Truck

Abstract

To provide a truck in which a projecting part easily regulates the movement of a wheel part in a state that trucks are vertically stacked, and the trucks stacked on the upper side are easily stabilized.SOLUTION: A carriage includes a base part for placing a load and a caster part 3. The caster portion 3 is attached to a lower surface of the base portion. The base portion includes a recessed portion 54 and a projecting portion 55. The recessed part 54 is recessed from the placement surface 510 above the base part and houses the wheel part 31 of the caster part 3. The protruding portion 55 protrudes upward from the central portion of the recessed portion 54 and restricts the movement of the wheel portion 31 accommodated in the recessed portion 54. A protruding length L21 of the protruding portion 55 from the bottom surface 542 of the recessed portion 54 is greater than 5mm and less than 16mm.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to a dolly. [Background technology]

[0002] Patent Document 1 describes a roller carriage that includes a bottom frame and wheels attached to the underside of the bottom frame. In this roller carriage, the bottom frame is provided with a recess for accommodating the wheels and a protrusion for restricting the wheels accommodated in the recess. This makes it difficult for the upper roller carriage to shift sideways relative to the lower roller carriage when the roller carriages are stacked one above the other. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 8-503438 Summary of the Invention [Problem to be solved by the invention]

[0004] In the roller carriage shown in Patent Document 1, the protrusion protrudes upward from the bottom surface of the center of the recess. However, if the protruding length of the protruding portion is short, the wheel will easily climb over the protruding portion, making it difficult for the protruding portion to restrict the movement of the wheel housed in the recessed portion. On the other hand, if the protruding length of the protrusion is long, when stacking roller carriages one on top of the other, the wheels will get caught on the protrusion, and will not be stored in the recesses, leaving the wheels floating, making the roller carriage stacked on top unstable. The present disclosure was invented in consideration of the above-mentioned conventional problems, and aims to provide a trolley in which, when the trolleys are stacked one on top of the other, the protrusions make it easy to restrict the movement of the wheel sections, thereby making it easy to stabilize the trolleys stacked on top of each other. [Means for solving the problem]

[0005] In order to solve the above problems, a dolly according to one embodiment of the present disclosure includes a synthetic resin base for placing a load on it, and caster units. The caster units are attached to the underside of the base. The base has a recess and a protrusion. The recess is recessed from the upper loading surface of the base and houses the wheel units of the caster units. The protrusion protrudes upward from the center of the recess and regulates the movement of the wheel units housed in the recess. The protrusion's protrusion length from the bottom surface of the recess is more than 5 mm and less than 16 mm. The synthetic resin has a flexural modulus of elasticity of 1000 to 1800 MPa. [Effects of the Invention]

[0006] In the trolley according to the present disclosure, when the trolleys are stacked one on top of the other, the protrusions tend to restrict the movement of the wheel sections, making it easier for the trolleys stacked on top to be stable. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view of a truck according to an embodiment, seen obliquely from above. [Figure 2] FIG. 2 is an exploded perspective view of the above-mentioned truck as seen obliquely from above. [Figure 3] FIG. 3 is a plan view of the above bogie. [Figure 4] FIG. 4 is a side cross-sectional view of the above bogie. [Figure 5] FIG. 5 is a side cross-sectional view of the above trucks stacked one on top of the other. [Figure 6] FIG. 6 is an enlarged side cross-sectional view of a main part of the above truck. [Figure 7] FIG. 7 is a side cross-sectional view showing a modified example of the above truck. [Figure 8] FIG. 8 is a perspective view of a modified example of the carriage according to the embodiment, seen obliquely from above. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Overview As shown in FIG. 1, a dolly 1 according to one embodiment includes a base 2 for placing an object to be loaded, and caster units 3. The caster units 3 are attached to the underside of the base 2. The base 2 has a recess 54 and a protrusion 55. The recess 54 is recessed from a loading surface 510 above the base 2 and houses the wheel units 31 of the caster units 3. The protrusion 55 protrudes upward from the center of the recess 54 and restricts movement of the wheel units 31 housed in the recess 54. As shown in FIG. 6, a protrusion length L21 of the protrusion 55 from a bottom surface 542 of the recess 54 is more than 5 mm and less than 16 mm. In the dolly 1 according to one embodiment, the wheel portion 31 of the caster unit 3 is housed in the recess 54 of the base portion 2, and the movement of the wheel portion 31 is restricted by the protrusion 55. As a result, when the dollies 1 are stacked one on top of the other, the upper dolly 1 is less likely to slide sideways relative to the lower dolly 1. Furthermore, in the dolly 1 according to one embodiment, the protrusion length L21 of the protrusion 55 from the bottom surface 542 of the recess 54 exceeds 5 mm. As a result, when the dollies 1 are stacked one on top of the other, the protrusion 55 easily restricts the movement of the wheel portion 31. Furthermore, in the dolly 1 according to one embodiment, the protrusion length L21 of the protrusion 55 from the bottom surface 542 of the recess 54 is less than 16 mm. As a result, when the dollies 1 are stacked one on top of the other, the wheel portion 31 is less likely to get caught on the protrusion 55.

[0009] 2. One embodiment 2-1.Details Next, the bogie 1 of this embodiment shown in FIGS. 1 to 6 will be described in more detail with reference to the drawings.

[0010] 2-2. Cart As shown in Fig. 1, the dolly 1 includes a base portion 2 and a caster portion 3. The dolly 1 is a transport dolly used to transport a load by human power. The dolly 1 can be stacked above and below another dolly 1 placed on the ground, and the lower dolly 1 can move when the dollies 1 are stacked above and below. The carriage 1 has a rectangular shape in a plan view. In the following, the up-down direction is defined based on the state in which the carriage 1 is placed. Furthermore, the direction along the long side of the carriage 1 is defined as the long side direction, and the direction along the short side of the carriage 1 is defined as the short side direction.

[0011] 2-3. Caster part As shown in Fig. 4, the caster unit 3 has a wheel unit 31 and a support unit 32. Four caster units 3 are attached to the underside of the base unit 2. Each of the four caster units 3 has the same shape. The wheel unit 31 has an axle 311 and a tire 312. The wheel unit 31 is suspended and supported by a support unit 32. In this embodiment, the diameter L20 of the wheel unit 31 is 64 mm to 101 mm, and tires 312 having diameters L20 of 2.5 in (64 mm), 3 in (75 mm), and 4 in (100 mm) are mainly targeted. Here, in this disclosure, the symbol "to" indicating a numerical range includes the upper and lower limits. The wheel axle 311 is located at the center of the tire 312. The wheel axle 311 supports the tire 312 so that it can rotate freely. This allows the carriage 1 to move. The tire 312 is made of, for example, rubber. Note that the tire 312 may be made of a material other than rubber, such as resin. The support part 32 has an upper piece 321 and a pivot shaft 323. The support part 32 is made of, for example, metal. Note that the support part 32 may be made of a material other than metal. The upper piece 321 is in the shape of a rectangular plate. The upper piece 321 is fixed to the underside of the base part 2. The upper end of a swivel shaft 323 is connected to the upper piece 321. The swivel shaft 323 swivels around an axis that is substantially vertical to the upper piece 321. A pair of connecting pieces 322 extend downward from both ends of the swivel shaft 323. A wheel axle 311 that spans substantially horizontally is connected between the lower ends of the pair of connecting pieces 322. This allows the wheel part 31 connected to the connecting pieces 322 to swivel. The center 313 of the wheel axle 311 is located on a vertical line CL2 that is eccentric with respect to the vertical line CL1 of the center of the pivot shaft 323. An upper surface 552 of a protrusion 55 (described later) is located on the vertical line CL1 of the center of the pivot shaft 323. In addition, a bottom surface 542 of a recess 54 (described later) is located on the vertical line CL2 of the center 313 of the wheel axle 311. In this embodiment, when the diameter L20 of the wheel unit 31 is 2.5 inches and 3 inches, the eccentric distance L22 of the wheel unit 31, which is the length from the pivot axis 323 to the center part 313, is 21 mm to 28 mm, of which eccentric distances L22 of the wheel unit 31 of 21 mm, 27 mm, and 28 mm are of primary interest. Also, when the diameter L20 of the wheel unit 31 is 4 inches, the eccentric distance L22 of the wheel unit 31 is 31 mm to 35 mm, of which eccentric distances L22 of the wheel unit 31 of 31 mm, 32 mm, and 35 mm are of primary interest. The eccentric distance L22 of the wheel unit 31 is not particularly limited.

[0012] 2-4. Base As shown in Fig. 3, the base 2 has side members 4 and corner members 5. An object is placed on the top surface of the base 2. The base 2 has a rectangular shape in a plan view. In this embodiment, each side of the base 2 is approximately 30 cm to 100 cm. The shape of the base 2 in plan view is symmetrical about a line extending along the long side that passes through the center of the short side. The shape of the base 2 in plan view is also symmetrical about a line extending along the short side that passes through the center of the long side. A through-hole 20 that penetrates vertically is formed in the center of the base 2 in plan view.

[0013] 2-4-1. Side members As shown in Fig. 2, the side members 4 have long side members 41 and short side members 42. The side members 4 extend in the horizontal direction (the horizontal direction when the cart 1 is placed on a horizontal surface). The long side members 41 are two angle members 410 that extend along the long side direction of the base portion 2. The two angle members 410 are identical except that they are inverted relative to each other about a line along the long side direction that passes through the center of the short side direction. The angle iron 410 has a vertical piece 412 and a horizontal piece 413 that serves as a beam for supporting a load. The angle iron 410 is made of, for example, metal. The angle iron 410 may be made of a material other than metal, such as resin. The resin is made of a synthetic resin such as polypropylene, and the flexural modulus of polypropylene is 1000 to 1800 MPa, preferably 1100 to 1400 MPa. The flexural modulus is measured using a test method in accordance with JIS K 6924-2. The vertical piece 412 extends upward from the outer edge (the outer end side of the base part 2 in a plan view) of the horizontal piece 413. The vertical piece 412 functions as a restricting part (in other words, a fall prevention part) that restricts the load placed on the upper surface of the horizontal piece 413 from moving outward and falling from the horizontal piece 413. In the angle member 410, the vertical piece 412 and the horizontal piece 413 are integrally formed. This improves the bending rigidity of the horizontal piece 413 on which the load is placed and the entire dolly 1, making the dolly 1 less likely to bend and improving the strength of the dolly 1 against impact. The short side members 42 are two angle members 420 extending along the short side direction of the base portion 2. The two angle members 420 are identical except that they are inverted relative to each other about a line along the short side direction that passes through the center of the long side direction. The angle iron 420 has a vertical piece 422 and a horizontal piece 423 that serves as a beam for supporting the load. The angle iron 420 is made of, for example, metal. The angle iron 420 may be made of a material other than metal, such as resin. The resin is made of a synthetic resin such as polypropylene, and the flexural modulus of elasticity of polypropylene is 1000 to 1800 MPa, preferably 1100 to 1400 MPa. The vertical piece 422 extends upward from the outer edge (the outer end side of the base part 2 in a plan view) of the horizontal piece 423. The vertical piece 422 functions as a restricting part (in other words, a fall prevention part) that restricts the load placed on the upper surface of the horizontal piece 423 from moving outward and falling from the horizontal piece 423. In the angle member 420, the vertical piece 422 and the horizontal piece 423 are integrally formed. This improves the bending rigidity of the horizontal piece 423 on which the load is placed and the entire dolly 1, making the dolly 1 less likely to bend and improving the strength of the dolly 1 against impact.

[0014] 2-4-2. Corner parts The corner members 5 connect the side members 4. The corner members 5 and the side members 4 are fixed together by driving rivets (not shown) or the like into the side members 4 via the corner members 5. In this way, the base portion 2 is formed. The corner members 5 are arranged at the four corners of the base 2 in a plan view. The caster units 3 are attached to the undersides of the four corner members 5. The four corner members 5 are identical except that they are inverted from one another around a line extending in the long side direction that passes through the center of the short side direction. The four corner members 5 are also identical except that they are inverted from one another around a line extending in the short side direction that passes through the center of the long side direction. As shown in Figures 2 to 4, the corner member 5 has a horizontal piece 51 and a vertical piece 52. The corner member 5 is made of, for example, resin. The corner member 5 may be made of a material other than resin, such as metal. The resin is made of a synthetic resin such as polypropylene, and the flexural modulus of elasticity of polypropylene is 1000 to 1800 MPa, preferably 1100 to 1400 MPa. The horizontal piece 51 has a notch 53, a recess 54, a protrusion 55, and a rib 56. The horizontal piece 51 has a triangular shape in a plan view. The upper surface of the horizontal piece 51 serves as a placement surface 510 on which an object is placed. The loading surface 510 directly supports an object to be loaded. The loading surface 510 is a horizontal plane in a side view. The shape of the loading surface 510 in a side view is not particularly limited. Cutouts 53 are provided on the underside of the horizontal piece 51. The cutouts 53 are provided at the ends of the short sides and long sides of the outer periphery of the bogie 1. The ends of the horizontal pieces 413, 423 of the side member 4 are inserted into the cutouts 53. The recess 54 is formed in a part of the upper surface of the horizontal piece 51. The recess 54 is a portion recessed from the placement surface 510 above the horizontal piece 51. The recess 54 is circular in plan view. Note that the shape of the recess 54 in plan view is not particularly limited. The recess 54 functions as a storage section (wheel storage section) for storing the wheel section 31. In addition, the outer peripheral edge of the recess 54 also functions as a restricting section (in other words, a wheel derailment prevention section) that restricts movement of the wheel section 31. The diameter of the recess 54 in a plan view is preferably 40% to 70% of the longest length of the horizontal piece 51 in a plan view, and more preferably 50% to 60%. In this embodiment, the longest length of the horizontal piece 51 in a plan view is the length of the hypotenuse of the horizontal piece 51 in the triangular shape in a plan view of the horizontal piece 51. Furthermore, in order to form the recess 54 by making the length of the hypotenuse of the horizontal piece 51 in the triangular shape in a plan view of the horizontal piece 51 as short as possible, it is particularly preferable that the diameter of the recess 54 in a plan view exceeds 50% of the length of the hypotenuse of the horizontal piece 51 in the triangular shape in a plan view of the horizontal piece 51. This makes it difficult for the strength of the horizontal piece 51 to be reduced by the recess 54. The recess 54 has a recess inclined surface 541, a bottom surface 542, and a through-hole 543. The recess inclined surface 541 is a surface that slopes from above the mounting surface 510 toward the center of the recess 54. The recess inclined surface 541 is a concave curved surface. The wheel unit 31 placed on the bottom surface 542 comes into contact with the upper edge of the recess inclined surface 541. This restricts the wheel unit 31 from rotating around the axis of the wheel axle 311. The bottom surface 542 is continuous with the lower edge of the recessed portion inclined surface 541. The wheel unit 31 stored in the recessed portion 54 is placed on the bottom surface 542. The bottom surface 542 is annular in plan view. The bottom surface 542 is continuous with the lower end of the recessed portion inclined surface 541 in the horizontal direction. The bottom surface 542 is flat in side view, faces upward, and is parallel to the placement surface 510. The shape of the bottom surface 542 in side view is not particularly limited. The shape of the bottom surface 542 in side view may be, for example, a downwardly curved shape (a shape close to the outer circumferential surface of the wheel unit 31). The through-hole 543 is provided in the bottom surface 542. The through-hole 543 is formed in a part of the bottom surface 542 other than the center of the recess 54. The through-hole 543 is formed so as to penetrate the horizontal piece 51 in the bottom surface 542 from top to bottom. The through-hole 543 is provided, for example, to drain water, sand, etc. that accumulates on the bottom surface 542. The number of through-holes 543 that the recess 54 has is not particularly limited, and may be one or more. The recess 54 does not necessarily have to have the through-hole 543. In this embodiment, the vertical length L13 from the bottom surface 542 to the placement surface 510 (the recess depth L13 of the recess 54) is 10 mm. Note that the recess depth L13 of the recess 54 is not particularly limited. The recess depth L13 of the recess 54 is 5%, 9.9%, 10.10%, 13.16%, or 13.51% or more and 15.63% or less of the diameter L20 of the wheel portion 31, and preferably 5%, 9.9%, 10.10%, 13.16%, or 13.51% or more and 15.14% or less (see Table 1). The recess depth L13 of the recess 54 is not limited to 5%, 9.9%, 10.10%, 13.16%, or 13.51% or more and 15.63% or less. The recess depth L13 of the recess 54 may be 15.15%, 15.45%, 15.55%, or 15.64% or more and 30% or less of the diameter L20 of the wheel portion 31, or 15.15%, 15.45%, 15.55%, or 15.64% or more and 25% or less, or 15.15%, 15.45%, 15.55% or more, or 15.64% or more and 20% or less, or 15.15%, 15.45%, 15.55% or more, or 15.64% or more and 16% or less (see Table 2). The following table shows the recess depth L13 of the recess 54 for each ratio when the diameter L20 of the wheel portion 31 is 2.5 inches, 3 inches, and 4 inches. Note that the recess depth L13 of the recess 54 in the table below is a value that takes into account the tolerance of the diameter L20 of the wheel portion 31. That is, in Tables 1 and 2, the recess depth L13 of the recess 54 is listed as the upper or lower limit value of the allowable range of the recess depth L13 of the recess 54 that takes into account the tolerance of the diameter L20 of the wheel portion 31.

[0015] [Table 1]

[0016] [Table 2]

[0017] As shown in Fig. 4, the rib 56 is formed on the lower surface of the horizontal piece 51. The rib 56 protrudes downward from the horizontal piece 51. The rib 56 is a protruding member. The rib 56 is formed on the horizontal piece 51 in a portion other than the cutout portion 53 and the through hole 543. The rib 56 has a first rib 561, a second rib 562, and a third rib 563. The first rib 561 is formed in a portion that does not have the recess 54. The first rib 561 is provided at the end of the short side and the end of the long side. The end of the short side of the first rib 561 is a member that extends along the long side direction. In addition, the end of the long side of the first rib 561 is a member that extends along the short side direction. The two first ribs 561 have the same protruding length. In this embodiment, the vertical length L11 from the placing surface 510 to the lower end of the first rib 561 is 15 mm. Note that the vertical length L11 from the placing surface 510 to the lower end of the first rib 561 is not particularly limited. The second ribs 562 are formed in the portion of the horizontal piece 51 having the recessed portion 54. The second ribs 562 are a group of lattice-shaped ribs extending along the short side direction and the long side direction. The protruding lengths of the second ribs 562 are all the same. In a side view, the protruding portion 55 has a recess 550 recessed upward. By forming the recess 550 in this manner, the protruding portion 55 formed by the molding device is less likely to deform after molding. The second rib 562 crosses below the recess 550 of the protruding portion 55. Each second rib 562 is formed so as to straddle the recess 550 of the protruding portion 55. Thus, by forming the second rib 562 straddling the recess 550 of the protruding portion 55, the strength of the base portion 2 in the portion where the recess 550 is formed is improved. The third rib 563 is formed in the portion of the horizontal piece 51 having the recess 54. The third rib 563 is a member extending along the short side direction and the long side direction. The third rib 563 is located outside the second rib 562. A pair of retaining pieces 564 is formed in a part of the third rib 563. The pair of retaining pieces 564 are continuous with the lower end of the third rib 563. The space surrounded by the third rib 563 and the pair of holding pieces 564 is the space where the upper piece 321 of the caster unit 3 is attached. When the caster unit 3 is attached to the base 2, the second rib 562 is located between the upper piece 321 of the caster unit 3 and the lower surface of the bottom surface 542 of the recess 54. The second rib 562 and the third rib 563 are formed in the portion having the recess 54, thereby improving the strength of the base 2. The area of ​​the lower surface of the third rib 563 is preferably 5 to 15% of the area of ​​the bottom surface 542 of the recess 54, more preferably 6 to 12%, and even more preferably 7 to 10%. In this embodiment, the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562 is 13 mm. Note that the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562 is not particularly limited. As shown in FIG. 6, the vertical length L11 from the support surface 510 to the lower end of the first rib 561, the vertical length L12 from the bottom surface 542 to the lower end of the second rib 562, and the recess depth L13 of the recess 54 satisfy the following mathematical formula (1). Formula (1) L13 / L11 <L12 / L11 Satisfying the formula (1) means that the recess depth L13 of the recess 54 increases the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562. This improves the strength of the portion of the base 2 where the recess 54 is provided. 3 and 4, the protrusion 55 protrudes upward from the center of the recess 54. In this embodiment, the protrusion 55 has a truncated cone shape in a side view. The shape of the protrusion 55 in a side view is not particularly limited. The protruding portion 55 functions as a restricting portion (in other words, a wheel derailment prevention portion) that restricts movement of the wheel portion 31 placed on the bottom surface 542. The thickness of the horizontal piece 51 of the protruding portion 55 is the same as the thickness of the horizontal piece 51 of the recessed portion 54. In this embodiment, the protruding length L21 of the protruding portion 55 from the bottom surface of the recessed portion 54 exceeds 5 mm and is less than 16 mm. As shown in FIG. 6, the maximum protruding length from the bottom surface 542 of the recess 54 to the top surface of the protruding portion 55 (from the bottom surface 542 of the recess 54 of the protruding portion 55) is calculated based on the following formula (2) using the eccentric distance L22, which is the length from the vertical line CL1 of the center of the pivot shaft 323 to the center portion 313 in the horizontal direction, and the radius L23 of the wheel portion 31. Formula (2) Maximum protrusion length = L23-(L23^2-L22^2)^(1 / 2) Specifically, the length L24 of the other side of the stacked carts 1 can be calculated based on the Pythagorean theorem (Pythagorean theorem) of the following formula (2-1) from the eccentricity distance L22, which is the length of one side from the center 313 of the wheel part 31 of the upper cart 1 in the stacked state to the vertical line CL1 of the center of the swivel shaft 323 in the horizontal direction, and the radius L23 of the wheel part 31, which is the length of the hypotenuse from the center 313 of the wheel part 31 of the cart 1 in the stacked state to the upper surface 552 of the protrusion 55 of the lower cart 1 in the stacked state, Formula (2-1) L24 = (L23^2 - L22^2)^(1 / 2) The maximum protruding length of the protrusion 55 from the bottom surface 542 of the recess 54 can be calculated based on the following formula (2-2) from the length L24 of the other side when the trolleys 1 are stacked one above the other, which is calculated using the above formula (2-1), and the radius L23 of the wheel portion 31, which is the length in the vertical direction from the center 313 of the wheel portion 31 of the upper trolley 1 when the trolleys 1 are stacked one above the other. Formula (2-2) Maximum protrusion length = L23 - L24 A protruding length L21 of the protruding portion 55 from the bottom surface 542 of the recessed portion 54 is equal to or less than a maximum protruding length of the protruding portion 55 from the bottom surface 542 of the recessed portion 54. In addition, the maximum protruding length of the protruding portion 55 from the bottom surface 542 of the recessed portion 54 is equal to or less than a recess depth L13 of the recessed portion 54. The following tables show the maximum protrusion length for each eccentric distance L22 of the wheel portion 31 when the diameter L20 of the wheel portion 31 is 2.5 inches (Table 3), 3 inches (Table 4), and 4 inches (Table 5). Note that the maximum protrusion length in each of the tables below is the minimum and maximum values ​​within the allowable range, taking into account the tolerance of the diameter L20 of the wheel portion 31.

[0018] [Table 3]

[0019] [Table 4]

[0020] [Table 5]

[0021] 4, protrusion 55 has protrusion inclined surface 551 and upper surface 552. Protrusion inclined surface 551 extends obliquely upward from the peripheral edge portion in contact with bottom surface 542 toward the upper end portion of the center portion in plan view. Protrusion inclined surface 551 is a concave curved surface. An upper surface 552 is continuous with the upper edge of the protruding inclined surface 551. The upper surface 552 is continuous in the horizontal direction from the upper edge of the protruding inclined surface 551. The upper surface 552 is flat in a side view. The upper surface 552 is circular in a plan view. The shape of the upper surface 552 in a side view is not particularly limited. For example, the shape of the upper surface 552 in a side view may be a curved surface that protrudes upward. The following tables show the maximum protruding lengths when the upper surface 552 is a curved surface with R0.5 and when the upper surface 552 is a curved surface with R1.0 when the diameter L20 of the wheel section 31 is 2.5 inches (Table 6), 3 inches (Table 7), and 4 inches (Table 8). In addition, the maximum protrusion length in each table below indicates the minimum tolerance of the diameter L20 of the wheel portion 31 when the eccentric distance L22 is 21 mm and the maximum tolerance of the diameter L20 of the wheel portion 31 when the eccentric distance L22 is 28 mm.

[0022] [Table 6]

[0023] [Table 7]

[0024] [Table 8]

[0025] As described above, below the protrusion 55, the pivot 323 is located, which allows the direction of the wheel unit 31 to rotate relative to the upper piece 321 of the caster unit 3. As a result, even if the wheel unit 31 of the rotating caster unit 3 is facing in any direction, the tire 312 of the wheel unit 31 comes into contact with the periphery of the upper surface 552 or the protrusion slope 551. This restricts the wheel unit 31 from rotating around the axis of the wheel axle 311. The first inclination angle α1 of the recess slope 541, which extends diagonally upward from the bottom surface 542 of the recess 54 toward the placing surface 510, the second inclination angle α2 of the protrusion slope 551, which extends diagonally upward from the bottom surface 542 from the peripheral portion in contact with the bottom surface 542 of the recess 54 toward the upper end of the center portion in a planar view, and the radius L23 of the wheel portion 31 satisfy the following mathematical formula (3). Formula (3) α1≧(α2×36(mm)) / L23 Satisfying the formula (3) means that the second tilt angle α2 is greater than or equal to the first tilt angle α1 depending on the diameter L20 of the wheel part 31. In this embodiment, when the diameter L20 of the wheel section 31 is 2.5 inches or 3 inches, the second inclination angle α2 is greater than the first inclination angle α1, and when the diameter L20 of the wheel section 31 is 4 inches, the second inclination angle α2 is smaller than the first inclination angle α1. As shown in FIG. 6 , when the bogies 1 are stacked one above the other, the ease with which the wheel unit 31 of the upper bogie 1 moves and gets over the sloped recessed surface 541 of the recessed portion 54 of the lower bogie 1 is related to the recess depth L13 of the recessed portion 54. The deeper the recess depth L13 of the recessed portion 54, the larger the angle α3 of the movement direction of the wheel unit 31 of the upper bogie 1 with respect to the horizontal direction, making it more difficult for the wheel unit 31 of the upper bogie 1 to get over the sloped recessed surface 541 of the recessed portion 54 of the lower bogie 1. The angle α3 is approximately 45 degrees. The larger the angle α3, the more difficult it is for the wheel unit 31 of the upper bogie 1 to get over the sloped recessed surface 541 of the recessed portion 54 of the lower bogie 1. The second tilt angle α2, the first tilt angle α1, and the angle α3 satisfy the following formula (4). Formula (4) α1 / α3≧α2 / α3 Satisfying formula (4) means that the second tilt angle α2 is equal to or smaller than the first tilt angle α1 depending on the angle α3. Note that the second tilt angle α2 is not limited to being equal to or smaller than the first tilt angle α1 depending on the angle α3, and formula (5) below may also be satisfied. Formula (5) α1 / α3≦α2 / α3 Satisfying equation (5) means that the angle α3 makes the second tilt angle α2 greater than or equal to the first tilt angle α1. As shown in FIGS. 1 and 2 , a vertical piece 52 extends upward from the outer edge of the horizontal piece 51 (toward the outer end of the base portion 2 in a plan view). The vertical piece 52 functions as a restricting portion (in other words, a fall prevention portion) that restricts the outward movement of a load placed on the upper surface of the horizontal piece 51 so that the load does not move outward and fall from the horizontal piece 51. In this way, the vertical piece 52 and the horizontal piece 51 are integrally formed in the corner member 5, thereby improving the bending rigidity of the horizontal piece 51 on which the load is placed and the entire dolly 1, making the horizontal piece 51 (dolly 1) less likely to bend, and improving the strength of the dolly 1 against impact. In this embodiment, the restricting portion (inner surface) of the vertical piece 52 directly restricts the outward movement of the load. The vertical piece 52 has a groove 57. The groove 57 opens downward. The groove 57 is provided on both the short side edge and the long side edge. The vertical pieces 412, 422 of the side member 4 are inserted into the groove 57.

[0026] 2-5. When moving stacked carts As shown in FIG. 5 , when the bogies 1 are stacked one above the other and move in the longitudinal direction, the four wheel units 31 of the upper bogie 1 rotate to face the opposite side to the direction of travel. Here, when the bogies 1 are stacked one above the other, the direction of travel is defined as the forward direction, and the opposite side is defined as the rearward direction. When the bogies 1 are stacked one above the other, the four wheel units of the upper bogie 1 rotate to face the rearward direction. At this time, the outer peripheries of the two rearmost wheel units 31 of the four wheel units 31 are configured to come into contact with parts of the vertical pieces 52 of the lower bogie 1. When the bogies 1 are stacked one above the other and move, the vertical pieces 52 of the lower bogie 1 also function as a restricting unit (in other words, a wheel derailment prevention unit) that restricts the wheel units 31 of the upper bogie 1 from moving outward, so that the wheel units 31 of the upper bogie 1 housed in the recesses 54 of the lower bogie 1 do not move outward and derail from the base unit 2 of the lower bogie 1. When the bogies 1 are stacked one above the other and move in the short direction, the four wheel sections 31 of the upper bogie 1 rotate to face the opposite side to the direction of travel. Here, when the bogies 1 are stacked one above the other, the direction of travel is defined as the forward direction, and the opposite side is defined as the rearward direction. When the bogies 1 move in the stacked state, the four wheel sections of the upper bogie 1 rotate to face the rearward direction. At this time, the outer peripheries of the two rearward wheel sections 31 of the four wheel sections 31 are configured to come into contact with parts of the vertical pieces 52 of the lower bogie 1. When the bogies 1 move in the stacked state, the vertical pieces 52 of the lower bogie 1 also function as a restricting section (in other words, a wheel derailment prevention section) that restricts the wheel sections 31 of the upper bogie 1 from moving outward, so that the wheel sections 31 of the upper bogie 1 stored in the recesses 54 of the lower bogie 1 do not move outward and derail from the base section 2 of the lower bogie 1. When the bogies 1 are moved in a state where they are stacked one above the other, the horizontal piece 51 of the lower bogie 1 forms an area 58 where the wheel part 31 of the upper bogie 1 is not placed. The area 58 where the wheel part 31 of the upper bogie 1 is not placed is the part of the placing surface 510 above the horizontal piece 51 other than the recessed part 54 formed in the placing surface 510 above the horizontal piece 51. Specifically, the area 58 where the wheel part 31 of the upper bogie 1 is not placed is the part between the recessed part 54 and the vertical piece 52 of the lower bogie 1 (the space formed between the recessed part 54 and the vertical piece 52 of the lower bogie 1 where the wheel part 31 of the upper bogie 1 is not placed when the wheel part 31 of the upper bogie 1 is in contact with part of the vertical piece 52 of the lower bogie 1).

[0027] 2-6.Effects In the bogie 1 of this embodiment described above, the wheel portion 31 of the upper bogie 1 is stored in the recess 54 of the lower bogie 1, and the protrusion 55 of the lower bogie 1 prevents the wheel portion 31 of the upper bogie 1 from moving, making it less likely that the upper bogie 1 will shift sideways relative to the lower bogie 1. In addition, in the bogie 1 of this embodiment, the recess depth L13 of the recess 54 is 15.15% or more of the diameter of the wheel portion 31, so when the bogies 1 are stacked one on top of the other, the upper bogie 1 is less likely to shift sideways relative to the lower bogie 1. Furthermore, in the trolley 1 of this embodiment, the protruding length L21 of the protruding portion 55 from the bottom surface of the recessed portion 54 exceeds 5 mm, so that when the trolleys 1 are stacked one on top of the other, the protruding portion 55 easily restricts the movement of the wheel portion 31, making it easier for the trolley 1 stacked on top to be stable. In addition, in one embodiment of the trolley 1, the protruding length L21 of the protruding portion 55 from the bottom surface 542 of the recess 54 is less than 16 mm, so when the trolleys 1 are stacked one on top of the other, the wheel portion 31 is less likely to get caught on the protruding portion 55. Furthermore, in the bogie 1 of this embodiment, if there is a recess 54 in the base 2, the strength of the base in the portion where the recess 54 is located will be weakened. Therefore, by making the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562 longer than the recess depth L13 of the recess 54, the strength of the base 2 in the portion where the recess 54 is located can be increased. In addition, in the bogie 1 of this embodiment, the recessed portion 54 is formed along the rotating wheel portion 31. Therefore, the wheel portion 31 can be stored in the recess 54 without having to consider the direction in which the wheel portion 31 faces. Furthermore, in the trolley 1 of this embodiment, a swivel shaft 323 that can rotate relative to the upper piece 321 of the caster unit 3 is located below the protrusion 55, so that even if the wheel unit 31 of the swivel caster unit 3 is facing in any direction, it comes into contact with the upper edge of the protrusion slope 551, thereby restricting the wheel unit 31 from rotating around the axis of the wheel axle 311. In addition, in the trolley 1 of this embodiment, the outer surface of the wheel portion 31 of the rotating caster portion 3 comes into contact with the recessed portion slope 541 of the recessed portion 54, thereby restricting the wheel portion 31 from rotating around the axis of the wheel axle 311.

[0028] 3. Variations The shape, size, material, etc. of the carriage 1 are not particularly limited. Furthermore, the base portion 2 does not necessarily have to have the through-holes 20 that penetrate vertically. In addition, in the base portion 2, the side members 4 and the corner members 5 may be formed integrally. The base may be a rectangular flat plate with high and low ribs W formed on the back side (caster side) of the plate and a circular rib formed on the outer periphery of the back side of the plate, and may be integrally molded by injection molding using a synthetic resin such as polypropylene. The base may also be molded from a synthetic resin such as polypropylene, and the flexural modulus of the polypropylene is 1000 to 1800 MPa, preferably 1100 to 1400 MPa, and more preferably 1200 to 1300 MPa. Moreover, the side member 4 does not necessarily have to have the vertical pieces 412, 422, and may have only the horizontal pieces 413, 423. Moreover, the corner member 5 does not have to have the vertical piece 52, and may have only the horizontal piece 51. The shape of the recess 54 may be any shape that corresponds to the size of the turning range of the wheel unit 31. The recess depth L13 of the recess 54 may be any depth that corresponds to the diameter L20 of the wheel portion 31. Furthermore, when the trolleys 1 are stacked one above the other and are moving, the outer circumferential portions of two of the four wheel sections 31 of the upper trolley 1 are configured to come into contact with a portion of the vertical piece, but this is not limited to this, and the outer circumferential portion of at least one of the four wheel sections 31 of the upper trolley 1 may be configured to come into contact with a portion of the vertical piece 52 of the lower trolley 1, or all of the four wheel sections 31 of the upper trolley 1 may be configured not to come into contact with the vertical piece 52 of the lower trolley 1. 7 shows another example of the dolly 1. In this example, the rib 56 further includes a fourth rib 565. The fourth rib 565 is a protruding member extending along the short side direction. The fourth rib 565 is formed in a portion of the recess 54 of the horizontal piece 51, which has the recess slope 541. The fourth rib 565 is located between the vertical piece 52 and the third rib 563 in a side view. The vertical length L11 from the placement surface 510 to the lower end of the first rib 561, the vertical length L14 from the lower end of the fourth rib 565 to the upper end of the fourth rib 565, and the vertical length L15 from the upper end of the fourth rib 565 to the placement surface 510 satisfy the following formula (6): Formula (6) L15 / L11 <L14 / L11 The above formula (6) and the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562 satisfy the following formula (7). Note that the bogie 1 according to the other example is mostly the same as the bogie 1 according to the first embodiment, and therefore, redundant explanations will be omitted. Formula (7) L15 / L11 <L12 / L11<L14 / L11 Another example of the dolly 1 is shown in FIG. 8. In this example, the base 2 is configured as a single flat plate. In this case, the base 2 serves as a loading surface 510 on which an object is directly placed. Recesses 54 are located at the four corners of the base 2. Note that the dolly 1 according to this example is largely the same as the dolly 1 according to the first embodiment, and therefore a duplicated description will be omitted.

[0029] 4. Summary Like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the first aspect has the following configuration. That is, the dolly 1 of the first embodiment comprises a base 2 for placing an object to be loaded, and caster units 3. The caster units 3 are attached to the underside of the base 2. The base 2 has a recess 54 and a protrusion 55. The recess 54 is recessed from a loading surface 510 above the base 2, and houses the wheel units 31 of the caster units 3. The protrusion 55 protrudes upward from the center of the recess 54, and regulates the movement of the wheel units 31 housed in the recess 54. The protrusion length L21 of the protrusion 55 from the bottom surface 542 of the recess 54 is more than 5 mm and less than 16 mm. In the bogie 1 of the first embodiment having the above configuration, a recess 54 that stores the wheel portion 31 and a protrusion 55 that restricts movement of the wheel portion 31 are provided in the center of the recess 54, so that when the bogies 1 are stacked one on top of the other, the upper bogie 1 is less likely to shift sideways relative to the lower bogie 1. Furthermore, in the bogie 1 of the first embodiment having the above configuration, the protrusion length L21 of the protrusion 55 from the bottom surface of the recess 54 exceeds 5 mm, so that when the bogies 1 are stacked one on top of the other, the protrusion 55 easily restricts movement of the wheel portion 31, and the bogie 1 stacked on top is more likely to be stabilized. Furthermore, in the bogie 1 of the first embodiment having the above configuration, the protrusion length L21 of the protrusion 55 from the bottom surface of the recess 54 is less than 16 mm, so that when the bogies 1 are stacked one on top of the other, the wheel portion 31 is less likely to get caught on the protrusion 55. Furthermore, like the bogie 1 of the first embodiment and its modified example described above, the bogie 1 of the second aspect additionally includes the following configuration in addition to the configuration of the first aspect. That is, in the bogie 1 of the second embodiment, the base 2 further has a rib 56 protruding downward from the base 2. The rib 56 has a first rib 561 formed in a portion of the base 2 that does not have the recess 54, and a second rib 562 formed in a portion of the base 2 that has the recess 54. A length L11 from the mounting surface 510 of the base 2 to the lower end of the first rib 561, a length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562, and a recess depth L13 of the recess 54 satisfy the following mathematical formula (1). Formula (1) L13 / L11 <L12 / L11 In the second embodiment of the bogie 1 having the above-mentioned configuration, if there is a recess 54 in the base portion 2, the strength of the base portion where the recess 54 is located will be weakened. Therefore, by making the vertical length L12 from the bottom surface 542 of the recess 54 to the lower end of the second rib 562 longer than the recess depth L13 of the recess 54, the strength of the base portion 2 where the recess 54 is located can be increased. Furthermore, like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the third aspect additionally includes the following configuration in addition to the configuration of the first or second aspect. That is, in the trolley 1 of the third embodiment, the caster section 3 is configured so that, in a plan view, the center 313 of the wheel section 31 can rotate around a rotation axis that extends in the vertical direction, and the rotation central axis is located on a straight line that passes through the center 313 and extends in the longitudinal direction of the wheel section 31. The maximum protruding length of the protruding section 55 from the bottom surface 542 of the recessed section 54 is calculated based on the following mathematical formula (2) using the eccentric distance L22, which is the length from the rotation axis to the center 313, and the radius L23 of the wheel section 31. The protruding length L21 of the protruding section 55 from the bottom surface 542 of the recessed section 54 is equal to or less than the maximum protruding length. Formula (2) Maximum protrusion length = L23-(L23^2-L22^2)^(1 / 2) In the bogie 1 of the third embodiment having the above configuration, the length of the protrusion can be set to an appropriate protrusion length by calculating the maximum protrusion length from the eccentric distance L22 and the radius L23 of the wheel portion 31. Furthermore, in the bogie 1 of the third embodiment having the above configuration, when the protrusion length of the protrusion 55 from the bottom surface 542 of the recess 54 is equal to or less than the maximum protrusion length, compared to when the protrusion length of the protrusion 55 from the bottom surface 542 of the recess 54 is equal to or greater than the maximum protrusion length, when the bogies 1 are stacked, the wheel portion 31 of the upper bogie 1 is less likely to get caught on the protrusion 55 of the lower bogie 1 and the wheel portion 31 of the upper bogie 1 is more likely to be stored in the recess 54 of the lower bogie 1. Furthermore, like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the fourth aspect additionally includes the following configuration in addition to the configuration of the third aspect. That is, in the truck 1 of the fourth embodiment, the eccentric distance L22 is equal to or greater than 21 mm and equal to or less than 35 mm. In the bogie 1 of the fourth aspect having the above configuration, the recessed portion 54 of the bogie 1 is formed in accordance with the turning of the wheel portion 31, and therefore the recessed portion 54 of the bogie 1 can be made compact. Furthermore, like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the fifth aspect additionally includes the following configuration in addition to the configurations of the first to fourth aspects. That is, in the bogie 1 of the fifth embodiment, the diameter L20 of the wheel portion 31 is not less than 64 mm and not more than 101 mm. In the bogie 1 of the fifth aspect having the above configuration, the diameter L20 of the wheel portion 31 is set to be equal to or greater than 64 mm and equal to or less than 101 mm, so that the bogie 1 can easily overcome unevenness in the floor surface. Furthermore, like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the sixth aspect additionally includes the following configuration in addition to the configurations of the first to fifth aspects. That is, in the carriage 1 of the sixth embodiment, the protruding length L21 is less than the recess depth L13 of the recess 54. In the dolly 1 of the sixth aspect having the above configuration, the protruding length L21 is less than the recess depth L13 of the recess 54, so that the load can be placed on the placement surface 510 stably. Furthermore, like the truck 1 of the embodiment and its modified example described above, the truck 1 of the seventh aspect additionally includes the following configuration in addition to the configurations of the first to sixth aspects. That is, in the seventh embodiment of the bogie 1, the protrusion 55 comes into surface contact with the wheel part 31 and has a protrusion slope 551 that extends obliquely upward from the peripheral edge that contacts the bottom surface 542 toward the upper end of the center in plan view. In the seventh embodiment of the bogie 1 having the above configuration, when the bogies 1 are stacked one on top of the other, the wheel portion 31 of the upper bogie 1 comes into surface contact with the protrusion slope 551 of the protrusion 55 of the lower bogie 1, thereby preventing the protrusion 55 from coming into point contact with the wheel portion 31 and damaging the wheel portion 31. Furthermore, like the truck 1 of the embodiment and its modified example described above, the truck 1 of the eighth aspect additionally includes the following configuration in addition to the configurations of the first to seventh aspects. That is, in the carriage 1 of the eighth embodiment, the thickness of the base portion 2 having the protruding portion 55 is the same as the thickness of the base portion 2 having the recessed portion . In the eighth aspect of the bogie 1 having the above configuration, the cost of the bogie 1 can be reduced and the weight of the bogie 1 can be made lighter without reducing the strength, rigidity, durability, quality, etc. of the protrusion 55 of the bogie 1. Furthermore, like the bogie 1 of the embodiment and its modified example described above, the bogie 1 of the ninth aspect additionally includes the following configuration in addition to the configurations of the first to eighth aspects. That is, in the dolly 1 of the ninth aspect, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 is formed on the peripheral portion of the bottom surface 542 and has a recess slope 541 that extends obliquely upward from the bottom surface 542 toward the placement surface 510 at a first inclination angle α1. The protrusion 55 has a protrusion slope 551 that extends obliquely upward from the bottom surface 542 at a second inclination angle α2 from the peripheral portion in contact with the bottom surface 542 toward the upper end of the center in plan view. The second inclination angle α2 satisfies the following mathematical formula (3) based on the first inclination angle α1 and the radius L23 of the wheel unit 31. Formula (3) α1≧(α2×36(mm)) / L23 In the truck 1 of the ninth aspect having the above configuration, the wheel portion 31 can be more effectively restricted by the protrusion 55. Furthermore, like the truck 1 of the embodiment and its modified example described above, the truck 1 of the tenth aspect additionally includes the following configuration in addition to the configurations of the first to eighth aspects. That is, in the dolly 1 of the tenth aspect, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 is formed on the peripheral portion of the bottom surface 542, and has a recess slope 541 that extends obliquely upward from the bottom surface 542 toward the placement surface 510 at a first inclination angle α1. The protrusion 55 has a protrusion slope 551 that extends obliquely upward from the bottom surface 542 at a second inclination angle α2 from the peripheral portion in contact with the bottom surface 542 toward the upper end of the center in plan view. The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel unit 31 with respect to the horizontal direction satisfy the following mathematical formula (4). Formula (4) α1 / α3≧α2 / α3 In the dolly 1 of the tenth aspect having the above configuration, the wheel portion 31 can be easily and effectively restricted by the protruding portion inclined surface 551 and the recessed portion inclined surface 541. Furthermore, like the carriage 1 of the embodiment and its modified example described above, the carriage 1 of the eleventh aspect additionally includes the following configuration in addition to the configurations of the first to eighth aspects. That is, in the dolly 1 of the eleventh aspect, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 is formed on the peripheral portion of the bottom surface 542 and has a recess slope 541 that extends obliquely upward from the bottom surface 542 toward the placement surface 510 at a first inclination angle α1. The protrusion 55 has a protrusion slope 551 that extends obliquely upward from the bottom surface 542 at a second inclination angle α2 from the peripheral portion in contact with the bottom surface 542 toward the upper end of the center in plan view. The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel unit 31 with respect to the horizontal direction satisfy the following mathematical formula (5). Formula (5) α1 / α3≦α2 / α3 In the dolly 1 of the eleventh aspect having the above configuration, the wheel portion 31 can be easily and effectively restricted by the protruding portion inclined surface 551 and the recessed portion inclined surface 541 . The present disclosure has been described above based on the embodiments shown in the accompanying drawings, but the present disclosure is not limited to the above embodiments, and appropriate design changes are possible within the intended scope of the present disclosure. [Explanation of symbols]

[0030] 1 cart 2 base 3 Caster part 31 Wheel section 313 Center 510 Placement surface 54 Recess 542 bottom 55 Protrusion 56 Ribs 561 First Rib 562 Second Rib

Claims

1. a platform for placing a load; A synthetic resin cart having a caster portion attached to the underside of the base portion, The base portion is a recess that is recessed from the upper mounting surface of the base portion and that houses the wheel portion of the caster portion; a protrusion that protrudes upward from a center of the recess and restricts movement of the wheel unit housed in the recess, a protruding length of the protrusion from the bottom surface of the recess is more than 5 mm and less than 16 mm; The synthetic resin has a flexural modulus of 1000 to 1800 MPa. Cart.

2. The base portion further includes a rib protruding downward from the base portion, The rib is a first rib formed on a portion of the base portion that does not have the recess; a second rib formed in a portion of the base having the recess, A length L11 from the mounting surface of the base portion to the lower end of the first rib, a length L12 from the bottom surface of the recess to the lower end of the second rib, and a recess depth L13 of the recess satisfy the following mathematical formula (1): The carriage according to claim 1 . Formula (1) L13 / L11<L12 / L11

3. The caster unit is configured such that, in a plan view, the center of the wheel unit can rotate around a rotation axis extending in the vertical direction, and the rotation center axis is located on a straight line passing through the center and extending in the longitudinal direction of the wheel unit, The maximum protruding length of the protruding portion from the bottom surface of the recessed portion is calculated based on the following formula (2) from an eccentric distance L22, which is the length from the pivot shaft to the center, and a radius L23 of the wheel portion: A protrusion length L21 of the protrusion from the bottom surface of the recess is equal to or less than the maximum protrusion length. The bogie according to claim 1 or 2. Formula (2) Maximum protrusion length = L23 - (L23^2 - L22^2)^(1 / 2)

4. The eccentric distance is 21 mm or more and 35 mm or less. The truck according to claim 3.

5. The diameter of the wheel portion is 64 mm or more and 101 mm or less. The carriage according to claim 3

6. The protruding length is less than the recess depth of the recess. The carriage according to claim 1 .

7. The protrusion has a sloped surface that is in surface contact with the wheel portion and extends obliquely upward from a peripheral edge that contacts the bottom surface toward an upper end of a central portion in a plan view. The carriage according to claim 1 .

8. The thickness of the base portion having the protrusion is the same as the thickness of the base portion having the recess. The carriage according to claim 1 .

9. a bottom surface of the recessed portion facing upward and parallel to the placement surface; the recess is formed on the peripheral edge of the bottom surface and has a recess slope that extends obliquely upward from the bottom surface toward the placement surface at a first inclination angle α1, the protrusion has a protrusion inclined surface that extends obliquely upward from the bottom surface at a second inclination angle α2 from a peripheral edge portion that contacts the bottom surface toward an upper end portion of a center portion in a plan view, The second inclination angle α2 satisfies the following formula (3) based on the first inclination angle α1 and the radius L23 of the wheel portion, The carriage according to claim 1 . Formula (3) α1≧(α2×36 (mm)) / L23

10. a bottom surface of the recessed portion facing upward and parallel to the placement surface; the recess is formed on the peripheral edge of the bottom surface and has a recess slope that extends obliquely upward from the bottom surface toward the placement surface at a first inclination angle α1, the protrusion has a protrusion inclined surface that extends obliquely upward from the bottom surface at a second inclination angle α2 from a peripheral edge portion that contacts the bottom surface toward an upper end portion of a center portion in a plan view, The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel section with respect to the horizontal direction satisfy the following mathematical formula (4): The carriage according to claim 1 . Formula (4) α1 / α3≧α2 / α3

11. a bottom surface of the recessed portion facing upward and parallel to the placement surface; the recess is formed on the peripheral edge of the bottom surface and has a recess slope that extends obliquely upward from the bottom surface toward the placement surface at a first inclination angle α1, the protrusion has a protrusion inclined surface that extends obliquely upward from the bottom surface at a second inclination angle α2 from a peripheral edge portion that contacts the bottom surface toward an upper end portion of a center portion in a plan view, The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel section with respect to the horizontal direction satisfy the following mathematical formula (5): The carriage according to claim 1 . Formula (5) α1 / α3≦α2 / α3

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