Patent Application
20160223971
1. Field of the Invention
The present invention relates to a fixing device included in the image forming apparatus using electrophotographic technology.
2. Description of the Related Art
In general, fixing devices mounted in an image forming apparatus, such as a copying machine and a laser printer, convey a recording medium through a nip portion formed by a first fixing member and a second fixing member that are in pressure contact with each other and heat-fix an unfixed toner image onto the recording medium.
Among such fixing devices, some fixing devices include a pair of pressure mechanisms that urge both ends of the first fixing member against the second fixing member using the elastic force of a helical compression spring so that the first fixing member and the second fixing member to are in pressure contact with each other. To improve the pressure balance between the two pressure mechanism, a configuration that aligns the winding end positions of the helical compression springs disposed at both ends has been developed (refer to Japanese Patent No 3501616). However, the fixing device described in Japanese Patent No. 3501616 has the following issues. That is, by aligning the positions of the winding ends of the helical compression springs, the pressures at both the ends of the fixing member are forced to be the same. In such a technology, since at the ends of the helical compression spring, the protrusion level of the spring winding end of the coil in the axial direction of the coil is the highest, the portions in the vicinity of the spring winding ends receive a large reaction force from spring supporting portions, as indicated by outlined arrows illustrated in
In addition, a configuration that corrects the balance between the reaction forces exerted on a helical compression spring by cutting and grinding the spring terminals has been developed. However, if the helical compression spring having cut and ground spring ends is employed in fixing devices, the cost increases. In addition, the following issue arises. That is, the helical compression spring having cut and ground spring ends has a small thickness of the coil in the vicinity of the winding end and, thus, the rigidity easily decreases. If a high load is imposed on the thin coil portion, the spring deforms. As a result, the pressure in the nip portion decreases.
According to an aspect of the present invention, a fixing device for fixing a toner image onto a recording medium by conveying and heating the recording medium on which the toner image is formed at a nip portion is provided. The fixing device includes a first fixing member, a second fixing member configured to form the nip portion together with the first fixing member, a frame configured to support the second fixing member, and a pair of pressure mechanisms provided on either end of the first fax member in a longitudinal direction of the first fixing member. The pressure mechanisms urge the first fixing member against the second fixing member. Each of the pressure mechanisms includes a lever having one end supported by the frame in a rotatable manner in a pressure direction in which the first fixing member is urged and a helical compression spring disposed between a first spring support portion provided on the other end of the lever and a second spring support portion provided on the frame. The pressure mechanism urges the first fixing member against the second fixing member via the lever by an elastic force of the spring. At least one of the first spring supporting portion and the second spring supporting portion includes a first supporting area and a second supporting area closer to the spring in an axial direction of the spring than the first supporting area, the first supporting area is in contact with an area of the spring close to a winding end of the spring, and the second supporting area is in contact with an area of the spring farther away from the winding end in a winding direction of the spring than the first supporting area.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
A fixing device 72 according to the present exemplary embodiment is described below with reference to
According to the present exemplary embodiment, the fixing device 72 includes a cylindrical film 10, a heater 30 in contact with the inner peripheral surface of tine film 10, and a pressure roller 20. The heater 30 forms a fixing nip portion N2 together with the pressure roller 20 via the film 10. The fixing device 72 conveys, in the fixing nip portion N2, a recording medium having a toner image formed thereon and, simultaneously, heats the toner image. Thus, the toner image is fixed onto the recording medium. The fixing device 72 further includes a heater holder 41 that supports the heater 30, a pressure stay 42 that increases the bending rigidity, and a fixing flange 45 serving as a regulating member that regulates the movement of the film 10 in the longitudinal direction.
The film 10, the heater 30, the heater holder 41, the pressure stay 42, and the fixing flange 45 are integrated into a film unit (a first fixing member). According to the present exemplary embodiment, the fixing device 72 is configured to urge the film unit against the pressure roller 20 (a second fixing member).
The film 10 includes a base layer 11 and the release layer 12 provided on the outer surface of the base layer 11. In addition, to increase fixability, an elastic layer 13 formed of, for example, silicone rubber may be disposed between the base layer 11 and the release layer 12. If the elastic layer 13 is provided, an unfixed toner image T borne by a recording medium P can be encompassed and, thus, the heat can be uniformly provided to the toner image. It is desirable that the thickness of the elastic layer 13 be 50 μm and greater and 500 μm or less in order to reduce the warm-up time. The base layer 11 can be generated by forming a thin-wall metal having a high thermal conductivity, such as SUS or Ni, or a heat resistant resin, such as polyimide resin, a polyamide-imide resin, or PEEK, into a thin-wall flexible continuous belt. To form the release layer 12, a fluorine contained resin, such as PFA, PTFE, FEP, or a mixture thereof, is coated on the outer surface of the base layer 11. Alternatively, the outer surface of the base layer 11 is covered by a tube made of the above-described resin. To increase the durability of the release layer 12, it is desirable that the thickness of the release layer 12 be 5 μm and greater. In addition, if the release layer 12 is too thick, the thermal conductivity decreases and, thus, the fixability decreases. Accordingly, it is desirable that the thickness of the release layer 12 be 50 μm and less.
The heater holder 41 is made of liquid crystal polymer, a phenol resin, PPS, or PEEK. The heater holder 41 is formed so as to have a transverse section in the shape of a half-moon gutter. The lower surface of the heater holder 41 (a surface adjacent to the pressure roller 20) has a groove 41a having a recess shape formed along the longitudinal direction of the heater holder 41. The heater 30 is supported by the groove 41a. The film 10 is loosely fitted onto the outer periphery of the heater holder 41. Both ends of the heater holder 41 having the loosely fitting film 10 are supported by both ends of a frame 91 via the fixing flanges 45. As illustrated in
As illustrated in
The heater 30 is in contact with the inner peripheral surface of the film 10 and heats the film 10. The heater 30 includes an elongated substrate extending in the longitudinal direction. The substrate can be formed as a ceramic (e.g., alumina or aluminum nitride) substrate or a heat resistant resin (e.g., polyimide, PPS, or liquid crystal polymer) substrate. The substrate has a heating resistor layer on the back surface thereof (a surface remote from the pressure roller 20) along the longitudinal direction of the substrate. The beating resistor layer is applied to the substrate in a band-like shape. The heating resistor layer is formed of, for example, Ag/Pd (silver-palladium), RuO2, or Ta2N. In addition, the substrate has glass coat on the back surface thereof in order to protect the heating resistor layer and ensure electrical insulation. Furthermore, the substrate has a sliding layer on a surface thereof that is in contact with the inner peripheral surface of the film 10 in order to increase the slidability. The sliding layer is formed of, for example, a heat resistant resin (e.g., a polyimide or polyamide-imide resin) or glass coat. According to the present exemplary embodiment, the size of the substrate of the heater 30 is 350 mm in the longitudinal direction, 10 mm in the short direction, and 0.6 mm in the thickness direction.
The pressure stay 42 is formed into a U shape using a material having rigidity (e.g., a metal). The pressure stay 42 is disposed on the upper surface of the heater holder 41 (a surface distant from the pressure roller 20) inside the film 10. The pressure stay 42 urges both ends of the pressure stay 42 in the longitudinal direction toward the axial line of the pressure roller 20 via the fixing flange 45 supported by the frame 91. Thus, the heater 30 is urged against the surface of the pressure roller 20 via the film 10, and an inner nip N3 having a predetermined width is formed between the heater 30 and the film 10. In addition, a fixing nip N2 having a predetermined width is formed between the film 10 and the pressure roller 20. Heat necessary for the heat fixing of the unfixed toner image T is transferred from the heater 30 to the film 10 in the inner nip N3, and the heat is transferred from the film 10 to the recording medium P in the fixing nip N2. At that time, the recording medium is conveyed.
Upon receiving a print instruction, a control unit 44 drives a motor serving as a driving source to rotate a drive gear disposed at an end of the core shaft portion 21 of the pressure roller 20 in the longitudinal direction. Thus, the pressure roller 20 rotates at a predetermined circumferential velocity in a direction of an arrow. At that time, a rotary force that attempts to rotate the film 10 in a direction opposite to the rotational direction of the pressure roller 20 is exerted on the film 10 due to a frictional force generated between the surface of the pressure roller 20 and the surface of the film 10 in the fixing nip N2. In this manner, the film 10 is driven to rotate in the direction of the arrow at a circumferential velocity that is substantially the same as that of the pressure roller 20 outside the heater holder 41 with the inner peripheral surface of the film 10 in contact with the sliding layer of the heater 30.
A thermistor 35 serving as a temperature detecting unit detects the temperature of the film 10 and outputs a temperature detection signal to the control unit 44. The thermistor 35 is disposed so as to be capable of detecting the temperature of an area through which the recording medium P having any of all the sizes allowable for the fixing device 72 passes. The control unit 44 receives the temperature detection signal from the thermistor 35 and controls the power supplied to the heating resistor layer on the basis of the temperature detection signal so that the film 10 has a predetermined target temperature. In this manner, the recording medium P having the unfixed toner image T thereon is led to the fixing nip N2 along an entry guide 28 with the temperature of the film 10 maintained at the predetermined target temperature. Thereafter, the recording medium P is pinched by the film 10 and the pressure roller 20 and is conveyed. In the conveyance stage, the heat of the film 10 heated by the heater 30 and the pressure from the fax nip N2 are applied to the recording medium P. Due to the heat and pressure, the unfixed toner image T is fixed onto the surface of the recording medium P. After passing through the fixing nip N2, the recording medium P is separated from the film 10 by self stripping and is elected by the conveyance roller 26. The pressure mechanism according to the present exemplary embodiment is described below with reference to
Each of a pair of the pressure mechanisms includes a lever 84, a turning center 91b of the lever 84 and a spring support portion 93 (a second spring support portion) provided in the frame 91, and a helical compression spring 87. The pressure mechanisms are provided at either end of the film 10 in the longitudinal direction.
The lever 84 is a member having one end supported by the turning center 91b in the frame 91 in a rotatable manner in a direction in which the film 10 is pressed.
The helical compression spring 87 is disposed and compressed between a spring support portion 840 (a first spring support portion) provided at the other end of the lever 84 and a spring support portion 93 of the frame 91. The other end of the lever 84 supports a lower end 87a of the helical compression spring 87. In contrast, the spring support portion 93 is provided in the frame 91 and supports an upper end 87b of the helical compression spring 87. The spring support portion 93 has a function of regulating the height of the helical compression spring 87 so that the pressure of the helical compression spring 87 is maintained at a predetermined pressure (a specified load). According to the present exemplary embodiment, the helical compression spring 87 has a free height of 35 mm and a specified height of 27 mm upon pressurization. The lever 84 can rotate about the turning center 91b due to the elastic force of the helical compression spring 87 and exerts a pressure Ft on the fixing flange 45 via the lever 84. Thus, the lever 84 can urge the film unit against the pressure roller 20. Note that by moving the lever 84 in a direction in which the helical compression spring 87 is compressed using a cam member 95, the pressure applied in the fixing nip N2 can be released.
The spring supporting portion according to the present exemplary embodiment is described below with reference to
While the present exemplary embodiment has been described with reference to the closed-end helical compression spring, the same effect can be provided even when an open-end helical compression spring is employed.
As illustrated in
As described above, according to the present invention, the fixing device having a pair of pressure mechanisms using a helical compression spring can reduce the inclination of the helical compression spring and can reduce a decrease in the pressure in the nip portion. While the above-described exemplary embodiment has been described with reference to a right-handed helical compression spring, the same effect can be provided even when a left-handed helical compression spring is employed. That is, it is only required that the spring support areas are formed so as to be closer to the spring in the axial direction of the spring as the spring extends away from the winding end of the spring in the winding direction.
A fixing device 72 according to the present exemplary embodiment is described below with reference to
According to the present exemplary embodiment, the fixing device 72 includes a cylindrical film 10, a heater 30 in contact with the inner peripheral surface of the film 10, and a pressure roller 20. The heater 30 forms a fixing nip portion N2 together with the pressure roller 20 via the film 10. The fixing device 72 conveys, in the fixing nip portion N2, a recording medium having a toner image formed thereon and, simultaneously, heats the toner image. Thus, the toner image is fixed onto the recording medium. The fixing device 72 further includes a heater holder 41 that supports the heater 30, a pressure stay 42 that increases the bending rigidity, and a fixing flange 45 serving as a regulating member that regulates the movement of the film 10 in the longitudinal direction. The film 10, the heater 30, the heater holder 41, the pressure stay 42, and the fixing flange 45 are integrated into a film unit (a first fixing member). According to the present exemplary embodiment, the fixing device 72 is configured to urge the film unit against the pressure roller 20 (a second fixing member). The film 10 includes a base layer 11 and the release layer 12 provided on the outer surface of the base layer 11. In addition, to increase fixability, an elastic layer 13 formed of, for example, silicone rubber may be disposed between the base layer 11 and the release layer 12. If the elastic layer 13 is provided, an unfixed toner image T borne by a recording medium P can be encompassed and, thus, the heat can be uniformly applied to the toner image. It is desirable that the thickness of the elastic layer 13 be 50 μm and greater and 500 μm or less in order to reduce the warm-up time. The base layer 11 can be generated by forming a thin-wall metal having a high thermal conductivity, such as SUS or Ni, or a heat resistant resin, such as polyimide resin, a polyamide-imide resin, or PEEK, into a thin-wall flexible continuous belt.
To form the release layer 12, a fluorine contained resin, such as PFA, PTFE, FEP, or a mixture thereof, is coated on the outer surface of the base layer 11. Alternatively, the outer surface of the base layer 11 is covered by a tube made of the above-described resin. To increase the durability, it is desirable that the thickness of the release layer 12 be 5 μm and greater. In addition, if the release layer 12 is too thick, the thermal conductivity decreases and, thus, the fixability decreases. Accordingly, it is desirable that the thickness of the release layer 12 be 50 μm and less.
The heater holder 41 is made of liquid crystal polymer, a phenol resin, PPS, or PEEK. The heater holder 41 is formed so as to have a transverse section in the shape of a half-moon gutter. The lower surface of the heater holder 41 (a surface adjacent to the pressure roller 20) has a groove 41a having a recess shape formed along the longitudinal direction of the heater holder 41. The heater 30 is supported by the groove 41a. The film 10 is loosely fitted onto the outer periphery of the heater holder 41. Both ends of the heater holder 41 (in the longitudinal direction) having the loosely fitting film 10 are supported by both the ends of a frame 91 (not illustrated) via the fixing flange 45.
As illustrated in
As illustrated in
To form the release layer 24, a fluorine contained resin, such as PFA, PTFE, FEP, or a mixture thereof, is coated. Alternatively, a tube made of the above-described resin is used as the release layer 24.
According to the present exemplary embodiment, the core shaft portion 21 is formed from an iron core shaft having φ22, and the elastic layer 22 is formed of the silicone rubber having a thickness of 4 mm. The release layer 24 is formed from a PFA tube having a thickness of 50 μm.
The heater 30 is in contact with the inner peripheral surface of the film 10 and heats the film 10. The heater 30 includes an elongated substrate extending in the longitudinal direction. The substrate can be formed as a ceramic (e.g., alumina or aluminum nitride) substrate or a heat resistant resin (e.g., polyimide, PPS, or liquid crystal polymer) substrate. The substrate has a heating resistor layer on the back surface thereof (a surface remote from the pressure roller 20) along the longitudinal direction of the substrate. The heating resistor layer is applied to the substrate in a band-like shape. The heating resistor layer is formed of, for example, Ag/Pd (silver-palladium), RuO2, or Ta2N. In addition, the substrate has glass coat on the back surface thereof in order to protect the heating resistor layer and ensure electrical insulation. Furthermore, the substrate has a sliding layer on a surface thereof that is in contact with the inner peripheral surface of the film 10 in order to increase the slidability. The sliding layer is formed of, for example, a heat resistant resin (e.g., a polyimide or polyamide-imide resin) or glass coat. According to the present exemplary embodiment, the size of the substrate of the heater 30 is 350 mm in the longitudinal direction, 10 mm in the short direction, and 0.6 mm in the thickness direction.
The pressure stay 42 is formed into a U shape using a material having rigidity (e.g., a metal). The pressure stay 42 is disposed on the upper surface of the heater holder 41 (a surface remote from the pressure roller 20) inside the film 10. The pressure stay 42 urges both ends of the pressure stay 42 in the longitudinal direction toward the axial line of the pressure roller 20 via the fixing flange 45 supported by the frame 91. Thus, the heater 30 is urged against the surface of the pressure roller 20 via the film 10, and an inner nip N3 having a predetermined width is formed between the heater 30 and the film 10. In addition, a fixing nip N2 having a predetermined width is formed between the film 10 and the pressure roller 20. Heat necessary for the heat fixing of the unfixed toner image T is transferred from the heater 30 to the film 10 in the inner nip N3, and the heat is transferred from the film 10 to the recording medium P in the fixing nip N2. At that time, the recording medium is conveyed.
Upon receiving a print instruction, a control unit 44 drives a motor serving as a driving source to rotate a drive gear disposed at an end of the core shaft portion 21 of the pressure roller 20 in the longitudinal direction. Thus, the pressure roller 20 rotates at a predetermined circumferential velocity in a direction of an arrow. At that time, a rotary force that attempts to rotate the film 10 in a direction opposite to the rotational direction of the pressure roller 20 is exerted on the film 10 due to a frictional force generated between the surface of the pressure roller 20 and the surface of the film 10 in the fixing nip N2. In this manner, the film 10 is driven to rotate in the direction of the arrow at a circumferential velocity that is substantially the same as that of the pressure roller 20 outside the heater holder 41 with the inner peripheral surface of the film 10 in contact with the sliding layer of the heater 30.
A thermistor 35 serving as a temperature detecting unit detects the temperature of the film 10 and outputs a temperature detection signal to the control unit 44. The thermistor 35 is disposed so as to be capable of detecting the temperature of an area through which the recording medium P having any of all the sizes allowable for the fixing device 72 passes. The control unit 44 receives the temperature detection signal from the thermistor 35 and controls the power supplied to the heating resistor layer on the basis of the temperature detection signal so that the film 10 has a predetermined target temperature.
In this manner, the recording medium P having the unfixed toner image T thereon is led to the fixing nip N2 along an entry guide 28 with the temperature of the film 10 maintained at the predetermined target temperature. Thereafter, the recording medium P is pinched by the film 10 and the pressure roller 20 and is conveyed. In the conveyance stage, the heat of the film 10 heated by the heater 30 and the pressure from the fixing nip N2 are applied to the recording medium P. Due to the heat and pressure, the unfixed toner image T is fixed onto the surface of the recording medium P. After passing through the fixing nip N2, the recording medium P is separated from the film 10 by self stripping and is ejected by the conveyance roller 26.
The pressure mechanism according to the present exemplary embodiment is described below with reference to
Each of a pair of the pressure mechanisms includes a lever 84, a turning center 91b and a spring support portion 93 provided in the frame 91, and a helical compression spring 87. The pressure mechanisms are provided at either end of the film 10 in the longitudinal direction.
The lever 84 is a member having one end supported by the turning center 91b in the frame 91 in a rotatable manner in a direction in which the film 10 is pressed. The helical compression spring 87 is disposed and compressed between the other end of the lever 84 and a spring support portion 93 of the frame 91. The other end of the lever 84 supports a lower end 87a of the helical compression spring 87. In contrast, the spring support portion 93 is formed in the frame 91 and supports the upper end 87b of the helical compression spring 87. The spring support portion 93 has a function of regulating the height of the helical compression spring 87 so that the pressure of the helical compression spring 87 is maintained at a predetermined pressure (a specified load). According to the present exemplary embodiment, the helical compression spring 87 has a free height of 35 mm and a specified height of 27 mm upon pressurization. The lever 84 can rotate about the turning center 91b due to the elastic force of the helical compression spring 87 and exerts a pressure Ft on the fixing flange 45 via the lever 84. Thus, the lever 84 can urge the film unit against the pressure roller 20. Note that by moving the lever 84 in a direction in which the helical compression spring 87 is compressed using a cam member 95, the pressure applied in the fixing nip N2 can be released.
In the following description of the helical compression spring, the direction of an arrow R illustrated in
The pressure mechanism according to the present exemplary embodiment is characterized in that the winding direction of the helical compression spring 87R is opposite to the winding direction of the helical compression spring 87L. In the present exemplary embodiment illustrated in
The behavior of the helical compression spring 87 when the helical compression spring 87 is compressed and the effect in the above-described configuration are described below.
In addition, the slope of the central axis of the helical compression spring 87R is symmetrical to the slope of the central axis of the helical compression spring 87L with respect to the transverse plane in the middle of the film 10 in the longitudinal direction. Similarly, a pressure vector FsR of the helical compression spring 87R is symmetrical to a pressure vector FsL of the helical compression spring 87L with respect to the transverse plane in the middle of the film 10 in the longitudinal direction
According to the present exemplary embodiment, the point 84c of application of the pressure Ft is shifted toward the middle of the film in the longitudinal direction. However, a distance dL between a point 84cL of application of the pressure Ft applied to a left film guide 45 and a left nip end is the same as a distance dR between a point 84cR of application of the pressure Ft applied to a right film guide 45 and a right nip end. In addition, in the configuration according to the present exemplary embodiment, the center 87aC of the lower end, which is the point of effort of the pressure Fs, is shifted in the recording medium conveyance direction. However, a distance ML between the center 87LaC of the lower end, which is the point of effort of the left pressure Fs, and a turning center 91bL is the same as a distance MR between the center 87RaC of the lower end, which is the point of effort of the left pressure Fs, and a turning center 91bR. Accordingly, the pressures Fs applied to the turning center 91b on the right and left sides are the same. As a result, a difference in surface pressure applied to the turning center 91b between right and left is less likely to occur and, thus, the difference in fixability level between right and left portions of the image can be reduced.
For ease of understanding of the effect of the present exemplary embodiment, the pressure configuration of a comparative example is described below. In the Comparative example, the helical compression spring 87R and the helical compression spring 87L are of the same type. Accordingly, the winding directions of the helical compression spring 87R and the helical compression spring 87L are the same. In addition, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L, or the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L if the helical compression spring 87L is rotated about the axis by 180°. In Comparative example 1 described below, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the position of the winding end of the helical compression spring 87L. In contrast, in Comparative example 2 described below, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L if the helical compression spring 87L is rotated about the axis by 180°.
When the helical compression spring 87 is compressed and, thus, a pressure is generated, the lever 84 moves from the position thereof in the configuration in which an ideal helical compression spring is employed illustrated in
The result of comparison of Comparative example 1, Comparative example 2, and the present exemplary embodiment in terms of the difference in fixability in the longitudinal direction of an image is illustrated in Table 1. In addition, the result of comparison of Comparative example 1, Comparative example 2, and the present exemplary embodiment in terms of gloss level in the longitudinal direction is illustrated in Table 2.
In the evaluation, Xerox Business 4200 (75 g/m2) letter paper sheets were used as the recording media P. In addition, a uniform image that covered the entire page of the recording medium was printed as the toner image T, which was heat fixed to the recording media P using the fixing devices having the above-described configurations.
To evaluate the fixability performance, an adhesive cellophane tape was put on the toner image fixed onto the recording medium P by a surface pressure of 0.49 N/cm2 (50 gf/cm2) for one minute and, thereafter, the cellophane tape was removed. Then, evaluation was made on the basis of the level of the image failure of the toner image (caused by the removal of the cellophane tape). If the image failure exceeds 5% of the toner image, the fixability performance is evaluated as “poor”. In contrast, if the image failure is less than or equal to 5% of the toner image, the fixability performance is evaluated as “excellent”.
The gloss evaluation was made using a gloss meter available from Nippon Denshoku Industries Co., LTD. If the measured value is less than or equal to 10%, the gloss is evaluated as “poor”. If the measured value is between 10% and 13%, the gloss is evaluated as “fair”. If the measured value is greater than or equal to 13%, the gloss is evaluated as “excellent”. The fixability performance and the gloss were evaluated in the following manner. That is, three points were selected in the recording medium so as to be arranged in a direction perpendicular to the recording medium conveyance direction (hereinafter referred to as “three points in the longitudinal direction of the film 10”). The mean value of the measured values at each of the three points in the recording medium conveyance direction was calculated. The three mean values were used for evaluation in the longitudinal direction of the film. The three points in the recording medium conveyance direction are points 39.4 mm, 139.4 mm, and 239.4 mm from the leading edge of the recording medium in the recording medium conveyance direction. The three points in the longitudinal direction of the film 10 are two points 30 mm from the right edge and the left edge in a direction perpendicular to the recording medium conveyance direction and a point 107.95 mm from each of the edges (in the middle of the recording medium in the direction perpendicular to the recording medium conveyance direction).
As can be seen from the results indicated by Tables 1 and 2, according to the present exemplary embodiment, the difference in the fixability performance and the difference in the gross between right and left can be reduced more than in each of the Comparative examples 1 and 2.
The following configuration is discussed below. That is, as illustrated in
In addition, as described above, for the configuration that rotates the lever 84 using the cam member 95 and pushes up the helical compression spring 87 to compress the helical compression spring 87 to release the pressure, the effect of improvement using the present exemplary embodiment is great. Since the helical compression spring 87 is more compressed when the pressure is released than under the pressurization condition, the helical compression spring 87 bends more than under the pressurization condition. Thus, the force to straighten out the bend increases. Consequently, the force to move the lever 84 increases, and the moving distance increases. Accordingly, the difference in the surface pressure in the nip between right and left caused by the movement of the lever in the Comparative examples 1 and 2 is increased. However, according to the configuration of the present exemplary embodiment, even when the moving distance is large, the right and left levers 84 move in the opposite directions. Accordingly, the difference in the surface pressure in the nip between right and left is less likely to occur.
As described above, according to the present exemplary embodiment, the difference in fixability and gloss (uneven fixability and uneven gloss) in an image can be reduced. In addition, since the difference in the surface pressure in the nip between right and left can be reduced, the difference in the conveyance force between both the ends of a recording medium is less likely to occur and, thus, the occurrence of wrinkling on a recording medium can be prevented.
In Comparative example 1 and Comparative example 2, wear of the rotary member is accelerated at a point at which the surface pressure in the nip is high. Thus, the lifetime of the fixing device is reduced. According to the configuration of the present exemplary embodiment, the difference in the surface pressure in the nip can be reduced. Thus, the lifetime of the fixing device can be increased from that of each of Comparative example 1 and Comparative example 2.
Note that the effect to increase the recording medium conveyance performance in the fixing nip N2 of the pressure mechanism of the fixing device according to the present exemplary embodiment can be applied to recording medium conveyance devices that convey a recording medium using a nip portion formed by two rotary members (first and second rotary members) in tight contact with each other, in addition to fixing devices.
A fixing device according to the third exemplary embodiment is described below with reference to
According to the present exemplary embodiment, the winding direction of a helical compression spring 87R is opposite to the winding direction of a helical compression spring 87L. In addition, the position of the winding end of the helical compression spring 87R is substantially symmetrical to the position of the winding end of the helical compression spring 87L with respect to the transverse plane in the middle of the film 10 in the longitudinal direction. In
According to the present exemplary embodiment, when the helical compression spring 87 is compressed and thus, the pressure is generated, the lever 114 moves in a direction so that the bend of the helical compression spring 87 is released. Since the winding directions of the helical compression spring 87R and the helical compression spring 87L are opposite to each other and, in addition, the positions of the winding ends are located so as to be substantially symmetrical, the directions in which the levers 114 move to reduce the bends are symmetrical with respect to the transverse plane in the middle of the film 10 in the longitudinal direction. Accordingly, as illustrated in
In addition, the slope of the central axis of the helical compression spring 87R is symmetrical to the slope of the central axis of the helical compression spring 87L with respect to the transverse plane in the middle of the film 10 in the longitudinal direction. Similarly, a pressure vector FsR of the helical compression spring 87R is symmetrical to a pressure vector FsL of the helical compression spring 87L with respect to the transverse plane in the middle of the film 10 in the longitudinal direction.
For ease of understanding of the effect of the present exemplary embodiment, the pressure configuration of a comparative example is described below. In the comparative example, the helical compression spring 87R and the helical compression spring 87L are of the same type. Accordingly, the winding directions of the helical compression spring 87R and the helical compression spring 87L are the same. In addition, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L, or the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L if the helical compression spring 87L is rotated about the axis by 180°. In Comparative example 3 described below, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the position of the winding end of the helical compression spring 87L. In contrast, in Comparative example 4 described below, the helical compression spring 87R and the helical compression spring 87L are disposed so that the position of the winding end of the helical compression spring 87R has the same phase as the winding end of the helical compression spring 87L if the helical compression spring 87L is rotated about the axis by 180°.
Comparative example 3 is described below.
The directions in which the helical compression springs 87 move the levers 84 to straighten out the bends thereof are opposed 180° from each other. Accordingly, the positions are determined as illustrated in
According to the present exemplary embodiment, the point 84c of application of the pressure Ft is shifted so as to be close to the middle of the film 10 in the longitudinal direction of the film 10. However, the distance dL between the point 84cL of application of the pressure Ft applied to the left film guide 45 and the left nip end is the same as the distance dR between the point 84cR of application of the pressure Ft applied to the right film guide 45 and the right nip end. In addition, the center 87aC of the lower end, which is the point of effort of the pressure Fs, is shifted in the recording medium conveyance direction. However, the distance between the center 87LaC of the lower end, which is the point of effort of the left pressure Fs and the turning center 91bL is the same as the distance between the center 87RaC of the lower end, which is the point of effort of the right pressure Fs, and the turning center 91bR. Thus, the moment arms on the right and left sides are the same. As a result, according to the configuration of the present exemplary embodiment, the difference in pressure between right and left is less likely to occur.
According to the present exemplary embodiment, the y-axis component of the pressure vector FsR of the helical compression spring 87R and the y-axis component of the pressure vector FsL of the helical compression spring 87L have the same sign and, thus, the same direction. Accordingly, a force that rotates the heater holder 41 and the film 10 is negligibly generated. Consequently, an intersect angle is negligibly formed between the longitudinal axis of the film 10 and the longitudinal axis of the pressure roller 20. As described above, according to the present exemplary embodiment, uneven fixability and uneven gloss are less likely to occur in the image.
The result of comparison of the above-described Comparative examples 3 and 4 and the present exemplary embodiment in terms of the difference in fixability along the length of an image is given in Table 3. In addition, the result of comparison of Comparative examples 3 and 4 and the present exemplary embodiment in terms of the difference in gloss along the length of an image is given in Table 4.
The evaluation method is the same as that described in the second exemplary embodiment. The results in Tables 3 and 4 indicate that the configuration according to the present exemplary embodiment reduces the difference in fixability and the difference in gloss throughout an image more than the configurations of Comparative examples 3 and 4.
As described above, according to the present exemplary embodiment, the fixing device having a configuration that negligibly generates the difference in fixability and gloss throughout an image. In addition, since the difference in the surface pressure in the nip between right and left can be reduced, the difference in conveyance force between both the ends is less likely to occur and, thus, the rate of occurrence of paper wrinkling can be reduced. Furthermore, by employing the configuration according to the present exemplary embodiment, the difference in the surface pressure in the nip can be reduced and, thus, the lifetime of the fixing device can be increased.
Note that the effect of the pressure mechanism of the fixing device according to the present exemplary embodiment to improve the sheet transportability can be applied to recording medium conveyance devices that convey a recording medium using a nip portion formed by two rotary members (first and second rotary members) in tight contact with each other, in addition to fixing devices.
As another example of application, the lever 114 and the cam member 95 (i.e., a pressure release mechanism) may be removed from the configuration of the present exemplary embodiment. Even in such a case, like the present exemplary embodiment, the winding direction of the helical compression spring 87R. is set so as to be opposite to the winding direction of the helical compression spring 87L. In addition, the position of the winding end of the helical compression spring 87R is set so as to be substantially symmetrical to the position of the winding end of the helical compression spring 87L. In this manner, the fixing device that negligibly generates the difference in fixability and the difference in gloss throughout an image can be provided.
In the configuration without the lever 114 and the cam member 95 (i.e., a pressure release mechanism), the helical compression spring 87 directly applies pressure on the fixing flange 45 without using the lever 114. In such a case, in the configuration of Comparative example 3, the fixing flange 45 moves in the longitudinal direction of the film by a value equivalent to a play given by assembling of the fixing flange 45. Accordingly, the point 84c of application of the pressure Ft is shifted in the longitudinal direction of the film and, thus, the difference between the distance dL and the distance dR is generated. Consequently, the difference in the surface pressure in the nip between right and left occurs and, thus, the difference in fixability and the difference in gloss between right and left occur. In the configuration of Comparative example 4, an intersect angle is formed between the longitudinal axis of the film 10 and the longitudinal axis of the pressure roller 20. Accordingly, the difference in fixability and the difference in gloss between right and left occur. As described above, in the configurations of the comparative examples, the difference in fixability and the difference in gloss throughout an image (i.e., uneven fixability and uneven gloss) are generated. In contrast, in configurations similar to the configuration according to the present exemplary embodiment, since the fixing flanges 45 move in a right-left symmetrical manner. Thus, the difference in the surface pressure is less likely to occur. In this manner, the difference in fixability and the difference in gloss between right and left can be reduced.
An image forming apparatus according to the fourth exemplary embodiment is described below. The image forming apparatus includes the recording medium conveyance device of the present invention. Note that according to the present exemplary embodiment, description of constituent elements that are similar to those of the second exemplary embodiment is not repeated. Unlike the second exemplary embodiment, the spring support portion 93 is replaced with an upper end supporting table 130, and the position of the upper end supporting table 130 is fixed by a regulating member 94.
According to the second exemplary embodiment, by regulating the height of the helical compression spring 87 to a specified height, a predetermined pressure is obtained. However, a variation of the spring constant and a variation of the free height occur among helical compression springs. Accordingly, even when the spring lengths are regulated so as to be specified heights, a difference in pressure between right and left occurs, in reality. According to the present exemplary embodiment, by addressing the above-described issue, a configuration capable of adjusting the pressure to a predetermined pressure can be provided.
The pressure mechanism that applies the pressure Ft is described below with reference to
The upper end supporting table 130 is a spring terminal supporting member that fixedly supports the upper end 87b of the helical compression spring 87. The upper end supporting table 130 is movable in a direction in which the helical compression spring 87 is compressed. In addition, the movement of the upper end supporting table 130 is regulated in a direction in which the helical compression spring 87 is compressed by the regulating member 94.
Adjustment of the pressure is performed in the following manner. That is, the upper end supporting table 130 is moved by a jig (not illustrated) so that the pressure of the helical compression spring 87 is maintained at predetermined pressure. At that time, the pressure of the helical compression spring 87 is measured by a pressure meter attached to the jig via the upper end supporting table 130. The upper end supporting table 130 is fixed at a position at which the measured value of the pressure meter is the predetermined pressure by the regulating member 94. In this manner, the position of the upper end supporting table 130 in a pressure direction of the helical compression spring 87 is regulated relative to the frame 91 and, thus, the predetermined pressure is obtained. According to the present exemplary embodiment, the regulating member 94 is formed from a screw. The screw is screwed in the pressure direction of the helical compression spring 87, and the top end of the screw supports the upper end supporting table 130. In this manner, the position of the upper end supporting table 130 is regulated.
According to the present exemplary embodiment, the pressure mechanism is supported by the top end of the screw serving as the regulating member 94, and the position of the upper end supporting table 130 is regulated. Accordingly, the upper end supporting table 130 is easily inclined. As described above in the second exemplary embodiment, to straighten out the bend of the helical compression spring 87 occurring when the helical compression spring 87 is compressed, the helical compression spring 87 moves the lever 84 and, thus, is inclined from the direction of the pressure Ft. Consequently, the spring end surface at the upper end 87b is inclined in a direction in which the amount of compression of the helical compression spring 87 decreases and the inclination of the helical compression spring 87 from the direction of the pressure Ft increases. In this manner, the lever 84 is moved.
Accordingly, as in the second exemplary embodiment, in the present exemplary embodiment, the helical compression spring 87R having a winding direction that is opposite to the winding direction of the helical compression spring 87L is employed. In addition, the position of the winding end of the helical compression spring 87R is set so as to be substantially symmetrical to the position of the winding end of the helical compression spring 87L. As a result, an effect that is the same as the effect of the second exemplary embodiment can be obtained. That is, the difference in the surface pressure in the nip between right and left is reduced, and the difference in fixability and the difference in gloss throughout an image can be reduced.
By employing the above-described configuration, a fixing device that negligibly generates the difference in fixability and the difference in gloss throughout an image can be provided.
In addition, by employing the configuration according to the present exemplary embodiment, the difference in the surface pressure in the nip between right and left can be reduced. Thus, the difference in conveyance force between both the ends is less likely to occur. As a result, the rate of occurrence of paper wrinkling can be reduced.
Furthermore, by employing the configuration according to the present exemplary embodiment, the difference in the surface pressure in the nip can be reduced and, thus, the lifetime of the fixing device can be increased.
Note that according to the present exemplary embodiment, even when like the third exemplary embodiment, the position of the helical compression spring is changed, the same effect can be obtained.
The effect to increase the recording medium conveyance performance in the fixing nip N2 of the pressure mechanism of the fixing device according to the present exemplary embodiment can be applied to recording medium conveyance devices that convey a recording medium using a nip portion formed by two rotary members in tight contact with each other, in addition to fixing devices.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention 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 Application No. 2015-015749 filed Jan. 29, 2015 and No. 2015-074301 filed Mar. 31, 2015, which are hereby incorporated by reference herein in their entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-015749 | Jan 2015 | JP | national |
| 2015-074301 | Mar 2015 | JP | national |
