Patent Description:
An image forming apparatus includes a fixing device that fixes an unfixed toner image born on a recording material to the recording material.

The fixing device includes a rotation member pair including a heating rotary member and a pressure rotary member. The heating rotary member is rotationally driven to apply heat to the unfixed toner image. The pressure rotary member is rotationally driven to pressurize the heating rotary member to form a fixing nip portion with the heating rotary member. When a recording material with an unfixed toner image thereon is conveyed to the fixing nip portion, the recording material is heated by the heating rotary member and pressurized by the pressure rotary member, so that the unfixed toner image is fixed to the recording material.

There is a possibility of occurrence of hot offset in the fixing device. The hot offset is a phenomenon in which the unfixed toner adheres to the surface of the heating rotary member without being fixed to the recording material, due to the heat of the heating rotary member being excessively transferred to the unfixed toner. The toner (the hot offset toner) remaining on the surface of the heating rotary member due to the hot offset may adhere to the subsequent sheet and cause an image defect.

To address the issue, <CIT> discusses a configuration in which a web unit is provided in a fixing unit to eliminate the hot offset toner. A web made of an unwoven fabric or the like can remove the hot offset toner from the heating rotary member to clean the heating rotary member.

The web used to clean the surface of the heating rotary member is wound by rotation of a winding roller. As the amount of the wound web increases, the outer diameter of the wound web increases. For this reason, when the winding roller winds the web, the rotation amount of the winding roller is changed based on the outer diameter of the wound web.

A solenoid is used in the web unit of the fixing device discussed in <CIT>. The solenoid has a function of changing the rotation amount of the winding roller based on the outer diameter of the wound web when the winding roller winds the web. The fixing device adopts a method in which the web unit using the solenoid controls the winding amount of the web based on the outer diameter of the wound web.

In the conventional web unit using the solenoid, a lever moved by the solenoid rotates the winding roller via a gear to wind the web. In a case where a desired amount of the web is wound using the solenoid, a large error may occur in the winding amount of the web due to the configuration.

In addition, the web is wound more by the amount corresponding to the occurring error in order to prevent the winding amount from becoming less than the desired amount for the cleaning if the error occurs. Thus, there is a possibility that the consumption of the web may increase with the conventional web unit.

The prior art also comprises document <CIT>, which discloses an image forming apparatus as per the preamble of appended claim <NUM>. The prior art further comprises documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>, which also disclose image forming apparatuses. However, none of these documents teach or suggest the characterising features of appended claim <NUM>.

The present invention is directed to an image forming apparatus capable of winding a web accurately.

According to a first aspect of the present invention, there is provided an image forming apparatus as specified in claims <NUM> to <NUM>.

<FIG> schematically illustrates a configuration of an image forming apparatus <NUM> according to an embodiment of the present invention. As illustrated in <FIG>, the image forming apparatus <NUM> includes four image forming units PY, PM, PC, and PK for yellow, magenta, cyan, and black, respectively. These image forming units are arranged along a moving direction (indicated by an arrow) of an intermediate transfer belt <NUM>. First, processes for forming a toner image on the intermediate transfer belt <NUM> will be described using the image forming unit PY for yellow as an example.

A charging device <NUM> uniformly charges a surface of a photoconductive drum <NUM> rotationally being driven (in a charging process). Next, an exposure unit <NUM> emits a laser beam to the surface of the photoconductive drum <NUM> based on input image data to form an electrostatic latent image on the surface of the photoconductive drum <NUM> (in an exposure process). Then, a development unit <NUM> forms a yellow toner image on the photoconductive drum <NUM> (in a development process). A primary transfer roller <NUM> applies a voltage with a polarity opposite to that of the yellow toner image, to the intermediate transfer belt <NUM>. Accordingly, the yellow toner image on the photoconductive drum <NUM> is transferred onto the intermediate transfer belt <NUM> at a primary transfer portion n1 (in a primary transfer process). The yellow toner remaining on the surface of the photoconductive drum <NUM> without being transferred to the intermediate transfer belt <NUM> is scraped off by a toner cleaner <NUM> and removed from the surface of the photoconductive drum <NUM>. The series of processes are performed in a similar manner by the image forming unit PM for magenta, the image forming unit PC for cyan, and the image forming unit PK for black. As a result, a full color toner image is formed on the intermediate transfer belt <NUM>.

The toner image on the intermediate transfer belt <NUM> is conveyed to a secondary transfer portion n2 formed by a pair of secondary transfer rollers <NUM> and <NUM>. Sheets of a recording material S are picked up from a recording material cassette <NUM> one by one in synchronization with a conveyance timing of the toner image, and the recording material S is fed to the secondary transfer portion n2, so that the toner image on the intermediate transfer belt <NUM> is transferred onto the recording material S (in a secondary transfer process).

The recording material S with the toner image transferred thereon is conveyed to a fixing device <NUM>. The fixing device <NUM> applies heat and pressure to the recording material S to fix the toner image to the recording material S (in a fixing process). The recording material S with the toner image fixed thereon is discharged to a discharge tray <NUM>.

The image forming apparatus <NUM> can also form a monochrome image. In the case of forming a monochrome image, only the image forming unit PK for black is driven among the plurality of image forming units.

A description will be given of a duplex printing for forming images on both sides of the recording material S. The recording material S with an image formed on one side thereof is discharged from the fixing device <NUM> and then guided to a paper path <NUM> by a flapper <NUM>. When the recording material S is conveyed to a reversing path <NUM> through the paper path <NUM>, the recording material S is conveyed in a switch-back manner on the reversing path <NUM>. Then, the recording material S passes through a duplex path <NUM> and is conveyed to a paper path <NUM>. At this time, the recording material S is in a front-back reversed state. The recording material S is then conveyed again to the secondary transfer portion n2 to transfer a toner image onto the recording material S. The toner image is then fixed to the recording material S by the fixing device <NUM>. The recording material S with the images on both sides thereof is discharged to the discharge tray <NUM>.

The processes from the charging process to the discharge process for discharging the recording material S with the toner image fixed thereon to the discharge tray <NUM> are referred to as image forming processing (a print job). In addition, a period during which the image forming processing is performed is referred to as "during image forming processing (during a print job)".

Next, the fixing device <NUM> according to the present embodiment will be described with reference to <FIG>.

In the present embodiment, the fixing device <NUM> using a rotatable endless fixing belt <NUM> is employed. Referring to <FIG>, the recording material S is conveyed in a direction indicated by an arrow α. The fixing device <NUM> includes a heating rotary member <NUM> and a pressure rotary member <NUM>. The heating rotary member <NUM> includes the fixing belt <NUM>. The pressure rotary member <NUM> forms a fixing nip portion N with the fixing belt <NUM> by making contact with the fixing belt <NUM> to apply pressure to the fixing belt <NUM>.

The heating rotary member <NUM> includes the fixing belt <NUM>, a steering roller <NUM>, a fixing pad (a pad member) <NUM>, and a heating roller <NUM>. The fixing pad <NUM> and the heating roller <NUM> are brought into contact with an inner circumferential surface of the fixing belt <NUM>. The fixing belt <NUM> is stretched around the fixing pad <NUM> and the heating roller <NUM>.

The heating roller <NUM> is formed of metal such as aluminum or stainless-steel and has an cylindrical shape. In the present embodiment, the heating roller <NUM> is formed of an aluminum pipe with an outer diameter of <NUM>. A halogen heater <NUM> is disposed in the heating roller <NUM>, as a heating unit for heating the fixing belt <NUM>. The heating roller <NUM> is heated to a predetermined temperature by the halogen heater <NUM>. The fixing belt <NUM> is heated by the heating roller <NUM> that is heated by the heat of the halogen heater <NUM>. The fixing belt <NUM> is controlled to be at a predetermined target temperature corresponding to grammage of the recording material S (a fixing target) based on a temperature detection result of a fixing temperature detection sensor (not illustrated).

The heating unit is not limited to the halogen heater <NUM>, and the heating roller <NUM> may be heated, for example, using an electromagnetic induced heating (IH) method. The heating roller <NUM> is rotationally driven in a direction indicated by an arrow R2 by receiving a driving force from a motor (not illustrated).

The fixing belt <NUM> is excellent in thermal conductivity and heat resistance and is, for example, a thin endless belt with an inner diameter of <NUM>. In the present embodiment, the fixing belt <NUM> has a three-layer structure including a base layer, an elastic layer on the outside of the base layer, and a release layer on the outside of the elastic layer. The base layer is <NUM> in thickness and made of polyimide (PI) resin, the elastic layer is <NUM> in thickness and made of silicone rubber, and the release layer is <NUM> in thickness and made of perfluoroalkoxy alkane (PFA), which is a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene, as fluororesin. The fixing belt <NUM> is rotationally driven by the pressure rotary member <NUM> (described below) being rotationally driven while pressurizing the fixing pad <NUM> via the fixing belt <NUM>. Since the heating roller <NUM> is rotationally driven by receiving the driving force from the motor (not illustrated), the fixing belt <NUM> is also rotationally driven by the rotational driving force of the heating roller <NUM>.

The fixing pad <NUM> is arranged on the inner circumferential surface of the fixing belt <NUM> so as to face the pressure rotary member <NUM> across the fixing belt <NUM>. In the present embodiment, the fixing belt <NUM> and the fixing pad <NUM> can smoothly slide with each other with a lubricant sheet containing silicone oil or a lubricant such as silicone oil interposed between the fixing belt <NUM> and the fixing pad <NUM>. Thus, the oil such as the silicone oil is applied to the inner circumferential surface of the fixing belt <NUM>.

The pressure rotary member <NUM> includes an aluminum cylindrical core metal, an elastic layer with a thickness of <NUM> on the outside of the core metal, and a release layer for improving separability from toner on the outside of the elastic layer.

The pressure rotary member <NUM> is rotationally driven in a direction indicated by an arrow R1. Accordingly, the fixing belt <NUM> sandwiched between the pressure rotary member <NUM> and the fixing pad <NUM> is rotationally driven by the rotational driving force of the pressure rotary member <NUM>.

The pressure rotary member <NUM> can be moved by a contact/separation mechanism that moves the pressure rotary member <NUM> to make contact with or separate from the fixing belt <NUM>. The contact/separation mechanism includes a frame <NUM> and a drive motor (not illustrated). The frame <NUM> is supported by the image forming apparatus <NUM>. The frame <NUM> supports the pressure rotary member <NUM>. The frame <NUM> is configured to rotate about a rotation shaft <NUM> serving as a rotation axis by receiving a driving force from the drive motor (not illustrated). When the frame <NUM> is rotated clockwise on the paper surface of <FIG> by the drive motor (not illustrated) with the rotation shaft <NUM> as the rotation axis, the pressure rotary member <NUM> is moved in a direction indicated by an arrow P. This brings the pressure rotary member <NUM> into contact with the fixing pad <NUM> across the fixing belt <NUM> in a vertical direction with respect to the conveyance direction α of the recording material S (which refers to a contact state). Accordingly, the fixing nip portion N is formed. In the present embodiment, the fixing nip portion N is formed with a total pressure force of <NUM> N and a width of <NUM>. When the frame <NUM> is rotated counterclockwise on the paper surface of <FIG> with the rotation shaft <NUM> as the rotation axis, the pressure rotary member <NUM> becomes separated from the fixing belt <NUM> (which refers to a separation state).

As described above, the recording material S with the unfixed toner image born thereon is nipped and conveyed by the heating rotary member <NUM> and the pressure rotary member <NUM> at the fixing nip portion N to apply heat and pressure to the recording material S, so that the unfixed toner image is fixed to the recording material S.

As described above, the image forming apparatus <NUM> according to the present embodiment has a configuration including the fixing device <NUM> using the endless fixing belt <NUM>, i.e., a belt type fixing device. However, the configuration is not limited thereto. As illustrated in <FIG>, the fixing device <NUM> may be configured to perform fixing processing on the recording material S using a roller pair of the heating rotary member <NUM> and the pressure rotary member <NUM>.

Next, a web unit <NUM> and a collection roller <NUM> will be described with reference to <FIG> and <FIG>.

The fixing device <NUM> fixes the toner to the recording material S using heat and pressure. If excessive heat is applied to the toner on the recording material S, the toner may adhere to the heating rotary member <NUM> without being fixed to the recording material S, due to the toner being excessively melted on the recording material S. This phenomenon is called hot offset. If the toner adhering to the heating rotary member <NUM> is not collected due to the hot offset, the hot offset toner adheres to the subsequent sheet and is fixed thereto since the heating rotary member <NUM> is rotated. As a result, there is a possibility that an area of the sheet on which the hot offset toner is fixed may cause an image defect.

To address the issue, the web unit <NUM> is used to collect the hot offset toner. The web unit <NUM> collects the toner adhering to the heating rotary member <NUM>. Accordingly, the image defect due to the hot offset can be suppressed.

The web unit <NUM> includes a web <NUM>, a supply roller <NUM>, a winding roller <NUM>, and a pressing roller <NUM>.

The collection roller <NUM> is rotationally driven while being in contact with the surface of the fixing belt <NUM>. The hot offset toner adheres to the surface of the fixing belt <NUM> in a state of being melted by the heat applied at the fixing nip portion N. The collection roller <NUM> according to the present embodiment has an outer diameter of <NUM> and is formed of stainless-steel (SUS) <NUM> that has higher compatibility with the melted toner than the surface of the release layer of the fixing belt <NUM>. Thus, the melted toner is transferred to the surface of the collection roller <NUM>.

The toner transferred to the surface of the collection roller <NUM> is collected from the collection roller <NUM> by the web <NUM> made of an unwoven fabric or the like. The web unit <NUM> includes the pressing roller <NUM> for pressing the web <NUM> against the collection roller <NUM>. The web <NUM> forms a predetermined nip width while being pressed against the collection roller <NUM> by the pressing roller <NUM>. The toner transferred to the collection roller <NUM> is collected by the web <NUM>.

The web <NUM> used to collect the toner is wound by the winding roller <NUM>. In the present embodiment, the winding roller <NUM> winds the web <NUM>, for example, at a rate of <NUM> per four A4-size sheets. One end portion of the web <NUM> is wound by the winding roller <NUM>, and the other end portion is wound around the supply roller <NUM>. The unused web <NUM> is wound around the supply roller <NUM>, and when the web <NUM> is wound by the winding roller <NUM>, the unused web <NUM> is supplied from the supply roller <NUM>. Accordingly, the unused web <NUM> is supplied to the contact portion with the collection roller <NUM> to collect the toner adhering to the surface of the fixing belt <NUM>.

The web <NUM> is made of an unwoven fabric having a total length of <NUM>. When the web <NUM> for collecting the toner runs out due to the fixing processing on the recording material S, the web <NUM> is to be replaced with a new one. In this case, the user that uses the image forming apparatus <NUM> calls a serviceman to have the web unit <NUM> replaced with a new one. In one embodiment, the life of the web unit <NUM> is prolonged because the number of times of calling a service man decreases as the life of the web unit <NUM> increases.

The reason why the web <NUM> collects the toner via the collection roller <NUM> will be described. The web <NUM> is made of an unwoven fabric or the like. Thus, if the web <NUM> is directly brought into contact with the fixing belt <NUM>, not via the collection roller <NUM>, deterioration of the surface of the fixing belt <NUM> can progress faster. If the deterioration of the surface of the fixing belt <NUM> progresses fast, the replacement frequency increases, which increases the time and effort of the user. Thus, the collection of toner via the collection roller <NUM> made of a metal enables the increase of the life of the fixing belt <NUM> because the web <NUM> does not directly make contact with the fixing belt <NUM>. Unevenness of the surface of the fixing belt <NUM> is reflected in the gloss of the image formed on the recording material S. If the web <NUM> is directly brought into contact with the surface of the fixing belt <NUM>, unevenness occurs on the surface of the fixing belt <NUM> and this may cause gloss unevenness on the image formed on the recording material S. Thus, the gloss unevenness can be suppressed by using the configuration in which the web <NUM> is not in direct contact with the surface of the fixing belt <NUM> and the toner is collected via the collection roller <NUM>.

The web unit <NUM> has a mechanism (not illustrated) for enabling the web <NUM> to make contact with and separate from the collection roller <NUM>. The collection roller <NUM> also has a mechanism (not illustrated) for making contact with and separating from the fixing belt <NUM>. In a case where a print job is not received by the control unit <NUM>, the collection roller <NUM> is separated from the fixing belt <NUM>. In a case where a print job is received by the control unit <NUM>, the collection roller <NUM> is brought into contact with the fixing belt <NUM> and a surface temperature of the collection roller <NUM> rises. Thus, when the toner on the surface of the fixing belt <NUM> comes into contact with the collection roller <NUM>, the toner is easily kept in a dissolved state. This makes it easier to move the toner on the surface of the fixing belt <NUM> to the collection roller <NUM>. The surface temperature of the collection roller <NUM> becomes sufficiently high, and the web <NUM> is brought into contact with the collection roller <NUM> one second before the recording material S is conveyed to the fixing nip portion N. The web <NUM> is kept in contact with the collection roller <NUM> and the collection roller <NUM> is kept in contact with the fixing belt <NUM> until the print job is completed.

In a case where the print job is completed, the web <NUM> is separated from the collection roller <NUM> after the last sheet of the recording material S in the print job has passed through the fixing nip portion N.

The web <NUM> is wound in such a manner that the winding roller <NUM> is rotated to wind the used web <NUM>. The amount of the web <NUM> wound by the winding roller <NUM> gradually increases as the used web <NUM> is wound, and the outer diameter of the web <NUM> wound by the winding roller <NUM> increases. If the rotation amount of the winding roller <NUM> is made constant, the winding amount of the web <NUM> increases as the outer diameter of the wound web <NUM> increases. To make the winding amount of the web <NUM> constant, the rotation amount of the winding roller <NUM> is to be controlled based on the outer diameter of the wound web <NUM>. If the rotation amount of the winding roller <NUM> is made constant without considering the outer diameter of the wound web <NUM>, the web <NUM> is used more than necessary because the winding amount gradually increases, which reduces the life of the web <NUM>.

To address the issue, the rotation amount of the winding roller <NUM> has been conventionally controlled considering the outer diameter of the wound web <NUM>. The control has been performed by a web unit using a solenoid.

Conventionally, the rotation amount of the winding roller <NUM> has been controlled based on the outer diameter of the wound web <NUM> by using the solenoid. In a case where the rotation amount of the winding roller <NUM> is controlled using the solenoid, the winding amount is controlled by regulating an operation amount of the solenoid per time based on the outer diameter of the wound web <NUM>.

Levers moved by the solenoid rotate the winding roller <NUM> via a gear to wind the web <NUM>. In a case where a desired amount of the web <NUM> is wound using the solenoid, a large error occurs in the winding amount of the web <NUM> due to the configuration.

One of the reasons for the large error in the winding amount of the web <NUM> is contact between the levers. In a case where a desired amount of the web <NUM> is wound using the solenoid, many levers are to be used. More specifically, three levers including a lever [<NUM>] moving along with the outer diameter of the wound web <NUM>, a lever [<NUM>] moving along with the operation of the solenoid, and a lever [<NUM>] regulating the moving amount of the lever [<NUM>] along with the movement of the lever [<NUM>], are to be used.

These levers are in contact with each other in the above-described configuration.

The contact positions of the levers gradually change with the change in the outer diameter of the wound web <NUM>. The change in the contact positions of the levers is very small. It is thus difficult to consider the change in the contact positions of the levers. As a result, the error in the winding amount of the web <NUM> occurs. In other words, the error is to be reduced by using a configuration that reduces the contact between the levers.

In addition, because the web <NUM> made of an unwoven fabric or the like is thin, the outer diameter of the wound web <NUM> changes slightly. Thus, to wind a desired amount of the web <NUM> with a high accuracy, the outer diameter of the wound web <NUM> is to be detected accurately. Conventionally, a gear has been used to detect the outer diameter of the wound web <NUM>. When a gear is used, the outer diameter of the web can be accurately detected by finely cutting a notched portion of the gear. However, there was a limit for machining the notched portion of the gear. Therefore, the error in detecting the outer diameter of the wound web <NUM> increased.

In the conventional web unit, the web <NUM> is wound more by the amount corresponding to the occurring error so that the winding amount does not fall below the desired amount for the cleaning if the error occurs. Accordingly, the consumption of the web <NUM> is increased by the amount corresponding to the large error generated in the conventional web unit. Consequently, the life of the web <NUM> is reduced.

To address the issue, in the present embodiment, a configuration including a variable resistor <NUM> and a winding motor <NUM> is used to wind a desired amount of the web <NUM> with a high accuracy. Details of the configuration will be described below.

With reference to <FIG>, a description will be given of a mechanism in which the variable resistor <NUM> converts the outer diameter of the wound web <NUM> into a resistance value via a contact member <NUM> (refer to <FIG>) according to the present embodiment. The fixing device <NUM> includes an outer diameter detection unit <NUM> (refer to <FIG>) for detecting the outer diameter of the wound web <NUM>. <FIG> schematically illustrate an example of a configuration of the outer diameter detection unit <NUM>. <FIG> illustrates a state where the web unit <NUM> is new and has not been wound yet by the winding roller <NUM>. <FIG> illustrates a state where the outer diameter of the web <NUM> wound by the winding roller <NUM> is large as a result of the web <NUM> being wound by the winding roller <NUM> in a direction indicated by an arrow A.

The contact member <NUM> of the outer diameter detection unit <NUM> illustrated in <FIG> includes a contact portion 221a and a contact portion 221b. The contact portion 221a of the contact member <NUM> is urged and brought into contact with the outer surface of the wound web <NUM>. The contact portion 221b of the contact member <NUM> is in contact with a ring gear <NUM>. Depending on the outer diameter of the wound web <NUM>, the contact portion 221a of the contact member <NUM> is rotated in a direction indicated by an arrow B in <FIG>. Then, the contact portion 221b of the contact member <NUM> is rotated in a direction indicated by an arrow C to rotate the ring gear <NUM> in a direction indicated by an arrow D. A gear portion of the ring gear <NUM> is engaged with a step gear <NUM>. When the ring gear <NUM> is rotated in the direction indicated by the arrow D, the step gear <NUM> is rotated in a direction indicated by an arrow E. The step gear <NUM> is engaged with a gear portion <NUM> of the variable resistor <NUM>. A gear shaft of the gear portion <NUM> of the variable resistor <NUM> is a D-cut shaft and is fit to a rotation portion 225a of the variable resistor <NUM>. Accordingly, when the step gear <NUM> is rotated in the direction indicated by the arrow E, the gear portion <NUM> is rotated in a direction indicated by an arrow F and the rotation portion 225a of the variable resistor <NUM> is rotated in a direction indicated by an arrow G. More specifically, when the web <NUM> is wound by the winding roller <NUM> to increase the outer diameter of the wound web <NUM>, the position of the contact member <NUM> is changed to cause the rotation portion 225a of the variable resistor <NUM> to rotate. Thus, when the web <NUM> is wound by the winding roller <NUM> and the outer diameter of the wound web <NUM> increases, a resistance value R12 of the variable resistor <NUM> increases. The resistance value R12 of the variable resistor <NUM> is configured to change based on the rotation amount of the rotation portion 225a.

A relationship between the rotation portion 225a of the variable resistor <NUM> and the resistance value R12 of the variable resistor <NUM> will be described with reference with <FIG>.

<FIG> is a circuit diagram illustrating a detection circuit of the variable resistor <NUM> according to the present embodiment. The variable resistor <NUM> includes a terminal <NUM>, a terminal <NUM>, and a terminal <NUM>. The terminals <NUM> to <NUM> of the variable resistor <NUM> illustrated in <FIG> correspond to the terminals <NUM> to <NUM> of the variable resistor <NUM> illustrated in <FIG>. The terminal <NUM> is connected to the rotation portion 225a. The resistance value R12 between the terminals <NUM> and <NUM> and a resistance value R23 between the terminals <NUM> and <NUM> are changed based on the angle (the rotation amount) of the rotation portion 225a.

The terminals <NUM> to <NUM> of the variable resistor <NUM> are connected to a control circuit board <NUM>. The terminal <NUM> is connected to a ground (GND) terminal, the terminal <NUM> is connected to a terminal of the control unit <NUM> as a detection voltage Vsns, and the terminal <NUM> is connected to a power source (<NUM> V).

In the present embodiment, assume that a total resistance value R13 of the variable resistor <NUM> between the terminals <NUM> and <NUM> is <NUM> kΩ, and the angle (the rotation amount) of the rotation portion 225a of the variable resistor <NUM>, the resistance value R12 between the terminals <NUM> and <NUM>, and the resistance value R23 between the terminals <NUM> and <NUM> are changed. In this case, the following formula (<NUM>) is satisfied.

In addition, since the terminal <NUM> having the total resistance value R13 of the variable resistor <NUM> is connected to the power source (<NUM> V), the detection voltage Vsns is input to the control unit <NUM> connected to the terminal <NUM>. The detection voltage Vsns is obtained by dividing the power source (<NUM> V) based on the resistance values R12 and R23, and can be obtained using the following formula (<NUM>).

As a result, the position of the contact member <NUM> can be obtained as an electrical signal by using the detection voltage Vsns.

When the web <NUM> is wound by the winding roller <NUM> and the outer diameter of the wound web <NUM> increases, the resistance value R12 of the variable resistor <NUM> increases. The detection voltage Vsns increases with the increase of the resistance value R12 of the variable resistor <NUM>.

A relationship between the outer diameter of the wound web <NUM> and the rotation angle of the variable resistor <NUM> will be described with reference to <FIG>. In the present embodiment, assume that the outer diameter of the winding roller <NUM> is Φ12 mm and the outer diameter of the wound web <NUM> at the time when the web <NUM> to be wound by the winding roller <NUM> runs out (at the time of end-of-life of the web <NUM>) is Φ50 mm. Also assume that the rotation angle of the variable resistor <NUM> is between <NUM> degrees and <NUM> degrees. More specifically, the angle of the variable resistor <NUM> is <NUM> degrees at the time of starting use of the web <NUM>, and the rotation angle of the variable resistor <NUM> is <NUM> degrees at the time of end-of-life of the web <NUM>.

A relationship between the rotation angle of the variable resistor <NUM> and a voltage value to be output will be described with reference to <FIG>. Assume that the time of starting use of the web unit <NUM> before shipment is a point (<NUM>) and the rotation portion 225a of the variable resistor <NUM> at the point (<NUM>) is at <NUM> degrees. The detection voltage Vsns at the point (<NUM>) is assumed to be a detection voltage value Va. Through the use of the web <NUM>, the outer diameter of the wound web <NUM> increases and the resistance value R12 of the variable resistor <NUM> (between the terminals <NUM> and <NUM>) also increases. Accordingly, the detection voltage Vsns increases and reaches a point (<NUM>) at the time of end-of-life of the web <NUM>. Assume that the rotation angle of the rotation portion 225a of the variable resistor <NUM> at the point (<NUM>) is <NUM> degrees and the detection voltage Vsns at the point (<NUM>) is a detection voltage value Vb.

A memory <NUM> (see <FIG>) stores information data of the web <NUM>. The information data includes the detection voltage value Va, which is a detection voltage value before shipment, and the detection voltage value Vb, which is a detection voltage value at the time of end-of-life of the web <NUM>.

The control unit <NUM> is electrically connected to the terminals <NUM> to <NUM> of the variable resistor <NUM>, and can obtain the resistance value R12 of the variable resistor <NUM>. Thus, the control unit <NUM> can obtain the detection voltage Vsns using the formula (<NUM>). The control unit <NUM> is also connected to the winding motor <NUM>. In the present embodiment, the winding motor <NUM> is a motor for rotating the winding roller <NUM>. The control unit <NUM> controls the rotation amount of the winding motor <NUM> based on the obtained detection voltage Vsns. More specifically, in the present embodiment, in a case where the winding roller <NUM> can wind the web <NUM> by <NUM> in one rotation operation of the winding roller <NUM>, the toner on the surface of the fixing belt <NUM> can be collected and the possibility of an image defect on the subsequent sheet can be suppressed. For this reason, a desired amount of the web <NUM> to be wound in one rotation operation of the winding roller <NUM> is <NUM>. The rotation amount of the winding motor <NUM> is decreased as the outer diameter of the wound web <NUM> increases so that the amount of the web <NUM> to be wound by the winding roller <NUM> is <NUM>. At this time, the control unit <NUM> rotates the winding motor <NUM> by controlling the rotation amount of the winding motor <NUM> based on the value of the obtained detection voltage Vsns.

In the present embodiment, a stepping motor is used as the winding motor <NUM>. The control unit <NUM> controls the rotation amount of the stepping motor by controlling the number of pulses input to the stepping motor, thereby controlling the amount of the web <NUM> to be wound.

Furthermore, the amount of the unused web <NUM> gradually decreases as the winding motor <NUM> winds the web <NUM>, and a replacement timing of the web <NUM> approaches. The memory <NUM> stores the detection voltage value Vb that is a voltage value at the time of end-of-life of the web <NUM>. Thus, the control unit <NUM> can determine whether the detection voltage Vsns has reached the detection voltage value Vb. This makes it possible to determine the replacement timing of the web <NUM>.

In a case where the web <NUM> is replaced with a new one, the amount of the web <NUM> wound by the winding roller <NUM> is reset. Thus, the outer diameter of the wound web <NUM> corresponding to the amount of the web <NUM> wound by the winding roller <NUM> is also reset. Since the contact member <NUM> is urged toward the outer surface of the wound web <NUM>, the detection voltage Vsns is returned to the detection voltage value Va, which is the value at the time of starting use of the web <NUM>.

In the present embodiment, the levers are not in contact with each other in a period after the resistance value R12 of the variable resistor <NUM> is converted into the detection voltage Vsns and before the winding roller <NUM> is rotated. With this configuration, the above-described error caused by the contact between the levers can be reduced compared with the conventional configuration. In this way, the error in the winding amount of the web <NUM> can be reduced to suppress the consumption of the web <NUM>. As a result, the life of the web <NUM> can be prolonged.

The outer diameter of the wound web <NUM> increases little by little because the web <NUM> is thin. Thus, in the present embodiment, the variable resistor <NUM> is used in the web unit <NUM> to obtain the detection voltage Vsns. Since the detection voltage Vsns is an electrical signal, the detection voltage Vsns can be changed corresponding to a small change in the outer diameter of the wound web <NUM>. Thus, the control unit <NUM> can control the rotation amount of the winding motor <NUM> finely.

As a specific example, in a case where the resistance value R12 of the variable resistor <NUM> is small, the wound web <NUM> is small in amount and also in diameter. Accordingly, the rotation amount of the winding roller <NUM> is controlled to be large. On the other hand, in a case where the resistance value R12 of the variable resistor <NUM> is large, the wound web <NUM> is large in amount and also in outer diameter. Accordingly, the rotation amount of the winding roller <NUM> is controlled to be small. At this time, the rotation amount of the winding roller <NUM> can be set finely based on the position of the contact member <NUM>. Thus, the web <NUM> can be wound accurately. As a result, the life of the web <NUM> can be prolonged.

While the variable resistor <NUM> of a rotation type (in which a sliding member rotates) is used in the present embodiment, different types of the variable resistor <NUM> may be used. For example, the variable resistor <NUM> including the rotation portion 225a of a slide type may be used.

In the present embodiment, a rotary volume which is the variable resister <NUM> of a rotation type is used. This is because it can be arranged in a space saving manner as compared with the slide type.

The position of the contact member <NUM> is converted into the resistance value R12 by the variable resistor <NUM>. The detection voltage Vsns is obtained from the resistance value R12, and the winding motor <NUM> controls the winding roller <NUM> based on the detection voltage Vsns. As a result, the web <NUM> can be wound accurately, so that the life of the web <NUM> can be prolonged.

The control unit <NUM> controls the rotation amount of the winding motor <NUM>. At this time, the control unit <NUM> uses the detection voltage Vsns, not the resistance value R12 obtained from the variable resistor <NUM>. The variable resistor <NUM> is made of metal. Generally, the electric resistivity of the metal tends to increase as the temperature rises. For this reason, the resistance value R12 obtained from the variable resistor <NUM> changes depending on the temperature of an external environment. For example, in a case where the control unit <NUM> controls the rotation amount of the winding motor <NUM> using the resistance value R12, the rotation amount of the winding motor <NUM> changes depending on the temperature of the external environment. As a result, the error in the winding amount of the wound web <NUM> increases. On the other hand, it can be said that the detection voltage Vsns obtained using the formula (<NUM>) is less dependent on the temperature of the external environment than the resistance value R12. For this reason, the control unit <NUM> controls the winding motor <NUM> using the detection voltage Vsns. Accordingly, the web <NUM> can be wound accurately.

Next, a modification example of the present embodiment will be described with reference to <FIG> and <FIG>. Descriptions of the same components as those described above will be omitted.

<FIG> is a graph illustrating a relationship X between the detection voltage Vsns and the rotation angle of the variable resistor <NUM> according to the present modification example. <FIG> is a graph illustrating the relationship X between the rotation angle of the variable resistor <NUM> and the detection voltage Vsns according to the present modification example.

<FIG> illustrates a state in which the relationship X obtained based on the rotation angle of the variable resistor <NUM> and the detection voltage Vsns is not linear. <FIG> illustrates a state in which the relationship X obtained based on the rotation angle of the variable resistor <NUM> and the detection voltage Vsns is linearly corrected.

As illustrated in <FIG>, the relationship X between the rotation angle of the variable resistor <NUM> and the detection voltage Vsns is sometimes non-linear. Before shipment, the memory <NUM> stores information data about detection voltage values at five points in total, i.e., the detection voltage value Va of the variable resistor <NUM> at the time of starting use of the web unit <NUM>, the detection voltage value Vb at the time of end-of-life of the web unit <NUM>, and detection voltage values Vc, Vd, and Ve at three points therebetween. The control unit <NUM> reads and writes the information data from and to the memory <NUM>. The control unit <NUM> linearly corrects the relationship X based on the obtained information about the detection voltage values at five points, as illustrated in <FIG>. Furthermore, the control unit <NUM> controls the driving amount of the winding motor <NUM> based on the linearly corrected relationship X, so that the web <NUM> is wound accurately by the winding motor <NUM>.

In a case where the relationship X between the rotation angle of the variable resistor <NUM> and the detection voltage Vsns is not linear, the difference between the values of the detection voltage Vsns is small in an area where the inclination of the relationship X is small. For this reason, even a slight detection error may cause an erroneous detection of the outer diameter of the winding roller <NUM> to lower the driving amount accuracy of the winding motor <NUM>. On the other hand, the detection error can be reduced by linearly correcting the relationship X.

According to the above-described present embodiment, even if the relationship X obtained based on the rotation amount of the variable resistor <NUM> and the detection voltage Vsns is not linear, the web <NUM> can be wound accurately. As a result, the life of the web <NUM> can be prolonged.

While in the present embodiment, the linear correction is performed using the information about the detection voltage values at five points in total, i.e., the detection voltage value Va at the start of use (when the web has not received any toner), the detection voltage value Vb at the end of life (when the web is considered to be fully wound), and the detection voltage values Vc, Vd, and Ve at three points therebetween, the number of detection voltage values can be optionally selected and the linear correction may be performed based on information about detection voltage values at more points.

While in the present embodiment, voltage detection is performed by equally dividing the rotation amount of the variable resistor <NUM> to determine intervals between the detection voltage values Va and Vd. However, the intervals may be determined optionally.

Claim 1:
An image forming apparatus (<NUM>) comprising:
a heating rotary member (<NUM>) configured to heat toner born on a recording material (S);
a pressure rotary member (<NUM>) configured to pressurize the heating rotary member (<NUM>), wherein the heating rotary member (<NUM>) and the pressure rotary member (<NUM>) form a fixing nip portion (N) and fix a toner image to the recording material (S) at the fixing nip portion (N) while nipping and conveying the recording material (S) with the toner born thereon;
a web (<NUM>) configured to collect toner adhering to a surface of the heating rotary member (<NUM>) without being fixed to the recording material (S);
a winding roller (<NUM>) configured to wind the web (<NUM>);
a motor (<NUM>) configured to rotate the winding roller (<NUM>) to wind the web (<NUM>); the image forming apparatus (<NUM>) being characterised in that it further comprises:
a contact member (<NUM>) configured to make contact with an outer surface of the web (<NUM>) wound by the winding roller (<NUM>) and move based on a position of the outer surface;
a variable resistor (<NUM>) having a resistance value (R12) and configured to change the resistance value (R12) depending on a position of the contact member (<NUM>); and
control means (<NUM>) configured to control a rotation amount of the motor (<NUM>) based on the resistance value (R12),
wherein the contact member (<NUM>) includes a first lever (221a) configured to make contact with the outer surface of the web (<NUM>),
wherein the first lever (221a) is configured to swing based on an outer diameter of the web (<NUM>) wound by the winding roller (<NUM>), and
wherein the contact member (<NUM>) includes a second lever (221b) operatively coupled to a gear mechanism (<NUM>, <NUM>, <NUM>) of the image forming apparatus (<NUM>), the second lever (221b) being arranged to be rotated when the first lever (221a) swings, the second lever (221b) being further arranged to rotate the gear mechanism (<NUM>, <NUM>, <NUM>), the gear mechanism (<NUM>, <NUM>, <NUM>) being arranged to rotate a rotation portion (225a) of the variable resistor (<NUM>), the rotation angle of the variable resistor (<NUM>) corresponding to a rotation angle of the said rotation portion (225a).