-receiving unit 29 has a function of receiving light and converting the received light into an electrical signal.
The light-emitting unit 28 is fixed to a sensor fixing portion 30c of the first guide unit 30. The light-receiving unit 29 is fixed to a sensor fixing portion 31c of the second guide unit 31. The sheet passing portion 30a of the first guide unit 30 has a first opening portion 30d through which light in an optical path connecting the light-emitting unit 28 and the light-receiving unit 29 passes. The sheet passing portion 31a of the second guide unit 31 has a second opening portion 31d through which the light in the optical path connecting the light-emitting unit 28 and the light-receiving unit 29 passes.
It is desirable to use a light emitting diode (LED) which consumes little power and emits electroluminescence for the light-emitting unit 28. In addition, when the LED is used, an arrangement space can be further saved by adopting a surface mounted type LED rather than a shell type one. The above-described arrangement of the light-emitting unit 28 and the light-receiving unit 29 may be in reverse order.
Operations of the sheet detection mechanism 20 according to the present exemplary embodiment are described. First,
Next,
As described above, the sheet detection mechanism 20 is disposed immediately behind the fixing film 19a and the pressure roller 19b in the sheet conveyance direction. The sheet detection mechanism 20 has a configuration in which a state in which the light emitted from the light-emitting unit 28 is blocked by the sheet S and does not reach the light-receiving unit 29 is regarded as a sheet existing state (a state in which a sheet is detected). This configuration can eliminate sliding damage on the sheet S caused by a conveyance guide near the sheet detection mechanism 20 and accurately switch the diverter 46 when the sheet S is conveyed at a higher speed. The reason is described below.
Recently, there is a tendency to miniaturize an apparatus by suppressing a height of the apparatus. When a low height apparatus is designed, a curvature of a conveyance path after passing the fixing unit is forced to be large in many cases. At the same time, productivity improvement in two-sided printing (high-speed printing) is also demanded.
A conveyance path having a large curvature becomes a factor causing sliding damage on an image. On the other hand, high-speed printing requires increase of precision in operations at switching timing of the diverter which operates when the sheet detection mechanism detects an edge portion of the sheet S.
In order to prevent damage on an image, it is necessary to increase a width of the sheet conveyance path (a distance in a vertical direction with respect to the sheet S surface) provided from the fixing film 19a and the pressure roller 19b to the diverter 46 so that the sheet S does not actively abut on the conveyance guide. However, when the width of the sheet conveyance path is increased, an orientation of the sheet S passing through the sheet conveyance path is unstable. Especially, the orientation is greatly affected by a degree of curl of the sheet S. Thus, it is difficult to accurately detect the edge portion of the sheet S.
Therefore, when the sheet detection mechanism 20 which detects the sheet S when the sheet S blocks the light from the light-emitting unit 28 is adopted as in the present exemplary embodiment, the edge portion of the sheet S can be accurately detected. For example, in the case of a sheet detection mechanism which detects the sheet S by reflecting the light from the light-emitting unit 28 on the sheet S surface, there is a possibility that detection accuracy varies depending on an orientation of the sheet S, however, the sheet detection mechanism 20 according to the present exemplary embodiment can suppress such a possibility.
Next, an air blow configuration in the sheet detection mechanism 20 is described. When the sheet (plain paper) S which adsorbed moisture passes through the fixing nip portion N and is subjected to heating and fixing processing, the sheet S generates high temperature water vapor. The sheet detection mechanism 20 is disposed above the fixing nip portion N in the vertical direction, the generated the water vapor reaches the sheet detection mechanism 20 by natural convection. When the water vapor enters from the opening portions 30d and 31d of the sheet detection mechanism 20 and reaches the light-emitting unit and the light-receiving unit 29, dew condensation may occur, and the apparatus may malfunction. In addition, when the light-emitting unit 28 and the light-receiving unit 29 become high temperature by heat transfer from the fixing unit 18 to the sheet detection mechanism 20, these units may malfunction. Therefore, an air blow configuration is required to prevent dew condensation in the light-emitting unit 28 and the light-receiving unit 29 and temperature rise of these elements.
A lid member 32 is attached to the first guide unit 30 so as to cover the light-emitting unit 28, and the first guide unit 30 and the lid member 32 form a duct. In addition, a duct member 33 is attached to an edge portion in a −Y direction of the lid member 32. The duct member 33 has a hollow structure and can send air to the duct formed by the first guide unit 30 and the lid member 32 as illustrated in
Next,
An air flow in the air blow configuration in the sheet detection mechanism according to the present exemplary embodiment is described with reference to
As described above, in the case that the duct is installed only one of two guide units, air can be sent to the optical element units respectively disposed on both of the two guide units. Accordingly, the image forming apparatus can be miniaturized while preventing dew condensation in the sheet detection mechanism 20 and malfunction of the sensor caused by a heat source. According to the present exemplary embodiment, the optical path and the air duct from the light-emitting unit 28 to the light-receiving unit 29 are formed in the same route, however, the optical path and the air duct may be in different routes. In addition, the light-emitting unit and the light-receiving unit may be arranged in reverse order with each other.
Further, according to the configuration of the present exemplary embodiment, an optical path length and an air duct length are respectively the shortest lengths, and following effects can be achieved. More specifically, a light emission amount of the light-emitting unit can be reduced as the optical path length is shorter, and thus effects of saving power and extending life of the light-emitting unit can be achieved. Further, an air blow amount of the fan can be reduced as the air duct length is shorter, and thus effects of miniaturization and power saving of the fan can be achieved. Furthermore, an air amount to be blown to the sheet conveyance path can be reduced as the air duct length is shorter, and thus it can prevent an adverse effect on an image which is caused by locally cooling the fixing nip portion.
Next, a second exemplary embodiment is described with reference to
The light-emitting unit 28 and the light-receiving unit 29 are mounted on the first guide unit 30 disposed above the pressure roller 19b. Further, the light-emitting unit 28 and the light-receiving unit 29 are mounted on a single substrate 35 so as to improve assemblability. The reflection member 36 for reflecting the light from the light-emitting unit 28 is disposed on the second guide unit 31 disposed above the fixing film 19a.
The pressure roller 19b does not have a heat source like a heater, so that the electrical components like the light-emitting unit 28 and the light-receiving unit 29 are less likely to be thermally damaged by being disposed above the pressure roller 19b than by being disposed above the fixing film 19a including the heat source therein. The reflection member 36 is not an electrical component and less likely to be thermally damaged than the light-emitting unit 28 and the light-receiving unit 29.
In addition, a sheet S is detected when the sheet S blocks the light from the light-emitting unit 28 as similar to the first exemplary embodiment, and an edge portion of the sheet S can be accurately detected as described according to the first exemplary embodiment. Further, according to the present exemplary embodiment, a glossy sheet metal is used as the reflection member 36. An aluminum deposited polyethylene terephthalate (PET) sheet and a mirror of which a glass surface is vapor deposited with aluminum or silver may be used as the reflection member 36, however, a sheet metal is desirable in consideration of output stability of the light-receiving unit 29. Especially, stainless steels are desirable, and SUS430 is the most desirable therein. According to the present exemplary embodiment, a stainless steel (SUS430 (thickness t=0.4 mm)) is used as a sheet metal. As a surface finish code of stainless steel, surface finish 2B is used. There are following three reasons why a sheet metal, especially a stainless steel (SUS430) is desirable.
The first reason is that a stable output can be obtained even if an ambient temperature changes a lot. If a mounting portion of the reflection member 36 integrally molded with the second guide unit 31 is deformed by thermal expansion, a surface of the reflection member is hardly deformed by rigidity of the reflection member 36 itself. Thus, a position accuracy of the reflection member is stabilized with respect to the light-emitting unit 28 and the light-receiving unit 29, a light amount illuminating the light-receiving unit 29 is stabilized, and accordingly output of the light-receiving unit 29 is stabilized.
The second reason is that when a stainless steel is used as a sheet metal, the stainless steel is resistant to surface corrosion in a high humidity environment. In the fixing unit, the sheet S is heated and generates water vapor. Thus, stainless steels which are resistant to corrosion in a high humidity environment are suitable. A plated sheet metal may be used, however, if the surface of the reflection member 36 is damaged during assembly or use, the sheet metal may be easily corroded therefrom, thus a material which is resistant to corrosion by single unit as a stainless steel is suitable. As main types of stainless steels, there are SUS304 including chromium and nickel and SUS430 including chromium. SUS304 has higher corrosion resistance than SUS430, however, only water vapor is generated the most in the image forming apparatus, thus SUS430 may be used.
The third reason is that SUS430 can inexpensively obtain glossy surface compared to SUS304. As described above, SUS304 includes nickel and thus is more expensive than SUS430. In addition, SUS304 has higher corrosion resistance and causes irregularity on its surface in acid pickling for surface finishing compared to SUS430. Glossiness is lost by the irregularity. Thus, SUS430 can increase a light amount to be reflected to the light-receiving unit 29.
Next, a sheet detection operation is described.
The sheet detection mechanism may have a configuration for reflecting the light from the light-emitting unit 28 twice inside of the reflection member 36. A specific example of such a reflection member 36 is a U-shaped prism. However, as the number of reflections is larger, a deviation of a reflection angle becomes larger, and reliability of the sheet detection mechanism may be impaired. Therefore, the configuration in which the light is reflected once by the reflection member 36 is desirable as in the present exemplary embodiment. Further, as described above, in the configuration for reflecting twice, the reflection member 36 is required to have a thickness in a light advancing direction like a U-shaped prism, however, in the configuration for reflecting once, the reflection member 36 can have a plate shape, and the apparatus can be miniaturized.
The sheet detection mechanism 34 using the reflection member according to the present exemplary embodiment may erroneously detect presence or absence of the sheet S when dew condensation occurs on the reflection member 36. When many minute water droplets adhere to the reflection member 36 due to the dew condensation, the light emitted from the light-emitting unit 28 is irregularly reflected by the water droplets on the reflection member 36 surface, and a light amount reaching the light-receiving unit 29 is reduced. In that case, if there is no sheet S in the sheet detection mechanism 34, it may be erroneously detect that the sheet S exists. Therefore, according to the present exemplary embodiment, the air blow configuration is required to prevent dew condensation on the reflection member 36.
According to the present exemplary embodiment, the lid member 32 and the duct member 33 are configured as described in the first exemplary embodiment, and the descriptions thereof are omitted since the same contents. First,
Next, an air flow is described. First, air is blown from a fan, which is not illustrated, disposed inside the image forming apparatus main body 100. Next, the blown air is taken into the guide portion 33a of the duct member 33. The air blow is sent to the air duct which is bent at a right angle from the guide portion 33a and formed by the sheet passing portion 30a, the bottom surface portion 30b, and the exhaust guide 30e of the first guide unit 30 and the lid member 32. The air blow is branched into two directions of the gaps G1 and G2.
The air passing through a first air duct provided with the gap G1 passes the gap G1 between the sheet passing portion 30a of the first guide unit 30 and the light-emitting unit 28, further passes from the opening portion 30d to the opening portion 31d across the sheet conveyance path, and reaches the reflection member 36.
The air passing through a second air duct provided with the gap G2 passes the gap G2 and reaches the light-receiving unit 29. The air further passes through a gap between the light-receiving unit 29 and the exhaust guide 30e, passes from the opening portion 30f to the opening portion 31d across the sheet conveyance path, and reaches the reflection member 36. The air blow through the first and second air ducts cools the light-emitting unit 28 and the light-receiving unit 29 and prevents water vapor from entering from the opening portions 30d, 30f, and 31d of the sheet detection mechanism 34. The above-described air blow configuration prevents the light-emitting unit 28 and the light-receiving unit 29 from becoming high temperature and prevents dew condensation in the light-emitting unit 28, the light-receiving unit 29, and the reflection member 36.
As described above, according to the present exemplary embodiment, the configuration is described in which both of the light-emitting unit 28 and the light-receiving unit 29 are arranged away from the fixing film 19a, and the duct is provided only one of the two guide units but the optical element units respectively disposed on both of the two guide units are cooled. Accordingly, the light-emitting unit 28 and the light-receiving unit 29 can be thermally protected, and air can be supplied to the light-emitting unit 28, the light-receiving unit 29, and the reflection member 36 while suppressing enlargement of the apparatus.
Next, a third exemplary embodiment is described with reference to
If a sheet detection mechanism 38 is disposed on a position easily affected by an external light source, such as a sheet discharge port of the image forming apparatus, the sheet detection mechanism 38 may cause erroneous detection due to stray light. As the size of the image forming apparatus main body is reduced, a possibility that the stray light enters is increased.
Thus, according to the present exemplary embodiment, a configuration is described which prevents erroneous detection by disposing the light-receiving unit 29 on a position at which the stray light hardly reaches as illustrated in
Next, a sheet detection operation is described. The light from the light-emitting unit 28 enters from the opening portion 31d of the second guide unit 31 to the opening portion 30d of the first guide unit 30 across the sheet conveyance path and reaches the reflection member 36. The illuminating light is reflected on the surface of the reflection member 36 and reaches the light-receiving unit 29. Accordingly, an electric current flows in the light-receiving unit 29, and the sheet detection mechanism 38 becomes a state in which the sheet S is not detected. A state that the sheet detection mechanism 38 detects the sheet S is similar to that according to the second exemplary embodiment, and thus the description thereof is omitted.
Next, a fourth exemplary embodiment is described with reference to
The apparatus according to the present exemplary embodiment can suppress dew condensation in the light-emitting unit 28 and the light-receiving unit 29 of the sheet detection mechanism 20 in the case of instantaneous interruption of power supply to the printer main body.
When continuous printing is performed on a plurality of moisture absorbed sheets S, high temperature water vapor generated from the sheet S when the sheet S passes through the fixing nip portion N is retained inside the fixing unit 18. Especially, the water vapor is retained in a space enclosed by the fixing film 19a, the pressure roller 19b, and guide units 30 and 31. Since the air blow to the sheet detection mechanism 20 is continued after completion of printing, the water vapor retained inside the fixing unit 18 usually does not flow backward from the sheet conveyance path via the opening portions 30d, 30f, and 31d and reach the light-emitting unit 28, the light-receiving unit 29, and the reflection member 36. However, when power supply to the printer main body is instantaneously interrupted by reason of power outage, disconnection of power cable, and the like during printing, power supply to the fan, which is not illustrated, for blowing air to the sheet detection mechanism 20 is instantaneously interrupted. In that case, a part of the water vapor retained inside the fixing unit 18 may enter from the sheet conveyance path via the opening portions 30d, 30f, and 31d of the sheet detection mechanism 20 and reach the light-emitting unit 28, the light-receiving unit 29, and the reflection member 36, and dew condensation may occur therein.
Thus, according to the present exemplary embodiment, water vapor generated during printing is constantly diffused during printing so as not to retain in the space enclosed by the fixing film 19a, the pressure roller 19b, and the guide units 30 and 31. In the configuration of the sheet detection mechanism 20 according to the present exemplary embodiment, the air duct sending air to the sheet detection mechanism 20 is branched into a first air duct 41 (41a and 41b) and a second air duct 42 in the middle. The first air duct 41 is used to send air to the light-emitting unit 28 and the reflection member 36 of the sheet detection mechanism 20 (a route of an arrow 41a). The second air duct 42 is used to send air to the inside of the fixing unit 18 so as to make water vapor harder to retain inside the fixing unit 18. Accordingly, in the case of instantaneous interruption of power supply to the printer main body, water vapor entering from the opening portions 30d, 30f, and 31d of the sheet detection mechanism can be reduced, and dew condensation in the light-emitting unit 28, the light-receiving unit 29, and the reflection member 36 can be suppressed. The air duct 41b is a route sending air to a mechanism other than the fixing unit 18 in the printer.
In
As illustrated in
The air blow configuration via the second air duct is not limited to the above-described configuration, and another air blow configuration may be adopted. An example of the other air blow configuration is illustrated in
According to the configuration in the present exemplary embodiment, one air duct is branched into an air duct for sending air to the optical element units of the sheet detection mechanism 20 and an air duct for sending air to the inside of the fixing unit 18, and accordingly the image forming apparatus can be miniaturized.
Next, a fifth exemplary embodiment is described. The same components and components having the same functions as those of the first to the fourth exemplary embodiments are denoted by the same reference numerals, and descriptions thereof are omitted.
A configuration is described which can improve productivity when a sheet S to be conveyed is a small size sheet. A small size sheet represents a sheet of which a width is smaller than a sheet having a maximum width which can be used in a printer in a width direction perpendicular to a conveyance direction.
When air is sent to the inside of the fixing unit via the second air duct as according to the fourth exemplary embodiment, temperatures of the fixing members such as the fixing film 19a and the pressure roller 19b are lowered. Especially, when air directly hits the fixing film 19a, the toner fixing property may be deteriorated by lowering of a surface temperature as described above. However, even when air is sent to the pressure roller 19b, there is an influence. When air is sent to the pressure roller 19b, a surface temperature of the pressure roller 19b is lowered, and the surface temperature of the fixing film 19a is also slightly lowered which abuts on the pressure roller and rotates. The lowering of temperature also affects the temperature of the heater 50, and more electricity is required to maintain the heater temperature detected by the temperature detection unit 51a at a predetermined temperature. In other words, a heat quantity to be supplied from the heater 50 to the fixing film 19a is increased by an influence of the air from the second air duct.
According to the air blow configuration by the second air duct 42 to the inside of the fixing unit 18, air is strongly blown near a center portion in a longitudinal direction (an axial direction) of the pressure roller 19b. Therefore, a temperature difference occurs in the longitudinal direction of the pressure roller 19b, the temperature near the center portion in the longitudinal direction at which the air is blown strongly becomes lower, and a temperature near an edge portion in the longitudinal direction at which the air is blown mildly becomes higher. An area near the edge portion in the longitudinal direction at which the temperature of the pressure roller 19b becomes higher corresponds to a non-sheet passing area through which a large size sheet passes but a small size sheet does not pass. Therefore, especially when printing is continuously performed on small size sheets (when fixing processing is performed), the non-sheet passing area of the pressure roller 19b further accumulates heat, and temperature is increased. Accordingly, a temperature of the non-sheet passing area detected by the temperature detection units 51b and 51c is increased.
The apparatus according to the present exemplary embodiment performs the control same as that described according to the first exemplary embodiment, more specifically, when a detected temperature of the temperature detection units 51b and 51c exceeds a predetermined threshold temperature, the apparatus suspends sheet conveyance of a next sheet (extends a sheet passing interval) until the detected temperature becomes the threshold temperature or lower. During this extended period, the fixing film 19a is rotated to eliminate temperature unevenness.
As described above, when a heat quantity to be supplied from the heater 50 to the fixing film 19a is increased, a temperature increase amount detected by the temperature detection units 51b and 51c becomes larger, and a time until the temperature reaches the above-described threshold temperature becomes shorter. In addition, a time for rotating the fixing film 19a until the temperature detected by the temperature detection units 51b and 51c becomes the threshold temperature or lower is elongated, and productivity of the sheet S is lowered. The influence thereof is larger as a width of the sheet S is narrower, namely, the non-sheet passing area is larger.
On the other hand, a sheet having narrower width generates less water vapor amount, and a water vapor amount retained inside the fixing unit 18 is reduced. Therefore, when a small size sheet is passed, an air amount necessary for preventing water vapor from retaining inside the fixing unit 18 is reduced, and an air amount sent to the inside of the fixing unit 18 via the second air duct 42 can be relatively less amount.
Thus, according to the present exemplary embodiment, an air amount to be sent to the pressure roller 19b via the second air duct 42 (see the fourth exemplary embodiment) can be changed in response to a sheet width of the sheet S. When the sheet width of the sheet S is small, the air amount to be sent to the pressure roller 19b via the second air duct is reduced in a range that the light-emitting unit 28 and the light-receiving unit 29 of a sheet detection mechanism 39 do not cause dew condensation. The air amount sent to the pressure roller 19b is reduced, and accordingly lowering of the surface temperature near the center portion in the longitudinal direction of the pressure roller 19b can be lessen, and the heat quantity to be supplied from the heater 50 to the fixing film 19a can be suppressed from increasing. In addition, the temperature increase amount in the non-sheet passing area detected by the temperature detection units 51b and 51c can be suppressed, and the productivity of the sheet S can be suppressed from lowering.
The configurations of the sheet detection mechanism 39, the lid member 32, the duct member 33, and the duct member 40 according to the present exemplary embodiment are the same as those according to the fourth exemplary embodiment, and thus descriptions thereof are omitted. According to the present exemplary embodiment, the rotation number of a fan sending air to the duct member can be changed, and the air amount supplied to the inside of the fixing unit 18 via the second air duct 42 is changed in response to the sheet width of the sheet S.
Relationships between the sheet width of the sheet S and an air amount supplied to the duct member 33 according to the present exemplary embodiment are shown in Table 1. When an air amount in the case that a sheet width W of the sheet S is A4 or larger (210 mm W) is regarded as 100%, the air amount is regarded as 75% when the sheet width W of the sheet S is A5 or larger and smaller than A4 (148 mm W<210 mm), and the air amount is regarded as 50% when the sheet width W of the sheet S is smaller than A5 (W<148 mm). According to the above-described configuration, productivity of a small size sheet can be improved while suppressing dew condensation in the light-emitting unit 28 and the light-receiving unit 29 of the sheet detection mechanism 39.
As long as a configuration is to suppress an air amount sent to the inside of the fixing unit when a small size sheet passes than an air amount sent when a maximum size sheet passes, a configuration other than that according to the present exemplary embodiment may be used. An example of an air blow configuration other than that according to the present exemplary embodiment is illustrated in
Next, a sixth exemplary embodiment is described. The same components and components having the same functions as those of the first to the fifth exemplary embodiments are denoted by the same reference numerals, and descriptions thereof are omitted.
The fixing unit 18 is provided with two sheet detection mechanisms. A first sheet detection mechanism is a non-contact type sensor which is disposed between the fixing nip portion N and the decurl roller pair 157 and optically detects the sheet S.
The non-contact type sensor according to the present exemplary embodiment includes the light-emitting unit 28 and the light-receiving unit 29 disposed inside of the first guide unit 30 on the pressure roller 19b and the reflection member 36 disposed inside of the second guide unit 31 on the fixing film 19a as described in the second exemplary embodiment. The first guide unit 30 is combined with the lid member 32 serving as a guide in the two-sided conveyance and unitized as the sheet discharge unit 70.
A second sheet detection mechanism is a contact type sensor which is disposed downstream of the decurl roller pair 157 and physically detects the sheet S. The contact type sensor includes a sensor member 104 such as a photo-interrupter disposed inside of the first guide unit 30 on the pressure roller 19b and a flag member 108 acting on the sensor member 104. The flag member 108 includes an abutment portion 105 on which the sheet S abuts, a rotation shaft 106, and a light-blocking unit 107 for blocking the light from the sensor member 104. When the sheet S abuts on the abutment portion 105, the flag member 108 rotates centering around the rotation shaft 106, and the light-blocking unit 107 blocks an optical axis of the sensor member 104. Accordingly, presence of the sheet is detected.
These sheet detection mechanisms have following functions. The non-contact type sensor is used for a case in which printing is performed on a sheet hardly transmits the light from the light-emitting unit 28 such as plain paper. The contact type sensor is used for a case in which printing is performed on a sheet easily transmits light such as an overhead projector transparency (OHT). These sensors have a function of generating a trigger signal for switching a position of the diverter 46 illustrated in
The non-contact type sensor is disposed on a position closer to the fixing nip portion N than the contact type sensor. The reason is described. A print speed is faster when printing is performed on a sheet such as plain paper detected by the non-contact type sensor than when printing is performed on a sheet such as OHT. Thus, a distance that the sheet advances from when a jam of the sheet is detected to when conveyance of the sheet is stopped at the fixing nip portion N is longer in the case of the sheet such as plain paper, and it is necessary to stop the conveyance as quickly as possible. If a distance from the fixing nip portion N to the non-contact type sensor is shortened as much as possible, a degree of bend of the sheet S when a jam occurs can be reduced, and it is easy for a user to perform jam recovery. Further, the contact type sensor is disposed downstream of the decurl roller pair 157, and the fixing unit 18 can be miniaturized. As illustrated in
In the case that a jam occurs when the sheet S passes through the fixing nip portion N, it is desirable to separate members forming the fixing nip portion N (the heating unit and the pressure member) to facilitate removal of a jammed sheet. The fixing unit 18 according to the present exemplary embodiment includes a configuration for abutting and separating the heating unit and the pressure member. According to the present exemplary embodiment, the fixing film 19a is a portion which is brought into contact with the pressure member in the heating unit brought into contact with an unfixed toner image on a sheet, and the fixing film 19a is difficult to be directly rotated. Therefore, the pressure roller 19b as the pressure member is driven to rotate, and the fixing film 19a is configured to be followingly rotated, and when the heating member and the pressure member abut on and separate from each other, the heating unit having the fixing film 19a is only moved.
Next, an abutment and separation mechanism of the fixing unit 18 is described.
A gear 120 for transmitting driving to the rotation shaft 119 is provided on one side of the rotation shaft 119. Further, gears 121 and 122 for driving the pressure roller 19b are provided, and a driving force from a motor, which is not illustrated, as a driving source installed in the image forming apparatus main body 100 is transmitted to the gears 120, 121, and 122. When it is necessary to release the fixing nip portion N, the force is transmitted to the cams 117 and 118 via the gear 120, and the cams 117 and 118 rotate. When phases of the cams 117 and 118 are changed, the power that the pressure plates 112 and 113 push down the flanges 102 and 103 is changed. Accordingly, the fixing film 19a abuts on or separates from the pressure roller 19b. When a jam occurs, the both units are separated to release the fixing nip portion N. In a state in which the fixing nip portion N is released, the sheet S jammed in the fixing unit 18 can be easily removed.
The fixing unit 18 can be attached to and detached from the image forming apparatus main body 100 for replacement of the fixing unit 18 and jam recovery by a user. As illustrated in
Configurations and operations of the sheet detection mechanism according to the present exemplary embodiment are described. First, a configuration of the non-contact type sensor is described.
Next, a configuration of the contact type sensor is described.
According to the present exemplary embodiment, in order to make a rotation range (a rotation angle) of the light-blocking unit 107 smaller than a rotation range (a rotation angle) of the abutment portion 105, the abutment portion 105 and the light-blocking unit 107 are respectively integrated with different shafts on the rotation shaft 106. More specifically, the abutment portion 105 is integrated with a rotation shaft 148, and the light-blocking unit 107 is integrated with a rotation shaft 149. A coil spring 150 is attached to the rotation shaft 148 of the abutment portion 105. The coil spring 150 urges the rotating abutment portion 105 toward a home position direction when the light-blocking unit 107 becomes unmovable in the rotation direction. An abutting portion 151 is provided at an edge portion of the rotation shaft 148 of the abutment portion 105, and an abutting portion 152 is provided at an edge portion of the rotation shaft 149 of the light-blocking unit 107. The abutting portion 151 and the abutting portion 152 abut on each other. A photo-interrupter is used as the sensor member 104. The sensor member 104 is attached to the first guide unit 30.
Next, operations of the above-described non-contact type sensor are described.
As described above, the rotation angle of the light-blocking unit 107 is made smaller than the rotation angle of the abutment portion 105, and thus a space for disposing the light-blocking unit 107 can be reduced.
First, the sheet discharge unit 70 according to the present exemplary embodiment is described.
Next, jam recovery in the fixing unit 18 is described. As illustrated in
According to the present exemplary embodiment, the reflection member 36 is used in the non-contact type sensor, however, a configuration for detecting the sheet S by reflecting light on the sheet S surface and a configuration for detecting the sheet S by arranging the light-emitting unit 28 and the light-receiving unit 29 across the sheet conveyance path can obtain the similar effects if the optical path is formed to be inclined relative to a direction perpendicular to the rotation shaft in a state in which a sheet conveyance guide is moved to a direction widening a space of the sheet conveyance path.
Further, according to the present exemplary embodiment, the non-contact type sensor is installed in the fixing unit 18, however, the present disclosure can be applied to the non-contact type sensor installed in a unit other than the fixing unit. For example, as illustrated in
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Applications No. 2016-213530, filed Oct. 31, 2016 and No. 2017-008885, filed Jan. 20, 2017 which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-213530 | Oct 2016 | JP | national |
| 2017-008885 | Jan 2017 | JP | national |
