Patent Publication Number: US-11375875-B2

Title: Roller device and dishwasher including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2018-0143594, filed on Nov. 20, 2018, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     The disclosure relates to a roller device having improved rolling performance and a dishwasher including the same. 
     2. Description of Related Art 
     in general, a dishwasher is a device for washing tableware by injecting high-pressure washing water on the tableware, and may normally perform preliminary washing, main washing, rinsing, and drying. 
     In the preliminary washing process, washing water is injected without the addition of a detergent to remove dregs from the tableware, and in the main washing process, washing water is injected and at the same time the detergent is supplied by a detergent supply device so that the tableware may be washed. 
     In the rinsing process, washing water may be injected to wash off the detergent, and in the drying process, water remaining in the tableware may be removed. 
     A basket for receiving tableware may be provided in a washing tub in which the tableware are washed. In order for a user to conveniently put in or out tableware, the basket may be installed to withdrawn through a front surface of the washing tub. A roller device is installed at opposite sides of the basket to guide the movement of the basket. 
     In general, the basket at which the roller device is installed may be moved by rolling motion along a rail using a roller or the like. However, the method of moving the basket using only the roller may cause severe friction and noise. 
     A separate ball bearing may be additionally used in the roller to guide the basket. However, in the roller in which a separate ball bearing is used, the stricture for supporting the ball bearing may be vulnerable in durability, and the manufacturing cost thereof may increase. 
     SUMMARY 
     It is an aspect of the disclosure to provide a roller device including a plurality of balls and shafts improved to enhance the rolling performance of a roller, and a dishwasher including the same. 
     It is another aspect of the disclosure to provide a roller device improved such that a roller is provided with a seating portion capable of performing a retainer function together, and a dishwasher including the same. 
     It is another aspect of the disclosure to provide a roller device including a coupling member improved such that a roller, a plurality of balls, and a shaft are firmly coupled to each other, and a dishwasher including the same. 
     Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure. 
     In accordance with an aspect of the disclosure, a dishwasher includes a cabinet including a washing tub, a basket provided inside the washing tub, a shaft unit coupled to the basket and including a shaft, a plurality of balls rotating along an outer circumferential surface of the shaft, and a roller rotatably coupled to the shaft and including a plurality of seating portions spaced apart from each other to seat the plurality of balls, wherein at least one of the plurality of seating portions receives two or more of the plurality of balls. 
     The shaft may include a first shaft configured to allow the plurality of balls to rotate, and a second shaft having a step outward from the first shaft to prevent the plurality of balls from being separated from the plurality of seating portions. 
     The first shaft may include a cylindrical shape such that the plurality of balls rotates in point contact with the first shaft. 
     An outer circumferential surface of the first shaft with which the plurality of balls is in contact may form a straight line. 
     The roller may include a wheel portion configured to roll along opposite side portions of a lower plate of the washing tub, and a stopper portion forming a step outward from the wheel portion to prevent the wheel portion from being separated from the opposite side portions. 
     The plurality of seating portions may be recessed outward from an inner circumferential surface of the wheel portion and may constitute a groove opened in a direction of directing to the stopper portion to prevent the plurality of balls from being constrained to the plurality of seating portions. 
     The roller may further include a bottom portion bent from the wheel portion to cover an outer side of the roller, and the bottom portion may include a placement hole configured such that the plurality of balls is spaced apart from an inner surface of the bottom portion and seated in the plurality of seating portions. 
     The placement hole may be connected to the plurality of seating portions. 
     The shaft unit may further include a shaft body coupled to the basket, and the shaft may protrude from the shaft body and may be fixed to the shaft body such that the plurality of balls and the roller rotate around the shaft. 
     The shaft unit may include a basket coupling portion configured to be coupled to one of the plurality of horizontally arranged horizontal wires constituting the basket, an anti-rotation portion configured to interfere with the other one of the plurality of horizontal wires to prevent the shaft unit from rotating around the horizontal wire coupled to the basket coupling portion, and an anti-movement portion configured to interfere with one of a plurality of vertically arranged vertical wires constituting the basket to prevent the shaft unit from moving along the plurality of horizontal wires. 
     The dishwasher may further include a coupling member configured to connect the roller and the shaft, wherein the coupling member may include a base portion, a body portion protruding from the base portion, and a head portion extending from the body portion. 
     The roller may further include a boss including a coupling hole into which the coupling member is inserted. 
     The shaft may include an insertion hole into which the boss is inserted. 
     The boss may include a head stopper configured to catch the head portion inserted into the coupling hole, and the shaft may include a base stopper configured to catch the base portion inserted into the insertion hole. 
     A gap between an outer surface of the boss and an inner surface of the insertion hole may be larger than a gap between an outer surface of the shaft and an inner surface of the plurality of seating portions and the plurality of balls seated in the plurality of seating portions. 
     In accordance with another aspect of the disclosure, a dishwasher includes a cabinet including a washing tub, a basket provided inside the washing tub, and a roller device configured to withdraw the basket from the washing tub, wherein the roller device includes a shaft unit including a shaft, a plurality of balls configured to rotate along an outer circumferential surface of the shaft, and a roller including a wheel portion configured to be rotatable about the shaft and a seating portion having an opened end to prevent the plurality of balls from being constrained and recessed outward from an inner circumferential surface of the wheel portion, and wherein an outer circumferential surface of the shaft with which the plurality of balls is in contact forms a straight line. 
     A plurality of the seating portions may be provided to be spaced apart from each other, and at least one of the plurality of seating portions may receive two or more of the plurality of balls. 
     In accordance with another aspect of the disclosure, a roller device includes a plurality of balls, a shaft unit including a shaft including a cylindrical shape such that the plurality of balls rotate along an outer circumferential surface thereof, and a roller rotatably coupled to the shaft and including a plurality of seating portions spaced apart from each other to seat the plurality of balls, wherein two or more of the plurality of balls is seated in the plurality of seating portions, respectively. 
     The roller device may further include a coupling member configured to connect the roller and the shaft. 
     The roller may further include a boss including a coupling hole into which the coupling member is inserted, and the shaft may include an insertion hole into which the boss and the coupling member are inserted. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation; the term “or,” is inclusive, meaning and/or; the phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term “controller” means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. 
     Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device. 
     Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects of the disclosure will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a perspective view of a dishwasher according to the disclosure; 
         FIG. 2  illustrates a cross-sectional view of the dishwasher according to the disclosure; 
         FIG. 3  is a view illustrating a roller device coupled to a basket in the dishwasher according to the disclosure; 
         FIG. 4  is a view illustrating the roller device rolling along opposite sides of a lower plate in the dishwasher according to the disclosure; 
         FIG. 5  illustrates an exploded perspective view of the roller device in the dishwasher according to the disclosure; 
         FIG. 6  is a view illustrating a roller in the dishwasher according to the disclosure; 
         FIG. 7  is a view illustrating a state in which a plurality of balls is received in a seating portion of the roller in the dishwasher according to the disclosure; 
         FIG. 8  illustrates a cross-sectional view of the roller device in the dishwasher according to the disclosure; and 
         FIG. 9  illustrates an enlarged view of a portion of the cross section of the roller device illustrated in  FIG. 8  in the dishwasher according to the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 through 9 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device, 
     The embodiments described herein and the configurations shown in the drawings are only examples of embodiments of the disclosure, and various modifications may be made at the time of filing of the disclosure to replace the embodiments and drawings of the present specification. 
     Like reference numbers or signs in the various figures application represent parts and components that perform substantially the same functions. 
     The terms used herein are for the purpose of describing the embodiments and are not intended to restrict and/or to limit the disclosure. For example, the singular expressions herein may include plural expressions, unless the context clearly dictates otherwise. 
     The terms “comprises” or “has” are intended to indicate that there are features, numbers, steps, operations, elements, parts, or components thereof described in the specification, and do not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, parts, or components thereof. 
     It will be understood that although the terms “first,” “second,” etc. may be used herein to describe various components, these components should not be limited by these terms, and the terms are only used to distinguish one component from another. 
     For example, without departing from the scope of the disclosure, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. The term “and/or” includes any combination of a plurality of related items or any one of a plurality of related items. 
     In addition, directions such as “front,” “rear,” “upper,” “lower,” etc. used in the present specification are defined based on the drawings, and the shape and position of each component are not limited by these terms. 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. 
     A roller device according to the disclosure may be applied to household appliances such as a basket of a dishwasher and a basket of an oven, and all the products that move in rolling motion such as furniture drawers. Hereinafter the roller device according to the disclosure will be described based on an example applied to the dishwasher. 
     Particularly, in the case of the basket of the dishwasher, the front of the basket may be lifted to have a predetermined inclination in order to prevent water remaining inside the washing tub from leaking to the outside. 
     Therefore, in general, in a case where the friction force of the roller is reduced by adding a separate ball bearing to the roller so that the roller performance is excessively enhanced, the basket may not be maintained in a withdrawn state and may be retracted back into place by the inclination. Accordingly, the user may be inconvenienced when putting tableware into the basket or taking the tableware out of the basket. 
     Therefore, there may be a need to use a roller capable of rolling motion with an appropriate friction force such that the basket of the dishwasher may be maintained in the withdrawn state. 
       FIG. 1  illustrates a perspective view of a dishwasher according to the disclosure, and  FIG. 2  illustrates a cross-sectional of the dishwasher according to the disclosure. 
     As illustrated in  FIGS. 1 and 2 , a dishwasher  1  according to the disclosure may include a cabinet  10  forming an outer appearance and a washing tub  12  provided inside the cabinet  10 . 
     The cabinet  10  may be formed in a box shape. However, the shape of the cabinet  10  is not limited thereto, may be formed in the shape of a cylinder or a polygonal column, and may be formed in a box shape of a polyhedron other than a hexahedron. In addition, the cabinet  10  may be formed in various shapes that may be applied as an external shape. 
     The washing tub  12  may be provided in a substantially box shape and may include a front surface open to put into and out tableware. The open front surface of the washing tub  12  may be opened and closed by the door  11 . The door  11  may be rotatably coupled to the cabinet  10 . 
     The washing tub  12  may be formed in a shape corresponding to the outer shape of the cabinet  10 . The washing tub  12  may be formed in a box shape, but the shape of the washing tub  12  is not limited thereto. 
     The washing tub  12  may be formed in the shape of a cylinder or a polyhedral column and may also be formed in a box shape of a polyhedron other than a hexahedron. On the other hand, the washing tub  12  is not necessarily formed in a shape corresponding to the outer shape of the cabinet  10 . 
     The washing tub  12  may include an upper plate  12   a  constituting an upper surface of the washing tub  12 , opposite side plates  12   b  constituting side surfaces of the washing tub  12 , a rear plate  12   c  constituting a rear surface of the washing tub  12 , and a lower plate  12   d  constituting a lower surface of the washing tub  12 . 
     The door  11  may rotate in a predetermined direction and open and close the washing tub  12 . 
     One end of the door  11  may be provided with a hinge to rotate the door  11  in the predetermined direction. 
     The door  11  may be provided in the front of the washing tub  12 , and a user may open the door  11  to put the tableware into and out of the washing tub  12 . The door  11  may be provided with a handle so that the user may easily open and close the door  11 . 
     The dishwasher  1  may include a basket  60  provided inside the washing tub  12  to receive the tableware and a rail  13  to support the basket  60 . The basket  60  may include wires  61 ,  62 ,  63  (refer to  FIG. 3 ) to allow the washing water to pass through without remaining. 
     The basket  60  may include an upper basket  60   a  and a lower basket  60   b . The upper basket  60   a  may be supported by the rail  13 , and the lower basket  60   b  may be supported by opposite side portions  12   e  of the lower plate  12   d.    
     The upper basket  60   a  and the lower basket  60   b  may be configured to be slidable back and forth through the rail  13  and the opposite side portions  12   e  of the lower plate  12   d  in the washing tub  12 . 
     The dishwasher  1  may include a sump  20  to collect and store the washing water, and a supply pipe  30  configured to supply the washing water to an injecting device  40 . The sump  20  may be provided with a washing pump  21  for pumping the stored water into the injecting device  40 . 
     The injecting device  40  may include a first injecting, device  41  provided above the upper basket  60   a  a second injecting device  42  provided between the upper basket  60   a  and the lower basket  60   b , and a third injecting device  43  provided below the lower basket  60   b.    
     The first injecting device  41  may be configured to rotate about a first rotation shaft  41   a , and the second injecting device  42  may be configured to rotate about a second rotation shaft  42   a.    
     The first injecting device  41  may inject the washing water toward the tableware received in the upper basket  60   a , and the second injecting device  42  may inject the washing water toward the tableware received in the upper basket  60   a  and the lower basket  60   b.    
     The third injecting device  43  may be configured to be fixed to one side of the washing tub  12 , unlike the first injecting device  41  and the second injecting device  42 . The third injecting device  43  may inject the washing water in a substantially horizontal direction. Therefore, the washing water injected from the third injecting device  43  may not direct to the tableware. 
     The third injecting device  43  may include a nozzle  44  through which the washing water is injected. A plurality of the nozzles  44  may be provided. The plurality of nozzles  44  may be arranged in a line and spaced apart from each other by a predetermined distance approximately from one side surface to the opposite side surface of the washing tub  12 . 
     The washing water injected in a substantially horizontal direction from the nozzle  44  of the third injecting device  43  may be changed in direction by a switching device  50  disposed inside the washing tub  12  and then may direct to the tableware received in the lower basket  60   b.    
     The switching device  50  may be constrained to a guide rail  52  by a holder  51  and may be configured to be movable along the guide rail  52 . 
     The supply pipe  30  may include a first supply pipe  31  configured to supply the washing water pumped by the washing pump  21  to the first injecting device  41  and the second injecting device  42 , and a second supply pipe  32  configured to supply the washing water to the third injecting device  43 . 
     A heater  15  to heat the washing water and a drain pump  22  to drain the washing water may be provided below the washing tub  12 . 
     The basket  60  may be provided to be withdrawn through the front surface of the washing tub  12 . 
     Accordingly, the dishwasher  1  may include a wheel  14  or a roller device  100  to guide the basket  60  to be withdrawn toward the front of the washing tub  12 . 
     The basket  60  is withdrawn along the wheel  14  or the roller device  100  to receive the tableware and pushed back into the washing tub  12 , and then the tableware may be washed. When the washing of the tableware is completed, the basket  60  may be withdrawn through the front surface of the washing tub  12  and the washed tableware may be taken out. 
     The wheel  14  or the roller device  100  may be disposed between the washing tub  12  and the basket  60  so that the basket  60  may be supported by the washing tub  12 . The wheel  14  or the roller device  100  may be coupled to the opposite sides of the basket  60 . 
     The upper basket  60   a  may include the wheel  14  and the lower basket  60   b  may include the roller device  100 . However, the disclosure is not limited thereto, and the upper basket  60   a  may also include the roller device  100  instead of the wheel  14 . 
       FIG. 3  is a view illustrating a roller device coupled to a basket in the dishwasher according to the disclosure, and  FIG. 4  is a view illustrating the roller device rolling along opposite sides of a lower plate in the dishwasher according to the disclosure. 
     As illustrated in  FIGS. 3 and 4 , the roller device  100  may include a shaft unit  120  coupled to the basket  60  (refer to  FIG. 2 ), and a roller  130  rotatably coupled to a shaft  121  provided to allow the basket  60  to be withdrawn from the washing tub  12 . 
     The shaft unit  120  may include a shaft body  120   a , and a basket coupling portion  124  provided on the shaft body  120   a  to be coupled to one of the plurality of horizontally arranged horizontal wires  61  and  62  constituting the basket  60 . 
     Two of the basket coupling portions  124  may be provided to be symmetrical to the shaft body  120   a . However, the disclosure is not limited thereto. 
     The basket coupling portion  124  may have elasticity. The basket coupling portion  124  may include a ring shape with opened one side. 
     The one horizontal wire  61  of the plurality of horizontally arranged horizontal wires  61  and  62  constituting the basket  60  may be coupled to the basket coupling portion  124  through the opened one side of the elastic basket coupling portion  124 . 
     However, the disclosure is not limited thereto, and the basket coupling portion  124  may include various shapes within a limit capable of coupling the shaft unit  120  to the basket  60 . 
     The shaft unit  120  may include an anti-rotation portion  125  configured to interfere with the other horizontal wire  62  of the plurality of horizontal wires  61  and  62  to prevent the shaft unit  120  from rotating around the horizontal wire  61  coupled to the basket coupling portion  124 . 
     A plurality of the anti-rotation portions  125  may be provided. The anti-rotation portion  125  may be provided in the vicinity of the basket coupling portion  124 . The anti-rotation portion  125  may be provided above the basket coupling portion  124 . 
     The anti-rotation portion  125  may prevent the shaft unit  120  from rotating in both directions around the horizontal wire  61  coupled to the basket coupling portion  124 . 
     For example, one of the anti-rotation portion  125  may be disposed to interfere with one side of the horizontal wire  62  to prevent the shaft unit  120  from rotating in one direction, and two of the anti-rotation portions  125  may be disposed to interfere with the other side of the horizontal wire  62  to prevent the shaft unit  120  from rotating in the other direction. 
     However, the disclosure is not limited thereto, and the shape and number of the anti-rotation portions  125  may be variously provided within a limit capable of preventing the shaft unit  120  from rotating around the horizontal wire  61  coupled to the basket coupling portion  124 . 
     The shaft unit  120  may include an anti-movement portion  126  configured to interfere with one of a plurality of vertically arranged vertical wires  63  constituting the basket  60  to prevent the shaft unit  120  from moving along the plurality of horizontal wires  61  and  62 . 
     The vertical wire  63  may prevent the shaft unit  120  from moving in the front and rear directions by being inserted into a groove of the anti-movement portion  126 . 
     The anti-movement portion  126  may be provided at the center of the shaft body  120   a . However, the disclosure is not limited thereto, and the shape and number of the anti-movement portions  126  may be variously provided within a limit capable of preventing the shaft unit  120  from moving along the plurality of horizontal wires  61  and  62 . 
     The roller  130  may include a wheel portion  132  configured to roll along the opposite side portions  12   e  of the lower plate  12   d  of the washing tub  12 , and a stopper portion  138  forming a step outward from the wheel portion  132  to prevent the wheel portion  132  from being separated from the opposite side portions  12   e.    
     The wheel portion  132  may roll along an upper surface of the opposite side portions  12   e . As the wheel portion  132  according to the disclosure rolls along opposite side portions  12   e  of the lower plate  12   d , a separate rail for the wheel portion  132  may not be included, thereby reducing the manufacturing cost. 
     The wheel portion  132  and the stopper portion  138  may include a cylindrical shape. The diameter of the cross section of the stopper portion  138  may be larger than the diameter of the cross section of the wheel portion  132 . The stopper portion  138  may form a step outward from the wheel portion  132 . The stopper portion  138  may extend outward along a radial direction from the wheel portion  132 . 
     Thus, the stopper portion  138  interferes with the side surface of the opposite side portions  12   e  of the plate  12   d , so that the wheel portion  132  from being separated from the opposite side portions  12   e  may be prevented. 
       FIG. 5  illustrates an exploded perspective view of the roller device in the dishwasher according to the disclosure.  FIG. 6  is a view illustrating a roller in the dishwasher according to the disclosure.  FIG. 7  is a view illustrating a state in which a plurality of balls is received in a seating portion of the roller in the dishwasher according to the disclosure.  FIG. 8  illustrates a cross-sectional view of the roller device in the dishwasher according to the disclosure. 
     As illustrated in  FIGS. 5 to 8 , the roller device  100  (see  FIG. 4 ) may include a ball  110  provided such that the roller device  100  enables a rolling motion with a predetermined frictional force. A plurality of the balls  110  may be provided. 
     The number of the balls  110  is composed of eight, but the disclosure is not limited thereto. The number of balls  110  may be variously provided within a limit in which the roller device  100  enables the rolling motion with the predetermined friction force. 
     The roller device  100  may include a shaft unit  120  including the shaft  121  provided such that the ball  110  rotates along an outer circumferential surface thereof, and a roller  130  rotatably provided around the shaft  121 . 
     The roller  130  may include a seating portion  135  provided to seat the ball  110 . A plurality of the seating portions  135  may be provided to be spaced apart from each other. 
     The shaft  121  may include a first shaft  121   a  provided to allow the plurality of balls  110  to rotate, and a second shaft  121   b  forming a step outward from the first shaft  121   a  to prevent the plurality of halls  110  from being separated from the plurality of seating portions  135 . 
     The first shaft  121   a  may include a cylindrical shape such that the plurality of balls  110  rotate in point contact with the first shaft  121   a . An outer circumferential surface of the first shaft  121   a  with which the plurality of balls  110  is be in contact may form a straight line. 
     Therefore, as the shaft  121  according to the disclosure includes the first shaft  121   a  having a cylindrical shape, a groove for a separate raceway to allow the ball  110  to roll may be omitted, so that the shaft  121  may be easily taken out of a mold. 
     The shaft  121  may protrude from the shaft body  120   a  and may fixed to the shaft body  120   a  such that the plurality of balls  110  and the roller  130  rotate around the shaft  121 . The shaft  121  may be integrally formed with the shaft body  120   a.    
     Accordingly, in the roller device  100  according to the disclosure, the roller  130  and the plurality of balls  110  rotate around the shaft  121 , while the shaft  121  may be fixed without rotating. 
     The roller  130  may be coupled to the shaft  121  to be rotatable about the shaft  121 . The roller  130  may include a receiving portion  131  configured to receive the shaft  121 . 
     The receiving portion  131  may receive the shaft  121  and the plurality of balls  110 . The receiving portion  131  may be constituted by a bottom portion  133  and a wheel portion  132  bent from the bottom portion  133 . The receiving portion  131  may have a shape in which one surface is opened by the wheel portion  132  and the bottom portion  133 . 
     The ball  110  received in the receiving portion  131  may be positioned between the shaft  121  and the roller  130 . The ball  110  may be positioned between an outer surface of the first shaft  121   a  and an inner surface of the wheel portion  132 . 
     At least one of the plurality of seating portions  135  may receive two or more ones of the plurality of balls  110 .  FIG. 3  illustrates that two of the balls  110  are received in one of the seating portions  135 , but the disclosure is not limited thereto. 
     For example, two or more of the balls  110  may be received in one of the seating portion  135 . 
     The plurality of seating portions  135  is recessed outward from an inner circumferential surface of the wheel portion  132  and may constitute a groove opened in a direction of directing to the stopper portion  138  to prevent the plurality of balls  110  from being constrained to the plurality of seating portions  135 . 
     That is, the plurality of seating portions  135  according to the disclosure may not include an undercut portion. Therefore, the roller  130  may be easily taken out from the mold. 
     In general, the plurality of balls  110  may not be spaced apart from each other, and all of the plurality of balls  110  may be continuously arranged and received in the receiving portion  131 . In this case, however, because friction between the plurality of balls  110  may excessively affect the rolling performance of the roller  130  and the number of the balls  110  requires more than the number of the balls  110  when the plurality of balls  110  is spaced apart from each other, the manufacturing cost of the roller device  100  may increase. 
     Therefore, to solve this, the roller device  100  may include a retainer configured to allow the plurality of balls  110  to be spaced apart from each other in the receiving portion  131 . However, when a separate retainer is added, the manufacturing cost of the roller device  100  may increase. 
     Accordingly, in the roller device  100  according to the disclosure, the seating portion  135  formed with the groove on an inner surface of the roller  130  may perform a retainer function without adding a separate retainer to the roller  130 . 
     In addition, unlike the case where only one ball  110  is seated on one of the seating portion  135 , two or more of the halls  110  are seated on one of the seating portion  135  of the disclosure, so that the rolling performance of the roller  130  may be greatly improved and the friction noise may be reduced. 
     The number of seating portions  135  according to the disclosure is four, but the disclosure is not limited thereto. 
     The roller  130  may include the bottom portion  133  bent from the wheel portion  132  to cover an outer side of the roller  130 , and the bottom portion  133  may include a placement hole  137  configured such that the plurality of halls  110  is spaced apart from an inner surface of the bottom portion  133  and seated in the plurality of seating portions  135 . 
     A plurality of placement holes  137  may be provided. Eight of the placement holes  137  are provided, but the disclosure is not limited thereto. The number of placement holes  137  may be variously provided within the number corresponding to the plurality of balls  110 . 
     The placement hole  137  may be connected to the plurality of seating portions  135 . One of the seating portion  135  may be connected to two of the placement holes  137 . However, the disclosure is not limited thereto. 
     The ball  110  may be spaced apart from the bottom portion  133  and received inside the seating portion  135 . The placement hole  137  may be configured to allow a separate lifting member, which is configured such that the ball  110  is spaced apart from the bottom portion  133  to penetrate, when the roller device  100  is seated in a separate assembly device in order to assemble the roller device  100 . 
     The roller  130  may include a boss  136  configured to prevent the shaft  121  from being separated from the roller  130 . The boss  136  may protrude from the bottom portion  133 . 
     The boss  136  may protrude from the bottom portion  133  toward the shaft  121 . The boss  136  may protrude from the bottom portion  133  in a direction in which the roller  130  is coupled to the shaft  121 . 
     The shaft  121  may include an insertion hole  123  in which the boss  136  is inserted. The insertion hole  123  may include a hollow such that the boss  136  may be inserted. 
     The boss  136  may include a cylindrical shape. However, the disclosure is not limited thereto. One end of the boss  136  may be composed of four portions by being spaced apart from each other. The boss  136  may have a predetermined elastic force. However, the present disclosure is not limited thereto. 
     Therefore, the boss  136  may be easily inserted into the insertion hole  123  of the shaft  121 . 
     The roller  130  may include a guide portion  139  provided to guide the roller device  101  when the roller device  100  is seated in the separate assembly device for assembly. A plurality of the guide portion  139  may be provided. The guide portion  139  may be provided at the stopper portion  138 . However, the disclosure is not limited thereto. 
     The roller device  100  according to the disclosure may include a coupling member  140  to couple the roller  130  and the shaft  121 . 
     Because the roller device  100  according to the disclosure does not include the raceway on the outer circumferential surface of the shaft  121  and the undercut portion of the seating portion  135  to facilitate taking out from the mold, coupling through a forced press between the shaft  121 , the roller  130 , and the plurality of balls  110  may be difficult. 
     Therefore, the roller device  100  according to the disclosure may couple the roller  130  and the shaft  121  through the separate coupling member  140 . 
     The coupling member  140  may include a base portion  141 , a body portion  142  protruding from the base portion  141 , and a head portion  143  extending from the body portion  142 . The base portion  141  may have a disk shape, the body portion  142  may have a cylindrical shape, and the head portion  143  may have a diameter larger than the diameter of the cross section of the body portion  142 . However, the disclosure is not limited thereto. 
     The head portion  143  may extend outward from the body portion  142 . 
     The boss  136  may include a coupling hole  134  into which the coupling member  140  is inserted. The shaft  121  may include the insertion hole  123  into which the boss  136  is inserted. 
     The boss  136  may include a head stopper  136   a  configured to catch the head portion  143  inserted into the coupling hole  134 , and the shaft  121  may include a base stopper  127  configured to catch the base portion  141  inserted into the insertion hole  123 . 
     The head stopper  136   a  may have a diameter larger than the diameter of the coupling hole  134 , and the base stopper  127  may have a diameter larger than the diameter of the insertion hole  123 . The base stopper  127  may form a step outward from the insertion hole  123 . 
     Therefore as the base portion  141  is caught by the base stopper  127  and the head portion  143  is caught by the head stopper  136   a , the roller  130  may be prevented from being separated from the shaft  121 . 
     Hereinafter the process of assembling the roller device  100  will be described. 
     First, the plurality of balls  110  may be received in the receiving portion  131  of the roller  130 . Next, the roller  130  that receives the plurality of balls  110  may be seated in the separate assembly device. 
     In this process, the guide portion  139  of the roller  130  may easily guide the roller  130  to the assembly device. 
     When the roller  130  receiving the plurality of balls  110  is accommodated in the assembly device, the separate lifting member may be inserted through the placement hole  137  of the roller  130 . 
     The plurality of balls  110  received in the receiving portion  131  may be positioned at a height corresponding to the seating portion  135  by the lifting member, and may be disposed in the seating portion  135  in a radial direction by a pneumatic pressure, a magnetic force, or the like of the assembly device. 
     Next, in a state where the positions of the plurality of balls  110  is maintained, the shaft  121  is inserted toward the roller  130  so that the boss  136  is inserted into the insertion hole  123 , and the coupling member  140  is inserted into the insertion hole  123  of the shaft  121  and the coupling hole  134  of the boss  136  to couple the roller  130  and the shaft  121 , thereby completing the assembly of the roller device  100 . 
     Therefore, because the roller device  100  according to the disclosure may be easily assembled by the assembly device, the convenience of assembly may be improved and the manufacturing time of the roller device  100  may be shortened. 
       FIG. 9  illustrates an enlarged view of a portion of the cross section of the roller device illustrated in  FIG. 8  in the dishwasher according to the disclosure. As illustrated in  FIG. 9 , a gap G between an outer surface of the boss  136  and an inner surface of the insertion hole  123  is larger than a gap between the outer surface of the first shaft  121   a  and an inner surface of the plurality of seating portions  135  and the plurality of balls  110  seated in the plurality of seating portions  135 . 
     That is, the gap G between an outer surface of the boss  136  and the inner surface of the insertion hole  123  is larger than a value obtained by subtracting a diameter D of the ball  110  from a gap S between the outer surface of the first shaft  121   a  and the inner surface of the seating portion  135 . 
     The ball  110  received in the seating portion  135  may be spaced apart from the roller  130  or the shaft  121  by a predetermined distance to enable rolling motion. 
     Due to the gap between the ball  110 , the roller  130 , and the shaft  121 , when the roller device  100  is twisted by an external force, the plurality of balls  110  may be separated from the seating portion  135 . 
     Therefore, to prevent this, the roller  130  according to the disclosure may include the boss  136  inserted into the insertion hole  123 . 
     When the roller device  100  is twisted by the external force, the boss  136  is caught by the interference with the insertion hole  123 , thereby preventing the plurality of balls  110  from being separated from the seating portions  135 . 
     As is apparent from the above, the disclosure can improve the convenience of use by enhancing the rolling performance of a roller. 
     The disclosure can reduce the manufacturing cost of a roller device by the roller being provided with a seating portion capable of performing a retainer function together. 
     The disclosure can prevent a plurality of balls from being separated from the rollers and a shaft by an external force by improving such that the roller, the plurality of balls, and the shaft are firmly coupled to each other. 
     The technical spirit of the disclosure has been described above, but the scope of the disclosure is not limited thereto. 
     It will be understood by those of skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the disclosure. 
     Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.