Trolley

Abstract

To provide a cart in which a protruding part easily restricts the movement of a wheel part when the carts are stacked vertically, and the carts stacked on top are easily stabilized. [Solution] The dolly includes a base for placing an object to be loaded, and a caster unit 3. The caster unit 3 is attached to the underside of the base. The base has a recess 54 and a protrusion 55. The recess 54 is recessed from a loading surface 510 above the base, and houses a wheel unit 31 of the caster unit 3. The protrusion 55 protrudes upward from the center of the recess 54, and restricts movement of the wheel unit 31 housed in the recess 54. A protruding length L21 of the protrusion 55 from a bottom surface 542 of the recess 54 exceeds 5 mm and is less than 16 mm.

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 storing the wheels and a protrusion for restricting the wheels stored 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 on top of 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] Incidentally, in the roller carriage shown in Patent Document 1, the protrusion protrudes upward from the bottom surface at the center of the recess. However, if the protruding length of the protrusion is short, the wheel will easily climb over the protrusion, making it difficult for the protrusion to restrict the movement of the wheel stored in the recess. On the other hand, if the protruding length of the protrusion is long, when the roller carriages are stacked one on top of the other, the wheels will get caught on the protrusion, and instead of being stored in the recesses, the wheels will be left floating, making the roller carriage stacked on top unstable. The present disclosure has been invented in consideration of the above-mentioned problems in the conventional art, and aims to provide a trolley in which, when the trolleys are stacked one on top of the other, the protruding portion makes it easy to restrict the movement of the wheel portion, thereby making it easy to stabilize the trolley stacked on top. [Means for solving the problem]

[0005] In order to solve the above problems, a dolly according to an embodiment of the present disclosure includes a synthetic resin base for placing a load thereon, and caster parts. The caster parts are attached to the underside of the base. The base has a recess and a protrusion. The recess is recessed from the upper placement surface of the base and houses the wheel parts of the caster parts. The protrusion protrudes upward from the center of the recess and regulates the movement of the wheel parts housed in the recess. The protrusion has a protruding length from the bottom surface of the recess that is more than 5 mm and less than 16 mm. The synthetic resin has a flexural modulus of 1000 to 1800 MPa. Effect of the Invention

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

[0007] [Figure 1] FIG. 1 is a perspective view of a cart according to one embodiment, seen obliquely from above. [Diagram 2] FIG. 2 is an exploded perspective view of the above truck as viewed obliquely from above. [Diagram 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. [Diagram 5] FIG. 5 is a side cross-sectional view of the above carts in a stacked state. [Figure 6] FIG. 6 is an enlarged side cross-sectional view of a main part of the above bogie. [Figure 7] FIG. 7 is a side sectional view showing a modified example of the above bogie. [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 PREFERRED EMBODIMENTS

[0008] 1. Overview As shown in FIG. 1, a dolly 1 according to an embodiment includes a platform 2 for placing a load, and a caster unit 3. The caster unit 3 is attached to the lower surface of the platform 2. The platform 2 has a recess 54 and a protruding unit 55. The recess 54 is recessed from a placement surface 510 above the platform 2, and houses the wheel unit 31 of the caster unit 3. The protruding unit 55 protrudes upward from the center of the recess 54, and restricts the movement of the wheel unit 31 housed in the recess 54. As shown in FIG. 6, a protruding length L21 of the protruding unit 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 part 31 of the caster part 3 is stored in the recess 54 of the base part 2, and the movement of the wheel part 31 is restricted by the protruding part 55. As a result, when the dollies 1 are stacked vertically, the upper dolly 1 is less likely to slip sideways relative to the lower dolly 1. Also, in the dolly 1 according to one embodiment, the protruding length L21 of the protruding part 55 from the bottom surface 542 of the recess 54 exceeds 5 mm. As a result, when the dollies 1 are stacked vertically, the protruding part 55 easily restricts the movement of the wheel part 31. Also, in the dolly 1 according to one embodiment, the protruding length L21 of the protruding part 55 from the bottom surface 542 of the recess 54 is less than 16 mm. As a result, when the dollies 1 are stacked vertically, the wheel part 31 is less likely to get caught on the protruding part 55.

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

[0010] 2-2.Trolley 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 for transporting a load by human power. The dolly 1 can be stacked above and below the dolly 1 placed on the ground, and the dolly 1 on the lower side can move when the dollies 1 are stacked above and below. The dolly 1 is rectangular in plan view. In the following, the up-down direction is defined based on the state in which the dolly 1 is placed. The direction along the long side of the dolly 1 is defined as the long side direction, and the direction along the short side of the dolly 1 is defined as the short side direction.

[0011] 2-3. Caster section 4, the caster unit 3 has a wheel unit 31 and a support unit 32. Four caster units 3 are attached to the lower surface of the base unit 2. Each of the four caster units 3 has the same shape. The wheel section 31 has a wheel axle 311 and a tire 312. The wheel section 31 is supported by being suspended from the support section 32. In this embodiment, the diameter L20 of the wheel section 31 is 64 mm to 101 mm, and tires 312 having diameters L20 of the wheel section 31 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 limit and the lower limit. The wheel axle 311 is located at the center of the tire 312. The wheel axle 311 supports the tire 312 so as to be freely rotatable. This allows the dolly 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, and examples of the material other than rubber include resin. The support portion 32 has an upper piece 321 and a pivot shaft 323. The support portion 32 is made of, for example, metal. Note that the support portion 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 unit 2. The upper end of a rotating shaft 323 is connected to the upper piece 321. The rotating shaft 323 rotates 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 rotating 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 unit 31 connected to the connecting piece 322 to rotate. 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 portion 31 is 2.5 inches and 3 inches, the eccentric distance L22 of the wheel portion 31, which is the length from the pivot shaft 323 to the center portion 313, is 21 mm to 28 mm, and the eccentric distances L22 of the wheel portion 31 of 21 mm, 27 mm, and 28 mm are mainly targeted. When the diameter L20 of the wheel portion 31 is 4 inches, the eccentric distance L22 of the wheel portion 31 is 31 mm to 35 mm, and the eccentric distances L22 of the wheel portion 31 of 31 mm, 32 mm, and 35 mm are mainly targeted. The eccentric distance L22 of the wheel portion 31 is not particularly limited.

[0012] 2-4. Base 3, the platform 2 has side members 4 and corner members 5. An object is placed on the upper surface of the platform 2. The platform 2 has a rectangular shape in a plan view. In this embodiment, each side of the platform 2 is approximately 30 cm to 100 cm. The shape of the base 2 in plan view is symmetrical with respect to a line 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 with respect to a line 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 2, the side members 4 have a long side member 41 and a short side member 42. The side members 4 extend in the horizontal direction (the horizontal direction when the dolly 1 is placed on a horizontal surface). The long side members 41 are two angle members 410 extending along the long side direction of the base portion 2. The two angle members 410 are identical except that they are inverted with respect to each other about a line along the long side direction that passes through the center of the short side direction. The angle bar 410 has a vertical piece 412 and a horizontal piece 413 that serves as a beam for supporting a load. The angle bar 410 is made of, for example, metal. The angle bar 410 may be made of a material other than metal, and examples of the material other than metal include resin. The resin is made of a synthetic resin such as polypropylene, and the flexural modulus of polypropylene is 1000 to 1800 MPa, and preferably 1100 to 1400 MPa. The flexural modulus is measured by 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 platform 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 bar 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 to each other except that they are inverted with respect to 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 a load. The angle iron 420 is made of, for example, metal. The angle iron 420 may be made of a material other than metal, and examples of the material other than metal include 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, and preferably 1100 to 1400 MPa. The vertical piece 422 extends upward from the outer edge (the outer end side of the platform 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 bar 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 disposed at the four corners of the base 2 in a plan view. The caster parts 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 each other about a line along the long side direction that passes through the center in the short side direction. The four corner members 5 are identical except that they are inverted from each other about a line along the short side direction that passes through the center in the long side direction. 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, and 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 placement surface 510 directly supports an object to be loaded. The placement surface 510 is a horizontal plane in a side view. The shape of the placement surface 510 in a side view is not particularly limited. A cutout portion 53 is provided on the underside of the horizontal piece 51. The cutout portions 53 are provided at the ends of the short sides and the long sides of the outer periphery of the cart 1. The ends of the horizontal pieces 413, 423 of the side member 4 are inserted into the cutout portions 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 the movement of the wheel section 31. The diameter of the recess 54 in plan view is preferably 40% to 70% of the longest length of the side piece 51 in plan view, and more preferably 50% to 60%. In this embodiment, the longest length of the side piece 51 in plan view is the length of the hypotenuse of the side piece 51 in the triangular shape of the side piece 51 in plan view. In addition, in order to form the recess 54 by shortening the length of the hypotenuse of the side piece 51 in the triangular shape of the side piece 51 in plan view as much as possible, it is particularly preferable that the diameter of the recess 54 in plan view exceeds 50% of the length of the hypotenuse of the side piece 51 in the triangular shape of the side piece 51 in plan view. This makes it difficult for the strength of the side 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 inclines 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 slope 541. The wheel section 31 stored in the recess 54 is placed on the bottom surface 542. The bottom surface 542 is annular in a plan view. The bottom surface 542 is continuous with the lower end of the recessed slope 541 in the horizontal direction. The bottom surface 542 is flat in a side view, faces upward, and is parallel to the placement surface 510. The shape of the bottom surface 542 in a side view is not particularly limited. The shape of the bottom surface 542 in a side view may be, for example, a downwardly curved shape (a shape close to the outer circumferential surface of the wheel section 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 vertically penetrate the horizontal piece 51 in the bottom surface 542. The through hole 543 is provided, for example, to drain water, sand, and the like accumulated 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 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 part 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. In other words, in Tables 1 and 2, the recess depth L13 of the recess 54 is the upper or lower limit 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 in a portion of the horizontal piece 51 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 mounting surface 510 to the lower end of the first rib 561 is 15 mm. Note that the vertical length L11 from the mounting 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 second ribs 562 each have the same protruding length. In the side view, the protruding portion 55 has a recess 550 recessed upward. By forming the recess 550 in this manner, the protruding portion 55 molded by the molding device is less likely to deform after molding. The second rib 562 crosses the lower part of 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 a 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 holding pieces 564 is formed in a part of the third rib 563. The pair of holding 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 in which the upper piece 321 of the caster part 3 is attached. When the caster part 3 is attached to the base part 2, the second rib 562 is located between the upper piece 321 of the caster part 3 and the lower surface of the bottom surface 542 of the recessed part 54. The second rib 562 and the third rib 563 are formed in a portion having the recessed part 54, thereby improving the strength of the base part 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 recessed part 54, more preferably 6 to 12%, and further 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 the 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 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, based on the following formula (2). Formula (2) Maximum protruding length = L23-(L23^2-L22^2)^(1 / 2) Specifically, the length L24 of the other side when the trolleys 1 are stacked vertically can be calculated based on the eccentricity distance L22, which is the length of one side from the center 313 of the wheel section 31 of the upper trolley 1 in the state where the trolleys 1 are stacked vertically in the horizontal direction to the vertical line CL1 of the center of the swivel shaft 323, and the radius L23 of the wheel section 31, which is the length of the hypotenuse from the center 313 of the wheel section 31 of the trolley 1 in the state where the trolleys 1 are stacked vertically in the diagonal downward direction to the upper surface 552 of the protruding portion 55 of the lower trolley 1, based on the Pythagorean theorem (Pythagoras' theorem) of the following formula (2-1): Formula (2-1) L24 = (L23^2 - L22^2)^(1 / 2) The maximum protruding length of protrusion 55 from bottom surface 542 of 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 vertically obtained by 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 to the bottom surface 542 of the recess 54 of the lower trolley 1 when the trolleys 1 are stacked vertically. Formula (2-2) Maximum protruding 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 table shows 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 table 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 an 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. The upper surface 552 is continuous with the upper edge of the protruding inclined surface 551. The upper surface 552 is continuous with the upper edge of the protruding inclined surface 551 in the horizontal direction. 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 protruding upward. Here, the maximum protruding length when the upper surface 552 is a curved surface with R0.5 and the maximum protruding length when the upper surface 552 is a curved surface with R1.0 are shown in the following table when the diameter L20 of the wheel part 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 protruding portion 55, the turning shaft 323 is located, which allows the direction of the wheel portion 31 to turn with respect to the upper piece 321 of the caster portion 3. As a result, even if the turning wheel portion 31 of the caster portion 3 faces in any direction, the tire 312 of the wheel portion 31 comes into contact with the periphery of the upper surface 552 or the protruding portion inclined surface 551. Therefore, the wheel portion 31 is restricted from rotating around the axis of the wheel axle 311. A first inclination angle α1 of the recess slope 541 extending diagonally upward from the bottom surface 542 toward the support surface 510 with respect to the bottom surface 542 of the recess 54, a second inclination angle α2 of the protrusion slope 551 extending diagonally upward from the bottom surface 542 from the peripheral portion in contact with the bottom surface 542 toward the upper end of the center when viewed in a plane with respect to the bottom surface 542 of the recess 54, and a 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 inclination angle α2 is greater than or equal to the first inclination angle α1 depending on the diameter L20 of the wheel part 31. In this embodiment, when the diameter L20 of the wheel portion 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 portion 31 is 4 inches, the second inclination angle α2 is smaller than the first inclination angle α1. As shown in FIG. 6, when the carts 1 are stacked one on top of the other, the ease with which the wheel section 31 of the upper cart 1 moves and gets over the inclined recessed surface 541 of the recessed surface 54 of the lower cart 1 is related to the recess depth L13 of the recessed surface 54. The deeper the recess depth L13 of the recessed surface 54, the larger the angle α3 of the direction in which the wheel section 31 of the upper cart 1 moves with respect to the horizontal direction, making it more difficult for the wheel section 31 of the upper cart 1 to get over the inclined recessed surface 541 of the recessed surface 54 of the lower cart 1. The angle α3 is approximately 45 degrees. The larger the angle α3, the more difficult it is for the wheel section 31 of the upper cart 1 to get over the inclined recessed surface 541 of the recessed surface 54 of the lower cart 1. The second inclination angle α2, the first inclination angle α1, and the angle α3 satisfy the following formula (4). Formula (4) α1 / α3≧α2 / α3 Satisfying the formula (4) means that the second tilt angle α2 is smaller than or equal to the first tilt angle α1 depending on the angle α3. Note that the second tilt angle α2 is not limited to being smaller than or equal to the first tilt angle α1 depending on the angle α3, and the following formula (5) 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 (the outer end side of the platform 2 in plan view). The vertical piece 52 functions as a restricting portion (in other words, a fall prevention portion) that restricts the outward movement of the 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, so that the bending rigidity of the horizontal piece 51 on which the load is placed and the entire dolly 1 is improved, making the horizontal piece 51 (the 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 load from moving outward. 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 carts that are stacked As shown in FIG. 5, when the trolleys 1 move in the longitudinal direction in a state where the trolleys 1 are stacked up and down, the four wheel parts 31 of the upper trolley 1 turn so as to face the opposite side to the traveling direction. Here, the traveling direction is the forward direction in a state where the trolleys 1 are stacked up and down, and the opposite side is the rear direction. When the trolleys 1 are stacked up and down, the four wheel parts of the upper trolley 1 turn so as to face the rear direction. At this time, the outer periphery parts of the two rear wheel parts 31 out of the four wheel parts 31 are configured to come into contact with a part of the vertical piece 52 of the lower trolley 1. When the trolleys 1 move in a state where they are stacked up and down, the vertical piece 52 of the lower trolley 1 also functions as a restricting part (in other words, a wheel derailment prevention part) that restricts the wheel parts 31 of the upper trolley 1 from moving outward so that the wheel parts 31 of the upper trolley 1 stored in the recessed part 54 of the lower trolley 1 do not move outward and derail from the base part 2 of the lower trolley 1. When the trolleys 1 move in the short direction in a state where the trolleys 1 are stacked up and down, the four wheel parts 31 of the upper trolley 1 turn so as to face the opposite side to the traveling direction. Here, when the trolleys 1 are stacked up and down, the traveling direction is the forward direction, and the opposite side is the rear direction. When the trolleys 1 move in a state where they are stacked up and down, the four wheel parts of the upper trolley 1 turn so as to face the rear. At this time, the outer periphery parts of the two rear wheel parts 31 out of the four wheel parts 31 are configured to come into contact with a part of the vertical piece 52 of the lower trolley 1. When the trolleys 1 move in a state where they are stacked up and down, the vertical piece 52 of the lower trolley 1 also functions as a restricting part (in other words, a wheel derailment prevention part) that restricts the wheel parts 31 of the upper trolley 1 from moving outward so that the wheel parts 31 of the upper trolley 1 stored in the recessed part 54 of the lower trolley 1 do not move outward and derail from the base part 2 of the lower trolley 1. When the trolleys 1 are moved in a state where they are stacked one above the other, the horizontal piece 51 of the lower trolley 1 forms an area 58 where the wheel section 31 of the upper trolley 1 is not placed. The area 58 where the wheel section 31 of the upper trolley 1 is not placed is a portion of the placement surface 510 above the horizontal piece 51 other than the recessed portion 54 formed in the placement surface 510 above the horizontal piece 51. Specifically, the area 58 where the wheel section 31 of the upper trolley 1 is not placed is a portion between the recessed portion 54 and the vertical piece 52 of the lower trolley 1 (a space portion where the wheel section 31 of the upper trolley 1 is not placed, which is formed between the recessed portion 54 and the vertical piece 52 of the lower trolley 1 when the wheel section 31 of the upper trolley 1 is in contact with a part of the vertical piece 52 of the lower trolley 1).

[0027] 2-6.Effects In the trolley 1 of this embodiment described above, the wheel portion 31 of the upper trolley 1 is stored in the recess 54 of the lower trolley 1, and the protrusion 55 of the lower trolley 1 prevents the wheel portion 31 of the upper trolley 1 from moving, making it less likely that the upper trolley 1 will shift sideways relative to the lower trolley 1. In addition, in the trolley 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 that when the trolleys 1 are stacked one on top of the other, the upper trolley 1 is less likely to shift sideways relative to the lower trolley 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 tends to restrict the movement of the wheel portion 31, making the trolley 1 stacked on top more stable. In addition, in the trolley 1 according to one embodiment, the protruding length L21 of the protruding portion 55 from the bottom surface 542 of the recess 54 is less than 16 mm, so that 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 trolley 1 of this embodiment, if a recess 54 is present in the base 2, the strength of the base at 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 at the portion where the recess 54 is located can be increased. In addition, in the dolly 1 of this embodiment, the recess 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 is rotatable relative to the upper piece 321 of the caster unit 3 is located below the protrusion 55. Therefore, even if the rotating wheel unit 31 of the caster unit 3 is facing in any direction, it comes into contact with the upper edge of the protrusion inclined surface 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 peripheral surface of the wheel portion 31 of the swiveling caster portion 3 comes into contact with the recessed portion inclined surface 541 of the recessed portion 54, thereby restricting the rotation of the wheel portion 31 around the axis of the wheel axle 311.

[0028] 3. Variations The shape, size, material, etc. of the cart 1 are not particularly limited. Furthermore, the base portion 2 does not necessarily need to have the through-hole 20 that penetrates vertically. Moreover, in the base portion 2, the side members 4 and the corner members 5 may be formed integrally. In addition, 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 annular ribs formed on the outer periphery of the back side of the plate, and molded integrally by injection molding using a synthetic resin such as polypropylene. The base may be made of a synthetic resin such as polypropylene, and the flexural modulus of 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 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 . Furthermore, the shape of the recess 54 may be any shape that corresponds to the size of the turning range of the wheel unit 31 . Further, the recess depth L13 of the recess 54 may be a depth corresponding to the diameter L20 of the wheel portion 31. In addition, when the trolleys 1 are moved in a stacked state, the outer circumferential portions of two of the four wheel portions 31 of the upper trolley 1 are configured to contact a part of the vertical piece, but this is not limited to this, and the outer circumferential portion of at least one of the four wheel portions 31 of the upper trolley 1 may be configured to contact a part of the vertical piece 52 of the lower trolley 1, or all of the four wheel portions 31 of the upper trolley 1 may be configured not to contact the vertical piece 52 of the lower trolley 1. Moreover, another example of the dolly 1 is shown in FIG. 7. 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 having the recess slope 541. The fourth rib 565 is located between the vertical piece 52 and the third rib 563 in a side view. A vertical length L11 from the placement surface 510 to the lower end of the first rib 561, a vertical length L14 from the lower end of the fourth rib 565 to the upper end of the fourth rib 565, and a 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 dolly 1 according to the other example is mostly the same as the dolly 1 according to the embodiment, so a duplicated description 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 platform 2 is configured as a single flat plate material as a whole. In this case, the platform 2 serves as a placement surface 510 on which an object is directly placed. The recesses 54 are disposed at the four corners of the platform 2. Note that the dolly 1 according to this example is mostly the same as the dolly 1 according to the first embodiment, and therefore a duplicated description will be omitted.

[0029] 4. Summary Like the cart 1 of the embodiment and its modified example described above, the cart 1 of the first aspect has the following configuration. That is, the dolly 1 of the first embodiment includes a base portion 2 for placing a load, and a caster portion 3. The caster portion 3 is attached to the lower surface of the base portion 2. The base portion 2 has a recess 54 and a protrusion 55. The recess 54 is recessed from a placement surface 510 above the base portion 2, and stores the wheel portion 31 of the caster portion 3. The protrusion 55 protrudes upward from the center of the recess 54, and regulates the movement of the wheel portion 31 stored in the recess 54. A protrusion length L21 of the protrusion 55 from a bottom surface 542 of the recess 54 exceeds 5 mm and is less than 16 mm. In the first embodiment of the dolly 1 having the above configuration, the recess 54 for storing the wheel part 31 and the protrusion 55 for restricting the movement of the wheel part 31 are provided in the center of the recess 54, so that when the dollies 1 are stacked vertically, the upper dolly 1 is less likely to slip sideways relative to the lower dolly 1. In the first embodiment of the dolly 1 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 dollies 1 are stacked vertically, the protrusion 55 easily restricts the movement of the wheel part 31, and the dolly 1 stacked on top is easily stabilized. In the first embodiment of the dolly 1 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 dollies 1 are stacked vertically, the wheel part 31 is less likely to get caught on the protrusion 55. 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 dolly 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 trolley 1 having the above-mentioned configuration, if there is a recess 54 in the base 2, the strength of the base at 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 at the portion where the recess 54 is located can be increased. Like the trolley 1 of the embodiment and its modified example described above, the trolley 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 dolly 1 of the third embodiment, the caster section 3 is configured such that, in a plan view, the center 313 of the wheel section 31 can rotate around a rotation axis extending 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 formula (2) from 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 protruding length = L23-(L23^2-L22^2)^(1 / 2) In the trolley 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 part 31. In the trolley 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 more than the maximum protrusion length, the wheel part 31 of the upper trolley 1 is less likely to get caught on the protrusion 55 of the lower trolley 1 when stacking the trolleys 1, and the wheel part 31 of the upper trolley 1 is more likely to be stored in the recess 54 of the lower trolley 1. Like the trolley 1 of the embodiment and its modified example described above, the trolley 1 of the fourth aspect additionally includes the following configuration in addition to the configuration of the third aspect. That is, in the bogie 1 of the fourth embodiment, the eccentric distance L22 is not less than 21 mm and not more than 35 mm. In the bogie 1 of the fourth embodiment having the above-mentioned configuration, the recess 54 of the bogie 1 is formed in response to the turning of the wheel portion 31, so that the recess 54 of the bogie 1 can be made compact. Like the cart 1 of the embodiment and its modified example described above, the cart 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 trolley 1 of the fifth embodiment having the above-mentioned configuration, the diameter L20 of the wheel portion 31 is set to be 64 mm or more and 101 mm or less, so that the trolley 1 can easily overcome unevenness and the like on the floor surface. Like the cart 1 of the embodiment and its modified example described above, the cart 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 embodiment having the above-mentioned 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. Like the cart 1 of the embodiment and its modified example described above, the cart 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 dolly 1, the protrusion 55 comes into surface contact with the wheel portion 31 and has a protrusion inclined surface 551 that extends obliquely upward from the peripheral edge portion in contact with the bottom surface 542 toward the upper end portion of the center portion in a plan view. In the seventh embodiment of the trolley 1 having the above-mentioned configuration, when the trolleys 1 are stacked one on top of the other, the wheel portion 31 of the upper trolley 1 comes into surface contact with the protruding portion inclined surface 551 of the protruding portion 55 of the lower trolley 1, thereby preventing the protruding portion 55 from coming into point contact with the wheel portion 31 and damaging the wheel portion 31. Like the bogie 1 of the embodiment and its modified example described above, the bogie 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 54 . In the eighth aspect of the trolley 1 having the above-mentioned configuration, the cost of the trolley 1 can be reduced and the weight of the trolley 1 can be made lighter without reducing the strength, rigidity, durability, and quality of the protrusion 55 of the trolley 1. 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 embodiment, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 has a recess slope 541 formed on the peripheral portion of the bottom surface 542 and extending 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 extending 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 portion of the center portion in a 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 portion 31. Formula (3) α1≧(α2×36(mm)) / L23 In the dolly 1 of the ninth aspect having the above-mentioned configuration, the wheel portion 31 can be easily restricted by the protrusion 55 effectively. Like the cart 1 of the embodiment and its modified example described above, the cart 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 embodiment, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 has a recess slope 541 formed on the peripheral portion of the bottom surface 542 and extending 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 extending 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 portion in a plan view. The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel portion 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-mentioned 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. Like the cart 1 of the embodiment and its modified example described above, the cart 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 embodiment, the bottom surface 542 of the recess 54 faces upward and is parallel to the placement surface 510. The recess 54 has a recess slope 541 formed on the peripheral portion of the bottom surface 542 and extending 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 extending 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 portion in a plan view. The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel portion 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-mentioned 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 attached 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 section 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 dolly 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 accommodates the wheel portion of the caster portion; a protrusion protruding upward from a center portion of the recess and restricting movement of the wheel portion housed in the recess, The length of the protrusion from the bottom surface of the recess is more than 5 mm and less than 16 mm. the law of nature, The synthetic resin has a flexural modulus of 1000 to 1800 MPa; 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 consisting of a lattice-shaped rib group extending along a side of the base portion in a portion of the base portion having the recess; a third rib made of a member extending along a side of the base portion in a portion having the recess and positioned outside the second rib, A length L11 from the mounting surface of the base 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 caster unit is configured such that, in a plan view, a center of the wheel unit can rotate around a rotation axis extending in a vertical direction, and the rotation axis is located on a straight line that passes through the center and extends in a longitudinal direction of the wheel unit, The maximum protruding length of the protrusion from the bottom surface of the recess 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 protruding length L21 of the protruding portion from a bottom surface of the recessed portion is equal to or less than the maximum protruding length, The recess has a recess depth of 13.16% or more and 15.14% or less of a diameter of the wheel portion, an area of ​​a lower surface of the third rib is 5 to 15% of an area of ​​a bottom surface of the recess; The eccentric distance is equal to or greater than 21 mm and equal to or less than 35 mm, The diameter of the wheel portion is equal to or greater than 64 mm and equal to or less than 101 mm, The protruding length is less than the recess depth of the recess, the protrusion has a protrusion slope that is in surface contact with the wheel portion and extends obliquely upward from a peripheral edge portion that is in contact with the bottom surface toward an upper end portion of a central portion in a plan view, a thickness of the base portion having the protruding portion is equal to a thickness of the base portion having the recessed portion; a bottom surface of the recess faces upward and is parallel to the placement surface; the recess is formed on a peripheral portion of the bottom surface and has a recess inclined surface extending 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 central 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, Trolley. Formula (1) L13 / L11<L12 / L11 Formula (2) Maximum protrusion length = L23 - (L23^2 - L22^2)^(1 / 2) Formula (3) α1≧(α2×36 (mm)) / L23

2. A platform for placing a load; A synthetic resin dolly 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 accommodates the wheel portion of the caster portion; a protrusion protruding upward from a center portion of the recess and restricting movement of the wheel portion housed in the recess, The length of the protrusion from the bottom surface of the recess is more than 5 mm and less than 16 mm. the law of nature, The synthetic resin has a flexural modulus of 1000 to 1800 MPa; 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 consisting of a lattice-shaped rib group extending along a side of the base portion in a portion of the base portion having the recess; a third rib made of a member extending along a side of the base portion in a portion having the recess and positioned outside the second rib, A length L11 from the mounting surface of the base 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 caster unit is configured such that, in a plan view, a center of the wheel unit can rotate around a rotation axis extending in a vertical direction, and the rotation axis is located on a straight line that passes through the center and extends in a longitudinal direction of the wheel unit, The maximum protruding length of the protrusion from the bottom surface of the recess 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 protruding length L21 of the protruding portion from a bottom surface of the recessed portion is equal to or less than the maximum protruding length, The recess has a recess depth of 13.16% or more and 15.14% or less of a diameter of the wheel portion, an area of ​​a lower surface of the third rib is 5 to 15% of an area of ​​a bottom surface of the recess; The eccentric distance is equal to or greater than 21 mm and equal to or less than 35 mm, The diameter of the wheel portion is equal to or greater than 64 mm and equal to or less than 101 mm, The protruding length is less than the recess depth of the recess, the protrusion has a protrusion slope that is in surface contact with the wheel portion and extends obliquely upward from a peripheral edge portion that is in contact with the bottom surface toward an upper end portion of a central portion in a plan view, a thickness of the base portion having the protruding portion is equal to a thickness of the base portion having the recessed portion; a bottom surface of the recess faces upward and is parallel to the placement surface; the recess is formed on a peripheral portion of the bottom surface and has a recess inclined surface extending 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 central portion in a plan view, The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel portion with respect to the horizontal direction satisfy the following mathematical formula (4), Trolley. Formula (1) L13 / L11<L12 / L11 Formula (2) Maximum protrusion length = L23 - (L23^2 - L22^2)^(1 / 2) Formula (4) α1 / α3≧α2 / α3

3. A platform for placing a load; A synthetic resin dolly 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 accommodates the wheel portion of the caster portion; a protrusion protruding upward from a center portion of the recess and restricting movement of the wheel portion housed in the recess, The length of the protrusion from the bottom surface of the recess is more than 5 mm and less than 16 mm. the law of nature, The synthetic resin has a flexural modulus of 1000 to 1800 MPa; 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 consisting of a lattice-shaped rib group extending along a side of the base portion in a portion of the base portion having the recess; a third rib made of a member extending along a side of the base portion in a portion having the recess and positioned outside the second rib, A length L11 from the mounting surface of the base 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 caster unit is configured such that, in a plan view, a center of the wheel unit can rotate around a rotation axis extending in a vertical direction, and the rotation axis is located on a straight line that passes through the center and extends in a longitudinal direction of the wheel unit, The maximum protruding length of the protrusion from the bottom surface of the recess 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 protruding length L21 of the protruding portion from a bottom surface of the recessed portion is equal to or less than the maximum protruding length, The recess has a recess depth of 13.16% or more and 15.14% or less of a diameter of the wheel portion, an area of ​​a lower surface of the third rib is 5 to 15% of an area of ​​a bottom surface of the recess; The eccentric distance is equal to or greater than 21 mm and equal to or less than 35 mm, The diameter of the wheel portion is equal to or greater than 64 mm and equal to or less than 101 mm, The protruding length is less than the recess depth of the recess, the protrusion has a protrusion slope that is in surface contact with the wheel portion and extends obliquely upward from a peripheral edge portion that is in contact with the bottom surface toward an upper end portion of a central portion in a plan view, a thickness of the base portion having the protruding portion is equal to a thickness of the base portion having the recessed portion; a bottom surface of the recess faces upward and is parallel to the placement surface; the recess is formed on a peripheral portion of the bottom surface and has a recess inclined surface extending 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 central portion in a plan view, The second inclination angle α2, the first inclination angle α1, and the angle α3 of the wheel portion with respect to the horizontal direction satisfy the following mathematical formula (5). Trolley. Formula (1) L13 / L11<L12 / L11 Formula (2) Maximum protrusion length = L23 - (L23^2 - L22^2)^(1 / 2) Formula (5) α1 / α3≦α2 / α3

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