Patent Grant
9568868
The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2012-026148 filed in Japan on Feb. 9, 2012.
1. Field of the Invention
The present invention relates to an image forming apparatus including a fixing device.
2. Description of the Related Art
As a fixing device used in an image forming apparatus such as a copier, a printer, a facsimile, or an MFP including any of these, a device including a belt-shaped or film-shaped fixing member having an endlessly moving surface and having lower heat capacity, and a heat source for heating the fixing member has been known (for example, see Japanese Patent Application Laid-open No. 2007-334205, Japanese Patent Application Laid-open No. 2007-233011, Japanese Patent Application Laid-open No. 2010-032625, and Japanese Patent Application Laid-open No. 2010-217257). The provision of the fixing member with lower heat capacity can drastically reduce the energy required for heating the fixing member and shorten the warm-up time or first printing time. Here, the warm-up time refers to the time required for increasing the temperature of the fixing member when powered on, for example, from normal temperature to a predetermined printable temperature (reload temperature). The first printing time refers to the time after the reception of a printing request through printing preparation and printing operation until the completion of discharge of paper.
In the conventional fixing device described above, for surely heating a recording medium such as paper to which an image is transferred, a wider range of the fixing member is heated than a range of the fixing member where the printing medium passing a nip portion is in contact in a width direction orthogonal to the surface moving direction. Then, the temperature rise in a part of the range where the surface of the fixing member is heated, that is not in contact with the recording medium, i.e., a portion that corresponds to the outside of both ends of the recording medium in a width direction thereof becomes larger than that in a portion that is in contact with the recording medium; thus, a high-temperature portion having high temperature is formed locally on the surface of the fixing member. The high-temperature portion on the surface of the fixing member is easily formed particularly in the fixing device in which the fixing member with an endless belt form is directly heated as described in Japanese Patent Application Laid-open No. 2007-233011. The formation of the high-temperature portion on the surface of the fixing member might causes the fixing failure such as a hot-offset image or gloss unevenness when the passage of a recording medium with small width is followed by the passage of a recording medium with large width through a nip portion.
Meanwhile, in the image forming apparatus including the fixing device, there has been a request for shortening the image forming time required for forming an image on the recording medium.
Therefore, there is a need for an image forming apparatus that is capable of preventing the occurrence of fixing failure due to the inhomogeneous distribution of temperature of the fixing member in a width direction of the recording medium, which is orthogonal to a recording medium conveying direction, and is capable of shortening the image forming time required for forming the images on these recording media in the case where an image is formed on a recording medium with a size in the width direction, at a nip portion of the fixing device, less than or equal to a predetermined size, and then, an image is formed on a recording medium with the size in the width direction larger than the predetermined size.
According to an embodiment, there is provided an image forming apparatus including a fixing device. The fixing device includes a rotatable fixing member having an endlessly moving surface; a heat source that heats the fixing member; a rotatable pressing member that is pressed and comes in pressure-contact with the fixing member so as to form a nip portion therebetween; a rotary drive unit that rotationally drives the fixing member or the pressing member; and a control unit configured to control the rotary drive unit to perform heat-equalizing rotation of the fixing member and the pressing member for equalizing distribution of temperature of the surface of the fixing member in a width direction orthogonal to a recording medium conveying direction at the nip portion, after a recording medium having a size less than or equal to a predetermined size in the width direction passes the nip portion and before a recording medium having a size greater than the predetermined size in the width direction passes the nip portion. The control unit is configured to select a termination condition of the heat-equalizing rotation from among a plurality of different kinds of termination conditions based on image formation related information related to next image formation performed after the heat-equalizing rotation.
The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.
An embodiment of the present invention is described below with reference to drawings. Note that in the drawings used for describing the embodiment of the present invention, the members or components in configurations having the same function or the same shape are denoted with the same reference symbol as long as discrimination is possible, and the description is not repeated.
First, the entire configuration of an image forming apparatus according to this embodiment of the present invention is described.
In
Each of the photosensitive drums 20Y, 20C, 20M, and 20Bk is surrounded by various devices for performing image formation processing in accordance with the rotation of the photosensitive drum. Here, description is made of the photosensitive drum 20Bk performing black image formation. The photosensitive drum 20Bk is surrounded by a charging device 30Bk, a developing unit 40Bk, a primary transfer roller 12Bk as a primary transfer unit, and a cleaning device 50Bk, which perform the image formation processing along the rotation direction of the photosensitive drum 20Bk. For writing an electrostatic latent image on the charged photosensitive drum 20Bk, an optical writing device 8 as an exposing unit for light-exposing a surface of the photosensitive drum 20Bk is used.
The optical writing device 8 includes a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a reflection mirror, a rotatable polygonal mirror (polygon mirror) as a light deflector, and the like. The optical writing device 8 irradiates a surface of each of the photosensitive drums 20Y, 20C, 20M, and 20Bk with writing light (laser light) Lb on the basis of image data, so that an electrostatic latent image is formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk.
The overlapping and transferring onto the transfer belt 11 are performed so that the visible images (toner images) formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk are overlapped on and transferred to the same position of the transfer belt 11 in a process where the transfer belt 11 moves in the A1 direction in the drawing. More specifically, primary transfer bias is applied to each of the primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed to face the photosensitive drums 20Y, 20C, 20M, and 20Bk with the transfer belt 11 interposed therebetween, respectively. With the primary transfer rollers 12Y, 12C, 12M, and 12Bk to which the primary transfer bias is applied, the visual images (toner images) formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk are overlapped and transferred while the timing is displaced from the upstream side to the downstream side of the A1 direction of the transfer belt 11.
The primary transfer rollers 12Y, 12C, 12M, and 12Bk have the transfer belt 11 interposed between the primary transfer rollers 12Y, 12C, 12M, and 12Bk and the corresponding photosensitive drums 20Y, 20C, 20M, and 20Bk, thereby forming a primary transfer nip. The primary transfer rollers 12Y, 12C, 12M, and 12Bk are connected to a power supply, which is not shown, so that primary transfer bias including a predetermined direct-current voltage (DC) and/or alternating-current voltage (AC) is applied to the primary transfer rollers 12Y, 12C, 12M, and 12Bk.
The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side of the A1 direction in the drawing. The photosensitive drums 20Y, 20C, 20M, and 20Bk are provided in the image forming units which form the images of yellow, cyan, magenta, and black, respectively.
The image forming apparatus 1000 includes, in addition to the image forming units, a transfer belt unit (transferring device) 10 disposed above the photosensitive drums 20Y, 20C, 20M, and 20Bk, a secondary transfer roller 5 as a secondary transfer unit, a transfer belt cleaning device 13, and the optical writing device 8 disposed below the image forming units.
The transfer belt unit 10 includes, in addition to the transfer belt 11 as the aforementioned endless belt and the primary transfer rollers 12Y, 12C, 12M, and 12Bk, a plurality of belt supporting members such as a driving roller 72 and a driven roller 73 around which the transfer belt 11 is wound. By rotationally driving the driving roller 72, the transfer belt 11 runs around (rotate) in an arrow A1 direction in the drawing. The driving roller 72 also serves as a secondary transfer backup roller facing the secondary transfer roller 5 via the transfer belt 11. The driven roller 73 also serves as a cleaning backup roller facing the transfer belt cleaning device 13 via the transfer belt 11. Since the driven roller 73 also has a function as a tension applying unit relative to the transfer belt 11, the driven roller 73 is provided with a strength increasing unit including a spring or the like. A transferring device 71 is formed so as to include the transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the transfer belt cleaning device 13.
The secondary transfer roller 5 is disposed facing the transfer belt 11, and is rotated following the transfer belt 11. The secondary transfer roller 5 has the transfer belt 11 held between the secondary transfer roller 5 and the driving roller 72 which also serves as the secondary transfer backup roller, thereby forming a secondary transfer nip. In a manner similar to the above primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5 is also connected to a power supply, which is not shown, so that secondary transfer bias including a predetermined direct-current (DC) voltage and/or alternating-current (AC) voltage is applied to the secondary transfer roller 5.
The transfer belt cleaning device 13 is disposed facing the driven roller 73 via the transfer belt 11 and cleans the surface of the transfer belt 11. In the illustrated example, the belt cleaning device 13 includes a cleaning brush and a cleaning blade disposed abutted on the transfer belt 11. A waste toner transportation hose, which is not shown, extending from the belt cleaning device 13 is connected to the entrance of a waste toner container, which is not shown.
Moreover, the image forming apparatus 1000 includes a paper cassette (paper feeding device) 61 as a recording medium storage unit in which paper S as a recording medium is stored, a registration roller pair 4 as a recording medium feeding unit, and a paper tip sensor, which is not shown, as a recording medium tip detecting unit. The paper cassette 61 is disposed in a lower part of the body of the image forming apparatus 1000, and includes a feeding roller 3 as a recording medium feeding unit which abuts on a top surface of the uppermost sheet of paper S. When the feeding roller 3 is rotated and driven counterclockwise, the uppermost sheet S is fed toward the registration roller pair 4.
Moreover, the printer body includes a paper conveying path for letting the paper P pass the secondary transfer nip from the paper cassette 61 out of the device. The registration roller pair 4 for conveying the paper P to the secondary transfer unit (secondary transfer nip) is disposed on the upstream side in the paper conveying direction as compared with the secondary transfer roller 5 in this paper conveying path R. The registration roller pair 4 feeds the paper S conveyed from the paper cassette 61 to the secondary transfer unit (secondary transfer nip) between the secondary transfer roller 5 and the transfer belt 11 at a predetermined timing in accordance with the timing at which a toner image is formed by the image station including the image forming units. The paper tip sensor detects the arrival of the tip of the paper S at the registration roller pair 4.
Here, the paper as the recording medium includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (such as coat paper or art paper), tracing paper, OHP sheets, recording sheets, and the like. In addition to the paper cassette 61 such as the paper cassette, a manual bypass paper feeding mechanism that allows the manual supply of paper may be provided.
The image forming apparatus 1000 includes a fixing device 100 as a fixing unit for fixing the toner image on the paper S to which the toner image has been transferred, a discharging roller 7 as a recording medium discharging unit, a discharge tray 17 as a recording medium mount unit, and toner bottles 9Y, 9C, 9M, and 9Bk as toner containers. The discharging roller 7 discharges the fixed paper S out of the body of the image forming apparatus 1000. The discharge tray 17 is disposed in an upper part of the body of the image forming apparatus 1000, and has the paper S discharged out of the image forming apparatus 1000 by the discharging roller 7 mounted thereon.
The toner bottles 9Y, 9C, 9M, and 9Bk are filled with toners of yellow, cyan, magenta, and black, respectively, and are detachably attached to the bottle containers provided below the discharge tray 17 in the upper part of the printer body. A replenishment path, which is not shown, is provided between the toner bottles 9Y, 9C, 9M, and 9Bk and the developing units 40Y, 40C, 40M, and 40Bk, and through this replenishment path, the toner is supplied from the toner bottles 9Y, 9C, 9M, and 9Bk to the corresponding developing units 40Y, 40C, 40M, and 40Bk.
Although detailed illustration is omitted, the transfer belt cleaning device 13 attached to the transferring device 71 includes a cleaning brush and a cleaning blade which are provided to face and abut on the transfer belt 11. With this cleaning brush and cleaning blade, foreign substances such as the remaining toner on the transfer belt 11 are removed and the transfer belt 11 is thus cleaned. The transfer belt cleaning device 13 includes a discharging unit, which is not shown, for transporting and abandoning the remaining toner removed from the transfer belt 11.
Next, the basic operation of the image forming apparatus 1000 with the above configuration is described.
Upon the start of the image forming operation in the image forming apparatus 1000, the photosensitive drums 20Y, 20C, 20M, and 20Bk in the image forming units are rotated and driven clockwise in the drawing by a driving device, which is not shown, and surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk are uniformly charged to a predetermined polarity by the charging devices 30Y, 30C, 30M, and 30Bk. The charged surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk are irradiated with laser light from the optical writing device 8, thereby forming an electrostatic latent image on each of the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk. On this occasion, the image information provided by the exposure for the photosensitive drums 20Y, 20C, 20M, and 20Bk is image information of a single color obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. By supplying the toner to the electrostatic latent images formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk with the developing units 40Y, 40C, 40M, and 40Bk, the electrostatic latent images are made into visual images (visualized) as toner images.
Upon the start of the image forming operation, the driving roller (secondary transfer backup roller) 72 is rotated and driven counterclockwise in
After that, when the toner images on the photosensitive drums 20Y, 20C, 20M, and 20Bk have reached the primary transfer nip along with the rotation of the photosensitive drums 20Y, 20C, 20M, and 20Bk, the toner images on the photosensitive drums 20Y, 20C, 20M, and 20Bk are sequentially overlapped on and transferred to the transfer belt 11 by the transfer electric field formed at the primary transfer nip. In this manner, the full-color toner image is held on the surface of the transfer belt 11. The toner on the photosensitive drums 20Y, 20C, 20M, and 20Bk that cannot be transferred to the transfer belt 11 is removed by the cleaning devices 50Y, 50C, 50M, and 50Bk. After that, the electrification on the surfaces of the photosensitive drums 20Y, 20C, 20M, and 20Bk is eliminated by an electrification eliminator, which is not shown, thereby initializing the surface potential.
In the lower part of the image forming apparatus, the feeding roller 3 starts to rotate and drive, thereby sending the paper P from the paper cassette 61 to the conveying path. The paper P sent into the conveying path is sent to the secondary transfer nip between the secondary transfer roller 5 and the driving roller (secondary transfer backup roller) 72 in accordance with the timing determined by the registration roller pair 4. On this occasion, a transfer voltage with the polarity opposite to the polarity of the charging of the toner of the toner image on the transfer belt 11 is applied to the secondary transfer roller 5, whereby a predetermined transfer electric field is formed at the secondary transfer nip.
After that, when the toner images on the transfer belt 11 have reached the secondary transfer nip along with the running around of the transfer belt 11, the toner images on the transfer belt 11 are collectively transferred to the paper P by the transfer electric field formed at the secondary transfer nip. The remaining toner on the transfer belt 11, which cannot be transferred to the paper P, is removed by the transfer belt cleaning device 13, and the removed toner is conveyed and collected into a waste toner container, which is not shown.
After that, the paper P is conveyed to the fixing device 100, and the toner image on the paper P is fixed on the paper P by the fixing device 100. Then, the paper P is discharged out of the device by the discharging roller 7, and stored on the discharge tray 17.
The above description has been made of the image formation operation for forming the full-color image on the paper; however, a monochromatic image may be formed using any one of the four image forming units, or two- or three-color image may be formed using two or three of the four image forming units.
Next, a more specific configuration example of the fixing device 100 that can be used for the image forming apparatus 1000 with the above configuration will be described.
The fixing belt 121 is directly heated by the radiation heat from the halogen heater 123 from the inner peripheral side thereof. The nip forming member 124 is provided inside the fixing belt 121, i.e., for the inside surrounded by the inner peripheral side of the fixing belt 121, and is disposed so that the nip forming member 124 directly slides on the inner surface of the fixing belt 121 or so that the nip forming member 124 indirectly slides with a slide sheet, which is not shown, interposed therebetween.
In the example of
The fixing belt 121 includes a thin and flexible endless belt member (including a film). More specifically, the fixing belt 121 includes a base material on the inner peripheral side, which is formed using a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a release layer on the outer peripheral side formed using tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) or polytetrafluoroethylene (PTFE). The release layer provides a release property so as to avoid the adhesion of the toner. Between the base material and the release layer may be provided an elastic layer formed using a rubber material such as silicone rubber, expandable silicone rubber, or fluorine rubber. When an unfixed image is pressed and fixed, the presence of the elastic layer such as a silicone rubber layer makes it less probable to cause the microscopic unevenness on the surface of the belt to be transferred to the image with gloss unevenness like an orange peel surface (orange peel surface image) and to remain on the solid part of the image. In order to prevent the occurrence of the gloss unevenness like an orange peel surface (orange peel surface image) effectively, for example, the silicone rubber layer preferably has predetermined thickness or more (for example, 100 [μm] or more). By the deformation of the silicone rubber layer, the microscopic unevenness of the belt surface is absorbed to improve the orange peel surface image.
The pressing roller 122 includes: a core metal 122a; an elastic layer 122b provided on the outer peripheral surface side of the core metal 122a and including expandable silicone rubber, silicone rubber, fluorine rubber, or the like; and a release layer 122c provided for a surface of the elastic layer 122b and including PFA, PTFE, or the like. The pressing roller 122 is pressed toward the fixing belt 121 by a pressing unit such as a spring, which is not shown, and abuts on the nip forming member 124 via the fixing belt 121. At a portion where the pressing roller 122 and the fixing belt 121 are in pressure-contact with each other, the elastic layer 122b of the pressing roller 122 is crushed to form the nip portion N with predetermined width.
The pressing roller 122 is configured to rotate and drive by transmission of a driving force applied via a gear or the like from a drive source such as a motor, which is not shown, provided for the body of the image forming apparatus 1000. The rotation and driving of the pressing roller 122 transmits its driving force to the fixing belt 121 at the nip portion N, thereby driving the fixing belt 121 to rotate together.
The fixing belt 121 is rotated following the pressing roller 122. In the configuration example of
Although the pressing roller 122 is a solid roller in this embodiment, the pressing roller 122 may be a hollow roller. In the latter case, the inside of the pressing roller 122 may be provided with a heat source such as a halogen heater. In the absence of the elastic layer, the heat capacity is reduced to improve the fixing property; however, there is a risk of gloss unevenness caused in the solid part of the image due to the transfer of the microscopic unevenness on the belt surface to the image when the unfixed toner is crushed for fixture. To prevent this, the elastic layer is desirably provided with a thickness of 100 [μm] or more. By the provision of the elastic layer with a thickness of 100 [μm] or more, the microscopic unevenness can be absorbed due to the elastic deformation of the elastic layer 122b; therefore, the occurrence of the gloss unevenness can be avoided.
The elastic layer 122b of the pressing roller 122 may be solid rubber. When there is no heat source inside the pressing roller 122, rubber with high heat-insulating property such as sponge rubber may be used as the elastic layer 122b. The use of the rubber with high heat-insulating property such as sponge rubber makes it difficult to take the heat off from the fixing belt 121, which is more desirable. The fixing member such as the fixing belt 121 which is the heating rotator and the pressing member such as the pressing roller 122 which is the counter rotator may have the configuration in which, instead of being in pressure contact with each other, they are simply in contact with each other without pressure application.
Both ends of the halogen heater 123 are fixed to a side plate 142 of the fixing device 100 (see
The nip forming member 124 includes a base pad 131, and a slide sheet (low-friction sheet) 130 provided on a surface of the base pad 131. The base pad 131 is provided in a rectangular form continuously in an axial direction of the fixing belt 121 or an axial direction of the pressing roller 122, and determines the shape of the nip portion N by receiving the pressure force from the pressing roller 122.
The base pad 131 of the nip forming member 124 is fixed and supported by the stay 125. This can prevent the nip forming member 124 from being bent by the pressure of the pressing roller 122 and provide the uniform nip width along the axial direction of the pressing roller 122.
The base pad 131 of the nip forming member 124 is formed using a heat-resistance member that can resist a temperature of 200° C. or more. Thus, the thermal deformation of the nip forming member 124 in the toner fixing temperature range is prevented and the stable state of the nip portion N is secured to stabilize the output image quality. For the base pad 131, general heat-resistant resin can be used such as polyether sulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyether nitrile (PEN), polyamide imide (PAI), or polyether ether ketone (PEEK).
The slide sheet 130 may be disposed on at least a surface of the base pad 131 that faces the fixing belt 121. Thus, the fixing belt 121 slides relative to the low-friction sheet during the rotation of the fixing belt 121, so that the drive torque in the fixing belt 121 is reduced, thereby reducing the load on the fixing belt 121 by the friction power. Note that the slide sheet may be omitted.
The stay 125 is desirably formed using a metal material with high mechanical strength, such as stainless steel or iron for satisfying the anti-bending function of the nip forming member 124. The base pad 131 is also desirably formed using a material with a certain degree of hardness for securing the strength. As the material for the base pad 131, a resin such as liquid crystal polymer (LCP), metal, ceramic, or the like can be used.
The reflecting member 126 is disposed between the stay 125 and the halogen heater 123. In this embodiment, the reflecting member 126 is fixed to the stay 125. As the material for the reflecting member 126, aluminum, stainless steel, or the like is given. By the provision of the reflecting member 126, the light (radiation heat) radiated from the halogen heater 123 toward the stay 125 is reflected to the fixing belt 121. This can increase the amount of light of the radiation heat delivered to the fixing belt 121, so that the fixing belt 121 can be efficiently heated. Instead of providing the reflecting member 126, a surface of the stay 125 or the like may be subjected to mirror surface processing to provide the similar effect.
Various configuration devises have been made on the fixing device 100 according to this embodiment for further improving energy saving property and the first printing time and the like.
Specifically, the fixing belt 121 can be directly heated at a portion other than the nip portion N by the halogen heater 123 (direct heating type). In this embodiment, nothing is interposed between the halogen heater 123 and the left part of the fixing belt 121 in
For reducing the heat capacity of the fixing belt 121, the fixing belt 121 is reduced in thickness and diameter. Specifically, the thicknesses of the base material, the elastic layer, and the separation type layer of the fixing belt 121 are set in the range of 20 to 50 [μm], 100 to 300 [μm], and 10 to 50 [μm], respectively, so that the total thickness is set to 1 [mm] or less. The diameter of the fixing belt 121 is set in the range of 20 to 40 [mm]. For further reducing the heat capacity, the thickness of the entire fixing belt 121 is desirably set to 0.2 [mm] or less, and more desirably to 0.16 [mm] or less. The diameter of the fixing belt 121 is desirably set to 30 [mm] or less.
Note that in this embodiment, the diameter of the pressing roller 122 is set in the range of 20 to 40 [mm], and the diameter of the fixing belt 121 and the diameter of the pressing roller 122 are configured to be equal to each other. However, the configuration is not limited to this. For example, the diameter of the fixing belt 121 may be smaller than that of the pressing roller 122. In this case, the curvature of the fixing belt 121 at the nip portion N is smaller than that of the pressing roller 122, so that the paper (recording medium) P discharged from the nip portion N is easily separated from the fixing belt 121.
As a result of reducing the diameter of the fixing belt 121 as mentioned above, the space inside the fixing belt 121 is reduced. However, when the stay 125 is formed to have a concave shape with the both sides folded, and houses the halogen heater 123 inside the concave shape, the stay 125 and the halogen heater 123 can be disposed inside the small space.
As illustrated in
Moreover, as illustrated in
Although not illustrated, a blocking member for blocking the heat from the halogen heater 123 is provided between the fixing belt 121 and the halogen heater 123 at each end of the fixing belt 121 in the axial direction. This can suppress excessive temperature rise in a paper non-feeding region of the fixing belt during the continuous paper feeding, and prevent thermal deterioration or damage of the fixing belt.
A basic operation example of the fixing device 100 according to this embodiment is described with reference to
By turning on a power supply switch (main power supply ON) of the image forming apparatus 1000 body, the warm-up operation is started. Specifically, the power is supplied to the halogen heater 123, and the pressing roller 122 starts to rotate and drive clockwise in
When the fixing belt 121 has reached the predetermined temperature, the power supply to the halogen heater 123 is turned off to drop the temperature of the fixing belt 121 to the fixing temperature. After that, the paper P carrying an unfixed toner image T in the aforementioned image forming process is conveyed in an arrow A1 direction of
The paper P with the toner image T fixed thereon is conveyed in an arrow A2 direction of
Upon the completion of the image forming operation, the fixing device moves on to the stand-by mode with the temperature of the fixing belt 121 maintained at predetermined temperature (90° C. in this embodiment) lower than the fixing temperature, or a sleep mode (energy-saving mode) with the power supply to the halogen heater 123 or the rotation and driving of the pressing roller 122 stopped. Whether the mode is set to the stand-by mode or the sleep mode after the image forming operation can be set from an operation unit 151 (see
The fixing device 100 illustrated in
In order to dispose the stay 125 as large as possible in the small space, the nip forming member 124 is formed to be small, on the contrary, in the fixing device 100 illustrated in
For further securing the strength of the stay 125, in this embodiment, the stay 125 includes a base part 125a extending in the paper conveying direction (upward and downward in
The strength of the stay 125 is improved when the rising part 125b of the stay 125 is formed longer in the abutting direction of the pressing roller 122. A tip of the rising part 125b desirably faces as close to the inner peripheral surface of the fixing belt 121 as possible. However, the rotation involves a certain degree of vibration (disorder of behavior) of the fixing belt 121; therefore, when the tip of the rising part 125b is too close to the inner peripheral surface of the fixing belt 121, there is a risk that the fixing belt 121 touches the tip of the rising part 125b. In particular, in the configuration including the thin fixing belt 121 as in this embodiment, the vibration of the fixing belt 121 is intense; in this case, the position of the tip of the rising part 125b needs to be carefully set.
Specifically, in this embodiment, the distance d between the tip of the rising part 125b of the stay 125 and the inner peripheral surface of the fixing belt 121 in the abutting direction of the pressing roller 122 is preferably at least 2.0 [mm], desirably 3.0 [mm] or more. Meanwhile, when the fixing belt 121 is thick to some extent to cause almost no vibration, the distance d can be set to 0.02 [mm]. When the reflecting member 126 is attached to the tip of the rising part 125b as in this embodiment, the distance d needs to be set so that the reflecting member 126 does not touch the fixing belt 121.
By disposing the tip of the rising part 125b of the stay 125 as close to the inner peripheral surface of the fixing belt 121 as possible, the rising part 125b can be disposed long in the abutting direction of the pressing roller 122. Thus, even in the configuration including the fixing belt 121 with small diameter, the mechanical strength of the stay 125 can be improved.
In the fixing device 100 in the configuration example illustrated in
In the fixing device 100 in the configuration example illustrated in
Moreover, when the nip forming member 124 also functions as a guide, an additional guide is not necessary, in which case nothing is necessary between the inner peripheral surface of the fixing belt 121 and the upstream side part and the downstream side part of the stay 125 in the paper conveying direction (so that they face each other directly). This allows the stay 125 to be disposed as large as possible in the limited space in the fixing belt 121 because the stay 125 can be disposed close to the inner peripheral surface of the fixing belt 121 on the upstream side and the downstream side of the paper conveying direction. As a result, even in the configuration in which the fixing belt 121 is reduced in diameter for the reduction in heat capacity like in the fixing device 100 in the above configuration example, the strength of the stay 125 can be secured and the bending of the nip forming member 124 by the pressing roller 122 can be prevented and the fixing property can be improved.
Moreover in the fixing device 100 in the configuration examples illustrated in
In the case of the device in which the rotation speed of the pressing roller 122 is high and the number of sheets of paper fed in a minute is large, a thermistor (pressing thermistor) for detecting the temperature of the pressing roller 122 may be provided. In a high-speed machine with the rotation speed of the pressing roller 122 set high, the shortage of the quantity of heat of the fixing belt 121 easily occurs. Therefore, in the warm-up operation, the surface temperature of the pressing roller 122 is detected by the pressing thermistor, and when the surface temperature of the pressing roller 122 and the surface temperature of the fixing belt 121 have reached their predetermined temperatures, the fixing operation is started. A thermistor detecting the temperature of the pressing roller 122 may be added in the paper non-feeding region of the pressing roller 122. For example, when sheets of paper with a small size are continuously fed, there is a risk that the end of the pressing roller 122 or the fixing belt 121 has abnormally high temperature to cause malfunction of the device. Therefore, to avoid the malfunction, the thermistor disposed in this paper non-feeding region detects the temperature and when the temperature has reached the predetermined temperature or more, the device is controlled to stop.
A control unit 200 as a controller includes a controller unit 200a and an engine control unit 200b.
The controller unit 200a includes a CPU, a ROM, a RAM, and the like, and is connected to the engine control unit 200b, the operation unit 151, an external communication interface unit 152, and the like. The controller unit 200a executes a preinstalled control program to control over the entire image forming apparatus 1000 or over the input from the external communication interface unit 152 or the operation unit 151, for example. The controller unit 200a accepts the input of an instruction from a user, which has been input through the operation unit 151, and performs various types of processing in accordance with the input of the instruction, for example. The controller unit 200a receives image data or an instruction of a print job (image forming job) from an external host computer device or the like via the external communication interface unit 152, controls the engine control unit 200b, and controls the image forming operation for forming and outputting a color image or a monochromatic image onto the paper. The controller unit 200a also has a function as a measuring unit for measuring the time for idling the fixing belt 121 and the pressing roller 122 for equalizing the temperature more quickly by decreasing the temperature of the high-temperature part of the fixing belt 121.
The engine control unit 200b includes a CPU, a ROM, a RAM, and the like and by executing the preinstalled control program, performs the control over a printer engine (the image forming units, the optical writing device 8, the fixing device 100, and the like) for performing the image formation operation on the basis of the instruction from the controller unit 200a. For example, in the image forming operation mode, the engine control unit 200b controls the power supply to the halogen heater 123 or controls a pressing roller driving unit 129 for rotating and driving the pressing roller 122 so that the temperature of the fixing belt 121 detected by the temperature sensor 127 becomes a predetermined target temperature.
The image forming apparatus 1000 according to this embodiment has three modes: the image forming operation mode; the stand-by mode; and the sleep mode. The image forming operation mode refers to the state in which the image forming apparatus 1000 performs the image formation operation. The stand-by mode refers to the state in which the image forming apparatus 1000 waits for the execution instruction of the image formation operation. The sleep mode refers to the state in which the power consumption is lower than that in the stand-by mode. In the image forming operation mode, for example, in the fixing device 100, the warm-up operation for increasing the temperature of the fixing belt 121 to a predetermined fixing target temperature (for example 158 to 170° C.) is performed and then the fixing operation is performed. In the stand-by mode, the temperature of the fixing belt 121 in the fixing device 100 is maintained at a predetermined temperature (for example 90° C.) lower than the fixing target temperature in the image forming operation mode. In the sleep mode, the power supply to the printer engine or the engine control unit 200b in the fixing device 100 or the like is stopped, so that the power supply to the halogen heater 123 and the rotation and driving of the pressing roller 122 are impossible.
Next, the control over the fixing temperature of the fixing device in the image forming apparatus with the above configuration will be described.
As illustrated in
The center-heating halogen heater 123a of the fixing device 100 illustrated in
To prevent this abnormal image, after the execution of the continuous image forming jobs, heat-equalizing rotation is performed for equalizing the temperature of the fixing belt 121 by reducing the temperature of the high-temperature portions in such a manner that only the fixing belt 121 and the pressing roller 122 are idled with the paper P not conveyed. However, if the constant heat-equalizing rotation is always performed after the execution of the continuous image forming jobs, constant waiting time is generated, which causes the completion time of the next image forming job to be late by the amount of the waiting time. This results in that the total printing time becomes longer.
In view of this, the present inventors have conducted concerted studies and found that it is effective to appropriately select the termination condition of the heat-equalizing rotation depending on the content of the next image forming job as the image formation related information related to the next image formation to be performed after the heat-equalizing rotation. In other words, it has been found that the occurrence of the fixing failure due to the unequal distribution of the temperature of the fixing belt 121 in the width direction can be prevented and the image forming time required for forming the image on the paper P can be shortened by appropriately selecting the termination condition such as the temperature of the fixing belt 121 or the time of the heat-equalizing rotation on the basis of the image information such as whether the image to be formed according to the next image forming job is the full-color image or the monochromatic image or of the image formation related information such as the size magnitude correlation of the paper P fixed and conveyed according to the previous job and the next job.
Moreover,
As indicated in
The control of the heat-equalizing rotation will be specifically described using the flow chart of
Upon the start of the image forming operation, the control of the heat-equalizing rotation (hereinafter, “control A”) is performed (Step S1). During the control A, state transition into another control is prohibited. Upon the completion of the execution of the previous job (here, the first job), whether the next job has been decided or not is determined (Step S2). If the next job has been decided (Yes in Step S2), the paper width of the next job and the paper width of the previous job are compared (Step S3). Meanwhile, if the next job has not been decided (No in Step S2), the heat-equalizing rotation for the full-color image is performed in view of the safety. Then, when the paper width of the next job is larger than that of the previous job (Yes in Step S3), whether the next job is the full-color image (FC) printing or not is determined (Step S4); when the paper width of the next job is smaller than or equal to that of the previous job (No in Step S3), the control A terminates because no abnormal image is formed. In this case, the termination of the control A does not lead to the heat-equalizing rotation; therefore, there is no waiting time for the heat-equalizing rotation and thus, the printing time for the next job is shortened.
In the case where the next job is the full-color image (FC) mode in Step S4 (Yes in Step S4), determination of transition condition A1 is performed (Step S5); in the case where the next job is not the full-color image (monochromatic (B/W)) mode (No in Step S4), determination of transition condition A2 is performed (Step S6).
Here, the determination of transition condition A1 in Step S5 is the process for determining the termination condition of the heat-equalizing rotation on the basis of the condition of the previous job from the condition determination table in Table 1 below, by which “when next job is unknown or FC mode” is selected.
In the condition determination table in Table 1, a plurality of termination conditions are set for each paper width of the previous job. For example, when the paper width L of the previous job satisfies B4T<L≦DLT (257 [mm]<L≦279.4 [mm]) and the paper feeding time t1 of the previous job satisfies t1<set time 101, the termination condition of the heat-equalizing rotation is set as follows: detection temperature (written as “sensor temperature” in Table 1, and this similarly applies to the following description) of the thermistor 127d≦120[° C.]; and control A passage time t2=0. When the paper width L of the previous job is the same and the paper feeding time t1 of the previous job satisfies set time 101≦t1, the termination condition of the heat-equalizing rotation is set as follows: detection temperature of the thermistor 127d≦120[° C.]; and set time 102≦control A passage time t2.
Similarly, the determination of transition condition A2 of Step S6 is the process for determining the termination condition of the heat-equalizing rotation on the basis of the condition of the previous job from the condition determination table in Table 1, by which “when next job is B/W mode” is selected. For example, when the paper width L of the previous job satisfies B4T<L≦DLT (257 [mm]<L≦279.4 [mm]) and the paper feeding time t1 of the previous job satisfies t1<set time 101, the termination condition of the heat-equalizing rotation is set as follows: detection temperature as the sensor temperature of the thermistor 127d≦125[° C.]; and control A passage time t2=0. When the paper width L of the previous job is the same and the paper feeding time t1 of the previous job satisfies set time 101≦t1, the termination condition of the heat-equalizing rotation is set as follows: detection temperature of the thermistor 127d≦125[° C.]; and set time 102 control A passage time t2.
In this manner, in the example of the condition determination table in Table 1, the sensor temperature is set differently between when the next job is unknown or FC mode and when the next job is B/W mode, for each paper width L of the previous job. The monochromatic image (B/W) has a wider allowance for the abnormal image such as hot offset or gloss unevenness than the full-color image (FC); therefore, the temperature can be set higher for the monochromatic image in the termination condition for the heat-equalizing rotation. Thus, in the case where the next job is the monochromatic image printing (B/W mode), the waiting time of the heat-equalizing rotation can be shortened as compared with the full-color (FC) image printing; therefore, the printing time of the next job can be shortened.
In Table 1 above, for example B4T represents the paper width when a B4-sized sheet of paper is fed in portrait orientation, DL represents an 11×7-inch-sized sheet of paper, and LT represents an 8½×11-inch-sized sheet of paper, which is often used abroad. Moreover, the temperature of the paper non-feeding part where the paper P does not pass is gradient in the axial direction; therefore, the reference value relative to the sensor temperature (detected temperature) is set in accordance with the paper width as appropriate (for example, 120[° C.], 125[° C.], 140[° C.], 145[° C.], 150[° C.], 155[° C.], 200[° C.], and 210[° C.] in Table 1). The set time 101, 103, 105, 107, 109, and 111 in Table 1 represent the reference time set in advance relative to the previous job paper feeding time t1. The set time 102, 104, 106, 108, 110, and 112 in Table 1 represent the reference time set in advance relative to the control A passage time t2.
Then, in the case where the next job is the full-color image, the determination of transition condition A1 is performed in Step S5, and the heat-equalizing rotation of the fixing belt 121 is started (Step S7). The heat-equalizing rotation is continued until the condition of the transition condition A1 is satisfied (Step S8). For example, when the paper width L of the previous job satisfies B4T<L≦DLT (257 [mm]<L≦279.4 [mm]) and the paper feeding time t1 of the previous job satisfies the set time 101≦t1, the heat-equalizing rotation ends upon the satisfaction of the condition of the detected temperature of the thermistor 127d≦120[° C.] or the set time 102≦control A passage time t2 (Step S9).
Meanwhile, when the next job is not the full-color image, the determination of transition condition A2 is performed in Step S6, and the heat-equalizing rotation of the fixing belt 121 is started (Step S10). The heat-equalizing rotation is continued until the condition of the transition condition A2 is satisfied (Step S11). For example, when the paper width L of the previous job satisfies B4T<L≦DLT (257 [mm]<L≦279.4 [mm]) and the paper feeding time t1 of the previous job satisfies the set time 101≦t1, the heat-equalizing rotation ends upon the satisfaction of one of or both the condition of the detected temperature of the thermistor 127d≦125[° C.] and the condition of the set time 102≦control A passage time t2 (Step S12).
As described using the flow chart of
Although not indicated in Table 1, the hot offset or gloss unevenness easily occurs in a half-tone image; therefore, the termination condition of the heat-equalizing rotation may be set a little higher as long as the image is letter script. As for the resolution of the image, the temperature for a low-resolution image may be set higher than that for a high-resolution image.
The detection may be performed not based on the temperature but based on the experimentally obtained numeral value and the number of sheets of paper and time of the previous job to set the heat-equalizing rotation time.
The control for shortening the time of the heat-equalizing rotation can be applied to not just the heat-equalizing rotation performed between the continuous different jobs but also to the heat-equalizing rotation performed in the case where the size is switched to the larger paper width size in one job.
Moreover, during the heat-equalizing rotation, turning off the halogen heater 123 is more effective for shortening the heat-equalizing rotation time because the temperature of the high-temperature portion of the fixing belt 121 is dropped more quickly.
The above described is an example, and the present invention provides the unique effect for every aspect described below.
Aspect A
The image forming apparatus 1000 includes the fixing device 100, and the fixing device 100 includes: the fixing member such as the rotatable fixing belt 121 having an endlessly moving surface; the heat source such as the halogen heater 123 that heats the fixing member; the pressing member such as the rotatable pressing roller 122 that is pressed and comes in pressure-contact with the fixing member so as to for a nip portion therebetween; and the rotary drive unit such as the pressing roller driving unit 129 that rotationally drives the fixing member or the pressing member. Further provided is the control unit such as the control unit 200 configured to control the rotary drive unit to perform heat-equalizing rotation of the fixing member and the pressing member for equalizing distribution of temperature of the surface of the fixing member in a width direction orthogonal to a recording medium conveying direction at the nip portion N, after a recording medium such as paper P having a size less than or equal to a predetermined size in the width direction passes the nip portion N and before a recording medium having a size greater than the predetermined size in the width direction passes the nip portion N. The control unit is further configured to select a termination condition of the heat-equalizing rotation from among a plurality of different kinds of termination conditions based on image formation related information related to next image formation performed after the heat-equalizing rotation.
According to this aspect, as described in the embodiment, the heat-equalizing rotation of the fixing member and the pressing member for equalizing the distribution of the temperature of the surface of the fixing member in the width direction is performed after the recording medium having a size less than or equal to a predetermined size in the width direction orthogonal to the recording medium conveying direction passes the nip portion N and before the recording medium having a size greater than the predetermined size in the width direction passes the nip portion N. This heat-equalizing rotation can prevent the occurrence of fixing failure that is caused by the inhomogeneous distribution of the temperature of the fixing member in the width direction. As the termination condition of the heat-equalizing rotation, any one of the plurality of different kinds of termination conditions is selected based on the image formation related information related to the next image formation performed after the heat-equalizing rotation; on the basis of the selected termination condition, the heat-equalizing rotation is terminated. Since the appropriate termination condition for the heat-equalizing rotation is thus selected in accordance with the image formation related information, the image forming time required for forming an image on the recording medium can be shortened as compared with the case in which the heat-equalizing rotation is completed under the same termination condition regardless of the image formation related information.
Aspect B
In Aspect A described above, the image forming apparatus further includes a temperature detecting unit such as a temperature sensor that detects temperature of at least one of members constituting the fixing device 100. The termination conditions include a condition that a detection result of the temperature detecting unit matched with a predetermined temperature set in advance. According to this aspect, as described in the embodiment, the termination condition of the heat-equalizing rotation involving the rotation of the fixing member is selected based on the detection result of the temperature of at least one of the members constituting the fixing device 100 related to the temperature of the surface of the fixing member forming the nip portion through which the recording medium passes; therefore, the heat-equalizing rotation is performed neither too much nor too little in accordance with the temperature of the surface of the fixing member, thereby increasing the accuracy of the control for equalizing the distribution of the temperature of the surface of the fixing member in the width direction.
Aspect C
In Aspect B described above, the temperature detecting unit such as the temperature sensor 127 detects the temperature of the fixing member such as the fixing belt 121. According to this aspect, as described in the embodiment, the termination condition of the heat-equalizing rotation involving the rotation of the fixing member is selected based on the detection result of the temperature of the fixing member forming the nip portion through which the recording medium passes; therefore, the accuracy of the control for equalizing the distribution of the temperature on the surface of the fixing member in the width direction can be further increased.
Aspect D
In any of Aspects A to C described above, the plural kinds of termination conditions include the condition that a predetermined time has passed from start of the heat-equalizing rotation. According to this aspect, as described in the embodiment, the termination condition of the heat-equalizing rotation involving the rotation of the fixing member is selected based on the predetermined passage time obtained in advance from experiments or the like; therefore, the accuracy of the control for equalizing the distribution of the temperature of the surface of the fixing member in the width direction can be further increased.
Aspect E
In any of Aspects A to D described above, the image formation related information related to the next image formation performed after the heat-equalizing rotation is image information of an image formed after the heat-equalizing rotation. According to this aspect, as described in the embodiment, the termination condition of the heat-equalizing rotation involving the rotation of the fixing member is selected based on the image information of the image formed after the heat-equalizing rotation; therefore, the accuracy of the control for equalizing the distribution of the temperature of the surface of the fixing member in the width direction can be further increased. For example, in the case where the image formed after the heat-equalizing rotation is a monochromatic image, the fixing failure is difficult to occur even though the accuracy of the control for equalizing the distribution of the temperature of the surface of the fixing member in the width direction is slightly worse than that for a full-color image; therefore, the temperature can be set higher or the time can be set shorter in the termination condition of the heat-equalizing rotation. In this manner, the occurrence of the fixing failure can be prevented more surely in accordance with the image formed after the heat-equalizing rotation, and the image forming time required for forming the image on the recording medium can be shortened more surely.
Aspect F
In any of Aspects A to D described above, the image formation related information related to the next image formation performed after the heat-equalizing rotation is the size information in the width direction of a recording medium on which an image is formed after the heat-equalizing rotation. According to this aspect, as described in the embodiment, the termination condition of the heat-equalizing rotation involving the rotation of the fixing member is selected based on the size information of the recording medium in the width direction on which the image is formed after the heat-equalizing rotation; therefore, the accuracy of the control for equalizing the distribution of the temperature on the surface of the fixing member in the width direction can be further increased. For example, in the case where the size of the recording medium in the width direction on which the image is formed after the heat-equalizing rotation is less than or equal to the size of the recording medium in the width direction which has passed the nip portion N before the heat-equalizing rotation, the fixing failure due to the unequal distribution of the temperature in the width direction of the fixing member does not occur; therefore, the heat-equalizing rotation is not necessary, in which case the image forming time required for forming the image on the recording medium can be shortened more surely.
Aspect G
In any of Aspects A to F described above, when the image formation related information related to the next image formation performed after the heat-equalizing rotation cannot be acquired, the control unit selects and uses, from among the plural kinds of termination conditions, a termination condition under which the longest heat-equalizing rotation is performed. According to this aspect, as described with reference to the above embodiment, when the image formation related information related to the next image formation performed after the heat-equalizing rotation cannot be acquired, i.e., when the next image job is unknown, the control unit selects and uses, from among the plural kinds of termination conditions, the termination condition (termination condition under which the longest heat-equalizing rotation (in the embodiment, the heat-equalizing rotation for the full-color image) is performed; therefore, the sufficient heat-equalizing rotation is performed in view of the safety. Thus, the occurrence of the fixing failure due to the inhomogeneous distribution of the temperature of the fixing member in the width direction can be prevented more surely.
Aspect H
In any of Aspects A to G described above, in the case of performing a plurality of image forming jobs continuously in which recording media for having images formed thereon are different in size in the width direction, the control unit performs the heat-equalizing rotation after the recording medium at a completion time of the image forming job for forming the image on the recording medium with a size less than or equal to a predetermined size passes the nip portion N and before the recording medium at a start time of the next image forming job for forming the image on the recording medium with a size greater than the predetermined size passes the nip portion, and the image formation related information related to the next image formation performed after the heat-equalizing rotation is information of the next image forming job. According to this aspect, as described in the embodiment, in the case of performing the plurality of image forming jobs continuously in which recording media for having images formed thereon are different in size in the width direction, control is performed so as to select the termination condition of the heat-equalizing rotation involving the rotation of the fixing member based on the information of the next image forming job; therefore, the accuracy of control for equalizing the distribution of the temperature on the surface of the fixing material in the width direction can be increased.
Aspect I
In any of Aspects A to H described above, the pressing member is configured to be rotationally driven, the fixing member has a hollow internal space capable of housing therein the heat source such as the halogen heater 123, and is a belt member or a film member capable of being driven in accordance with the pressing member which is rotationally driven, and the fixing device 100 further includes the nip forming member 124 provided in the internal space of the fixing member so as to form the nip portion N under pressure applied from the pressing member via the fixing member.
According to this aspect, as described in the embodiment, the predetermined nip portion can be formed between the fixing member and the pressing member by making the nip forming member provided in the internal space of the fixing member receive the pressure applied from the pressing member via the fixing member. The fixing member is heated by the heat source disposed in the hollow internal space and is driven following the pressing member which is rotationally driven, so that the temperature of the nip portion moving by the contact between the fixing member and the pressing member can be maintained at predetermined temperature necessary for the fixture.
Moreover, since the fixing member formed of the belt member heated by the heat source has smaller heat capacity than the fixing member formed of a roller member or the like, the energy required for heating the fixing member can be drastically reduced, the energy-saving property can be improved, and the warm-up time and first printing time can be shortened. Moreover, even in the case of the use of the fixing member which easily has a high-temperature portion in which the temperature is locally high when a small recording medium with a small size in the width direction passes through the nip portion N due to the reduction in heat capacity, the occurrence of the fixing failure due to unequal temperature distribution of the fixing member in the width direction can be prevented and the image forming time required for forming an image on the recording medium can be shortened.
Aspect J
In any of Aspects A to I described above, the heat source such as the halogen heater 123 heats directly the fixing member such as the fixing belt 121 through radiation heat. According to this aspect, as described with reference to the above embodiment, the provision of a metal thermal conductor for conducting heat between the heat source and the fixing member is not necessary; therefore, the energy-saving property can be improved and the warm-up time and first printing time can be shortened further.
The embodiment of the present invention has been described so far; needless to say, the present invention is not limited to the embodiment above and various modifications can be made without departing from the content of the present invention. Further, the fixing device according to the present invention can be mounted on, not just the color laser printer illustrated in
According to the present invention, in the case where an image is formed on a recording medium with a size in a width direction thereof which is orthogonal to a recording medium conveying direction at a nip portion of the fixing device, less than or equal to a predetermined size, and then, an image is formed on a recording medium with the size in the width direction larger than the predetermined size, the occurrence of fixing failure due to the inhomogeneous distribution of temperature of the fixing member in the width direction can be prevented and the image forming time required for forming the images on these recording media can be shortened.
Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
| Number | Date | Country | Kind |
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