Wheel and method for manufacturing a wheel

Abstract

[Problem] To provide an omnidirectional wheel capable of reducing manufacturing costs and a method for manufacturing the wheel. [Solution] The wheel (30) includes: a core (32) obtained by forming a tubular member (140) including a plurality of V-shaped notches (142) in a first side surface into an annular shape by closing the V-shaped notches; and free rollers (60) rotatably assembled via bearings (122) onto each linear portion (120) of the tubular member located between adjacent V-shaped notches, each bearing including an inner race (124) and an outer race (126). A cutting projection (130) and a projection (38) are provided on the other side surface of the tubular member opposite to the first side surface, and the cutting projection and the projection engage end surfaces of the corresponding inner races to anchor the inner races to the core.

Description

Technical Field

[0001] The present invention relates to a wheel and a method for manufacturing a wheel. Background Art

[0002] Omnidirectional wheels are known for use in omnidirectional vehicles such as passenger cars, transport devices, and robots. Known omnidirectional wheels include an annular core member and a plurality of free rollers supported by the core member so as to be rotatable about the center line of the core member. See, for example, Patent Document 1.

[0003] According to this prior art, a plurality of inner sleeves (fixed members), each having a tubular shape, are fixedly assembled on the core member. In order to keep each inner sleeve fixed on the core member, the shape and size of the inner sleeve are selected such that the inner sleeve contacts the radial outside of the core member and contacts the radial inside of the core member at both axial ends of the inner sleeve. Each free roller is supported by the core member so as to be rotatable about the circular axis of the core member via a ball bearing including an inner race and an outer race, the inner race having an inner circumferential surface bonded to the outer circumferential surface of the inner sleeve, and the outer race being freely rotatable relative to the inner race.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-210035 Summary of the Invention

[0007] Tasks to be Accomplished by the Invention

[0008] Since the inner sleeves according to the prior art disclosed in Patent Document 1 need to have an inner hole with precise shape and size, machining of the inner sleeves is difficult. Therefore, the manufacturing cost of the inner sleeves becomes high, and wheels that require a large number of inner sleeves become very expensive.

[0009] In view of this problem of the prior art, the main object of the present invention is to provide a wheel of the omnidirectional wheel type that can be manufactured at low cost and a method for manufacturing such a wheel.

[0010] Means for Accomplishing the Tasks

[0011] To achieve this object, a specific aspect of the present invention provides a wheel (30) comprising: a core member (32) constituted by a tubular member (140), on one side of which a plurality of V-shaped notches (142) are formed, and the tubular member is bent into an annular shape to enclose the notches; and a plurality of free rollers (60), each free roller being rotatably assembled via a bearing (122) on a linear portion (120) of the tubular member located between a pair of adjacent V-shaped notches, the bearing being provided with an inner race (124) and an outer race (126), wherein on the other side of the tubular member opposite to the one side, a projection (130) is provided for each inner race to engage the end surface of the inner race and fixedly fasten the inner race to the core member.

[0012] Therefore, the inner race of the bearing is fixed to the core member by the projection. As a result, the free roller can be attached to the core member in such a way that movement of the free roller along the center line of the core member (hereinafter referred to as the rotation direction) is prevented, and the free roller can freely rotate around the center line. Thus, a separate fixing member (inner sleeve) is not required to fixedly fasten the inner race of each bearing to the core member, thereby reducing the manufacturing cost of the wheel.

[0013] Preferably, each projection extends as a cantilever from the end portion of the corresponding V-shaped notch towards one side of the corresponding linear portion.

[0014] As a result, the projection can project from the outer peripheral surface of the linear portion, so that movement of the free roller in the rotation direction can be restricted by the projection.

[0015] Preferably, the tubular member is provided with a pair of protrusions (138) in the portion of the V-shaped notch, the pair of protrusions protruding towards each other on the one side of the tubular member, and each protrusion provides a protruding portion protruding from the outer peripheral surface of the linear portion.

[0016] Therefore, movement of the inner race of each bearing in the rotation direction can also be restricted by the protrusion. Thus, compared with the case where no protrusion is provided, movement of the free roller in the rotation direction is more firmly restricted.

[0017] Preferably, each projection is cut so that the tubular member is bent to enclose the V-shaped cutout, resulting in the projection protruding.

[0018] As a result, the projection automatically protrudes by bending the tubular member in a manner that restricts movement of the free roller in the rotation direction. Thus, a step of protruding the projection to restrict movement of the free roller in the rotation direction is not required, thereby simplifying the wheel manufacturing process.

[0019] To achieve this object, another aspect of the present invention provides a method for manufacturing a wheel (30), the wheel comprising: a core member (32) formed of a tubular member (140), a plurality of V-shaped notches (142) being formed on one side of the tubular member, and the tubular member being bent into an annular shape to enclose the notches; and a plurality of free rollers (60), each free roller being rotatably assembled via a bearing (122) on a linear portion (120) of the tubular member located between a pair of adjacent notches, the bearing being provided with an inner race (124) and an outer race (126), the method for manufacturing the wheel comprising: a machining step of forming the plurality of V-shaped notches on the one side of the linearly extending tubular member and forming a projection (130) on the other side of the tubular member opposite to the one side; a positioning step of assembling the plurality of free rollers on the corresponding linear portions of the tubular member via the bearings; and a fixing step of bending the tubular member to enclose the V-shaped notches and rotating the tubular member into the core member, and engaging the projection with an end surface of the corresponding inner race.

[0020] Therefore, the inner race of the bearing is fixed to the core member by the projection. As a result, the free rollers can be attached to the core member in such a manner that movement of the free rollers along the center line of the core member (hereinafter referred to as the rotation direction) is prevented, and the free rollers can freely rotate around the center line. Thus, a separate fixing member (inner sleeve) is not required to fixedly fasten the inner race of each bearing to the core member, thereby reducing the manufacturing cost of the wheel.

[0021] Preferably, each projection extends as a cantilever from an end portion of the corresponding V-shaped notch toward the corresponding linear portion.

[0022] As a result, the projection can project from the outer peripheral surface of the linear portion, so that movement of the free roller in the rotation direction can be restricted by the projection.

[0023] Preferably, in the fixing step, by bending the tubular member to enclose the V-shaped notches, the projection automatically projects and engages with an end surface of the corresponding inner race.

[0024] As a result, each projection automatically projects by bending the tubular member in such a manner as to restrict movement of the corresponding free roller in the rotation direction. Therefore, a step of projecting the projection in order to restrict movement of the free roller in the rotation direction is not required, thereby simplifying the wheel manufacturing process.

[0025] Preferably, the fixing step includes the steps of inserting a prescribed tool (156) into each V-shaped notch and projecting the corresponding projection to engage with an end surface of the corresponding inner race.

[0026] Therefore, each protruding member can protrude to engage with the inner race of the corresponding bearing, such that the inner race of the bearing can be fixed to the core member.

[0027] Preferably, the machining step includes forming the V-shaped notch such that a pair of protrusions (138) are formed in portions of each V-shaped notch that face each other on one side and protrude towards each other, and the fixing step includes collapsing the protrusions such that the protrusions are each provided with a protruding portion that protrudes outward from the outer peripheral surface of the corresponding linear portion.

[0028] Therefore, by engaging the protrusions with the inner race of the corresponding bearing, the inner race of the bearing can be fixed to the core member in a more secure manner.

[0029] Effects of the present invention

[0030] Therefore, the present invention provides an omnidirectional wheel type of wheel that can be manufactured at low cost and a method for manufacturing such a wheel. Description of the drawings

[0031] Figure 1 is a perspective view of an inverted pendulum vehicle equipped with a wheel manufactured according to an embodiment of the present invention.

[0032] Figure 2 includes (A) a perspective view of the wheel according to the present invention and (B) an enlarged view of the portion in (A) surrounded by a double-dashed line.

[0033] Figure 3 is a cross-sectional view taken along the line III-III of Figure 2 .

[0034] Figure 4 is a cross-sectional view of the tubular member taken along its length.

[0035] Figure 5 (A) is a perspective view of the tubular member seen from above, and (B) is a perspective view of the tubular member seen from below.

[0036] Figure 6 is an explanatory diagram showing the positioning step.

[0037] Figure 7 is an explanatory diagram showing the crimping step.

[0038] Figure 8 is an explanatory diagram showing the fixing step in the method for manufacturing a wheel according to the first embodiment of the present invention.

[0039] Figure 9 is an explanatory diagram showing the fixing step in the method for manufacturing a wheel according to the second embodiment of the present invention. ​​​​​​​​​DETAILED IMPLEMENTATION MANNER

[0040] The inverted pendulum vehicle equipped with a wheel manufactured according to an embodiment of the present invention will be described below with reference to the accompanying drawings.

[0041] <<First Embodiment>>

[0042] As Figure 1 shown, the inverted pendulum type vehicle is an example of an omnidirectional vehicle capable of moving in the front-rear direction and the lateral direction, and is provided with a vehicle body frame 10 forming the vehicle body structure. The vehicle body frame 10 includes: a pair of upper members, one at the front and the other at the rear; two pairs of leg members 14 that hang down from the left and right ends of the upper member 12; and a pair of lower support plates 16 provided on either side to connect the lower ends of the leg members 14 to each other on the corresponding side. The upper parts of the upper members 12 commonly support a saddle 18 configured to support the buttocks of the occupant. Each of the lower support plates 16 is equipped with a footrest 20 for supporting the corresponding foot of the occupant.

[0043] The main wheels 30 (wheels) and the left and right drive disks 70 are arranged between the left and right leg members 14 and between the lower support plates 16. The main wheels 30 are driven wheels and are in contact with the ground to support the occupant sitting on the saddle 18. The left drive disk 70 and the right drive disk 70 are symmetrically arranged on either side of the main wheel 30, and each drive disk 70 is composed of a component including a hub 72, a disk 74, and a plurality of retainers 76 that are circumferentially arranged at regular intervals and are supported by the hub 72 and the disk 74 at both ends thereof. Each drive disk 70 is supported by the vehicle body frame 10 via a laterally extending support shaft 22 so as to be rotatable about a central axis extending substantially in the horizontal direction. More specifically, the vehicle body frame 10 supports the right drive disk 70 and the left drive disk 70 via a common support shaft 22, so as to be rotatable independently about a substantially horizontal central axis extending laterally.

[0044] Each drive disk 70 carries a plurality of drive rollers 78 that are circumferentially arranged at regular intervals via the corresponding retainers 76. Each drive roller 78 can rotate about a rotation axis inclined with respect to the rotation axis (central axis) of the drive disk 70. Only the drive rollers 78 located on the lower side are in contact with the outer peripheral surface of the free roller 60 (driven roller) (to be described below) of the main wheel 30 on the ground contact side (lower side) of the main wheel 30 in a symmetric relationship from both sides on its outer peripheral surface (located radially inside the main wheel 30). The drive rollers 78 on the ground contact side press on the free roller 60 of the main wheel 30, and the free roller 60 is in contact with the ground under the load applied by the occupant sitting on the saddle 18 to the support shaft 22 via the vehicle body frame 10.

[0045] The hourglass-shaped adjusting roller 102 is attached to the vehicle body frame 10 so as to be rotatable about an axis parallel to the central axis of the support shaft 22. The adjusting roller 102 extends in the lateral direction through the upper portion of the main wheel 30, and the arcuate narrowing portion of the adjusting roller 102 contacts the outer peripheral surface (radially inside the main wheel 30) of the free roller 60 located on the upper side of the main wheel 30, thereby preventing the main wheel 30 from tilting laterally or moving vertically relative to the vehicle body frame 10.

[0046] A plurality of adjusting rollers 110 that roll on the outer peripheral surfaces of these free rollers 60 are mounted on the support member 108 in a concentric arrangement around the support shaft 22 in a freely rotatable manner, and the free rollers 60 are located in front of and behind the grounded free roller 60. The adjusting roller 110 contacts the outer peripheral surface of the free roller 60, thereby inserting the outer peripheral surface (radially inner and outer peripheral surfaces of the main wheel 30) of the free roller 60 between the adjusting rollers 110 from the side. The adjusting roller 110 restricts the rotation of the main wheel 30 about the vertical line passing through the ground contact point or restricts the yaw motion of the main wheel 30 relative to the vehicle body frame 10 by contacting those free rollers before and after the vertical line passing through the ground contact point. The adjusting roller 110 further restricts the rolling motion and pitching moment of the main wheel 30 relative to the vehicle body frame 10.

[0047] As described above, the lower portion of the main wheel 30 is inserted between the left and right drive rollers 78 and between the left and right adjusting rollers 110 in the axial direction, while the upper portion of the main wheel 30 is supported by the adjusting roller 102, so that the main wheel 30 maintains an upright posture, such that its central axis extends substantially horizontally under the inverted pendulum control.

[0048] Each drive disk 70 is concentrically engaged with the driven pulley 80. A portion of the vehicle body frame 10 located above the main wheel 30 is provided with a gearbox 82 mounted above the main wheel 30. Each side wall of the gearbox 82 is provided with an electric motor 84 ( Figure 1 only the electric motor for the left drive disk 70 is shown in the figure) and a drive pulley 86 ( Figure 1 only the drive pulley for the left drive disk 70 is shown in the figure). A reduction gear unit (not shown in the figure) is provided inside the gearbox 82, and the reduction gear unit transmits the rotations of the left and right electric motors 84 to the left and right drive pulleys 86 at a reduced speed respectively. An endless toothed belt 88 ( Figure 1 only the toothed belt for the drive disk 70 on the left side is shown in the figure) is looped around each drive pulley 86 and the corresponding driven pulley 80. As a result, the left and right drive disks 70 can be rotated and driven independently.

[0049] The trailing wheel support arm 92 is pivotally connected to the lower support plate 16 via a support shaft 90 at its base end. The trailing wheel support arm 92 extends rearward from the base end away from the main wheel 30 and is pivotable relative to the vehicle body frame 10 in a substantially vertical direction about the central axis of the support shaft 90. The trailing wheel support arm 92 supports a full-wheel trailing wheel 94 (auxiliary wheel) at its free end so as to be rotatable about a substantially horizontal central axis orthogonal to the rotation center line of the drive disc 70. The trailing wheel 94 is rotationally driven by an electric motor 96 mounted on the trailing wheel support arm 92.

[0050] The electrical box 98 is attached to the front of the gear box 82. The electrical box 98 contains an electronic control unit, a gyro sensor, a motor drive unit, etc. The electronic control unit controls the left and right electric motors 84 so that the vehicle body frame 10 maintains a substantially upright posture through an inverted pendulum control process, and also controls the rotation operation of the electric motor 96. Although not shown in the figure, the vehicle body frame 10 is equipped with a battery for powering these electrical components.

[0051] When the left and right electric motors 84 are driven in the same direction and at the same speed, the left and right drive discs 70 rotate in the same direction at the same speed. As a result, the main wheel 30 rotates about a rotation center line that coincides with the center of its annular structure. At this time, since there is no rotational speed difference between the left and right drive discs 70, the free rollers 60 of the main wheel 30 do not rotate, and thus the inverted pendulum type vehicle travels straight forward or backward.

[0052] When the left and right electric motors 84 are driven in different rotational directions and / or at different rotational speeds, a rotational speed difference that appears between the left and right drive discs 70 generates a force component orthogonal to the circumferential (tangential) force acting on the contact surface between the drive rollers 78 of the left and right drive discs 70 and the free rollers 60 of the main wheel 30. As a result, the free rollers 60 rotate about their respective central axes.

[0053] Since the rotation of the free rollers 60 is determined by the rotational speed difference between the left and right drive discs 70, when the left and right drive discs 70 rotate in the same speed in opposite directions, the main wheel 30 does not rotate at all, and only the free rollers 60 rotate about themselves. As a result, a traveling force in the lateral direction is applied to the main wheel 30, and the inverted pendulum type vehicle travels in the lateral direction (sideways movement). When the left and right drive discs 70 rotate in the same direction at different speeds, the free rollers 60 rotate about themselves while the main wheel 30 rotates about itself, causing the inverted pendulum type vehicle to tilt and travel forward or backward.

[0054] When the trailing wheel 94 is rotationally driven by the electric motor 96, the inverted pendulum type vehicle rotates about the grounding point of the main wheel 30. Therefore, the trailing wheel 94 serves as a wheel for steering the inverted pendulum type vehicle. When the main wheel 30 and the trailing wheel 94 are simultaneously rotationally driven, the rotation or rotation center of the vehicle moves according to the driving wheel pattern.

[0055] Subsequently, details of the main wheel 30 according to the present embodiment will be described below with reference to the accompanying drawings. As Figure 2 shown in (A) of [[ID=]], the main wheel 30 has a core member 32 having a regular polygonal ring shape centered on the rotation center line C of the main wheel 30. As Figure 3 shown, the core member 32 is composed of a plurality of cylindrical linear portions 120 (linear portions) having the same structure. The linear portions 120 each linearly extend and are connected to each other at their both ends. Hereinafter, for convenience of explanation, the line connecting the center points of the cross-sections of the linear portions 120 will be referred to as the annular center line X, and the direction along the annular center line X will be referred to as the rotation direction.

[0056] As Figure 2 shown in (A) and (B) of [[ID=]], free rollers 60 are respectively provided on the outer peripheral surfaces of the linear portions 120. As Figure 3 shown, each free roller 60 includes a cylindrical inner member 60A and an outer member 60B. The outer member 60B is coaxial with the inner member 60A and is connected to the outer peripheral surface of the inner member 60A. The inner member 60A is made of a metal such as stainless steel, and the outer member 60B is made of a synthetic resin such as rubber.

[0057] As Figure 3 shown, the linear portion 120 passes through the inner hole of the corresponding free roller 60. A ball bearing 122 (bearing) is provided between each linear portion 120 and the corresponding free roller 60, so that the free roller 60 is rotatably assembled on the core member 32 via the ball bearing 122.

[0058] Each ball bearing 122 has an inner race 124, an outer race 126, and a plurality of rolling elements 128 disposed between the inner race 124 and the outer race 126. The inner race 124 is an annular metal member through which the core member 32 (linear portion 120) passes. The outer race 126 is also an annular metal member coaxially surrounding the inner race 124. The rolling elements 128 may be made of spherical metal members and contact the outer peripheral surface of the inner race 124 and the inner peripheral surface of the outer race 126. Therefore, the outer race 126 can rotate relative to the inner race 124 about the center line of the inner race 124.

[0059] The inner hole of each free roller 60 is fitted with the corresponding ball bearing 122 in a coaxial relationship, and the outer peripheral surface of the ball bearing 122 (i.e., the outer peripheral surface of its outer race 126) is bonded to the inner peripheral surface of the free roller 60 by in-situ vulcanization of rubber, so that the free roller 60 can rotate relative to the inner race 124 of the ball bearing 122 about the axis of the inner race 124.

[0060] As Figure 2As shown in (B) thereof, each linear portion 120 has a cylindrical shape extending along the annular center line X. Hereinafter, the portion of each linear portion 120 that faces the rotation center line C of the linear portion 120 and is closest to the rotation center line C is referred to as the inner end 120A. The portion of each linear portion 120 that faces away from the rotation center line C of the linear portion 120 and is farthest from the rotation center line C is referred to as the outer end 120B.

[0061] A pair of protrusions 130 are provided at the outer end 120B of each linear portion 120. Each protrusion 130 extends inward along the length of the linear portion 120 from the end of the linear portion 120 as a cantilever beam and protrudes away from the rotation center line C.

[0062] As Figure 3 shown, the free end 130A of each protrusion 130 abuts against the end face of the inner race 124 in the axial direction to prevent the inner race 124 from moving along the length of the linear portion 120 and rotating about the axis of the linear portion 120. Thus, the inner race 124 is fixedly fastened to the core member 32. In this way, each free roller 60 is supported by the core member 32 so as to be rotatable about the annular center line X, wherein the inner race 124 is fixed to the core member 32, and the free roller 60 is coupled to the outer race 126.

[0063] At each axial end of the inner end 120A of the linear portion 120, a cutout 134 is provided, and the cutout 134 cuts into the inner end 120A of the linear portion 120 in a substantially rectangular shape from the axial end of the inner end 120A of the linear portion 120. Each cutout 134 defines a substantially rectangular through hole 136 that communicates with the inner hole of the core member 32, and the through hole 136 cooperates with the same cutout 134 formed in the adjacent linear portion 120.

[0064] As Figure 2 shown in (B), the through hole 136 is formed to straddle the ends of two linear portions 120 when viewed from a direction orthogonal to the rotation center line C. When viewed from a direction orthogonal to the rotation center line C, each through hole 136 can overlap with the protrusions 130 provided at the opposite ends of two corresponding linear portions 120.

[0065] On the wall surface defining the through hole 136, a pair of protrusions 138 that protrude toward each other in the rotation direction are provided. The protrusions 138 are bent toward the rotation center line C. A part of each protrusion 138 is located on the rotation center line C side with respect to the outer surface of the inner end 120A of the linear portion 120. As a result, each protrusion 138 includes a portion that protrudes outward (toward the rotation center line C) from the outer peripheral surface of the linear portion 120.

[0066] Each protrusion 138 is in contact with the axial end surface of the corresponding inner race 124. As a result, the inner race 124 is prevented from moving along the length direction of the linear portion 120 and from rotating about the central axis of the linear portion 120. Therefore, the bonding force between the inner race 124 and the core member 32 is even stronger than in the case where only the raised member 130 is used, thereby minimizing the clicking sound of the free roller 60.

[0067] Subsequently, a method for manufacturing the main wheel 30 will be described with reference to Figures 4 to 9 The manufacturing method includes a plurality of manufacturing steps, including a machining step, a positioning step, and a fixing step. The machining step includes forming a prepared linearly extending tubular member 140 into a predetermined shape. The positioning step includes assembling the free roller 60 to the machined tubular member 140 via the ball bearing 122. The fixing step includes bending the tubular member 140 into a regular polygonal annular shape to form it into the core member 32 and fixing the inner race 124 of the ball bearing 122 to the core member. Each of the machining step, the positioning step, and the fixing step will be described in more detail below.

[0068] In the machining step, the operator first prepares the linearly extending tubular member 140. The tubular member 140 is a cylindrical metal member and is composed of a stainless steel round tube in this embodiment. More specifically, in the machining step, after fixing the tubular member 140, the operator operates a machine tool to form a plurality of V-shaped notches 142 on the upper surface (one side surface) of the tubular member 140 at regular intervals along the length direction of the tubular member 140, as shown in Figure 4 and Figure 5 (A) of. The machine tool may include any device capable of cutting or machining a workpiece and includes a laser cutting machine in this embodiment.

[0069] As shown in Figure 5 (A) of, each V-shaped notch 142 includes a pair of wedge-shaped portions 144 cut downward from the upper surface of the tubular member 140 on either side thereof and a pair of extensions 146 provided on the upper surface side of the wedge-shaped portions 144. The wedge-shaped portions 144 have a wedge shape in a side view (horizontal view). The extensions 146 are formed by cutting the tubular member 140 in a rectangular shape away from each other along the length direction of the tubular member 140 from the upper surface side of the wedge-shaped portions 144. Each extension 146 has a generally rectangular shape extending away from the upper surface side of the wedge-shaped portion 144 in the length direction. The wall surfaces defining the inner ends of each extension 146 face the corresponding portions of the adjacent extension 146 in the length direction. The wall surfaces defining the inner ends of each extension 146 are provided with protrusions 138 so as to face the corresponding portions in the adjacent extension 146.

[0070] Next, by operating the machine tool, the operator forms an incision portion 148 between the ends of each V-shaped notch 142 on the lower surface side of the tubular member 140, as shown in Figure 5 (B) thereof. Each incision portion 148 forms a protruding member 130 constituted by a cantilever beam that extends from the end of the incision portion 148 adjacent to the end of the V-shaped notch 142 toward another protruding member 130 formed on the other end of the same linear portion 120. More specifically, each incision portion 148 formed in the tubular member 140 forms a protruding member 130. In the present embodiment, the incision portion 148 extends along the length direction of the tubular member 140, and each incision portion 148 is provided with a pair of longitudinal portions 148A that extend adjacent to each other in the circumferential direction and a transverse portion 148B that connects the ends of the longitudinal portions 148A far from the ends of the corresponding V-shaped notches 142 in the circumferential direction.

[0071] Once the formation of the V-shaped notches 142 and the incision portions 148 is completed, the operator finishes the machining step and performs the positioning step.

[0072] In the positioning step, the operator prepares a plurality of ball bearings 122, to which the free rollers 60 are pre-bonded to the outer race 126 thereof, and inserts the machined tubular member 140 into the inner hole of the inner race 124, as shown in Figure 6 FIG. Thereafter, the operator positions the ball bearings 122 such that the inner races 124 are each located between two adjacent V-shaped notches 142 of the tubular member 140. As a result, each free roller 60 is assembled to the portion of the tubular member 140 located between the incision portions 148 via the corresponding ball bearing 122. At this time, the axial end portions of each extension portion 146 and the axial end portions of the corresponding inner race 124 are preferably aligned with each other in a plan view.

[0073] Then, as shown in Figure 7 FIG., the operator performs a crimping step by fixing the tubular member 140 to a prescribed support member 150, inserting a jig 152 (tool) into the extension portion 146, and applying a prescribed load to the protrusion 138 to contract the protrusion 138. The magnitude of the load applied to the protrusion 138 is selected such that the free end of the protrusion 138 protrudes more outward than the upper portion of the outer peripheral surface of the tubular member 140 located between the adjacent V-shaped notches 142. When collapsed in this manner, the protrusion 138 contacts the end surface and corners of the inner race 124. As a result, the movement of the inner race 124 in the length direction of the tubular member 140 is restricted, and the rotation of the tubular member 140 about its axis is restricted, so that the inner race 124 is temporarily fixed to the tubular member 140. The protrusion 138 may optionally contact the inner peripheral surface of the inner race 124.

[0074] Once the crimping step has been performed and the temporary fixing of all the inner races 124 has been completed, the operator has completed the positioning step and proceeds to the fixing step.

[0075] In the fixing step, as shown in (A) to (C) of Figure 8 , the operator bends the tubular member 140 to which the inner race 124 is temporarily fixed so as to form a regular polygonal shape centered on a predetermined axis. At this time, the operator holds the bent tubular member 140 until the wedge portion 144 of the V-shaped notch 142 is closed, and the wall surfaces defining the wedge portion 144 come into contact with each other as indicated by the arrows in (A) and (B) of Figure 8 . During this bending process, the portion of the tubular member 140 located between the V-shaped notches 142 is substantially not deformed and remains in a straight shape to form the linear portion 120.

[0076] When the portion of the tubular member 140 located between the adjacent linear portions 120 is bent, the raised member 130 spontaneously rises out of the inner hole of the tubular member 140 and projects from the outer peripheral surface of the linear portion 120 (see (B) and (C) of Figure 8 ). Accordingly, the raised member 130 abuts against the end face and corners of the corresponding inner race 124 in the axial direction at its free end 130A, and as a result, the raised member 130 engages the corresponding inner race 124. Due to the engagement between the inner race 124 and the raised member 130, the movement of the inner race 124 in the axial direction with respect to the tubular member 140 and the rotation of the inner race 124 about the axis of the tubular member 140 are restricted, and as a result, the inner race 124 is fixedly fastened to the tubular member 140.

[0077] Thereafter, the operator welds the ends of the tubular member 140 to each other, and then welds the wall surfaces defining the wedge portion 144 to each other, so that the tubular member 140 is formed into the core member 32 and the main wheel 30 is completed.

[0078] Next, the effects of the main wheel 30 (wheel) constructed as described above and the method for manufacturing the main wheel 30 will be discussed below. The inner race 124 of each ball bearing 122 is engaged by the corresponding raised member 130 and fixedly fastened to the core member 32. In this way, the free rollers 60 can be attached to the core member 32 in such a manner that the movement in the rotational direction is restricted while the rotation about their own axes can be freely performed.

[0079] Since each inner race 124 is fixed to the core member 32 by the corresponding raised member 130, no additional fixing members (such as inner sleeves) are required to fix the inner race 124 of the ball bearing 122. Therefore, the number of components constituting the main wheel 30 can be reduced, and the manufacturing cost of the main wheel 30 can be lowered.

[0080] The raised member 130 is located on the surface opposite to the side surface (upper surface) provided with the V-shaped notch 142, and is formed as a cantilever extending from the outer side adjacent to the end of the V-shaped notch 142 to the inner side of the corresponding linear portion 120. As a result, when the tubular member 140 is bent to enclose the wedge-shaped portion 144 of the V-shaped notch 142, the raised member 130 spontaneously rises away from the inner hole of the tubular member 140 until the end surface of the raised member 130 abuts against the end surface of the corresponding inner seat ring 124. As a result, the inner seat ring 124 is automatically fixed to the core member 32. In this way, by bending the tubular member 140, the movement of the free roller 60 in the rotational direction is automatically restricted. Therefore, in order to restrict the movement of the free roller 60 in the rotational direction, there is no need for a working step of raising the raised member 130. Therefore, the manufacturing process of the main wheel 30 is simplified, and the manufacturing cost of the main wheel 30 can be reduced.

[0081] In the positioning step, each inner seat ring 124 is fixed to the tubular member 140 by collapsing and deforming the protrusion 138, so as to protrude from the outer peripheral surface of the linear portion 120. Therefore, according to the present embodiment, since each inner seat ring 124 is fixed to the core member 32 by the protrusion 138 in addition to the raised member 130, compared with the case where the protrusion 138 is not provided, the movement of the inner seat ring 124 in the rotational direction can be prevented in a more reliable manner, and the free roller 60 can be prevented from vibrating.

[0082] <<Second Embodiment>>

[0083] The main wheel 30 of the second embodiment of the present invention is similar in structure to the main wheel of the first embodiment, and the difference from the main wheel of the first embodiment lies only in its manufacturing method. Therefore, the method for manufacturing the main wheel 30 of the second embodiment will be described below.

[0084] The manufacturing method of the main wheel 30 according to the second embodiment includes a plurality of manufacturing steps, including a machining step, a positioning step, and a fixing step. The machining step and the positioning step of the second embodiment are similar to those of the first embodiment, and the difference between the second embodiment and the first embodiment lies only in the fixing step. The fixing step of the second embodiment will be described in detail below.

[0085] Similar to the first embodiment, the operator temporarily fixes the inner seat ring 124 and performs the fixing step. In the fixing step, as Figure 9As shown, the operator fixes the tubular member 140 to the specified support member 154, and then inserts the specified fixture 156 (tool) into each V-shaped notch 142 to raise the raised members 130. At this time, the operator raises each raised member 130 to such an extent that the raised member contacts the end surface of the corresponding inner race 124. Once each raised member 130 engages the end surface of the inner race 124, the inner race is prevented from moving to the side of the raised member 130.

[0086] In the fixing step, the operator inserts the fixture 156 into the V-shaped notch 142 one by one to raise all the raised members 130. As a result, the inner race 124 is completely fixed to the tubular member 140 by being locked from both axial sides by the raised members 130.

[0087] Thereafter, as in the first embodiment, the operator temporarily connects the two ends of the tubular member 140 to each other by welding, and then welds the wall surfaces defining the wedge portion 144 to each other. Thus, the tubular member 140 is formed in the core member 32, and the main wheel is completed.

[0088] Subsequently, the effects of the manufacturing method of the main wheel 30 configured as described above will be discussed below. In the present embodiment, by inserting the fixture 156 into the V-shaped notch 142, the raised members can be raised in a more reliable manner. In addition, by adjusting the insertion stroke of the fixture 156, the raised height of the raised member 130 can be adjusted. As a result, the inner race 124 and the raised member 130 can be reliably engaged with each other, so that the inner race 124 can be more reliably and fixedly fixed to the tubular member 140 (core member 32).

[0089] The present invention has been described based on specific embodiments of the present invention, but the present invention is not limited to these embodiments and can be modified in various ways without departing from the scope of the present invention. In the foregoing embodiments, the ends of the inner race 124 in the rotational direction are each engaged by a single raised member 130 to fixedly fasten the inner race 124 to the core member 32, but the present invention is not limited to such an arrangement. The ends of the inner race 124 in the rotational direction may also each be engaged with a plurality of raised members 130. In addition, a single free roller 60 is provided for each linear portion 120, but two or more free rollers 60 may be provided for each linear portion.

[0090] Reference numerals

[0091] 30: Main wheel (wheel)

[0092] 32: Core member

[0093] 60: Free roller

[0094] 120: Linear portion

[0095] 122: Ball bearing (bearing)

[0096] 124: Inner race

[0097] 126: Outer race

[0098] 130: Protrusion

[0099] 138: Protrusion

[0100] 140: Tubular member

[0101] 142: V-notch

[0102] 156: Fixture (tool)

Claims

1. A wheel, comprising: a core member formed of a tubular member having a plurality of V-shaped notches formed on one side thereof, and the tubular member being bent into an annular shape to enclose the notches; and a plurality of free rollers, each free roller being rotatably assembled via a bearing on a linear portion of the tubular member located between a pair of adjacent V-shaped notches, the bearing having an inner race and an outer race, wherein a raised piece of each inner race is formed by cutting and raising a portion of the tubular member on the other side opposite to the one side, so as to engage the end surface of the inner race and fixedly fasten the inner race to the core member.

2. The wheel according to claim 1, wherein, Each raised piece extends as a cantilever from an end portion of a corresponding V-shaped notch toward one side of a corresponding linear portion.

3. The wheel according to claim 1, wherein, The tubular member is provided with a pair of protrusions in a portion of the V-shaped notch, the pair of protrusions protruding toward each other on the one side of the tubular member, and each protrusion provides a protruding portion protruding from an outer peripheral surface of the linear portion.

4. The wheel according to any one of claims 1 to 3, wherein, The tubular member is cut so that the tubular member is bent to enclose the V-shaped notch, resulting in the raising of the raised piece.

5. A method for manufacturing a wheel, the wheel comprising: a core member formed of a tubular member having a plurality of V-shaped notches formed on one side thereof, and the tubular member being bent into an annular shape to enclose the notches; and a plurality of free rollers, each free roller being rotatably assembled via a bearing on a linear portion of the tubular member located between a pair of adjacent notches, the bearing having an inner race and an outer race, the method for manufacturing a wheel comprising: a machining step of forming the plurality of V-shaped notches on the one side of the linearly extending tubular member, and forming a raised piece by cutting a portion of the tubular member on the other side opposite to the one side; a positioning step of assembling the plurality of free rollers on the corresponding linear portions of the tubular member via the bearings; and a fixing step of bending the tubular member to enclose the V-shaped notches and turning the tubular member into the core member, and raising the raised piece to engage with an end surface of a corresponding inner race.

6. The method for manufacturing a wheel according to claim 5, wherein, Each raised piece extends as a cantilever from an end portion of a corresponding V-shaped notch toward a corresponding linear portion.

7. The method for manufacturing a wheel according to claim 5, wherein, In the fixing step, by bending the tubular member to enclose the V-shaped notch, the raised piece automatically raises and engages with an end surface of a corresponding inner race.

8. The method for manufacturing a wheel according to claim 5, wherein, The fixing step includes the steps of inserting a specified tool into each V-shaped notch and raising a corresponding raised piece to engage with an end surface of a corresponding inner race.

9. The method for manufacturing a wheel according to any one of claims 5 to 8, wherein, The machining step includes forming the V-shaped notches such that a pair of protrusions are formed in portions of each V-shaped notch opposite to each other on one side and protrude toward each other, and the fixing step includes collapsing the protrusions such that each protrusion is provided with a protruding portion protruding outward from an outer peripheral surface of a corresponding linear portion.

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