BACKGROUND

[0001] A cam structure may be used to change an operational mode of a device or a position, phase, or the like of a component in the device. A load may be applied to a movable object in a direction in which the movable object is maintained at a certain position. The load may be provided by an elastic member such as a spring. The load may be modified in proportion to a deformation amount of the elastic member. In the above structure, a load profile of the cam follows a change profile of an elastic force of the elastic member. A load of a driving motor driving the cam is changed in accordance with the load profile of the cam. A change in the load of the driving motor may cause noise or vibration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] Various examples will be described below by referring to the following figures.

[0003] FIGS. 1 through 3 are schematic structural diagrams illustrating a cam driving device, in which a movable object is located at a top dead position, a middle position, and a bottom dead position, respectively, according to an example.

[0004] FIG. 4 illustrates examples of load torque profiles of load torques respectively applied to a rotation cam, a first gear, a second gear, and a driving motor, and a reduction ratio profile, in the example of the cam driving device illustrated in FIGS. 1 through 3.

[0005] FIG. 5 is a schematic structural diagram of a cam driving device according to an example.

[0006] FIG. 6 illustrates examples of load torque profiles of load torques respectively applied to a rotation cam, a first gear, a second gear, and a driving motor, in the example of the cam driving device illustrated in FIG. 5.

[0007] FIG. 7 is a schematic structural diagram of a cam driving device according to an example.

[0008] FIG. 8 is a schematic structural diagram of an image forming apparatus according to an example.

[0009] FIGS. 9 and 10 are schematic structural diagrams of a fuser, wherein FIG. 9 illustrates a state in which a fusing nip is formed according to an example, and FIG. 10 illustrates a state in which the fusing nip is released according to an example.

[0010] FIGS. 11 and 12 are diagrams illustrating an intermediate transfer roller, wherein FIG. 11 illustrates a state in which the intermediate transfer roller is located at a pressurization position according to an example, and FIG. 12 illustrates a state in which the intermediate transfer roller is located at a release position according to an example.

DETAILED DESCRIPTION

[0011] An example structure including a cam for moving a movable object that may be used in various devices is described below. In an example, the cam may be rotated. The movable object may be moved, for example, between an initial position and a target position. A load may be applied to a movable object, for example, in a direction in which the movable object is maintained in an initial position. The load may be provided by an elastic force of an elastic member, for example. While the movable object is moved between the initial position and the target position and returns to the initial position again, an amount of elastic force may vary. A load torque applied to the cam may also vary in accordance with a variation in the amount of the elastic force. A driving motor to drive the cam may be selected by considering a maximum value of the load torque applied to the cam. For example, the driving motor may be selected to generate a rated torque corresponding to a sum of a maximum value of a load torque applied to the cam and a certain margin. In an example, while the driving motor is rotated, the load torque applied to the driving motor is varied. Based on an amount of variation of the load torque being relatively large, vibration and noise may be generated. [0012] A cam driving device according to an example includes a movable object, a rotary cam to move the movable object, a load applying member to apply a load between the movable object and the rotary cam, a driving motor, and a reducer arranged between the rotary cam and the driving motor. In an example, while the rotary cam is rotated, a load applied to the rotary cam may periodically vary. The reducer may have a structure to reduce a variation in a load torque applied to the driving motor. The reducer may have a structure in which a reduction ratio thereof varies periodically. A phase of a reduction ratio profile of the reducer may correspond (e.g., be identical) to a phase of a load profile of the rotary cam. For example, a phase of a maximum value of a load applied to the rotary cam may correspond (e.g., be identical) to a phase of a maximum value of the reduction ratio of the reducer. In addition, a phase of a minimum value of a load applied to the rotary cam may correspond (e.g., be identical) to a phase of a minimum value of the reduction ratio. Based on a phase of a reduction ratio profile of the reducer corresponding (e.g., being identical) to a phase of a load profile of the rotary cam, it may include a case where the two phases correspond to each other, and may also include a case where phases of a maximum value and a minimum value of a load applied to the rotary cam correspond to phases of a maximum value and a minimum value of a reduction ratio of the reducer within an error range and a case where the phases differ so little from each other as to not be considered different from each other. Accordingly, a difference between the maximum value and the minimum value of the load torque applied to the driving motor is reduced. In other words, a change range of the load torque of the driving motor is reduced, thereby reducing vibration or noise of the driving motor. Also, based on using a direct current motor as the driving motor, a variation in a rotational speed of the driving motor is reduced, thereby allowing the rotary cam to rotate stably.

[0013] Various reducers may be provided. For example, the reducer may be implemented by using a gear having a pitch circle having a radius varying according to an angular phase. The reducer may be implemented using a first gear having a first pitch circle profile corresponding to a load profile of the rotary cam and a second gear having a second pitch circle profile having an opposite phase to that of the first pitch circle profile. The first gear may include a driven gear connected to the rotary cam, and the second gear may include a driving gear connected to the driving motor. The first gear and the second gear may include an eccentric gear. The first gear and the second gear may include an elliptical gear.

[0014] An example cam driving device may be applied to an image forming apparatus. For example, the cam driving device may be used as a structure to form or release a fusing nip between a heating member and a pressurization member in a fuser. For example, the cam driving device may be used as a structure to move an intermediate transfer roller to form or release an intermediate transfer nip between a photoconductor and an intermediate transfer belt hereinafter, examples of a cam driving device, a fuser, an intermediate transfer belt assembly, and an image forming apparatus including the same will be described by referring to the attached drawings. In the following description, components having substantially the same functions will be labeled with the same reference numerals and a repeated description thereof may be omitted.

[0015] FIGS. 1 through 3 are schematic structural diagrams illustrating a cam driving device, in which a movable object is located at a top dead position, a middle position, and a bottom dead position, respectively, according to an example.

[0016] Referring to FIGS. 1 through 3, a cam driving device 1000 may include a movable object 10, a rotary cam 20 to move the movable object 10 according to a rotational phase of the rotary cam 20, a load applying member 30 to apply a load between the movable object 10 and the rotary cam 20, a driving motor 50, and a reducer 40 arranged between the driving motor 50 and the rotary cam 20 and having a reduction ratio profile of which a phase corresponds (e.g., is identical) to that of a load profile of the rotary cam 20.

[0017] The rotary cam 20 may include a cam portion 22 and a central shaft 21. In an example, a distance of the cam portion 22 from the central shaft 21 varies according to a rotational phase of the rotary cam 20. The cam portion 22 may contact the movable object 10. The movable object 10 may be moved between a top dead position (FIG. 1) and a bottom dead position (FIG. 3) according to a rotational phase of the rotary cam 20. The load applying member 30 may apply a force to the movable object 10 such that the movable object 10 and the cam portion 22 contact each other. The load applying member 30 may apply a force to the movable object 10 in a direction in which the movable object 10 is moved between any one of the top dead position and the bottom dead position. For example, the load applying member 30 may be implemented using a spring to apply, to the movable object 10, an elastic force in a direction in which the movable object 10 is located at the bottom dead position.

[0018] The rotary cam 20 may be rotated by the driving motor 50. The reducer 40 may be arranged between the rotary cam 20 and the driving motor 50. The driving motor 50 may be directly connected to the reducer 40 and may be connected to the reducer 40 via a power transmission member such as a gear, a belt, etc. Although not illustrated in the drawings, a reduction structure with a fixed reduction ratio may be arranged between the driving motor 50 and the reducer 40. Accordingly, a value of a load torque applied to the driving motor 50 may be reduced overall. The rotary cam 20 may be directly connected to the reducer 40 and may be connected to the reducer 40 via a power transmission member such as a gear, a belt, etc.

[0019] A load torque acting on the rotary cam 20 is dependent on a cam radius of the cam portion 22, a force applied to the movable object 10 by the load applying member 30, and a coefficient of friction between the cam portion 22 and the movable object 10. Based on a cam radius being r, a force applied to the movable object 10 by the load applying member 30 being f, and a coefficient of friction being m, a load torque is t = pxfxr. The cam radius is r1 , r2, and r3 at the top dead position, the middle position, and the bottom dead position, respectively, and r1 > r2 > r3. The force applied to the movable object 10 by the load applying member 30 is proportional to a deformation amount of the load applying member 30. Based on a free field of the load applying member 30 being d, a deformation amount of the load applying member 30 is d-d1, d-d2, d-d3 at the top dead position, the middle position, and the bottom dead position, respectively, and (d- d1 ) > (d-d2) > (d-d3). Accordingly, based on a force applied to the movable object 10 by the load applying member 30 being f1 , f2, and f3 at the top dead position, the middle position, and the bottom dead position, respectively, and f1 > f2 > f3, the load torque of the rotary cam 20 is t = pxfxr, and thus, T1 = pxfl xrl, T2 = pxf2*r2, t3 = p*f3*r3 at the top dead position, the middle position, and the bottom dead position, respectively, and T1 > T2 > T3. While the rotary cam 20 is rotated once, the movable object 10 is moved between the top dead position, the bottom dead position, and the top dead position again, and the load torque applied to the rotary cam 20 is a maximum value, a minimum value, and the maximum value again. A load torque profile of the rotary cam 20 may have a form that gradually decreases between the maximum value and the minimum value and gradually increases between the minimum value and the maximum value.

[0020] The load torque of the rotary cam 20 may be reduced by the reducer 40 and applied to the driving motor 50. The reducer 40 may have a structure of reducing a change range of a motor load torque applied to the driving motor 50. For example, the reducer 40 may have a reduction ratio profile of which a phase corresponds (e.g., is identical) to that of the load profile of the rotary cam 20, that is, the load torque profile. For example, based on the load torque of the rotary cam 20 being the greatest, the reducer 40 may have a maximum reduction ratio, and based on the load torque of the rotary cam 20 being the smallest, the reducer 40 may have a minimum reduction ratio. The reduction ratio may gradually decrease between a maximum value and a minimum value thereof and may gradually increase between the minimum value and the maximum value thereof. The reduction ratio profile of the reducer 40 may not have a completely identical phase to that of the load profile of the rotary cam 20, and there may be a slight phase difference between the reduction ratio profile and the load profile. Flere, the phase difference may refer to a level at which a reduction ratio of the reducer 40 becomes almost maximum based on the load torque of the rotary cam 20 being the largest and the reduction ratio of the reducer 40 becomes almost minimum based on the load torque of the rotary cam 20 being the smallest. [0021] The reducer 40 may include a first gear 41 and a second gear 42. A central shaft 411 of the first gear 41 may be coaxial with the central shaft 21 of the rotary cam 20. The first gear 41 may be connected to the rotary cam 20 via a power transmission member such as a gear, a belt, etc. A rotational phase of the first gear 41 may correspond to (e.g., be the same as) a rotational phase of the rotary cam 20. A central shaft 421 of the second gear 42 may be a rotational axis of the driving motor 50. The second gear 42 may be connected to the driving motor 50 via a power transmission member such as a gear, a belt, etc.

[0022] The first gear 41 may have a first pitch circle 412. In an example, the first gear 41 may have a first pitch circle profile corresponding to the load profile of the rotary cam 20. Having the first pitch circle profile corresponding to the load profile of the rotary cam 20 refers to a situation in which a radius of a pitch circle of the first gear 41 engaged with the second gear 42 is the largest when the cam radius of the cam portion 22 of the rotary cam 20 facing the movable object 10 is the largest. For example, a radius of the first pitch circle 412 of the first gear 41 may be the largest at a position where the first gear 41 is engaged with the second gear 42 based on the load torque of the rotary cam 20 being the largest, and the radius of the first pitch circle 412 of the first gear 41 may be the smallest at a position where the first gear 41 is engaged with the second gear 42 based on the load torque of the rotary cam 20 being the smallest. The second gear 42 may be engaged with the first gear 41. The second gear 42 may have a second pitch circle 422. The second gear 42 may have a second pitch circle profile having a phase opposite to that of the first pitch circle profile. Having the second pitch circle profile having an opposite phase to that of the first pitch circle profile refers to a situation in which a radius of the second pitch circle 422 corresponding to a radius of the first pitch circle 412 is the smallest or the largest based on the radius of the first pitch circle 412 being respectively the largest or the smallest at a position where the first gear 41 and the second gear 42 are engaged with each other.

[0023] For example, the first gear 41 and the second gear 42 may include an eccentric gear. The first pitch circle 412 and the second pitch circle 422 may be circular and have a corresponding (e.g., equal) diameter. The central shaft 411 of the first gear 41 may be eccentric with respect to a center 413 of the first pitch circle 412 by a first distance. Likewise, the central shaft 421 of the second gear 42 may be eccentric from a center 423 of the second pitch circle 422 by a second distance. In an example, the first distance and the second distance may be equal to each other. A distance between axes of the first gear 41 and the second gear 42, for example, a distance AX between the central shaft 411 of the first gear 41 and the central shaft 421 of the second gear 42, is uniform. At a point where the first gear 41 and the second gear 42 are engaged with each other, a sum of a radius of the first pitch circle 412 of the first gear 41 and a radius of the second pitch circle 422 of the second gear 42 is equal to the distance AX between the central shaft 411 of the first gear 41 and the central shaft 421 of the second gear 42. Accordingly, the first gear 41 and the second gear 42 may be rotated while being engaged with each other. At the point where the first gear 41 and the second gear 42 are engaged with each other, based on the radius of the first pitch circle 412 of the first gear 41 being P1 , and the radius of the second pitch circle 422 of the second gear 42 being P2, a reduction ratio of the reducer 40 is defined as P1/P2. For example, based on a reduction ratio of the reducer 40 being RD1 = P11/P21, RD2 = P12/P22, and RD3 = P13/P23 at the top position, the middle position, and the bottom position, respectively, RD1 > RD2 > RD3, phases of a maximum value T1 and a minimum value T3 of a load torque profile of the rotary cam 20 may correspond to phases of the maximum value RD1 and the minimum value RD3 of the reduction ratio of the reducer 40, respectively. The phases of the maximum value T1 and the minimum value T3 of the load torque profile of the rotary cam 20 may coincide with the phases of the maximum value RD1 and the minimum value RD3 of the reduction ratio of the reducer 40, respectively, and may also be nearly identical or similar, if not completely identical.

[0024] FIG. 4 illustrates examples of load torque profiles of load torques respectively applied to a rotation cam, a first gear, a second gear, and a driving motor and a reduction ratio profile in the example of the cam driving device illustrated in FIGS. 1 through 3.

[0025] In FIG. 4, ®, (2), and (3) indicate a top dead position, a middle position, and a bottom dead position, respectively. Referring to FIG. 4, load torque profiles of the rotary cam 20 and the first gear 41 have the same phase. The load torque profile of the second gear 42 has an opposite phase to that of the first gear 41. As the reducer 40 is included, a load torque of the second gear 42 is smaller than a load torque of the first gear 41. The load torque profiles of the second gear 42 and the driving motor 50 have the same phase. In FIG. 4, the load torque profiles of the rotary cam 20 and the first gear 41 are shown to have completely identical phases, but the two phases may deviate from each other within a certain error range and may be considered to be the same also based on the two phases not significantly deviating from each other.

[0026] Referring to FIG. 4, the load torque of the rotary cam 20 is not constant while the rotary cam 20 is rotated once. Based on a reducer having a fixed reduction ratio being used, the load torque transmitted to the driving motor 50 has the same phase as that of the load torque of the rotary cam 20, and a magnitude of the load torque is reduced. A difference LTV201 in the load torque between the top dead position and the middle position is greater than a difference LTV202 in the load torque between the middle position and the bottom dead position. During one rotation of the rotary cam 20, a maximum change range of the load torque is LTV201+LTV202. In this case, based on the movable object 10 being moved between the middle position and the top dead position, a relatively high load is applied to the driving motor 50, and based on the movable object 10 being moved between the middle position and the bottom dead position, the magnitude of the load torque is reduced and a difference between a maximum load torque and a minimum load torque over the driving motor 50, that is, a torque variance, is relatively large. In addition, to secure a stable operation of the cam driving device 1000, the driving motor 50 is selected to have a rated torque that is about 10 % to about 30 % greater than the maximum load torque. Accordingly, the price of the driving motor 50 may be increased. In addition, while the driving motor 50 is rotating, a torque variance may be relatively large, generating vibration and driving noise. In addition, based on a direct current motor being used as the driving motor 50, a rotational speed of the motor may be not uniform. [0027] According to an example, as the reducer 40 having a reduction ratio of which a phase is opposite to that of the load torque profile of the rotary cam 20 is used, a variance of a load torque applied to the driving motor 50 while the driving motor 50 is rotated may be very small. That is, as illustrated in FIG. 4, the reducer 40 may have a reduction ratio profile with a relatively large reduction ratio in a section between the middle position and the top dead position and a relatively small reduction ratio in a section between the middle position and the bottom dead position. Accordingly, a change range LTV50 of a load torque applied to the driving motor 50 is reduced and thus vibration of the driving motor 50 and noise resulting therefrom may be reduced. Further, since the driving motor 50 may be rotated at an almost uniform speed, a relatively low-cost direct current motor may be used as the driving motor 50. The direct current motor has a simple driving circuit, and thus, the cost of the cam driving device 1000 may be reduced.

[0028] FIG. 5 is a schematic structural diagram of a cam driving device according to an example. FIG. 6 illustrates examples of load torque profiles of load torques respectively applied to a rotation cam, a first gear, a second gear, and a driving motor in the example of the cam driving device illustrated in FIG. 5. [0029] In FIG. 6, ®, (2), and (3) indicate a top dead position, a middle position, and a bottom dead position, respectively. A cam driving device 1000-1 according to an example is different from the cam driving device 1000 illustrated in FIGS. 1 through 3 in that a profile of a cam portion 22-1 of a rotary cam 20-1 is nearly identical to a profile of the first and second pitch circles 412 and 422 of the first gear 41 and the second gear 42. According to an example, while the driving motor 50 is rotated, a load torque applied to the driving motor 50 may be uniform, as illustrated in FIG. 6. In addition, based on a direct current motor being used as the driving motor 50, the driving motor 50 may be rotated at a nearly uniform speed. A load torque applied to the driving motor 50 may also be varied by the error of the manufacture of components, assembly error, or the like, as denoted by a dashed line.

[0030] FIG. 7 is a schematic structural diagram of a cam driving device according to an example.

[0031] Referring to FIG. 7, a cam driving device 1000-2 is different from the cam driving device 1000 illustrated in FIGS. 1 through 3 in that a rotary cam 20-2 having a cam portion 22-2 of an elliptical form and a reducer 40-2 including a first elliptical gear 41-2 and a second elliptical gear 42-2 respectively having a first pitch circle 412-2 and a second pitch circle 422-2 are included. The rotary cam 20-2 includes the cam portion 22-2 of an elliptical form. While the rotary cam 20-2 is rotated once, the movable object 10 is moved between the top dead position and the bottom dead position twice. The first elliptical gear 41-2 has the first pitch circle 412-2 of an elliptical form. A profile of the first pitch circle 412-2 corresponds to a load profile of the rotary cam 20-2. The second elliptical gear 42-2 is engaged with the first elliptical gear 41-2. The second elliptical gear 42-2 has the second pitch circle 422-2 in an elliptical form. In an example, form factors of the first pitch circle 412-2 and the second pitch circle 422-2 are identical. The second elliptical gear 42-2 may have a second pitch circle profile having an opposite phase to that of the first pitch circle profile. Having the first pitch circle profile corresponding to the load profile of the rotary cam 20-2 indicates that a radius of the first pitch circle 412-2 of the first elliptical gear 41-2, as determined from a central shaft 411 -2 of the first elliptical gear 41 -2, engaged with the second elliptical gear 42-2 is largest based on a cam radius of the cam portion 22-2 of the rotary cam 20-2 being the largest. Having the second pitch circle profile having an opposite phase to that of the first pitch circle profile indicates that a radius of the second pitch circle 422-2, as determined from a central shaft 421-2 of the second elliptical gear 42-2, corresponding to a radius of the first pitch circle 412- 2 is the smallest or the largest based on the radius of the first pitch circle 412-2 being respectively the largest or the smallest at a position where the first elliptical gear 41-2 and the second elliptical gear 42-2 are engaged with each other. According to the above example, the load torque applied to the driving motor 50 may be substantially uniform. In addition, based on a direct current motor being used as the driving motor 50, the driving motor 50 may be rotated at a nearly uniform speed.

[0032] Hereinafter, examples of a structure to which the above-described cam driving device may be applied will be described.

[0033] FIG. 8 is a schematic structural diagram of an image forming apparatus according to an example. In the example of FIG. 8, the image forming apparatus prints a color image on a print medium P by using an electrophotographic method.

[0034] Referring to FIG. 8, a plurality of developing devices 210, an exposure device 250, an intermediate transfer belt 260, a transfer roller 270, and a fuser 280 are illustrated.

[0035] The plurality of developing devices 210 may include four developing devices 210 for forming toner images of yellow (Y), magenta (M), cyan (C), and black (K) colors. In the four developing devices 210, developers of the cyan (C), magenta (M), yellow (Y), and black (K) colors may be respectively accommodated. The developers of the cyan (C), magenta (M), yellow (Y), and black (K) colors may be supplied to the four developing devices 210 from four developer cartridges 220 respectively accommodating the developers of the cyan (C), magenta (M), yellow (Y), and black (K) colors.

[0036] Each of the developing devices 210 may include a photosensitive drum 212, on a surface of which an electrostatic latent image may be formed, and a developing roller 211 to supply a developer to the electrostatic latent image and develop the same to a visible toner image. The photosensitive drum 212 is an example of a photoconductor, on a surface of which an electrostatic latent image may be formed. The photosensitive drum 212 may include a conductive metal pipe and a photosensitive layer formed on an outer circumference thereof. A charging roller 215 is an example of a charger to charge the photosensitive drum 212 to have a uniform surface electric potential. Instead of the charging roller 215, a charging brush, a corona charger, or the like may be used.

[0037] Although not illustrated in the drawings, the developing devices 210 may further include a charging roller cleaner to remove foreign substances, such as a developer and dust, adhered to the charging roller 215, a regulating member to regulate an amount of developer supplied to a development region in which the photosensitive drum 212 and the developing roller 211 face each other, or the like. A cleaning member 217 is to remove a developer remaining on a surface of the photosensitive drum 212 after an intermediate transfer process to be described later. The cleaning member 217 may be, for example, a cleaning blade that may contact with the surface of the photosensitive drum 212 and scrape a developer. Although not illustrated in the drawing, the cleaning member 217 may include a cleaning brush that may rotate to contact the surface of the photosensitive drum 212 and scrape a developer.

[0038] The exposure device 250 is to irradiate light modulated in accordance with image information, to the photosensitive drum 212, and form an electrostatic latent image on the photosensitive drum 212. Examples of the exposure device 250 include a laser scanning unit (LSU) using a laser diode as a light source, a light emitting diode (LED) exposure device using an LED as a light source, or the like.

[0039] A developer may include, for example, toner or toner and a carrier. The developing roller 211 may be arranged apart from the photosensitive drum 212. A distance between an outer circumferential surface of the developing roller

211 and an outer circumferential surface of the photosensitive drum 212 may be, for example, several tens to hundreds of microns. The developing roller 211 may include a magnetic roller. In addition, the developing roller 211 may be in a form in which a magnet is arranged in a rotating developing sleeve. In the developing devices 210, toner and a carrier are mixed, and the toner may be adhered to a surface of a magnetic carrier. The magnetic carrier may be adhered to a surface of the developing roller 211 and transported to the development region in which the photosensitive drum 212 and the developing roller 211 face each other. The regulating member (not shown) is to regulate an amount of developer transported to the development region. The toner may be supplied to the photosensitive drum

212 by a developing bias voltage applied between the developing roller 211 and the photosensitive drum 212, and the electrostatic latent image formed on the surface of the photosensitive drum 212 may be developed to a visible toner image. [0040] The intermediate transfer belt 260 may temporarily accommodate the toner image developed on the photosensitive drum 212 of the four developing devices 210. The intermediate transfer belt 260 may be supported by a plurality of support rollers 262, 263, 264, and 265 and move in circles. Four intermediate transfer rollers 261 may be arranged at positions respectively facing the photosensitive drums 212 of the four developing devices 210, with the intermediate transfer belt 260 therebetween. The intermediate transfer rollers 261 are to press the intermediate transfer belt 260 toward the photosensitive drum 212 to form an intermediate transfer nip. An intermediate transfer bias voltage may be applied to the intermediate transfer rollers 261 to intermediately transfer the toner image developed on the photosensitive drum 212, onto the intermediate transfer belt 260. The transfer roller 270 may be located to face the intermediate transfer belt 260. The transfer roller 270 may be located to face, for example, the support roller 262 and may be pressed toward the intermediate transfer belt 260 to form a transfer nip. A print medium P may be withdrawn from a paper feeding unit 290 and supplied to the transfer nip along a feed path 291. A transfer bias voltage for transferring the toner image on the intermediate transfer belt 260 to the print medium P may be applied to the transfer roller 270. The fuser 280 is to apply heat and/or pressure to the toner image on the print medium P to fuse the same on the print medium P. The print medium P on which printing is completed may be discharged by a discharge roller 292.

[0041] An image forming apparatus may include various members to vary positions thereof, and to this end, an example cam driving device described with reference to FIGS. 1 through 7 may be applied. For example, the cam driving device may be applied to the fuser 280 to form or release a fusing nip. For example, the cam driving device may be used to form or release an intermediate transfer nip. hereinafter, examples of the cam driving device applied to an image forming apparatus will be described.

[0042] FIGS. 9 and 10 are schematic structural diagrams of a fuser, wherein FIG. 9 illustrates a state in which a fusing nip is formed according to an example, and FIG. 10 illustrates a state in which the fusing nip is released according to an example.

[0043] Referring to FIGS. 9 and 10, a heating member of the fuser and a backup member are included. The heating member and the backup member may be pressed against each other to form a fusing nip 101. In an example, the heating member may be a flexible continuous belt 120. The backup member may be a backup roller 110. A heater 130 may be located inside the continuous belt 120 to heat the continuous belt 120. The backup roller 110 may be located outside the continuous belt 120 to face the heater 130. An elastic member 170 may provide a pressing force to the continuous belt 120 to form the fusing nip 101. In an example, the elastic member 170 may provide a pressing force to the heater 130. According to the pressing force of the elastic member 170, the heater 130 and the backup roller 110 may be pressed against each other with the continuous belt 120 therebetween, thereby forming the fusing nip 101. The heater 130 may heat the continuous belt 120 at the fusing nip 101. Based on the print medium P, on a surface of which a toner image is formed, passing through the fusing nip 101 , the toner image may be fused on the print medium P by the heat and pressure. [0044] The pressing force provided by the elastic member 170 to the continuous belt 120 may be varied. For example, while fusing is performed, a sufficient pressing force may be provided to the continuous belt 120 to improve the fusing characteristics, and, while fusing is not performed, the pressing force may be reduced or released to reduce stress applied to the continuous belt 120 or the backup roller 110. To this end, a cam driving device 1000-3 may be used. In an example, the cam driving device 1000 illustrated in FIGS. 1 through 3 may be applied as the cam driving device 1000-3.

[0045] Referring to FIGS. 9 and 10, a pressurization lever 160 that is pivotable about a hinge 161 is illustrated. The pressurization lever 160 corresponds to the movable object 10. The elastic member 170 corresponds to the load applying member 30, and may be, for example, a compression coil spring to apply an elastic force to the pressurization lever 160. The heater 130 may be supported by a support member 140. A pressurization bracket 150 may be supported by the support member 140 and protrude outwardly from a widthwise edge of the continuous belt 120. The pressurization lever 160 may press the pressurization bracket 150 to form the fusing nip 101. The pressurization lever 160 may be driven by the rotary cam 20. The cam portion 22 of the rotary cam 20 may face a cam contacting portion 162 of the pressurization lever 160. As described above with reference to FIGS. 1 through 3, the rotary cam 20 may be connected to the driving motor 50 with the reducer 40 therebetween.

[0046] As illustrated in FIG. 9, based on a maximum radius potion 22a of the cam portion 22 contacting the cam contacting portion 162 of the pressurization lever 160, the pressurization lever 160 may be pivoted about the hinge 161 to reach a top dead position (second position). In this state, an elastic force of the elastic member 170 is not applied to the continuous belt 120, and thus the fusing nip 101 may be released. While the fusing nip 101 is released, a jam of the print medium P caused in the fusing nip 101 may be removed.

[0047] In the state illustrated in FIG. 9, based on the rotary cam 20 rotating by 180 degrees, as illustrated in FIG. 10, a minimum radius portion 22b of the cam portion 22 faces the cam contacting portion 162 of the pressurization lever 160. In this orientation, the minimum radius portion 22b of the cam portion 22 may be apart from the cam contacting portion 162 of the pressurization lever 160. The pressurization lever 160 may be pivoted about the hinge 161 by an elastic force of the elastic member 170 to reach a bottom dead position (first position). The pressurization lever 160 may press the heater 130 with the pressurization bracket 150 and the support member 140 therebetween, and the fusing nip 101 may be formed between the continuous belt 120 and the backup roller 110.

[0048] Although not illustrated in the drawings, in the state illustrated in FIG. 9, based on the rotary cam 20 rotating by 90 degrees, the pressurization lever 160 may be located at a middle position, and the pressing force of the elastic member 170 may be reduced. In this state, a printing operation on the print medium P, for example, an envelope, may be performed. Accordingly, wrinkles may be prevented from the envelope in a fusing process. In various examples, as the cam driving device 1000-3 moving the pressurization lever 160 to the top dead position, middle position, and bottom dead position, the cam driving device 1000- 1 or 1000-2 illustrated in FIG. 5 or FIG. 7 may be applied.

[0049] Referring again to FIG. 8, during printing, the intermediate transfer rollers 261 may be located at a pressurization position where the intermediate transfer rollers 261 press the intermediate transfer belt 260 to bring the intermediate transfer belt 260 into contact with the photosensitive drum 212 to form an intermediate transfer nip. Based on a long time passing after the intermediate transfer nip is formed, deformation of the intermediate transfer rollers 261 , damage to the surface of the photosensitive drum 212 and a surface of the intermediate transfer belt 260 due to friction, and damage to the photosensitive layer of the photosensitive drum 212 due to static electricity may be generated. Considering this potential damage, based on printing not being performed, the intermediate transfer rollers 261 may be moved from the pressurization position to a release position where the pressing force applied to the intermediate transfer belt 260 is lifted to release the intermediate transfer nip. A cam driving device 1000-4 may be applied to move the intermediate transfer roller 261 between the pressurization position and the release position.

[0050] FIGS. 11 and 12 are diagrams illustrating an intermediate transfer roller, wherein FIG. 11 illustrates a state in which the intermediate transfer roller is located at a pressurization position according to an example, and FIG. 12 illustrates a state in which the intermediate transfer roller is located at a release position according to an example.

[0051] Referring to FIGS. 11 and 12, the intermediate transfer belt 260, the intermediate transfer roller 261 , a holder 310, an elastic member 320, and a slider 330 are illustrated. The intermediate transfer roller 261 may be located within the intermediate transfer belt 260. The holder 310 is to rotatably support the intermediate transfer roller 261 and may be moved between the pressurization position, at which the intermediate transfer roller 261 presses the intermediate transfer belt 260 to the outside, and the release position, at which the pressing force is lifted. The intermediate transfer roller 261 may be rotatably supported by the holder 310. The holder 310 may include a hinge 311 and a first arm 312 and a second arm 313 extending from the hinge 311 in different directions from each other. The holder 310 may be supported by a first side frame (not shown) to be pivotable about the hinge 311. An end portion of the intermediate transfer roller 261 may be rotatably supported by the first arm 312 of the holder 310. The holder 310 may be pivoted about the hinge 311 to move the intermediate transfer roller 261 between the pressurization position and the release position. The holder 310 may be elastically biased to be pivoted in a direction in which the intermediate transfer roller 261 is located at the pressurization position by the elastic member 320. Although not illustrated in the drawings, the other end portion of the intermediate transfer roller 261 may be supported by a second side frame (not shown) facing the first side frame, by the same structure described above to be moved between the pressurization position and the release position. A protrusion 314 axially protruding from the second arm 313 may be provided on the second arm 313 of the holder 310.

[0052] The slider 330 may be connected to the holder 310 and slid between a first position (FIG. 11) at which the holder 310 is located at the pressurization position and a second position (FIG. 12) at which the holder 310 is located at the release position. For example, a pair of sliders 330 may be supported to be slid between each of the first position and the second position, respectively, on the first side frame and the second side frame. An interference protrusion 331 to interfere with the protrusion 314 of the holder 310 may be provided on the slider 330. Although not illustrated in the drawings, four intermediate transfer rollers 261 may be supported by the holder 310 in moving directions D1 and D2 of the slider

330 and arranged to be pivoted between the pressurization position and the release position, and four interference protrusions 331 respectively corresponding to the protrusions 314 of the four holders 310 may be provided on the slider 330.

[0053] As illustrated in FIG. 11, based on the slider 330 being slid in the direction D1 to be at the first position, the interference protrusions 331 are apart from the protrusions 314 of the holder 310. Accordingly, the holder 310 may be pivoted about the hinge 311 by the elastic force of the elastic member 320 in direction B1, and the intermediate transfer rollers 261 may be located at the pressurization position. The intermediate transfer rollers 261 may press the intermediate transfer belt 260 to the photosensitive drum 212 to form an intermediate transfer nip. As illustrated in FIG. 12, based on the slider 330 being slid in the direction D2 to be at the second position, the interference protrusions

331 may push the protrusions 314 of the holder 310 in the direction D2. In that case, the holder 310 may be pivoted about the hinge 311 in an opposite direction of the elastic force of the elastic member 320, that is, in direction B2, and the intermediate transfer rollers 261 may be located at the release position. As the pressing force applied by the intermediate transfer rollers 261 to the intermediate transfer belt 260 is lifted, the intermediate transfer nip between the intermediate transfer belt 260 and the photosensitive drum 212 may be released.

[0054] The cam driving device 1000-4 may be applied to move the slider 330 between the first position and the second position. The cam driving device 1000 illustrated in FIGS. 1 through 3 may be applied as the cam driving device 1000-4. In this case, the slider 330 corresponds to the movable object 10, and the elastic member 320 corresponds to the load applying member 30. A rotary cam 340 may be in contact with the slider 330 and rotate, sliding the slider 330 between the first position and the second position. The rotary cam 340 may rotatably support the first and second side frames with respect to a central shaft 341. The rotary cam 340 includes a cam portion 342. The rotary cam 340 corresponds to the rotary cam 20 of the cam driving device 1000. The slider 330 may include first and second contact portions 332 and 333 to selectively contact the cam portion 342 according to a rotational phase of the rotary cam 340.

[0055] Referring to the example of FIG. 11, the cam portion 342 of the rotary cam 340 is in contact with the first contact portion 332. The slider 330 is at the first position. As the interference protrusions 331 are apart from the protrusions 314 of the holder 310, the elastic force of the elastic member 320 may not be applied to the slider 330. A load torque applied to the rotary cam 340 may be minimized. A state in which the slider 330 is located at the first position corresponds to a state in which the movable object 10 illustrated in FIG. 3 is located at the bottom dead position. The first gear 41 and the second gear 42 may be engaged with each other such that a reduction ratio of the reducer 40 may be minimized.

[0056] In the state illustrated in FIG. 11 , based on the rotary cam 340 being rotated, the cam portion 342 starts to contact the second contact portion 333, and the slider 330 starts to slide in the direction D2. After the interference protrusions 331 of the slider 330 have contacted the protrusions 314 of the holder 310 and the slider 330 is further slid in the direction D2, the interference protrusions 331 push the protrusions 314 of the holder 310 in the direction D2. The holder 310 may be rotated about the hinge 311 in an opposite direction of the elastic force of the elastic member 320, that is, in the direction B2. Due to the elastic force of the elastic member 320, a force hindering sliding of the slider 330 in direction D2 may be applied to the slider 330, and according to this force, a load torque may be applied to the rotary cam 340. Until the rotary cam 340 is rotated by, for example, 180 degrees, the load torque is gradually increased. Based on the rotary cam 340 being rotated by 180 degrees, as illustrated in FIG. 12, the slider 330 reaches the second position, and the intermediate transfer rollers 261 reach the release position at which the intermediate transfer nip is released. In a state in which the slider 330 is located at the second position, the load torque applied to the rotary cam 340 is maximized. The state in which the slider 330 is located at the second position corresponds to a state in which the movable object 10 is located at the top dead position, as illustrated in FIG. 1. The first gear 41 and the second gear 42 may be engaged with each other such that the reduction ratio of the reducer 40 may be maximized. In various examples, as the cam driving device 1000-4 moving the slider 330 to the first position, the cam driving device 1000-1 or 1000- 2 illustrated in FIG. 5 or FIG. 7 may be applied.

[0057] It should be understood that examples described herein should be considered in a descriptive sense and not for purposes of limitation. Descriptions of features or aspects within each example should typically be considered as available for other similar features or aspects in other examples. While examples have been described with reference to the figures, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.